Biology subjects

Franklin, R. J. M.

Publications and source records attributed to Franklin, R. J. M..

7 recordsLinked to original sources

bioRxiv2025

Spontaneous differentiation across cell lineages of separate germ layer origin during progenitor cell-mediated regeneration of the central nervous system

During CNS regeneration, neuroepithelial-derived oligodendrocyte progenitor cells (OPCs) can cross germ-layer boundaries to generate neural-crest-derived Schwann cells (SCs). However, the underlying mechanism and disease relevance of this unique phenomenon of cellular plasticity is unclear. Here, we combine single cell genomics in rodent models of CNS injury and samples from multiple sclerosis patients to characterise OPC-derived SCs. We discover that integrin signalling and bone morphogenetic protein (BMP) activation activate a core SOX10/OLIG2 transcriptional circuit to drive OPC-to-SC differentiation. We show that OPC-derived SCs myelinate in vitro and in vivo, and unlike peripheral SCs, can integrate into astrocyte-rich territories. Together, these findings define a conserved molecular mechanism of adult plasticity, enabling the control of OPC fate choices beyond their germ layer origin for CNS repair.

neuroscience↗

bioRxiv2024

Transcriptional profiles of murine oligodendrocyte precursor cells across the lifespan

Oligodendrocyte progenitor cells (OPCs) are highly dynamic, widely distributed glial cells of the central nervous system (CNS) that are responsible for generating myelinating oligodendrocytes during development. By also generating new oligodendrocytes in the adult CNS, OPCs allow formation of new myelin sheaths in response to environmental and behavioral changes and play a crucial role in regenerating myelin following demyelination (remyelination). However, the rates of OPC proliferation and differentiation decline dramatically with aging, which may impair homeostasis, remyelination, and adaptive myelination during learning. To determine how aging influences OPCs, we generated a novel transgenic mouse line that expresses membrane-anchored EGFP under the endogenous promoter/enhancer of Matrilin-4 (Matn4-mEGFP) and performed high-throughput single-cell RNA sequencing, providing enhanced resolution of transcriptional changes during key transitions from quiescence to proliferation and differentiation across the lifespan. Comparative analysis of OPCs isolated from mice aged 30 to 720 days, revealed that aging induces distinct inflammatory transcriptomic changes in OPCs in different states, including enhanced activation of HIF-1 and Wnt pathways. Inhibition of these pathways in acutely isolated OPCs from aged animals restored their ability to differentiate, suggesting that this enhanced signaling may contribute to the decreased regenerative potential of OPCs with aging. This Matn4-mEGFP mouse line and single-cell mRNA datasets of cortical OPCs across ages help to define the molecular changes guiding their behavior in various physiological and pathological contexts.

neuroscience↗

bioRxiv2023

Circulating Platelets Modulate Oligodendrocyte Progenitor Cell Differentiation During Remyelination

Revealing unknown cues that regulate oligodendrocyte progenitor cell (OPC) function in remyelination is important to optimise the development of regenerative therapies for multiple sclerosis (MS). Platelets are present in chronic non-remyelinated lesions of MS and an increase in circulating platelets has been described in experimental autoimmune encephalomyelitis (EAE) mice, an animal model for MS. However, the contribution of platelets to remyelination remains unexplored. Here we show platelet aggregation in proximity to OPCs in areas of experimental demyelination. Partial depletion of circulating platelets impaired OPC differentiation and remyelination, without altering blood-brain barrier stability and neuroinflammation. Transient exposure to platelets enhanced OPC differentiation in vitro, whereas sustained exposure suppressed this effect. In a mouse model of thrombocytosis (CALRHET), there was a sustained increase in platelet aggregation together with a reduction of newly-generated oligodendrocytes following toxin-induced demyelination. These findings reveal a complex bimodal contribution of platelet to remyelination and provide insights into remyelination failure in MS.

neuroscience↗

bioRxiv2023

Combination-Based Drug Screening for Induced Oligodendrocyte Differentiation Enables Mechanistic Insight and Identifies Optimal Drug Pairs for Remyelination

Remyelination-promoting agents have significant potential utility as therapies for the treatment of demyelinating diseases, including multiple sclerosis. Clemastine and bexarotene have recently been evaluated in Phase II clinical trials to evaluate their potential in this context, with evidence for drug-induced remyelination being observed in both trials. Efficacy levels for both agents as monotherapies, as well as dose-limiting toxicities, highlight the need for more effective approaches. Additionally, questions about the relevance of M1R as the target of clemastine, and also around a mechanism involving accumulation of 8,9-unsaturated sterols, remain. Here, we have identified potent alternatives to clemastine (i.e., doxepin and orphenadrine), which are predicted to have superior tolerability and efficacy profiles and provide mechanistic insight related to M1R, and have completed pairwise drug combination screens using diverse classes of OPC differentiation-inducing agents. Vitamin D receptor agonists were found to enhance M1R antagonist-induced OL differentiation. Select compounds implicated in 8,9-unsaturated sterol accumulation synergistically enhanced the activity of bexarotene in OPCs, which resulted in insights that implicate a critical role for liver-X-receptor in the mechanisms of both sterol-dependent and bexarotene-induced remyelination.

