Selenoprotein S expression in reactive astrocytes following brain injury.

Selenoprotein S (SelS) is an endoplasmic reticulum (ER)-resident protein involved in the unfolded protein response. Besides reducing ER-stress, SelS attenuates inflammation by decreasing pro-inflammatory cytokines. We have recently shown that SelS is responsive to ischemia in cultured astrocytes. To check the possible association of SelS with astrocyte activation, here we investigate the expression of SelS in two models of brain injury: kainic acid (KA) induced excitotoxicity and cortical mechanical lesion. The regulation of SelS and its functional consequences for neuroinflammation, ER-stress, and cell survival were further analyzed using cultured astrocytes from mouse and human. According to our immunofluorescence analysis, SelS expression is prominent in neurons and hardly detectable in astrocytes from control mice. However, brain injury intensely upregulates SelS, specifically in reactive astrocytes. SelS induction by KA was evident at 12 h and faded out after reaching maximum levels at 3-4 days. Analysis of mRNA and protein expression in cultured astrocytes showed SelS upregulation by inflammatory stimuli as well as ER-stress inducers. In turn, siRNA-mediated SelS silencing combined with adenoviral overexpression assays demonstrated that SelS reduces ER-stress markers CHOP and spliced XBP-1, as well as inflammatory cytokines IL-1β and IL-6 in stimulated astrocytes. SelS overexpression increased astrocyte resistance to ER-stress and inflammatory stimuli. Conversely, SelS suppression compromised astrocyte viability. In summary, our results reveal the upregulation of SelS expression in reactive astrocytes, as well as a new protective role for SelS against inflammation and ER-stress that can be relevant to astrocyte function in the context of inflammatory neuropathologies.