ABSTRACT
The biophysical environment of membrane phospholipids affects structure, function, and stability of membrane-bound proteins.1,2 Obesity can disrupt membrane lipids, and in particular, alter the activity of sarco/endoplasmic reticulum (ER/SR) Ca2+-ATPase (SERCA) to affect cellular metabolism.3-5 Recent evidence suggests that transport efficiency (Ca2+ uptake / ATP hydrolysis) of skeletal muscle SERCA can be uncoupled to increase energy expenditure and protect mice from diet-induced obesity.6,7 In isolated SR vesicles, membrane phospholipid composition is known to modulate SERCA efficiency.8-11 Here we show that skeletal muscle SR phospholipids can be altered to decrease SERCA efficiency and increase whole-body metabolic rate. The absence of skeletal muscle phosphatidylethanolamine (PE) methyltransferase (PEMT) promotes an increase in skeletal muscle and whole-body metabolic rate to protect mice from diet-induced obesity. The elevation in metabolic rate is caused by a decrease in SERCA Ca2+-transport efficiency, whereas mitochondrial uncoupling is unaffected. Our findings support the hypothesis that skeletal muscle energy efficiency can be reduced to promote protection from obesity.
Subject(s)
Calcium/metabolism , Energy Metabolism , Muscle, Skeletal/metabolism , Phospholipids/metabolism , Animals , Diet, High-Fat , Ion Transport , Methylation , Mice , Mice, Knockout , Muscle, Skeletal/enzymology , Obesity/enzymology , Obesity/genetics , Phosphatidylethanolamine N-Methyltransferase/genetics , Phosphatidylethanolamine N-Methyltransferase/metabolism , Sarcoplasmic Reticulum Calcium-Transporting ATPases/metabolismABSTRACT
Muscular dystrophy is accompanied by a reduction in activity of sarco/endoplasmic reticulum Ca(2+)-ATPase (SERCA) that contributes to abnormal Ca(2+) homeostasis in sarco/endoplasmic reticulum (SR/ER). Recent findings suggest that skeletal muscle fatty acid synthase (FAS) modulates SERCA activity and muscle function via its effects on SR membrane phospholipids. In this study, we examined muscle's lipid metabolism in mdx mice, a mouse model for Duchenne muscular dystrophy (DMD). De novo lipogenesis was ~50% reduced in mdx muscles compared to wildtype (WT) muscles. Gene expressions of lipogenic and other ER lipid-modifying enzymes were found to be differentially expressed between wildtype (WT) and mdx muscles. A comprehensive examination of muscles' SR phospholipidome revealed elevated phosphatidylcholine (PC) and PC/phosphatidylethanolamine (PE) ratio in mdx compared to WT mice. Studies in primary myocytes suggested that defects in key lipogenic enzymes including FAS, stearoyl-CoA desaturase-1 (SCD1), and Lipin1 are likely contributing to reduced SERCA activity in mdx mice. Triple transgenic expression of FAS, SCD1, and Lipin1 (3TG) in mdx myocytes partly rescued SERCA activity, which coincided with an increase in SR PE that normalized PC/PE ratio. These findings implicate a defect in lipogenesis to be a contributing factor for SERCA dysfunction in muscular dystrophy. Restoration of muscle's lipogenic pathway appears to mitigate SERCA function through its effects on SR membrane composition.
Subject(s)
Calcium/metabolism , Lipogenesis , Muscular Dystrophies/metabolism , Phosphatidylcholines/biosynthesis , Phosphatidylethanolamines/biosynthesis , Sarcoplasmic Reticulum/metabolism , Animals , Fatty Acid Synthase, Type I/genetics , Fatty Acid Synthase, Type I/metabolism , Male , Mice , Mice, Inbred mdx , Muscular Dystrophies/genetics , Muscular Dystrophies/pathology , Nuclear Proteins/genetics , Nuclear Proteins/metabolism , Phosphatidate Phosphatase/genetics , Phosphatidate Phosphatase/metabolism , Phosphatidylcholines/genetics , Phosphatidylethanolamines/genetics , Sarcoplasmic Reticulum/genetics , Sarcoplasmic Reticulum/pathology , Sarcoplasmic Reticulum Calcium-Transporting ATPases/genetics , Sarcoplasmic Reticulum Calcium-Transporting ATPases/metabolism , Stearoyl-CoA Desaturase/genetics , Stearoyl-CoA Desaturase/metabolismABSTRACT
OBJECTIVE: Sarcolipin (SLN) regulates muscle energy expenditure through its action on sarco/endoplasmic reticulum Ca(2+) -ATPase (SERCA) pump. It is unknown whether SLN-dependent respiration has relevance to human obesity, but whole-transcriptome gene expression profiling revealed that SLN was more highly expressed in myocytes from individuals with severe obesity (OB) than in lean controls (LN). The purpose of this study was to examine SLN-dependent cellular respiratory rates in LN and OB human muscles. METHODS: Primary myocytes were isolated from muscle biopsy from seven LN and OB Caucasian females. Cellular respiration was assessed with and without lentivirus-mediated SLN knockdown in LN and OB myocytes. RESULTS: SLN mRNA and protein abundance was greater in OB compared to LN cells. Despite elevated SLN levels in wild-type OB cells, respiratory rates among SLN-deficient cells were higher in OB compared to LN. Obesity-induced reduction in efficiency of SLN-dependent respiration was associated with altered sarcoplasmic reticulum phospholipidome. CONCLUSIONS: SLN-dependent respiration is reduced in muscles from humans with severe obesity compared to lean controls. Identification of the molecular mechanism that affects SLN efficiency might lead to interventions that promote an increase in skeletal muscle energy expenditure.