Effects of substitution of Cx43 by Cx32 on myocardial energy metabolism, tolerance to ischaemia and preconditioning protection

Abstract

Connexin 43 (Cx43) plays an important role in cardioprotective signalling by mechanisms at least in part independent of gap junctional communication. To investigate whether this role is related to specific properties of this connexin isoform, we used a knock-in mouse model in which the coding region of Cx43 is replaced by that of Cx32. Homozygous Cx43KI32 mice showed reduced cell-to-cell Lucifer Yellow transfer (P < 0.01), but QRS duration and left ventricular fractional shortening (echocardiography) were similar to those in wild-type animals. NMR spectroscopy detected reduced ATP and increased lactate content in myocardium from homozygous Cx43KI32 animals (P < 0.05). Despite this, isolated homozygous Cx43KI32 hearts showed smaller infarcts after ischaemia-reperfusion (40 min/60 min) as compared to hearts from heterozygous and wild-type animals (13 and 31% reduction, respectively, P < 0.05). Cardiac myocytes isolated from Cx43KI32 mouse hearts also showed a reduced rate of cell death after simulated ischaemia-reperfusion. In a separate series of experiments, both ischaemic (4 cycles of 3.5 min of ischaemia and 5 min of reperfusion) and pharmacological (50 μmol l −1 diazoxide, 10 min) preconditioning reduced infarct size in hearts from wild-type mice (by 24.84 and 26.63%, respectively, P < 0.05), but only ischaemic preconditioning was effective in hearts from heterozygous animals and both preconditioning strategies failed to protect Cx43KI32 homozygous hearts. These results demonstrate that Cx43 has an important and previously unknown modulatory effect in myocardial energy metabolism and tolerance to ischaemia, and plays a critical role in preconditioning protection, by mechanisms that are specific for this connexin isoform.

Single intravenous low-dose injections of connexin 43 mimetic peptides protect ischemic heart in vivo against myocardial infarction

“…Similar results have also been described in transgenic mice models [15,16]. Remarkably, whereas all these studies addressed the role of connexins forming gap junctions, none of them excludes the possibility that these effects were due to actions on unapposed Hc.…”

Excessive degradation of adenine nucleotides by up-regulated AMP deaminase underlies afterload-induced diastolic dysfunction in the type 2 diabetic heart

“…Since ATP depletion was not necessarily associated with ventricular dysfunction depending on the animal model [45], the threshold of ATP level that affects diastolic function might vary according to the status of SERCA2a. In a previous study, we showed that SERCA2a protein expression was reduced by endoplasmic reticulum (ER) stress-mediated degradation in OLETF at 25-30 weeks of age, when significant changes in ryanodine receptor 2 and phospholamban were not observed [10].…”

Redox balance and cardioprotection

“…In this ROS formation and spreading may play an important role the presence of connexin 43 (Cx43) in the mitochondrial inner membrane [17,62,84,160,182,184] (see also below).…”

“…In fact, it has been demonstrated that Diazoxide (a drug supposed to cause protection by increasing ROS production through actions on mK ATP channels) may induce both pre-and postconditioning protection [62,84,160]. However, replacement of Cx43 by Cx32 in mice is characterized by loss of preconditioning protection, in particular when induced by Diazoxide [184]. Moreover, the failure of cardiomyocytes from Cx43 +/-mice to be protected by Diazoxide, has been attributed to the attenuated ROS generation [84].…”