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Adipose tissue is one of the main regulative sites for energy metabolism. Excess lipid storage and expansion of white adipose tissue (WAT) is the primary contributor to obesity, a strong predisposing factor for development of insulin resistance. Sentrin-specific protease (SENP) 2 has been shown to play a role in metabolism in murine fat and skeletal muscle cells, and we have previously demonstrated its role in energy metabolism of human skeletal muscle cells. In the present work, we have investigated the impact of SENP2 on fatty acid and glucose metabolism in primary human fat cells by using cultured primary human adipocytes to knock down the SENP2 gene. Glucose uptake and oxidation, as well as accumulation and distribution of oleic acid into complex lipids were decreased, while oleic acid oxidation was increased in SENP2-knockdown cells compared to control adipocytes. Furthermore, lipogenesis was reduced by SENP2-knockdown in adipocytes. Although TAG accumulation relative to total uptake was unchanged, there was increased mRNA expression of metabolically relevant genes such as UCP1 and PPARGC1A and mRNA and proteomic data revealed increased levels of mRNA and proteins related to mitochondrial function by SENP2-knockdown. In conclusion, SENP2 is an important regulator of energy metabolism in primary human adipocytes and its knockdown reduce glucose metabolism and lipid accumulation, while increasing lipid oxidation in human adipocytes.

Additional file 1: Table S1. Study subject characteristics on biopsy day. Figure S1. Cell viability. Results are expressed as the percentage of cell viability relative to the control (= non-treated cells). a) Individual groups represent viability of cells exposed for 96 h to different concentrations of noradrenaline. Data are presented a s the mean ± SEM (n = 4 subjects). Values for each experimental condition were measured in triplicates in each subject. b) Individual groups represent viability of cells exposed for 96 h to ethanol (= propofol vehicle; 0.1%), 0.1 mM noradrenaline alone and c) different concentrations (μg/mL) of either propofol alone or mixture of propofol and 0.1 mM noradrenaline. Data are presented as the mean ± SEM (n = 7 subjects). Values for each experimental condition were measured in triplicates in each subject. Note: NA = noradrenaline. *** p < 0.001 vs. control group. Figure S2. Kinetic graph on XF24 Analyzer demonstrates changes after propofol at various concentrations. Real-time measurement of OCR at baseline and after sequential injection of oligomycin, FCCP and Antimycin A. Each data-point represents the mean of 7 independent samples (subjects) measured in tri- or tetraplicates normalized to protein content. Error bars indicate standard error of the mean. Different colours represent different groups exposed to propofol (0; 2.5; 10 µg/mL). Figure S3. A) Global mitochondrial parameters. Basal respiration, maximal respiratory capacity, ATP production and non-mitochondrial respiration. N = 7 replicates with 21–28 wells for each condition normalized to protein content. Error bars indicate standard error of the mean. B) Mitochondrial mass calculated as a fraction (%) of a cell surface area in 2D cross-sectional images. Figure S4. Uptake of CO2 production and lactic acid metabolism. A) Uptake of [14C]palmitic acid. B) [14C]lactic acid oxidation. C) [14C]lactic acid uptake. Note: NA = noradrenaline. Error bars in each graph indicate standard error of the mean. Note: NA = noradrenaline. Figure S5. Flow cytometry. Histogram showing MTG intensity of individual cell groups. Data are presented as the mean ± SEM (n = 2–3 experiments per each group). Note: NA = noradrenaline. Figure S6. Mitochondrial membrane potential. A) Myoblasts after staining with MitoTracker™ Green FM (left), TMRE (in the middle) and after staining of both agents (right). Experiments were performed at least at 60 cells per each group from n = 3 independent experiments (cells from 3 individual subjects). B) Determination of ∆ψm was expressed as TMRE/MTG ratio. The mitochondrial uncoupling agent FCCP was used as a positive control. Note: MTG = MitoTracker™ Green FM; TRME = tetramethylrhodamine ethyl ester; FCCP = carbonyl cyanide-4-(trifluoromethoxy)phenylhydrazone, NA = noradrenaline. Error bars indicate standard error of the mean. *p < 0.05, ***p < 0.001 vs. control group. Figure S7. Analysis of lipid droplets. A) Quantification of LD mass by cross-sectional area of BODIPY 493/503 normalized to cell area. B) LD size assessed by cross-sectional area of individual LDs. C) LD number normalized to cell area. Experiments were performed at least at 38 cells per each condition from 2 independent measurements (= 2 individual subjects). Error bars indicate standard error of the mean. ***p < 0.001 vs. control group.