Effect of Platelet-Activating Factor on Barrier Function of ARPE-19 Cells

Calpain-2 Facilitates Autophagic/Lysosomal Defects and Apoptosis in ARPE-19 Cells and Rats Induced by Exosomes from RPE Cells under NaIO3 Stimulation

Although accumulated evidence supports the notion that calpain contributes to eye disease, the mechanisms by which calpain promotes RPE injury are not defined. The present study is aimed at investigating whether the effect of NaIO₃-exos (exosomes derived from RPE cells under NaIO₃ stimulation) on the dysfunction of the autophagy-lysosomal pathway (ALP) and apoptosis is based on its regulation of calpain activation in ARPE-19 cells and rats. The results showed that calpain-2 activation, ALP dysfunction, and apoptosis were induced by NaIO₃-exos in ARPE-19 cells. NaIO₃-exo significantly increased autophagic substrates by activating lysosomal dysfunction. ALP dysfunction and apoptosis in vitro could be eliminated by knocking down calpain-2 (si-C2) or the inhibitor calpain-2-IN-1. Further studies indicated that NaIO₃-exo enhanced calpain-2 expression, ALP dysfunction, apoptosis, and retinal damage in rats. In summary, these results demonstrate for the first time that calpain-2 is one of the key players in the NaIO₃-exo-mediated ALP dysfunction, apoptosis, and retinal damage and identify calpain-2 as a promising target for therapies aimed at age-related macular degeneration (AMD).

Changes in transepithelial electrical resistance and intracellular ion concentration in TGF-β-induced epithelial-mesenchymal transition of retinal pigment epithelial cells

OBJECTIVE

This study aimed to investigate the changes in transepithelial electrical resistance (TEER) and ion concentrations, and their relationship in TGF-β-induced epithelial-mesenchymal transition (EMT) of retinal pigment epithelial (RPE) cells.

METHODS

RPE cell line ARPE-19 was employed and treated with 10 ng/ml TGF-β1 and TGF-β2 to establish the EMT model in vitro. The EMT markers fibronectin, N-cadherin, occludin, zona occludens 1(ZO-1) and claudin-19 were investigated by western blot and immunofluorescence. CellZscope system was used to monitor the TEER values. Fluorescent probe, flow cytometry and automatic microplate reader were employed to detect the changes of Ca2+, Mg2+, Zn2+, Na+ and K+ in ARPE-19 cells.

RESULTS

The TGF-β1-induced EMT of ARPE-19 cells was marked by the disruption of the distribution of occludin, ZO-1, and claudin-19. The development of TEER was significantly disturbed in both TGF-β1 and TGF-β2 treatment groups. Also, the time course of the maximum slope indicated that the fastest decrease in TEER values occurred after 36 hours. The concentrations of Ca2+, Mg2+, Zn2+, and K+ increased in TGF-β1- and TGF-β2-treated ARPE-19 cells, while the concentration of Na+ decreased. Significant inverse correlations were detected between the concentrations of Ca2+, Mg2+, Zn2+, and K+ and TEER values in ARPE-19 cells treated with TGF-β1. The Na+ concentration and TEER values showed a positive correlation. Similar results were observed in the TGF-β2 treatment group. The time-effect analysis showed that the concentrations of Ca2+, Mg2+, Zn2+ and K+ increased and peaked after 72, 72, 48, and 72 h, respectively, with the extension of TGF-β1 treatment time. In the TGF-β2 treatment group, the Ca2+, Mg2+, Zn2+, and K+ concentrations were also upregulated and reached their highest after 72, 72, 72, and 36 h, respectively. In contrast, the concentration of Na+ decreased and reached the lowest after 48 h in the TGF-β1 treatment group and after 72 h in the TGF-β2 treatment group.

CONCLUSION

TGF-β1 and TGF-β2 disrupted the ARPE-19 cell monolayer, disturbed TJs integrity, downregulated TEER values, and changed intracellular ion permeability. These findings might help further understand the EMT of RPE cells during PVR.

Non-Tumor CCAAT/Enhancer-Binding Protein Delta Potentiates Tumor Cell Extravasation and Pancreatic Cancer Metastasis Formation

CCAAT/enhancer-binding protein delta (C/EBPδ) is a transcription factor involved in apoptosis and proliferation, which is downregulated in pancreatic ductal adenocarcinoma (PDAC) cells. Loss of nuclear C/EBPδ in PDAC cells is associated with decreased patient survival and pro-tumorigenic properties in vitro. Interestingly however, next to C/EBPδ expression in tumor cells, C/EBPδ is also expressed by cells constituting the tumor microenvironment and by cells comprising the organs and parenchyma. However, the functional relevance of systemic C/EBPδ in carcinogenesis remains elusive. Here, we consequently assessed the potential importance of C/EBPδ in somatic tissues by utilizing an orthotopic pancreatic cancer model. In doing so, we show that genetic ablation of C/EBPδ does not significantly affect primary tumor growth but has a strong impact on metastases; wildtype mice developed metastases at multiple sites, whilst this was not the case in C/EBPδ^-/- mice. In line with reduced metastasis formation in C/EBPδ^-/- mice, C/EBPδ-deficiency also limited tumor cell dissemination in a specific extravasation model. Tumor cell extravasation was dependent on the platelet-activating factor receptor (PAFR) as a PAFR antagonist inhibited tumor cell extravasation in wildtype mice but not in C/EBPδ^-/- mice. Overall, we show that systemic C/EBPδ facilitates pancreatic cancer metastasis, and we suggest this is due to C/EBPδ-PAFR-dependent tumor cell extravasation.