Epithelial expression of matrix metalloproteinase‐26 is elevated at mid‐cycle in the human endometrium

The human endometrium is a dynamic tissue, which undergoes extensive tissue remodelling during the menstrual cycle. Due to their involvement in such processes, several well‐characterized matrix metalloproteinases (MMP) have previously been studied in the endometrium. MMP‐26 is a newly described matrilysin. We studied MMP‐26 mRNA in 39 normal endometrial samples obtained across the menstrual cycle. Tissue distribution and cycle variation was examined using in‐situ hybridization, Northern blot analyis and real time PCR. The probes for Northern blot analysis and real time PCR recognized non‐overlapping sequences. MMP‐26 was localized exclusively in epithelial cells of both glands and the luminal surface. Expression increased during the proliferative phase to a maximum at mid‐cycle, then decreased to non‐detectable levels in the late secretory and menstrual phases. Expression of MMP‐26 mRNA in endometrial tissue explants in vitro required stimulation with both estradiol and progesterone. The tissue content of c‐jun mRNA was assayed, since c‐jun, as part of the enhancer complex AP‐1, may be involved in regulation of MMP‐26 gene transcription. The pattern of c‐jun expression over the menstrual cycle was similar to that of MMP‐26. Epithelial expression in the peri‐ and post‐ovulatory stages of the menstrual cycle suggests the involvement of MMP‐26 in reproductive processes.