The unique properties of mesenchymal stromal/stem cells (MSCs) to self-renew and their multipotentiality have rendered them attractive to researchers and clinicians. In addition to the differentiation potential, the broad repertoire of secreted trophic factors (cytokines) exhibiting diverse functions such as immunomodulation, anti-inflammatory activity, angiogenesis and anti-apoptotic, commonly referred to as the MSC secretome, has gained immense attention in the past few years. There is enough evidence to show that the one important pathway by which MSCs participate in tissue repair and regeneration is through its secretome. Concurrently, a large body of MSC research has focused on characterization of the MSC secretome; this includes both soluble factors and factors released in extracellular vesicles, for example, exosomes and microvesicles. This review provides an overview of our current understanding of the MSC secretome with respect to their potential clinical applications.
Human mesenchymal stem cells (hMSCs) hold great promise in cardiac fibrosis therapy, due to their potential ability of inhibiting cardiac myofibroblast differentiation (a hallmark of cardiac fibrosis). However, the mechanism involved in their effects remains elusive. To explore this, it is necessary to develop an in vitro cardiac fibrosis model that incorporates pore size and native tissue-mimicking matrix stiffness, which may regulate cardiac myofibroblast differentiation. In the present study, collagen coated polyacrylamide hydrogel substrates were fabricated, in which the pore size was adjusted without altering the matrix stiffness. Stiffness is shown to regulate cardiac myofibroblast differentiation independently of pore size. Substrate at a stiffness of 30 kPa, which mimics the stiffness of native fibrotic cardiac tissue, was found to induce cardiac myofibroblast differentiation to create in vitro cardiac fibrosis model. Conditioned medium of hMSCs was applied to the model to determine its role and inhibitory mechanism on cardiac myofibroblast differentiation. It was found that hMSCs secrete hepatocyte growth factor (HGF) to inhibit cardiac myofibroblast differentiation via downregulation of angiotensin II type 1 receptor (AT1R) and upregulation of Smad7. These findings would aid in establishment of the therapeutic use of hMSCs in cardiac fibrosis therapy in future.