3.1 SKF treatment exhibits poor efficacy on treating PQ poisoning induced pulmonary fibrosis
We recently identified STIM1 as another molecular target of PQ, which results in intracellular calcium burden and EMT in AT II cells(Yang et al., 2022). Hence, we assumed that inhibition of calcium influx mediated by STIM1 would be a potential strategy for treating PQ toxicity and pulmonary fibrosis. We therefore examined the efficacy of SKF96365 (SKF), a SOCE inhibitor and a TRP channel blocker, in treating PQ-poisoned mice. As shown in Fig. 1A, consistent with previous reports, PQ significantly induces the production of hydroxyprolin, a product of collagen degradation acting as one of the parameters for reflecting the severity of pulmonary fibrosis (Spagnolo et al., 2020), which was impressively reduced with SKF co-treatment (Fig. 1A). However, SKF treatment did not improve the survival rate of PQ poisoning. All the mice either in the PQ group or the PQ + SKF group died with a similar rate (data not shown). Moreover, we further monitored the morphological change of lungs in the survived mice by H&E staining and Masson staining, and found severe pulmonary fibrosis in the PQ-poisoned mice either with or without SKF co-treatment (Fig. 1B). Note, it seemed that SKF alone would lead to sort of pulmonary fibrosis, indicating that both intracellular calcium burden or calcium deficiency would be harmful to lung homeostasis. Consistently, PQ-poisoned mice exhibited gradual weight loss following the progression of the disease, which was not well alleviated by SKF, yet SKF treatment showed a temporary remission in day 1 (Fig. 1C). Taken together, these observations suggested that SKF was not sufficient to reverse PQ toxicity and pulmonary fibrosis, yet with a reduction in hydroxyproline production.