Bacterial cell wall components regulate adipokine secretion from visceral adipocytes

Abstract

Recent studies suggest a relationship between intestinal microbiota and metabolic syndromes; however, the underlying mechanism remains unclear. To clarify this issue, we assessed the effects of bacterial cell wall components on adiponectin, leptin and resistin secretion from rat visceral adipocytes in vitro. We also measured the relative population of Firmicutes and Bacteroidetes in fecal microbiota and the amount of fecal mucin as an intestinal barrier function, when mice were fed a high-fat diet. In the present study, we demonstrated that bacterial cell wall components affect the secretion of adipokines, depending on the presence of antigens from gram-positive or gram-negative bacteria. Lipopolysaccharide markedly inhibited adiponectin, leptin, and resistin secretion, whereas peptidoglycan increased adiponectin secretion and decreased resistin secretion in vitro. In vivo experiments showed that the high-fat diet increased the population of Firmicutes and decreased that of Bacteroidetes. In contrast, the high-fat diet downregulated the stool output and fecal mucin content. These results demonstrate that bacterial cell wall components affect the onset of metabolic syndromes by mediating the secretion of adipokines from visceral adipose tissue. Furthermore, we believe that metabolic endotoxemia is not due to the increasing dominance of gram-negative bacteria, Bacteroidetes, but due to the depression of intestinal barrier function.

Keywords: adipokine secretion; gut microbiota; lipopolysaccharide; peptidoglycan; visceral adipocyte.

Fig. 1

Effects of LPS concentration on adiponectin secretion. Adiponectin concentration in culture supernatants after stimulation with LPS was determined using an adiponectin ELISA kit (n = 4) as described in Materials and Methods, sections 2.3 and 2.4.

Fig. 2

Immunohistochemical staining for cellular adiponectin. Adiponectin was stained in visceral adipocytes as described in Materials and Methods, section 2.6. Red: adiponectin, green: nuclei (H33258 stain). A, B: control; C, D: 100 ng/ml LPS was added. The scale bar is 100 µm.

Fig. 3

Effects of bacterial cell wall components on adipokine secretion. One hundred ng/ml LPS, lipoteichoic acid (LTA), N-acetylmuramyl-l-alanyl-d-isoglutamine hydrate (MDP), or peptidoglycan (PGN) was added to the visceral adipocyte culture on day 6 after the start of culturing. After further incubation for 48 h, the adiponectin, leptin, and resistin concentrations in the culture supernatant were measured using ELISA kits. A: adiponectin (n = 4), B: leptin (n = 4), C: resistin (n = 4). *p<0.05, **p<0.01 vs control.

Fig. 4

A: Time course of body weight in control mice and mice fed with high-fat diet (with induced obesity). B: Stool output from control mice and mice with high-fat diet-induced obesity. C: Relative population of Firmicutes and Bacteroidetes phyla to all bacteria. D: Fecal mucin contents of control mice and mice with high-fat diet-induced obesity. Fecal mucin content was determined using a fluorimetric assay that discriminates O-linked glycoproteins (mucins) from N-linked glycoproteins. STD: standard diet (n = 5); HFD: high-fat diet group (n = 5). *p<0.05, **p<0.01 vs STD.