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A single-cell atlas deconstructs heterogeneity across multiple models in murine traumatic brain injury and identifies novel cell-specific targets

ABSTRACT: The problem of traumatic brain injury (TBI) heterogeneity has been a critical barrier to successful translation of therapies in the field. TBI heterogeneity exists in the patient substrate pre-injury (genetics, sex, comorbidities), external injury characteristics (severity, mechanism), and resultant post-injury host response that is responsible for deleterious secondary injury processes (seizures, neuroinflammation, neurodegeneration) and repair/regeneration. Identification of final common molecular pathways and signatures that integrate this vast heterogeneity could be valuable for guiding biomarkers, therapeutic targets, and predictive enrichment. In this study, we present the first large-scale searchable murine single-cell atlas of the transcriptomic response to TBI in 339,357 cells as a foundational step in molecularly deconstructing TBI heterogeneity. We identify 23 cell types with massive heterogeneity in the single-cell response across extrinsicand intrinsic factors, that has been underestimated. Majority of response to TBI was unique to individual cell populations with minimal overlap even within a single injury-model thus highlighting the importance of cell-level resolution. Through this effort, we report novel cell-specific targets and a previously unrecognized role for specific microglial and ependymal subtypes in post-TBI pathophysiology that is highly variable depending on the extrinsic and intrinsic factors studied. One ependymal subtype was a hub of neuroinflammatory signaling after contusional-TBI, particularly related to Il-1b. A single microglial-lineage along pseudotime (comprising 3 microglial subtypes) was a key mediator of host-response after TBI, and shared features with disease associated microglia noted in Alzheimer’s disease and other neurodegenerative disorders, potentially providing a link between TBI and accelerated neurodegeneration. One microglial subtype within this lineage emerged as a key target – it was the only cell type of all 23 that retained persistent and marked gene expression changes 6 months post contusional-TBI. We identify sexually dimorphic gene expression and pathway vulnerabilities with cell-specific differences in both immune and non-immune biological processes. These likely contribute to sex-based outcome and warrant further study to facilitate discovery of cell- and sex-specific druggable targets. Active changes in brain regions distal from the site of primary TBI impact included infiltration of specific microglial populations as well as cell-specific transcriptomic changes in several genes and inflammatory processes distinct from both the peri-contusional and naïve signatures. This atlas validates several known contributors in TBI pathophysiology, and also identifies previously unrecognized targets and avenues for further research. Beyond our presented exemplar analyses (including pathways of clinical interest like sulfonylurea-receptor-1), the companion searchable atlas serves as a foundation for countless future efforts to understand cell-specific heterogeneity after TBI (https://shiny.crc.pitt.edu/cerebri/) as well as numerous other neurological diseases with overlapping pathophysiology.

ORGANISM(S): Mus musculus

PROVIDER: GSE269748 | GEO | 2024/07/02

REPOSITORIES: GEO

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Project description:Background: Traumatic brain injury (TBI) often results in diverse molecular responses, challenging traditional proteomic studies that measure average changes at tissue levels and fail to capture the complexity and heterogeneity of the affected tissues. Spatial proteomics offers a solution by providing insights into sub-region-specific alterations within tissues. This study focuses on the hippocampal sub-regions, analyzing proteomic expression profiles in mice at the acute (1 day) and subacute (7 days) phases of post-TBI to understand subregion-specific vulnerabilities and long-term consequences. Methods: Three mice brains were collected from each group including Sham, 1-day post-TBI and 7-day post-TBI. Hippocampal subregions were extracted using Laser Microdissection (LMD); and subsequently analyzed by label-free quantitative proteomics. Results: The spatial analysis reveals region-specific protein abundance changes, highlighting the elevation of FN1, LGALS3BP, HP, and MUG-1 in the stratum moleculare (SM), suggesting potential immune cell enrichment post-TBI. Notably, established markers of chronic traumatic encephalopathy, IGHM and B2M, exhibit specific upregulation in the dentate gyrus bottom (DG2) independent of direct mechanical injury. Metabolic pathway analysis identifies disturbances in glucose and lipid metabolism, coupled with activated cholesterol synthesis pathways enriched in SM at 7-Day post-TBI and subsequently in deeper DG1 and DG2 suggesting a role in neurogenesis and onset of recovery. Coordinated activation of neuroglia and microtubule dynamics in DG2 suggest recovery mechanisms in less affected regions. Cluster analysis revealed spatial variations post-TBI, indicative of dysregulated neuronal plasticity and neurogenesis and further predisposition to neurological disorders. TBI-induced protein upregulation (MUG-1, PZP, GFAP, TJP, STAT-1 and CD44) across hippocampal sub-regions indicates shared molecular responses and links to neurological disorders. Spatial variations were demonstrated by proteins dysregulated in both or either of the time-points exclusively in each subregion (ELAVL2, CLIC1 in PL, CD44 and MUG-1 in SM, and SHOC2, LGALS3 in DG). Conclusions: Utilizing advanced spatial proteomics techniques, the study unveils the dynamic molecular responses in distinct hippocampal subregions post-TBI. It uncovers region-specific vulnerabilities and dysregulated neuronal processes, and potential recovery-related pathways that contribute to our understanding of TBI’s neurological consequences and provides valuable insights for biomarker discovery and therapeutic targets.

Project description:After spinal cord injury, ependymal cells considered as stem cells activate, proliferate and differentiate mainly into glial cells. To understand this further at the molecular level, we performed RNA profiling of these cells in situ using laser-dissection and also when they are cultured as neurospheres in different conditions (growth, differentiation, dedifferentiation) Abstract: Numerous vertebrates, including Human, maintain a pool of immature cells in the ependymal region of the adult spinal cord. During injury, these ependymal cells, considered as multipotent stem cells, rapidly activate, proliferate and generate neurons and glial cells in lower vertebrates or mainly glial cells in mammals. The mechanisms underlying this activation are ill-defined and we intended to fill this gap by performing RNA profiling of mouse ependymal region after lesion. Bioinformatics and immunofluorescence identified activation of STAT3 and ERK/MAPK signaling in ependymal cells after injury. This was also accompanied by downregulation of cilia-associated genes and FoxJ1, a central transcription factor of ciliogenesis. Six genes were upregulated more than 20 fold, namely Crym, Ecm1, Ifi202b, Nupr1, Osmr, Rbp1, Thbs2 whereas only one, Acta1 was downregulated to this extent. We explored further the role and regulation in ependymal cells of Osmr, the receptor for oncostatin (OSM). This inflammatory cytokine is specifically expressed by microglia cells and we observed interactions between these cells and ependymal cells in vivo. Using culture of ependymal cells in neurospheres, we found that several cytokines induced OSMR, OSM being the most potent. OSMR is also upregulated by co-culture with OSM-expressing microglial cells. Treatment of spinal cord neural stem cells with OSM decreased their proliferation, upregulate p-Stat3 and reduced their differentiation into oligodendrocyte-lineage Olig1+ cells. These results suggest an important role for microglia-derived oncostatin in the activation and fate of spinal cord ependymal cell.