Connexin43 hemichannels mediate small molecule exchange between chondrocytes and matrix in biomechanically-stimulated temporomandibular joint cartilage

Abstract

Objective Connexin (Cx) 43 hemichannels play a role in mechanotransduction. This study was undertaken in order to determine if Cx43 hemichannels were activated in rat temporomandibular joint (TMJ) chondrocytes under mechanical stimulation. Methods Sprague-Dawley rats were stimulated dental-mechanically. Cx43 expression in rat TMJ cartilage was determined with immunohistochemistry and real-time PCR, and Cx43 hemichannel opening was evaluated by the extra- and intracellular levels of prostaglandin E2 (PGE2). Both primary rat chondrocytes and ATDC5 cells were treated with fluid flow shear stress (FFSS) to induce hemichannel opening. The Cx43 expression level was then determined by real-time PCR or western blotting, and the extent of Cx43 hemichannel opening was evaluated by measuring both PGE2 release and cellular dye uptake. Results Cx43 expression and intra- and extracellular PGE2 levels were increased in mechanically-stimulated rat TMJ cartilage compared to the unstimulated control. The FFSS treatment increased Cx43 expression and induced Cx43 hemichannel opening in primary rat chondrocytes and ATDC5 cells indicated by enhanced PGE2 release and dye uptake. Furthermore, the Cx43 hemichannel opening could be blocked by the addition of 18β-glycyrrhetinic acid, a connexin channel inhibitor, Cx43-targeting siRNA, or by withdrawal of FFSS stimulation. The migration of cytosolic Cx43 protein to the plasma membrane in ATDC5 cells was still significant after 8h post 2-h FFSS treatment, and the Cx43 protein level was still high at 48h which returned to control levels at 72h after treatment. Conclusion Cx43 hemichannels are activated and mediate small molecule exchange between TMJ chondrocytes and matrix under mechanical stimulation.

Unilateral anterior crossbite induces aberrant mineral deposition in degenerative temporomandibular cartilage in rats

“…UAC and sham procedures were approved by the Ethics Committee of the Fourth Military Medical University and applied to the rats as we previously described 34,35 . Briefly, after each rat was anesthetized by a single intraperitoneal injection of 1% pentobarbital sodium (0.35 ml/100 g weight), a small metal tube (length = 2.5 mm, inside diameter = 3 mm) was bonded to the left maxillary incisor [Fig.…”

“…Aberrant dental occlusion in human can induce degeneration of temporomandibular joint (TMJ) 29–33 . Recently, we have developed a unilateral anterior crossbite (UAC) procedure that could induce OA-like changes in the TMJ cartilage of rats and mice 34–37 . These models mimic human conditions of malocclusion and allow studies on the progression of cartilage/bone changes following the mechanical defects.…”

Physiological roles of connexins and pannexins in reproductive organs

“…Therefore, it could be postulated that, through the formation of functional hemichannels, Cxs could participate in the regulation of intraluminal epididymis medium composition. In support of this hypothesis, it is interesting to note that Cx43-based hemichannels were found to release prostaglandin E2 [82], a prostaglandin synthesized by the epididymis basal cells to act on principal cells [83,84]. The role of these hemichannels remains to be elucidated in reproductive organs.…”

Gap Junction Coupled Cells, Barriers and Systemic Inflammation

“…The importance of the effect is seen in the chondrocytes in joints, that are connected to each other via cell-to-cell interactions and form functional gap junctions that express Cx43 [32]. They can sustain the propagation of intercellular Ca 2+ waves in rabbits, humans, and equines [33,34] and form hemichannels that exchange signals within the extracellular space [35,36]. In the adult cartilage, chondrocytes exist as individual cells embedded in the extracellular matrix, and gap junctions are mainly expressed by the flattened chondrocytes facing the outer cartilage layer where intercellular communication occurs [37].…”