• Focus Group Topics
• Summary of Key Points and Research Directions
• An Agenda for TBI Drug Research
• Summary
• Bibliography

DLF Mission

Scientific Rationale

In recent years, neuroscientists have accumulated a deeper understanding of how genes control brain plasticity — the capacity of the brain to repair or modify its connections, especially in response to injury. Several genetically controlled modulators have been identified that inhibit neuronal repletion, axonal regeneration and sprouting, and synaptic reconnection in the aging or injured brain. At the same time, there have been significant advances in tools and methods — such as human induced pluripotent stem cell (iPSC) derived cellular models, optical electrophysiology, genomically-targeted medicines, and high-throughput screening methods — that, in combination, show much promise for identifying drugs to improve outcomes associated with previously untreatable neurological conditions.  For instance, there is growing evidence of the effectiveness of antisense oligonucleotides (ASOs) and other genomically-targeting small molecule medicines that interact with genetic controls and transcriptional products to ameliorate symptoms of several neurological diseases. When applied to TBI, these pharmacologic agents show potential to “downregulate” the genetic modulators which inhibit repletion, regrowth, and reconnection in the brain and central nervous system.  It is now quite possible to synthesize a strand of nucleic acid — an ASO — that will bind to the messenger mRNA of a particular gene and inactivate it, effectively turning that gene “off”.  Put another way, the inhibition of the inhibition of neurologic recovery is one key pathway that the Dan Lewis Foundation is exploring. 

ASOs have been shown to be effective in decreasing the negative symptoms of a variety of disorders. Examples of ASO-based therapies, recently approved by the FDA, for previously untreatable disorders include Formiversen for Cytomegalovirus Retinitis, Mipomersen for Homozygous Familial Hypercholesterolemia, Eteplirsen for Duchenne Muscular Dystrophy,  Nusinersen for Spinal Muscular Atrophy, and  Milasen for Batten Disease. In the context of TBI drug research, we believe it may be possible to apply ASOs to “turn off” genetic regulatory systems that cause neurons to stop proliferating and which limit the formation of new synapses as part of the developmental process. Intervening with specifically designed ASOs may promote cortical regeneration and synaptic reconnections, especially in the context of consistently targeted rehabilitation therapies. 

Additional research pathways that the Foundation will pursue spring from Dr. Mark Bear’s work on the mGluR theory of Fragile X mental retardation. His subsequent efforts to find drug therapies have demonstrated that restoration of cortical synaptic function is demonstrable in animal models and very likely to be possible in humans. Dr. Stephen Strittmatter’s  work involving  anti-NOGO antibodies to block NOGO molecules (which inhibit regeneration)(Wang et al., 2020) has shown that regrowth and sprouting of axons in the central nervous system can be achieved. Recently, a small body of literature has emerged that identifies the role of the LYNX1 gene as a down-regulator of neuroplasticity in a rodent model (Morishita et al., 2010).  A LYNX1 knock-out model seems to promote neuroplasticity that is otherwise lost. We will investigate the possibility that knock-down of this gene in a patient with cortical injury might permit cortical repair or regeneration.

In sum, the Dan Lewis Foundation for Brain Regeneration Research will empirically evaluate strategies for unlocking a regenerative capacity in the damaged adult human brain by designing genomically targeted pharmacologic agents that can reactivate cortical plasticity. A world class group of neuroscientists and biomedical innovators has been assembled to specify and prioritize the Foundation’s research goals. We will accomplish these goals by providing seed funding for programmatic research at major academic laboratories, by sponsoring post-doctoral fellowships for applicants whose preliminary work shows exceptional promise in our specified priority areas, by working with biotechnology companies, and by coordinating our work with leading brain injury advocacy and policy groups. Our overarching goal is to make safe and effective pharmacological treatments available to persons with moderate and severe brain injuries within the next 3 to 5 years. 



Overview

No specific drugs exist to stimulate functional recovery in an injured brain during the months and years after a traumatic brain injury.  The complexity of brain biology, structure, and function has limited, thus far, both the discovery of drug targets and the creation of medicines to help heal a damaged brain.  Recent advances in cell biology, neuroscience, biotechnology, genomically-targeting medicines, and machine learning computational have converged and renewed hope that drugs can be developed to drive brain regeneration.  Any such future drugs, administered in the context of intense training and supported by various biomechanical and computational prostheses, would create new hope for individuals with severe traumatic brain injuries.

The DLF’s 1st Annual Summit Meeting on Brain Regeneration Research was convened on August 6-7, 2021 in Boston, Massachusetts to explore ideas that may help to advance this field of research and to guide the DLF’s sponsored research agenda. During the initial evening of the meeting, Dr. Hal Lewis provided welcoming remarks (a transcript of those remarks is provided below).Additional presentations included orientation to the DLF’s goals, overview of the scientific underpinnings of the DLF’s mission, and a motivational presentation Dr. Michael Tranfaglia regarding the evolution of FRAXA and its mission to research and discover medicines to arrest and/or reverse the negative effects of Fragile X Syndrome.

On the second day of the meeting, round table discussions and topical focus groups considered key questions for consideration in planning and specifying the DLF’s research roadmap. Those key questions, major discussion points, and research priorities are summarized in a later section of this report.

I want to extend a hearty greeting to each of you participating in this seminal event for the Dan Lewis Foundation whether you are here in Boston or joining via Zoom. We are grateful for the time you have given us and for the contributions you will make towards specifying the research agenda we hope to support. I know how significant and productive your work is and how valuable your time is…so we will try to utilize the time you have generously given us efficiently and productively. Welcome and thank you very, very much.

I want to extend a few additional “thank you’s”. First, to our project secretary, Margaret Nicholson, who has done a wonderful job of organizing this meeting. Margaret has efficiently operationalized our aspirations for this conference into a working management plan…and carried out that plan in a remarkably short amount of time. Thank you, Margaret, very much.

