Strain uses gap junctions to reverse stimulation of osteoblast proliferation by osteocytes

Connexin 43 in the function and homeostasis of osteocytes: a narrative review

Background and Objective

Connexin 43 (Cx43) is the main gap junction (GJ) protein and hemichannel protein in bone tissue. It is involved in the formation of hemichannels and GJs and establishes channels that can communicate directly to exchange substances and signals, affecting the structure and function of osteocytes. CX43 is very important for the normal development of bone tissue and the establishment and balance of bone reconstruction. However, the molecular mechanisms by which CX43 regulates osteoblast function and homeostasis have been less well studied, and this article provides a review of research in this area.

Methods

We searched the PubMed, EMBASE, Cochrane Library, and Web of Science databases for studies published up to June 2023 using the keywords Connexin 43/Cx43 and Osteocytes. Screening of literatures according to inclusion and exclusion guidelines and summarized the results.

Key Content and Findings

Osteocytes, osteoblasts, and osteoclasts all express Cx43 and form an overall network through the interaction between GJs. Cx43 is not only involved in the mechanical response of bone tissue but also in the regulation of signal transduction, which could provide new molecular markers and novel targets for the treatment of certain bone diseases.

Conclusions

Cx43 is expressed in osteoblasts, osteoclasts, and osteoclasts and plays an important role in regulating the function, signal transduction, and mechanotransduction of osteocytes. This review offers a new contribution to the literature by summarizing the relationship between Cx43, a key protein of bone tissue, and osteoblasts.

Inhibition of gap junction communication between cells can induce apoptosis of corpus cavernosum smooth muscle in guinea pigs

In this study, we aimed to investigate the effect of gap junction (GJ) on apoptosis of smooth muscle. Forty adult male guinea pigs were randomly divided into four groups with 10 guinea pigs in each group. Adeno-associated virus (AAV) and Gap27 were injected at the root of the corpus cavernosum. Two weeks later, the corpus cavernosum tissue was taken to be tested. The expression of Cx43 and α-SMC protein was detected by immunofluorescence and Western blotting. The content of corpus cavernosum smooth muscle was detected by Masson trichrome staining. Apoptosis was detected by TUNEL staining and Western blotting. The results showed that Gap27 did not affect Cx43 but decreased the expression of smooth muscle. The results of TUNEL staining and detection of apoptosis-related proteins showed that apoptosis was induced by Gap27. In addition, we found that corpus cavernosum injection of AAV could induce obvious apoptosis. In this study, we examined the effect of inhibition of gap junction on smooth muscle, and suggested that the decrease of gap junction function may be a potential mechanism of smooth muscle apoptosis.

Enhanced gene delivery in tumor cells using chemical carriers and mechanical loadings

Intracellular delivery of DNA is considered a challenge in biological research and treatment of diseases. The previously reported transfection rate by commercially available transfection reagents in cancer cell lines, such as the mouse lung tumor cell line (TC-1), is very low. The purpose of this study is to introduce and optimize an efficient gene transfection method by mechanical approaches. The combinatory transfection effect of mechanical treatments and conventional chemical carriers is also investigated on a formerly reported hard-to-transfect cell line (TC-1). To study the effect of mechanical loadings on transfection rate, TC-1 tumor cells are subjected to uniaxial cyclic stretch, equiaxial cyclic stretch, and shear stress. The TurboFect transfection reagent is exerted for chemical transfection purposes. The pEGFP-N1 vector encoding the green fluorescent protein (GFP) expression is utilized to determine gene delivery into the cells. The results show a significant DNA delivery rate (by ~30%) in mechanically transfected cells compared to the samples that were transfected with chemical carriers. Moreover, the simultaneous treatment of TC-1 tumor cells with chemical carriers and mechanical loadings significantly increases the gene transfection rate up to ~ 63% after 24 h post-transfection. Our results suggest that the simultaneous use of mechanical loading and chemical reagent can be a promising approach in delivering cargoes into cells with low transfection potentials and lead to efficient cancer treatments.

Diet and Exercise: a Match Made in Bone

PURPOSE OF REVIEW

Multiple dietary components have the potential to positively affect bone mineral density in early life and reduce loss of bone mass with aging. In addition, regular weight-bearing physical activity has a strong positive effect on bone through activation of osteocyte signaling. We will explore possible synergistic effects of dietary components and mechanical stimuli for bone health by identifying dietary components that have the potential to alter the response of osteocytes to mechanical loading.

RECENT FINDINGS

Several (sub)cellular aspects of osteocytes determine their signaling towards osteoblasts and osteoclasts in response to mechanical stimuli, such as the osteocyte cytoskeleton, estrogen receptor α, the vitamin D receptor, and the architecture of the lacunocanalicular system. Potential modulators of these features include 1,25-dihydroxy vitamin D3, several forms of vitamin K, and the phytoestrogen genistein. Multiple dietary components potentially affect osteocyte function and therefore may have a synergistic effect on bone health when combined with a regime of physical activity.

Strain uses gap junctions to reverse stimulation of osteoblast proliferation by osteocytes

Identifying mechanisms by which cells of the osteoblastic lineage communicate in vivo is complicated by the mineralised matrix that encases osteocytes, and thus, vital mechanoadaptive processes used to achieve load-bearing integrity remain unresolved. We have used the coculture of immunomagnetically purified osteocytes and primary osteoblasts from both embryonic chick long bone and calvariae to examine these mechanisms. We exploited the fact that purified osteocytes are postmitotic to examine both their effect on proliferation of primary osteoblasts and the role of gap junctions in such communication. We found that chick long bone osteocytes significantly increased basal proliferation of primary osteoblasts derived from an identical source (tibiotarsi). Using a gap junction inhibitor, 18β-glycyrrhetinic acid, we also demonstrated that this osteocyte-related increase in osteoblast proliferation was not reliant on functional gap junctions. In contrast, osteocytes purified from calvarial bone failed to modify basal proliferation of primary osteoblast, but long bone osteocytes preserved their proproliferative action upon calvarial-derived primary osteoblasts. We also showed that coincubated purified osteocytes exerted a marked inhibitory action on mechanical strain-related increases in proliferation of primary osteoblasts and that this action was abrogated in the presence of a gap junction inhibitor. These data reveal regulatory differences between purified osteocytes derived from functionally distinct bones and provide evidence for 2 mechanisms by which purified osteocytes communicate with primary osteoblasts to coordinate their activity.