Abstract / Summary
Abstract Background Chronic obstructive pulmonary disease (COPD) is characterized by pathological alterations including alveolar structure destruction and small airway remodeling. However, the dynamic evolution of alveolar structural damage from the initiation of risk factor exposure to irreversible alveolar structural destruction of COPD remains to be fully elucidated. Concurrently, silent information regulator 1 (SIRT1), as a key regulator of metabolism and cellular stress, warrants further investigation regarding its potential role during the period from exposure to risk factors in COPD to the onset of irreversible alveolar structural destruction. Methods 120 male C57BL/6N mice were randomly divided into wild-type (WT) and cigarette smoke plus Lipopolysaccharide (CS-model) groups. CS-model was induced by 12-week cigarette smoke (CS) exposure combined with intratracheal lipopolysaccharide (LPS, 2mg/kg) twice on Day1 and Day14. Alveolar epithelial cell-specific SIRT1 gain- and loss-of-function models were constructed using adeno-associated virus (AAV6.2FF) with SIRT1 overexpression or inhibition vectors. Tissue samples were collected biweekly for 12 weeks. In vitro, A549 cells were treated with cigarette smoke extract (CSE, 50µg/mL) and LPS (10µg/mL). SIRT1 activation (SRT1720) and inhibition (EX527) as well as Nuclear factor erythroid 2-related factor 2(Nrf2) modulation (NK252, ML385) were applied to investigate mechanisms. Lung function, histology (HE, MASSON), protein expression (Western blot), and immunofluorescence were assessed at multiple time points(2,4,6,8,10 and 12 weeks). Results CS-model mice exhibited significant weight loss, alveolar destruction, impaired lung function, and elevated inflammatory markers (NLRP3, TNF-ɑ). Type II alveolar epithelial cells(AT2) proliferation and differentiation declined as early as 2 weeks, while Type I alveolar epithelial cells(AT1) loss was evident at 6 weeks. The AT2/AT1 ratio gradually decreased from 4 weeks, reaching the lowest value at 12 weeks. SIRT1 and Nrf2 expression levels peaked at 2 weeks but significantly declined from 4 weeks, reaching nadir at 12 weeks. AAV-mediated SIRT1 overexpression improved lung histology and function, restored AT2/AT1 ratio, and reduced inflammation, apoptosis, and barrier dysfunction compared to the CS-model group. In vitro, SIRT1 activation with SRT1720 and Nrf2 activation with NK252 both improved cell viability and reduced apoptosis. In terms of cell proliferation, the SIRT1 agonist + Nrf2 inhibitor combination was superior to the SIRT1 inhibitor + Nrf2 agonist combination; in terms of cell apoptosis, the SIRT1 inhibitor + Nrf2 agonist combination was superior to the SIRT1 agonist + Nrf2 inhibitor combination. Conclusions During CS-model progression from onset to severe alveolar destruction, alveolar epithelial cells exhibited a time-dependent pattern of compensation at 2 weeks, decompensation at 4 weeks, and progressive injury thereafter. Abnormal AT2 proliferation and differentiation at 2 weeks suggests AT2 dysfunction maybe is an early driving event in CS-model. SIRT1 and Nrf2 expression dynamics closely mirrored AT2 cell changes, implying their regulatory role. SIRT1 overexpression conferred protective effects dependent on CS-model pathological