I want to express my gratitude to the members of the foundation’s Scientific Advisory Board for their enthusiasm and guidance in shaping the goals of the DLF. These very accomplished, very thoughtful, and very kind individuals have been generous with their time, expertise, and wisdom. I can’t thank them enough. 

I particularly want to thank David Margulies, who assisted me in founding the Dan Lewis Foundation and has served as co-chair of the DLF Board of Directors for his leadership and hard work, especially during the early developmental stages of the DLF. David has been tremendous in sharing his wide ranging skills and his vision of what the DLF might become. 

Finally, I want to express my deep appreciation to the neuroscientific community as a whole for your dedication to exploring and understanding the workings of the central nervous system. From the granular level to the systems level, astounding amounts of data are being amassed, organized, and analyzed at speeds never thought to be possible until recently. This burgeoning knowledge base has led to successful treatments for several neurological and neuromuscular disorders and will doubtless lead to many, many more. From my vantage point, this embodies what is best about we humans--the collective effort to pursue knowledge that will benefit all—it is quite wondrous. 

Just a few weeks ago, all the media buzz centered on Richard Bransen’s and Jeff Bezos’ flights to the boundaries of outer space. Laudable in many ways.... Clearly, there is a strong human impulse to explore the unknown and clearly there is much unknown about outer space that is worth finding out about. But to me, what is even more spectacular, are the combined efforts of the scientific community to explore “inner space”…the inner space of the human brain. I’ve always been a fan of the film “Fantastic Voyage” and the book “The Magic School Bus Goes Inside the Human Body”. But seriously, to me, exploration of this “inner space” is of extraordinary value, representing an exciting journey of nearly infinite complexity and immeasurable benefit. 

Now, I’m going to show you a video consisting of two segments that paint a picture of my son, Dan, pre- and post-accident. The first segment is from a video tribute created by his college friends, shortly after his accident. The sound track in this part is from a recording of the acoustic cello group that Dan co-founded—the group is named Low Strung—playing their version of the classic rock song Dream On by Aerosmith. On this track, you will hear Dan playing the lead cello part. The video includes pictures of Dan relaxing with friends, playing his cello in various settings, and on the road during the cross-country bicycle trip that ended so abruptly. Thankfully, no pictures of him sitting in class taking notes. How boring would that be? You wouldn’t know from this video clip, but Dan was a very serious student primarily interested in advanced mathematics, physics, computer science, and literature.

The second segment shows Dan in some rehab activities over the last few years. Each section is about three (3) minutes long.

Click here to watch the video 

The contrast is stark and striking. Dan is essentially a different person now. For many years after Dan’s catastrophic injuries, my wife and I and Dan’s younger siblings, Katie and Peter, experienced two different Dans. It was as if there were two different universes in which Dan existed. This experience is very common for families of persons who have suffered severe brain injuries. It is an experience that is very difficult to reconcile with emotionally. The pain of realizing that a loved one has been so dramatically and negatively transformed in an instant—literally an instant—is very difficult to overcome. 

I should note that Dan continues to make functional progress, albeit, painstakingly slowly .Now, he can do a little arithmetic, he can read and spell some simple words, and make simple choices. He is showing improvement in bowing his cello and plucking simple patterns.

Unfortunately, he cannot work the finger board with his left hand due to left side hemiparesis. 

From a distance, these gains may not look like they amount to much but from up close they seem remarkable. For years, I talked to many people, many doctors, many scientists about whether there was anything that could be done to speed up Dan’s progress. The result of these conversations was almost always deflating. 

After Dan had gotten to a point of reasonable medical stability, I read a lot about stem cell treatments, attended stem cell seminars, talked to anyone I could find with ideas about stem cell treatments. But the outcome data regarding stem cell treatment for TBI were not convincing, the evaluation methods were generally not rigorous, and the risks--for instance--the risk of tumor formation, led me to realize that the medical science was not yet sufficiently advanced to pursue this treatment for Dan. 

About six years ago,  I began to search for information about other potential paths towards regeneration of the brain that might give hope to the possibility of meaningful functional gains. The idea began to germinate that I might not have to be resigned to the tragedy of Dan’s life, that biomedical innovations might hold hope for significant improvement. Gradually in various discussions, I became aware that a multi-modal approach including genomically targeting drugs, bioengineered devices, computerized brain interfaces, and newest stem cell methodologies in the context of aggressive rehabilitation and therapies did, indeed, hold hope for brain regeneration. 

About 2½ years ago, I reconnected with David, a friend from our schoolboy years in the small New Jersey town in which we were raised. Back those many years ago, we had fun working on middle school and high school projects. As we exchanged stories about our families, Dan’s situation entered the conversation. As the conversation progressed, it became clear that we both had professional experience in neurological disorders and TBI, me as a clinical and research psychologist and David as a physician as well as a bioinformatics and biotechnology expert. David picked up on my desire to do something transformational to help Dan and the hundreds of thousands of persons in the chronic stage of living with a severe brain injury. And so the seeds of the Dan Lewis Foundation for Brain Regeneration Research were planted. 

This is what led to the formation of the Dan Lewis Foundation. With the help of an excellent Board of Directors and a terrific group of neuroscientists, we have decided to focus initially on supporting discovery of neurogenic drugs. We are inspired by the work of Foundations such as FRAXA, Cure SMA, and the Cystic Fibrosis Foundation---exciting work catalyzing advocacy, resources, information, and research to address the challenges associated with these disorders. You will hear from Michael Tranfaglia, co-founder of FRAXA, in a few minutes.

We, of course, recognize that TBI itself--unlike most other neurological disorders--is not linked to genetic factors. This makes our challenge quite great--but we believe that this challenge can be met by the scientific community within the next 5 to 10 years,

In sum, the overarching goal of the Dan Lewis Foundation is to pursue breakthroughs that will, one day, improve the lives of those affected by serious brain injury. We aspire to make a broad range of biomedical therapies available to the very large population of people with moderate and severe brain injuries.

