Abstract 180: Myocyte-Specific Excision of the Murine Vinculin Gene Leads to Arrhythmias, Sudden Death and Heart Failure due to Dissolution of the Intercalated Disc Structure
Vinculin (Vin) is a ubiquitously expressed protein that plays a dynamic role in actin cytoskeleton assembly. Being located at intercalated discs (ICDs) as well as in cell-to-matrix adhesions, Vin anchors the myocyte sarcomere to the cell membrane. Metavinculin (MVin) is a muscle-specific splice variant of Vin, and mutated MVin is found in patients with cardiomyopathy. Since global knockout (KO) of Vin is embryonic lethal we generated cardiac-myocyte specific Vin KO mice. Cre excision of the floxed Vin/MVin exon 3 was mediated by the myosin light chain-2 ventricular promoter. Homozygous Cre-excision of Vin showed no embryonic lethality (n=309). Compared to littermate controls, Vin KO mice less than 3 months old had preserved cardiac function but showed: A) eccentric cardiac hypertrophy by echo and a 29% increase in heart weight/ tibia length ratio (p<0.006, n=15) B) up-regulation of hypertrophic markers by RT-PCR (ANF- 3.9 fold, p<0.007 and BNP - 4.1 fold, p<0.029, n=5) C) cardiac arrhythmias by conscious telemetry, ranging from Type I AV-block, to complete heart block and sudden death by polymorphous non-sustained ventricular arrhythmia (n≥3); and D) altered cardiac ultrastructure with morphologically abnormal ICDs, reduced adherens junctions, increased separation of myofibrils adjacent to ICDs and Z-lines, as well as swollen mitochondria (n=5). Vin KO mice older than 3 months, developed a cardiomyopathic phenotype and compared to littermate controls showed: A) a 71% reduction of MVin protein levels (p<0.0007, n=3) B) histological fibrosis and LV dilation; C) depressed cardiac function by 14 weeks (42 and 44% decrease in FS and Vcf, respectively, p< 0.001, n≥5) D) reduced expression of Vin associated proteins (55% of cadherin and 42% of β-1D integrin (p≤0.03, n=3) and E) 97% mortality by 20 weeks vs. none in control (n=39).
Conclusion: This is the first report of tissue-specific inactivation of the Vin gene. Analysis of this cardiac-specific Vin KO model indicates that reduced Vin protein expression causes dissolution of the ICD. This model provides new evidence of Vin’s role in mechanical/electrical coupling of cardiac myocytes in the working myocardium and provides mechanistic data regarding how Vin mutations in man might predispose to cardiomyopathy.