Knockout of proteoglycan versican in cardiac remodeling after myocardial infarction

Knockout of proteoglycan versican in cardiac remodeling after myocardial infarction

Introduction:
Versican is a large multifunctional chondroitin sulfate proteoglycan expressed in several cell types such as stromal cells, especially fibroblasts, and immune cells. Its specific binding to HA molecules makes versican a modulator of extracellular matrix. Thereby versican may play a crucial role in cardiac remodeling after acute myocardial infarction (AMI). In addition, several fibrotic diseases, such as AMI, are known to be associated with a pathological elevated unfolded protein response (UPR) signaling.

Objectives: Our aim is to investigate versican’s role after AMI and to define the central mechanisms in which it is involved, including its function in UPR signaling. Especially considering the well-known duality of versican in inflammatory processes depending on tissue and cell type, the differential effects of versican on fibrotic remodeling after myocardial infarction remains to be clarified. A cell-specific KO of versican allows us to consider the role of versican expressed by fibroblasts differentiated from other cell populations.  

Materials and methods: Mice with ubiquitous and fibroblast-specific conditional knockout of versican and Cre-/+ mice without loxP-flanked versican alleles as control underwent 45’ closed-chest cardiac ischemia/reperfusion (I/R) to induce myocardial infarction. Cardiac function was measured by echocardiography. Cardiac cell composition and gene expression was analyzed via single cell sequencing followed by in vitro analysis of unfolded protein response in isolated cardiac fibroblasts. 

Results: Versican gene expression is elevated early in hearts after AMI (6h) and stays upregulated in the infarct zone for up to 3 weeks. Single-cell RNA sequencing shows that versican is expressed mainly by cardiac fibroblasts and that genes associated to endoplasmic reticulum (ER) stress are overrepresented in versican KO cells. Indeed, ubiquitous conditional knockout of versican leads to a limitation of ventricular dilation (EDV as well as ESV) after AMI. Mechanistically versican deficiency diminishes fibroblast activation after ischemia/reperfusion and the unfolded protein response as observed by reduced expression of UPR target genes in cardiac fibroblasts (e.g., Hspa5, Manf and Creld2) which are known to limit fibrotic remodeling. Consistently fibroblast-specific KO of versican shows signs of reduced cardiac fibrosis after myocardial infarction due to a reduced isovolumic relaxation time (IVRT) compared to wild type control.

Conclusion: Global as well as fibroblast-specific knockout of versican in mice results in a protective phenotype due to limiting of fibrotic remodeling after myocardial infarction. Furthermore, for the first time versican is linked to ER stress and unfolded protein response.