Myosin1f-mediated neutrophil migration contributes to acute neuroinflammation and brain injury after stroke in mice.

ABSTRACT

BACKGROUND: During the acute stroke phase, neutrophils from the peripheral blood are first to arrive in the ischemic brain, which then attracts other immune cells that exacerbate neuroinflammation in the ischemic tissue. Myosin1f was reported to specifically mediate neutrophil migration in the peripheral tissues, but whether it plays a critical role in the neuroinflammatory response after ischemic stroke remains unknown. In this study, we aim to test the hypothesis that myosin1f-mediated neutrophil migration is critical in acute neuroinflammation induced by ischemic stroke. METHODS: Myosin1f -/- and wild type (WT) mice were subjected to transient middle cerebral artery occlusion (MCAO). To determine which cells determine myosin1f's transmigration ability, bone marrow transplantation, neutrophil depletion, and adoptive neutrophil transfer were performed. The myosin1f RNA level was assessed in peripheral neutrophils by reverse transcription polymerase chain reaction (RT-PCR) at 1 day and 3 days after stroke. The infiltrating neutrophils were quantified by immunofluorescence staining and FACS at 72 h after reperfusion. RESULTS: The myosin1f -/- mice had significantly smaller infarctions than the myosin1f +/+ mice. Bone marrow transplantation from myosin1f -/- mice to recipient mice also had smaller infarctions compared to animals receiving bone marrow from myosin1f +/+ mice. By performing neutrophil depletion and adoptive transfer, we confirmed that myosin1f acts mainly in circulating neutrophils. RT-PCR showed that myosin1f gene expression was increased in the circulating blood neutrophils at 3 days after ischemia. The confocal immunostaining and FACS results confirmed that fewer neutrophils infiltrated into the ischemic brain in myosin1f -/- mice compared to WT mice. CONCLUSIONS: Myosin1f determines neutrophil migration into the ischemic hemisphere, which directly affects stroke outcome.