Inflammatory signaling sensitizes Piezo1 mechanotransduction in articular chondrocytes as a pathogenic feed-forward mechanism in osteoarthritis.

Abstract

Osteoarthritis (OA) is a painful and debilitating condition of synovial joints without any disease-modifying therapies [A. M. Valdes, T. D. Spector, <i>Nat. Rev. Rheumatol.</i> 7, 23-32 (2011)]. We previously identified mechanosensitive PIEZO channels, PIEZO1 and PIEZO2, both expressed in articular cartilage, to function in chondrocyte mechanotransduction in response to injury [W. Lee <i>et al.</i>, <i>Proc. Natl. Acad. Sci. U.S.A.</i> 111, E5114-E5122 (2014); W. Lee, F. Guilak, W. Liedtke, <i>Curr. Top. Membr.</i> 79, 263-273 (2017)]. We therefore asked whether interleukin-1-mediated inflammatory signaling, as occurs in OA, influences <i>P</i>iezo gene expression and channel function, thus indicative of maladaptive reprogramming that can be rationally targeted. Primary porcine chondrocyte culture and human osteoarthritic cartilage tissue were studied. We found that interleukin-1α (IL-1α) up-regulated Piezo1 in porcine chondrocytes. Piezo1 expression was significantly increased in human osteoarthritic cartilage. Increased Piezo1 expression in chondrocytes resulted in a feed-forward pathomechanism whereby increased function of Piezo1 induced excess intracellular Ca²⁺ at baseline and in response to mechanical deformation. Elevated resting state Ca²⁺ in turn rarefied the F-actin cytoskeleton and amplified mechanically induced deformation microtrauma. As intracellular substrates of this OA-related inflammatory pathomechanism, in porcine articular chondrocytes exposed to IL-1α, we discovered that enhanced Piezo1 expression depended on p38 MAP-kinase and transcription factors HNF4 and ATF2/CREBP1. CREBP1 directly bound to the proximal <i>PIEZO1</i> gene promoter. Taken together, these signaling and genetic reprogramming events represent a detrimental Ca²⁺-driven feed-forward mechanism that can be rationally targeted to stem the progression of OA.