Damien Daniel Pearse

Glial cells shape inflammatory resolution, metabolic support, debris clearance, axonal preservation, and myelin repair after CNS injury and neurodegeneration. These functions have motivated two related but non-equivalent therapeutic strategies, either the transplantation and replacement of living glia or the delivery of glia-derived extracellular vesicles (EVs). A viable cell graft can persist, migrate, phagocytose, integrate with host tissue, and adapt its transcriptional and secretory programs after administration. EVs cannot reproduce these autonomous cellular functions, but they can transfer proteins, lipids, metabolites, and nucleic acids as finite, engineerable packages that may be repeated. Microglia provide the principal comparison because the same lineage can be transplanted, replaced, genetically engineered, or used to generate therapeutic EVs. Strategies targeting the microglial compartment include CNS-wide niche repopulation and pathology-responsive engineering, with early human evidence from hematopoietic transplantation in a small uncontrolled cohort with CSF1R-associated microgliopathy, whereas glial EV therapeutics remain predominantly preclinical. Producer-cell state is also critical because microglial EVs can support repair or propagate inflammatory and proteopathic signals. We compare glial cell and EV strategies across CNS trauma and neurodegeneration in terms of biological capability, evidence level, biodistribution, potency, manufacturing, and safety. The proposed framework separates two questions: (1) whether pathology requires replacement of a missing or intrinsically defective cellular population or function (Replace) versus changing the functional state of surviving recipient cells without replacing the population (Reprogram), and, when applicable, (2) what spatial and temporal delivery (Relay) is required, including whether exposure must be local and persistent or distributed and repeatable. Because matched cell-versus-EV studies are rare and the evidence base is asymmetric, this framework is a mechanistic guide for hypothesis generation rather than a ranking of platform efficacy in specific neurological injury or disease paradigms.

Spinal cord injury (SCI) triggers a secondary injury cascade characterized by persistent innate immune activation, chronic neuroinflammation, and progressive tissue loss that limits functional recovery. Here, we evaluated a systemic combination treatment using propentofylline (PPF), a glial modulator, together with interleukin-4 (IL-4), a cytokine associated with repair-related myeloid responses. In vitro, PPF enhanced IL-4-dependent induction of arginase-1 (ARG1) in TNFα-primed BV2 microglia. In vivo, adult Fischer rats of both sexes received vehicle, PPF, IL-4, or combined PPF + IL-4 beginning within 1 h after moderate T8 contusive SCI and continuing daily for 14 days. Locomotor recovery was assessed longitudinally for 8 weeks, followed by histological and immunohistochemical analyses. Combined PPF + IL-4 treatment produced the greatest improvement in gross and skilled locomotor recovery compared with vehicle, or either monotherapy. At 8 weeks post-SCI, the combined therapy aligned with a reduction in chronic lesion-associated p-p38 MAPK, decreased pP65 NFkB (RelA) activation, increased expression of reparative factors ARG1 and CD206, as well as reduced lesion cavitation and trends toward greater gray and white matter preservation. Stratification of functional data by sex showed BBB improvements with combined PPF + IL-4 in both males and females after SCI. Together, these findings show that combined systemic PPF and IL-4 treatment was associated with improved functional recovery, reduced lesion cavitation, and changes in lesion-associated molecular and histological endpoints after SCI, supporting further preclinical investigation.

Reliable characterization of circulating extracellular vesicles (EVs) in rodents may be significantly influenced by how blood is collected, yet systematic comparisons of commonly used sampling methods remain limited. Here, we directly evaluate the effects of cardiac puncture and perfusate blood collection on EV yield and surface-marker profiles in naïve mice, as well as in mice subjected to neurotrauma using a contusion spinal cord injury (SCI) model. Using matched isolation procedures and MACSPlex immunophenotyping, we analyzed newly generated cardiac puncture plasma alongside previously published perfusate-derived datasets, with both cohorts matched for age, sex, weight, injury severity, and post-injury timepoint. Cardiac puncture produced substantially higher particle concentrations due to access to undiluted blood, whereas perfusate samples exhibited modest increases in select markers, such as CD9, consistent with method-associated influences on platelet-derived vesicles. Despite these quantitative differences, both approaches yielded broadly similar EV phenotypes, and SCI-associated marker patterns remained stable across sampling methods. The consistency between cardiac puncture and perfusate datasets validates the robustness of our earlier perfusate-based findings and demonstrates that key biological signatures are preserved regardless of collection technique. These results provide practical guidance for optimizing murine EV studies and underscore the importance of methodological transparency and standardization in preclinical EV research.

