Roles of Type III Collagen in the Matrix Assembly and Mechanobiology of Cartilage

ABSTRACT Osteoarthritis (OA) is characterized by the irreversible breakdown of cartilage extracellular matrix (ECM). Current regenerative strategies cannot fully restore the biomechanical functions of cartilage, as they do not fully recapitulate the collagen fibrillar architecture of native ECM. This project will study the activities of the regulatory fibril-forming type III collagen (collagen III) in directing cartilage matrix assembly and chondrocyte mechanotransduction at different stages of post-natal growth, maintenance and disease. Our central hypothesis is that collagen III regulates cartilage ECM biomechanics and chondrocyte mechanotransduction through its effects on collagen fibril assembly and integrin switching, and that loss of collagen III increases cartilage susceptibility to OA. Specifically, we will elucidate the activities of collagen III in the formation and maintenance of cartilage (Aim 1), in injury-induced cartilage degradation in OA (Aim 2), as well as in the neo-matrix assembly and chondrocyte mechanotransduction (Aim 3). In Aim 1, we will determine if loss of collagen III impairs ECM fibril assembly, pericellular matrix (PCM) integrity, chondrocyte mechanosensing and gene expression during the post-natal growth and aging. In Aim 2, we will first determine if loss of collagen III accelerates cartilage degeneration and OA progression in post-traumatic OA induced by the following destabilization of the medial meniscus surgery (DMM model). We will then determine if collagen III delays the degradation of collagen II and aggrecan in response to inflammatory factors known to drive OA progression. In Aim 3, we will first determine if collagen III regulates the assembly of neo-matrix synthesized by chondrocytes cultured in 3D hydrogel under the stimulation of dynamic loading. Next, we will delineate the effects of collagen III on regulating the integrin switching of chondrocytes and downstream mechanosensitive pathways, with a focus on integrin α11. To elucidate the role of collagen III in cartilage, a number of innovative approaches will be used. We generated a novel inducible collagen III deficient (i.e., Col3a1F/+, Col3a1F/F) mouse model to study the dose-dependent effects of collagen III by temporal targeting of collagen III in cartilage. We will apply a multidisciplinary analysis paradigm that integrates atomic force microscopy (AFM)-nanomechanical tests, immunofluorescence imaging and laser capture microdissection. These techniques will enable us to study the impact of collagen III on cartilage composition, structure, mechanics and cell mechanotransduction, and to determine mechanisms by which it regulates matrix remodeling and mechanosensation. Successful completion of this study will establish collagen III as an essential constituent responsible for ECM structural integrity and cell mechanotransduction of cartilage. Outcomes will provide a new basis for improving cartilage tissue engineering using collagen III-based biomaterials and elucidate new collagen III-dependent mechanisms to serve as targets for OA intervention.