CXCR4 Cardiac Specific Knockout Mice Develop a Progressive Cardiomyopathy.

Thomas J Larocca,Georges E Haddad,Perry Altman,Lahouaria Hadri,Roger J Hajjar,Edward Wang,Mark W Burke,Andrew A Jarrah,Ron Gordon,Sima T Tarzami

doi:10.3390/ijms20092267

Abstract

Activation of multiple pathways is associated with cardiac hypertrophy and heart failure. We previously published that CXCR4 negatively regulates β-adrenergic receptor (β-AR) signaling and ultimately limits β-adrenergic diastolic (Ca2+) accumulation in cardiac myocytes. In isolated adult rat cardiac myocytes; CXCL12 treatment prevented isoproterenol-induced hypertrophy and interrupted the calcineurin/NFAT pathway. Moreover; cardiac specific CXCR4 knockout mice show significant hypertrophy and develop cardiac dysfunction in response to chronic catecholamine exposure in an isoproterenol-induced (ISO) heart failure model. We set this study to determine the structural and functional consequences of CXCR4 myocardial knockout in the absence of exogenous stress. Cardiac phenotype and function were examined using (1) gated cardiac magnetic resonance imaging (MRI); (2) terminal cardiac catheterization with in vivo hemodynamics; (3) histological analysis of left ventricular (LV) cardiomyocyte dimension; fibrosis; and; (4) transition electron microscopy at 2-; 6- and 12-months of age to determine the regulatory role of CXCR4 in cardiomyopathy. Cardiomyocyte specific-CXCR4 knockout (CXCR4 cKO) mice demonstrate a progressive cardiac dysfunction leading to cardiac failure by 12-months of age. Histological assessments of CXCR4 cKO at 6-months of age revealed significant tissue fibrosis in knockout mice versus wild-type. The expression of atrial naturietic factor (ANF); a marker of cardiac hypertrophy; was also increased with a subsequent increase in gross heart weights. Furthermore, there were derangements in both the number and the size of the mitochondria within CXCR4 cKO hearts. Moreover, CXCR4 cKO mice were more sensitive to catocholamines, their response to β-AR agonist challenge via acute isoproterenol (ISO) infusion demonstrated a greater increase in ejection fraction, dp/dtmax, and contractility index. Interestingly, prior to ISO infusion, there were significant differences in baseline hemodynamics between the CXCR4 cKO compared to littermate controls. However, upon administering ISO, the CXCR4 cKO responded in a robust manner overcoming the baseline hemodynamic deficits reaching WT values supporting our previous data that CXCR4 negatively regulates β-AR signaling. This further supports that, in the absence of the physiologic negative modulation, there is an overactivation of down-stream pathways, which contribute to the development and progression of contractile dysfunction. Our results demonstrated that CXCR4 plays a non-developmental role in regulating cardiac function and that CXCR4 cKO mice develop a progressive cardiomyopathy leading to clinical heart failure.

Highlights

Cardiovascular disease (CVD) continues to be the leading cause of death in the United States [1,2]
Hemodynamic evidence of increased left ventricular end-diastolic (EDV), increased end-systolic volume (ESV), and decreased ejection fraction (Figure 1C) further suggest global pump dysfunction secondary to myocardial hypertrophy (* p < 0.05, (** p < 0.01). These findings provide additional evidence that there is significant, ongoing cardiac remodeling in C-X-C Receptor 4 (CXCR4) conditional knockout (cKO) mice hearts and that this remodeling likely drives the longitudinal effects of the CXCR4/C-X-C Ligand 12 (CXCL12) axis on cardiac dysfunction and progression to clinical heart failure
CXCR4 cKO mice showed mild cardiac dysfunction as early as 4-months of age, and by 12 months of age they had worsened fractional shortening and ejection fraction compared to wild-type mice, in addition to increased gross heart weight

Summary

Introduction

Cardiovascular disease (CVD) continues to be the leading cause of death in the United States [1,2]. CHF is a complex multifactorial syndrome leading to myocardial contractile dysfunction and reduced cardiac output [4,5]. While the development of cardiac dysfunction involves multiple distinct biochemical pathways, we are interested in small glycoproteins termed “chemokines”, one of the largest subclasses in the cytokine group. Several therapeutic approaches have been designed to neutralize chemokines in hopes of reducing inflammatory cell migration and subsequent inflammation [6,7]. These methods have not yet been commercially successful, due in part to the fact that the mechanisms underlying chemokine modulation of cardiac function are poorly understood [8]

Methods

Results

Conclusion