The Neuroprotective Functions of Selenoprotein M and its Role in Cytosolic Calcium Regulation

Abstract

Selenoproteins contain the trace element selenium incorporated as selenocysteine, the 21^st amino acid. Some members of the selenoprotein family, such as the glutathione peroxidases, have well-characterized antioxidant activity, functioning in enzymatic breakdown of hydroperoxides to protect cells against oxidative stress. However, the functions of many of the 25 human selenoproteins, including the brain-enriched selenoprotein M, are unknown. We investigated selenoprotein M function by manipulating expression in murine hippocampal HT22 cells, cerebellar astrocyte C8-D1A cells, and primary neuronal cultures. Overexpression of the protein resulted in a reduction in reactive oxygen species and apoptotic cell death in response to oxidative challenge with hydrogen peroxide. In contrast, knock-down of selenoprotein M using shRNA in primary neuronal cultures caused apoptotic cell death comparable to levels resulting from addition of hydrogen peroxide. Calcium measurements with the indicator cameleon demonstrated that overexpression of selenoprotein M decreased calcium influx in response to hydrogen peroxide. Additionally, knock-down of selenoprotein M expression in cortical cultures caused higher baseline levels of cytosolic calcium than in control cells. These results suggest that selenoprotein M may have an important role in protecting against oxidative damage in the brain and may potentially function in calcium regulation. Antioxid. Redox Signal. 12, 809–818.