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 duringin vitrohuman 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 culturedin vitro. Gene expression levels ofLOX, LOXL1,andLOXL2significantly decreased during endometrial stromal cell decidualizationin vitro. In contrast,LOXL3andLOXL4gene 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 decidualizationin 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.