RbFox Genes in Congenital Heart Disease and Cardiomyopathy
Abstract
Hypoplastic left heart syndrome (HLHS) is one of the most devastating forms of congenital heart defect (CHD) that results from underdevelopment of the left side of the heart. The cardinal features of the disease are (1) a very small or “hypoplastic” left ventricle (LV) that is unable to squeeze properly to push oxygenated blood to the body; (2) a narrow aorta, which connects heart to the body’s circulatory system; and (3) small or nonexistent valves. Altogether, this constellation of structural abnormalities creates poor “systemic” or body circulation. Because HLHS is uniformly lethal if left untreated, three surgeries are normally performed that result in recruitment of the right ventricle (RV) to sustain the entire circulatory system. While more patients are surviving to adulthood following these palliative surgeries, the long-term outcomes can be poor as the RV often fails, leaving transplantation as the only option. Because donor infant hearts are scarce, many patients succumb to their disease prior to transplant. Consequently, the emotional, financial, physical, and psychological burden placed on both civilian and military families is extremely high with HLHS representing the greatest cause of morbidity and mortality in infants born with a CHD. HLHS has been very difficult to study in the lab because the genetic causes of the disease have been unknown. This has led to a lack of suitable animal models to dissect the mechanisms underlying the cardiac abnormalities. For example, whether one of the structural defects is responsible for the others or whether they all arise independently is unknown. Progress was recently achieved on the genetic causes of HLHS by sequencing DNA of newborns with the disease. Mutations in the Rbfox2 gene were found more often in these babies, suggesting that defective Rbfox2 function might be causing the condition. However, this hypothesis has yet to be tested in an animal model. Moreover, because Rbfox2 has not been previously linked to cardiovascular development, the mechanism by which Rbfox2 functions to generate a normal heart during embryogenesis is not known. The zebrafish is a popular vertebrate model system for studying the genetics of cardiovascular development and disease. Among many reasons that make zebrafish so powerful is their genetic similarity to humans and their conserved cardiovascular development. Taking advantage of these and other attributes, we created mutations in two zebrafish Rbfox genes (Rbfox1L and Rbfox2 – “double mutant embryos”) to learn (1) whether Rbfox mutations are causal for CHDs, and (2) whether the heart defects observed would accurately mirror those seen in HLHS patients. We found that Rbfox double mutant embryos die within 4 days of life from severe cardiovascular abnormalities that include at least two cardinal features of HLHS -- a hypoplastic ventricle with compromised pump function and a narrow aorta. Although we have not yet analyzed valve formation in Rbfox double mutant animals, we suspect that they will also be affected. Interestingly, we learned that the muscle fibers in each ventricular muscle cell are disrupted in Rbfox double mutants, suggesting that compromised pump function might be the primary cause of all of the cardiovascular deficiencies. While heart development is normal in single mutant zebrafish, progressive heart failure develops in Rbfox2 adults that is lethal by 5 months of age, implicating Rbfox2 as a risk factor for early onset cardiomyopathy. Thus, we have created the first clinically relevant zebrafish model of HLHS, which demonstrates for the first time that Rbfox mutations are causal for the disease. We plan to exploit our unique system over the next 3 years to gain new mechanistic insights into the roles of Rbfox in developing and maintaining the heart. In Aim 1, we will study the cardiovascular defects in Rbfox double mutant embryos in more detail and distinguish primary from secondary structural m
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Mar 10, 2021
- Source ID
- W81XWH2010165
Entities
People
- Caroline E Burns
Organizations
- United States Army