On the different roles of AT1 and AT2 receptors in stretch-induced changes of connexin43 expression and localisation

Abstract

Cyclic mechanical stretch (CMS) and angiotensin II (ATII) play an important role in cardiac remodelling. Thus, we aimed to examine how ATII affects CMS-induced changes in localisation and expression of the gap junction protein connexin43 (Cx43). Neonatal rat cardiomyocytes cultured on gelatin-coated Flexcell cell culture plates were kept static or were exposed to CMS (110 % of resting length, 1 Hz) for 24 h with or without additional ATII (0.1 μmol/L). Moreover, inhibitors of ATII receptors (AT-R) were used (for AT(1)-R: losartan 0.1 μmol/L, for AT(2)-R: PD123177 0.1 μmol/L). Thereafter, the cardiomyocytes were investigated by immunohistology, PCR and Western blot. After 24 h of CMS, cardiomyocytes were significantly elongated and orientated 75 ± 1.6° nearly perpendicular to the stretch axis. Furthermore, CMS significantly accentuated Cx43 at the cell poles (ratio Cx43 polar/lateral static: 2.32 ± 0.17; CMS: 10.08 ± 3.2). Additional ATII application significantly reduced Cx43 polarisation (ratio Cx43 polar/lateral ATII: 4.61 ± 0.42). The combined administration of ATII and losartan to CMS further reduced Cx43 polarisation to control levels, whilst the AT(2)-R blocker PD123177 restored polarisation. Moreover, CMS and ATII application resulted in a significant Cx43 protein and Cx43 mRNA up-regulation which could be blocked by losartan but not by PD123177. Thus, CMS results in a self-organisation of the cardiomyocytes leading to elongated cells orientated transversely towards the stretch axis with enhanced Cx43 expression and Cx43 accentuation at the cell poles. ATII enhances total Cx43 mRNA and protein expression probably via AT(1)-R (=inhibitory effect of losartan) and reduces Cx43 polarisation presumably via AT(2)-R, since PD123177 (but not losartan) inhibited the negative effects of ATII on polarisation.

Connexin 43 is an emerging therapeutic target in ischemia/reperfusion injury, cardioprotection and neuroprotection

“…Loss of N-cadherin reduces Cx43 expression at gap junctions (Li et al, 2008;Li et al, 2005;Palatinus et al, 2011;Zhu et al, 2010). As cyclic stretch increases N-cadherin in cardiomyocytes, it also increases total Cx43 expression and polarization of Cx43 to the longitudinal sites (Salameh et al, 2012). The increases in Cx43 expression and localisation to gap junctions in stretched cardiomyocytes involve angiotensin II, Akt, Erk1/2 and glycogen synthase kinase (GSK) 3ß (Salameh et al, 2012;Salameh et al, 2010a;Salameh et al, 2010b;Shyu et al, 2001).…”

“…As cyclic stretch increases N-cadherin in cardiomyocytes, it also increases total Cx43 expression and polarization of Cx43 to the longitudinal sites (Salameh et al, 2012). The increases in Cx43 expression and localisation to gap junctions in stretched cardiomyocytes involve angiotensin II, Akt, Erk1/2 and glycogen synthase kinase (GSK) 3ß (Salameh et al, 2012;Salameh et al, 2010a;Salameh et al, 2010b;Shyu et al, 2001). Angiotensin II also increases Cx43 expression (Dodge et al, 1998;Polontchouk et al, 2002) and N-cadherin expression in cardiomyocytes (Adam et al, 2010).…”

Real-Time In Vivo Imaging of Mouse Left Ventricle Reveals Fluctuating Movements of the Intercalated Discs

“…It is worthwhile to note that continual folding/unfolding of the ID membranes may sustain high expression levels of Cx43 in the GJ (and perinexii). Accumulating evidence shows that repeated stretching of the membranes enhances Cx43 expression in neonatal rat cardiomyocytes [32]. Therefore, it is safe to consider that this scenario applies to the adult heart in that an ongoing and intermittent load on the GJ (and perinexii) may sustain high expression levels of Cx43 in the GJ (and perinexii) by promoting electronic conduction.…”

Remodeling of Cardiac Gap Junctional Cell–Cell Coupling

“…Moreover, the cell axis orientation depended on the stretch axis [50]. The effects of a cyclic mechanical stretch can be modulated by angiotensin II (Salameh et al, 2012) [51] and by alpha-and beta-adrenoceptor stimulation (Salameh et al, 2010a) [52]. Figure 1 summarizes the effects of cyclic mechanical stretch on the localization of cardiac gap junctions.…”

“…ACE-inhibitor therapy reduced AF-induced fibrosis (Boldt et al, 2006) [80]. Further investigations in cultured cardiomyocytes revealed that the stretch-induced self-organization of cells with cell elongation and polarization of Cx43 could be modulated by angiotensin II: angiotensin II enhanced Cx43 expression via AT(1)-receptors but reduced Cx43 polarization via AT(2)-receptors (Salameh et al, 2012) [51]. Regarding the underlying mechanism, angiotensin II seems to activate CTGF via the activation of Rac1 and nicotinamide adenine dinucleotide phosphate oxidase.…”