Altered Connexin 43 and Connexin 45 protein expression in the heart as a function of social and environmental stress in the prairie vole

Abstract

Exposure to social and environmental stressors may influence behavior as well as autonomic and cardiovascular regulation, potentially leading to depressive disorders and cardiac dysfunction including elevated sympathetic drive, reduced parasympathetic function, and ventricular arrhythmias. The cellular mechanisms that underlie these interactions are not well understood. One mechanism may involve alterations in the expression of Connexin43 (Cx43) and Connexin45 (Cx45), gap junction proteins in the heart that play an important role in ensuring efficient cell-to-cell coupling and the maintenance of cardiac rhythmicity. The present study investigated the hypothesis that long-term social isolation, combined with mild environmental stressors, would produce both depressive behaviors and altered Cx43 and Cx45 expression in the left ventricle of prairie voles - a socially monogamous rodent model. Adult, female prairie voles were exposed to either social isolation (n = 22) or control (paired, n = 23) conditions (4 weeks), alone or in combination with chronic mild stress (CMS) (1 week). Social isolation, versus paired control conditions, produced significantly (p < 0.05) increased depressive behaviors in a 5-min forced swim test, and CMS exacerbated (p < 0.05) these behaviors. Social isolation (alone) reduced (p < 0.05) total Cx43 expression in the left ventricle; whereas CMS (but not isolation) increased (p < 0.05) total Cx45 expression and reduced (p < 0.05) the Cx43/Cx45 ratio, measured via Western blot analysis. The present findings provide insight into potential cellular mechanisms underlying altered cardiac rhythmicity associated with social and environmental stress in the prairie vole.

Keywords: Cardiac arrhythmic susceptibility; chronic mild stress; connexins; depression; microtus; social isolation.

Figure 1

Details of the chronic mild stress (CMS) procedure used in the present study design.

Figure 2

The impact of social isolation and chronic mild stress (CMS) on depressive behaviors in the 5-min forced swim test (FST). Mean (± standard error of the mean, SEM) duration of immobility in the FST in paired (P, n=9), paired + CMS (P+CMS, n=14), isolated (I, n=11), and isolated + CMS (I+CMS, n=11). Statistical symbols indicate value is significantly different (P < 0.05, using 2-factor, independent groups ANOVA and Fisher’s Least Significant Difference post-hoc analyses) from: * = paired group only; ^# = all other groups. Note: the remainder of 300 seconds is composed of active coping behaviors.

Figure 3

A representative Western blot of connexin43 (Cx43) and connexin45 (Cx45) expression in the left ventricle, relative to the loading control (glyceraldehyde 3-phosphate dehydrogenase, GAPDH), for a set of paired (P) and isolated (I) prairie voles in the presence and absence of chronic mild stress (CMS).

Figure 4

The impact of social isolation and chronic mild stress (CMS) on connexin43 (Cx43) and connexin45 (Cx45) expression in the left ventricle. Expression levels of Cx43 (A) and Cx45 (B) were determined by Western blot and normalized to the GAPDH loading control. In addition, the ratio of Cx43/Cx45 (C) was determined after normalization of Cx43 and Cx45 to GAPDH. Data are represented as the mean and standard error of the mean (SEM) for each group relative to control (paired). Quantification (mean ± SEM) of Cx43 and Cx45 expression for paired (P, n=8), paired + CMS (P+CMS, n=9), isolated (I, n=9), and isolated + CMS (I+CMS, n=9). Statistical symbol indicates the value is significantly different (P< 0.05, using 2-factor, independent groups ANOVA and Student’s t-tests with a Bonferroni correction) from: * = paired group; ^ = isolated group.