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Mesenchymal stem cells (MSCs) have emerged as important tools for cell therapy; therefore, identification of factors capable of governing their ex vivo expansion become essential. In this study we demonstrate that human adipose-derived stem cells (ASCs) express all components of the bone morphogenetic protein (BMP)/BMP receptor signaling pathway and respond to BMP4 inducing upregulated expression of its specific target genes Id1-Id4. Moreover, ASCs grown in a medium reduced in serum produce endogenous BMP4 that could affect autocrinely ASC growth. On the contrary, dorsomorphin, an inhibitor of BMP signaling pathway, decreases cell numbers yielded from ASC cultures in correlation with increased apoptosis and decreased cycling cells. Therefore, BMP4 emerges as a possible factor for ex vivo expanding human ASCs. Our results demonstrate that, as other morphogens, BMP4 effects on human MSCs are dose dependent. High doses significantly increased apoptosis and drastically reduced cell proliferation, whereas low doses of BMP4 (0.01-0.1 ng/mL) significantly increase culture cell content, reduce the number of apoptotic cells, and increase that of cycling cells. Further, treatment of human ASCs with low doses of BMP4 does not modify expression of Nanog and Oct4, two transcription factors involved in self-renewal and pluripotency of stem cells or avoid their osteogenic or osteoblastic differentiation capacities when cultured in adequate inducing media, as shown by the induction of specific gene expression (CEBP, PPARγ, and RUNX2). Our results therefore support BMP4 as a promising factor for expanding human adipose tissue-derived MSCs maintaining their properties of stemness and multipotency.

Bone morphogenetic proteins (BMPs), members of the transforming growth factor-b superfamily, are multifunctional polypeptides regulating a broad spectrum of functions in embryonic and adult tissues. Recent reports have demonstrated that BMPs regulate the survival, proliferation and differentiation of several cell types in the immune system. In this study, we investigate the effects of BMP signaling activation on the capacity of human dendritic cells (DCs) to stimulate immune responses. Human DCs express type I and type II BMP receptors (BMPRIA, BMPRIB, type IA activin receptor, BMPRII) and BMP signal transduction molecules (Smad1, 5, and 8, as well as Smad4). On BMP stimulation, Id1-3 (inhibitor of differentiation 1-3/DNA binding) mRNA expression is upregulated and this effect can be blocked with the inhibitor dorsomorphin, showing that the canonical BMP signal transduction pathway is functionally active in DCs. BMP signaling activation promotes the phenotypic maturation of human DCs by increasing the expression of co-stimulatory molecules and also CD83, programmed cell death ligand 1 (PD-L1) and PD-L2, and stimulates cytokine secretion, mainly interleukin-8 and tumor necrosis factor-a. Accordingly, BMP-treated DCs exhibit an enhanced T-cell stimulatory capacity. BMP signaling also enhances the survival of human DCs increasing the Bcl-2/Bax ratio. Finally, the expression of Runx transcription factors is increased in mature DCs, and the mRNA levels of Runx1-3 are upregulated in response to BMP stimulation, indicating that Runx transcription factor family may mediate the effects of BMP signaling in human DC maturation.

Natural killer (NK) cells are critical for innate tumor immunity due to their specialized ability to recognize and kill neoplastically transformed cells. However, NK cells require a specific set of cytokine-mediated signals to achieve optimal effector function. Th1-associated cytokines promote effector functions that are inhibited by the prototypic Th2 cytokine IL4 and the TGFb superfamily members TGFb1 and activin-A. Interestingly, the largest subgroup of the TGFb superfamily are the bone morphogenetic proteins (BMP), but the effects of BMP signaling on NK cell effector functions have not been evaluated. Here, we demonstrate that blood-circulating NK cells express type I and II BMP receptors, BMP-2 and BMP-6 ligands, and phosphorylated isoforms of Smad-1/-5/-8, which mediate BMP family member signaling. In opposition to the inhibitory effects of TGFb1 or activin-A, autocrine BMP signaling was supportive to NK cell function. Mechanistic investigations in cytokine and TLR-L-activated NK cells revealed that BMP signaling optimized IFNg and global cytokine and chemokine production, phenotypic activation and proliferation, and autologous dendritic cell activation and target cytotoxicity. Collectively, our findings identify a novel auto-activatory pathway that is essential for optimal NK cell effector function, one that might be therapeutically manipulated to help eradicate tumors. Cancer Res; 74(18); 5019-31. Ó2014 AACR.

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