A 7‐day high‐fat, high‐calorie diet induces fibre‐specific increases in intramuscular triglyceride and perilipin protein expression in human skeletal muscle

Abstract

Key points We have recently shown that a high‐fat, high‐calorie (HFHC) diet decreases whole body glucose clearance without impairing skeletal muscle insulin signalling, in healthy lean individuals. These diets are also known to increase skeletal muscle IMTG stores, but the effect on lipid metabolites leading to skeletal muscle insulin resistance has not been investigated. This study measured the effect of 7 days’ HFHC diet on (1) skeletal muscle concentration of lipid metabolites, and (2) potential changes in the perilipin (PLIN) content of the lipid droplets storing intramuscular triglyceride (IMTG). The HFHC diet increased PLIN3 protein expression and redistributed PLIN2 to lipid droplet stores in type I fibres. The HFHC diet increased IMTG content in type I fibres, while lipid metabolite concentrations remained the same. The data suggest that the increases in IMTG stores assists in reducing the accumulation of lipid metabolites known to contribute to skeletal muscle insulin resistance. Abstract A high‐fat, high‐calorie (HFHC) diet reduces whole body glucose clearance without impairing skeletal muscle insulin signalling in healthy lean individuals. HFHC diets also increase skeletal muscle lipid stores. However, unlike certain lipid metabolites, intramuscular triglyceride (IMTG) stored within lipid droplets (LDs) does not directly contribute to skeletal muscle insulin resistance. Increased expression of perilipin (PLIN) proteins and colocalisation to LDs has been shown to assist in IMTG storage. We aimed to test the hypothesis that 7 days on a HFHC diet increases IMTG content while minimising accumulation of lipid metabolites known to disrupt skeletal muscle insulin signalling in sedentary and obese individuals. We also aimed to identify changes in expression and subcellular distribution of proteins involved in IMTG storage. Muscle biopsies were obtained from the m. vastus lateralis of 13 (11 males, 2 females) healthy lean individuals (age: 23 ± 2.5 years; body mass index: 24.5 ± 2.4 kg m−2), following an overnight fast, before and after consuming a high‐fat (64% energy), high‐calorie (+47% kcal) diet for 7 days. After the HFHC diet, IMTG content increased in type I fibres only (+101%; P < 0.001), whereas there was no change in the concentration of either total diacylglycerol (P = 0.123) or total ceramides (P = 0.150). Of the PLINs investigated, only PLIN3 content increased (+50%; P < 0.01) solely in type I fibres. LDs labelled with PLIN2 increased (+80%; P < 0.01), also in type I fibres only. We propose that these adaptations of LDs support IMTG storage and minimise accumulation of lipid metabolites to protect skeletal muscle insulin signalling following 7 days’ HFHC diet.

The microenvironment matters: the secret life of intramuscular lipid droplets

“…The histochemical demonstration of the LD microenvironment by the current study (Whytock et al .) complements the observation that subcellular compartmentalization of lipid metabolites is associated with discrepant metabolic measures (Perreault et al . 2018).…”

“…2012). In the current paper, the HFHC diet increases muscle PLIN2‐positive LDs while muscle diacylglycerol and ceramide, key intermediates capable of triggering cellular dysfunction, remained unchanged (Whytock et al .). These observations support the role of free fatty acid sequestration in modifying the metabolic effect of high‐fat exposure.…”

“…peripheral distribution of PLIN proteins, LDs or PLIN‐coated LDs. Lastly, in type I fibres, HFHC feeding increased PLIN3 protein content, but not PLIN3 positive LDs, whereas the HFHC diet did not alter PLIN2 protein content but increased PLIN2‐positive LDs (Whytock et al .). The effect of HFHC feeding on the PLIN–LD relationship is particularly notable, as these findings highlight the discrepancy between PLIN protein levels and their localization with specific populations of LDs.…”

“…2001). In an article in this issue of The Journal of Physiology , Whytock and colleagues use sophisticated histochemical techniques to identify the microenvironment of muscle LDs in response to a 7‐day high‐fat, high‐calorie (HFHC) diet (Whytock et al . 2020). The investigators focus on the effects of HFHC on localization of LDs between muscle fibre types, between central and peripheral cellular regions, and specifically on LD colocalization with the perilipin (PLIN) family of LD proteins.…”

Young, healthy males and females present cardiometabolic protection against the detrimental effects of a 7-day high-fat high-calorie diet

“…Overall, 7 days of HFHC diet did not induce changes in whole-body insulin sensitivity (Matsuda ISI), or indices of hepatic or muscle insulin resistance. This was somewhat surprising considering previous studies have reported a reduction in measurements of insulin sensitivity following the same 7-day HFHC diet in young, healthy lean individuals [35,36,48,49]. The current study was novel, however, in measuring and characterising high cardio-respiratory fitness and high physical activity levels of the participants.…”