We will continue to raise funds and direct such funds toward the most promising and empirically supported biomedical therapeutics. By supporting programmatic research, the foundation aspires to expedite clinical trials - joint efforts between research institutions, biotech companies, and patients and their families.

As I’ve described to you, Dan and our family have been on quite a journey. I am so grateful to all of you for lighting the path on which our journey must continue and, perhaps, for accompanying us as we travel onward. This is a journey that will delve into that part of us that makes us truly human. A journey which many philosophers would agree takes us as close as possible to the seat of the human soul. A journey into “inner space” which seeks to improve the lives of millions of individuals and their families who have experienced severe TBI, who are hoping for more than resignation and acceptance, who are hoping for real improvement in the capacity to function and participate in family and community life.

Thank you all very much!

Conference Participants

• David Margulies, MD, Harvard Medical School (ret.)/Q-State Biosciences
• Hal Lewis, PhD, University of Colorado (ret.)
• Graham T. Dempsey, PhD, Q-State Biosciences
• Michael Crair, PhD, Yale University
• Stephen Strittmatter, MD, PhD, Yale University
• Sudhir Agrawal, PhD, ARNAY Sciences/University of Massachusetts Medical School
• Alan Kopin, MD, Tufts University School of Medicine
• Daniel Geschwind, MD, PhD, UCLA
• Ed Boyden, PhD, MIT
• Guo-li Ming, MD, PhD, University of Pennsylvania
• Hongjun Song, PhD, University of Pennsylvania
• Larry Benowitz, PhD, Harvard Medical School
• Jeffery D. Kocsis, PhD, Yale University
• Lorenz Studer, MD, Sloan Kettering Institute
• Marius Wernig, MD, Stanford University
• Roman Giger, PhD, MS, University of Michigan Medical School
• S Thomas Carmichael, MD, PhD, UCLA
• Steve Goldman, MD, PhD, University of Rochester
• Michael Tranfaglia, MD, FRAXA

Focus Group Topics

This report briefly summarizes current thinking in several key areas of research that are essential to the development of new medical treatments to improve long term outcomes for persons with moderate/severe TBI.  These areas include: (a) methods to quantify brain injury; (b) methods of inducing the formation of new synapses and axonal repair after injury; (c) methods to stimulate the production of new neurons (endogenously or ex vivo) to replace lost neural substrate; and (d) methods to design, develop, and test medicines that directly interact with the control mechanisms of synaptogenesis, axonal regeneration, and neurogenesis.

A wide range of questions provided a focus for the round table discussions and the action planning sessions that comprised a majority of the meeting time. These questions are listed below:

• What quantitative methods are required: (a) to more precisely characterize brain function over time following a traumatic brain injury, and (b)  to evaluate the efficacy of  treatments?(Smith et al., 2019; Nadel et al., 2021; Yoo and Choi, 2021)
• What experimental models, organisms, techniques, or systems (in vitro and in vivo) will be crucial to develop therapies for TBI in the chronic phase after injury?
• What is the role of bioactive materials in promoting brain healing?(Lacalle-Aurioles et al., 2020; Tan et al., 2020) 
•  How is synaptogenesis regulated?(Gatto and Broadie, 2010; Harris, 2020)  
• What genomic networks control development and synapse formation in the human brain?(van Dyck and Morrow, 2017) 
• How is the transcriptional activity that mediates synaptogenesis regulated during normal development? 
• How do CNS synapses react to TBI?(Jamjoom et al., 2021) 
• How can brain synaptogenesis be reactivated after TBI?(Wen et al., 2017) 
• Can residual cortex be ‘remapped’ after TBI?(Wittenberg, 2010; Takase and Regenhardt, 2021)
•  What genomic networks control neurogenesis in the human brain?(Tirone et al., 2013; Bergmann, Spalding and Frisén, 2015; Nagappan, Chen and Wang, 2020) (Poplawski et al., 2020)
• What neurogenesis normally takes place in adults?(Kumar et al., 2019) 
• Why don’t CNS neurons regenerate?(Schwab and Strittmatter, 2014; Wang et al., 2020) 
• How can neurogenesis be reactivated in different regions of the brain during adulthood?(Richardson, Sun and Bullock, 2007; Sun, 2014) 
• How does TBI affect neurogenesis?(Zheng et al., 2013) 
• How might neurogenesis and accurate axonal projections be stimulated after TBI?
•  Can stem cell therapy or other cellular repletion therapies play a useful role in promoting recovery during the chronic phase of recovery after a traumatic brain injury?(Zheng et al., 2013; Cox, 2018; Xiong et al., 2018) 
• Does work with organoids have any practical or theoretical implications for cellular repletion therapy efforts?(Oyefeso et al., 2021)
•  What is the current state of research to repair spinal cord injuries?
•  What lessons and/or analogies should be taken from SCI research and applied to brain regeneration research?(Hirokawa et al., 2017; Li et al., 2020; Mohammed et al., 2020; Puls et al., 2020)
•  Can genomically targeting medicines be used to reactivate neurogenesis, synaptogenesis, and axonal projection after a traumatic brain injury?
• Do any existing pharmacologic therapies have efficacy in the chronic phase after an injury? 
• What therapies or approaches hold promise for TBI in the chronic phase?(Xiong et al., 2015) How can the results of prior clinical trials assist in the design of future trials? 

Summary of Key Points and Research Directions

The need for new drugs to treat traumatic brain injuries 

The magnitude of the problem of traumatic brain injury is well understood.  The clinical, economic, familial, and personal impacts of a serious traumatic brain injury have been described and quantified by many others. Whether caused by war, contact sports, motor vehicle accidents, street violence, strokes, degenerative brain or other disease conditions, or other tragic mishaps, a serious brain injury has devastating and life-altering consequences for the injured individual and his/her family (Iaccarino et al., 2018).

