Flavin-Containing Monooxygenase-3 and 5: Tissue Distribution, Age-Related Expression and Regulation by Endoplasmic Reticulum Stress

Zhen Xu, University of Rhode Island


Background Flavin-containing monooxygenases (FMO) constitute a class of major oxidative enzymes. FMO3 and FMO5 are two major FMOs that are highly expressed in the liver. The study was performed to determine regulated expression of both enzymes by age, fructose, therapeutic agents and endoplasmic reticulum (ER) stressors. The expression of both enzymes in 32 extrahepatic tissues was determined as well. Methods The tissue distribution of FMO3 and FMO5 was determined by immunohistochemistry. For age-related expression, livers were collected and divided into 5 age groups: I (< 31 days), II (35-70 days), III (89-119 days), IV (123-198 days), and V (>18 years of age). These samples were analyzed for the expression of FMO3 and FMO5 by RT-qPCR and Western blotting. For the regulated expression by other factors, human primary hepatocytes were treated with a chemical and the expression was determined. The reporter activity was determined in response to these chemicals. Results FMO3 and FMO5 were strongly stained in the liver but exhibited overlapping and distinct expression patterns in extrahepatic tissues. Both enzymes showed a neonatal surge in mRNA expression and were correlated well with age during the first seven months after birth. Both enzymes were suppressed by ER stressors and induced by the steatotic agent valporic acid. Interestingly, fructose induced FMO5 mRNA but did not activate the FMO5 reporter. Conclusions The expression of FMO3 and FMO5 varies depending on a tissue, age, ER stress and nutritional status. Of significance are the abundant presence of FMO3 and FMO5 in some endocrine cells and regulated expression by ER-stressors and fructose. These observations conclude that FMO3 and FMO5, in addition to xenobiotic metabolism, are involved in pathogenesis, particularly related to metabolic diseases.

Subject Area

Pharmaceutical sciences

Recommended Citation

Zhen Xu, "Flavin-Containing Monooxygenase-3 and 5: Tissue Distribution, Age-Related Expression and Regulation by Endoplasmic Reticulum Stress" (2017). Dissertations and Master's Theses (Campus Access). Paper AAI10622974.