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Elevated circulating fatty acids (FAs) contribute to obesity-associated metabolic complications, but the mechanisms by which insulin suppresses lipolysis are poorly understood. We show that α/β-hydrolase domain-containing 15 (ABHD15) is required for the anti-lipolytic action of insulin in white adipose tissue (WAT). Neither insulin nor glucose treatments can suppress FA mobilization in global and conditional Abhd15-knockout (KO) mice. Accordingly, insulin signaling is impaired in Abhd15-KO adipocytes, as indicated by reduced AKT phosphorylation, glucose uptake, and de novo lipogenesis. In vitrodata reveal that ABHD15 associates with and stabilizes phosphodiesterase 3B (PDE3B). Accordingly, PDE3B expression is decreased in the WAT of Abhd15-KO mice, mechanistically explaining increased protein kinase A (PKA) activity, hormone-sensitive lipase (HSL) phosphorylation, and undiminished FA release upon insulin signaling. Ultimately, Abhd15-KO mice develop insulin resistance. Notably, ABHD15expression is decreased in humans with obesity and diabetes compared to humans with obesity and normal glucose tolerance, identifying ABHD15 as a potential therapeutic target to mitigate insulin resistance.

Adipose triglyceride lipase (ATGL) is the rate-limiting enzyme mediating triglyceride (TG) hydrolysis. The lack of ATGL results in TG accumulation in multiple tissues, underscoring the critical role of ATGL in maintaining lipid homeostasis. Recent evidence suggests that ATGL affects TG metabolism via activation of peroxisome proliferator-activated receptor α (PPARα). To investigate specific effects of intestinal ATGL on lipid metabolism we generated mice lacking ATGL exclusively in the intestine (ATGLiKO). We found decreased TG hydrolase activity and increased intracellular TG content in ATGLiKO small intestines. Intragastric administration of [3H]trioleate resulted in the accumulation of radioactive TG in the intestine, whereas absorption into the systemic circulation was unchanged. Intraperitoneally injected [3H]oleate also accumulated within TG in ATGLiKO intestines, indicating that ATGL mobilizes fatty acids from the systemic circulation absorbed by the basolateral side from the blood. Down-regulation of PPARα target genes suggested modulation of cholesterol absorption by intestinal ATGL. Accordingly, ATGL deficiency in the intestine resulted in delayed cholesterol absorption. Importantly, this study provides evidence that ATGL has no impact on intestinal TG absorption but hydrolyzes TGs taken up from the intestinal lumen and systemic circulation. Our data support the role of ATGL in modulating PPARα-dependent processes also in the small intestine.

Obesity is characterized by excessive adipose tissue mass and associated with type 2 diabetes and cardiovascular diseases. To fight obesity and its sequels, elucidating molecular events that govern adipocyte differentiation and function is of key importance. MicroRNAs (miRNAs) are a novel class of non-coding, regulatory RNAs that have been shown to regulate crucial cellular processes, including differentiation. Several studies have already assigned miRNAs to distinct functions in murine adipocyte differentiation but only a few studies did so for humans.Here, we investigated the function of miR-30c in human adipogenesis. miR-30c expression was increased during adipogenesis of human multipotent adipose-derived stem (hMADS) cells, and miR-30c overexpression enforced adipocyte marker gene induction and triglyceride accumulation. miRNA target prediction revealed two putative direct targets of miR-30c, PAI-1(SERPINE1) and ALK2(ACVR1, ACTRI), both inversely regulated to miR-30c during adipogenesis and responsive to miR-30c overexpression. Luciferase reporter assays confirmed PAI-1and ALK2as direct miR-30c targets. Moreover, reciprocal expression between miR-30c and PAI-1could also be demonstrated in white adipose tissue of obesity mouse models, suggesting a potential physiological role of miR-30c for PAI-1regulation in the obese state. Validating PAI-1and ALK-2as miR-30c mediators in adipogenesis revealed that not single silencing of PAI-1or ALK2, but only co-silencing of both phenocopied the pro-adipogenic miR-30c effect. Thus, miR-30c can target two, so far not interconnected genes in distinct pathways, supporting the idea that miRNAs might coordinate larger regulatory networks than previously anticipated.