Scleraxis regulates myocardial extracellular matrix synthesis and homeostasis (1152.14)

The cardiac extracellular matrix (ECM) functions as a source of mechanical and biochemical cues for cellular differentiation and growth in addition to its role as a physical scaffold for cellular constituents. The mechanisms governing basal ECM production are incompletely understood. Our laboratory has previously demonstrated the role of scleraxis (Scx) as a required regulator of human collagen Iα2 gene expression. Here we investigate the consequences of loss of Scx on matrix composition and turnover. We hypothesized that Scx functions to broadly regulate cardiac ECM production. DNA microarray analyses of Scx null (KO) murine hearts revealed marked changes in ECM components occurring due to loss of Scx. Histological assessment of Scx KO hearts revealed a marked reduction in abundance of collagen fibrils and overall fibrotic components as compared to wildtype (WT) hearts. Immunoblotting and qPCR analyses of these hearts confirmed a significant downregulation of fibrillar collagen types I, III and V. shRNA‐ mediated knockdown of Scx further refined the role of Scx as a direct regulator of these collagen genes. The expression of proteoglycan components including fibromodulin and lumican were reduced in Scx KO myocardium. Matrix metalloproteinases (MMPs), a prime regulator of matrix degradation and homeostasis, were also significantly altered in their expression particularly MMP2 and MMP9 as demonstrated by gelatin zymography and qPCR analyses. Thus Scx may be a direct modulator of the activity of these remodeling enzymes. The widespread effects of scleraxis deletion supports a central role for scleraxis in governing the normal expression and structure of the cardiac ECM. Grant Funding Source : Supported by the Canadian Institutes of Health Research and St. Boniface Research Foundation