AG-041R stimulates cartilage matrix synthesis without promoting terminal differentiation in rat articular chondrocytes

Small molecule compounds promote the proliferation of chondrocytes and chondrogenic differentiation of stem cells in cartilage tissue engineering

The application of tissue engineering to generate cartilage is limited because of low proliferative ability and unstable phenotype of chondrocytes. The sources of cartilage seed cells are mainly chondrocytes and stem cells. A variety of methods have been used to obtain large numbers of chondrocytes, including increasing chondrocyte proliferation and stem cell chondrogenic differentiation via cytokines, genes, and proteins. Natural or synthetic small molecule compounds can provide a simple and effective method to promote chondrocyte proliferation, maintain a stable chondrocyte phenotype, and promote stem cell chondrogenic differentiation. Therefore, the study of small molecule compounds is of great importance for cartilage tissue engineering. Herein, we review a series of small molecule compounds and their mechanisms that can promote chondrocyte proliferation, maintain chondrocyte phenotype, or induce stem cell chondrogenesis. The studies in this field represent significant contributions to the research in cartilage tissue engineering and regenerative medicine.

Cartilage regeneration and ageing: Targeting cellular plasticity in osteoarthritis

Ageing processes play a major contributing role for the development of Osteoarthritis (OA). This prototypic degenerative condition of ageing is the most common form of arthritis and is accompanied by a general decline, chronic pain and mobility deficits. The disease is primarily characterized by articular cartilage degradation, followed by subchondral bone thickening, osteophyte formation, synovial inflammation and joint degeneration. In the early stages, osteoarthritic chondrocytes undergo phenotypic changes that increase cell proliferation and cluster formation and enhance the production of matrix-remodelling enzymes. In fact, chondrocytes exhibit differentiation plasticity and undergo phenotypic changes during the healing process. Current studies are focusing on unravelling whether OA is a consequence of an abnormal wound healing response. Recent investigations suggest that alterations in different proteins, such as TGF-ß/BMPs, NF-Kß, Wnt, and Cx43, or SASP factors involved in signalling pathways in wound healing response, could be directly implicated in the initiation of OA. Several findings suggest that osteoarthritic chondrocytes remain in an immature state expressing stemness-associated cell surface markers. In fact, the efficacy of new disease-modifying OA drugs that promote chondrogenic differentiation in animal models indicates that this may be a drug-sensible state. In this review, we highlight the current knowledge regarding cellular plasticity in chondrocytes and OA. A better comprehension of the mechanisms involved in these processes may enable us to understand the molecular pathways that promote abnormal repair and cartilage degradation in OA. This understanding would be advantageous in identifying novel targets and designing therapies to promote effective cartilage repair and successful joint ageing by preventing functional limitations and disability.

Transient down-regulation of cbfa1/Runx2 by RNA interference in murine C3H10T1/2 mesenchymal stromal cells delays in vitro and in vivo osteogenesis, but does not overtly affect chondrogenesis

In order to ensure that MSCs designed for in vivo cartilage repair do not untowardly differentiate into osteoblasts and mineralize in situ, we tested whether siRNA-induced suppression of cbfa1/Runx2 affected the osteogenic and chondrogenic differentiation potential of the murine cell line C3H10T1/2. Anti-cbfa1/Runx2 siRNA decreased the levels of cbfa1/Runx2 mRNA and protein by 65-80%, and also markedly reduced the expression of osteoblast-related genes such as Dlx5, osterix, collagen type I, alkaline phosphatase (AP), osteocalcin, SPARC/osteonectin and osteopontin, leading to a temporal expression of AP enzyme activity and mineralization potential delayed by at least some 7-9 days. Furthermore, siRNA-transfected cells, grown under chondrogenic conditions did not display biologically significant changes in the expression of aggrecan, collagen type II or type X, or histology when grown in micropellets or monolayer cultures. Finally, when cells were propagated in osteogenic medium and injected into the tibial muscles of SCID mice, no overtly mineralized bone tissue emerged. These experiments indicate that a major transient reduction of cbfa1/Runx2 expression in MSCs is sufficient to delay osteoblastic differentiation, both in vitro and in vivo, while chondrogenesis seemed to be sustained.

AG-041R, a novel indoline-2-one derivative, stimulates chondrogenesis in a bipotent chondroprogenitor cell line CL-1

OBJECTIVE

To examine the chondrogenic activity of AG-041R and its mode of action in a bipotent chondroprogenitor cell line CL-1.

DESIGN

Chondrogenic activity of AG-041R in CL-1 was examined by histology, alcian blue pH 1.0 intensity and mRNA expression of cartilage matrix proteins (collagen type II, aggrecan). Chondrogenic activities of other CCK2/gastrin receptor antagonists were also examined. Since TGF-beta1 induces dominant chondrogenesis and suppressed adipogenesis in CL-1, induction of TGF-beta by AG-041R was examined by enzyme linked immunosorbent assay. Involvement of MAP kinases in the chondrogenic effect of AG-041R in CL-1 was examined by Western blotting and MAP kinase inhibitors.

RESULTS

AG-041R induced dominant chondrogenesis and marked suppression of adipogenesis in CL-1. Neither of the other CCK2/gastrin receptor antagonists tested showed chondrogenic activity in CL-1. AG-041R increased alcian blue pH 1.0 intensity and mRNA expression of collagen type II and aggrecan. TGF-beta1 and -beta2 proteins were increased by AG-041R. The chondrogenic activity of AG-041R in CL-1 was blocked by TGF-beta neutralizing antibody or inhibitors for activation of latent TGF-beta. AG-041R activated both Erk (p44/42) and p38 MAP kinases in CL-1. Inhibition of Erk (p44/42) by PD98059 canceled the adipogenesis suppression by AG-041R in CL-1. Inhibition of p38 by SB202190 completely canceled the chondrogenic activity of AG-041R in CL-1.

CONCLUSION

AG-041R has chondrogenic activity in CL-1 not related to CCK2/gastrin receptor antagonism. It is suggested that TGF-beta induction and the activation of MAP kinases mediate the chondrogenic activity of AG-041R in CL-1.