Insulin-like peptide 5 (INSL5), a member of the insulin/relaxin superfamily, can activate the G-protein-coupled receptor relaxin/insulin-like family peptide receptor 4 (RXFP4), but its precise biological functions are largely unknown. Recent studies suggest that INSL5/RXFP4 is involved in the control of food intake and glucose homoeostasis. We report in the present study that RXFP4 is present in the mouse insulinoma cell line MIN6 and INSL5 augments glucose-stimulated insulin secretion (GSIS) both in vitro and in vivo. RXFP4 is also expressed in the mouse intestinal L-cell line GLUTag and INSL5 is capable of potentiating glucose-dependent glucagon-like peptide-1 (GLP-1) secretion in GLUTag cells. We propose that the insulinotrophic effect of INSL5 is probably mediated through stimulation of insulin/GLP-1 secretion and the INSL5/RXFP4 system may be a potential therapeutic target for Type 2 diabetes.

Obesity and non-alcoholic fatty liver disease are the most common metabolic disorders in society today. Previously, we found that supplementing the maternal diet during pregnancy with chocolate and fructose has negative effects on the well-being of the offspring that were ameliorated if the offspring were fed a normal diet during postnatal life. In the present study, we investigated whether feeding offspring a high-fat diet would augment the maternal programming effects and whether extra protein supply can correct the low birth weight resulting from the chocolate-supplemented maternal diet. Pregnant Sprague-Dawley rats were divided into three groups and fed either standard chow (normal nutrition; NN), chocolate- and fructose-supplemented standard chow with casein sodium (overnutrition; ON) or the supplemented standard chow without casein sodium (malnutrition; MN) throughout pregnancy. Male offspring were weaned on either standard or high-fat chow. Dams in the MN group exhibited moderate weight gain, consumed 50% less protein (P < 0.001) but more carbohydrates during gestation and delivered pups with a 12% lower birth weight (P < 0.05) than pups in the NN group, results that are consistent with previous findings. When fed on a high-fat diet after birth, pups from dams in the MN group (MNHD) had 30% more body fat (P = 0.023) and liver triglyceride (TG) levels that were double (P < 0.01) those in offspring in the other groups, leading to fatty livers in these offspring at 14 weeks of age. Hepatic expression of the PPARα, ApoB100, MTTP, CPT1 and SREBP1c genes was significantly downregulated in the MNHD group (P < 0.05 for all), indicating changes in lipid metabolism. Although dams in the ON group exhibited marked gestational weight gain (P < 0.01), they gave birth to normal weight pups that only manifested mild increases in body fat and liver TG content (P < 0.05), without significant changes in the expression of most genes when fed with the high-fat diet. The results suggest that the extra protein supply in the form of casein sodium was able to correct some negative programming effects of the chocolate and fructose supplementation of the maternal diet, which, in conjunction with a high-fat diet in the offspring, may facilitate the onset of metabolic disorders, with impaired liver gene expression possibly a key contributor.

Transglutaminase (abbreviated as TG,EC2.3.2.13) can catalyze the acyl transfer reaction of peptides in protein, but it can only catalyze a certain acyl transfer reaction instead of every acyl group. Protein is widely used to modify protein in food industry because it is safe and non-toxic and the catalyzed product can be digested and absorbed by human body. In this paper, the catalytic mechanism of protein substrate for MTG (Microbial TG) was studied in order to provide theoretical basis for the follow-up research and application of MTG. The results show that within 1%~4%, the total amount of biopolymer produced increases linearly, and then it remains basically unchanged. The catalytic amount of MTG to substrate and catalytic efficiency are contradictory. Under the condition of fixed MTG concentration, the higher the substrate concentration, the smaller the catalytic efficiency, and it shows a linear downward trend. When the concentration is 10%, the gel strength is the highest, reaching 68.09g. When the concentration of protein is low, protein-solvent interaction is dominant, and the system is not easy to form gel. The lower the hydrophobicity of protein surface, the easier it is to be catalyzed by MTG. However, the surface hydrophobicity of soybean globulin is in the middle, and MTG has moderate catalytic activity for it.