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

Advances in acute stroke care, including endovascular thrombectomy and improved neurocritical management, have increased survival after ischemic stroke. However, stroke remains a leading cause of long-term disability, with many survivors experiencing persistent neurological and cognitive impairments. The chronic neurological consequences of stroke, particularly its potential to accelerate brain aging, remain poorly understood.

We examined chronic neurobehavioral changes at 2 and 6 months after middle cerebral artery occlusion in male C57Bl/6 mice. Behavioral assessments included the open field test (OFT), novel object recognition test (NORT), fear conditioning (FC), nesting activity, and tail suspension testing. Transcriptomic profiling was performed using RNA isolated from the ipsilateral hemisphere and flow cytometric analysis was utilized to assess microglial/macrophage phenotypes, and senescent-like phenotypes (SA-βGal and lipofuscin) in stroke mice. Neuropathological evaluation of human brain samples from patients with chronic stroke was performed by immunohistochemistry (IHC) to quantify demyelination (MBP), neuronal apoptosis (TUNEL), and Aβ42.

Experimental stroke led to consistent cognitive dysfunction and motor decline up to 6 months after ischemic injury. Histological and flow cytometric analyses revealed a significant increase in hippocampal gliosis, white matter degradation, senescent cell accumulation, and dysregulated microglial function. Histological analysis of postmortem human brains showed marked microgliosis, elevated senescent cell burden and increased amyloid deposition. Transcriptomic analysis demonstrated persistent upregulation of apoptosis-related pathways, microglial activation signatures, and complement cascade components.

Our findings demonstrate that ischemic stroke induces enduring neurodegenerative-like changes, a maladaptive and non-resolving myeloid/microglial response, and cognitive impairment. These findings support the concept that stroke accelerates brain aging ("inflamm-aging"), characterized by premature cellular senescence, altered microglial states, and ongoing neurodegeneration. Targeting senescence and chronic inflammation may represent promising therapeutic strategies to preserve long-term cognitive health after stroke.