FIGURE 6.

Cartoon depicting two parallel pathways in mast cells leading to fibroblast activation and excess collagen production. One pathway depicts classic mast cell degranulation with release of pro-fibrotic mediators like histamine and renin (ANG II), acting on the resident receptors on fibroblasts that activate the collagen synthesis pathway. The other pathway is the newly identified exosome pathway where shed exosomes are taken up in the cytosol of fibroblasts leading to proline hydroxylation and increased collagen production.