Animal models of hypertension

Investigation of changes in apelin receptor mRNA and protein expression in the myocardium and aorta of rats with two-kidney, one-clip (2K1C) Goldblatt hypertension

Experimental and clinical evidences suggest that apelin and its receptor APJ are involved in the pathogenesis of cardiovascular complications. However, the role of apelin/APJ in hypertension is not sufficiently understood. Because chronic kidney diseases lead to hypertension and cardiac failure, we investigated the changes in apelin receptor gene expression in the myocardium and aorta of rat models of kidney disease hypertension. Two-kidney, one-clip (2K1C) hypertension was produced by placing a clip around the renal artery. Four and 16 weeks later, blood pressure, left ventricular end-diastolic pressure (LVEDP), serum apelin, and angiotensin II were measured. The messenger RNA (mRNA) and protein of APJ were determined by reverse transcription polymerase chain reaction (RT-PCR) and Western blotting. Chronic hypertensive rats had approximately 10 times higher LVEDP (P < 0.001). 2K1C decreased serum apelin from 220 ± 11 to 170 ± 10 pg/mL in 16 weeks (P < 0.05). The mRNA expression of APJ significantly decreased in the heart and aorta at 4 weeks. At 16 weeks, the reduction was not significant in the heart but was significant in the aorta. At 4 weeks, the expression of the APJ protein significantly decreased in the heart but not in the aorta. At 16 weeks, APJ protein was significantly decreased only in the aorta. Reduction of serum apelin and downregulation of apelin receptors in both the heart and aorta may play a role in the pathophysiology of hypertension and cardiac failure in 2K1C hypertensive rats.

Functional role of HSP90 complexes with endothelial nitric-oxide synthase (eNOS) and calpain on nitric oxide generation in endothelial cells

Although several reports have indicated that eNOS is a highly sensitive calpain substrate, the occurrence of a concomitant Ca(2+)-dependent activation of the synthase and of the protease has never been analyzed in specific direct experiments. In this study, we have explored in vivo how eNOS can undergo Ca(2+)-dependent translocation and activation, protected against degradation by activated calpain. Here we demonstrate that following a brief exposure to Ca(2+)-loading, the cytosolic eNOS-HSP90 complex recruits calpain in a form in which the chaperone and the synthase are almost completely resistant to digestion by the protease. Furthermore, in the presence of the HSP90 inhibitor geldanamycin, a significant decrease in NO production and an extensive degradation of eNOS protein occurs, indicating that dissociation from membranes and association with the chaperone is correlated to the protection of the synthase. Experiments with isolated membrane preparations confirm the primary role of HSP90 in dissociation of eNOS from caveolae. Prolonged exposure of cells to Ca(2+)-loading resulted in an extensive degradation of both eNOS and HSP90, accompanied by a large suppression of NO production. We propose that the protective effect exerted by HSP90 on eNOS degradation mediated by calpain represents a novel and critical mechanism that assures the reversibility of the intracellular trafficking and activation of the synthase.