Cartilage degradation and osteoarthritis: can lack of mechanical stimulation and subchondral bone insufficiency upregulate catabolic genes?
Problem or question being addressed
The bald truth is: articular cartilage cover may be reduced/lost when subchondral bone cannot bear it anymore. Several studies have shown that mechanical and biological insufficiency of the subchondral bone may precede joint cartilage degeneration. Of course, cartilage damage can be the primary event and cause secondary changes in the subchondral bone. Either way, increasing evidence points to a cross-talk between chondrocytes and subchondral bone cells leading to articular degeneration. The cascade of events that follows involves a reduction in the physiological load to which the subchondral region must be subjected, production of inflammatory cytokines, increased bone resorption, reactive increase in bone formation/subchondral sclerosis, neoangiogenesis, cartilage degradation and a cycle of self-destruction. The resulting osteoarthritis, affects millions of people around the world, causing chronic pain, joint deformity, functional limitation, reduced quality of life and a great economic, emotional and financial impact. But what is the primary molecular and cellular event that triggers this whole process? And how to avoid it?
Rationale for your approach
Arthritis may be triggered by the absence of stimulus (there is an optimal stimulus to which tendons, ligaments, bones and cartilages must be submitted to avoid the degenerative process), excess load/stimulation (supraphysiological), trauma, infection, tumors, surgeries and their complications or several of these factors combined. It is the factor that follows this initial event, but which precedes the entire cascade of events mentioned above that is the focus of this project. Our theory is that primary or idiopathic arthrosis is mainly caused by the absence of adequate joint stimulation that would lead to the expression of genes that produce proteinases such as MMPS, ADAMTS, elastase and cathepsin, nitric oxide, cyclooxygenase and pro-inflammatory cytokines such as IL -1B, TNF-a, IL-6, IL-8. On the other hand, an optimal mechanical stimulus could maintain the homeostasis of the joint microenvironment.
Several studies have shown that subchondral bone insufficiency can lead to joint degeneration. For example, the association between osteoporosis and osteoarthritis has already been demonstrated. Also, patients with giant cell tumors of the distal femur undergoing massive curettage of the region evolve with joint degeneration even when there is no direct involvement of the articular cartilage.
Details of suggested approach
The aim of the study is to evaluate the effect of controlled mechanical stimulation with and without the addition of mesenchymal stromal cells on gene expression and homeostasis of the knee joint microenvironment. For this, osteochondral plugs/fragments from healthy subjects will be divided into 4 groups. The fragments will be placed in a standardized culture medium and will be allocated in control groups (no load) with and without BMAC and groups with load associated or not with BMAC.
• Group 1 control – no load (n = 6).
• Group 2 control + BMAC without load (n = 6).
• Group 3: load only (n = 6).
• Group 4: load + BMAC (n=6).
The plugs will be placed on 6-well BioPress™ Compression Plates that will be connected to a Flexcell system which allows for standardization and controlled application of load to a 3D cell culture. The system allows, for example, to simulate periods of greater and lesser activity within a day. All information on loads carried out is captured in real time by the manufacturer's software.
The culture medium will be changed every 3 days and stored for protein assays. After 12 days, tissues from all groups will be digested for chondrocytes isolation followed by assessment of cell viability and other tests. The groups will be further assessed by reverse-transcription polymerase chain reaction (RT-PCR), Western blotting, fluorescence-activated cell sorting (FACS), and immunohistochemistry for specific assessment of catabolic and anabolic gene expression.
How it will affect the broader field
Identifying a potential cause of arthrosis can help in the development of prevention measures and in the establishment of more effective therapeutic modalities, helping to reduce costs with hospitalizations and more expensive treatment options, increasing the quality of life, autonomy and survival of the population as one all.
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