Cardiomyopathy in the Golden Retriever Model of Duchenne Muscular Dystrophy: Phenotype, Gene Expression and Metabolic Studies
Abstract
Through three distinct papers, this dissertation aims to increase understanding of cardiomyopathy in golden retriever muscular dystrophy (GRMD), an important model for Duchenne muscular dystrophy (DMD). Unlike the mdx mouse, GRMD dogs develop progressive cardiomyopathy homologous in onset and severity to DMD. In both, cardiomyopathy develops around adolescence, progressing to dilation and eventual heart failure. Clinical cardiomyopathy occurs later than skeletal muscle involvement and is now the major cause of death in DMD. Skeletal and cardiac disease severity do not necessarily track together, suggesting possible different pathogenetic mechanisms. A comprehensive understanding of GRMD cardiomyopathy will be key to using this preclinical model. First, we report cardiac lesions in a large group of GRMD and carrier dogs. We found semi-quantitative scoring and fibrosis quantification correlate with disease progression and semi-quantitative scores correlated with vascular hypertrophy and late gadolinium enhancement on cardiac MRI. The nature of some lesions suggested functional hypoxia may contribute to disease progression. Next, we evaluated expression of potential genetic biomarkers in GRMD hearts. Left and right ventricles from 41 dogs (7 normal, 6 carrier, 28 GRMD) were analyzed by qRT-PCR for five genes previously associated with disease in DMD or GRMD: brainderived neurotropic factor (BDNF), utrophin, matrix-metalloproteinase-9, a-disintegrinand-metallopeptidase-domain-12, and osteopontin (SPP1). BDNF and SPP1 protein levels were assessed by western blot. There was differential expression of BDNF and SPP1 in GRMD hearts, extending work suggesting BDNF is preferentially increased in GRMD LV and showing that SPP1 expression tracks with cardiomyopathy evolution. Finally, we evaluated glucose metabolism as a potential biomarker in GRMD. Skeletal muscle from normal, carrier, and GRMD pelvic limbs and LV were analyzed by mRNA profiling, qPCR, western blotting, and immunofluorescence microscopy for the glucose transporter (GLUT4). Physiologic glucose handling was measured by fasting glucose tolerance test, insulin levels, and PET-CT using the glucose analog 2-deoxy-2- [18F]fluoro-D-glucose. We found that altered glucose metabolism in GRMD skeletal and cardiac muscle can be monitored with molecular, biochemical, and in vivo imaging and potentially utilized as a biomarker for disease progression and therapeutic response. Together, these studies deepen the understanding of the histologic, physiologic and metabolic changes in GRMD cardiomyopathy.
Citation
Schneider, Sarah Morar (2019). Cardiomyopathy in the Golden Retriever Model of Duchenne Muscular Dystrophy: Phenotype, Gene Expression and Metabolic Studies. Doctoral dissertation, Texas A & M University. Available electronically from https : / /hdl .handle .net /1969 .1 /184979.