Adipose stromal cells express functional toll-like receptors

Abstract

Mesenchymal Stromal Cells (MSC) need to be licensed by immune cells or inflamed tissue to exert their immunomodulatory capacity. Ligation of different toll-like receptors (TLRs) has been demonstrated to polarize MSC towards an anti- or a pro-inflammatory phenotype. This, however, has been demonstrated so far only in MSC derived from human bone marrow, cultivated in fetal bovine serum (FBS). First the expression of TLRs in adipose-tissue derived MSC was assessed, comparing the effects of culture in FBS or human serum. Second, functionality of TLRs was investigated by measuring IL6 and IL8 secretion after stimulation with TLR agonists. It was addressed whether adipokine secretion is induced by TLR ligation and finally whether immunoregulatory properties of ASC are chained. ASC expressed a number of TLRs, however only TLR3 and 4 appeared to be functional, because only poly I:C and LPS stimulation resulted in secretion of proinflammatory cytokines IL6 and IL8. So far we were unable to recapitulate findings of polarization by different TLR ligands, duration of stimulation or concentration of the agonist. Cultivation in human serum reduced the expression intensity of TLRs as assessed by flow cytometry and led to a chemotactic cytokine profile. ASCs grown in FBS, however, represented an inflammatory secretion profile. Secretion of proinflammatory adipokines was increased by TLR3 and TLR4 agonists, but adipose-derived hormones, such as adiponectin and leptin remained unchained. Immunomodulatory capacities remained unaffected by TLR stimulation. MSCs home to sites of injury where they will likely encounter TLR agonists. The cultivation in humanized culture conditions in contrast to FBS may alter the functional and thus therapeutic properties of ASCs/MSCs and needs to be studied in detail to assess the impact of changing culture conditions.