Effect of Cytoskeletal Disruption on Mechanotransduction of Hydrostatic Pressure by C3H10T1/2 Murine Fibroblasts

Cyclic hydrostatic pressure of physiological magnitude (< 10 MPa) stimulates chondrogenic differentiation of mesenchymal stem cells, but mechanotransduction mechanisms are not well understood. It was hypothesized that an intact cytoskeleton would be required for uninhibited mechanotransduction of hydrostatic pressure. Therefore we examined the effects of drugs which selectively interfere with actin and tubulin polymerization on pressure-induced upregulation of aggrecan and col2a1 (type II collagen) mRNA expression. C3H10T1/2 cells were cultured as pellets in either 4µM cytochalasin D or 4µM nocodazole and subjected to 3 days of cyclic hydrostatic compression (1 Hz, 5 MPa, 2 h per day). Phalloidin staining and indirect immunostaining with anti α-tubulin antibody confirmed disruption of microfilament and microtubule assemblies, respectively. Real time RT-PCR revealed that both drugs substantially lowered the basal level of aggrecan and col2a1 mRNA, but that neither drug prevented a pressure-stimulated increase in gene expression relative to the altered basal state. Thus upregulation of macromolecular gene expression by cyclic hydrostatic pressure did not require a completely intact cytoskeleton

Percutaneous arthrodesis

It has been generally accepted that residual cartilage and subchondral bone has to be removed in order to get bony fusion in arthrodeses. In 1998 we reported successful fusion of 11 rheumatoid ankles, all treated with percutaneous fixation only. In at least one of these ankle joints there was cartilage left. More than 25 rheumatoid patients with functional alignment in the ankle joint have subsequently been operated on with the percutaneous technique, and so far we have had only one failure. In a rabbit study we tested the hypothesis that even a normal joint can fuse merely by percutaneous fixation. The patella was fixated to the femur with lag screw technique without removal of cartilage, and in 5 of 6 arthrodeses with stable fixation bony fusion followed. Depletion of synovial fluid seemed to be the mechanism behind cartilage disappearance. The stability of the fixation achieved at arthrodesis surgery is an important factor in determining success or failure. Dowel arthrodesis without additional fixation proved to be deleterious. Ankle arthrodesis can be successfully performed in patients with rheumatoid arthritis by percutaneous screw fixation without resection of the joint surfaces. This procedure has two advantages: first, it is less traumatic, second, both the arch-shaped geometry and the subchondral bone are preserved, and thus both could contribute to the postoperative stability of the construct. Intuitively, preservation of the arch-shape should increase rotational stability. The results of our experimental sawbone study indicate that the arch shape and the subchondral bone should be preserved. The importance of this is likely to increase in weak rheumatoid bone. In a finite element study the initial stability provided by two different methods of joint preparation and different screw configurations in ankle arthrodesis, was compared. Overall, inserting the two screws at a 30-degree angle with respect to the long axis of the tibia, and crossing them above the fusion site improved stability for both joint preparation techniques. The question rose whether patients with osteoarthritis could also be operated on with the percutaneous fixation technique. The first metatarsophalangeal joint in patients with hallux rigidus was chosen as an appropriate joint to test the technique. In this small series we have shown that it is possible to achieve bony fusion with a percutaneous technique in an osteoarthrotic joint in humans, but failed to say anything about the fusion rate

Articular cartilage tissue engineering: the role of signaling molecules

Effective early disease modifying options for osteoarthritis remain lacking. Tissue engineering approach to generate cartilage in vitro has emerged as a promising option for articular cartilage repair and regeneration. Signaling molecules and matrix modifying agents, derived from knowledge of cartilage development and homeostasis, have been used as biochemical stimuli toward cartilage tissue engineering and have led to improvements in the functionality of engineered cartilage. Clinical translation of neocartilage faces challenges, such as phenotypic instability of the engineered cartilage, poor integration, inflammation, and catabolic factors in the arthritic environment; these can all contribute to failure of implanted neocartilage. A comprehensive understanding of signaling molecules involved in osteoarthritis pathogenesis and their actions on engineered cartilage will be crucial. Thus, while it is important to continue deriving inspiration from cartilage development and homeostasis, it has become increasingly necessary to incorporate knowledge from osteoarthritis pathogenesis into cartilage tissue engineering