The Role of Notch Signaling in Osteoarthrosis - A Preclinical Study with Focus on the Notch2- and Notch3 Receptor in a Murine Osteoarthrosis Model.

• Applicant: Dr. Tobias Malte Ballhause
• Subject Area: Orthopaedics, Traumatology, Reconstructive Surgery
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 553191093

Osteoarthritis (OA) is a disease of the joints that affects almost all people with increasing age. This results in cartilage damage with remodeling of the subchondral lamella and a reduced joint space. The increasing life expectancy of people and the growing proportion of people who are overweight will further increase the incidence of OA. Therefore, research into therapeutic options is of utmost importance. The Notch signaling pathway regulates cell differentiation. Previous work has shown that both the Notch2 and -3 receptors have a regulatory influence on cartilage, bone and synovial tissue. All three tissue types are pathologically altered in OA. In contrast to the Notch1 receptor, whose blockade has a protective influence on the development of OA, there are no specific studies on Notch2 and -3. In mouse lines with Notch2 overexpression (HCS) and Notch3 deficiency (N3(d/d)), the influence of the respective mutated receptor on the differentiation of primary bone and cartilage cells will be investigated. The diuretic spironolactone is a global inhibitor of the Notch signaling pathway. However, the influence on the signaling cascade in bone and cartilage cells has not yet been specifically investigated. The treatment of cells with spironolactone will be used to search for dose-dependent changes in the Notch signaling cascade and associated signaling pathways. Since OA is a disease of the entire joint, in vivo experiments with the mutant mouse lines are planned. For this purpose, the anterior cruciate ligament of HCS and N3(d/d) mice and the corresponding wild-type animals will be cut (ACLT). This causes knee OA in the right hind leg. After 4 and 8 weeks, the knee joints are examined by molecular biology, radiology and histology. In the case of the HCS mice, a more severe OA is to be expected. The increased activity of the Notch2 receptor leads to increased activation of matrix metalloprotease-13, which has a catabolic effect on the cartilage tissue. In the N3(d/d) mice, the OA should be lower compared to wild-type animals, due to a weaker immune response. Finally, the investigation of Notch receptors in osteoarthritic human femoral heads is planned. The femoral head will be divided into regions depending on the anatomical position and exposure to mechanical load. An altered expression of the Notch receptors in the differently weight-bearing regions can be assumed. The expression pattern of the Notch receptors will be correlated with the severity of the OA as well as the preoperative pain perception and functionality in the hip joint of the patients. This translational part of the project will provide an insight into the involvement of the individual Notch receptors and the arthritic remodeling processes in the human hip joint.

• DFG Programme: Research Grants
• Co-Investigator: Professor Johannes Keller, Ph.D.