Primary cilia can act as either a negative or positive regulator of the hedgehog (Hh) signaling pathway. Many cartilage tumors are characterized by abnormal activation of the Hh pathway. Here, we report that the presence of primary cilia occurs at a low frequency (12.4%) in neoplastic chondrocytes from malignant human chondrosarcomas, compared with chondrocytes from normal articular cartilage (67.7%). To determine the function of primary cilia in cartilaginous neoplasia, we studied benign cartilage tumors that are formed in mice by chondrocyte-specific overexpression of Gli2, a downstream transcriptional activator of the Hh pathway. Col2A1-Gli2 mice were crossed with Ift88+/− mice, which display a partial loss of ciliogenesis. Surprisingly, cartilage tumors developed in Ift88+/− mice that were phenotypically similar to those that arise in Col2A1-Gli2 mice. Further activation of the Hh pathway was observed in Col2A1-Gli2; Ift88+/− mice compared with either Col2A1-Gli2 or Ift88+/− mice, which was associated with an increased incidence of cartilage tumors. Chondrosarcomas were established in explant cultures, and treated with choral hydrate, which disrupts the functional primary cilia. Thus, treatment resulted in hyperactivity of the Hh signaling pathway, as well as cellular changes that could promote tumor growth. Primary cilia functions to inhibit Hh signaling in neoplastic chondrocytes. The activation of Hh signaling is sufficient to induce benign cartilage tumors without another oncogenic initiating event. Moreover, as primary cilia suppress Hh pathway activation in chondrosarcoma, cellular mechanisms inhibiting proper cilia function may be important in maintaining the neoplastic phenotype.

ObjectiveWith no effective therapies to attenuate cartilage degeneration in osteoarthritis (OA), the result is pain and disability. Activation of hedgehog (HH) signaling causes changes related to the progression of OA, with higher levels of Gli‐mediated transcriptional activation associated with increased disease severity. To elucidate the mechanism through which this occurs, this study sought to identify genes regulated by HH signaling in human OA chondrocytes.MethodsUsing human OA cartilage samples, microarray analyses were performed to detect changes in gene expression when the HH pathway was modulated. Results were analyzed for differentially expressed genes, grouped into functional networks, and validated in independent samples. To investigate the effects of chondrocyte‐specific sterol accumulation, we generated mice lacking Insig1 and Insig2, which are major negative regulators of cholesterol homeostasis, under Col2a1 regulatory elements.ResultsHH signaling was found to regulate genes that govern cholesterol homeostasis, and this led to alterations in cholesterol accumulation in chondrocytes. A higher level of Gli‐mediated transcription resulted in accumulation of intracellular cholesterol. In genetically modified mice, chondrocyte‐specific cholesterol accumulation was associated with an OA phenotype. Reducing cholesterol accumulation attenuated the severity of OA in mice in vivo and decreased the expression of proteases in human OA cartilage in vitro.ConclusionHH signaling regulates cholesterol homeostasis in chondrocytes, and intracellular cholesterol accumulation contributes to the severity of OA. Our findings have therapeutic implications, since reduction of HH signaling reversed cholesterol accumulation and statin treatment attenuated cartilage degeneration.

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Desmoid tumors (aggressive fibromatosis) are locally invasive soft tissue tumors that lack the ability to metastasize. There are no directed therapies or standard treatment plan, and chemotherapeutics, radiation, and surgery often have temporary effects. The majority of desmoid tumors are related to T41A and S45F mutations of the beta-catenin encoding gene (CTNNB1). Using broad spectrum metabolomics, differences were investigated between paired normal fibroblast and desmoid tumor cells from affected patients. There were differences identified, also, in the metabolomics profiles associated with the two beta-catenin mutations, T41A and S45F. Ongoing drug screening has identified currently available compounds which inhibited desmoid tumor cellular growth by more than 50% but did not affect normal fibroblast proliferation. Two drugs were investigated in this study, and Dasatinib and FAK Inhibitor 14 treatments resulted in unique metabolomics profiles for the normal fibroblast and desmoid tumor cells, in addition to the T41A and S45F. The biochemical pathways that differentiated the cell lines were aminoacyl-tRNA biosynthesis in mitochondria and cytoplasm and signal transduction amino acid-dependent mTORC1 activation. This study provides preliminary understanding of the metabolic differences of paired normal and desmoid tumors cells, their response to desmoid tumor therapeutics, and new pathways to target for therapy.

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Desmoid tumor (also called aggressive fibromatosis) is a lesion of mesenchymal origin that can occur as a sporadic tumor or a manifestation of the preneoplastic syndrome, familial adenomatous polyposis caused by a mutation in adenomatous polyposis coli (APC). This tumor type is characterized by the stabilization of β-catenin and activation of Tcf-mediated transcription. Cell transplantation data suggest that desmoid tumors are derived from mesenchymal progenitor cells (MSCs). As such, modulating cell signaling pathways that regulate MSC differentiation or proliferation, such as hedgehog (Hh) signaling, could alter the tumor phenotype. Here, we found that Hh signaling is activated in human and murine desmoid tumors. Inhibiting Hh signaling in human cell cultures decreased cell proliferation and β-catenin protein levels. Apc(+)/Apc(1638N) mice, which develop desmoid tumors, develop smaller and fewer tumors when Hh signaling was inhibited either genetically (by crossing Apc(+)/Apc(1638N) mice with mice lacking one copy of a Hh-activated transcription factor, Gli2 (+/-) mice) or using a pharmacologic inhibitor. Both in mice and in human tumor cell cultures, β-catenin and Hh-mediated signaling positively regulate each other's activity. These data show that targeting a pathway that regulates MSC differentiation influences desmoid tumor behavior, providing functional evidence supporting the notion that these tumors are derived from mesenchymal progenitors. It also suggests Hh blockade as a therapeutic approach for this tumor type.

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