Differential regulation of cellular stress responses by the endoplasmic reticulum-resident Selenoprotein S (Seps1) in proliferating myoblasts versus myotubes

Abstract

The antioxidant Selenoprotein S (Seps1, Selenos) is an endoplasmic reticulum (ER)‐resident protein associated with metabolic and inflammatory disease. While Seps1 is highly expressed in skeletal muscle, its mechanistic role as an antioxidant in skeletal muscle cells is not well characterized. In C2C12 myotubes treated with palmitate for 24 h, endogenous Seps1 protein expression was upregulated twofold. Two different siRNA constructs were used to investigate whether decreased levels of Seps1 exacerbated lipid‐induced oxidative and ER stress in C2C12 myotubes and myoblasts, which differ with regards to cell cycle state and metabolic phenotype. In myoblasts, Seps1 protein knockdown of ~50% or ~75% exacerbated cellular stress responses in the presence of palmitate; as indicated by decreased cell viability and proliferation, higher H2O2 levels, a lower reduced to oxidized glutathione (GSH:GSSG) ratio, and enhanced gene expression of ER and oxidative stress markers. Even in the absence of palmitate, Seps1 knockdown increased oxidative stress in myoblasts. Whereas, in myotubes in the presence of palmitate, a ~50% knockdown of Seps1 was associated with a trend toward a marginal (3‐5%) decrease in viability (P = 0.05), decreased cellular ROS levels, and a reduced mRNA transcript abundance of the cellular stress marker thioredoxin inhibitory binding protein (Txnip). Furthermore, no enhancement of gene markers of ER stress was observed in palmitate‐treated myotubes in response to Seps1 knockdown. In conclusion, reduced Seps1 levels exacerbate nutrient‐induced cellular stress responses to a greater extent in glycolytic, proliferating myoblasts than in oxidative, differentiated myotubes, thus demonstrating the importance of cell phenotype to Seps1 function.

<i>Coix lacryma-jobi</i> Seed Oil Reduces Fat Accumulation in Nonalcoholic Fatty Liver Disease by Inhibiting the Activation of the p-AMPK/SePP1/apoER2 Pathway

“…But SePP1 was a newly defined liver factor in recent years. Its function is still unclear 29 . Sepp1 full-length expression product in human plasma contains 10 Sec residues.…”

High glucose and TGF-β1 reduce expression of endoplasmic reticulum-resident selenoprotein S and selenoprotein N in human mesangial cells

“…inhibited SELENOS expression in three colon cancer cell lines and the results showed ER stress markers did not increase even in the presence of the ER stress inducer [20]. Recent study also reported that no enhancement of gene markers of ER stress was observed in palmitate-treated myotubes rather than myoblasts response to SELENOS knockdown [21]. Combined with our finding, the major reason for these inconsistent results may be the difference in the types of studied cells.…”

Controversies about selenium supplementation

“…It is highly expressed within skeletal muscle and plays an important role in muscle growth and development. Selenoproteins are becoming increasingly important in proper muscle contraction [26,27]. The degradation of 50-75% of SE-LENOS1 in myoblasts resulted in an increased susceptibility to oxidative stress, decreased proliferation and life span off cells, higher concentration of H2O2, decreased reduced glutathione (GSH), glutathione disulfide-oxidized (GSSG) and an increased expression of endoplasmic reticulum genes and oxidative stress markers (26).…”

“…Selenoproteins are becoming increasingly important in proper muscle contraction [26,27]. The degradation of 50-75% of SE-LENOS1 in myoblasts resulted in an increased susceptibility to oxidative stress, decreased proliferation and life span off cells, higher concentration of H2O2, decreased reduced glutathione (GSH), glutathione disulfide-oxidized (GSSG) and an increased expression of endoplasmic reticulum genes and oxidative stress markers (26). The SELENOS1 is responsible for regulating contraction and reaction to oxidative stress in quickly contracting muscles [28].…”