Hideyuki Sone

Low-density lipoprotein receptor-related protein 5 (LRP5) is essential for normal cholesterol metabolism and glucose-induced insulin secretion

A Wnt coreceptor low-density lipoprotein receptor-related protein 5 (LRP5) plays an essential role in bone accrual and eye development. Here, we show that LRP5 is also required for normal cholesterol and glucose metabolism. The production of mice lacking LRP5 revealed that LRP5 deficiency led to increased plasma cholesterol levels in mice fed a high-fat diet, because of the decreased hepatic clearance of chylomicron remnants. In addition, when fed a normal diet, LRP5-deficient mice showed a markedly impaired glucose tolerance. The LRP5-deficient islets had a marked reduction in the levels of intracellular ATP and Ca2+ in response to glucose, and thereby glucose-induced insulin secretion was decreased. The intracellular inositol 1,4,5-trisphosphate (IP3) production in response to glucose was also reduced in LRP5−/− islets. Real-time PCR analysis revealed a marked reduction of various transcripts for genes involved in glucose sensing in LRP5−/− islets. Furthermore, exposure of LRP5+/+ islets to Wnt-3a and Wnt-5a stimulates glucose-induced insulin secretion and this stimulation was blocked by the addition of a soluble form of Wnt receptor, secreted Frizzled-related protein-1. In contrast, LRP5-deficient islets lacked the Wnt-3a-stimulated insulin secretion. These data suggest that Wnt/LRP5 signaling contributes to the glucose-induced insulin secretion in the islets.

Absorption and Effectiveness of Orally Administered Low Molecular Weight Collagen Hydrolysate in Rats

Collagen, a major extracellular matrix macromolecule, is widely used for biomedical purposes. We investigated the absorption mechanism of low molecular weight collagen hydrolysate (LMW-CH) and its effects on osteoporosis in rats. When administered to Wistar rats with either [(14)C]proline (Pro group) or glycyl-[(14)C]prolyl-hydroxyproline (CTp group), LMW-CH rapidly increased plasma radioactivity. LMW-CH was absorbed into the blood of Wistar rats in the peptide form. Glycyl-prolyl-hydroxyproline tripeptide remained in the plasma and accumulated in the kidney. In both groups, radioactivity was retained at a high level in the skin until 14 days after administration. Additionally, the administration of LMW-CH to ovariectomized stroke-prone spontaneously hypertensive rats increased the organic substance content and decreased the water content of the left femur. Our findings show that LMW-CH exerts a beneficial effect on osteoporosis by increasing the organic substance content of bone.

Molecular Identification and Characterization of Two Medium-chain Acyl-CoA Synthetases, MACS1 and the Sa Gene Product

In this study, we identified and characterized two murine cDNAs encoding medium-chain acyl-CoA synthetase (MACS). One, designated MACS1, is a novel protein and the other the product of the Sa gene (Sa protein), which is preferentially expressed in spontaneously hypertensive rats. Based on the murine MACS1 sequence, we also identified the location and organization of the human MACS1 gene, showing that the human MACS1 and Sa genes are located in the opposite transcriptional direction within a 150-kilobase region on chromosome 16p13.1. Murine MACS1 and Sa protein were overexpressed in COS cells, purified to homogeneity, and characterized. Among C4–C16 fatty acids, MACS1 preferentially utilizes octanoate, whereas isobutyrate is the most preferred fatty acid among C2–C6 fatty acids for Sa protein. Like Sa gene transcript, MACS1 mRNA was detected mainly in the liver and kidney. Subcellular fractionation revealed that both MACS1 and Sa protein are localized in the mitochondrial matrix. 14C-Fatty acid incorporation studies indicated that acyl-CoAs produced by MACS1 and Sa protein are utilized mainly for oxidation.

Biotin enhances glucose-stimulated insulin secretion in the isolated perfused pancreas of the rat

The effects of biotin on insulin secretion in pair-fed control rats and biotin-deficient rats were investigated using the method of isolated pancreas perfusion. Isolated pancreas perfusion was performed using 20 mM glucose, 10 mM arginine, and 20 mM glucose plus various concentrations of biotin (20 mM glucose + biotin solution) as stimulants of insulin secretion. The insulin response to 20 mM glucose in biotin-deficient rats was approximately 22% of that seen in control rats. The level of the insulin response to 10 mM arginine was also significantly lower in biotin-deficient rats than in control rats. These results indicate that insulin release from the pancreas was disturbed in biotin-deficient rats. The insulin responses to 20 mM glucose + 1 mM biotin in biotin-deficient and control rats increased to 165% and 185%, respectively, of that to 20 mM glucose. These biotin-induced increases in glucose-stimulated insulin release were evident within the first few minutes of the infusion. An enhancement of the arginine-induced insulin response in control rats was not found when arginine and biotin was administered. These results suggest that biotin may play an important role in the mechanism by which glucose stimulates insulin secretion from the beta cells of the pancreatic islets.