Introduction: The loss of white matter integrity after ischemic stroke contributes to long-term sensorimotor and cognitive deficits. Elucidating the mechanisms for white matter protection or recovery is therefore important to improve stroke outcomes. This study investigates the function of TGFα, a member of the epidermal growth factor family, in white matter recovery after stroke and elucidate the mechanisms of action.
Methods: Cerebral ischemia was induced by transient (60 min) middle cerebral artery occlusion (tMCAO) in wild type and TGFα knockout mice. The spatiotemporal pattern of TGFα expression was evaluated by immunofluorescent staining at 1, 3, 5, 14, 21 and 35 days after tMCAO. Sensorimotor (rota-rod test, adhesive-remove test and open field test) and cognitive (Morris water-maze test) functions were assessed up to 35 days after stroke. White matter injury was quantified by MBP (myelin basic protein) and SMI32 (recognizes damaged non-phosphorylated neurofilament proteins) staining. The direct effect of TGFα on oligodendrocytes were evaluated in vitro using primary cultures. Live/dead cell staining and LDH (lactate dehydrogenase) assay were used to assess oligodendrocytes death after 90 min oxygen and glucose deprivation (OGD).
Result: Cerebral ischemic induced an abrupt and transient increase of TGFα in the brain. The expression of TGFα was mainly increased in microglia and neurons. TGFα deficiency resulted in exacerbation in sensorimotor and cognitive deficits up to 35 days after tMCAO. MAP2 (microtubule-associated protein 2) staining at 3 days and 35 days showed lager tissue loss in TGFα knockout mice as compared with wild type stroke mice. Importantly. TGFα knockout mice also exhibited impaired white matter integrity, as revealed by the loss of MBP staining and elevation in SMI32 staining, at 35 days after stroke. Correlation analysis demonstrated positive correlation between white matter integrity and functional outcomes after stroke in TGFα knockout mice and wild type mice. In vitro study confirmed that TGFα (5, 10 or 20 ng/ml) protected oligodendrocyte precursor cells and oligodendrocytes against OGD.
Conclusion: TGFα is important for maintaining white matter integrity and improving neurological recovery after stroke.