HDAC class IIa expression and regulation in human endometrial tissues and stromal cells during the menstrual cycle

Background: Histone Deacetylases (HDACs) are a class of enzymes that deacetylate the lysine residues on the protruding histone tails, causing tightening of the chromatin structure and making genes inaccessible to be transcribed. Class I and II HDACs have been involved in cell cycle regulation and progression. Class 1 HDACs have been widely studied in endometrial pathologies and menstrual cycle regulation. Studies have shown that class IIa HDACs (4, 5, 7, and 9) regulate the cell cycle, proliferation, and differentiation. But any potential roles for class IIa HDACs in endometrial biology have not been explored. This study aims to characterise the temporal expression of class IIa HDACs in the endometrium and their regulation by steroid hormones in human endometrial stromal cells (HESCs). Methods: mRNA expression and protein expression of HDAC 4, 5, 7, and 9 were analyzed in endometrial tissue biopsies collected from premenopausal women throughout the menstrual cycle by real-time quantitative PCR and fluorescent western blot analysis, respectively. Effect of hormonal regulation on class IIa HDAC expression was studied in endometrial stromal cell line following treatments with estrogen (E2) and estrogen-progesterone combined (E2+P4) over 24hrs, 48hrs, and 72hrs period. The cells were also treated with HDAC inhibitor Trichostatin A (TSA) combined with the steroid hormones. Results: In endometrial tissue, mRNA expression of class IIa HDACs showed cyclic changes. HDACs 5 and 7 were significantly upregulated during the early secretory phase, while HDAC9 was upregulated during the mid-secretory phase, compared to other cycle stages. In addition, HDAC 5 and 9 proteins were significantly upregulated in the human endometrium during the secretory phase, compared to the proliferative stage. Protein expression levels of class IIa HDACs in HESCs were upregulated in response to the combined estrogen-progesterone treatment for 24 and 48 hrs, in vitro. While TSA mitigated these hormonal effects.. Conclusions: This study shows that class IIa HDACs are expressed in the human endometrium in a cyclic pattern and are influenced by steroid hormones. Suggesting their possible involvement in menstrual cycle regulation and endometrial pathologies.