Systemic neutralization of TGF-β attenuates osteoarthritis

Targeting subchondral bone mesenchymal stem cell activities for intrinsic joint repair in osteoarthritis

Osteoarthritis (OA) is a common age-related disease with complex pathophysiology. It is characterized by wide-ranging tissue damage and ultimate biomechanical failure of the whole joint. However, signs of tissue adaptation and attempted repair responses are evident in OA-affected osteochondral tissues. Highlighted in this review article is the role of bone-resident mesenchymal stem cells (MSCs) in these bone remodeling responses, and a proposal that targeting MSC activities in OA subchondral bone could represent a novel approach for intrinsic joint regeneration in OA. The development of these therapies will require better understanding of MSC proliferation, migration and differentiation patterns in relation to OA tissue damage and further clarification of the molecular signaling events in these MSCs during disease progression.

Osteoarthritis (OA) is a joint disorder, in which the cartilage, the underlying bone and other joint tissues are affected. Recent evidence demonstrating attempted repair responses in these OA tissues challenges the traditional view of OA as a degenerative disorder. Signs of tissue regeneration are particularly evident in the bone located directly underneath the damaged cartilage, where increased stem cell activity has been observed. Targeting these stem cells could represent a novel approach for intrinsic joint regeneration in OA. To progress with developing these novel therapies, a better understanding of stem cell function in normal and OA joint tissues is needed.

Deferoxamine synergizes with transforming growth factor-β signaling in chondrogenesis

Osteoarthritis, also known as degenerative arthritis or degenerative joint disease, is an epidemic disease that affects millions of people worldwide. Despite extensive recent work on the cellular biology of osteoarthritis, the precise mechanisms involved are still poorly understood and there is no effective treatment for this disease. The role of transforming growth factor-beta (TGF-β) in promoting chondrogenesis and inducing the expression of cartilage-specific extracellular matrix molecules to form cartilage is well-established. Historically, TGF-β has been considered to prevent osteoarthritis, but recent work suggests that TGF-β overexpression accelerates the progression of osteoarthritis in vivo. Clinically, it is therefore important to limit TGF-β expression while still providing effective treatment of osteoarthritis. One possible approach to achieve this effect would be to use a combination of TGF-β with other small molecular chemical compounds. Hypoxia promotes chondrogenesis and the usefulness of deferoxamine, a chelating agent that mimics hypoxia, in stimulating chondrogenesis has been investigated in clinical trials. In this study, we investigated the role of deferoxamine in TGF-β-induced chondrogenesis in pre-chondrogenic cells and examined whether deferoxamine synergizes with the TGF-β signaling pathway to promote chondrocyte differentiation.

Recent developments in emerging therapeutic targets of osteoarthritis

Purpose of review

Despite the tremendous individual suffering and socioeconomic burden caused by osteoarthritis, there are currently no effective disease-modifying treatment options. This is in part because of our incomplete understanding of osteoarthritis disease mechanism. This review summarizes recent developments in therapeutic targets identified from surgical animal models of osteoarthritis that provide novel insight into osteoarthritis pathology and possess potential for progression into preclinical studies.

Recent findings

Several candidate pathways and processes that have been identified include chondrocyte autophagy, growth factor signaling, inflammation, and nociceptive signaling. Major strategies that possess therapeutic potential at the cellular level include inhibiting autophagy suppression and decreasing reactive oxygen species (ROS) production. Cartilage anabolism and prevention of cartilage degradation has been shown to result from growth factor signaling modulation, such as TGF-β, TGF-α, and FGF; however, the results are context-dependent and require further investigation. Pain assessment studies in rodent surgical models have demonstrated potential in employing anti-NGF strategies for minimizing osteoarthritis-associated pain.

Summary

Studies of potential therapeutic targets in osteoarthritis using animal surgical models are helping to elucidate osteoarthritis pathology and propel therapeutics development. Further studies should continue to elucidate pathological mechanisms and therapeutic targets in various joint tissues to improve overall joint health.

Osteoarthritis year in review 2016: biology

This review highlights a selection of literature in the area of osteoarthritis biology published between the 2015 and 2016 Osteoarthritis Research Society International (OARSI) World Congress. Highlights were selected from a pubmed search covering cartilage, bone, inflammation and pain. A personal selection was made based, amongst other things, on topics presented during the 2015 conference. This covers circadian rhythm, TGF-β signaling, autophagy, SIRT6, exercise, lubricin, TLR's, pain and NGF. Furthermore, in this review we have made an effort to connect these seemingly distant topics into one scheme of connections between them, revealing a theoretical big picture underneath.

Bone-cartilage crosstalk: a conversation for understanding osteoarthritis

Although cartilage degradation is the characteristic feature of osteoarthritis (OA), it is now recognized that the whole joint is involved in the progression of OA. In particular, the interaction (crosstalk) between cartilage and subchondral bone is thought to be a central feature of this process. The interface between articular cartilage and bone of articulating long bones is a unique zone, which comprises articular cartilage, below which is the calcified cartilage sitting on and intercalated into the subchondral bone plate. Below the subchondral plate is the trabecular bone at the end of the respective long bones. In OA, there are well-described progressive destructive changes in the articular cartilage, which parallel characteristic changes in the underlying bone. This review examines the evidence that biochemical and biomechanical signaling between these tissue compartments is important in OA disease progression and asks whether such signaling might provide possibilities for therapeutic intervention to halt or slow disease development.