Expression of Lysyl Oxidase Family Enzymes During Human Endometrial Decidualization

Lysyl oxidases (LOXs), comprising lysyl oxidase (LOX) and lysyl oxidase like 1-4 (LOXL1-4), constitute a highly conserved enzyme family. Their primary function is the crosslinking of collagen and elastic fibers, thereby modulating the structure and function of the extracellular matrix. Our primary objective was to elucidate the localization of LOXs within human endometrial tissues and to investigate the expression profile of LOXs during in vitro human endometrial stromal cell decidualization. Immunohistochemical localization revealed that all LOXs were expressed in human endometrium during both the proliferative and secretory phases of menstrual cycle. All five LOXs were expressed in human endometrial stromal cells cultured in vitro. Gene expression levels of LOX, LOXL1, and LOXL2 significantly decreased during endometrial stromal cell decidualization in vitro. In contrast, LOXL3 and LOXL4 gene expression remained unaffected. Protein levels of LOX, LOXL1, and LOXL3 also showed a significant reduction. Additionally, conditioned media analysis revealed abundant secretion and release of LOX and LOXL1-3 into the extracellular space at all time points examined, with their levels remaining constant. The primary targets of LOXs, collagen and elastic fibers, undergo significant synthesis and processing during endometrial stromal cell decidualization in vitro. This observation was supported by the differential gene expression levels of factors involved in their processing and assembly. Collectively, this study demonstrates the expression of LOXs in the human endometrium and their potential role in extracellular matrix reorganization during decidualization.