neuroscience↗

bioRxiv2021

The role of complex IV activity in the axonal response of mitochondria to demyelination in experimental disease models of multiple sclerosis

Axon loss is a cardinal neuropathological feature of multiple sclerosis (MS). Axonal injury in MS and experimental disease models is most frequently detected in acutely demyelinating regions. Furthermore, acute axonal injury consistently correlates with the extent of inflammatory demyelination. Following lysolecithin-induced demyelination, we recently reported a compensatory response in neurons, where mitochondria move from the cell body to the acutely demyelinated axon and increase the mitochondrial content. We termed this energetics phenomenon, that is also evident in MS, the axonal response of mitochondria to demyelination (ARMD). In the present study, we assessed axonal mitochondrial content as well as axonal mitochondrial respiratory chain complex IV activity (COX) of axons and related these to axonal injury in nine different experimental disease models. We consistently found ARMD in all experimental disease models. However, the increase in mitochondrial content within demyelinated axons was not always accompanied by a proportionate increase in COX activity, particularly in experimental autoimmune encephalomyelitis (EAE). Axonal COX activity inversely correlated with the extent of axonal injury in experimental disease models. Our findings indicate that ARMD is a consistent and prominent finding and emphasises the need to preserve axonal mitochondrial COX activity in inflammatory demyelination, paving the way for the development of novel neuroprotective therapies.

neuroscience↗

bioRxiv2020

Single Cell Sequencing Reveals Glial Specific Responses to Tissue Processing & Enzymatic Dissociation in Mice and Humans

A key aspect of nearly all single cell experiments is the necessity to dissociate intact tissues into single cell suspensions for processing. While many protocols have been optimized for optimal cell yield, they have often overlooked the effects that dissociation can have on ex vivo gene expression changes during this process. Microglia, the brains resident macrophages, are a highly dynamic population that are extremely sensitive to their microenvironment and have been shown to dramatically alter their transcriptome upon stimulation. We demonstrate that use of enzymatic dissociation methods on mouse central nervous system (CNS) tissue induces an aberrant gene expression signature in microglia that can significantly confound downstream analysis. To minimize this issue, we developed a flexible protocol, that can be used with existing enzymatic protocols for fresh tissue, to eliminate artifactual gene expression while allowing for increased cell type diversity and yield. We demonstrate efficacy of this protocol in analysis of diverse CNS cell types and sorted myeloid populations while using enzymatic dissociation. Generation of new and reanalysis of previously published human brain single nucleus RNAseq (snRNA-seq) datasets reveal that a similar signature is also present in post-mortem tissue. Through novel snRNA-seq analysis of acutely-resected neurosurgical tissue we demonstrate that this signature can be induced in human tissue due to technical differences in sample processing. These results provide key insight into the potential confounds of enzymatic digestion and provide a solution to allow for enzymatic digestion for scRNA-seq while avoiding ex vivo transcriptional artifacts. Analysis of human tissue reveals potential for artifacts in current and future snRNA-seq datasets that will require deeper analysis and careful consideration to separate true biology from artifacts related to post-mortem processes.

neuroscience↗

bioRxiv2019

Specific oligodendrocyte populations have differential spatial distribution and susceptibility to injury

Oligodendrocytes (OLs), the myelinating cells of the central nervous system, are transcriptionally heterogeneous,1 the origin and functional consequences of which are unknown. Functional heterogeneity of MOLs might correlate with the local environment or their interactions with different neuron types.2 Here, we show that distinct MOL populations have spatial preference in the mammalian central nervous system and differential susceptibility to traumatic spinal cord injury. We also show that the generation of distinct MOL populations is independent of the OPC developmental origin. We found that OPCs originating from the previously described developmental waves3-5 have comparable potential to differentiate into the main MOL populations. Furthermore, we found that MOL type 2 (MOL2) is enriched in the spinal cord and almost absent in the brain, while MOL5/6 is enriched with age in all analyzed regions. MOL2 and MOL5/6 also have differential preference for motor and sensory tracts in the spinal cord. In the context of disease, we found that MOL2 and MOL5/6 have differential susceptibility to traumatic spinal cord injury, where MOL2 are lost and MOL5/6 increased their contribution to the OL lineage. Importantly, MOL2 susceptibility is disease specific, as we found MOL2 is not lost in a mouse model of multiple sclerosis. Our results demonstrate that the MOL populations, previously described by single-cell transcriptomics,1 have distinct spatial preference and responses. We anticipate our study to pave the way for a better understanding of the MOL populations-specific functional roles in development, health, and disease, allowing for better targeting of the OL subtypes important for the regeneration and repair of the central nervous system.

neuroscience↗