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Connexin 43 downregulation and dephosphorylation in nonischemic heart failure is associated with enhanced colocalized
1Department of Medicine, University of Illinois at Chicago, IL 60612, USA.
Insights
In heart failure (HF), connexin43 (Cx43) expression and phosphorylation decrease, leading to reduced cell coupling. Increased protein phosphatase 2A (PP2A) activity in HF exacerbates this uncoupling, suggesting Cx43 modulation as a therapeutic target.
Area of Science:
- Cardiovascular Research
- Molecular Cardiology
- Cellular Electrophysiology
Background:
- Nonischemic heart failure (HF) is associated with ventricular arrhythmias, potentially linked to altered gap junction protein function, particularly connexin43 (Cx43).
- Understanding Cx43 expression, phosphorylation, and its regulation by protein phosphatases is crucial for elucidating conduction abnormalities in HF.
Purpose of the Study:
- To investigate Cx43 expression and phosphorylation status in the left ventricle (LV) of a rabbit model of nonischemic HF and human idiopathic dilated cardiomyopathy.
- To examine the role of protein phosphatases PP1 and PP2A in regulating Cx43 dephosphorylation and intercellular coupling in HF.
Main Methods:
- Western blot analysis of Cx43 mRNA and protein expression, and Cx43 phosphorylation states in rabbit and human LV tissue.
- Immunohistochemical colocalization studies of Cx43 with protein phosphatases PP1 and PP2A.
- Assessment of intercellular coupling using Lucifer Yellow dye transfer and pharmacological manipulation with okadaic acid.
Main Results:
- HF rabbits showed significant decreases in Cx43 mRNA (29%) and total protein (34%), with a 64% increase in non-phosphorylated Cx43 (Cx43-NP) in the LV.
- Similar alterations in Cx43 expression and phosphorylation were observed in human idiopathic dilated cardiomyopathy LV.
- Increased colocalization of PP2A with Cx43 was observed in HF, correlating with reduced intercellular coupling, which was partially restored by okadaic acid.
Conclusions:
- Nonischemic HF in rabbits and humans is characterized by reduced Cx43 expression and altered phosphorylation, contributing to cardiac uncoupling.
- Elevated PP2A activity, colocalized with Cx43, appears to drive increased Cx43-NP levels and impaired cell-cell communication in HF.
- Targeting Cx43 phosphorylation represents a potential therapeutic strategy to improve cardiac conduction in heart failure patients.
Abstract:
In nonischemic heart failure (HF), ventricular tachycardia initiates by a nonreentrant mechanism, but there is altered conduction (that could lead to re-entry) that could arise from changes in gap junctional proteins, especially connexin43 (Cx43). We studied Cx43 expression and phosphorylation state in the left ventricle (LV) from an arrhythmogenic rabbit model of nonischemic HF and from patients with HF attributable to idiopathic dilated cardiomyopathy. We also investigated the role of protein phosphatases that dephosphorylate Cx43--PP1 and PP2A. In HF rabbit LV, Cx43 mRNA and total protein were decreased by 29% and 34%, respectively (P<0.05 and P<0.001). In controls, Cx43 was primarily in the phosphorylated state, but with HF there was a 64% increase in nonphosphorylated Cx43 (Cx43-NP, normalized to total Cx43; P<0.05). Similar results were noted in HF rabbit myocytes (P<0.05) and in human idiopathic dilated cardiomyopathy LV (P<0.05). We found that PP1 and PP2A colocalized with Cx43 in rabbit LV. With HF, the level of colocalized PP2A increased >2.5-fold (P<0.002), whereas colocalized PP1 was unchanged. We also found intercellular coupling (assessed by Lucifer Yellow dye transfer) was markedly reduced in HF. However, okadaic acid (10 nmol/L) reduced the amount of Cx43-NP and significantly improved cell coupling in HF. Thus, in nonischemic HF in rabbits and humans, there is a decrease in both Cx43 expression and phosphorylation that contributes to uncoupling. Increased levels of PP2A that colocalize with Cx43 can underlie enhanced levels of Cx43-NP in HF. Modulation of Cx43 phosphorylation may be a potential therapeutic target to improve conduction in HF.
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