Abstract 8707: Expression of LMNA-N195K Variant of A-type Lamins Results in Reduced Expression of Cav1.2 Channels, I Ca,L and Sudden Death in Mice
Background: Lamin A/C proteins, encoded by the LMNA gene, are intermediate filament proteins of the nuclear lamina, and predominantly expressed in differentiated cells including cardiomyocytes. Mutations in LMNA are associated with laminopathies, congenital diseases affecting muscle and homeostasis. One of the laminopathies associated with a missense mutation (N195K) in the A-type lamins results in dilated cardiomyopathy (DCM) with arrhythmias and sudden death. However it is unknown how the mutation in this LMNA gene contributes to the mechanism of arrhythmia and sudden death.
Methods and results: To investigate this we used a mouse line expressing the Lmna —N195K (LmnaN195K/N195K). Mutant mice demonstrated reduced fractional shortening, LV mass, wall thickness and dilated cardiomyopathy by echocardiography at 6 weeks consistent with human DCM, and died at an early age (6–7 weeks). Comparative cDNA microarray analysis from LmnaN195K/N195K and the wild type (WT) control ventricles at 6 weeks age revealed significant alterations in the expression of ion channels, transporter proteins, caveolins and associated proteins such as MAP kinases. Transmission electron microscopy analysis showed structural alterations of the ventricular myocytes with increase in number of caveolae. Quantitative Western blot analysis confirmed reduced expression for Cavβ (2 fold) subunits of the L-type Ca2+ channel. In contrast the expression levels of Cav3 (2.5 fold) was significantly increased. To investigate the functional impact of Lmna N195K on the I Ca,L, we transiently expressed either the WT LMNA+GFP, Lmna N195K+GFP or GFP (control) in isolated neonatal mouse ventricular myocytes and performed whole cell patch clamp analysis. Transient expression of Lmna N195K significantly reduced (58 %) peak I Ca,L (−6.0 ± 2 pA/pF, n=9) compared to GFP control (−14 ± 2 pA/pF, n=8). Expression of WT LMNA did not affect the I Ca,L (−14.2 ± 2.5 pA/pF, n=8) compared to control.
Conclusion: We conclude that Lmna N195K mutation results in reduced expression of ion channels and scaffolding proteins in the left ventricle with a significant reduction in peak I Ca,L in ventricular myocytes and these may contribute to the mechanism of arrhythmia and dilated cardiomyopathy.
- © 2010 by American Heart Association, Inc.