The secretome of adipose stem cells primed for TSG-6 expression protects retinal endothelial barrier function and suppresses microglial activation

Abstract

Purpose : Retinal inflammation may play a role in the development of visual defects following concussions. We have shown that adipose-derived stem cells (ADSCs) can limit retinal damage from blast injury and improve visual function. TNF-α stimulated gene-6 (TSG-6) is an anti-inflammatory protein released by mesenchymal cells that correlates with anti-inflammatory potency across donor lines. Here, we identify optimal stimuli to induce TSG-6, characterize the composition and immune-potency of this ADSC secretome, and investigate TSG-6 signaling as a therapeutic mechanism.

Methods : Cytokines were screened to identify combinations that increased TSG-6 expression. Shotgun proteomics were performed to characterize the proteins in untreated and cytokine primed ADSC-CM. Mouse microglial cells were treated with lipopolysaccharide (LPS) in the presence or absence of ADSC-CM and mRNA expression for M1/M2 phenotype markers and nitric oxide release assays were performed. IL-10 was measured from peripheral blood mononuclear cells treated with LPS and ADSC-CM. siRNA was used to knockdown TSG-6 in ADSCs to assess the role of TSG-6 silencing. The efficacy of ADSC-CM on TNF-α- induced retinal vascular permeability was assessed by measuring trans-endothelial resistance (TER) of retinal endothelial cell monolayers.

Results : The combination of IFN-γ with TNF-α synergistically increase the expression of TSG-6 at least 5-fold over TNF-α alone. Proteomic characterization of ADSC-CM further identified the anti-oxidant enzymes SOD2 and SOD3 as proteins whose expression is increased by IFN-γ with TNF-α. Immune-modulatory IDO1 was increased in IFN-γ. Cytokine primed ADSC-CM potently promotes IL-10 expression by LPS treated human PBMCs and suppresses expression of pro-inflammatory gene transcripts and the production of nitric oxide by LPS treated mouse microglial cells. ADSC-CM containing TSG-6, but not ADSC-CM from TSG-6 knockdown cells, partially rescues TNF-α induced junctional disruption in endothelial cell monolayers.

Conclusions : ADSCs respond to an inflammatory milieu by secreting several therapeutically valuable proteins, and TSG-6 expression and SOD activity correlate with the therapeutic potency of ADSC-CM. These molecular mechanisms may account for the therapeutic effects of ADSCs in vivo.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.