The role of PTHrP signaling for the mechano-response of mesenchymal progenitors and chondrocytes

• Applicant: Dr. Justyna Buchert
• Subject Area: Orthopaedics, Traumatology, Reconstructive Surgery
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 467123401

The influence of biomechanical cues on cartilage is acknowledged and abnormal mechanical loading is one of the main causes of cartilage matrix degeneration, resulting in osteoarthritis (OA). Since cartilage lacks intrinsic healing capacity and there are no therapies to cure OA, joint replacement remains the only treatment option. OA is characterized by increased cell matrix catabolism concomitant with decreased cell anabolic activity. It is crucial to elucidate mechanisms that translate loading forces into aberrant cell metabolism and identify viable targets for joint movement-based or pharmacological therapies that will prevent or heal OA. The challenge in mechanobiology is the high number of variables and the resulting difficulty in studies comparison and hence extraction of targetable mechano-induced molecules that regulate cell phenotype. According to literature and our own data, parathyroid hormone-related protein (PTHrP) is stimulated by mechanical loading in engineered cartilage, and it is known for its rapid, time-controlled effects on skeletal tissue differentiation and metabolism, depending on a continuous versus intermittent exposure. Here we propose that mechano-induced PTHrP plays a role in orchestrating time-relevant metabolic processes within cartilage tissue, dictating the balance between matrix anabolism and catabolism upon mechanical stimulation. It may further influence chondrogenesis and explain the antihypertrophic effects described in response to loading. To test our hypothesis, we will apply a loss-of-function approach and create induced pluripotent stem cell (iPSC)-derived mesenchymal progenitors with abrogated PTHrP gene function, by using CRISPR/Cas gene editing and analysis of cell properties in the absence of PTHrP expression. PTHrP has been described to act either as a secreted factor and initiate cell signaling upon binding to the receptor, or in an intracrine manner by direct translocation to the nucleus. Therefore, by modulation of PTHrP localization signals within the transcript sequence, we will also study whether PTHrP-dependent actions upon mechanical stimulation are receptor-dependent or intracrine. In addition we will also establish mechanosenstive reporter assay. To our knowledge, this will be the first investigation addressing the role of a specific molecule by the gene editing knock-out in mechanotransduction and the first study to analyze PTHrP mode of action in a context of temporal- and mechano-regulated changes in cell metabolism. Overall, this knowledge could help to develop improved protocols for production of cartilage tissue engineering constructs for treatment of cartilage defects. Furthermore, unraveling these mechanisms can have a major impact on finding specific targets for pharmacological treatments against OA, or markers for beneficial loading to design personalized joint movement therapies that would aid anabolic cartilage reaction and hence prevent or reverse osteoarthritis progression.

• DFG Programme: Research Grants