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.