Mechanisms of Primary Cilia Regulating Tendon Enthesis Development and Regeneration

PROJECT SUMMARY 40% of the population over the age of 60 experiences a rotator cuff tear. The high failure rates of rotator cuff tear after surgical repair or non-surgical treatment make it a major clinical challenge. The outcome failures accompany the formation of scar tissues at the tendon-to-bone insertion (tendon enthesis) with disorganized architecture and deteriorated function. Development of effective therapeutics has been hampered by limited knowledge of enthesis development biology and mechanobiology and an incomplete understanding of endogenous mechanisms governing enthesis pathogenesis and healing. To bridge this knowledge gap, the current proposal seeks to elucidate how tendon enthesis responds to its mechanical and biochemical environment during development and healing processes. It is known that a combination of mechanical force and distinct pathways, including hedgehog (Hh) signaling, drive enthesis formation, promote remodeling of mature enthesis, and affect enthesis healing. Recently, our studies have indicated that the primary cilium, a solitary antenna protruding from mammalian cell surface, potentially functions as a hub for mechanotransduction and Hh signaling. Building on our previous work, the objective of this proposal is to gain a mechanistic understanding of the role of primary cilia in concentrating and synchronizing mechanical and Hh signals during enthesis development and healing. To achieve this objective, we will determine identities and activities of ciliated enthesis cells during enthesis development and mechanical adaptation (Specific Aim 1) and evaluate the regenerative capacity of ciliated enthesis cells for improving enthesis healing (Specific Aim 2). The approaches we will use include cilia-labeled and cilia-deleted transgenic mouse models, different established loading models, cell transplantation, and transcriptomics analysis, combined with structural, compositional, and biomechanical evaluation assays. At the conclusion of this project, we expect to identify new cilia-regulated mechano- transduction pathways during in vivo enthesis mechanical adaptation and suggest novel mechanisms by which cilia convert mechanical cues to cellular signaling events. The new findings of the role of primary cilia in enthesis healing will guide the development of novel pharmacological and mechanobiology therapeutics for treating rotator cuff tears.