3.3 Lysine inhibits PQ-induced EMT process in AT II cells
We and others both found that PQ-induced EMT is critical for pulmonary fibrosis. Our previous work further suggested that PQ-promoted STIM1-TRPC1 association and intracellular calcium burden are essential for EMT. We therefore wondered whether PQ-induced EMT would be reversed by lysine treatment. PQ treatment significantly reduced the expression of E-Cadherin, the epithelial marker, while enhanced the expression of Vimentin, the mesenchymal marker. Lysine treatment significantly alleviated the reduction of E-Cadherin and normalized the upregulated Vimentin in PQ- treated A549 cells (Fig. 2F). Similar results were observed in MLE-12 cells (Fig. 2G). Intriguingly, we have also examined the efficacy of lysine in STIM1-overexpressed A549 cells. Though lysine still inhibited PQ-induced EMT process (Fig. 2H), such inhibition seemed not to be as striking as those observed in normal A549 cells (Fig. 2F), indicating that cells with STIM1 overexpression were much sensitive to PQ stimulation and the efficacy of lysine could be ameliorated probably due to additional STIM1 targeted by PQ. We further confirmed the protective effect of lysine in PQ-induced EMT by analyzing the mRNA expression of E-Cadherin and Vimentin (Fig. 2I&2J). Note, we have repeatedly observed that lysine alone enhanced Vimentin expression in the protein level but not the mRNA level, indicating that lysine might affect Vimentin stability. Nevertheless, these results together suggest that lysine is sufficient to suppress PQ-induced EMT, indicating that lysine is a potential antidote for PQ poisoning and pulmonary fibrosis by reducing STIM1-TRPC1 activation.