Genetic ablation of Nrf2 enhances susceptibility to cigarette smoke–induced emphysema in mice

Abstract

Although inflammation and protease/antiprotease imbalance have been postulated to be critical in cigarette smoke-induced (CS-induced) emphysema, oxidative stress has been suspected to play an important role in chronic obstructive pulmonary diseases. Susceptibility of the lung to oxidative injury, such as that originating from inhalation of CS, depends largely on its upregulation of antioxidant systems. Nuclear factor, erythroidderived 2, like 2 (Nrf2) is a redox-sensitive basic leucine zipper protein transcription factor that is involved in the regulation of many detoxification and antioxidant genes. Disruption of the Nrf2 gene in mice led to earlier-onset and more extensive CS-induced emphysema than was found in wild-type littermates. Emphysema in Nrf2-deficient mice exposed to CS for 6 months was associated with more pronounced bronchoalveolar inflammation; with enhanced alveolar expression of 8-oxo-7,8-dihydro-2′-deoxyguanosine, a marker of oxidative stress; and with an increased number of apoptotic alveolar septal cells -predominantly endothelial and type II epithelial cells -as compared with wild-type mice. Microarray analysis identified the expression of nearly 50 Nrf2-dependent antioxidant and cytoprotective genes in the lung that may work in concert to counteract CS-induced oxidative stress and inflammation. The responsiveness of the Nrf2 pathway may act as a major determinant of susceptibility to tobacco smoke-induced emphysema by upregulating antioxidant defenses and decreasing lung inflammation and alveolar cell apoptosis.

Pulmonary Epithelial Neuropilin-1 Deletion Enhances Development of Cigarette Smoke–induced Emphysema

“…Doxycycline-containing chow was initiated 3 days before CS or FA exposure and was maintained for the duration of the exposure. As shown in Figure 2, this duration and dose of CS did not cause morphologic alterations in littermates, which is consistent with previous reports that indicate that up to 6 months of CS exposure may be required for the development of an emphysematous phenotype (44,55)…”

“…CS exposure was performed as previously described (44) and outlined in the online supplement. Briefly, at 10 weeks of age CCSP-rtTA/tetO-Cre/ Nrp1 flox/flox mice (n 5 16) and littermate controls (n 5 17) were divided into two groups.…”

“…Results were normalized to cells undergoing mock transfection and vehicle treatment (fetal bovine serum-free medium for CSE, or 0.1% ethanol for ceramide) for the same duration and compared with cells transfected with nontargeting siRNA. Both CSE and ceramide were previously reported to produce endothelial and alveolar septal cell apoptosis and airspace enlargement in rodent models (44,46) as well as endothelial and epithelial cell death in vitro (47)(48)(49)(50). Apoptosis was quantified using the Apopercentage kit (Biocolor Ltd., Accurate Chemical and Scientific Corporation, Westbury, NY) following the manufacturer's instructions.…”

“…Augmented apoptosis (39,44,46) and attenuated proliferation (56,57) of alveolar cells were shown to be critical for the maintenance of normal alveolar structure in other animal models of emphysema. Evidence suggests that high levels of Nrp1 may attenuate apoptosis (58).…”

Nippostrongylus brasiliensis infection leads to the development of emphysema associated with the induction of alternatively activated macrophages

“…The disease can be induced through smoke-inhalation [5,16], genetic modification [6,7], protease administration [17,18] and now we show that infection with the hookworm, Nb, is also capable of starting the process that results in this chronic disease. Interestingly, Th2-mediated allergic airway inflammatory responses are sufficient to induce airways hyperresponsiveness, but alone are not sufficient to drive alveolar wall damage, which results in emphysema (Fig.…”