In recent decades, research efforts and clinical strategies have focused on brain protection and salvage in the hours to first months after the occurrence of the injury.  ‘Best practices’ have been defined to reduce ischemia, infection, and inflammation surrounding the injury (Hawryluk et al., 2020). Methods have been developed to characterize the initial and evolving scope of tissue and functional damage.[ref]  Techniques to rehabilitate and retrain the injured individual have been created [ref]. Protocols have been defined for the use of medications to manage pain, spasms, residual seizures, and the neuropsychiatric sequelae of the injury. 

A number of charitable foundations (Spinal Cord Team, 2020), research institutes, and biopharmaceutical companies (Market Research Future, no date) are now focused on the challenges of biomedical treatments for TBI, although the predominant emphasis of these efforts is on the early weeks and months after an injury.

The brain’s innate abilities to recover some amount of function have been appreciated for decades (Nudo, 2013). The prevailing understanding is that there exists a period of time after an acute injury (3-12+ months) during which the preponderance of achievable functional recovery will be realized.  There is, in many cases, some modest ongoing recovery thereafter.  However, the biological factors which influence this recuperation window are incompletely understood ((Sofroniew, 2018). Thus far, efforts to develop medicines that can extend or expand endogenous recovery mechanisms have been unsuccessful, although a variety of approaches have been trialed (Xiong et al., 2015).

The core strategy of the DLF is to seek a better understanding of the brain’s own recuperative mechanisms and then to amplify or prolong these mechanisms to stimulate therapeutic brain regeneration. This report briefly summarizes current thinking in key areas of research that are essential to the development of new medical therapies for TBI.  These areas include: (a) methods to quantify brain injury; (b) methods of inducing the formation of new synapses and axonal repair after injury; (c.) methods to stimulate the production of new neurons (endogenously or ex vivo) to replace lost neural substrate; and (d) methods to design, develop, and test medicines that directly interact with the control mechanisms of synaptogenesis, axonal regeneration, and neurogenesis.

Definition and characterization of a traumatic brain injury:

A precursor to progress towards meaningful medical therapies for TBI is to carefully characterize and quantify damage to the injured individual’s brain and to develop metrics that can be applied to cohorts.  The heterogeneity of injuries (cause, severity, impact on measurable skill domains, age at onset, interval since injury) greatly complicates efforts to design trials for any candidate therapy.  The paucity of specific biomarkers of injury and healing is a further challenge to progress in the field.  Creating descriptive standards that characterize individuals and cohorts based on objective clinical and imaging data would help accelerate learning from future trials by permitting meaningful multicenter and cross-study data analysis.

Imaging to quantify traumatic brain injuries:

Various functional imaging techniques can be used to evaluate an initial brain injury and to assess the brain’s response to therapies [ref].  Accurate quantitative methods to characterize brain function over time and after treatments will be necessary for future clinical trials of new medicines (Smith et al., 2019; Nadel et al., 2021; Yoo and Choi, 2021).   One important recent development is the use of SV2A PET scanning, a method of quantifying new synapse formation and a potentially important metric of therapeutic efficacy (Cai et al., 2019).  Continued development of functional imaging methods with finer spatial and temporal resolution will be critical to the design and execution of future trials of new TBI medicines.  Additionally, it is important to develop neuropsychological and other behavioral measures that have adequate validity and reliability so that potential changes in brain function can be mapped to observable outcomes.

Useful disease models for TBI research:

Given the heterogeneity of lesions after brain trauma, it is essential to define specific lesions to be the substrate of either basic or translational research. Some have targeted the defects in skilled motor movements after damage to the motor cortex as a fertile area for focus (Takase and Regenhardt, 2021).  Studies of motor deficits are practical since outcome measurements are relatively straightforward and there are reasonably well-defined animal models of damage to the motor cortex ((Xiong, Mahmood and Chopp, 2013).  Others have proposed focusing future trials on expressive language production, motor planning, or vision. One particularly fertile model problem is the study of inducing plasticity to treat amblyopia.  Bear et. al. have recently demonstrated the feasibility of unlocking renewed plasticity in the visual cortex of adult primates, and new drugs are now en route to the clinic for this disorder (Fong et al., 2020).  Another potentially fertile area of work is the focus on inducing retinal regeneration, where efforts are underway to restore vision by the replacement of retinal neurons (Becker, Tumminia and Chiang, 2021).

In addition to well-validated animal models (Xiong, Mahmood and Chopp, 2013), the field of TBI research also requires in vitro experimental models.  Given the cost and ethical challenges of using non-human primates, it is important to create and validate cell- and tissue-based models that faithfully replicate key features of the biology in an intact animal.  Cell culture methods (of primary neurons; derived neurons; brain slices; organoids) continue to evolve.  High throughput drug screening systems have been developed that measure very subtle changes in the excitability characteristics of cells, slices, organoids, and intact animals. The most advanced of these systems utilize all-optical electrophysiology coupled with optogenetic probes to measure hundreds of excitability parameters from the interaction of thousands of compounds on many millions of single neurons (Williams et al., 2019).  While the mechanisms of TBI can’t be replicated in vitro, these in vitro models are critical to the identification of the genetic targets that influence the core processes of brain regeneration.  These models can be used to screen or design drugs, study target engagement, and evaluate mechanisms of action of drugs that affect the drivers of regeneration.

Multiple potential mechanisms of brain repair and recovery:

Several different mechanisms might be activated to heal an injured brain region.  Surviving neurons could create new connections (“synaptogenesis”) or repair damaged axons.  Damaged neurons could be replaced with repleted populations of neurons (“neurogenesis”) or introduced from compatible exogenous sources (“cellular repletion”).  Existing populations of neurons might be recruited to assume the functions formerly subtended by damaged or destroyed neurons (“remapping”).  All of these processes are controlled by neuronal transcriptional machinery. 

