Macrophages inhibit adipogenic differentiation of adipose tissue derived mesenchymal stem/stromal cells by producing pro-inflammatory cytokines.

Background: Mesenchymal stem/stromal cells (MSCs) and macrophages are critical components in many tissue microenvironments, including that in adipose tissue. The close interaction between MSCs and macrophages modulates various adipose-related disease development. However, the effects of macrophages on the fate of MSCs remain largely elusive. We here studied the effect of macrophages on the adipogenic differentiation of MSCs.

Methods: Macrophages were obtained from THP-1 cells treated with phorbol-12-myristate-13-acetate (PMA). The induced matured macrophages were then induced to undergo classically activated macrophage (M1) or alternatively activated macrophage (M2) polarization with Iipopolysaccharide (LPS)/interferon (IFN)-γ and interleukin (IL)-4/IL-13, respectively. The supernatants derived from macrophages under different conditions were applied to cultured human adipose tissue-derived mesenchymal stem/stromal cells (hADSCs) undergoing adipogenic differentiation. Adipogenic differentiation was evaluated by examining Oil Red O staining of lipid droplets and the expression of adipogenesis-related genes with real-time quantitative polymerase chain reaction (Q-PCR) and western blot analysis.

Results: The adipogenic differentiation of hADSCs was impaired when treated with macrophage-derived supernatants, especially that from the M1-polarized macrophage (M1-sup). The inhibitory effect was found to be mediated by the inflammatory cytokines, mainly tumor necrosis factor-α (TNF-α) and IL-1β. Blocking TNF-α and IL-1β with neutralizing antibodies partially alleviated the inhibitory effect of M1-sup.

Conclusion: Macrophage-derived supernatants inhibited the adipogenic differentiation of hADSCs in vitro, irrespective of the polarization status (M0, M1 or M2 macrophages). M1-sup was more potent because of the higher expression of pro-inflammatory cytokines. Our findings shed new light on the interaction between hADSCs and macrophages and have implications in our understanding of disrupted adipose tissue homeostasis under inflammation.