Abstract 11944: Heterozygous LmnaDelk32 Mutant Mice Showed Alterations of the Ubiquitin-Proteasome System and Developed Progressive Dilated Cardiomyopathy
Dilated cardiomyopathy (DCM) is associated with left ventricular dilatation and systolic dysfunction. It is a major cause of heart failure and cardiac transplantation. LMNA is the most frequent gene implicated in DCM with conduction and/or rhythm defects. It encodes nuclear envelope proteins, the lamin A/C. The pathophysiological mechanisms linking LMNA mutations to DCM remain to be elucidated. The aim of this study was to characterize the cardiac phenotype of mice carrying a Lmna mutation, which is associated with a severe phenotype in humans. The model was generated by targeted deletion of 3 nucleotides encoding lysine 32 in the Lmna gene (LmnadelK32). Heart function was assessed by serial echocardiography and ECG monitoring in heterozygous (Het) and wild-type (WT) mice. Cardiac lamin A/C mRNA and protein levels were measured by RT-qPCR and Western blot, respectively. Het mice did not show rhythm/conduction defect. They progressively developed cardiac dysfunction and DCM, leading to death between 35 and 70 weeks of age. Before the development of DCM, lamin A/C protein level was 50% lower, whereas Lmna mRNA level was 20% higher in Het than in WT mice, suggesting posttranscriptional regulation of mutant lamin. Treatment of Het neonatal cardiomyocytes with ubiquitin-proteasome system (UPS) inhibitors stabilized mutant lamin C, suggesting degradation via the UPS. After development of DCM, lamin A/C protein level did not differ between Het and WT mice, suggesting UPS impairment. Global function of UPS was therefore assessed in vivo by crossing Het and WT mice with UbG76V-GFP transgenic mice, expressing an UPS reporter substrate. Levels of UbG76V-GFP and ubiquitinated proteins were 2-fold higher in Het than in WT mice, supporting a global impairment of UPS in the heart of Het mice. In conclusion, these data show that Het LmnadelK32 mice are the first knock-in Lmna model developing a cardiac-specific phenotype at the heterozygous state. These findings provide evidence of degradation of mutant lamin by UPS, followed by its impairment with progression of DCM.
- © 2011 by American Heart Association, Inc.