Proteoglycan metabolism in the connective tissue of pregnant and non-pregnant human cervix. An in vitro study

Profound changes occur in the cervix during pregnancy. In particular, the connective tissue is remodelled. To elucidate the mechanisms behind this process, the metabolism of cervical connective tissue was studied using tissue cultures. Cervical biopsies from non-pregnant and pregnant women were incubated with [35S]sulphate. The proteoglycans of the tissue specimens were purified by ion-exchange and gel chromatography and characterized by SDS/PAGE and by enzymic degradation. In the non-pregnant cervix, the incorporation of [35S]sulphate into the proteoglycans was linear for 48 h. During the first 6 h of incubation the accumulation of chiefly one small labelled proteoglycan (apparent Mr 110,000) substituted with dermatan sulphate was recorded. This is in accordance with the known proteoglycan composition of non-pregnant cervical tissue. In addition, small amounts of two larger radioactive dermatan/chondroitin sulphate proteoglycans (apparent Mr values 220,000 and greater than 500,000) were recorded. After longer periods of incubation the proportion of heparan sulphate proteoglycans increased considerably. The pregnant tissue showed a clearly different composition of labelled proteoglycans. An increased accumulation of the two larger dermatan/chondroitin sulphate proteoglycans was seen in addition to the dominant small dermatan sulphate proteoglycan of the non-pregnant cervix. The rate of accumulation of these two proteoglycans was about 3 times higher in the pregnant tissue, whereas that of the small dermatan sulphate proteoglycan was only increased 2-fold. The fact that the concentration of proteoglycans in the pregnant cervix is approximately one-half of that in the non-pregnant cervix indicates that the turnover of proteoglycans in pregnant cervical tissue is significantly increased. The major effect of this profound change of metabolism was a 50% decrease in proteoglycan content and a 2-fold increased proportion of a dermatan sulphate proteoglycan with an apparent Mr of 220,000.