Molecular Engineering of Cartilage PCM Mechanotransduction in Osteoarthritis Using Biomimetic Proteoglycans

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Abstract Regeneration of osteoarthritic cartilage has been a largely unmet biomedical challenge for the past fifty years. Numerous strategies are being employed to harness the synthetic power of cells to generate new extracellular matrix in the hope of reversing the pain and dysfunction associated with osteoarthritis (OA), in keeping with the mission of the NIH to seek fundamental knowledge about of living systems and the application of that knowledge to enhance health, lengthen life, and reduce illness and disability. Of particular interest is the emerging role of the pericellular matrix (PCM), the region immediately surrounding the chondrocyte, due to its demonstrated importance in mediating chondrocyte mechanotransduction in both healthy and OA cartilage. In OA, degeneration of the PCM is one leading event of disease initiation, contributing to disrupted chondrocyte mechanotransduction and irreversible cartilage degradation. Thus, if we can engineer the properties of the PCM, there is a potential for us to modulate chondrocyte mechanosensitive activities, and in turn, to promote cartilage regeneration and/or to attenuate osteoarthritic cartilage degeneration. Our biomimetic proteoglycans (BPGs) have the niche effect of engineering cartilage PCM. We chemically end-attached 7-8 chondroitin sulfate glycosaminoglycans (CS-GAGs) to a poly(acrylic acid) (PAA) core (Mw ~10 kDa), resulting in a biomimetic proteoglycan, BPG10, with a bottle-brush nanostructure mimicking the native aggrecan. When infiltrated into bovine cartilage explants in vitro or intra-articularly injected into rabbit knees in vivo, BPG10 was preferentially localized in the PCM. This localization led to a significant increase in the micromodulus of the PCM in vitro, and in turn, significantly enhanced chondrocyte intracellular calcium signaling activities. The role of BPG10 is also relevant to OA. When infiltrated into human OA cartilage, BPG10 was also localized in the PCM, and enhanced the local PCM modulus, indicating a potential for restoring degenerative PCM and rescuing disrupted chondrocyte mechanosensitive activities. Given that the synthetic PAA core is not susceptible to physiologic enzymes, as are natural proteoglycans, BPG10 could also be resistant to chondrocyte catabolism in vivo. Our central hypothesis is that biomimetic proteoglycans will molecularly engineer the PCM, increasing the micromodulus of the PCM through interactions with native PCM molecules, thus promoting chondrocyte mechanotransduction and attenuating OA-induced cartilage degeneration. To test this hypothesis, we will: (1) study the physical interactions between BPG10 and cartilage matrix biomolecules; (2) determine if BPG10 augments the neo-PCM of chondrocytes in 3D culture and the PCM of degrading cartilage explants, and thus, modulates chondrocyte mechanotransduction and metabolic activities and (3) test if intra-articular administration of BPG10 attenuates the progression of OA in rabbits in vivo. In these studies, individual CS-GAGs will be tested as a control to examine the role of BPG10's unique structure.