IL-17-triggered downregulation of miR-497 results in high HIF-1α expression and consequent IL-1β and IL-6 production by astrocytes in EAE mice

Interleukin 17(IL-17)is increasingly recognized as a key factor that contributes to the pathogenesis of multiple sclerosis(MS)and its experimental mouse autoimmune encephalomyelitis(EAE)model.However,the roles and regulatory mechanisms of IL-17-induced pro-inflammatory cytokine production in EAE mice remain largely unclear.In this study,the expression of IL-17,hypoxia inducible factor-1α(HIF-1α),IL-1β,IL-6 and microRNA-497(miR-497),as well as their intrinsic associations,was investigated using EAE model mice and cultured astrocytes exposed to IL-17 in vitro.We observed markedly increased production of IL-17,HIF-1α,IL-1βand IL-6 in the brain tissues of EAE mice,while the expression and secretion of HIF-1α,IL-1βand IL-6 were also significantly increased when cultured primary astrocytes from mice were stimulated with IL-17.Meanwhile,the expression of miR-497 was downregulated both in vivo and in vitro.Subsequent in vitro experiments revealed that IL-17 induced the production of IL-1βand IL-6 in astrocytes through the upregulation of HIF-1αas a transcriptional factor,indicating that IL-17-mediated downregulation of miR-497 enhanced HIF-1αexpression.Furthermore,astrocytespecific knockdown of IL-17RA and HIF-1αor astrocyte-specific overexpression of miR-497 by infection with different lentiviral vectors containing an astrocyte-specific promotor markedly decreased IL-1βand IL-6 production in brain tissues and alleviated the pathological changes and score of EAE mice.Collectively,these findings indicate that decreased miR-497 expression is responsible for IL-17-triggered high HIF-1αexpression and consequent IL-1βand IL-6 production by astrocytes in EAE mice.