Biomechanical and compositional basement membrane defects due to a Col4a1 mutation affect cardiac morphology and function

Abstract

Collagen IV is a major constituent of basement membranes and mutations in the genes COL4A1 and COL4A2 present clinically as a variable, multi-system disorder called COL4A1 (Gould) syndrome. Evidence from case reports supports a cardiac component to this disease, but the phenotypic and functional implications affecting the heart, their progression and underlying mechanisms all remain poorly characterised. Indeed, the role of the basement membrane (BM) in adult cardiac disease remains underexplored. We set out to address these knowledge gaps by combining in-depth phenotypic and molecular analyses of a Col4a1 mutation on cardiac biology in a murine model (Col4a1^+/svc) of Gould Syndrome. This revealed morphological cardiac defects including cardiomyocyte hypertrophy with myocardial and vascular fibrotic remodelling that impaired cardiac function. The Col4a1 mutation causes systolic and diastolic dysfunction with reduced left ventricular developed pressure. Mechanistically, we show these defects are due to secretion of mutant protein and BM defects rather than collagen misfolding and proteotoxic stress. The BM defects lead to a pro-fibrotic state with increased fibrillar collagen deposition, cardiac stiffness, and ECM compositional defects. These are accompanied by altered regulation of pathways involved in sarcomere formation, sarcolemma stability and cardiomyocyte metabolism, establishing a molecular signature of COL4A1-related cardiac disease. Intriguingly, aspects of this molecular signature including cardiac metabolic pathways, regulation of cardiac muscle contraction and BM component expression, are shared with common cardiomyopathies such as coronary micro-embolism, and dilated, ischemic and hypertrophic obstructive cardiomyopathies. By defining the molecular and phenotypic cardiac components of Gould syndrome these data show that the BM is essential for maintaining systolic and diastolic function and that alterations to the BM leads to a fibrotic response. These data increase insight into the role of the basement membrane and collagen IV in cardiac biology, and highlights mechanisms shared between Gould syndrome and common adult cardiac disease.