Short-Chain Fatty Acids Differentially Affect Intracellular Lipolysis in a Human White Adipocyte Model

Abstract

Background and aims: Gut-derived short-chain fatty acids (SCFA), formed by microbial fermentation of dietary fibers, are believed to be involved in the etiology of obesity and diabetes. Previous data from our group showed that colonic infusions of physiologically relevant SCFA mixtures attenuated whole-body lipolysis in overweight men. To further study potential mechanisms involved in the antilipolytic properties of SCFA, we aimed to investigate the in vitro effects of SCFA incubations on intracellular lipolysis and signaling using a human white adipocyte model, the human multipotent adipose tissue-derived stem (hMADS) cells.

Methods: hMADS adipocytes were incubated with mixtures of acetate, propionate, and butyrate or single SCFA (acetate, propionate and butyrate) in concentrations ranging between 1 µmol/L and 1 mmol/L. Glycerol release and lipase activation was investigated during basal conditions and following β-adrenergic stimulation.

Results: SCFA mixtures high in acetate and propionate decreased basal glycerol release, when compared to control (P < 0.05), while mixtures high in butyrate had no effect. Also, β-adrenergic receptor mediated glycerol release was not significantly altered following incubation with SCFA mixtures. Incubation with only acetate decreased basal (1 µmol/L) and β-adrenergically (1 µmol/L and 1 mmol/L) mediated glycerol release when compared with control (P < 0.05). In contrast, butyrate (1 µmol/L) slightly increased basal and β-adrenergically mediated glycerol release compared with control (P < 0.05), while propionate had no effect on lipolysis. The antilipolytic effect of acetate was accompanied by a reduced phosphorylation of hormone-sensitive lipase (HSL) at serine residue 650. In addition, inhibition of Gi G proteins following pertussis toxin treatment prevented the antilipolytic effect of acetate.

Conclusion: The present data demonstrated that acetate was mainly responsible for the antilipolytic effects of SCFA and acts via attenuation of HSL phosphorylation in a Gi-coupled manner in hMADS adipocytes. Therefore, the modulation of colonic and circulating acetate may be an important target to modulate human adipose tissue lipid metabolism.

Keywords: acetate; adipose tissue; fat metabolism; gut microbiota; hormone-sensitive lipase; obesity.

Figure 1

Effect of short-chain fatty acid (SCFA) mixtures on basal and β-adrenergic receptor stimulated glycerol release in human multipotent adipose tissue-derived stem adipocytes. (A) Basal (non-stimulated) glycerol concentrations during 6 h incubation with 1 mmol/L or 1 µmol/L SCFA mixtures including acetate (C2), propionate (C3), and butyrate (C4). (B) Effect of 6 h incubation with 1 mmol/L or 1 µmol/L SCFA mixtures including acetate (C2), propionate (C3), and butyrate (C4) on β-adrenergic receptor stimulated (1 µmol/L isoprenaline) glycerol release; Values are given as means ± SD (n = 4–6 independent experiments). Statistical significance compared to basal indicated as asterisk (*) when P < 0.05 and double asterisk (**) when P < 0.01.

Figure 2

Effect of single short-chain fatty acid on basal and β-adrenergic receptor stimulated glycerol release in human multipotent adipose tissue-derived stem adipocytes. (A) Basal (non-stimulated) glycerol concentrations during 6 h incubation with 1 mmol/L or 1 µmol/L acetate (C2), propionate (C3), or butyrate (C4). (B) Effect of 6 h incubation with 1 mmol/L or 1 µmol/L acetate (C2), propionate (C3), or butyrate (C4) on β-adrenergic receptor stimulated (1 µmol/L isoprenaline) glycerol release; values are given as means ± SD (n = 4–7 independent experiments). Statistical significance when compared with basal indicated as asterisk (*) when P < 0.05 and as triple asterisk (***) when P < 0.001.

Figure 3

Acetate attenuates hormone-sensitive lipase (HSL) (SER 650) phosphorylation in human multipotent adipose tissue-derived stem adipocytes. (A) Representative Western blot showing that 1 µmol/L acetate (C2) reduced the relative amount of HSL phosphorylated on serine 650 in the presence of isoprenaline (ISO). In this blot, insulin was used as a control. See for corresponding entire blots in Figure S1 in Supplementary Material (B) Quantification of Western blot using ImageLab 3.0 normalized to total HSL (n = 4). Values are given as means ± SD. Statistical significance when compared with basal indicated as double asteriks (**) when P < 0.01; and when compared with ISO as dagger (^†) when P < 0.05.

Figure 4

Free fatty acid receptor (FFAR) 3 and FFAR2 are expressed at the RNA and protein level in human multipotent adipose tissue-derived stem adipocytes. (A) FFAR3/2 mRNA expression during adipocyte differentiation (days 0–12). (B) FFAR3/2 protein expression during adipocyte differentiation (days 0–14) (n = 1), See for corresponding entire blots in Figure S2 in Supplementary Material.

Figure 5

Pertussis toxin (PTX) abrogated acetate-induced inhibition (1 µmol/L) of isoprenaline (ISO)-mediated glycerol release in human multipotent adipose tissue-derived stem (hMADS) adipocytes. Values are given as individual points and means ± SD (n = 4 independent experiments). Statistical significance when compared to basal indicated as asterisk (*) when P < 0.01; and when compared with ISO as dagger (^†) when P < 0.001.

Figure 6

Proposed mechanism of the acetate-mediated antilipolytic effect in human adipocytes. The blunted fatty acid and glycerol release during acetate incubation is accompanied by a reduced phosphorylation of HSL_(SER650), indicating a role for protein kinase A in this antilipolytic process The free fatty acid receptor (FFAR) inhibitor pertussis toxin prevents the acetate–mediated antilipolytic effect, indicating a role for a Gi protein-coupled receptor mechanism (i.e., FFAR3 and/or FFAR2) in human adipocyte lipolysis.