Regulation of articular chondrocyte catabolic genes by growth factor interaction

Decreased SIRT1 Activity Is Involved in the Acute Injury Response of Chondrocytes to Ex Vivo Injurious Mechanical Overload

A better understanding of molecular events following cartilage injury is required to develop treatments that prevent or delay the onset of trauma-induced osteoarthritis. In this study, alterations to SIRT1 activity in bovine articular cartilage explants were evaluated in the 24 h following a mechanical overload, and the effect of pharmacological SIRT1 activator SRT1720 on acute chondrocyte injury was assessed. SIRT1 enzymatic activity decreased as early as 5 min following the mechanical overload, and remained suppressed for at least 24 h. The chondrocyte injury response, including apoptosis, oxidative stress, secretion of inflammatory mediators, and alterations in cartilage matrix expression, was prevented with pharmacological activation of SIRT1 in a dose-dependent manner. Overall, the results implicate SIRT1 deactivation as a key molecular event in chondrocyte injury following a mechanical impact overload. As decreased SIRT1 signaling is associated with advanced age, these findings suggest that downregulated SIRT1 activity may be common to both age-related and injury-induced osteoarthritis.

Harnessing Growth Factor Interactions to Optimize Articular Cartilage Repair

The failure of cartilage healing is a major impediment to recovery from joint disease or trauma. Growth factors play a central role in cell function and have been proposed as potential therapeutic agents to promote cartilage repair. Decades of investigation have identified many growth factors that promote the formation of cartilage in vitro and in vivo. However, very few of these have progressed to human trials. A growth factor that robustly augments articular cartilage healing remains elusive. This is not surprising. Articular cartilage repair involves multiple cellular processes and it is unlikely that any single agent will be able to optimally regulate all of them. It is more likely that multiple regulatory molecules may be required to optimize the maintenance and restoration of articular cartilage. If this is the case, then interactions among growth factors may be expected to play a key role in determining their therapeutic value. This review explores the hypothesis that growth factor interactions could help optimize articular cartilage healing.

Biochemical Aspects of Scaffolds for Cartilage Tissue Engineering; from Basic Science to Regenerative Medicine

Chondral defects are frequent and important causes of pain and disability. Cartilage has limited self-repair and regeneration capacity. The ideal approach for articular cartilage defects is the regeneration of hyaline cartilage with sustainable symptom-free constructs. Tissue engineering provides new strategies for the regeneration of functional cartilage tissue through optimized scaffolds with architectural, mechanical, and biochemical properties similar to the native cartilage tissue. In this review, the basic science of cartilage structure, interactions between proteins, stem cells, as well as biomaterials, scaffold characteristics and fabrication methods, as well as current and potential therapies in regenerative medicine will be discussed mostly from a biochemical point of view. Furthermore, the recent trends in scaffold-based therapies and supplementary factors in cartilage tissue engineering will be considered.

The synovium of human osteoarthritic joints retains its chondrogenic potential irrespective of age

The autologous synovium is a potential tissue source for local induction of chondrogenesis by tissue engineering approaches to repair articular cartilage defects such as they occur in osteoarthritis. It was the aim of the present study to ascertain whether the aging of human osteoarthritic patients compromises the chondrogenic potential of their knee-joint synovium and the structural and metabolic stability of the transformed tissue. The patients were allocated to one of the following two age categories: 54 - 65 years and 66 - 86 years (n = 7-11 donors per time point and experimental group; total number of donors: 64). Synovial biopsies were induced in vitro to undergo chondrogenesis by exposure to either bone morphogenetic protein-2 (BMP-2) alone, transforming growth factor-ß1 (TGF-ß1) alone, or a combination of the two growth factors, for up to 6 weeks. The differentiated explants were evaluated morphologically and morphometrically for the volume fraction of metachromasia (sulfated proteoglycans), immunohistochemically for type-II collagen, and for the gene-expression levels of anabolic chondrogenic markers as well as catabolic factors by a real-time polymerase-chain-reaction (RT-PCR) analysis. Quantitative metachromasia revealed that chondrogenic differentiation of human synovial explants was induced to the greatest degree by either BMP-2 alone or the BMP-2/TGF-1 combination, i.e. to a comparable level with each of the two stimulation protocols and within both age categories. The BMP-2/TGF-1combination protocol resulted in chondrocytes of a physiological size for normal human articular cartilage, unlike the BMP-2 alone stimulation that resulted in cell sizes of terminal hypertrophy. The stable gene-expression levels of the anabolic chondrogenic markers confirmed the superiority of these two stimulation protocols and demonstrated the hyaline-like qualities of the generated cartilage matrix. The gene-expression levels of the catabolic markers remained extremely low. The data also confirmed the usefulness of experimental in vitro studies with bovine synovial tissue as a paradigm for human synovial investigations. Our data reveal the chondrogenic potential of the human knee-joint synovium of osteoarthritic patients to be uncompromised by ageing and catabolic processes. The potential of synovium-based clinical engineering (repair) of cartilage tissue using autologous synovium may thus not be reduced by the age of the human patient.

Protective effects of ten oligostilbenes from Paeonia suffruticosa seeds on interleukin-1β-induced rabbit osteoarthritis chondrocytes

Background

Paeonia suffruticosa is an important traditional Chinese herb used to treat osteoarthritis (OA) and oligostilbenes are the main active ingredient of the seeds of P. suffruticosa. The monomer trans-resveratrol of this species was demonstrated to have chondroprotective effects as a lead compound for the treatment of osteoarthritis, but it has not been applied due to its low efficacy.

Methods

Oligostilbenes were isolated by chromatography and were identified by NMR and HPLC. A rabbit osteoarthritis chondrocyte model was induced by interleukin-1β and was treated with individual drugs to systematically evaluate their effects. Cell Counting Kit 8 was used to test their effects on cell viability, calculate EC₅₀ and plot a dose-response curve.Their effects on apoptosis were analyzed by Annexin V and PI staining, and the expression of chondrocyte-specific genes COL2A1, MMP13 and SOX9 was evaluated by real-time PCR.

Results

Paeonia suffruticosa seed extract could promote the cell viability of rabbit OA chondrocytes at low concentration and then ten oligostilbenes were isolated from it. Trans-oligostilbenes were better than their cis-forms, trimers and dimers were better than monomers for promoting the cell viability of rabbit osteoarthritis chondrocytes. None of the oligostilbenes was more effective than seed extract at the appropriate concentration; 1 μM oligostilbenes all showed various anti-apoptotic effects. Trans-gnetin H showed the best effect on proliferation and inhibition of MMP13 expression on OA chondrocytes, while trans-viniferin was most effective in promoting the expression of COL2A1 and SOX9.

Conclusions

Ten oligostilbenes from P. suffruticosa seed all have certain protective effects on OA chondrocytes at low concentration. The trans-viniferin and some trimers have the potential to be further developed for the treatment of osteoarthritis because they were more effective than resveratrol and diacerein. The synergistic effect that may exist between oligostilbenes also warrants further research.