Stimulating plasticity (compensatory synaptogenesis):

After a serious TBI, the recovery from neurologic deficits will rely on the brain’s ability to form new and functional synaptic connections, since it is presumed that plasticity is a manifestation of synaptogenesis.  Synaptogenesis is, in turn, a tightly regulated process that is under transcriptional controls with both developmental (temporal) and environmental inputs (Gatto and Broadie, 2010; Kolb, Harker and Gibb, 2017; Harris, 2020).   The neurochemistry of forming and regulating CNS synapses has been studied for decades and forms the basis of neuropharmacology efforts (Berry-Kravis et al., 2018).  Many different disorders are associated with or caused by abnormalities in synaptic development or function, and synaptic neurochemistry is the target of many different neuropsychiatric and neurodevelopmental drug development programs [ref](Lüscher and Isaac, 2009). More recently, there are insights about the details of the genomic systems that govern the creation of new synapses (Clayton et al., 2020); (van Dyck and Morrow, 2017) or limit neuronal repair.  The activity and state of transcriptional networks which control synaptogenesis are different at different developmental stages and, presumptively, during the various phases after a brain injury (Minatohara, Akiyoshi and Okuno, 2015; Engelmann and Haenold, 2016).  Certain specific genes and pathways have been identified in the brain and spinal cord to be involved in neuronal repair and re-activated plasticity (Wen et al., 2017; Lindborg et al., 2021).  It is believed that with a sufficiently detailed understanding of CNS transcriptional networks, it will be possible to develop genomically targeting medicines that modulate synaptogenesis and can be used to treat a range of neurologic disorders and injuries.(Hutson and Di Giovanni, 2019). 

Amblyopia (cortically-mediated ocular visual impairment) has proven to be a useful model of CNS synaptic plasticity.  It has long been known that the visual cortex is programmed by early life visual experiences.  If the visual cortex is deprived of input from one eye during early development, certain irreversible changes occur that limit recovery even if sight is restored.   Some of the factors that regulate the closure of the visual cortex plasticity window have now been identified, and these factors are being explored as druggable targets {Stritmatter; LYNX1} (Kraft, 2019).  It is hoped that successful trials to treat amblyopia may create a path toward more broadly applicable therapies to restore cortical plasticity to the adult brain.

Neurogenesis and neuronal repair:

Neurogenesis in the normal adult human brain is believed to be limited to the hippocampus and is not an important component of healing after an injury, especially in adults (Kumar et al., 2019).  Gradually, the specific genomic networks that control neurogenesis in the human brain are being identified (Tirone et al., 2013; Bergmann, Spalding and Frisén, 2015; Nagappan, Chen and Wang, 2020). 

Factors limiting the regeneration of CNS neurons have been identified (Schwab and Strittmatter, 2014; Wang et al., 2020). 

After certain injuries, populations of neurons survive but suffer damage to axonal projections.  Strittmatter and colleagues have focused on unlocking neuronal repair for patients with spinal cord injuries (Wang et al., 2020).  Two different classes of factors that inhibit neuronal repair after spinal cord injury have been identified: (i) factors associated with gliosis (scarring); and (ii) factors associated with myelin (Schwab and Strittmatter, 2014).  One example of the latter is Nogo-A.  It has been a drug target for 30 years, with antibodies that target Nogo-A one of the approaches that have been trialed (Sartori, Hofer and Schwab, 2020).  More recently, another approach to disinhibit neuronal repair has been to target the Nogo-66 receptor 1 (NgR1) since it is the target of several inhibitors (specifically myelin-associated glycoprotein and oligodendrocyte myelin glycoprotein).  AXER-204 is a synthetic trap for NgR1 ligands.  This drug has been tested in NHPs, demonstrated increased axonal sprouting and functional recovery caudal to an induced lesion, and is now being trialed in humans with spinal cord injuries (https://clinicaltrials.gov/ct2/show/NCT03989440). 

There is some thought that combinatorial approaches which address both gliosis and myelin inhibition (Griffin and Bradke, 2020) may be more effective in enhancing regeneration (Hutson and Di Giovanni, 2019) than targeting one process or the other.

It is not certain that progress in unlocking repair for SCI victims will generalize to other CNS lesions (Hirokawa et al., 2017; Li et al., 2020; Mohammed et al., 2020; Puls et al., 2020). But, in principle, there is reason to expect that other areas of the CNS can be targeted using analogous strategies.

Some injuries deplete the population of viable neurons, and, consequently, efforts are underway to stimulate active neuronal production from surviving precursor populations in situ.  Further work needs to be done to determine if neurogenesis can be selectively reactivated in different regions of the brain during adulthood (Richardson, Sun and Bullock, 2007; Sun, 2014).  It is also not clear if and how a traumatic brain injury itself directly affects neurogenesis (Zheng et al., 2013) or would alter a response to drug stimulants of neurogenesis, should any such stimulants be developed. 

Neuronal repletion:

Another approach that has been proposed to stimulate brain recovery and regeneration after a traumatic injury is to replace the lost neuronal population with some form of neural tissue.  A number of sources have been explored, including: (i.) generation of autologously derived neurons; (ii.) transplantation with neurons derived from a donor, either as primary neurons or as iPSC-derived neurons; and (iii) neurons which are derived from more advanced stages of 3-D tissue culture (e.g., organoids) [ref]. There is some early evidence that transplanted neurons can engraft and be functional.  This approach is being explored as a potential way to promote recovery during the chronic phase of recovery after a traumatic brain injury (Zheng et al., 2013; Cox, 2018; Xiong et al., 2018).  Cellular repletion therapies using a variety of cell sources are being intensively studied for spinal cord injuries, and lessons derived from these efforts will likely inform efforts to transplant cells for other CNS disorders (Assinck et al., 2017; Fischer, Dulin and Lane, 2020).  The efficacy of cells that are obtained from dissociated organoids may or may not have any practical or theoretical implications for cellular repletion therapy efforts (Oyefeso et al., 2021).

Concurrent retraining:

It is likely that any medicine or combination of medicines that is designed to interact with genomically specified targets would need to be coupled with intensive environmental stimuli, given the deep coupling of synaptogenesis and exteroceptive experiences.

