Spectrin-based Regulation Of Exosome Secretion In Cardiac Fibroblasts

Cardiac fibroblasts (CFs) not only modulate the extracellular matrix under physiological conditions, but also have the ability to sense local injury and respond with a phenotypic change and increased paracrine communication to distal cells. While a myriad of studies have focused on identifying the paracrine signals involved in recruitment and activation of CFs, the manner by which CF paracrine communication networks are tuned in response to chronic stress remains unclear. Previously, our lab found that stress-induced loss of the cytoskeletal protein, β IV -spectrin, regulates the CF phenotype and fibrosis. Therefore, we hypothesized that degradation of β IV -spectrin is a critical step in stress-induced communication involved in recruitment of distal CFs. In this study, we first collected conditioned media from WT and β IV -spectrin deficient (qv 4J ) CFs to test the effects on quiescent WT CFs. We found that the CFs treated with qv 4J -conditioned media showed increased proliferation and compaction rates, as well as altered gene expression in the recipient cells compared to those treated with WT-conditioned media. To further explore the role of β IV -spectrin in paracrine signaling, we isolated exosomes from WT- and qv 4J -conditioned media. We found that loss of β IV -spectrin in CFs resulted in an increased concentration of exosomes in conditioned media, that also induced increased proliferation in quiescent CFs. Furthermore, we found that genetic mice expressing degradation-resistant β IV -spectrin ( qv 3J mice) showed impaired CF recruitment and activation following myocardial infarction (MI) together with increased mortality and impaired fibrotic remodeling compared to WT. Finally, we demonstrate that exosomes from a WT-MI heart can improve fibrotic remodeling in qv 3J mice following MI. Our work identifies a novel role of the spectrin-based pathway in facilitating long-range communication in response to chronic stress.