Microglia-derived small extracellular vesicles (MGEVs) are key mediators of neuroimmune communication, yet their cross-species comparability and translational relevance remain poorly defined. Here, we establish a harmonized framework to compare the molecular and biochemical signatures of sEVs derived from immortalized mouse (BV2) and human (HMC3) microglial cells as well as assess their bioactivity on a human Schwann cell (HuSC) line. MGEVs were isolated via MISEV-aligned size-exclusion chromatography (SEC) and characterized by nanoparticle tracking analysis (NTA), transmission electron microscopy (TEM), and immunoblotting for canonical EV markers CD9, CD63, CD81, TSG101. Human and mouse MGEVs exhibited similar morphology but displayed distinct membrane tetraspanin protein enrichment patterns. Functionally, mouse and human MGEVs attenuated HuSC migration while enhancing HuSC proliferation and their resistance to H₂O₂-induced oxidative stress, with human MGEVs providing stronger protective effects, suggesting they retain similar core functional properties. Short, non-coding-miRNA sequencing analysis identified 196 shared miRNAs (Spearman ρ = 0.72) with species-specific enrichment: human MGEVs-derived miRNAs favored regenerative and metabolic pathways, whereas mouse MGEVs-derived miRNAs aligned more so with inflammatory signaling. This study delivers the first integrated cross-species blueprint of MGEVs, revealing conserved neuroprotective actions alongside species-biased miRNA cargo that define translational boundaries and highlight human-relevant MGEV signatures for therapeutic innovation, therefore contributing to the importance of considering these differences in translational research.

Transglutaminase 2 (TG2) is a multifunctional enzyme widely implicated in neuroinflammation and extracellular matrix (ECM) remodeling after central nervous

Spinal cord injury (SCI) remains a devastating neurological condition characterized by loss of sensory, motor and autonomic function. Despite decades of research, no FDA-approved regenerative therapies currently exist to restore lost function following SCI. Schwann cells (SCs) support axon regeneration, remyelination, and neuroprotection after SCI, with their therapeutic potential validated in clinical trials demonstrating safe and feasible transplantation in humans. Although SC transplantation has shown promising results, challenges remain, including modest graft survival, limited host integration, and restricted migration that collectively contribute to constrain efficacy. To address these limitations, biomaterial scaffolds have been explored as synergistic platforms to enhance SC delivery and function. When combined with natural or synthetic biomaterials such as hydrogels, nanofiber scaffolds, or ECM-mimetic matrices, SCs demonstrate improved survival, retention, spatial distribution, and regenerative activity. The intrinsic regenerative properties of SCs, first demonstrated in models of peripheral nerve injury, make them particularly well-suited for neural repair of the central nervous system (CNS) compared to other cell types and their effectiveness can be enhanced synergistically when combined with biomaterials. These constructs not only provide structural support but also modulate the lesion microenvironment, enhance axon growth and improve SC integration with host tissue. Combinatorial approaches incorporating biomaterials with SCs are emerging as next-generation strategies to optimize repair for clinical translation. This review focuses on current progress in SC-based therapies combined with biomaterials, highlighting key preclinical advances, clinical translation efforts, and the path forward toward effective regenerative interventions for SCI.

Neurodegenerative diseases (NDDs) such as Alzheimer’s, Parkinson’s, ALS, and Huntington’s pose a growing global challenge due to their complex pathobiology and aging demographics. Once considered as cellular debris, small extracellular vesicles (sEVs) are now recognized as active mediators of intercellular signaling in NDD progression. These nanovesicles (~30–150 nm), capable of crossing the blood–brain barrier, carry pathological proteins, RNAs, and lipids, facilitating the spread of toxic species like Aβ, tau, TDP-43, and α-synuclein. sEVs are increasingly recognized as valuable diagnostic tools, outperforming traditional CSF biomarkers in early detection and disease monitoring. On the therapeutic front, engineered sEVs offer a promising platform for CNS-targeted delivery of siRNAs, CRISPR tools, and neuroprotective agents, demonstrating efficacy in preclinical models. However, translational hurdles persist, including standardization, scalability, and regulatory alignment. Promising solutions are emerging, such as CRISPR-based barcoding, which enables high-resolution tracking of vesicle biodistribution; AI-guided analytics to enhance quality control; and coordinated regulatory efforts by the FDA, EMA, and ISEV aimed at unifying identity and purity criteria under forthcoming Minimal Information for Studies of Extracellular Vesicles (MISEV) guidelines. This review critically examines the mechanistic roles, diagnostic potential, and therapeutic applications of sEVs in NDDs, and outlines key strategies for clinical translation.

Spinal cord injury (SCI) triggers both local and systemic pathological responses that evolve over time and differ with injury severity. Small extracellular vesicles (sEVs), known mediators of intercellular communication, may serve as biomarkers reflecting these complex dynamics. In this study, we investigated whether SCI severity modulates the composition and abundance of circulating plasma-derived sEVs across subacute and chronic phases. Using a graded thoracic contusion model in mice, plasma was collected at defined timepoints post-injury. sEVs were isolated via size-exclusion chromatography and characterized using nanoparticle tracking analysis (NTA), transmission electron microscopy (TEM), and MACSPlex surface marker profiling. We observed an SCI-dependent increase in sEVs during the subacute (7 days) phase, most notably in moderate injuries (50 kdyne), with overall vesicle counts lower chronically (3 months). CD9 emerged as the predominant tetraspanin sEV marker, while CD63 and CD81 were generally present at low levels across all injury severities and timepoints. Surface sEV analysis revealed dynamic regulation of CD41⁺, CD44⁺, and CD61⁺ in the CD9⁺ sEV subset, suggesting persistent systemic signaling activity. These markers, traditionally associated with platelet function, may also reflect immune or reparative responses following SCI. Our findings highlight the evolving nature of sEV profiles after SCI and support their potential as non-invasive biomarkers for monitoring injury progression.

