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Heparin Binding Epidermal Like Growth Factor-Mediated Marrow Adipocyte Ablation Induces Profound Bone Formation

ABSTRACT: Products of adipocytes control bone cells and may therefore lead to new anti-osteoporosis therapies. To address this issue we mated mice expressing the primate diphtheria toxin receptor (DTR), which is equivalent to Heparin Binding Epidermal Like Growth Factor (HB-EGF), under control of a Stop-flox cassette, to those expressing adiponectin-Cre (ADQ-Cre). Injected diphtheria toxin (DT) completely eliminates white and brown adipose tissue in these DTRADQ mice and ablates marrow adipocytes. Medullary bone of DTRADQ mice begins to accumulate, due to stimulated osteoblast recruitment and differentiation, within 4 days of injected DT. By 10-14 days of DT administration to DTRADQ mice, trabecular bone has increased 1000%. Two months after fat ablation, cortical thickness has markedly increased as has bone strength. To gain insight into the signaling events by which DT/DTRADQ adipocyte ablation promotes osteogenesis we performed RNAseq analysis of marrow prior to and after 1-3 days of DT injection. This exercise confirms ablation of marrow adipocytes, as adiponectin expression is markedly reduced while enhanced expression of Col1a1 and Col1a2 genes is in keeping with stimulated osteogenesis. RNAseq analysis also indicates that DT/DTRADQ-induced osteogenesis is mediated by the BMPR pathway. For example, there is suppressed genetic expression of the specific BMPR inhibitors, chordin-like1 (CHRDL1) and gremlin1 (GREM1). This adipocyte ablation-mediated increase in bone mass is due to cooperative activation of BMP and EGF receptor signaling as adipocyte-produced inhibitors are suppressed and downstream targets activated or expressed. Medicinal inhibition of either signaling pathway prevents induction of the osteosclerotic phenotype. DTR-induced post-natal osteogenesis does not represent the products of peripheral fat depots and is more likely due to those of marrow adipocytes. Thus, anabolic drugs activating both BMP and EGF receptor signaling may be a means of profoundly increasing bone mass and treating osteoporosis.

ORGANISM(S): Mus musculus

PROVIDER: GSE154800 | GEO | 2020/11/06

REPOSITORIES: GEO

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Project description:The unique properties of the bone marrow allow for migration and proliferation of multipl myeloma (MM) cells, while also providing the perfect environment for development of quiescent, drug-resistant MM cell clones. Bone marrow adipocytes (BMAds), which have recently been identified as important contributors to systemic adipokine levels, bone strength, hematopoiesis, and progression of metastatic and primary bone marrow cancers, such as MM. Recent studies in myeloma suggest that BMAds can be reprogrammed by tumor cells to contribute to myeloma-induced bone disease, and reciprocally, BMAds support MM cells in vitro. Importantly, most data investigating BMAds have been generated using adipocytes derived by differentiating bone marrow-derived mesenchymal stromal cells (MSCs) into adipocytes in vitro using adipogenic media, due to the extreme technical challenges associated with isolating and culturing primary adipocytes. However, if studies could be performed with primary adipocytes, they likely will recapitulate in vivo biology better than MSC-derived adipocyte, as the differentiation process is artificial and differs from in vivo differentiation, and progenitor cell(s) of the primary BMAd may not be the same as the MSCs precursors used for adipogenic differentiation in vitro. Therefore, we developed and refined three methods for culturing primary BMAds (pBMAds): 2D coverslips, 2D transwells, and 3D silk scaffolds, all of which can be cultured alone or with MM cells to investigate bidirectional tumor-host signaling. To develop an in vitro model with a tissue-like structure to mimic the bone marrow microenvironment, we developed the first 3D, tissue engineered model utilizing pBMAds derived from human bone marrow. We found that pBMAds, which are extremely fragile, can be isolated and stably cultured in 2D for 10 days and in 3D for short term (~2 weeks) or long term (1 month) in vitro. To investigate the relationship between pBMAds and myeloma, MM cells can be added to investigate physical relationships through confocal imaging and soluble signaling molecules via mass spectrometry. In sum, we developed three in vitro cell culture systems to study primary bone marrow adipocytes and myeloma cells, which could be adapted to investigate many diseases and biological processes involving the bone marrow, including other bone-homing tumor types.

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Heparin Binding Epidermal Like Growth Factor-Mediated Marrow Adipocyte Ablation Induces Profound Bone Formation

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