Role of CTGF and PI3K/Akt signaling pathway in paraquat-induced mesenchymal changes in alveolar epithelial cells

Abstract

Objective: To investigate the role of connective tissue growth factor (CTGF) and PI3K/Akt signaling pathways in paraquat (PQ) -induced alterations in alveolar epithelial cell mesenchymalization (EMT) . Methods: In February 2023, RLE-6TN cells were divided into 2 groups, which were set as uncontaminated group and contaminated group (200 μmol/L PQ), and cellular EMT alteration, CTGF and PI3K/Akt signaling pathway related molecules expression were detected by cell scratch assay, qRT-PCR and western-blot assay. Using shRNA interference technology to specifically inhibit the expression of CTGF, RLE-6TN cells were divided into four groups: control group, PQ group (200 μmol/L PQ), interference group (transfected with a plasmid with shRNA-CTGF+200 μmol/L PQ), and null-loaded group (transfected with a plasmid with scramble- CTGF+200 μmol/L PQ), qRT-PCR and western blot were used to examine the alteration of the cellular EMT and the expression of molecules related to the activity of PI3K/Akt pathway. The PI3K/Akt signaling pathway was blocked by the PI3K inhibitor LY294002, and the expression of EMT-related molecules in cells of the control group, PQ group (200 μmol/L PQ), and inhibitor group (200 μmol/L PQ+20 μmol/L LY294002) was examined by qRT-PCR and western blot.The t-test was used to compare the differences between the two groups, while the analysis of variance (ANOVA) was applied to compare the differences among multiple groups. For further pairwise comparisons, the Bonferroni method was adopted. Results: The results of cell scratch test showed that compared with the uncontaminated group, RLE-6TN cells in the contaminated group had faster migration rate, lower mRNA and protein expression levels of E-Cadherin, and higher mRNA and protein expression levels of α-SMA, CTGF, PI3K and Akt, with statistical significance (P<0.05). After specific inhibition of CTGF expression, the mRNA and protein expression of CTGF, PI3K, Akt, and α-SMA in the cells of the interference group were significantly lower than that of the PQ group and the null-loaded group (P<0.05/6), whereas that of E-Cadherin was higher than that of the PQ group and the null-loaded group (P<0.05/6). Specifically blocking the PI3K/Akt signaling pathway, the mRNA and protein expression of PI3K, Akt and α-SMA in the cells of the inhibitor group was decreased compared with that of the PQ group (P<0.05/3), while the expression of E-Cadherin was elevated compared with that of the PQ group (P<0.05/3) . Conclusion: CTGF may promote PQ-induced alveolar epithelial cell EMT through activation of the PI3K/Akt signaling pathway. Inhibition of CTGF expression or blockade of PI3K/Akt signaling pathway activity can alleviate the extent of PQ-induced alveolar epithelial cell EMT.