Date on Master's Thesis/Doctoral Dissertation

5-2025

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Biochemistry and Molecular Biology

Degree Program

Biochemistry and Molecular Biology, PhD

Committee Chair

Jones, Steven

Committee Member

Clark, Barbara

Committee Member

Moore, Joseph

Committee Member

Clem, Brian

Committee Member

Smith, Melissa

Author's Keywords

Hyaluronan; fibroblasts; myocardial infarction; extracellular matrix; heart failure; fibrosis

Abstract

During acute myocardial infarction (MI), the composition of the extracellular matrix (ECM) undergoes significant changes. While collagen accumulation is one of the most well-documented ECM alterations, hyaluronan (HA) is equally abundant. However, the cellular sources, enzymatic regulation, and functional significance of HA accumulation remain largely unexplored. Here, we hypothesized that activated cardiac fibroblasts produce HA via hyaluronan synthase 2 (HAS2), facilitating scar formation and stability. Our findings demonstrate that HA accumulates post-MI and persists for at least four weeks. Through HA sizing techniques, we determined the molecular weight of this persistent HA. Additionally, RNA sequencing analysis of failing human hearts revealed that fibroblasts exhibit the most significant changes in Has2 expression. To further investigate fibroblast-derived HA, we employed gain- and loss-of-function approaches. transforming growth factor beta (TGFβ)-induced fibroblast activation led to a significant increase in Has2 mRNA expression and the subsequent accumulation of HA larger than 1 MDa. Deletion of Has2 abolished TGFβ-induced HA production, whereas overexpression of Has2 increased HA accumulation even in the absence of TGFβ activation. Interestingly, our data showed that Has2 manipulation had minimal effects on fibroblast proliferation, migration, or collagen production. Similarly, exposing fibroblasts to exogenous HA did not significantly impact fibroblast function. We also examined whether fibroblast-derived hyaluronidase 2 (HYAL2) contributes to HA degradation and found that HYAL2 had little effect on HA accumulation or fibroblast gene expression profiles. In vivo, fibroblast-specific Has2 deletion resulted in a reduction in cardiac function in males 7 d post-MI, despite no observed changes in cardiac fibrosis, collagen organization, hypertrophy, or vascular density. We show that activated fibroblasts produce high-molecular-weight HA (HAHMW) via Has2. Moreover, the reduction of fibroblast-derived HA exacerbates cardiac dysfunction in males post-MI, highlighting its potential role in ventricular remodeling. Activated fibroblasts produce high-molecular-weight hyaluronan via Has2, which occurs independent of other fibroblast functions. Fibroblast-derived Has2 supports cardiac function early after MI. The mechanism responsible for this and why it is not evident in female mice is unclear.

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