Progress in research on functional mechanisms of mesenchymal stem cells

Mesenchymal stem cells (MSCs) are a type of adult stem cells that are characterized by self-renewal and multipotent differentiation. MSCs can produce numerous bioactive molecules, depending on the stimulation of local environment. They can also facilitate hematopoiesis, produce trophic factors, activate endogenous stem or progenitor cells, promote tissue repair, and regulate the immune system. In addition, they can enhance angiogenesis, antiapoptosis, antioxidation, and antifibrosis, and migrate to injury sites. Advanced clinical trials show outstanding therapeutic effects of MSCs, especially in autoimmune-related diseases, injured tissues, and aging-related degenerative diseases. However, the in-depth functional mechanisms of MSCs remain unclear. In this review, we highlight the following functional mechanisms of MSCs: transdifferentiation and cell fusion, paracrine activity, cell-cell contact dependence, microvesicle secretion, mitochondrial transfer, and epigenetic regulation. In addition, we discuss methods to enhance the effectiveness of MSCs in clinical applications.