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Stroke-induced neurological dysfunction in aged mice is attenuated by preconditioning with young Sca-1 + stem cells.

AIMS
To date, stroke remains one of the leading causes of death and disability worldwide. Nearly three-quarters of all strokes occur in the elderly (>65-years-old), and a vast majority of these individuals develop debilitating cognitive impairments that can later progress into dementia. Currently there are no therapies capable of reversing the cognitive complications which arise following a stroke. Instead, current treatment options focus on preventing secondary injuries, as opposed to improving functional recovery.


METHODS
We reconstituted aged (20-month-old) mice with Sca-1 + bone marrow (BM) hematopoietic stem cells isolated from aged or young (2-month-old) EGFP + donor mice. Three months later the chimeric aged mice underwent cerebral ischemia/reperfusion by bilateral common carotid artery occlusion (BCCAO), after which cognitive function was evaluated. Immunohistochemical analysis was performed to evaluate host and recipient cells in the brain following BCCAO.


RESULTS
Young Sca-1 + cells migrate to the aged brain and give rise to beneficial microglial-like cells that ameliorate stroke-induced loss of cognitive function on tasks targeting the hippocampus and cerebellum. We also found that young Sca-1 + cell-derived microglial-like cells possess neuroprotective properties as they do not undergo microgliosis upon migrating to the ischemic hippocampus, whereas the cells originating from old Sca-1 + cells proliferate extensively and skew towards a pro-inflammatory phenotype following injury.


CONCLUSIONS
This study provides a proof-of-principle demonstrating that young BM Sca-1 + cells play a pivotal role in reversing stroke-induced cognitive impairments and protect the aged brain against secondary injury by attenuating the host cell response to injury.