Remapping the cortex:

In principle, therapeutic synaptogenesis might target either damaged regions of cortex that are undergoing repair or, alternatively, other regions of intact cortex that can be remapped to residual sensory afferents.  Some injuries might disrupt the cortex but leave sensory inputs relatively intact.  In this situation, the goal of stimulating synaptogenesis would be to up-regulate the remapping of other connected regions of cortex to assume the processing tasks previously assigned to now-damaged cortex. It may be that the regulation of synapse formation in intact cortex is under different transcriptional controls than the formation of new synapses in damaged cortex (Wittenberg, 2010; Takase and Regenhardt, 2021).

Drug development approach and strategy:

If, as anticipated, it is possible to identify genetically-defined targets that modulate synaptogenesis and neurogenesis, there are several different approaches to drug development to be explored.  Repurposing of existing drugs [ref], salvage of previously trialed compounds with good safety data, small molecule screening [ref], and rationally designed genomically targeting medicines (e.g., antisense oligonucleotides (‘ASOs’)) all can be explored.  The emergence of ASOs is particularly encouraging since these compounds can have exquisite specificity, good safety profiles, and very rapid development cycles [ref].  Successful drug development will likely require prioritization of the process(es) to be targeted (e.g, synaptogenesis, axonal regrowth, remyelination, neurogenesis, or some combination). The prospects for successful drug development will be enhanced if there are clear, genetically determined targets that have been substantiated in well-validated animal and ex vivo models. If genomic sequence data from well-characterized populations with good clinical data can be accessed, it may be possible to identify genomic correlates of either unusual susceptibility to injury or, alternatively, of longer and stronger regenerative processes following a brain injury.  These correlates might well be useful in the identification of additional genes and networks that influence the central processes of brain healing. 

Even though there have been no successful drug trials that demonstrate efficacy in the chronic phase after an injury, there is important learning from these trials (Xiong et al., 2015).

Brain-computer interfaces:

Substantial academic and commercial efforts have been applied to augment CNS and PNS functions using various computational methods and biomechanical devices.  It is now possible to create interfaces between neural tissue and computational prostheses which can have both afferent and efferent properties.  Such devices have the potential to augment endogenous healing from traumatic brain injuries (Ajiboye et al., 2017).  Exploration of the roles for biomechanical devices were outside the scope of the DLF meeting reported on here and will be explored in future meetings.

An Agenda for TBI Drug Research

1. Support continued development of imaging methods to quantify TBI damage and response to therapy.
2. Focus on functional imaging studies, especially studies that can quantitate synaptic activity over time.
3. Support novel approaches to promotion of plasticity after injury
4. Contribute funding to well-focused efforts to up-regulate plasticity in well-characterized models (i.e., drug treatment of amblyopia in experimental animal models) using both small molecules (especially repurposed approved drugs or other late-stage compounds with clean safety profiles) and genomically-targeting drugs.
5. Contribute funding to efforts to identify gene systems that promote synaptogenesis and axonal repair in both brain and spinal cord.
6. Contribute funding to efforts to identify existing drugs (repurposed or salvaged) or to design novel ASOs that can stimulate synaptogenesis and axonal repair.
7. Participate in genome-wide association studies of suitable populations to look for gene sequence variation that is associated with protracted plasticity periods after injury.  Variants that modify the duration of the recuperative window after a TBI may point to genes or networks that can be targeted by drug development efforts.
8. Identify gene systems that regulate neurogenesis.
9. Contribute funding to efforts to identify existing drugs (repurposed or salvaged) or to design novel ASOs that can stimulate neurogenesis.
10. Support research to use emerging and novel ex vivo models of neuronal and brain tissue function for the purposes of TBI drug development.
11. Support knockout screens for regulators of synaptogenesis, axonal repair, and neurogenesis in cellular models.
12. Participate in research efforts to couple highly-targeted external stimuli in trials of medications for TBI and SCI.
13. Contribute support and method development to cellular repletion trials for CNS disorders (i.e., use of iPSCs and derived dopaminergic neurons for PD).
14. Participate in academic and commercial efforts to develop bioengineering and computational prostheses for both brain and spinal cord injuries.
15. Participate in collaborative funding activities with other foundations and research institutes who share DLF’s mission.
16. Participate in advocacy efforts to define regulatory pathways that are suitable to the highly variable injuries in TBI and for highly individualized genomically targeting medicines.

Summary

The 1st Annual Summit Meeting on Brain Regeneration Research was a seminal event in delineating the DLF’s research priorities. Preeminent neuroscientists and biotechnologists, from outstanding universities and biotech companies across the country, came together to pose provocative questions, explore key issues, and discuss potential research solutions with enthusiasm and a high degree of collegiality. The meeting culminated in a three-hour exploration of the challenges that exist—as well as the resources and opportunities--that inhere in the field of brain regeneration.

All those involved shared the goal of promoting improved functional outcomes for persons with moderate and severe brain injuries and an increased sense of hope and well-being for those individuals and their families.

The DLF is committed to pursuing breakthroughs that will, one day, improve the lives of those affected by brain injuries. We aspire to make a broad range of biomedical therapies available to people with such injuries. We will continue to raise funds and direct such funds toward the most promising biomedical therapeutics. In doing so, the DLF seeks to improve the lives of millions of individuals and their families who have experienced severe TBI, who are hoping for more than resignation and acceptance, who are hoping for real improvement in the capacity to function and participate in family and community life.

The DLF extends our gratitude to every one of the scientists who participated in the DLF’s 1st Annual Summit Meeting on Brain Regeneration Research.



*Planning is underway for the DLF’s 2nd Annual Summit Meeting on Brain Regeneration Research anticipated to be held in the summer of 2022. The primary focus currently under consideration for this meeting is “Biomechanical and Computational Adjunctive Therapies”. Updates regarding this meeting will be posted soon on the DLF website.

