Abstract 2299: Gremlin 1 labels a mesenchymal progenitor in the gastrointestinal tract, bone and tumor microenvironment.

Proceedings: AACR 104th Annual Meeting 2013; Apr 6-10, 2013; Washington, DC Introduction: The cellular origin and contribution of mesenchymal stem cells (MSCs) in the gastrointestinal tract, bone marrow and tumor microenvironment are unknown. More specific markers of MSCs are needed. We hypothesized that Grem1 expression would be a specific marker of MSCs. Methods: We developed Grem1-BAC-CreERT, αSMA-BAC-CreERT, Grem1-BAC-EGFP-peptide 2A-DTR-peptide 2A-CreERT and Vimentin-BAC-CreERT transgenic lines to characterize the origin, function and kinetics of gastrointestinal, bone marrow and tumor-associated mesenchyme. These mice were crossed to reporters, Grem1fl/fl and diphtheria toxin associated lines. The cellular fate and function of the Grem1, αSMA and Vimentin expressing cells, was analyzed by direct fluorescence microscopy and immunostaining at several time points (up to 12 months) and in several cancer models. Results: In the bone marrow, Grem1 recombination was identified in a very rare population of CD45/Ter119/CD31 triple negative cells (0.004% of all cells from compact bone extraction). In the bone marrow, Grem1-EGFP identified a discrete population of perisinusoidal cells. Grem1-recombined cells dramatically expand within MSC cultures forming large colony forming units, with a CFU-F efficiency of 3%. Grem1-recombined cells could be differentiated in vitro into adipocytes, osteoblasts, chondrocytes and αSMA(+) myofibroblasts. Furthermore, these cells are long-lived, recoverable from the bone at least 9 months after tamoxifen induction and can be transplanted. In the small intestine, 24 hours after tamoxifen induction, there were single Grem1 recombined cells found immediately subjacent to the basement membrane. These initially rare αSMA(-) recombined cells expanded over the next 12 months to completely trace the periepithelial fibroblast sheath. In both the gut and bone marrow, perinatal tamoxifen induction led to dramatically accelerated lineage tracing. Syngeneic tumorigenicity and carcinogenesis studies (including hepatic metastatic model (splenic injection of MC38, C57Bl/6 colorectal cancer cell line), MNU/Hfelis and AOM/DSS gastrointestinal cancer models) in our Grem1-BAC-specific lines revealed that Grem1 marked a cellular origin of cancer-associated mesenchyme, although many cancer-associated fibroblasts also arise from a specific αSMA+ stromal population. The exact lineage relationship between these Grem1 and αSMA+ cells is being tested. Conclusions: Grem1-expression labels a specific mesenchymal progenitor in the bone and gut that can give rise to multiple mesenchymal lineages during development and in the peritumoral stroma. We are currently examining the functional relevance of these cells and Grem1 production in supporting the normal and pathological stem cell niche in the bone marrow, gut and tumor microenvironment. Citation Format: Daniel L. Worthley, Yiling Si, Samuel Asfaha, Benedikt Westphalen, Yagnesh Tailor, Michael Churchill, Jean-Philippe Pradere, Robert Schwabe, Siddhartha Mukherjee, Timothy Wang. Gremlin 1 labels a mesenchymal progenitor in the gastrointestinal tract, bone and tumor microenvironment. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2299. doi:10.1158/1538-7445.AM2013-2299