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 全世界。除了炎症和疼痛，骨性关节炎的一个特征是关节软骨(AC)的退化，以及 覆盖腹股沟关节并促进其弯曲的无血管组织。交流经得起数百万次循环 每年的机械负荷，而软骨细胞，组织中唯一的细胞底物，感受到这些负荷 通过机械门控离子通道。PIEZO1是软骨细胞高表达的钙离子通道 它可以通过机械负载或用Yoda1(一种Piezo1特异性激动剂)化学激活。我们的实验室 最近发现，Piezo1在骨关节炎软骨和白细胞介素1α(IL-1α)中的表达升高，是一种 促炎细胞因子存在于骨性关节炎中，驱动Piezo1的上调。Piezo1基因的高表达 在IL-1、α攻击的软骨细胞中，细胞内钙瞬变持续增加， 肌动蛋白细胞骨架的稀有化。在这里，我们的总体目标是了解Piezo1介导的变化 在高度炎症和损伤性时期，软骨细胞的生理学参与了骨性关节炎的进展 正在装车。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)和染色质重塑导致的核软化。CAAR是一种瞬变细胞 F-肌动蛋白从细胞外围快速解聚并在细胞周围聚合的反应。 产生保护性的动能屏障，保护原子核不受机械变形的影响。核子 由异染色质减少驱动的软化被证明是Piezo1依赖的，并在 在高机械应变期间将DNA损伤降至最低。而CAAR和核软化 被独立地描述为机械保护反应，它们在中介中的潜在相互作用 机械加载过程中的核机械保护和转录调控还有待研究。 核骨架和细胞骨架(LINC)复合体的连接物物理上系住了核层和 肌动蛋白是细胞骨架，已知它在染色质重塑中起作用。在给出了 LINC复合体，是介导核软化和核染色质流态化的有力候选者。 CAAR过程中的转录反应。总之，这些发现表明，Piezo1介导的CAAR可以 通过LINC复合体通过染色质重塑改变核力学性质并导致 在骨性关节炎过程中可能最终影响软骨细胞命运的转录变化。因此，我们假设 就像在骨性关节炎软骨中看到的那样，Piezo1的表达增加会导致CAAR反应延长，进而 通过LINC复合体触发染色质流态化，从而导致核软化和促进- IL-1α攻击软骨细胞中炎性基因的表达

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.