Abstract 4889: Coupling Factor 6 Enhances the Action of Angiotensin II and Causes Insulin Resistance in Mice
The lower values of intracellular pH are commonly observed in the hypertensive states including a high renin state. It is also reported that intracellular acidosis is related to the pathogenesis of diabetes by inducing insulin resistance in the skeletal muscle. We recently showed that the molecular rotary motor F1Fo complex, ATP synthase, is present at the plasma membrane, and that coupling factor 6 (CF6) forces the backward rotation of Fo after binding to F1, resulting in cellular acidosis (Hypertension, 2005). Using CF6-overexpressing transgenic (TG) mice and vascular smooth muscle cells (VSMC), we tested the hypothesis that CF6 enhances the action of angiotensin II (AngII) and causes insulin resistance. In TG mice, the introduced gene of human CF6 was expressed in overall tissues, and upregulated by 2 times. In the mesenteric arterioles isolated from TG mice, Ang II-induced vasoconstriction was enhanced compared with WT mice (p<0.05). Blockade of CF6 with its specific antibody remarkably attenuated the Ang II-induced vasoconstriction by 85±5% in TG mice and by 79±5% in WT mice, thereby eliminating the difference in contraction. In CF6-overexpressing (spontaneously hypertensive rats, SHR) VSMC, Ang II (10−7M)-induced increase in the spike phase of [Ca2+]i was higher compared with control (Wistar Kyoto rats) VSMC. In VSMC with a high affinity CF6 receptor (SHR), Ang II (10−7M)-induced increase in the spike phase of [Ca2+]i was enhanced by the presence of CF6 at 10−7M. All were blocked by PP1 at 50μM, a c-Src inhibitor. When the mice were fed with high sucrose diet (20%) for 8 weeks, the TG mice exhibited insulin resistance: In glucose-tolerance test, the plasma glucose level was higher until 1.5 hours (p < 0.05, two-way ANOVA), and insulin level at 1 hour was higher in TG mice (1111 ± 118 vs 400 ± 54 pg/ml, p < 0.05). The TG mice exhibited no change in tyrosine phosphorylation of β subunit of insulin receptor but the decreases in the protein expression of insulin receptor substrate-1 by 64 ± 9%, phosphatidylinositol-3 kinase activity, Akt phosporylation, and the plasma membrane GLUT-4 protein by 69 ± 11% in the skeletal muscle (n = 5, all p < 0.05). These indicate that CF6 enhances the action of AngII by c-Src signaling and thereby causes diet-induced insulin resistance in mice.