Abstract 317: Cardiac-specific Deletion Of Desmoplakin Causes Dilated Cardiomyopathy And Remodeling Of Gap Junctions
Desmoplakin (dsp) is an intracellular protein that links desmosomal adhesion molecules to the desmin cytoskeleton. A recessive C-terminal truncation in dsp has been linked to a form of dilated cardiomyopathy (Carvajal syndrome) whereas a dominant point mutation (S299R) has been implicated in ARVC. Germ-line deletion of dsp in mice causes early embryonic lethality. Thus, to define the role of dsp in the structure and function of the adult heart, we developed a cardiac-specific knockout by crossing floxed-dsp mice (dsp fl/fl) with a tamoxifen-inducible α-MHC-Cre line. Young adult animals (10–12 wk) were given tamoxifen for 3 days and the development of a cardiac phenotype was characterized by light microscopy and immunoblotting and immunohistochemistry of intercalated disk proteins. Dsp signal was undetectable in cardiac myocytes 8 days after tamoxifen was begun. Immunoblotting showed only a faint signal presumably representing dsp in non-cardiac myocytes. Gross and microscopic evaluation showed biventricular dilatation and diffuse piece-meal degeneration of cardiac myocytes by day 7. Myocardial damage progressed over the following weeks resulting in a dramatic picture of dilated cardiomyopathy with extensive multifocal areas of myocyte necrosis and replacement fibrosis involving LV, RV and septal areas. However, no accumulation of fat was observed histologically. Most animals exhibited signs of heart failure by 4 – 6 wk and either died or were euthanized by 7 wk. Immunostaining of Cx43 showed early (day 7) marked reduction in the amount of Cx43 reflecting fewer and smaller gap junctions at intercalated disks. Interestingly, no change was seen in the amount of signal for plakoglobin and plakophilin-2, both of which are major binding partners of dsp in desmosomes. However, junctional signal for the intermediate filament protein desmin disappeared, suggesting that connections between desmosomes and the desmin cytoskeleton were disrupted. These results indicate that junctional localization of plakoglobin and plakophilin-2 does not require dsp. Deletion of dsp causes rapid remodeling of gap junctions associated with diffuse RV and LV injury and necrosis and a clinicopathological picture of dilated cardiomyopathy reminiscent of Carvajal syndrome.
This research has received full or partial funding support from the American Heart Association, AHA Founders Affiliate (Connecticut, Maine, Massachusetts, New Hampshire, New Jersey, New York, Rhode Island, Vermont).