Subclinical atherosclerosis and its progression are modulated by PLIN2 through a feed-forward loop between LXR and autophagy.

BACKGROUND: Hyperlipidaemia is a major risk factor for cardiovascular disease, and atherosclerosis is the underlying cause of both myocardial infarction and stroke. We have previously shown that the Pro251 variant of perilipin-2 reduces plasma triglycerides and may therefore be beneficial to reduce atherosclerosis development. OBJECTIVE: We sought to delineate putative beneficial effects of the Pro251 variant of perlipin-2 on subclinical atherosclerosis and the mechanism by which it acts. METHODS: A pan-European cohort of high-risk individuals where carotid intima-media thickness has been assessed was adopted. Human primary monocyte-derived macrophages were prepared from whole blood from individuals recruited by perilipin-2 genotype or from buffy coats from the Karolinska University hospital blood central. RESULTS: The Pro251 variant of perilipin-2 is associated with decreased intima-media thickness at baseline and over 30 months of follow-up. Using human primary monocyte-derived macrophages from carriers of the beneficial Pro251 variant, we show that this variant increases autophagy activity, cholesterol efflux and a controlled inflammatory response. Through extensive mechanistic studies, we demonstrate that increase in autophagy activity is accompanied with an increase in liver-X-receptor (LXR) activity and that LXR and autophagy reciprocally activate each other in a feed-forward loop, regulated by CYP27A1 and 27OH-cholesterol. CONCLUSIONS: For the first time, we show that perilipin-2 affects susceptibility to human atherosclerosis through activation of autophagy and stimulation of cholesterol efflux. We demonstrate that perilipin-2 modulates levels of the LXR ligand 27OH-cholesterol and initiates a feed-forward loop where LXR and autophagy reciprocally activate each other; the mechanism by which perilipin-2 exerts its beneficial effects on subclinical atherosclerosis.

Global mRNA sequencing of human skeletal muscle: Search for novel exercise-regulated myokines.

OBJECTIVE: Skeletal muscle is an important secretory organ, producing and releasing numerous myokines, which may be involved in mediating beneficial health effects of physical activity. More than 100 myokines have been identified by different proteomics approaches, but these techniques may not detect all myokines. We used mRNA sequencing as an untargeted approach to study gene expression of secreted proteins in skeletal muscle upon acute as well as long-term exercise. METHODS: Twenty-six middle-aged, sedentary men underwent combined endurance and strength training for 12 weeks. Skeletal muscle biopsies from m. vastus lateralis and blood samples were taken before and after an acute bicycle test, performed at baseline as well as after 12 weeks of training intervention. We identified transcripts encoding secretory proteins that were changed more than 1.5-fold in muscle after exercise. Secretory proteins were defined based on either curated UniProt annotations or predictions made by multiple bioinformatics methods. RESULTS: This approach led to the identification of 161 candidate secretory transcripts that were up-regulated after acute exercise and 99 that where increased after 12 weeks exercise training. Furthermore, 92 secretory transcripts were decreased after acute and/or long-term physical activity. From these responsive transcripts, we selected 17 candidate myokines sensitive to short- and/or long-term exercise that have not been described as myokines before. The expression of these transcripts was confirmed in primary human skeletal muscle cells during in vitro differentiation and electrical pulse stimulation (EPS). One of the candidates we identified was macrophage colony-stimulating factor-1 (CSF1), which influences macrophage homeostasis. CSF1 mRNA increased in skeletal muscle after acute and long-term exercise, which was accompanied by a rise in circulating CSF1 protein. In cultured muscle cells, EPS promoted a significant increase in the expression and secretion of CSF1. CONCLUSION: We identified 17 new, exercise-responsive transcripts encoding secretory proteins. We further identified CSF1 as a novel myokine, which is secreted from cultured muscle cells and up-regulated in muscle and plasma after acute exercise.

Myostatin in relation to physical activity and dysglycaemia and its effect on energy metabolism in human skeletal muscle cells.

AIM: Some health benefits of exercise may be explained by an altered secretion of myokines. Because previous focus has been on upregulated myokines, we screened for downregulated myokines and identified myostatin. We studied the expression of myostatin in relation to exercise and dysglycaemia in skeletal muscle, adipose tissue and plasma. We further examined some effects of myostatin on energy metabolism in primary human muscle cells and Simpson-Golabi-Behmel syndrome (SGBS) adipocytes. METHODS: Sedentary men with or without dysglycaemia underwent a 45-min acute bicycle test before and after 12 weeks of combined endurance and strength training. Blood samples and biopsies from m. vastus lateralis and adipose tissue were collected. RESULTS: Myostatin mRNA expression was reduced in skeletal muscle after acute as well as long-term exercise and was even further downregulated by acute exercise on top of 12-week training. Furthermore, the expression of myostatin at baseline correlated negatively with insulin sensitivity. Myostatin expression in the adipose tissue increased after 12 weeks of training and correlated positively with insulin sensitivity markers. In cultured muscle cells but not in SGBS cells, myostatin promoted an insulin-independent increase in glucose uptake. Furthermore, muscle cells incubated with myostatin had an enhanced rate of glucose oxidation and lactate production. CONCLUSION: Myostatin was differentially expressed in the muscle and adipose tissue in relation to physical activity and dysglycaemia. Recombinant myostatin increased the consumption of glucose in human skeletal muscle cells, suggesting a complex regulatory role of myostatin in skeletal muscle homeostasis.