The Effect of Osteoarthritic Synovial Fluid on Immunomodulatory Properties of Adipose Mesenchymal Stem Cells
Authors: Cifù Adriana , Domenis Rossana , Moretti Massimo , Vicario Annalisa , Pistis Cinzia , Pozzi Massimo , Bassini Fabrizio , Di Benedetto Paolo , Causero Araldo , Fabris Martina , Niazi Kayvan R. , Soon‐Shiong Patrick , Curcio Francesco 
Published: June 2021

INTRODUCTIONThe capacity of adipose mesenchymal stem cells (AMSCs) to secrete a variety of trophic factors with diverse functions has motivated the interest of evaluating their local or systemic injection to stimulate tissue repair in different pathologies, including joint inflammatory diseases. The major mechanism by which AMSCs stimulates tissue repair is by paracrine activity and their interaction with the inflammatory microenvironment seem to have a critical role. It has recently been demonstrated that AMSCs, in addiction to soluble factors, release also exosomes, a subgroup of extracellular vesicles, that evoke similar biological effects to stem cells themselves. The purpose of this study is to investigate the immunomodulatory properties of AMSCs treated with synovial fluid (SF) collect from osteoarthritis joints exploring, in particular, if exosomes released from AMSCs are involved.METHODSAMSCs were cultured in the presence of a pool of SF derived from 14 patients with gonarthrosis for 24 h. Then, cells medium was replaced with exo‐free medium and after 24h supernatant was harvested and frozen at −20°C until use. The proliferation of AMSCs was measured by trypan blue exclusion count. Exosomes were isolated from AMSCs supernatant by polymer precipitation method (Exoquick‐TC) and characterized for the expression of exosomal markers (TSG101, CD81, CD9 and CD63) by western blot technique. AMSCs‐derived exosomes concentration was measured by Exocet kit. Isolated CD14+ monocytes were cultured for 10 days, during their differentiation into M1 macrophages, in presence of conditioned medium or exosomes from unstimulated or SF‐treated AMSCs. After treatment, macrophages were characterized for the expression of CD80 (M1 expression marker), CD163 or CD206 (M2 expression markers) by flow cytometry.RESULTS AND CONCLUSIONThe treatment with SF did not affected the proliferation rate of AMSCs, while increased the number of exosomes released by cells. Only conditioned medium of SF‐treated AMSCs was able to reverse the M1 phenotype of macrophage, polarizing toward the M2 phenotype. Isolated exosomes seem to simulate the effect observed after treatment with analogues conditioned medium. Of note, exosomes concentration has to be setting to find out the optimal experimental condition. In conclusion we suggest that the treatment with SF, as pro‐inflammatory stimulus, seem to activate AMSCs and promote the release of immunosuppressive factors. These data suggest that inflammatory microenvironment plays a fundamental role in the development of the anti‐inflammatory and immunomodulatory properties of AMSCs.Support or Funding InformationThis project was partially supported by an unrestricted grant from VivaBioCell S.p.A.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.