髙栁 武志

OBJECTIVES: Phosphate (Pi) induces differentiation of arterial smooth muscle cells to the osteoblastic phenotype by inducing the type III Na-dependent Pi transporter Pit-1/solute carrier family member 1. This induction can contribute to arterial calcification, but precisely how Pi stress acts on the vascular wall remains unclear. We investigated the role of extracellular Pi in inducing microstructural changes in the arterial wall. METHODS: Aortae of Pit-1-overexpressing transgenic (TG) rats and their wild-type (WT) littermates were obtained at 8 weeks after birth. The thoracic descending aorta from WT and TG rats was used for the measurement of wall thickness and uniaxial tensile testing. Structural and ultrastructural analyses were performed using light microscopy and transmission electron microscopy. Gene expression of connective tissue components in the aorta was quantified by quantitative real-time polymerase chain reaction. RESULTS: Aortic wall thickness in TG rats was the same as that in WT rats. Uniaxial tensile testing showed that the circumferential breaking stress in TG rats was significantly lower than that in WT rats (p<0.05), although the longitudinal breaking stress, breaking strain, and elastic moduli in both directions in TG rats were unchanged. Transmission electron microscopy analysis of the aorta from TG rats showed damaged formation of elastic fibers in the aortic wall. Fibrillin-1 gene expression levels in the aorta were significantly lower in TG rats than in WT rats (p<0.05). CONCLUSIONS: Pi overload acting via the arterial wall Pit-1 transporter weakens circumferential strength by causing elastic fiber malformation, probably via decreased fibrillin-1 expression.

(1) Background: Proglucagon-derived peptides (PDGPs) including glucagon (Gcg), GLP-1, and GLP-2 regulate lipid metabolism in the liver, adipocytes, and intestine. However, the mechanism by which PGDPs participate in alterations in lipid metabolism induced by high-fat diet (HFD) feeding has not been elucidated. (2) Methods: Mice deficient in PGDP (GCGKO) and control mice were fed HFD for 7 days and analyzed, and differences in lipid metabolism in the liver, adipose tissue, and duodenum were investigated. (3) Results: GCGKO mice under HFD showed lower expression levels of the genes involved in free fatty acid (FFA) oxidation such as Hsl, Atgl, Cpt1a, Acox1 (p &lt; 0.05), and Pparα (p = 0.05) mRNA in the liver than in control mice, and both FFA and triglycerides content in liver and adipose tissue weight were lower in the GCGKO mice. On the other hand, phosphorylation of hormone-sensitive lipase (HSL) in white adipose tissue did not differ between the two groups. GCGKO mice under HFD exhibited lower expression levels of Pparα and Cd36 mRNA in the duodenum as well as increased fecal cholesterol contents compared to HFD-controls. (4) Conclusions: GCGKO mice fed HFD exhibit a lesser increase in hepatic FFA and triglyceride contents and adipose tissue weight, despite reduced β-oxidation in the liver, than in control mice. Thus, the absence of PGDP prevents dietary-induced fatty liver development due to decreased lipid uptake in the intestinal tract.