Microglia, the resident immune cells of the central nervous system (CNS), play a crucial role in maintaining neural homeostasis but can also contribute to disease and injury when this state is disrupted or conversely play a pivotal role in neurorepair. One way that microglia exert their effects is through the secretion of small vesicles, microglia-derived exosomes (MGEVs). Exosomes facilitate intercellular communication through transported cargoes of proteins, lipids, RNA, and other bioactive molecules that can alter the behavior of the cells that internalize them. Under normal physiological conditions, MGEVs are essential to homeostasis, whereas the dysregulation of their production and/or alterations in their cargoes have been implicated in the pathogenesis of numerous neurodegenerative diseases, including Alzheimer’s disease (AD), Parkinson’s disease (PD), multiple sclerosis (MS), spinal cord injury (SCI), and traumatic brain injury (TBI). In contrast, MGEVs may also offer therapeutic potential by reversing inflammation or being amenable to engineering for the delivery of beneficial biologics or drugs. The effects of MGEVs are determined by the phenotypic state of the parent microglia. Exosomes from anti-inflammatory or pro-regenerative microglia support neurorepair and cell survival by delivering neurotrophic factors, anti-inflammatory mediators, and molecular chaperones. Further, MGEVs can also deliver components like mitochondrial DNA (mtDNA) and proteins to damaged neurons to enhance cellular metabolism and resilience. MGEVs derived from pro-inflammatory microglia can have detrimental effects on neural health. Their cargo often contains pro-inflammatory cytokines, molecules involved in oxidative stress, and neurotoxic proteins, which can exacerbate neuroinflammation, contribute to neuronal damage, and impair synaptic function, hindering neurorepair processes. The role of MGEVs in neurodegeneration and injury—whether beneficial or harmful—largely depends on how they modulate inflammation through the pro- and anti-inflammatory factors in their cargo, including cytokines and microRNAs. In addition, through the propagation of pathological proteins, such as amyloid-beta and alpha-synuclein, MGEVs can also contribute to disease progression in disorders such as AD and PD, or by the transfer of apoptotic or necrotic factors, they can induce neuron toxicity or trigger glial scarring during neurological injury. In this review, we have provided a comprehensive and up-to-date understanding of the molecular mechanisms underlying the multifaceted role of MGEVs in neurological injury and disease. In particular, the role that specific exosome cargoes play in various pathological conditions, either in disease progression or recovery, will be discussed. The therapeutic potential of MGEVs has been highlighted including potential engineering methodologies that have been employed to alter their cargoes or cell-selective targeting. Understanding the factors that influence the balance between beneficial and detrimental exosome signaling in the CNS is crucial for developing new therapeutic strategies for neurodegenerative diseases and neurotrauma.

Subacute spinal cord injury (SCI) displays a complex pathophysiology associated with pro-inflammation and ensuing tissue damage. Microglia, the resident innate immune cells of the CNS, in concert with infiltrating macrophages, are the primary contributors to SCI-induced inflammation. However, subpopulations of activated microglia can also possess immunomodulatory activities that are essential for tissue remodeling and repair, including the production of anti-inflammatory cytokines and growth factors that are vital for SCI recovery. Recently, reports have provided convincing evidence that sex-dependent differences exist in how microglia function during CNS pathologies and the extent to which these cells contribute to neurorepair and endogenous recovery. Herein we employed flow cytometry and immunohistochemical methods to characterize the phenotype and population dynamics of activated innate immune cells within the injured spinal cord of age-matched male and female rats within the first week (7 days) following thoracic SCI contusion. This assessment included the analysis of pro- and anti-inflammatory markers, as well as the expression of critical immunomodulatory kinases, including P38 MAPK, and transcription factors, such as NFκB, which play pivotal roles in injury-induced inflammation. We demonstrate that activated microglia from the injured spinal cord of female rats exhibited a significantly diminutive pro-inflammatory response, but enhanced anti-inflammatory activity compared to males. These changes included lower levels of iNOS and TLR4 expression but increased levels of ARG-1 and CD68 in females after SCI. The altered expression of these markers is indicative of a disparate secretome between the microglia of males and females after SCI and that the female microglia possesses higher phagocytic capabilities (increased CD68). The examination of immunoregulatory kinases and transcription factors revealed that female microglia had higher levels of phosphorylated P38^{Thr180/Tyr182} MAPK and nuclear NFκB pp50^Ser337 but lower amounts of nuclear NFκB pp65^Ser536, suggestive of an attenuated pro-inflammatory phenotype in females compared to males after SCI. Collectively, this work provides novel insight into some of the sex disparities that exist in the innate immune response after SCI and indicates that sex is an important variable when designing and testing new therapeutic interventions or interpretating positive or negative responses to an intervention.