Blocking connexin43 hemichannels prevents TGF‐β2 upregulation and epithelial–mesenchymal transition in retinal pigment epithelial cells

Abstract

Epithelial–mesenchymal transition (EMT) occurs when polarised epithelial cells change to a mesenchymal phenotype. EMT plays a role in several chronic conditions, including ocular diseases with retinal pigment epithelium (RPE) EMT associated with retinal diseases such as diabetic retinopathy (DR). Here, EMT results in breakdown of the blood‐retinal barrier (BRB) leading to sub‐retinal fluid deposition and retinal detachment. Previous studies have shown that blocking connexin43 (Cx43) hemichannels can protect against RPE BRB breakdown, but the underlying mechanism is unknown. To determine whether open Cx43 hemichannels may enable EMT of RPE cells and thus result in BRB breakdown, ARPE‐19 cells were either challenged with high glucose plus the inflammatory cytokines IL‐1β and TNF‐α (HG + Cyt) to simulate DR or treated with the Cx43 hemichannel blocker tonabersat alongside the HG + Cyt challenge. HG + Cyt induced a morphological change in RPE cells to a fibroblastic phenotype with a corresponding decrease in epithelial zonular occludens‐1 and an increase in the fibroblastic marker α‐SMA. The HG + Cyt challenge also induced loss of transepithelial electrical resistance while increasing dye passage between RPE cells. All of these changes were significantly reduced with tonabersat treatment, which also prevented HG + Cyt‐induced transforming growth factor‐β2 (TGF‐β2) release. In conclusion, Cx43 hemichannel block with tonabersat attenuated both TGF‐β2 release and RPE EMT under disease‐mimicking conditions, offering the potential to ameliorate the progression of EMT‐associated retinal diseases.

Effects of the Calix[4]arene Derivative Compound OTX008 on High Glucose-Stimulated ARPE-19 Cells: Focus on Galectin-1/TGF-β/EMT Pathway

“…Indeed, here, it is shown that the canonical markers of EMT such as, for instance, ACTA2 and FnI [ 10 , 30 ] are reduced by the treatment of the cells with OTX008. Worthy of note is that the EMT of polarized RPE cells is a process activated under pathological circumstances, such as inflammation, wound healing, and carcinogenesis, enabling epithelial cells to obtain an enhanced migration ability and increase their production of extracellular matrix components, leading to RPE dysfunction [ 31 ]. Loss of RPE functional integrity is the base for development of numerous retinal diseases, including inherited cone-rod degenerations, inherited macular degeneration, age-related macular degeneration, and proliferative vitreoretinopathy [ 28 ].…”

Cx43 Facilitates Mesenchymal Transition of Endothelial Cells Induced by Shear Stress

“…In the present study, we also found that the expression of Cx43 was increased in ECs induced by low laminar shear stress. It was widely depicted that Cx43 accelerated the EMT process [ 37 , 38 ], in which TGF signaling pathways play a vital role [ 39 ]. It is notable that TGF signaling pathways have been well established in the initiation of EndMT process [ 40 ].…”

Connexin 43: A Target for the Treatment of Inflammation in Secondary Complications of the Kidney and Eye in Diabetes

“…Connexin hemichannel blockers represent a promising future therapeutic option in the treatment of nephropathy and retinopathy. Research to date is persuasive and highlights promising beneficial effects of Cx43 inhibition on inflammation, tissue integrity and fibrosis [ 180 , 201 , 202 ]. However, the field requires further research to determine the effectiveness and efficacy of drugs and the long-term benefits.…”

“…As with onset and progression of tubulointerstitial fibrosis [ 167 ], the breakdown of the retinal pigment epithelium is associated with disassembly of junction proteins, namely ZO-1, E-cadherin, β-catenin and occludin and ultimately induction of EMT [ 179 ]. In fact, EMT of RPE cells is considered an initiating trigger in the loss of epithelial integrity and is driven by glucose-evoked changes in TGFβ [ 180 ]. Moreover, a recent study by Lyon et al identified that inflammation coupled with glycaemic damage mediates EMT of the RPE via aberrant Cx43 mediated hemichannel activity [ 50 ], whilst Peptide 5 blocked loss of ZO-1 expression and restores RPE permeability as measured by transepithelial resistance [ 125 ].…”