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

Alex B Addinsall,Sheree D Martin,Nicole Stupka,Xavier A Conlan,Fiona Collier,Victoria C Foletta

doi:10.14814/phy2.13926

Alex B Addinsall, Sheree D Martin + Show 4 more

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https://doi.org/10.14814/phy2.13926

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Journal: Physiological reports	Publication Date: Dec 1, 2018
Citations: 8	License type: cc-by

Affiliation: Deakin University, Barwon Health

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.

Highlights

IntroductionMetabolism and immunity are regulated by selenium in the form of selenocysteine (Sec), the 21st amino acid, which is incorporated into selenoproteins (Brown and Arthur 2001; Shchedrina et al 2010; Li et al 2014)
Selenium is an essential micronutrient (Brown and Arthur 2001)
A reduction in Seps1 protein expression by both siRNAs was measured in myoblasts with a 50% and 75% decrease following treatment with siRNA1 and siRNA2, respectively (P < 0.001; Fig. 1C)

Summary

Introduction

Metabolism and immunity are regulated by selenium in the form of selenocysteine (Sec), the 21st amino acid, which is incorporated into selenoproteins (Brown and Arthur 2001; Shchedrina et al 2010; Li et al 2014). There are 25 selenoproteins in the human genome (Kryukov et al 2003), including seven endoplasmic reticulum (ER)-resident selenoproteins (DIO2, SELENOF, SELENOK, SELENOM, SELENON, SELENOS, and SELENOT). The function of these selenoproteins is not well characterized; they have been implicated in oxidative and ER stress responses,. Seps and Cell Stress Responses in Myoblasts and Myotubes inflammation, calcium regulation, and the maintenance of membrane-associated multiprotein complexes ((Shchedrina et al 2011; Turanov et al 2014; Li et al 2018); reviewed here (Liu and Rozovsky 2015; Addinsall et al 2018a))

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Conclusion