Expression of heme oxygenase in the eutopic and ectopic endometrium in patients with adenomyosis

Heme oxygenase (HO) is the rate-limiting enzyme that catalyzes the degradation of heme into iron, carbon monoxide, and biliverdin. This enzyme has important functions in cellular homeostasis, including the regulation of oxidative load, apoptosis, and inflammation. Two isoforms of HO, the inducible HO-1 and the constitutive HO-2, are expressed and are known to play a role in the normal human endometrium throughout the menstrual cycle, but there is little evidence for HO expression and behavior in adenomyosis, which is the occurrence of intramural ectopic endometrial tissue. The aim of this study was to investigate the presence and localization of the two HO isoforms in both eutopic and ectopic endometrium of women with adenomyosis during the menstrual cycle. The oxidative stress and apoptosis related to HO-1 expression were also assessed. The expression of HO-1 and HO-2 in both eutopic and ectopic endometrium was confirmed, and their levels in the ectopic endometrium were lower than those in the eutopic endometrium. The cyclic variability of HO expression was lost in the ectopic endometrium during the menstrual cycle, whereas this variability was apparent in the eutopic endometrium. Moreover, HO-1 expression corresponded to apoptotic events in the eutopic endometrium. Constitutive HO-2 expression corresponded to endometrial proliferation and degradation. These results reveal that both HO-1 and HO-2 contribute little in the pathophysiology of adenomyosis.