Deconstructing Cartilage Mechanotransduction by Piezo Channels

骨关节炎（OA）是最常见的退行性关节疾病，影响超过3.5亿人 国际吧沿着炎症和疼痛，OA的一个标志是关节软骨（AC）的降解， 覆盖并促进关节弯曲的无血管组织。AC可承受数百万次循环 软骨细胞是组织中唯一的细胞基质， 通过机械门控离子通道。Piezo 1是软骨细胞中高表达的钙离子通道 它可以通过机械加载或与Yoda 1（一种Piezo 1特异性激动剂）化学激活。我们实验室 最近证实，骨关节炎软骨和白细胞介素-1 α（IL-1α）中Piezo 1表达升高， OA中存在的促炎细胞因子驱动Piezo 1的上调。Piezo 1表达增加 在IL-1α刺激的软骨细胞中，导致细胞内钙瞬变持续增加， 肌动蛋白细胞骨架的稀薄化。在此，我们的总体目标是了解Piezo 1介导的变化 在软骨细胞生理学中，在高度炎症和损伤期间， 加载中机械负荷和随后通过钙离子通道的钙内流导致钙- 介导的肌动蛋白重置（CaAR）和核软化通过染色质重塑。CaAR是一种瞬时细胞 在这种反应中，F-肌动蛋白从细胞周边迅速解聚，并在细胞周围聚合。 原子核产生一个保护性的动力屏障，保护原子核不受机械变形的影响。核 由异染色质减少驱动的软化被证明是Piezo 1依赖性的，并且在以下方面起作用： 在高机械应变期间最小化DNA损伤。虽然CaAR和核软化 被独立地表征为机械保护反应，它们在介导 在机械加载期间的核机械保护和转录调节还有待探索。 核骨架和细胞骨架的接头（LINC）复合物物理地束缚核纤层和细胞骨架。 肌动蛋白细胞骨架，并且已知它在染色质重塑中发挥作用。鉴于结构和功能的 LINC复合物，它是一个强有力的候选人，介导染色质液化过程中核软化， CaAR期间的转录反应。总之，这些发现表明，Piezo 1介导的CaAR可以 通过LINC复合物通过染色质重塑改变核机械特性，并导致 转录变化可能最终影响OA期间软骨细胞的命运。因此，我们假设 如OA软骨中所见，Piezo 1表达升高导致CaAR反应延长， 通过LINC复合物触发染色质液化，从而导致核软化和促细胞增殖的增加。 IL-1α刺激的软骨细胞中炎性基因表达。

Osteoarthritis (OA) is the most common degenerative joint disease, affecting more than 350 million people worldwide. Along with inflammation and pain, a hallmark of OA is the degradation of articular cartilage (AC), an avascular tissue that coats and facilitates the bending of diarthrodial joints. AC withstands millions of cyclic mechanical loads annually, and chondrocytes, the only cellular substrate in the tissue, sense these loads through mechanically gated ion channels. Piezo1 is a highly expressed calcium ion channel in chondrocytes that can be activated through mechanical loading or chemically with Yoda1, a Piezo1-specific agonist. Our lab recently demonstrated that Piezo1 expression is elevated in osteoarthritic cartilage and interleukin-1α (IL-1α), a pro-inflammatory cytokine present in OA, drives the upregulation Piezo1. The increased expression of Piezo1 in IL-1α-challenged chondrocytes led to a sustained increased intracellular calcium transient and the rarefication of the actin cytoskeleton. Herein, our overall goal is to understand how Piezo1-mediated changes in chondrocyte physiology contribute to the progression of OA during periods of high inflammation and injurious loading. Mechanical loading and subsequent calcium influx through calcium ion channels leads Calcium- mediated Actin Reset (CaAR) and nuclear softening via chromatin remodeling. CaAR is a transient cell response in which F-actin rapidly depolymerizes from the periphery of the cell and polymerizes around the nucleus to create a protective kinetic barrier that shields the nucleus from mechanical deformation. Nuclear softening driven by a decrease in heterochromatin was shown to be Piezo1 dependent and play a role in minimizing DNA damage during periods of high mechanical strain. While CaAR and nuclear softening have been characterized independently as mechanoprotective responses, their potential interplay in mediating nuclear mechanoprotection and regulation of transcription during mechanical loading has yet to be explored. The Linker of Nucleoskeleton and Cytoskeleton (LINC) complex physically tethers the nuclear lamina and the actin cytoskeleton, and it is known play a role in chromatin remodeling. Given the structure and function of the LINC complex, it is a strong candidate for mediating chromatin fluidification during nuclear softening and transcriptional responses during CaAR. Together these findings suggest that Piezo1-mediated CaAR could alter nuclear mechanical properties through chromatin remodeling via the LINC complex and lead to transcriptional changes that could ultimately affect chondrocyte cell fate during OA. Therefore, we hypothesize that elevated Piezo1 expression, as seen in OA cartilage, leads to a prolonged CaAR response which in turn triggers chromatin fluidification via the LINC complex thereby leading to an increase nuclear softening and pro- inflammatory gene expression in IL-1α-challenged chondrocytes.