Caveolin-1 and -3 dissociations from caveolae to cytosol in the heart during aging and after myocardial infarction in rat.

OBJECTIVE: Caveolins, the structural proteins of caveolae, modulate numerous signaling pathways including Nitric Oxide (NO) production. Among the caveolin family, caveolin-1 and -3 are mainly expressed in endothelial and muscle cells, respectively. In this study, we investigate whether (i) changes in caveolin abundance and/or distribution occur during cardiac aging and failure in rat, and (ii) the process could influence NO synthase (NOS) activity. METHODS: Using immunohistolabelling and Western blot approaches, expression and distribution of caveolins were analysed in adult (Ad), senescent (S-Sh) and myocardial infarction-induced failing (S-MI) hearts. NOS3/caveolin-1 interactions were evaluated by immunoprecipitation assays. RESULTS: At the microscope level, caveolin-1 distribution in the endothelial cells was unchanged between the groups. Conversely the typical distribution of caveolin-3 in myocyte sarcolemma was dramatically altered in S-MI rats, resulting in a heterogeneous pattern throughout the septum. Total abundance of caveolin-1 and -3 remained stable whatever the group. In the fractions free of caveolae (Triton X-100 soluble), the levels of caveolin-1 alpha and -3 increased with aging (+20%, and +104%, P<0.05 versus Ad, respectively) and were further enhanced in S-MI (+25%, +30%, P<0.05, P<0.001 versus S-Sh respectively). In these fractions, NOS3/caveolin-1 alpha complexes increased as well. In addition, NOS activity was negatively correlated to caveolin-1 level in the cytosolic fractions. CONCLUSIONS: We demonstrate that dissociation of caveolin from caveolae is associated with aging and heart failure, the process being related to the decreased NOS activity.

Cardiac modulations of ANG II receptor expression in rats with hypoxic pulmonary hypertension.

Right ventricular myocardial hypertrophy during hypoxic pulmonary hypertension is associated with local renin-angiotensin system activation. The expression of angiotensin II type 1 (AT(1)) and type 2 (AT(2)) receptors in this setting has never been investigated. We have therefore examined the chronic hypoxia pattern of AT(1) and AT(2) expression in the right and left cardiac ventricles, using in situ binding and RT-PCR assays. Hypoxia produced right, but not left, ventricular hypertrophy after 7, 14, and 21 days, respectively. Hypoxia for 2 days was associated in each ventricle with a simultaneous and transient increase (P < 0.05) in AT(1) binding and AT(1) mRNA levels in the absence of any significant change in AT(2) expression level. Only after 14 days of hypoxia, AT(2) binding increased (P < 0.05) in the two ventricles, concomitantly with a right ventricular decrease (P < 0.05) in AT(2) mRNA. Along these data, AT(1) and AT(2) binding remained unchanged in both the left and hypertrophied right ventricles from rats treated with monocrotaline for 30 days. These results indicate that chronic hypoxia induces modulations of AT(1) and AT(2) receptors in both cardiac ventricles probably through direct and indirect mechanisms, respectively, which modulations may participate in myogenic (at the level of smooth or striated myocytes) rather than in the growth response of the heart to hypoxia.

Angiotensin II AT(2) receptor inhibits smooth muscle cell migration via fibronectin cell production and binding.

To explore the vascular function of the angiotensin II (ANG II) AT(2) receptor subtype (AT(2)R), we generated a vascular smooth muscle cell (SMC) line expressing the AT(2)R (SMC-vAT(2)). The involvement of AT(2)R in the motility response of SMCs was examined in SMC-vAT(2) cells and their controls (SMC-v) cultured on either laminin or fibronectin matrix proteins with the agarose drop technique. All experiments were conducted in the presence of a saturating concentration of losartan to inactivate the AT(1)R subtype. Under basal conditions, both cell lines migrated outside drops, but on laminin only. Treatment with ANG II significantly inhibited the migration of SMC-vAT(2) but not SMC-v cells, and this effect was prevented by the AT(2)R antagonist CGP-42112A. The decreased migration of SMC-vAT(2) was not associated with changes in cell growth, cytoskeleton stiffness, or smooth muscle actin, desmin, and tenascin expression. However, it was correlated with increased synthesis and binding of fibronectin. Both responses were prevented by incubation with selective AT(2)R antagonists. Addition of GRGDTP peptide, which prevents cell attachment of fibronectin, reversed the AT(2)R inhibitory effect on SMC-vAT(2) migration. These results suggest that activated ANG II AT(2)R inhibits SMC migration via cellular fibronectin synthesis and associated cell binding.