Abstract 2727: A Novel Human Phospholamban Promoter Polymorphism in Dilated Cardiomyopathy Alters Glucocorticoid Nuclear Receptor Mediated Transcription Regulation
Dilated cardiomyopathy (DCM) is a complex disease process, where the normal heart function has been altered by specific or multiple signaling pathways. However, depressed calcium handling by the sarcoplasmic reticulum Ca-ATPase and its regulator phospholamban has been a key characteristic of human and experimental heart failure. Accumulating evidence indicates that increases in the relative levels of phospholamban to Ca-ATPase in failing hearts and resulting inhibition of Ca-sequestration during diastole, impairs contractility. Phospholamban is an endogenous inhibitor of the Ca-ATPase and plays a primary role in the deterioration of cardiac function. Mutations in the coding region of phospholamban have been associated with hereditary dilated cardiomyopathy. Here, we sought to identify naturally occurring phospholamban promoter genetic variations in non-familial heart failure patients in two ethnic populations. We screened 381 DCM patients and 296 normal subjects, using PCR based direct sequencing. A genetic variant in the phospholamban promoter region was identified, which increases its expression and may serve as a genetic modifier in dilated cardiomyopathy. The variant, a single nucleotide transition from A to C at position —36bp relative to the phospholamban transcriptional start site, was found only in the heterozygous form in one (0.33%) out of 296 normal subjects and in 22 (5.75%) out of 381 cardiomyopathy patients (heart failure at age of 18 – 44 years, ejection fraction 22 ± 9%). In vitro analysis, using luciferase as a reporter gene in rat neonatal cardiomyocytes, indicated that the phospholamban variant increased activity by 24% compared to wild type. Furthermore, the -36A to C substitution altered the specific sequence of the steroid receptor for the glucocorticoid nuclear receptor/transcription factor in the phospholamban promoter, resulting in enhanced binding to the mutated DNA site. These findings suggest that the -36A to C genetic variant in the evlutionary conserved region of the human phospholamban promoter may contribute to depressed contractility and accelerate functional deterioration in heart failure.