AMPK activation protects against diet induced obesity through Ucp1-independent thermogenesis in subcutaneous white adipose

Purpose: To investigate alterations in subcutaneous white adipose gene expression induced by genetic AMPK activation in vivo, in mice fed a chow or a high-fat diet. Methods: Subcutaneous white adipose tissue mRNA profiles of wild-type transgenic (WT-Tg) mice and mice expressing a gain-of-function AMPK mutant gamma1 subunit (D316A-Tg) were generated by deep sequencing. Results: RNA sequencing revealed over 3000 differentially expressed genes between WT-Tg and D316A-Tg subcutaneous white adipose tissue (WATsc) from mice fed a high fat diet (HFD), of which many were classified as 'skeletal muscle-associated'. Interestingly, uncoupling protein 1 (UCP1), associated with 'beige' adipocyte formation in WATsc, was not differentially expressed. On a chow diet, many differentially expressed genes were also identified, with gene ontology analysis identifiying glycolysis, TCA cycle and brown fat differentiation as highly enriched; key features of brown adipocyte identity. HFD-associated skeletal-muscle associated gene expression was either not significantly altered, or significantly down-regulated on a chow diet, indicating a diet-induced gene signature in D316A-Tg WATsc. Conclusions: Our study revealed gene signatures indicative of brown adipocyte development on a chow diet, where no overt metabolic phenotype was observed in gain-of-function animals. When fed a HFD, WATsc from D316A-Tg mice displayed a muscle-like gene signature, expressing key components of creatine and calcium thermogenic cycles including Ckmt2 (creatine kinase, mitochondrial 2) Atp2a1 (SERCA1-sarco/endoplasmic reticulum ATPase 1) and ryr1 (ryanodine receptor 1). UCP1 expression was not altered between WT-Tg and D316A-Tg mice fed a HFD. Our findings suggest a novel role for AMPK in the regulation of white adipocyte identity and a potentially novel cell population that, when metabolically challenged, preferrentially utilise muscle-like thermogenic futile cycles independent of UCP1 to mediate whole organism energy expenditure. Overall design: Whole subcutaneous white adipose tissue mRNA profiles were generated from mice fed either chow or 45% high-fat diet.

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Pollard AE, Martins L, Muckett PJ, Khadayate S, Bornot A, Clausen M, Admyre T, Bjursell M, Fiadeiro R, Wilson L, Whilding C, Kotiadis VN, Duchen MR, Sutton D, Penfold L, Sardini A, Bohlooly-Y M, Smith DM, Read JA, Snowden MA, Woods A, Carling D