Ó³»­´«Ã½

During acute myocardial infarction, the composition of the extracellular matrix changes remarkably. One of the most notable changes in the extracellular matrix is in the accumulation of collagen; however, hyaluronan rivals collagen in its abundance. Yet, the extent to which specific cells and enzymes may contribute to such accumulation has been largely unexplored. Here, we hypothesized that activated cardiac fibroblasts produce hyaluronan via hyaluronan synthase 2 (HAS2). We show that hyaluronan accumulates following myocardial infarction and persists through at least four weeks. Our analyses of failing heart RNA sequencing data suggest fibroblasts are the cells most changed in the expression of 2. Given these insights, we used HAS2 gain- and loss-of-function approaches to examine the extent to which activated cardiac fibroblasts produce hyaluronan. TGFβ-induced activation of fibroblasts caused a significant increase in 2 mRNA and concomitant accumulation of hyaluronan greater than 1 MDa in size. Deletion of 2 abrogated TGFβ-induced production of hyaluronan. In addition, overexpression of 2 was sufficient to cause an increase in hyaluronan accumulation in the absence of TGFβ-induced activation. Our data indicated negligible impacts of 2 on proliferation, migration, and collagen production. Exposing fibroblasts to exogenous hyaluronan also had minimal impact on fibroblasts. We also assessed whether fibroblast-borne 2 plays a role in the degradation of hyaluronan, and our data indicated little impact of 2 on hyaluronan accumulation (or even any impacts on the transcriptional profile of fibroblasts). Activated fibroblasts produce high molecular weight hyaluronan via 2, which occurs independent of other fibroblast functions.