Submitted April 18, 2007
Returned for revision May 9, 2007
Accepted August 9, 2007
Pregnancy
Uterine Stretch Regulates Temporal and Spatial Expression of Fibronectin Protein and Its Alpha 5 Integrin Receptor in Myometrium of Unilaterally Pregnant Rats
Oksana Shynlova *,
S. Joy Williams ,
Haley Draper ,
Bryan G. White ,
Daniel J. MacPhee ,
and
Stephen J. Lye
* To whom correspondence should be addressed. E-mail: shynlova{at}mshri.on.ca.
Abstract
The adaptive growth of the uterus during pregnancy is a critical event that includes an increased synthesis of extracellular matrix (ECM) proteins and a dynamic remodelling of smooth muscle cell (SMC)-ECM interactions. We have previously found a dramatic increase in expression of mRNA encoding Fibronectin (Fn) and its alpha 5 integrin receptor (Itga5) in pregnant rat myometrium near term. Since the myometrium at term is exposed to considerable mechanical stretch of the uterine wall by the growing fetus(es), the objective of this study was to examine its role in regulation of FN and ITGA5 expression at late gestation and during labor. Using myometrial tissue from unilaterally pregnant rats we investigated the temporal changes of Itga5 gene expression in gravid and empty uterine horns by northern blot and real-time PCR, in combination with immunoblot and immunofluorescence analysis of the temporal/spatial distribution of FN and ITGA5 proteins. In addition, we studied the effects of early progesterone (P4) withdrawal on Itga5 mRNA levels and ITGA5 protein detection. At all timepoints examined Itga5 mRNA levels were increased in gravid uterine horn compared to the empty horn (P<0.05). Immunoblot analysis confirmed higher ITGA5 and FN protein levels in the myometrium, associated with gravidity (P<0.05). Immunodetection of ITGA5 was constantly high in the longitudinal muscle layer, increased with gestational age in the circular muscle layer of the gravid horn and remained low in the empty one. ITGA5 and FN immunostaining in the gravid horn exhibited a continuous layer of variable thickness associated directly with the surface of individual SMCs. In contrast to the effects of stretch, P4 does not appear to regulate ITGA5 expression. We speculate that the reinforcement of FN-ITGA5 interaction (1) contributes to myometrial hypertrophy and remodeling during late pregnancy and (2) facilitates force transduction during the contractions of labor by anchoring hypertrophied SMCs to the uterine ECM.
Key words:
Pregnancy •
Progesterone •
Uterus •
cellular cohesion •
stretch