Bibliography

• Ajiboye, A. B. et al. (2017) ‘Restoration of reaching and grasping movements through brain-controlled muscle stimulation in a person with tetraplegia: a proof-of-concept demonstration’, The Lancet, 389(10081), pp. 1821–1830.
• Assinck, P. et al. (2017) ‘Cell transplantation therapy for spinal cord injury’, Nature neuroscience, 20(5), pp. 637–647.
• Becker, S. M., Tumminia, S. J. and Chiang, M. F. (2021) ‘The NEI Audacious Goals Initiative: Advancing the Frontier of Regenerative Medicine’, Translational vision science & technology, 10(10), p. 2.
• Bergmann, O., Spalding, K. L. and Frisén, J. (2015) ‘Adult Neurogenesis in Humans’, Cold Spring Harbor perspectives in biology, 7(7), p. a018994.
• Berry-Kravis, E. M. et al. (2018) ‘Drug development for neurodevelopmental disorders: lessons learned from fragile X syndrome’, Nature reviews. Drug discovery, 17(4), pp. 280–299.
• Cai, Z. et al. (2019) ‘PET imaging of synaptic density: A new tool for investigation of neuropsychiatric diseases’, Neuroscience letters, 691, pp. 44–50.
• Clayton, D. F. et al. (2020) ‘The role of the genome in experience-dependent plasticity: Extending the analogy of the genomic action potential’, Proceedings of the National Academy of Sciences of the United States of America, 117(38), pp. 23252–23260.
• Cox, C. S., Jr (2018) ‘Cellular therapy for traumatic neurological injury’, Pediatric research, 83(1-2), pp. 325–332.
• van Dyck, L. I. and Morrow, E. M. (2017) ‘Genetic control of postnatal human brain growth’, Current opinion in neurology, 30(1), pp. 114–124.
• Engelmann, C. and Haenold, R. (2016) ‘Transcriptional Control of Synaptic Plasticity by Transcription Factor NF-κB’, Neural plasticity, 2016, p. 7027949.
• Fischer, I., Dulin, J. N. and Lane, M. A. (2020) ‘Transplanting neural progenitor cells to restore connectivity after spinal cord injury’, Nature reviews. Neuroscience, 21(7), pp. 366–383.
• Fong, M.-F. et al. (2020) ‘Distinct Laminar Requirements for NMDA Receptors in Experience-Dependent Visual Cortical Plasticity’, Cerebral cortex , 30(4), pp. 2555–2572.
• Gatto, C. L. and Broadie, K. (2010) ‘Genetic controls balancing excitatory and inhibitory synaptogenesis in neurodevelopmental disorder models’, Frontiers in synaptic neuroscience, 2, p. 4.
• Griffin, J. M. and Bradke, F. (2020) ‘Therapeutic repair for spinal cord injury: combinatory approaches to address a multifaceted problem’, EMBO molecular medicine, 12(3), p. e11505.
• Harris, K. M. (2020) ‘Structural LTP: from synaptogenesis to regulated synapse enlargement and clustering’, Current opinion in neurobiology, 63, pp. 189–197.
• Hawryluk, G. W. J. et al. (2020) ‘Guidelines for the Management of Severe Traumatic Brain Injury: 2020 Update of the Decompressive Craniectomy Recommendations’, Neurosurgery, 87(3), pp. 427–434.
• Hirokawa, T. et al. (2017) ‘Regulation of axonal regeneration by the level of function of the endogenous Nogo receptor antagonist LOTUS’, Scientific reports, 7(1), p. 12119.
• Hutson, T. H. and Di Giovanni, S. (2019) ‘The translational landscape in spinal cord injury: focus on neuroplasticity and regeneration’, Nature reviews. Neurology, 15(12), pp. 732–745.
• Iaccarino, C. et al. (2018) ‘Epidemiology of severe traumatic brain injury’, Journal of neurosurgical sciences, 62(5), pp. 535–541.
• Jamjoom, A. A. B. et al. (2021) ‘The synapse in traumatic brain injury’, Brain: a journal of neurology, 144(1), pp. 18–31.
• Kolb, B., Harker, A. and Gibb, R. (2017) ‘Principles of plasticity in the developing brain’, Developmental medicine and child neurology, 59(12), pp. 1218–1223.
• Kraft, A. W. (2019) Molecular Mechanisms Responsible for Functional Cortical Plasticity during Development and after Focal Ischemic Brain Injury. Edited by J.-M. Lee. Washington University in St. Louis. Available at: https://www.proquest.com/dissertations-theses/molecular-mechanisms-responsible-functional/docview/2215340952/se-2.
• Kumar, A. et al. (2019) ‘ADULT NEUROGENESIS IN HUMANS: A review of basic concepts, history, current research, and clinical implications’, Innovations in clinical neuroscience, 16(5-6), pp. 30–37.
• Lacalle-Aurioles, M. et al. (2020) ‘Applying hiPSCs and biomaterials towards an understanding and treatment of traumatic brain injury’, Frontiers in cellular neuroscience, 14, p. 594304.
• Li, F. et al. (2020) ‘Glial Metabolic Rewiring Promotes Axon Regeneration and Functional Recovery in the Central Nervous System’, Cell metabolism, 32(5), pp. 767–785.e7.
• Lindborg, J. A. et al. (2021) ‘Optic nerve regeneration screen identifies multiple genes restricting adult neural repair’, Cell reports, 34(9), p. 108777.
• Lüscher, C. and Isaac, J. T. (2009) ‘The synapse: center stage for many brain diseases’, The Journal of physiology, 587(Pt 4), pp. 727–729.
• Market Research Future (no date) Traumatic brain injuries (TBI) treatment market 2019. Available at: https://www.medgadget.com/2019/05/traumatic-brain-injuries-tbi-treatment-market-2019-global-industry-analysis-with-top-companies-neuren-pharmaceuticals-ltd-ischemic-medicortex-teva-pharmaceutical-industries-ltd.html (Accessed: 28 September 2021).
