Myocardial Fibroblasts are a Primary Source High Molecular Weight Hyaluronan Production in the Failing Heart

Background: The extracellular matrix provides organizational context for solid organs. During disease, such as 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 terms of 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). Methods and Results: Using immunofluorescence, biochemical extraction, and ELISA, 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 expression of HAS2. Given these insights, we used HAS2 gain- and loss-of-function approaches to examine the extent to which activated cardiac fibroblasts produced hyaluronan. TGF-induced activation of fibroblasts caused a significant increase in Has2 mRNA and concomitant accumulation of hyaluronan greater than 1 MDa in size. Deletion of Has2 abrogated TGF-induced production of hyaluronan. In addition, overexpression of Has2 was sufficient to cause an increase in hyaluronan accumulation in the absence of TGF-induced activation. Given the magnitude of hyaluronan production, and that hyaluronan has been reported to have biologic activity, we then queried whether the primary functions of fibroblasts (proliferation, migration, and collagen production) were impacted by hyaluronan treatment. Our data indicated negligible impacts of Has2 on proliferation, migration, and collagen production. Exposing fibroblasts to exogenous hyaluronan also had minimal impact on fibroblasts. We also assessed whether fibroblast-borne Hyal2 plays a role in degradation of hyaluronan, and our data indicated little impact of Hyal2 on hyaluronan accumulation (or even any impacts on the transcriptional profile of fibroblasts). Conclusion: Activated fibroblasts produce high molecular weight hyaluronan, and the production of hyaluronan depends on Has2. The robust production of hyaluronan by fibroblasts does not appear to impact fibroblast function.