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Decreased Type I Collagen Expression in Human Uterine Cervix during Pregnancy

Departments of Obstetrics and Gynecology (M.I., N.U.) and Pathology (Y.M., A.O.), Wakayama Medical University, Wakayama 641-0012, Japan

Address all correspondence and requests for reprints to: Masaaki Iwahashi, M.D., Department of Obstetrics and Gynecology, Wakayama Medical University, Kimiidera 811-1, Wakayama 641-0012, Japan. E-mail: masaaki{at}wakayama-med.ac.jp.

To provide some insight into the mechanism of cervical ripening, the expression of type I collagen was investigated in human uterine cervical tissues obtained from the first (n = 4) and third (n = 3) trimesters of normal pregnancy. Indirect immunofluorescent staining was performed for type I collagen, and Northern blot analysis was done to assess expression of mRNA for the 1(I) chain. Collagens were also extracted from the human cervical tissues in the first and third trimesters of pregnancy. Immunohistochemical analysis revealed loose distribution of type I collagen in the uterine cervix of the first trimester compared with the third trimester of pregnancy. The relative levels of various collagens were evaluated by SDS-PAGE. The ratios of the intensity of the band of 1(I) to that of total collagen 1 chain in cervical tissues of the third trimester were significantly lower than those in cervical tissues of the first trimester of pregnancy (P < 0.05). In contrast, the ratios of the intensity of the band of 1(III) to that of total collagen 1 chain in cervical tissues of the third trimester were significantly higher than those in cervical tissues of the first trimester of pregnancy (P < 0.05). Northern blot analysis revealed that the cervical expression of mRNA for the 1(I) chain was significantly reduced in the third trimester compared with the first trimester of pregnancy (P < 0.01). These results suggest that type I collagen might play an important role in the maintenance of pregnancy and that decreased expression of this collagen could be associated with the process of uterine cervical ripening.

This work was partly supported by a research grant from the 1998 Wakayama Medical Award for Young Researchers.

Abbreviations: ECM, Extracellular matrix; mAb, monoclonal antibody; NO, nitric oxide; SSC, sodium chloride-sodium citrate.