BackgroundWe have previously demonstrated that cigarette smoke is associated with a significant reduction of retinoic acid in rat lungs and the formation of tracheal precancerous lesions. However, the underlying mechanism of cancer risk induced by vitamin A deficiency is unclear. The purpose of this study was to determine whether the cigarette smoke-induced depletion of vitamin A is related to changes in lung cancer risk-related molecular markers.ResultsWe investigated the roles of the retinoic acid receptors (RARs) as well as other biomarkers for potential cancer risk in the lungs of rats exposed to cigarette smoke. Twenty-four male weanling rats were fed a purified diet and divided equally into four groups. Three experimental groups were exposed to increasing doses of cigarette smoke from 20, 40 or 60 commercial cigarettes/day for 5 days/week. After 6 weeks, the retinoic acid concentrations in the lung tissue as measured via high performance liquid chromatography (HPLC) significantly decreased (P < 0.01) in cigarette smoke exposed groups. Western Blot analysis revealed that cigarette smoke exposure increased lung protein expression of RAR α in a threshold manner and decreased RAR β and RAR γ expression in a dose-dependent fashion. Protein expressions of cyclin E and proliferating cell nuclear antigen (PCNA) were increased significantly in a dose-dependent manner in cigarette smoke exposed-groups. Additionally, there was a significant increase in protein expression of cJun and cyclin D1 demonstrating a threshold effect similar to that exhibited by RARα, suggesting a potential independent signaling pathway for RARα in lung carcinogenesis.ConclusionsFindings from this study suggest that cigarette smoke-induced lung retinoic acid depletion may involve two independent pathways, RARα- and RARβ-mediated, responsible for the increased cancer risk associated with cigarette smoke-induced vitamin A deficiency.

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Cux1 is a transcriptional repressor gene and part of the network controlling G1‐S phase transition. It represses the expression of the cyclin kinase inhibitors (CKI) p21 and p27. To determine the function of Cux1, we generated transgenic mice constitutively expressing Cux1. These mice develop multiorgan hyperplasia resulting from the aberrant repression of p27. We have previously characterized the changes in kidney development, spermatogenesis, and liver development in the Cux1 transgenic mice. In this study we have focused on the changes in the lung resulting from constitutive Cux1 expression. Histological staining of mice lung tissue showed extensive inflammation, localized areas of atelectasis alternated to emphysema, severe bronchiectasis, thickened bronchial basal membrane, and pluristratification of bronchial epithelium interspaced with areas of necrosis. Peribronchial arteries exhibited mild media thickening and enlarged adventitia with significant presence of fibroblasts (trichrome staining). The damage, bronchiectasis, and inflammation in particular were more evident in lungs of Cux1 transgenic mice. In conclusion, our results suggest that increased Cux1 expression results in multiple lung pathologies and may contribute to bronchiectasis.

The purpose of the present study was to determine how dietary flaxseed oil altered specific biomarkers in its protection against bleomycin‐induced pulmonary fibrosis. Twenty weanling rats were randomly assigned to one of two groups: (1) a group fed a 15% (w/w) corn oil (control) diet and (2) a group fed a 15% flaxseed oil diet. Rats were fed their respective diets for 4 weeks prior to bleomycin treatment. Half of each group received either bleomycin or saline vehicle via oropharyngeal delivery. All rats were euthanized at day 7 post‐treatment. Formalin‐treated lung tissue were immunohistostained using antibodies for proliferating cell nuclear antigen (PCNA), Cux1 (CUTL1), and cyclin‐dependent kinase inhibitor 1B (p27). We found that PCNA was overly expressed in bleomycin‐induced rat lungs but was notably reduced in rats given the flaxseed oil‐supplemented diet. Expression of p27 was moderately reduced in rats given the flaxseed oil‐supplemented diet as compared with groups given corn oil. No significant differences were found for Cux1. Results indicate that PCNA may be another biomarker for pulmonary fibrosis and its decreased expression suggests that the dietary flaxseed oil inhibits proliferation of bleomycin‐treated lung cells.

CUX‐1 is a transcriptional repressor gene and part of the network controlling G1‐S phase transition by repressing the cyclin‐kinase inhibitors p21 and p27. CUX‐1 transgenic mice develop polycystic kidneys, reduced spermatogenesis, and liver fibrosis as a consequence of aberrant repression of p27. We reported that these mice also show severe pulmonary inflammation with vasculitis, bronchitis, bronchiectasis, and diffuse presence of fibroblasts.This study reports the presence of collagen using Image J software (NIH program) on slides of lungs of CUX‐1 mice stained by trichrome. Wild type mice were used as controls. An average of seven photographs at 400x magnification were taken on the lungs of each mouse.Collagen presence and intensity was 17.06% in lungs of CUX‐1 mice versus 8.73% the wild type mice (p<0.05). Fibrosis was mostly evident in the basal membrane and musculature of the ectasic bronchi and the peribronchial arteries. CUX‐1 mice also showed medial thickening, reduced lumen patency (64% versus 76% in wild type, p 0.015), and reduced media/adventitia ratio (42% versus 64% in wild type, p 0.018). Fibroblasts were particularly evident in the adventitia. Data using a specific rat stain for SMA‐1 confirm those ones observed with trichrome.Our data quantitatively confirms the presence of severe pulmonary fibrosis in these mice. Would some patients with polycystic kidney disease also have aberrant repression of p21 and p27 and develop pulmonary fibrosis?