Metabolic dysregulation and temporal dynamics of NF-κB-p65/NLRP3, TXNIP, endoplasmic reticulum and mitochondrial stress in silica-induced pulmonary fibrosis in rats

Abstract

Silica(SiO₂)-induced pulmonary fibrosis(PF), a global occupational illness, is characterized by lung dysfunction, inflammation, and extracellular matrix(ECM) deposition. SiO₂ generates PF via several complicated processes, but how they interact in PF initiation and progression is poorly studied. Here, male Sprague-Dawley rats were used to develop PF model by oropharyngeal instillation of SiO₂(50 mg/ml/rat). Control rats were administered with saline. Rats from control and SiO₂ induced groups were sacrificed on 7^th, 14^th, 21^st, and 28^th day post-SiO₂ exposure and examined the role of inflammatory, oxidative, endoplasmic reticulum(ER), and mitochondrial stress pathways in PF formation and progression longitudinally. Additionally, metabolomics analysis was conducted to unravel the metabolic anomalies related to PF progression. SiO₂ exposure caused histopathological and lung function alterations and increased collagen deposition longitudinally. Further, SiO₂ upregulated M2 macrophages and fibroblasts, and downregulated alveolar type II cells. Additionally, it caused a gradual upregulation in nuclear factor-κB-p65/NOD-like receptor protein 3-induced inflammation and pro-inflammatory cytokines over time. Further evaluation showed that SiO₂ caused oxidative stress by reducing antioxidants, increasing hypoxia-inducible factor 1-alpha and thioredoxin-interacting proteins, and upregulated apoptosis. SiO₂ exposure confirmed gradual EMT and PF progression via TGF-β1/Smad and Nrf2 signaling. Our investigation also demonstrated the involvement of a time-dependent increase in ER and mitochondrial stress in PF. Metabolomics analysis revealed a significant association between metabolic alterations and PF progression. Eight pathways were observed to change consistently across all time points in lung tissues. Proline emerged as the sole consistently altered metabolite across all time points in BALF. Wherease, 17 pathways were altered in time-dependent manner among them, 15 were downregulated and 2 were upregulated in the advanced stage of PF. Collectively, this work elucidates the underlying signaling and metabolic pathways associated with PF pathogenesis.