Background/Purpose: It is believed that chondrocytes in cartilage do not connect each other, as they are isolated inside their lacunae separated from each other by a distance between 5 to 60µm. In the same lacuna can co-exit several chondocytes interacting between them. However, how the chondrocytes from different lacuna interact between each other and timely respond to physical or chemicals stimuli, are largely unknown.

Methods: Scanning Electron Microscope. Immunofluorescence and Immunohistochemistry assays. For total RNA isolation: TRIZOL® method. Electrophysiology techniques: Dual Voltage-clamp methods, whole-cell/perforated patch experiments and study of glucose and oligonucleotides transference. Transwell co-culture system and mass spectrometry (LTQ Orbitrap). SILAC^® Dulbecco’s Modiffied Eagle’s Medium containing L-lisina [¹³C₆] and/or L-arginina [¹³C₆, ¹⁵N₄]. Co-immunoprecipitation experiments. In-gel digestion of immunoprecipitated proteins separated by SDS-PAGE were analysed using the nano-liquid chromatography coupled to mass spectrometry (MALDI-TOF/TOF). The identification of proteins was performed using ProteinPilot™ 3.0 Software.

Results:

We have found that articular chondrocytes have long cytoplasmic arms, between 5 to 200 µm in length, that travel across the ECM and physically connect the cytoplasm of cells located in distant lacuna. Our results suggest that chondrocytes communicate through gap junctions (GJ) channels form by different types of connexins. Patch-clamp methods demonstrate that cells interchange small molecules of nucleic acids through GJ channels form by Cx43. Transwell co-culture system combine with mass spectrometry analysis have revealed that the cytoplasmic projections and GJ play a nutritional role by exchange of glucose and amino acids. On the other hand, alteration on connexin protein levels and longer cytoplasmic arms were found in cartilage from patients with osteoarthrosis (OA).

Conclusion: The results here presented demonstrated that cells in cartilage are physically connected and cell-to-cell communication occurs through GJ channels.  These results will radically change the point of view of structural organization of cartilage, mechanotransduction, chondrocytes metabolism and cell signalling. Our results suggest that altered connexin channel functions are probably involved in the physiopathology of OA. These results will likely lead to the development of new therapeutic targets for OA.

ACR Meeting Abstracts - https://acrabstracts.org/abstract/long-distance-physical-connections-between-chondrocytes-cell-to-cell-communication-within-articular-cartilage/