Motion-based therapies have been applied to promote healing of arthritic joints. The goal of the current study was to determine the early molecular events that are responsible for the beneficial actions of motion-based therapies on meniscal fibrocartilage. Rabbit knees with Antigen-InducedArthritis (AIA) were exposed to continuous passive motion (CPM) for 24 or 48 h and compared to immobilized knees. The menisci were harvested and glycosaminoglycans (GAG), interleukin-1β (IL-1β), matrix metalloproteinase-1 (MMP-1), cyclooxygenase-2 (COX-2), and interleukin-10 (IL-10) were determined by histochemical analysis.Within 24 h, immobilized knees exhibited marked GAG degradation. The expression of proinflammatory mediators MMP-1, COX-2, and IL-1β was notably increased within 24 h and continued to increase during the next 24 h in immobilized knees. Knees subjected to CPM revealed a rapid and sustained decrease in GAG degradation and the expression of all proinflammatory mediators during the entire period of CPM treatment. More importantly, CPM induced synthesis of the anti-inflammatory cytokine IL-10. The results demonstrate that mechanical signals generated by CPM exert potent anti-inflammatory signals on meniscal fibrochondrocytes. Furthermore, these studies explain the molecular basis of the beneficial effects of CPM observed on articular cartilage and suggest that CPM suppresses the inflammatory process of arthritis more efficiently than immobilization.

Cells from Ewing sarcoma exhibit cellular features and express markers, suggesting that the tumor is of neuroectodermal origin. Because Notch signaling regulates the differentiation of neuroectodermal cells during development, we examined the role of Notch signaling in Ewing sarcomas. We found that Ewing sarcomas express Notch receptors, ligands, and the Notch target gene HES1. To determine the functional implications of Notch signaling, we expressed tetracycline-regulated constitutively active, dominant-negative (DN), or wild-type Notch-1 receptors in two Ewing sarcoma cell lines, or we treated the cell lines with a ␥-secretase inhibitor. Expression of the constitutively active Notch-1 reduced proliferation and expression of the DN Notch-1 reduced apoptosis in vitro. However, there was only a small difference in the volume of tumors that formed when the cell lines expressing these constructs were implanted in nude mice. Xenograft tumors derived from the cell lines expressing DN Notch-1 exhibited a neural phenotype. Treatment with a ␥-secretase inhibitor caused similar changes as expression of the DN construct. Notch signaling plays a role in cell differentiation, proliferation, and apoptosis in Ewing sarcoma, but its inhibition is only associated with a small change in tumor growth potential.

Aggressive fibromatosis is a mesenchymal neoplasm associated with mutations, resulting in beta-catenin-mediated transcriptional activation. We found that plasminogen activator inhibitor-1 (PAI-1) was upregulated fourfold in aggressive fibromatosis. We investigated the ability of beta-catenin to regulate a PAI-1 reporter, and found that PAI-1 is an indirect target. To determine the role of PAI-1 in vivo, a mouse containing a targeted deletion in Pai-1 was crossed with a mouse that develops aggressive fibromatosis and gastrointestinal tumors (Apc/Apc1638N mouse). Pai-1 deficiency reduced the number of aggressive fibromatosis tumors formed, but not the number of gastrointestinal tumors. Deficiency of Pai-1 reduced tumor cell proliferation and motility rate. Although PAI-1 can alter cell motility by competing for a common binding site on vitronectin, blocking this site did not alter the motility rate. The number of cells moving through matrigel (invasion rate) did not change with Pai-1 deficiency, but because of the low motility rate the invasion index (invasion rate/motility) was increased in Pai-1-deficient cells. This suggests a proteolytic effect for PAI-1 regulating cell invasiveness. Our study found that, although PAI-1 has cellular effects that could inhibit or enhance tumor growth, on balance, it acts as a tumor enhancer in aggressive fibromatosis.

Aggressive fibromatosis is a mesenchymal neoplasm associated with mutations resulting in beta-catenin mediated transcriptional activation. Plasminogen activator inhibitor-1 (PAI-1) is expressed at a high level in aggressive fibromatosis, and using transgenic mice, we found that PAI-1 plays an important role in aggressive fibromatosis tumor formation. Familial adenomatous polyposis is associated with Adenomatous Polyposis Coli gene mutations resulting in beta-catenin mediated transcriptional activation, yet only some patients develop aggressive fibromatosis. Since PAI-1 expression is influenced by a promoter 4G/5G polymorphism, we investigated the incidence of this polymorphism in familial adenomatous polyposis patients who did and who did not develop aggressive fibromatosis, as well as sporadic aggressive fibromatosis patients. There was a trend towards association of the 4G allele (associated with high PAI-1 expression) with the development of aggressive fibromatosis in familial adenomatous polyposis patients (50% vs. 19%, P = 0.1). In familial adenomatous polyposis patients who did not develop aggressive fibromatosis, there was a significantly lower proportion of patients with a 4G allele compared to the healthy control (19% vs. 51%, P = 0.0286). The lower incidence of 4G polymorphism in the PAI-1 promoter may be preventive against the development of aggressive fibromatosis. This data provides additional evidence supporting an important role for PAI-1 in the pathogenesis of aggressive fibromatosis.