Investigation in the role of L-type Ca2+ channel CaV1.2 in Achilles tendinopathy - PROJECT SUMMARY The tensile-bearing Achilles tendon is highly prone to acute- or overuse-induced injuries that lead to chronic tendon degeneration and heterotopic ossification (HO) called tendinopathy. Achilles tendinopathy is often associated with pain and disability with high socio-economic costs. The current standard of care for treating Achilles tendinopathy does not result in effective long-term functional recovery, although it provides short-term pain relief. The pathogenetic mechanisms of Achilles tendinopathy are largely unknown. Identification of early mediators in tendon in response to injury and elucidation of the cellular and molecular mechanisms underlying the pathogenesis of this disease will facilitate the development of new therapeutic strategies. Using novel transgenic mouse models with CaV1.2 wildtype or a gain-of-function mutant, we observed potent regulatory effects of increased Ca2+ influx through CaV1.2 on the development of Achilles tendinopathy with chondrocyte/osteoblast differentiation and ectopic bone formation. Using a reporter mouse line, our recent study found that expression of the CaV1.2 channel in tendon fibroblasts is robust during development but very restricted in adult Achilles tendons. In contrast, our preliminary data show substantial upregulation of Cav1.2 expression in response to cytokine injection (TNF-α or IL-1β) or Achilles partial transection, an injury that induces Achilles tendinopathy in wildtype mice. Substantial CaV1.2 channel expression is also observed in human diseased Achilles tendon by immunohistochemistry analysis. These new findings provide a rational linkage between high CaV1.2 expression and Achilles tendinopathy. Our population health studies of the TriNetX database further provide clinical evidence suggesting that aberrant CaV1.2 expression/activity is a potential molecular mechanism underlying Achilles tendinopathy. Therefore, we propose to test the overall hypothesis that increased Ca2+ influx through CaV1.2 acts as an early pathological mediator of Achilles tendinopathy; decrease of Ca2+ influx through CaV1.2 with L-type Ca2+ channel blockers (CCBs), conditional ablation of CaV1.2 or targeting a Ca2+-dependent signaling cascade downstream of CaV1.2 in tendon cells will ameliorate Achilles tendinopathy. To test this hypothesis, we propose three Specific Aims. In Aim 1, we will identify the tendon-specific role of Ca2+ signaling through CaV1.2 in regulating endochondral differentiation in tendon during AT development. In Aim 2, we will investigate CaV1.2 expression, the Ca2+ response and calcineurin activation in Achilles tendon in response to inflammation and mechanical stimulation. In Aim 3, we will evaluate the ability of L-type CCBs as a pharmacologic treatment to prevent and ameliorate Achilles tendinopathy in mice. We propose to fully characterize CaV1.2 gain-of-function and loss-of-function mouse models, the CaV1.2 reporter mouse line, the injury-induced mouse model, and surgically excised tendinopathy Achilles tissues from patients together with Ca2+ imaging and pharmacological approaches to address these aims. The findings of this proposal could provide a scientific rationale for repurposing the use of FDA-approved generic L-type CCBs to alleviate or treat Achilles tendinopathy.
