Immunohistochemical Expression of H3K9ac and H3K27ac in Premalignant and Malignant Tongue Lesions of Wild‐Type and Nos2‐Knockout Mice Treated With 4NQO

Background Nitric oxide is an important regulator of the epigenetic landscape of cellular homeostatic and pathological states, in which post‐translational modifications of the epigenome‐modulating enzymes are the most well described mechanism. Considering that alterations of the histone acetylation pattern were associated with oral cancer development and progression, the purpose of this study was to analyze the immunohistochemical expression of H3K9ac and H3K27ac at different stages of oral carcinogenesis induced by 4‐nitroquinoline‐ N ‐oxide (4NQO) in Nos2 +/+ (wild‐type) and Nos2 −/− (knockout) mice. Methods C57BL/6J and B6.129P2‐Nos2 tm1Lau /J mice were treated with 4NQO in the drinking water at 50 μg/mL for 16 weeks and observed for 8 weeks. Tongues were submitted to histopathological analysis and immunohistochemistry for H3K9ac and H3K27ac expression. The antigen–antibody reaction was analyzed with quickscore (QS). Results Both histone acetylation marks were expressed in the normal epithelium. QS values were higher in moderate dysplasia of Nos2 −/− mice ( p = 0.025) when compared to Nos2 +/+ , and mild dysplasia had lower values for H3K9ac when compared to moderate and severe dysplasia in the Nos2 −/− group ( p = 0.015). H3K27ac significantly increased from normal mucosa to mild dysplasia in Nos2 +/+ mice ( p = 0.007). Additionally, Nos2 +/+ mice had a higher number of H3K27ac‐positive mild dysplasias when compared to Nos2 −/− ( p = 0.023). Conclusion The pattern of histone acetylation changes in murine oral carcinogenesis, mainly when the epithelial lining of the tongue becomes dysplastic, and such epigenetic modifications might be iNOS‐mediated.