Beta1-adrenergic receptor gene polymorphisms in Mexican patients with idiopathic dilated cardiomyopathy

β1-adrenoceptor Arg389Gly polymorphism confers differential β-arrestin-binding tropism in cardiac myocytes

AIM

The β₁-adrenergic receptor (AR) Arg389Gly polymorphism affects efficacy of its procontractile signaling in cardiomyocytes and carriers' responses to β-blockers. To identify molecular mechanisms underlying functional differences between Arg389 and Gly389 β₁ARs, we examined their binding to β-arrestins (βarr-1 and -2), which mediate β₁AR signaling, in neonatal rat ventricular myocytes.

METHODS

We tested the β₁AR-βarr interaction via β₁AR immunoprecipitation followed by βarr immunoblotting.

RESULTS

βarr1 binds both variants upon isoproterenol, carvedilol or metoprolol treatment in neonatal rat ventricular myocytes. Conversely, the potentially beneficial in the heart βarr2 only interacts with the Arg389 receptor in response to isoproterenol or carvedilol.

CONCLUSION

Arg389 confers unique βarr2-interacting tropism to the β₁AR in cardiac myocytes, potentially underlying this variant's gain-of-function phenotype and better clinical responses to β-blockers.

β1 adrenergic receptor polymorphisms and heart failure: a meta-analysis on susceptibility, response to β-blocker therapy and prognosis

Aims

The risk stratification of patients for heart failure (HF) remains a challenge, as well as the anticipation of the response to β-blocker therapy. Since the pivotal role of β1 adrenergic receptor (β1-AR) in HF, many publications have studied the associations between the β1-AR polymorphisms (Ser49Gly and Arg389Gly) and HF, with inconsistent results. Thus, we performed a meta-analysis of studies to evaluate the impact of β1-AR polymorphisms on susceptibility to HF, the response to β-blocker therapy and the prognosis of HF.

Methods and Results

Electronic databases were systematically searched before August 2011. We extracted data sets and performed meta-analysis with standardized methods. A total of 27 studies met our inclusion criteria. It was found that in East Asians, the Gly389 allele and Gly389 homozygotes significantly increased the HF risk, while the Gly389 allele and Gly389 homozygotes trended to decrease the risk of HF in whites. With the similar reduction of heart rate, overall, the Arg389 homozygotes showed a better response to β-blocker therapy. Furthermore, the Arg389 homozygotes were significantly associated with better LVEF improvement in East Asians and a mixed population. And in white people, the Arg389 homozygotes made a greater LVESd/v improvement and trended to be associated with better LVEDd/v improvement. However, the prognosis of Arg389 homozygotes HF patients was similar to those with Gly389 carriers. The Ser49Gly polymorphism did not impact the risk or prognosis of HF.

Conclusion

Based on our meta-analysis, the Gly389 allele and Gly389 homozygotes were risk factors in East Asians while trending to protect whites against HF. Furthermore, Arg389 homozygote is significantly associated with a favorable response to β-blocker treatment in HF patients. However, neither of the two polymorphisms is an independent predictor of the prognosis of HF.

A meta-analysis of β1-adrenergic receptor gene polymorphisms in idiopathic dilated cardiomyopathy

Published data on the association between β1-adrenergic receptor gene polymorphisms and idiopathic dilated cardiomyopathy (IDCM) risk are inconclusive. To derive a more precise estimation of the relationship, a meta-analysis was performed. A total of 12 case-control studies including 2642 cases and 3136 controls provided data on the association between β1-adrenergic receptor gene polymorphisms and susceptibility to IDCM. Overall, no significantly elevated risk was associated with Arg389Gly polymorphisms for all genetic models. In the subgroup analysis by ethnicity, no statistically increased risk was found for Gly389Gly versus Arg389Arg (OR 0.73; 95% CI 0.54-0.99; Ph=0.35) and Gly389Gly versus Arg389Arg+Arg389Gly (OR 0.75; 95% CI 0.55-1.01; Ph=0.52) among Europeans. Meanwhile, significantly increased risk was found among Asians based on the relatively small sample size. Further, significantly elevated IDCM risk was associated with Ser49Gly polymorphisms for all genetic models. When stratified by ethnicity, statistical association was found among Asians for Gly49Gly versus Ser49Ser (OR 4.56; 95% CI 1.36-15.23; Ph=0.10) and Gly49Gly versus Ser49Ser+Ser49Gly (OR 4.49; 95% CI 1.33-15.15; Ph=0.12), but not among Europeans. In summary, this meta-analysis suggests that no statistically increased risk was found between β1-adrenergic receptor gene polymorphisms and susceptibility to IDCM among Europeans.

Rescue of familial cardiomyopathies by modifications at the level of sarcomere and Ca2+ fluxes

Cardiomyopathies are a heterogeneous group of diseases of the myocardium associated with mechanical and/or electrical dysfunction that frequently show inappropriate ventricular hypertrophy or dilation. Current data suggest that numerous mutations in several genes can cause cardiomyopathies, and the severity of their phenotypes is also influenced by modifier genes. Two major types of inherited cardiomyopathies include familial hypertrophic cardiomyopathy (FHC) and dilated cardiomyopathy (DCM). FHC typically involves increased myofilament Ca(2+) sensitivity associated with diastolic dysfunction, whereas DCM often results in decreased myofilament Ca(2+) sensitivity and systolic dysfunction. Besides alterations in myofilament Ca(2+) sensitivity, alterations in the levels of Ca(2+)-handling proteins have also been described in both diseases. Recent work in animal models has attempted to rescue FHC and DCM via modifications at the myofilament level, altering Ca(2+) homeostasis by targeting Ca(2+)-handling proteins, such as the sarcoplasmic reticulum ATPase and phospholamban, or by interfering with the products of different modifiers genes. Although attempts to rescue cardiomyopathies in animal models have shown great promise, further studies are needed to validate these strategies in order to provide more effective and specific treatments.