Mechanism of TNF-α-induced lipolysis in human adipocytes uncovered

Oncostatin M Induces Lipolysis and Suppresses Insulin Response in 3T3-L1 Adipocytes

Oncostatin M (OSM) is an immune cell-derived cytokine that is upregulated in adipose tissue in obesity. Upon binding its receptor (OSMR), OSM induces the phosphorylation of the p66 subunit of Src homology 2 domain-containing transforming protein 1 (SHC1), called p66Shc, and activates the extracellular signal-related kinase (ERK) pathway. Mice with adipocyte-specific OSMR deletion (Osmr^FKO) are insulin resistant and exhibit adipose tissue inflammation, suggesting that intact adipocyte OSM–OSMR signaling is necessary for maintaining adipose tissue health. How OSM affects specific adipocyte functions is still unclear. Here, we examined the effects of OSM on adipocyte lipolysis. We treated 3T3-L1 adipocytes with OSM, insulin, and/or inhibitors of SHC1 and ERK and measured glycerol release. We also measured phosphorylation of p66Shc, ERK, and insulin receptor substrate-1 (IRS1) and the expression of lipolysis-associated genes in OSM-exposed 3T3-L1 adipocytes and primary adipocytes from control and Osmr^FKO mice. We found that OSM induces adipocyte lipolysis via a p66Shc-ERK pathway and inhibits the suppression of lipolysis by insulin. Further, OSM induces phosphorylation of inhibitory IRS1 residues. We conclude that OSM is a stimulator of lipolysis and inhibits adipocyte insulin response. Future studies will determine how these roles of OSM affect adipose tissue function in health and disease.

Pseudomonas aeruginosa-derived pyocyanin reduces adipocyte differentiation, body weight, and fat mass as mechanisms contributing to septic cachexia

Pseudomonas aeruginosa, a leading cause of sepsis, produces pyocyanin, a blue-pigmented virulence factor. Sepsis is associated with cachexia, but mechanisms are unknown and conventional nutrition approaches are not effective treatments. Pyocyanin has affinity for the aryl hydrocarbon receptor (AhR), which is expressed on adipocytes and regulates adipocyte differentiation. The purpose of this study was to define in vitro and in vivo effects of pyocyanin on adipocyte differentiation and body weight regulation as relates to septic cachexia. In 3T3-L1 preadipocytes, pyocyanin activated AhR and its downstream marker CYP1a1, and reduced differentiation. Administration of pyocyanin to male C57BL/6J mice acutely reduced body temperature with altered locomotion, but caused sustained weight loss. Chronic pyocyanin administration to male and female C57BL/6J mice resulted in sustained reductions in body weight and fat mass, with adipose-specific AhR activation. Pyocyanin-treated male mice had decreased energy expenditure and physical activity, and increased adipose explant lipolysis. In females, pyocyanin caused robust reductions in body weight, adipose-specific AhR activation, and increased expression of inflammatory cytokines in differentiated adipocytes. These results demonstrate that pyocyanin reduces adipocyte differentiation and decreases body weight and fat mass in male and female mice, suggesting that pyocyanin may play a role in septic cachexia.

An ethanolic extract of Artemisia scoparia inhibits lipolysis in vivo and has antilipolytic effects on murine adipocytes in vitro

An ethanolic extract of Artemisia scoparia (SCO) has metabolically favorable effects on adipocyte development and function in vitro and in vivo. In diet-induced obese mice, SCO supplementation significantly reduced fasting glucose and insulin levels. Given the importance of adipocyte lipolysis in metabolic health, we hypothesized that SCO modulates lipolysis in vitro and in vivo. Free fatty acids and glycerol were measured in the sera of mice fed a high-fat diet with or without SCO supplementation. In cultured 3T3-L1 adipocytes, the effects of SCO on lipolysis were assessed by measuring glycerol and free fatty acid release. Microarray analysis, qPCR, and immunoblotting were used to assess gene expression and protein abundance. We found that SCO supplementation of a high-fat diet in mice substantially reduces circulating glycerol and free fatty acid levels, and we observed a cell-autonomous effect of SCO to significantly attenuate tumor necrosis factor-α (TNFα)-induced lipolysis in cultured adipocytes. Although several prolipolytic and antilipolytic genes were identified by microarray analysis of subcutaneous and visceral adipose tissue from SCO-fed mice, regulation of these genes did not consistently correlate with SCO's ability to reduce lipolytic metabolites in sera or cell culture media. However, in the presence of TNFα in cultured adipocytes, SCO induced antilipolytic changes in phosphorylation of hormone-sensitive lipase and perilipin. Together, these data suggest that the antilipolytic effects of SCO on adipose tissue play a role in the ability of this botanical extract to improve whole body metabolic parameters and support its use as a dietary supplement to promote metabolic resiliency.