Tissue Engineered Models of Adipose and Cancer
One of the main focuses in our lab is understanding the molecules and signaling pathways that direct the development of bone marrow adipose tissue. To do this, we design and utilize 3D bone marrow adipose tissue models (Figure 1).
Figure 1: Tissue Engineered Bone Marrow Adipose tissue cultured on a 3D silk scaffold. This image is a confocal maximum projection of human bone marrow-derived mesenchymal stem cells (MSCs) that have been differentiated into adipocyte. The green stain shows actin filaments using phalloidin stain, the red demonstrates lipid droplets inside cells using Oil Red O stain, and the purple/blue signal comes from the autofluorescence of the silk scaffold itself. Using these 3D models we have seen much more realistic adipose phenotype and gene expression compared to 2D adipogenesis (Fairfield et al, 2018).
One of the key molecules we have observed that can govern adipogenesis is sclerostin, which is a Wnt pathway antagonist (Figure 2). Our lab is currently validating the role of sclerostin in other animal models and elucidating the signaling cascade of sclerostin, and other molecules that induce bone marrow adipogenesis.
Figure 2: Sclerostin is a bone specific, osteocyte-derived molecule that inhibits Wnt signaling in MSCs to block osteogenesis. We have shown that bone marrow-derived MSCs follow an adipogenic lineage path when stimulated with sclerostin. Therefore, sclerostin is a bone-derived factor that facilitates communication between bone skeletal cells and bone adipocyte precursors, acting as a lineage switch molecule and influencing bone marrow adipose tissue formation. (Fairfield et al, 2017)
Bidirectional Signaling of Adipose and Multiple Myeloma
Multiple myeloma is an incurable cancer of the plasma cell (Figure 3a) that grows in the bone marrow niche. Multiple myeloma cells cause painful osteolysis in the skeleton (Figure 3b) and there is an urgent need to develop better therapies for this devastating disease. Although myeloma cells are dependent on the cells of this niche, their relationship with bone marrow adipocytes is relatively unknown. Despite this, there are many correlations between bone marrow adipose volume and the risk of developing myeloma, as well as the risk of relapsing after treatments fail in myeloma. Thus, our laboratory is very interested in understanding how bone marrow adipocytes and multiple myeloma cells communicate and interact in ways that lead to disease progression. We aim to develop novel therapies and identify new targets to treat myeloma and myeloma-associated bone diseases. We demonstrated that bone marrow adipocytes support drug resistance in myeloma cells, and that this occurs through soluble mediators. We have evidence that IL6, Notch signaling as well as fatty acid beta-oxidation can drive this phenomenon. Using our in vivo xenograft mouse model of GFP+, luciferase+, bone-homing human MM1S cells in an immunocompromised mouse, we have seen that decreasing bone marrow adipose tissue, using a sclerostin-neutralizing antibody, increases sensitivity of the human MM1S myeloma cell line to the anti-myeloma drug dexamethasone.
Figure 3: Multiple Myeloma. A) Same of patient skull with extensive osteolytic holes throughout the bone. B) H&E histology of myeloma cells, cancerous plasma cells.
We also saw that targeting sclerostin, in combination with dexamethasone, produces the best tumor burden outcomes and survival results in this mouse model (Figure 4). We are now looking at mechanisms explaining our results and determining how myeloma cells alter adipocytes as well. Preliminary data suggests that adipocytes undergo lipolysis when co-cultured with myeloma cells, which may lead to a release of lipids to fuel the tumor cells, although the reasons and molecules governing this process remain unclear.
Figure 4: Results of targeting sclerostin and dexamethasone in a mouse model of multiple myeloma. A) Bioluminescent data at day 33 after injection of MM1S cells. B) Survival curve analysis demonstrates the best survival outcomes when anti-sclerostin antibodies and dexamethasone treatments are combined.