Altered spontaneous calcium signaling of in situ chondrocytes in human osteoarthritic cartilage

Xiaoyuan Gong,Wenbin Xie,Xiang Ren,Bin Wang,Lingchuan Gu,Cheng Chen,Fuyou Wang,Liu Yang

doi:10.1038/s41598-017-17172-w

Abstract

Intracellular calcium ([Ca2+]i) signaling is an essential universal secondary messenger in articular chondrocytes. However, little is known about its spatiotemporal features in the context of osteoarthritis (OA). Herein, by examining the cartilage samples collected from patients undergoing knee arthroscopic surgery, we investigated the spatiotemporal features of spontaneous [Ca2+]i signaling in in situ chondrocytes at different OA stages. Our data showed zonal dependent spontaneous [Ca2+]i signaling in healthy cartilage samples under 4 mM calcium environment. This signal was significantly attenuated in healthy cartilage samples but increased in early-degenerated cartilage when cultured in 0 mM calcium environment. No significant difference was found in [Ca2+]i intensity oscillation in chondrocytes located in middle zones among ICRS 1–3 samples under both 4 and 0 mM calcium environments. However, the correlation was found in deep zone chondrocytes incubated in 4 mM calcium environment. In addition, increased protein abundance of Cav3.3 T-type voltage dependent calcium channel and Nfatc2 activity were observed in early-degenerated cartilage samples. The present study exhibited OA severity dependent spatiotemporal features of spontaneous [Ca2+]i oscillations of in situ chondrocytes, which might reflect the zonal specific role of chondrocytes during OA progression and provide new insight in articular cartilage degradation during OA progression.

Highlights

Osteoarthritis (OA), which involves the dysfunction of adult articular cartilage, is the most common form of joint disease with manifestations of damaged articular cartilage, and may result in arthralgia, joint deformation, and limited mobility in patients
It has been shown that chondrocytes respond to mechanical and chemical stimuli with [Ca2+]i signaling via modulating extracellular calcium influx and intracellular calcium release[6,7,8,9,10], and reflect its peri-cellular environment with repetitive spontaneous [Ca2+]i signaling when statically cultured[6,12], which plays a crucial role in regulating extracellular matrix (ECM) metabolic activity[12]
Based on the International Cartilage Research Society (ICRS) grading system, the severity of each collected human articular cartilage sample was verified by histomorphometry approaches

Summary

Introduction

Osteoarthritis (OA), which involves the dysfunction of adult articular cartilage, is the most common form of joint disease with manifestations of damaged articular cartilage, and may result in arthralgia, joint deformation, and limited mobility in patients. It has been shown that chondrocytes respond to mechanical and chemical stimuli with [Ca2+]i signaling via modulating extracellular calcium influx and intracellular calcium release[6,7,8,9,10], and reflect its peri-cellular environment (e.g. osmotic stress, growth factors, and cytokines) with repetitive spontaneous [Ca2+]i signaling when statically cultured[6,12], which plays a crucial role in regulating ECM metabolic activity[12]. Previous studies investigating chondrocyte [Ca2+]i signaling were mainly focused on cells removed from their physiological environment, such as 2D cultures or chondrocytes/gel constructs[6,18] These studies neglected the potential role of calcium channel activity linked to ECM, as well as the specialized peri-cellular matrix (PCM) that affected chondrocyte mechanics[19].

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