Although leptin and adiponectin are the predominant adipokines, how their circulating levels are regulated is incompletely understood. The present study tested whether intestinal epithelial cells influence the expression and secretion of these adipokines by adipocytes. Leptin gene expression and secretion by cultured human primary adipocytes and Simpson-Golabi-Behmel Syndrome adipocytes increased upon coculture with human enterocytic Caco-2 cells or incubation in conditioned medium of Caco-2 cells. Although adiponectin secretion increased, its mRNA levels decreased. Tissue homogenate of the ileum (but not the jejunum, colon, or liver) of nonobese C57BL/6J mice also stimulated leptin and adiponectin secretion by cultured murine 3T3-L1 adipocytes. However, ileal homogenate of obese KK-Ay mice had no effect on leptin and adiponectin secretion. We propose that as yet unidentified humoral factors released from intestinal epithelial cells are involved in regulating circulating leptin and adiponectin levels. Decreased production of such factors may contribute to hyperphagia in KK-Ay mice.

RegIII and RegIII are antimicrobial peptides expressed in intestinal epithelial cells.Expression of these peptides is reportedly decreased by high-fat diet (HFD) and increased by indigestible oligosaccharides in mice. Clearly, these dietary regimens change the structure of intestinal microbiota. We employed an intestinal microbiota transplantation (IMT) to test whether diet-induced changes in the expression of these peptides are mediated by gut microbiota. C57BL/6J mice were fed either a normal-fat diet (NFD), a HFD, or a NFD supplemented with or without 1-kestose (KES), an indigestible oligosaccharide. Ileal RegIII and RegIII mRNA levels were lower in mice receiving IMT from HFD-fed mice than in those receiving NFD-fed mice and higher in mice receiving IMT from KES-supplemented mice than in those receiving the mice without KES supplementation. Western blot analysis showed that serum RegIII levels changed in parallel with the ileal mRNA levels. We propose that HFDand KES-induced changes in the ileal RegIII and RegIII expression and in the circulating RegIIIβ levels are mediated, at least in part, by intestinal microbiota.

Although lipopolysaccharide (LPS)-binding protein (LBP) is an acute-phase protein mainly produced by hepatocytes, it has also been proposed to be a pro-inflammatory adipokine.Obesity and the consumption of a high-fat diet (HFD) are reportedly associated with elevated levels of LPS in plasma and free fatty acids (FFAs) in white adipose tissue (WAT). We examined whether circulating LPS or local FFAs are responsible for the HFD-induced increase of LBP in WAT. Male C57BL/6J mice were fed either a normal-fat diet (NFD) or an HFD. The mRNA levels in the liver and mesenteric WAT (mWAT), total FFA content in mWAT, and LBP and LPS concentrations in plasma were determined. The Lbp mRNA level in mWAT was higher in mice fed the HFD than in those fed the NFD for 3, 7, or 28 days or 14 weeks, whereas the hepatic Lbp mRNA level did not differ between the groups. The Lbp mRNA level in mWAT was also increased by the HFD in germ-free mice, which do not have gut microbiota, the source of LPS. The plasma LPS level did not show a significant correlation with the mWAT Lbp mRNA level. The total FFA content in mWAT was higher in mice fed the HFD than in those fed the NFD and positively correlated with the Lbp mRNA level. Supplementation with palmitic acid increased the Lbp mRNA level in 3T3-L1 adipocytes. We propose that local FFAs, but not circulating LPS, are the trigger for increased Lbp expression in mWAT of mice fed the HFD.