Nearly half of all joint injuries result in symptomatic post-traumatic osteoarthritis (PTOA) within 5 years of injury. Supraphysiologic mechanical loading of the joint, such as that occurring from a sports injury or accident, is believed to be mechanically perceived by the chondrocytes residing within the articular cartilage, initiating a cascade of catabolic and inflammatory gene expression and the synthesis of proteases and cytokines which accelerate the cartilage degradation present in symptomatic PTOA. Despite the extensive characterization of the osteoarthritic chondrocytes present in PTOA, the mechanisms by which chondrocytes perceive excessive mechanical loading, and the pathways linking injury mechanics to catabolic gene expression, are unknown. Currently there are no disease modifying osteoarthritis drugs (DMOADs) to treat, prevent, or delay the degradation of cartilage following injury. The recently discovered Piezo channels (Piezo1 and Piezo2) are the first class of ion channels directly responsive to mechanical stimulation in mammals. Our lab found that the Piezo channels selectively transduce high cellular deformation into intracellular signals, suggesting a novel mechanism through which supraphysiologic loading may directly initiate and propagate the catabolic gene expression of PTOA. Fundamental questions remain surrounding the role of Piezo activation in the chondrocyte?s response to mechanical loading, including: what threshold for cellular deformation activates the Piezo channels and how is this deformation is perceived in a three-dimensional environment? Isolating and identifying the deformation modes of chondrocyte mechanotransduction would be a major advance in our understanding of cellular mechanotransduction and the physiology of cartilage. Additionally, the influence on gene expression of mechanically-activated Piezo channels is unknown. Overall, this proposal seeks to establish the fundamental modes of mechanical activation of Piezo channels in chondrocytes and the downstream implications of Piezo activation. Specifically, in Aim 1 we will identify the cellular deformation thresholds driving Piezo activation and how loading a biomimetic three-dimensional hydrogel system elicits chondrocyte Piezo activation.
Aim 2 will then determine the role of Piezos on mechanically-activated gene expression. Together, completing these exciting aims will be accomplished with a coordinated experimental and computational approach. Funding of this grant will provide me a multidisciplinary experience to advance my computational and experimental training in tissue engineering to that of chondrocyte mechanobiology and gene regulation.
Post-traumatic osteoarthritis is a poorly understood disease initiated by an acute joint injury, which afflicts 6 million Americans but for which there are no disease modifying drugs for treatment or prevention. As the recent discovery of the mechanically-sensitive Piezo channels is a promising mechanism by which supraphysiologic loading may alter chondrocyte homeostasis, this grant will characterize the mechanical activation of Piezo channels at the cellular and tissue level and the subsequent gene regulation initiated by Piezo activation. This work will develop a fundamental understanding of Piezo channels in chondrocyte mechanotransduction and the consequences of Piezo activation on gene expression for developing therapies to treat or prevent post- traumatic osteoarthritis.!