Background White adipose tissue (WAT) is a rich source of mesenchymal stem cells (ADSC) which immunomodulatory and regenerative properties are well documented. Therapeutic effect of ADSC in experimental animal model of rheumatoid arthritis (RA) has been proved. ADSC express indoleamine 2,3-dioxygenase (IDO) and hem oxygenase-1 (HO-1). Activity of these enzymes mediate immunosuppresive properties of ADSC. WAT secrets abundant amounts of biologically active factors: e.g. classical adipokines (leptin, adiponectin), cytokines (TNF) named collectivley adipo(cyto)kines which influence processes ongoing in the rheumatic joint. In rheumatic joints adipokines and TNF are produced by both adipose tissue and synovial membrane. Therefore their concentration in synovial fluid is elevated. However, data concerning the effects of these adipo(cyto)kines on ADSC function are scarced.
Objectives To investigate whether selected adipo(cyto)kines i.e. leptin, low (LMW) and high (HMW) molecular weight adiponectin isoform and TNF exert any effect on IDO and HO-1 expression in rheumatoid ADSC.
Methods Articular adipose tissue (AAT) was obtained from RA patients during total knee joint replacement surgery. ADSC were isolated and cultivated in DMEM/F12/10%FCS medium. After passage 4 ADSC were re-seeded in the same medium and stimulated separately with human recombinant leptin (10ng/ml), TNF (10ng/ml), two adiponectin isoforms: HMW and LMW (4 and 10 μg/ml). IFNγ (10ng/ml) was used as a positive control. After 18 hours, cells were lysed, total RNA was isolated and subjected to cDNA synthesis. Expression of IDO and HO-1 mRNA were determined using Real-Time PCR technique. Gene quantity was normalized to GAPDH expression measured in every probe. The Wilcoxon signed-rank test was used for statistical analysis.
Results Unstimulated ADSC did not express IDO mRNA. All applied adipo(cyto)kines triggered IDO expression, but with different potency. TNF up-regulated IDO mRNA to 30% (p=0,028), LMW adiponectin to 8%, HMW adiponectin to 4% and leptin to 5% as compared to IFNγ-treated cells (100%). The LMW adiponectin was significantly more potent than leptin (p=0,043). By contrast to IDO, ADSC expressed HO-1 mRNA spontaneously. TNF treatment significantly reduced HO-1 mRNA level (p=0,028), while classical adipokines caused only very slight decrease. Despite this, LMW adiponectin was more potent in HO-1 expression downregulation than leptin (p=0,043).
Conclusions We report that adipo(cyto)kines exert dual effect on the expression of the enzymes responsible for immunosuppressive activity of ADSC, by up-regulating IDO and slightly down-regulating HO-1 mRNA. Modifying activity of examined adipo(cyto)kines is not equal, for TNF action is the strongest, LMW adiponectin seems to exert modulatory effect while HMW and leptin only slight effects. Thus, it is likely that in RA joints adipo(cyto)kines modify immunosuppressive properties of ADSC, but further studies are required to confirm this suggestion.
Funding: Supported by grant No. N/NZ5/00932 from National Science Center (Narodowe Centrum Nauki), Poland
Disclosure of Interest None Declared
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