• Minatohara, K., Akiyoshi, M. and Okuno, H. (2015) ‘Role of Immediate-Early Genes in Synaptic Plasticity and Neuronal Ensembles Underlying the Memory Trace’, Frontiers in molecular neuroscience, 8, p. 78.
• Mohammed, R. et al. (2020) ‘Evaluating the effectiveness of anti-Nogo treatment in spinal cord injuries’, Neural development, 15(1), p. 1.
• Morishita, H. et al. (2010) ‘Lynx1, a cholinergic brake, limits plasticity in adult visual cortex’, Science, 330(6008), pp. 1238–1240.
• Nadel, J. et al. (2021) ‘Emerging Utility of Applied Magnetic Resonance Imaging in the Management of Traumatic Brain Injury’, Medical sciences (Basel, Switzerland), 9(1). doi: 10.3390/medsci9010010.
• Nagappan, P. G., Chen, H. and Wang, D.-Y. (2020) ‘Neuroregeneration and plasticity: a review of the physiological mechanisms for achieving functional recovery postinjury’, Military Medical Research, 7(1), p. 30.
• Nudo, R. J. (2013) ‘Recovery after brain injury: mechanisms and principles’, Frontiers in human neuroscience, 7, p. 887.
• Oyefeso, F. A. et al. (2021) ‘Brain organoids: A promising model to assess oxidative stress-induced central nervous system damage’, Developmental neurobiology, (dneu.22828). doi: 10.1002/dneu.22828.
• Poplawski, G. H. D. et al. (2020) ‘Injured adult neurons regress to an embryonic transcriptional growth state’, Nature, 581(7806), pp. 77–82.
• Puls, B. et al. (2020) ‘Regeneration of Functional Neurons After Spinal Cord Injury via in situ NeuroD1-Mediated Astrocyte-to-Neuron Conversion’, Frontiers in cell and developmental biology, 8, p. 591883.
• Richardson, R. M., Sun, D. and Bullock, M. R. (2007) ‘Neurogenesis after traumatic brain injury’, Neurosurgery clinics of North America, 18(1), pp. 169–81, xi.
• Sartori, A. M., Hofer, A.-S. and Schwab, M. E. (2020) ‘Recovery after spinal cord injury is enhanced by anti-Nogo-A antibody therapy — from animal models to clinical trials’, Current Opinion in Physiology, pp. 1–6. doi: 10.1016/j.cophys.2019.11.001.
• Schwab, M. E. and Strittmatter, S. M. (2014) ‘Nogo limits neural plasticity and recovery from injury’, Current opinion in neurobiology, 27, pp. 53–60.
• Smith, L. G. F. et al. (2019) ‘Advanced neuroimaging in traumatic brain injury: an overview’, Neurosurgical focus, 47(6), p. E17.
• Sofroniew, M. V. (2018) ‘Dissecting spinal cord regeneration’, Nature, 557(7705), pp. 343–350.
• Spinal Cord Team (2020) The best traumatic brain injury organizations to donate to and why. Available at: https://www.spinalcord.com/blog/the-best-traumatic-brain-injury-organizations-to-donate-to-and-why (Accessed: 28 September 2021).
• Sun, D. (2014) ‘The potential of endogenous neurogenesis for brain repair and regeneration following traumatic brain injury’, Neural Regeneration Research, 9(7), pp. 688–692.
• Takase, H. and Regenhardt, R. W. (2021) ‘Motor tract reorganization after acute central nervous system injury: a translational perspective’, Neural Regeneration Research, 16(6), pp. 1144–1149.
• Tan, H. X. et al. (2020) ‘The use of bioactive matrices in regenerative therapies for traumatic brain injury’, Acta biomaterialia, 102, pp. 1–12.
• Tirone, F. et al. (2013) ‘Genetic control of adult neurogenesis: interplay of differentiation, proliferation and survival modulates new neurons function, and memory circuits’, Frontiers in cellular neuroscience, 7, p. 59.
• Wang, X. et al. (2020) ‘Nogo receptor decoy promotes recovery and corticospinal growth in non-human primate spinal cord injury’, Brain: a journal of neurology, 143(6), pp. 1697–1713.
• Wen, Z. et al. (2017) ‘Therapeutic Potentials of Synapses after Traumatic Brain Injury: A Comprehensive Review’, Neural plasticity, 2017, p. 4296075.
• Williams, L. A. et al. (2019) ‘Scalable Measurements of Intrinsic Excitability in Human iPS Cell-Derived Excitatory Neurons Using All-Optical Electrophysiology’, Neurochemical research, 44(3), pp. 714–725.
• Wittenberg, G. F. (2010) ‘Experience, cortical remapping, and recovery in brain disease’, Neurobiology of disease, 37(2), pp. 252–258.
• Xiong, L.-L. et al. (2018) ‘Neural Stem Cell Transplantation Promotes Functional Recovery from Traumatic Brain Injury via Brain Derived Neurotrophic Factor-Mediated Neuroplasticity’, Molecular neurobiology, 55(3), pp. 2696–2711.
• Xiong, Y. et al. (2015) ‘Investigational agents for treatment of traumatic brain injury’, Expert opinion on investigational drugs, 24(6), pp. 743–760.
• Xiong, Y., Mahmood, A. and Chopp, M. (2013) ‘Animal models of traumatic brain injury’, Nature reviews. Neuroscience, 14(2), pp. 128–142.
• Yoo, R.-E. and Choi, S. H. (2021) ‘The Emerging Role of Fast MR Techniques in Traumatic Brain Injury’, Investigative Magnetic Resonance Imaging, p. 76. doi: 10.13104/imri.2021.25.2.76.
• Zheng, W. et al. (2013) ‘Neurogenesis in Adult Human Brain after Traumatic Brain Injury’, Journal of neurotrauma, 30(22), p. 1872.