The Scientific Connotation of Yin-Yang Interdependence and Interpromotion: A Perspective from the Synthesis and Function of Estrogen

The Yin-Yang theory is the fundamental principle in traditional Chinese medicine (TCM). In this study, we investigate the scientific connotations of Yin-Yang interdependence and interpromotion by using the estrogen synthesis pathway and its function as a biological model. Yin-Yang interdependence refers to mutual reliance for existence, which is illustrated by cholesterol (Yin, the substantive raw material) and key enzyme activity (Yang, functional catalysis) in estrogen synthesis, where no reaction occurs without either. Yin-Yang interpromotion means synergistic support, such as androgens (Yin, substance) promoting estrogen synthesis via aromatase (ARO1, Yang, enzyme activity), maintaining estrogen homeostasis. Estrogen, a steroid hormone, is synthesized from cholesterol through a sequential conversion process (cholesterol → pregnenolone → progestogen/androgen → estrogen) occurring in the ovaries, placenta, and peripheral tissues, and it interacts bidirectionally with cholesterol, pregnenolone, progestogen, and androgen. The endogenous E2 remains at a relatively high level in ARO1-knockout homozygous female mice, hinting at an alternative E2 pathway. This study verifies Yin-Yang theory with modern biology, laying a foundation for future research on the alternative estrogen pathway and TCM-informed therapeutic targets for estrogen-related processes.