Mesenchymal stromal cell-secreted chemerin is a novel immunomodulatory molecule driving the migration of ChemR23-expressing cells

Background. Mesenchymal stromal cells (MSCs) are multipotent cells characterized by broad immunomodulatory properties exploited for the treatment of inflammatory disorders. However, the efficacy of MSC-based therapy is highly variable and tightly linked to MSC culture conditions and treatment schedule. Thus, the identification of novel key molecules regulating MSC immunomodulatory activities in vivo might constitute a crucial step toward the optimization of currently available clinical protocols. In this regard, herein, we sought to determine whether the newly identified chemotactic protein, chemerin, plays a role in MSC-mediated regulation of inflammation. Methods. Chemerin production by human MSCs was investigated under different culture conditions using enzyme-linked immunosorbent assay (ELISA). After purification, MSC secreted chemerin was identified using mass spectrometry analysis and the biological activity of secreted isoforms was evaluated using migration assay. Results. Bone marrow derived MSCs secrete chemerin and express its receptors ChemR23 and CCRL2. Chemerin production is dependent on culture conditions and increases upon stimulation with inflammatory cytokines. In particular, platelet lysate (PL)-MSCs produce higher levels of chemerin compared with fetal bovine serum (FBS)-MSCs. Furthermore, chemerin is secreted by MS Cs as an inactive precursor, which can be converted into its active form by exogenous chemerin-activating serine and cysteine proteases. Discussion. Our data indicate that, in response to various inflammatory stimuli, MSCs secrete high amounts of inactive chemerin, which can then be activated by inflammation-induced tissue pro teases. In light of these initial findings, we propose that further analysis of chemerin functions in vivo might constitute a crucial step toward optimizing MSC-based therapy for inflammatory diseases.