Abstract 9208: Association of Polymorphism in Glutamate-Cysteine Ligase Modifier Subunit Gene with Idiopathic Dilated Cardiomyopathy

Abstract

Myocardial mitochondrial dysfunction due to oxidative stress contributes to the pathogenesis of cardiomyopathy. Reduced glutathione (GSH) plays a crucial role in antioxidant defense mechanisms, and it is synthesized by glutamate-cysteine ligase (GCL) which is composed of catalytic (GCLC) and modifier (GCLM) subunits. We have found a polymorphism (-588C/T) in the 5’-flanking region of the GCLM gene in which the T allele showed lower promoter activity (40% of C allele) in response to oxidants and is associated with lower plasma GSH levels. This study examined the hypothesis that this polymorphism of GCLM gene may be associated with dilated cardiomyopathy (DCM). And, we studied potential role of GCLM in myocardial mitochondrial function using GCLM deficient (GCLM -/- ) mice. Methods and Results: The frequency of the polymorphism (-588C/T) of the GCLM gene was determined in 205 consecutive patients with non-familial idiopathic DCM and age- and sex-matched 253 normal healthy subjects. The T allele was highly frequent in patients with DCM, compared with control subjects (CT and TT genotypes: 36.2% in DCM vs. 18.6% in controls; P < 0.0001), and it was a significant risk factor for DCM, that was independent of hypertension, diabetes, smoking and BMI (OR 3.13, 95% CI 2.28 to 4.44; P < 0.0001). The mitochondrial GSH levels in myocardium were lower in GCLM -/- mice (39% of baseline GCLM +/+ ). Mitochondrial respiratory function in the myocardium of GCLM -/- mice had a reduction in the ADP-stimulated state 3 activity (60% of GCLM +/+ ). Hypoxia re-oxygenation induced greater mitochondrial damages in cultured GCLM -/- cardiomyocytes than GCLM +/+ cardiomyocytes, as evidenced by reduced membrane potential, increased protein carbonyl content, and increased GSSG/GSH rate in the isolated mitochondria. After myocardial ischemia-reperfusion, GCLM -/- mice had a greater dilation and systolic dysfunction of left ventricle (LV) than GCLM +/+ mice. Conclusions: The -588T polymorphism of the GCLM gene is associated with non-familial idiopathic DCM. This association is supported by the animal study that GCLM deletion increased susceptibility of myocardial mitochondria to oxidative damage through mitochondrial GSH reduction, which may potentially contribute to LV dysfunction.