A Comprehensive Overview of Estrogen: Physiological and Pathological Insights

Estrogens (estrone, estriol, and estradiol) are a class of steroidal hormones produced by developing ovarian follicles. These hormones induce various cyclic events in the uterine endothelium and vaginal epithelium and make the female body competent for conception and ultimately for motherly care. While estrogen is primarily produced by ovaries from cholesterol, the non-reproductive tissues including the brain, liver, and heart also produce a considerable amount of it. Apart from its important role in controlling sexual behavior and reproductive function, estrogen also functions in the regulation of various physiological functions including reproduction, skin physiology, cardiovascular health, skeletal homeostasis, bone integrity, electrolyte balance, cognition, and behavior. These biological functions are regulated by diffusion through the plasma membrane in vitro signaling through specific binding to nuclear receptors such as estrogen receptors (ERα and ERβ) or binding to cell membrane receptors such as GPR30 and ER-X. The signaling mechanism can be genomic (change in gene expression) or non-genomic (activation of various signaling cascades). Disruption in estrogen functioning has a pivotal role in the pathogenesis of many diseases such as osteoporosis, insulin resistance, neurodegenerative disease, obesity, and endometriosis. Also, dysregulation in the levels of estrogen has been linked to the development of many cancers such as breast cancer, etc. This chapter aims to summarize the complete insight of estrogen by providing a clear understanding of its synthesis, receptor binding, signaling, regulation of physiological functions, and role in various diseases.

Keywords: Breast cancer, Endometriosis, Estradiol, Estrogen, Estrogen receptors, Estrogen signaling, Estrogen synthesis, Lymphangioleiomyomatosis, Prostate cancer, Sex hormones, Steroidal hormones.