Do, T. H. | bioRxiv Science

bioRxiv2026

Repeated Mild Head Injury Establishes a Senescent Cranial Bone Marrow Niche that Impairs Brain Metabolism

Traumatic brain injury (TBI) of any severity is associated with long-term systemic inflammation and increased risk of peripheral comorbidities, yet the mechanisms driving immune dysregulation and accelerated aging after repeated mild head impacts remain poorly defined. Here, we investigated the acute and chronic effects of repeated mild TBI (rmTBI) on distal and proximal bone marrow compartments in the femur and calvaria, respectively. Using a modified weight-drop mouse model delivering rotational and acceleration-deceleration forces (3 hits/week for up to 16 weeks), rmTBI produced no mortality, skull fracture, hemorrhage, or brain leukocyte infiltration. One day after three consecutive impacts, rmTBI induced robust proliferation of LSK stem/progenitor cells in both femoral and calvarial marrow, evidenced by Ki67 expression, BrdU incorporation, and increased monocyte output. By 8 weeks (24 impacts), injury-induced proliferation subsided and LSK cells exhibited increased senescence-associated {beta}-galactosidase activity and upregulation of tumor suppressor genes. At 16 weeks (48 impacts), LSK populations were depleted at both sites, displaying reduced proliferative capacity, telomere shortening, and pancytopenia in otherwise young adult mice. Calvarial bone marrow cells exposed to rmTBI released a distinct cytokine and proteomic secretome marked by elevated IL-6, suppressed mitochondrial and metabolic signaling, and enhanced DNA repair pathways. Notably, skull-derived secretome factors impaired cortical and hippocampal mitochondrial metabolism, and reduced microglial mitochondrial membrane potential. Together, these findings identify replicative senescence of the brain-adjacent bone marrow niche as an early and progressive consequence of repeated mild head injury, linking rmTBI to long-lasting metabolic dysfunction, impaired immunity, and accelerated aging. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=140 SRC="FIGDIR/small/699107v1_ufig1.gif" ALT="Figure 1"> View larger version (42K): org.highwire.dtl.DTLVardef@683c8eorg.highwire.dtl.DTLVardef@15fc42forg.highwire.dtl.DTLVardef@48f398org.highwire.dtl.DTLVardef@170bbcc_HPS_FORMAT_FIGEXP M_FIG C_FIG

neuroscience↗

bioRxiv2025

Neuropathological hallmarks during the chronic phase of ischemic stroke in mice and humans

BackgroundImprovements in acute stroke treatment, including endovascular thrombectomy and critical care management, have increased survival rates post-stroke. However, stroke remains a leading cause of long-term disability and many survivors have significant neurological and cognitive deficits. Despite this, the chronic neurological sequelae and underlying secondary injury mechanisms induced by ischemic stroke remain understudied. MethodsThis study examined long-term neurobehavioral recovery and neuropathology at 2- and 6- months post-stroke in young (12-week-old) male C57Bl/6 mice after a 60-minute transient middle cerebral artery occlusion (MCAO) or sham surgery. Behavioral testing included the open field test (OFT), novel object recognition test (NORT), fear conditioning (FC), nesting activity, and tail suspension. Post-mortem brain samples from patients with chronic ischemic stroke were also assessed. Immunohistochemistry (IHC) was performed to assess demyelination (MBP), neuronal apoptosis (TUNEL), and A{beta}42 in human brains. Flow cytometric analysis was performed to assess microglial phenotypes, the chronic neuroimmune landscape, and to evaluate senescent-like phenotypes (SA-{beta}Gal and lipofuscin). Transcriptomic profiling was performed using RNA isolated from the ipsilateral hemisphere in stroke mice. ResultsExperimental stroke caused progressive cognitive and motor decline up to 6 months post-MCAO. IHC and flow cytometric analyses revealed a significant increase in TUNEL-positive neurons, cortical and hippocampal gliosis, white matter degradation, senescent cell accumulation, and altered microglial function. IHC analysis of postmortem human brains shows significantly increased levels of microgliosis, senescent cells and amyloid burden. Transcriptomic analysis revealed that pathways involving apoptosis, microglial activation and the complement pathway were chronically upregulated after stroke. ConclusionOur findings demonstrate that ischemic stroke induces a non-resolving microglial response and accelerated inflamm-aging in the brain, evidenced by premature senescence and elevated production of cytokines within the chronic infarct microenvironment. Senescent-like phenotypes and chronic neurodegenerative disease signatures may contribute to the progressive worsening of cognitive function post-stroke. These results suggest that chronic, ongoing neurodegeneration occurs late after stroke, even in younger mice. Mitigating these detrimental changes may offer viable targets for delayed treatment strategies for stroke.

neuroscience↗