498-P: Involvement of Phosphorylation of Beta-1 Integrin in Renin Production and Blood Pressure Regulation in Diabetic Nephropathy

Abstract

Diabetic nephropathy (DN) and hypertension exacerbate each other, but many aspects of the mechanisms between these two pathologies remain unclear. The juxtaglomerular cells (JGC) secrete renin and trigger the renin-angiotensin-aldosterone system involved in blood pressure regulation. Our previous immunohistochemical analysis showed JGC-specific phosphorylation of β1 integrin (Itg), a cellular matrix adhesion factor. Quantitative analysis indicated the negative correlation between the phosphorylated β1 (pβ1) Itg and renin expression in JGC. To analyze the details of this relationship, As4.1, a cell-line of JGC was used. As protein kinase C (PKC) subtype epsilon is a putative kinase of the β1 Itg in JGC, PKC activator (phorbol 12-myristate 13-acetate, PMA) and PKC inhibitor (bisindolylmaleimide I, BIM-1) as well as TGF β1 which is known to stimulate a pathway to phosphorylate β1 Itg in JGC were applied to the culture of As4.1 cells. After 24 hours, expression of the mRNA levels of renin was gained by BIM-1 but suppressed by PMA or TGF β1. In the course of the cell culture with PMA, the mRNA levels of renin was increased till 90 minutes after application. However, it decreased subsequently, ultimately to 10% of the baseline level. Additional application of PMA at 6, 12 and 24 hours after the first application of PMA did not reproduce the temporal increase of renin expression. Time course of the cell culture with TGF β1 showed continuous decrease of the mRNA levels of renin. As PMA has broad spectrum for PKC subtypes, it was estimated that some activated PKC subtypes promoted temporal increase of renin expression in the early phase, however, later changes of cell state produced by pβ1 Itg suppressed the renin expression irreversibly. Our results confirmed a negative correlation between pβ1 Itg and renin expression in JGC cell-line, suggesting a link between β1 Itg and the regulatory system that controls renin production and secretion. Disclosure K. Sawada: None. M. Toyoda: Speaker's Bureau; Self; Boehringer Ingelheim Pharmaceuticals, Inc., Daiichi Sankyo Company, Limited, Eli Lilly and Company, Kyowa Hakko Kirin Co., Ltd., Medtronic Japan Co., Ltd., Mitsubishi Tanabe Pharma Corporation, Novo Nordisk Inc., Sanofi, Sumitomo Dainippon Pharma Co., Ltd., Takeda Pharmaceutical Company Limited. N. Saito: None. M. Kimura: None. H. Moriya: None. M. Fukagawa: Research Support; Self; Kyowa Hakko Kirin Co., Ltd. Speaker's Bureau; Self; Bayer Yakuhin, Ltd., Kissei Pharmaceutical Co., Ltd., Ono Pharmaceutical Co., Ltd., Torii Pharmaceutical Co., Ltd.