Synergy between Piezo1 and Piezo2 channels confers high-strain mechanosensitivity to articular cartilage

Abstract

Diarthrodial joints are essential for load bearing and locomotion. Physiologically, articular cartilage sustains millions of cycles of mechanical loading. Chondrocytes, the cells in cartilage, regulate their metabolic activities in response to mechanical loading. Pathological mechanical stress can lead to maladaptive cellular responses and subsequent cartilage degeneration. We sought to deconstruct chondrocyte mechanotransduction by identifying mechanosensitive ion channels functioning at injurious levels of strain. We detected robust expression of the recently identified mechanosensitive channels, PIEZO1 and PIEZO2. Combined directed expression of Piezo1 and -2 sustained potentiated mechanically induced Ca 2+ signals and electrical currents compared with single-Piezo expression. In primary articular chondrocytes, mechanically evoked Ca 2+ transients produced by atomic force microscopy were inhibited by GsMTx4, a PIEZO-blocking peptide, and by Piezo1-or Piezo2-specific siRNA. We complemented the cellular approach with an explant-cartilage injury model. GsMTx4 reduced chondrocyte death after mechanical injury, suggesting a possible therapy for reducing cartilage injury and posttraumatic osteoarthritis by attenuating Piezo-mediated cartilage mechanotransduction of injurious strains.A rticular cartilage is a hydrated connective tissue that supports loads and minimizes friction in the diarthrodial joints. It has a highly differentiated extracellular matrix (ECM) composed primarily of type II collagen, the large aggregating proteoglycan, aggrecan, and water. Chondrocytes are the only cells in cartilage and are responsible for maintaining and remodeling cartilage through a homeostatic balance of anabolic and catabolic activities. Under normal physiologic conditions, chondrocytes are exposed to millions of cycles of mechanical loading per year (1). These mechanical signals play an important role in regulating chondrocyte anabolic and biosynthetic activity, as evidenced by cartilage atrophy following periods of disuse or immobilization (2-7). However, under abnormal loading conditions (e.g., due to obesity, trauma, or joint instability), mechanical factors play a critical role in the onset and progression of osteoarthritis (1). Such "injurious" loading has been modeled in vitro using explant culture systems that replicate many of the early cellular and molecular events characteristic of osteoarthritis (8). Osteoarthritis is a painful and debilitating disease of weight-bearing joints that affects over 26 million people in the United States (9) with posttraumatic arthritis being responsible for ∼12% of the incidence of osteoarthritis (10).Despite the critical importance of mechanical loading in health and disease of synovial joints, the mechanisms of mechanotransduction of chondrocytes are not fully understood and are likely to differ under physiologic and pathologic conditions (11)(12)(13)(14). Although many different mechanisms have been shown to be involved in chondrocyte mechanotransduction (13,(15)(16)(17), recent st...

Endothelial cation channel PIEZO1 controls blood pressure by mediating flow-induced ATP release

“…] i elevation induced through activation of PIEZO1 is due to PIEZO1-mediated influx and that the majority of the Ca 2+ signal results from downstream amplification mechanisms (41,42). Consistent with this, we found that endothelial loss of G q /G 11 strongly inhibited flow-induced increases in [Ca 2+ ] i (17).…”

Standardized Profiling of The Membrane-Enriched Proteome of Mouse Dorsal Root Ganglia (DRG) Provides Novel Insights Into Chronic Pain

“…Therefore, they are considered as potential targets for pharmacological interventions (98,(102)(103)(104). Moreover, Piezo2 channels confer mechanosensitivity to sensory neurons (105,106) as well as Merkel cells of the skin (107,108), and articular cartilage cells (109) highlighting the applicability of our spectral library to different tissues beyond DRG. However, despite successful enrichment of membrane proteins, our spectral library (and therefore our DIA-MS results) is not complete.…”

Mechanosensory Signaling in Enterochromaffin Cells and 5-HT Release: Potential Implications for Gut Inflammation

“…In addition to the Piezo2 channels, Piezo1 mechanosensitive ion channels have recently been shown to be important for the response to static forces by GI epithelial cells (Eisenhoffer et al, 2012). In chondrocytes, Piezo1 and Piezo2 channels cooperate to produce a mechanosensitive response (Lee et al, 2014). However, it is currently not known whether Piezo1 channels are expressed in EC cells and if expressed, if they cooperate with Piezo2 channels.…”