Osteoarthritis (OA) is a common degenerative joint disease characterized by the degenerative changes in joint cartilage and underlying bone. It commonly occurs in weightbearing joints like the knees, hips, and spine but can affect any joint in the body, resulting in symptoms such as pain, stiffness, and reduced range of motion. Post-traumatic osteoarthritis (PTOA) is a subtype of OA that occurs after a joint injury, such as a fracture, dislocation, or ligament tear, causing damage to the cartilage and other joint tissues leading to OA over time. PTOA accounts for a significant proportion of all OA cases. OA is a major cause of disability worldwide and poses a significant economic burden on both individuals and healthcare systems, including direct medical costs like doctor visits, medications, and surgeries, and indirect costs like lost productivity due to absenteeism or disability. The total cost of OA is estimated to be several percent of a country's GDP. Epidemiologically, OA is one of the most common chronic diseases, affecting millions worldwide. Its prevalence increases with age and is more common in women than in men. Other risk factors include obesity, joint injury, and repetitive use of certain joints. PTOA can affect individuals of any age and is often associated with sports injuries or accidents. It is estimated that about 12% of all OA cases are post-traumatic. Despite its prevalence and associated costs, there is no cure for OA or PTOA, and current treatments primarily focus on managing symptoms and improving joint function. These treatments include pain relievers (such as acetaminophen or nonsteroidal anti-inflammatory drugs), physical therapy, joint injections (such as corticosteroids or hyaluronic acid), and in severe cases, joint replacement surgery. However, these treatments often have limitations in terms of efficacy, side effects, and the fact that they do not stop the progression of the disease. For example, pain relievers can cause gastrointestinal issues, kidney or liver damage, and an increased risk of heart attack or stroke;​ injections may provide temporary relief but do not address the underlying cause of the disease, and joint replacement surgery is a major procedure with associated risks and a long recovery time. Preventive measures, such as maintaining a healthy weight, staying active, and avoiding joint injuries, can help reduce the risk of developing OA. For PTOA, prompt and appropriate treatment of joint injuries can help reduce the risk of developing OA later on. Therefore, finding new targets for drug development in OA is critically important to develop more effective and safer treatments that can stop or slow the progression of the disease, rather than just managing the symptoms.

Therefore, we first sought to investigate the role of different mechanosensors is translating different mechanical cues such as hydrostatic pressure and mechanical compression. We used primary porcine chondrocytes and either encapsulated them in agarose hydrogel or plated them on coverslip to apply hydrostatic pressure and mechanical compression on them respectively. First, we showed that TRPV1 channel is the mechanosensory of hydrostatic pressure since blocking this channel using its specific inhibitor increased the production of sGAG that was induced by hydrostatic pressure. On the other hand, we demonstrated that PIEZO1 channel, is the only channel in the PIEZO family that responds to high magnitudes of mechanical strain and injurious loads. We also showed that PIEZO1 is sensitive to membrane tension and manipulating the membrane can regulate the sensitivity of the PIEZO1 channel to both chemical and mechanical stimuli. Additionally, we observed that PIEZO1 channel is sensitive to rate of loading, and they need intracellular and extracellular Ca²⁺+ sources to be able to response to mechanical compression. Lastly, we took a novel approach and combined our experimental data with finite element modeling and determined the membrane strain threshold required for the PIEZO1 channel to get activated.

For the purpose of finding how regulating the PIEZO channels sensitivity can affect the progression of OA and PTOA, we investigated the role of polyunsaturated fatty acids including w3 and w6 fatty acids in regulating the functionality of the PIEZO channels. We showed that both w3 and w6 fatty acids were able to reduce the sensitivity of the PIEZO channels to both chemical and mechanical stimuli. Furthermore, we showed that supplementation of w6 fatty acids increase the level of inflammatory biomarker IL-6 and senescence marker MMP3 compared to the control. However, treating the chondrocytes with w3 decreased the level of IL-6, MMP3, and other senescence factor P53 showing the effect of w3 fatty acids on reducing inflammation and cellular aging.

Lastly, we assessed the role of voltage gated Ca²⁺+ channels (VGCCs) in regulating the PIEZO channels activity and see if the downstream effect of inhibiting the VGCCs on PIEZOs can be used as a therapeutic for OA and PTOA. We showed that blocking the L-type VGCCs activity using their specific antagonist Nifedipine can reduce the sensitivity of the PIEZO channels. However, blocking the T-type VGCCs activity using NNC-55 would significantly increase the sensitivity of the PIEZO channels. Moreover, we demonstrated that treating cartilage explants with Nifedipine would rescue the cartilage under injury, although, blocking the T-type channels induce more cell death in an injured cartilage explant.

Overall, understanding the mechanisms by which chondrocytes respond to physiologic or pathological cartilage loading is crucial for the development of new pharmacologic therapies to treat mechanically-regulated conditions such as PTOA. Our research has shown that dietary polyunsaturated fatty acids (PUFAs) can reduce the mechanosensitivity of PIEZO channels in chondrocytes in response to deformation, thereby elucidating the role of mechanobiology in cartilage health and disease. Moreover, w3 PUFAs were able to decrease the inflammatory and senescence markers in chondrocytes elucidating their positive effect on cell health. Additionally, we found that hypo-osmotic conditions, which may occur in early OA, can sensitize PIEZO activation of chondrocytes by increasing the apparent membrane tension. Furthermore, intracellular Ca²⁺+ activation is sensitive to the rate of loading, potentially due to the viscoelasticity of the cell or membrane. Lastly, we demonstrated that inhibiting the activity of the L-type VGCCs can rescue the cartilage under injury through regulating the activity of the PIEZO channels. These findings not only provide new insights into developing future OA therapeutics but also underscore the importance of understanding the intersection of different mechanisms involved in chondrocyte mechanotransduction. This knowledge can open new pathways for the development of pharmacologic therapies to treat mechanically-regulated conditions such as PTOA.