Loss of Grem1-articular cartilage progenitor cells causes osteoarthritis

Osteoarthritis (OA), which carries an enormous disease burden across the world, is characterised by irreversible degeneration of articular cartilage (AC), and subsequently bone. The cellular cause of OA is unknown. Here, using lineage tracing in mice, we show that the BMP-antagonist Gremlin 1 (Grem1) marks a novel chondrogenic progenitor (CP) cell population in the articular surface that generates joint cartilage and subchondral bone during development and adulthood. Notably, this CP population is depleted in injury-induced OA, and with age. OA is also induced by toxin-mediated ablation of Grem1 CP cells in young mice. Transcriptomic analysis and functional modelling in mice revealed articular surface Grem1-lineage cells are dependent on Foxo1; ablation of Foxo1 in Grem1-lineage cells led to early OA. This analysis identified FGFR3 signalling as a therapeutic target, and injection of its activator, FGF18, caused proliferation of Grem1-lineage CP cells, increased cartilage thickness, and reduced OA pathology. We propose that OA arises from the loss of CP cells at the articular surface secondary to an imbalance in progenitor cell homeostasis and present a new progenitor population as a locus for OA therapy.

Abstract 5089: The origin and contribution of the tumor stroma in colorectal cancer

Cancer-associated fibroblasts (CAFs) are a major constituent of the tumor microenvironment and play a critical part in cancer progression. However, the precise origin of the tumor stroma remains unknown, making it challenging to effectively target the cancer mesenchyme. Here, employing 4 different genetic fate mapping mouse models and a bone marrow transplantation model in combination with BrdU labeling, we uncovered a key contributor to the tumor stroma in colorectal cancer (CRC). We found that approximately half of a-smooth muscle actin (aSMA)+ CAFs emerge through proliferation in an AOM/DSS mouse model of CRC. Lineage tracing experiments revealed that intestinal leptin receptor (Lepr)-lineage stromal cells expanded and contributed to 75% of the aSMA+ proliferating CAFs. Notably, no aSMA+ CAFs in the tumor were derived from Krt19-lineage epithelial cells or bone marrow-transplanted cells, indicating no involvement of epithelial-mesenchymal transition and bone marrow recruitment to the tumor in this model. Moreover, RNA-sequencing of FACS-purified CRC mesenchymal cells identified MCAM (also known as CD146) as a CRC stroma-specific marker, which is expressed by Lepr-lineage cells. Analysis of human CRC samples showed that high MCAM expression was associated with a mesenchymal subtype of CRC and was independently prognostic of poor overall survival. Our data identify Lepr-lineage cells as a major source of the tumor stroma in CRC and suggest that targeting MCAM+ cells may serve as a novel therapeutic approach to restrain CRC progression.

Citation Format: Hiroki Kobayashi, Krystyna A. Gieniec, Tamsin RM Lannagan, Tongtong Wang, Samuel Asfaha, Yoku Hayakawa, Simon J. Leedham, Nicholas Arpaia, Siddhartha Mukherjee, Timothy C. Wang, Atsushi Enomoto, Masahide Takahashi, Susan L. Woods, Daniel L. Worthley. The origin and contribution of the tumor stroma in colorectal cancer [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5089.

Abstract 3977: Stromal BMP signaling imbalance mediated by GREM1 and ISLR regulates colorectal cancer progression

Introduction

Cancer-associated fibroblasts (CAFs), a heterogeneous component of the tumor microenvironment, substantially influence tumor progression. Bone morphogenetic proteins (BMP) play a critical part in defining the intestinal epithelial niche and either promote or retard cancer progression in a context-dependent manner. However, the role of BMP signaling in the colorectal cancer (CRC) stroma remains to be fully elucidated. This study investigated the significance of mesenchymal BMP signaling as a potential therapeutic target in CRC progression.

Design

Using CRC expression array data, we identified two CAF-specific factors involved in BMP signaling, then verified their upregulation in the human CRC stroma by in-situ hybridization (ISH). We took advantage of a preclinical mouse model of CRC hepatic metastasis to test approaches targeting the BMP signaling pathway.

Results

CRC microarray data identified GREM1 and ISLR as CAF-specific genes involved in BMP signaling. In colonic myofibroblasts, Grem1-overexpression inhibited BMP signaling whereas BMP7 signaling was augmented by Islr overexpression, suggesting opposing roles for GREM1 and ISLR in the regulation of BMP signaling. ISH using human rectal cancer samples revealed that GREM1 and ISLR were expressed in distinct CAF subpopulations and that GREM1 and ISLR expression predicted poor and favorable survival, respectively. Notably, Grem1 and Islr expression was differentially regulated by Foxl1, an intestinal mesenchyme-lineage transcription factor, and TGF-b, indicating a mechanism for generating fibroblast heterogeneity. Finally, adeno-associated virus 8-mediated in-vivo overexpression of Islr in hepatocytes retarded growth and generated more differentiated histology in CRC hepatic metastases.

