Spectrin-Based Regulation of Cardiac Fibroblast Cell-Cell Communication.

Cardiac fibroblasts (CFs) maintain the fibrous extracellular matrix (ECM) that supports proper cardiac function. Cardiac injury induces a transition in the activity of CFs to promote cardiac fibrosis. CFs play a critical role in sensing local injury signals and coordinating the organ level response through paracrine communication to distal cells. However, the mechanisms by which CFs engage cell-cell communication networks in response to stress remain unknown. We tested a role for the action-associated cytoskeletal protein β IV -spectrin in regulating CF paracrine signaling. Conditioned culture media (CCM) was collected from WT and β IV -spectrin deficient ( qv 4J ) CFs. WT CFs treated with qv 4J CCM showed increased proliferation and collagen gel compaction compared to control. Consistent with the functional measurements, qv 4J CCM contained higher levels of pro-inflammatory and pro-fibrotic cytokines and increased concentration of small extracellular vesicles (30-150 nm diameter, exosomes). Treatment of WT CFs with exosomes isolated from qv 4J CCM induced a similar phenotypic change as that observed with complete CCM. Treatment of qv 4J CFs with an inhibitor of the β IV -spectrin-associated transcription factor, STAT3, decreased the levels of both cytokines and exosomes in conditioned media. This study expands the role of the β IV -spectrin/STAT3 complex in stress-induced regulation of CF paracrine signaling.