Abstract 3393: Expression Patterns of the Cardiac Myofilament Proteins- Analysis of Surgical Myectomy Tissue from Patients with Sarcomeric Hypertrophic Cardiomyopathy
Background: Mutations in sarcomeric/myofilament proteins are commonly implicated in hypertrophic cardiomyopathy (HCM). However, the mechanisms underlying disease pathogenesis are not completely understood. Utilizing flash-frozen surgically resected left ventricular (LV) tissue from patients with obstructive HCM, we investigated the effect of sarcomeric HCM on tissue expression of various myofilament proteins.
Methods: Frozen surgical specimens from 47 patients with HCM who underwent septal myectomy at the Mayo Clinic between 1999 and 2003 were examined. Using PCR, DHPLC, and direct DNA sequencing, all were genotyped for mutations involving the 8 myofilament-encoding genes that currently comprise the clinically available genetic test for sarcomeric HCM. Whole protein lysate was extracted from the frozen myectomy tissues and levels of myosin binding protein C, myosin heavy chain, alpha actin and alpha actinin were analyzed by Western Blot; GAPDH was used as a loading control. Frozen LV tissue derived from normal hearts of accidental death victims served as a reference group.
Results: Overall, 25/47 (53%) patients had sarcomeric HCM including 13 patients with myosin binding protein C (MYBPC3) mutations and 10 with mutations in the beta myosin heavy chain (MYH7). Compared to normal heart tissue, the expression of myosin heavy chain was up-regulated significantly regardless of the underlying disease-causing genotype (genotype positive = genotype negative). However, there was gene-specific upregulation of myosin binding protein C with marked increases detected in patients with MYH7-HCM. In contrast, normal levels of myosin binding protein C were seen in patients with either MYBPC3-HCM or genotype-negative HCM.
Conclusions: This is the first study to examine the expression pattern of sarcomeric proteins in a large collection of flash frozen human HCM myectomy tissue. Up-regulated, genotype-specific cardiac tissue expression of myosin binding protein C among patients with MYH7 (beta myosin heavy chain)-HCM suggests a novel compensatory pathway underlying the development of cardiac hypertrophy for one of most common genetic subtypes of HCM.