oa A Dual Role of Il-6 in Bone Marrow and Adipose Tissue-Derived Preadipocyte Differentiation

Introduction

Preadipocytes constitute up to 50% of adipose tissue-derived stromal vascular fraction (SVF) and have the ability to differentiate into functional adipocytes in response to nutrient excess and metabolic demand. Impairment of the differentiation of SVF-derived preadipocytes in obesity is associated with increased risk of insulin resistance and type 2 diabetes (Guilherme et al. 2008). Various factors influence preadipocyte differentiation including inflammatory cytokines such as IL-6 (Lagathu et al. 2003). We have previously shown a negative correlation between IL-6 secretion in subcutaneous tissue-derived preadipocytes and their adipogenic capacity, and have also shown that treatment of subcutaneous-preadipocytes with IL-6 can cause impairment of their differentiation (Almuraikhi et al. 2014). In order to validate the role of IL-6 in preadipocyte differentiation, we tested the effect of IL-6 and two different anti-IL6 antibodies on the proliferation and differentiation of human preadipocytes derived from adipose tissue using preadipocytes derived from bone marrow mesenchymal stem cells (MSCs) as a control.

Methods

Human adult subcutaneous adipose tissue-derived SVF (n = 9, passage 2–5) were cultured and induced to differentiate into adipocytes as previously described (Lee et al. 2012). Human bone marrow mesenchymal stem cells (MSCs; n = 3, passage 3) were used as controls (Kafienah et al. 2006). Immunophenotyping of preadipocytes was performed using anti-human antibodies: CD31-FITC, NG2-PE, CD166-PerCP-efluor, CD105-APC, CD45-Alexa flour 700, CD11b- Brilliant Violet 421, CD73- Brilliant Violet 605 (all from R&D Systems). Samples were processed using FACSCanto II flow cytometer (BD Bioscience) and analyzed with FlowJo Software (Treestar). The effect of treatment with recombinant IL-6 (20 ng/ml, 206-IL-050, R&D Systems) and anti-IL-6 antibodies (1&10 μg/ml MAB206, 50&100 ng/ml AF-206-NA, R&D Systems) for the entire differentiation period on MSCs and adipose tissue-derived preadipocytes was evaluated as described previously (Almuraikhy and Elrayess 2014). Briefly, total number of nuclei (DAPI, indicator of cell viability) and differentiated adipocytes (Lipidtox positive cells) were scored in 20 fields per well by ArrayScan XTI (Thermo Scientific) using automated spot detection module. Differentiation capacity was assessed by calculating the ratio of Lipidtox positive cells/total number of stained nuclei (% adipogenic capacity). All protocols were approved by Institutional Research Boards of ADLQ and HMC (SCH-ADL-070, SCH-JOINT-111).

Results

Flow cytometry analysis of preadipocytes derived from human subcutaneous adipose tissue confirmed that the majority of cells expressed MSC markers (80 ± 10%), of which 38 ± 21% co-expressed NG2 (Fig. 1). Treatment of bone marrow MSCs and adipose tissue-derived preadipocytes with IL-6 resulted in a reduction in their differentiation capacity. Anti-IL-6 antibodies targeting soluble secreted IL-6 reduced differentiation capacity of both bone marrow and adipose tissue-derived preadipocytes without affecting cell viability (Fig. 2).

Discussion and conclusions

Our data show that subcutaneous adipose tissue-derived preadipocytes share similar markers with bone marrow-derived MSCs including a marker of perivascular cells that co-express NG2, potentially derived from small blood vessels present in the SVF (Baer and Geiger 2012). Although previous studies suggested that MSCs in the tissue represent less than 3% of total cellular composition (Baer and Geiger 2012), our data show that the in vitro expansion of these cells for up to 5 passages favored the enrichment of MSCs over other cell types, confirming previous findings (Astori et al. 2007). Our data suggest that chronic treatment of bone marrow-derived and adipose tissue-derived preadipocytes with IL-6 resulted in inhibition of differentiation. The inhibition was even greater when secreted IL-6 was neutralized with anti-IL6 antibodies. This indicates that low levels of IL-6 are necessary for preadipocyte differentiation whereas higher concentrations result in inhibition of adipogenesis, suggesting a dual role of IL-6 in preadipocyte differentiation in both bone marrow and adipose tissue-derived preadipocytes.

Acknowledgment

This research was sponsored by Qatar National Research Fund (QNRF), Grant number NPRP6-235-1-048.

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