Conclusion

These data suggest that increased stromal BMP signaling may ameliorate CRC progression and provide a rationale for targeting stromal BMP signaling to inhibit CRC progression and metastasis.

Citation Format: Hiroki Kobayashi, Krystyna A. Gieniec, Tongtong Wang, Josephine A. Wright, Nobumi Suzuki, Tamsin RM Lannagan, Yoku Hayakawa, Simon J. Leedham, Nicholas Arpaia, Siddhartha Mukherjee, Timothy C. Wang, Atsushi Enomoto, Masahide Takahashi, Daniel L. Worthley, Susan L. Woods. Stromal BMP signaling imbalance mediated by GREM1 and ISLR regulates colorectal cancer progression [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 3977.

Genetic editing of colonic organoids provides a molecularly distinct and orthotopic preclinical model of serrated carcinogenesis

OBJECTIVE

Serrated colorectal cancer (CRC) accounts for approximately 25% of cases and includes tumours that are among the most treatment resistant and with worst outcomes. This CRC subtype is associated with activating mutations in the mitogen-activated kinase pathway gene, BRAF, and epigenetic modifications termed the CpG Island Methylator Phenotype, leading to epigenetic silencing of key tumour suppressor genes. It is still not clear which (epi-)genetic changes are most important in neoplastic progression and we begin to address this knowledge gap herein.

DESIGN

We use organoid culture combined with CRISPR/Cas9 genome engineering to sequentially introduce genetic alterations associated with serrated CRC and which regulate the stem cell niche, senescence and DNA mismatch repair.

RESULTS

Targeted biallelic gene alterations were verified by DNA sequencing. Organoid growth in the absence of niche factors was assessed, as well as analysis of downstream molecular pathway activity. Orthotopic engraftment of complex organoid lines, but not BrafV600E alone, quickly generated adenocarcinoma in vivo with serrated features consistent with human disease. Loss of the essential DNA mismatch repair enzyme, Mlh1, led to microsatellite instability. Sphingolipid metabolism genes are differentially regulated in both our mouse models of serrated CRC and human CRC, with key members of this pathway having prognostic significance in the human setting.

CONCLUSION

We generate rapid, complex models of serrated CRC to determine the contribution of specific genetic alterations to carcinogenesis. Analysis of our models alongside patient data has led to the identification of a potential susceptibility for this tumour type.

Abstract 4058: DNA damage and tumour burden in mouse colon is increased in response to carcinogen exposure after induction of chronic inflammation - a more disease relevant model of colitis-associated colorectal cancer

Chronic inflammation (CI) such as inflammatory bowel disease increases the risk of developing colorectal cancer (CRC). Tumorigenesis is supported by inflammatory cytokines through increased cell proliferation and inhibiting apoptosis of neoplastic cells. The classic mouse model of colitis-associated CRC (CA-CRC) requires treatment with a mutagen (azoxymethane, AOM) followed by induction of inflammation through ingestion of a luminal irritant (dextran sulfate sodium, DSS). AOM is metabolized by colonic epithelium causing DNA damage through formation of mutagenic DNA adducts. Although the AOM + DSS model of CA-CRC is a valuable research model, it “reverses” events that take place in humans where CI typically precedes CRC. We hypothesise that CI sensitises colonic epithelium to DNA damage and predisposes the epithelium to neoplastic transformation.

In order to investigate this we reversed the AOM + DSS model to more accurately represent the disease process in humans. Using two experimental approaches we treated wildtype (WT) mice with AOM alone or with DSS then AOM and collected colonic tissue after 6 and 48 hours (short-term) or colonic tumours (long-term). Tumour number and size were quantified. Immunohistochemistry was used to analyse DNA damage, apoptosis, and proliferation. Formation of the DNA adduct O6MeG was measured by a modified method of HPLC, and qPCR was used to analyse expression of DNA damage signalling pathway components.

Compared with an AOM challenge alone, prior CI induction by DSS treatment increased DNA damage, reduced apoptosis, and increased tumour number and tumour size. This data reveals how prior CI modulates the colonic epithelial response to mutagen exposure in the short-term and how it promotes tumour formation in the long-term. In addition, this data demonstrates that the “reverse” model of CA-CRC can be successfully used as a more appropriate experimental framework to better understand the molecular mechanisms underpinning CA-CRC and will allow us to further investigate the relationship between prior CI, DNA damage, and tumour development.

Citation Format: Tamsin RM Lannagan, Mark T. Mano, Richard J. Head, Trevor Lockett, Matthias Ernst, Leah J. Cosgrove. DNA damage and tumour burden in mouse colon is increased in response to carcinogen exposure after induction of chronic inflammation - a more disease relevant model of colitis-associated colorectal cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4058.