Transforming growth factor α stimulates proliferation and migration of endogenous stem cells in ischemic injured brain

Abstract

Stroke is one of the leading causes of death or disorder worldwide. There are high mortality and serious sufferance after a stroke. However, the optimal therapy is still unknown. In an ischemic stroke, inflammatory cells such as monocyte infiltrate into lesion and surrounding area, and activated microglia secrete pro- or anti-inflammatory cytokines. In brain injury, activated microglia play a key role in immune response and inflammatory reaction. Microglia-derived macrophages perform phagocytosis or damage repair. Transforming growth factor-alpha (TGF-α) is known as an important cytokine that induces the proliferation and differentiation of neural progenitors in the brain. This study verifies that activated microglia can secrete TGF-α and establishes that TGF-α is one of the important factors that enhance neurogenesis and neuroprotection mediated by activated microglia in ischemic stroke. BV2 cell line was used as microglia for in vitro study. BV2 cells were stimulated to polarize to M1 subtype macrophage by LPS or M2 subtype macrophage by IL-4. The protein expression of TGF- α was higher in M2 subtype macrophage-conditioned media than M1 media created (2.5 folds) using ELISA. The level of mRNA was also higher in M2 subtype macrophage (10 folds) by RT-PCR. To confirm the effect of M2 subtype macrophage-conditioned media on ischemic injured brain, ICR mice (7-8weeks, male) underwent middle cerebral artery occlusion (MCAO) for 60 minutes. The ischemic injured brain was taken out 6 hours after injury and made as a tissue section with 200-㎛ thickness for ex-vivo study. The brain section was cultured with control media, M1 subtype microglia-conditioned media, or M2 subtype microglia-conditioned media for 3 days ex vivo. The proliferation and migration of neural stem cells (NSC) in ipsilateral subventricular zone (SVZ) was increased when cultured with M2 subtype

microglia-conditioned media. Neuronal differentiation of NSC was also increased M2 subtype microglia-conditioned media. These effects of M2 subtype microglia-conditioned media disappeared when TGF-α was eliminated. These results suggested that TGF-α is one of the key factors in enhancing neurogenesis and neuroprotection mediated by activated microglia in ischemic stroke.