Potent anti-inflammatory and neuroprotective effects of TGF-β1 are mediated through the inhibition of ERK and p47phox-Ser345 phosphorylation and translocation in microglial

TGF-beta 1 is one of the most potent endogenous immune modulators of inflammation. The molecular mechanism of its anti-inflammatory effect on the activation of the transcription factor NF-kappa B has been well-studied; however, the potential effects of TGF-beta 1 on other proinflammatory signaling pathways is less clear. In this study, using the well-established LPS and the 1-methyl-4-phenylpyridinium-mediated models of Parkinson's disease, we demonstrate that TGF-beta 1 exerts significant neuroprotection in both models via its anti-inflammatory properties. The neuroprotective effects of TGF-beta 1 are mainly attributed to its ability to inhibit the production of reactive oxygen species from microglia during their activation or reactivation. Moreover, we demonstrate that TGF-beta 1 inhibited LPS-induced NADPH oxidase (PHOX) subunit p47(phox) translocation from the cytosol to the membrane in microglia within 10 min. Mechanistic studies show that TGF-beta 1 fails to protect dopaminergic neurons in cultures from PHOX knockout mice, and significantly reduced LPS-induced translocation of the PHOX cytosolic subunit p47(phox) to the cell membrane. In addition, LPS-induced ERK phosphorylation and subsequent Ser(345) phosphorylation on p47(phox) were significantly inhibited by TGF-beta 1 pretreatment. Taken together, our results show that TGF-beta 1 exerted potent anti-inflammatory and neuroprotective properties, either through the prevention of the direct activation of microglia by LPS, or indirectly through the inhibition of reactive microgliosis elicited by 1-methyl-4-phenylpyridinium. The molecular mechanisms of TGF-beta 1-mediated anti-inflammatory properties is through the inhibition of PHOX activity by preventing the ERK-dependent phosphorylation of Ser(345) on p47(phox) in microglia to reduce oxidase activities induced by LPS.