IOWA CITY, Iowa-- Results from a University of Iowa Health Care study may help researchers to better understand and find ways to treat heart problems related to a certain type of muscular dystrophy.
In an article appearing in the Aug. 20 issue of the journal Cell, UI researchers outline, for the first time, a complex domino effect that ultimately leads to a type of heart disease known as cardiomyopathy, which exacerbates limb-girdle muscular dystrophy (LGMD).
"Our results have important implications for scientists developing gene therapy for limb-girdle muscular dystrophy and for neurologists who treat muscular dystrophy patients with cardiomyopathy," said Kevin Campbell, Ph.D., UI professor physiology and biophysics, and neurology, and a Howard Hughes Medical Institute investigator. "Our results suggest that drug therapy directed toward vascular smooth muscle could be effective in preventing and/or stabilizing cardiomyopathy in some cases of muscular dystrophy."
Campbell has focused much of his career on understanding and trying to find ways to treat the various forms of muscular dystrophy, a group of hereditary diseases characterized by progressive muscle weakness and degeneration. LGMD, which affects between one in 20,000 and one in 50,000 individuals, involves initial deterioration of shoulder and pelvic girdle muscles, with relative sparing of other muscle groups. Although various studies of patients with LGMD have shown eventual cardiac involvement, no one had ever established a correlation between the genetic mutation that causes LGMD and cardiomyopathy.
Based on his previous work, Campbell knew that genetic flaws in muscle cell proteins known as sarcoglycans caused LGMD. Sarcoglycans are a substructure of the bigger dystrophin-glycoprotein complex, which researchers believe protects muscle cells from contraction-induced damage.
Using genetically engineered mice, Campbell and his research team showed that those animals lacking a type of sarcoglycan, identified as the delta subunit, experienced severe muscular dystrophy with large areas of cardiac cell death. Campbell and other researchers in his lab determined that this disruption in the sarcoglycan complex upsets vascular function and causes injury in cardiac and skeletal muscles. This injury leads to cardiac complications, which exacerbate LGMD.
"A number of proteins in cardiac muscle have been shown to be involved in cardiomyopathy," Campbell said. "However, our study opens up a unique and important new avenue of research directed toward the involvement of the vascular smooth muscle sarcoglycan-sarcospan complex in the cause and progression of cardiomyopathy."
Now that Campbell's lab has identified the problem that leads to cardiomyopathy in patients with LGMD, the next step is to look at possible pharmacological treatments to prevent vascular smooth muscle dysfunction. Campbell also wants to investigate gene transfer as a way to repair the sarcoglycan complex in vascular smooth muscles and develop additional animal models to evaluate smooth muscle contributions to cardiomyopathy.
In addition to Campbell, the other two primary investigators of this most recent study included postdoctoral associates Ramon Coral-Vazquez, Ph.D., and Ronald D. Cohn, M.D., both members of Campbell's Howard Hughes Medical Institute lab team. Other UI collaborators included Joseph A. Hill, M.D., Ph.D., assistant professor of internal medicine; Robert M. Weiss, M.D., associate professor of internal medicine; Robin Davisson, Ph.D., assistant professor of anatomy and cell biology; Steve Moore, M.D., Ph.D., professor of pathology; and Roger Williamson, M.D., professor of obstetrics and gynecology.
In addition to support from the Howard Hughes Medical Institute, the Muscular Dystrophy Association also funded this research.
Journal
Cell