Insulin prevents fatty acid induced increase of adipocyte size

Abstract

Metabolic disorders related to obesity are largely dependent on adipose tissue hypertrophy, which involves adipocyte hypertrophy and increased adipogenesis. Adiposize is regulated by lipid accumulation as a result of increased lipogenesis (mainly lipid uptake in mature adipocytes) and reduced lipolysis. Using realtime 2D cell culture analyses of lipid uptake, we show (1) that high glucose concentration (4.5 g/L) was required to accumulate oleic acid increasing lipid droplet size until unilocularization similar to mature adipocytes in few days, (2) oleic acid reduced Peroxisome-Proliferator Activated Receptor Gamma (PPARG) gene transcription and (3) insulin counteracted oleic acid-induced increase of lipid droplet size. Although the lipolytic activity observed in high versus low glucose (1 g/L) conditions was not altered, insulin was found to inhibit oleic acid induced gene transcription required for lipid storage such as Cell Death Inducing DFFA Like Effectors (CIDEC) and G0S2 (G0 switch gene S2), possibly through PPARA activity. Although this signalling pathway requires more detailed investigation, the results point out the differential mechanisms involved in the pro-adipogenic effect of insulin in absence versus its protective effect on adiposity in presence of oleic acid uptake.Abbreviations: AICAR, 5-Aminoimidazole-4-carboxamide-1-D-ribofuranoside; AMPK, AMP-Activated protein kinase, ASCs, adipose stem cell; ATGL, adipose triglyceride lipase; BSA, Bovine serum albumin; CEBPA, CCAAT enhancer binding protein alpha; CIDEs, Cell Death Inducing DFFA Like Effectors; dA, differentiated adipocyte; DMEM, Dulbecco's Modified Eagle's Medium; FABPs, Fatty Acid Binding Proteins; FAT/CD36, Fatty acid translocase; FCS, Foetal calf serum; FN1, fibronectin 1; FFA, free fatty acid; G0S2, G0 switch gene S2; GLUTs, Glucose transporters; GPR120, G protein-coupled receptor 120; HG, high glucose; HSL, hormone sensitive lipase; INSR, insulin receptor; LG, low glucose; OA, oleic acid; PBS, Phosphate buffer saline; PPARs, Peroxisome-Proliferator Activated Receptors; PKA, Protein kinase cyclic AMP-dependent; PKG, Protein kinase cyclic GMP dependent; PTGS2, cytochrome oxidase 2; RTCA, realtime cell analysis; TG, triglyceride.

Keywords: Adipocyte; adiposize; lipid uptake; lipogenesis; lipolysis; realtime.

Graphical abstract

Figure 1.

Insulin counteracts oleic acid induced increase of adiposize in rat epididymal explants.

Figure 2.

Oleic acid uptake increases adiposize with inhibitory effect of insulin.

Figure 3.

Basal lipolysis induced by high glucose (4.5 g/L) during 2 hours is prevented by insulin in 3T3L1 partially differentiated adipocytes.

Figure 4.

Insulin prevents basal lipolysis induction by high glucose in human adipocytes independently of oleic acid.

Figure 5.

Anti-lipolytic effect of insulin results in an increase of adiposize.

Figure 6.

Oleic acid-induced gene transcription of adipogenic markers in high glucose media is counteracted by insulin in 3T3L1 adipocytes.

Figure 7.

Oleic acid increases adipogenic markers in 3T3-MBX adipocytes with repressive effect of insulin.

Figure 8.

Although oleic acid increases adipogenic marker FAT/CD36 with repressive effect of insulin, PPARG activation reduces OA-induced lipid accumulation in adipocytes.

Figure 9.

Gene dataset analyses of common transcriptional regulations by glucose, insulin and fatty acids in human cells (a) and in adipose tissue (b).

Figure 10.

Hypotheses describing the main pathways regulating adiposize.