Calcium signaling of in situ chondrocytes in articular cartilage under compressive loading: Roles of calcium sources and cell membrane ion channels

Abstract

Mechanical loading on articular cartilage can induce many physical and chemical stimuli on chondrocytes residing in the extracellular matrix (ECM). Intracellular calcium ([Ca ] ) signaling is among the earliest responses of chondrocytes to physical stimuli, but the [Ca ] signaling of in situ chondrocytes in loaded cartilage is not fully understood due to the technical challenges in [Ca ] imaging of chondrocytes in a deforming ECM. This study developed a novel bi-directional microscopy loading device that enables the record of transient [Ca ] responses of in situ chondrocytes in loaded cartilage. It was found that compressive loading significantly promoted [Ca ] signaling in chondrocytes with faster [Ca ] oscillations in comparison to the non-loaded cartilage. Seven [Ca ] signaling pathways were further investigated by treating the cartilage with antagonists prior to and/or during the loading. Removal of extracellular Ca ions completely abolished the [Ca ] responses of in situ chondrocytes, suggesting the indispensable role of extracellular Ca sources in initiating the [Ca ] signaling in chondrocytes. Depletion of intracellular Ca stores, inhibition of PLC-IP pathway, and block of purinergic receptors on plasma membrane led to significant reduction in the responsive rate of cells. Three types of ion channels that are regulated by different physical signals, TRPV4 (osmotic and mechanical stress), T-type VGCCs (electrical potential), and mechanical sensitive ion channels (mechanical loading) all demonstrated critical roles in controlling the [Ca ] responses of in situ chondrocyte in the loaded cartilage. This study provided new knowledge about the [Ca ] signaling and mechanobiology of chondrocytes in its natural residing environment. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:730-738, 2018.

Spontaneous calcium signaling of cartilage cells: from spatiotemporal features to biophysical modeling

“…These pathways can be grouped into 3 categories: extracellular Ca 2+ source, intracellular Ca 2+ store, and Ca 2+ ion channels on the plasma membrane. Several studies concluded that the stimulated calcium signaling in chondrocytes required an extracellular Ca 2+ source (13, 14). Previously, we also found that no calcium signaling can be initiated in osteocytes or osteoblasts when placing the cells in Ca 2+ ‐free medium.…”

Bioinformatics analysis reveals different gene expression patterns in chondrocytes from knee and finger joints: implications for the effect of mechanical stress in the osteoarthritic development

“…Meanwhile, the MAPK signaling pathway has been found to receive, transduce and convey mechanical information to the chondrocyte interior [37], which also evidenced by the enrichment of negative regulation of stress-activated MAPK cascade in the overlapped genes. Intracellular calcium signaling is among the earliest responses of chondrocytes to physical stimuli and plays an important role in the mechanobiology of chondrocytes in a natural residing environment [38]. Here, calcium ion binding was also found to be the significant enrichment for the DEGs, which suggested the role of calcium ion channel and downstream pathway in the mechanical stress-induced osteoarthritic development.…”

Mechanobiological modulation of in situ and in vivo osteocyte calcium oscillation by acoustic radiation force

“…A few studies have found [Ca 2+ ] responses under various mechanical stimulations . One of our previous studies utilized FLIPUS to induce Ca 2+ influx in vitro .…”