Integrin CD11b mediates α-synuclein-induced activation of NADPH oxidase through a Rho-dependent pathway

The activation of microglial NADPH oxidase (NOX2) induced by alpha-synuclein has been implicated in Parkinson's disease (PD) and other synucleinopathies. However, how alpha-synuclein activates NOX2 remains unclear. Previous study revealed that both toll-like receptor 2 (TLR2) and integrin play important roles in alpha-synuclein-induced microglial activation. In this study, we found that blocking CD11b, the a chain of integrin alpha(M)beta(2), but not TLR2 attenuated alpha-synuclein-induced NOX2 activation in microglia. The involvement of CD11b in alpha-synuclein-induced activation of NOX2 was further confirmed in CD11b(-/-) microglia by showing reduced membrane trans location of NOX2 cytosolic subunit p47(phox) and superoxide production. Mechanistically, alpha-synuclein bound to CD11b and subsequently activated Rho signaling pathway. alpha-Synuclein induced activation of RhoA and downstream ROCK but not Rac1 in a CD11b-dependent manner. Moreover, siRNA-mediated knockdown of RhoA impeded NOX2 activation in response to alpha-synuclein. Furthermore, we found that inhibition of NOX2 failed to interfere with the activation of RhoA signaling and interactions between alpha-synuclein and CD11b, further confirming that NOX2 was the downstream target of CD11b. Finally, we found that genetic deletion of CD11b abrogated alpha-synuclein-induced NOX2 activatoin in vivo. Taken together, our results indicated that integrin CD11b mediates alpha-synuclein-induced NOX2 activation through a RhoA-dependent pathway, providing not only a novel mechanistic insight but also a new potential therapeutic target for synucleinopathies.