Uterine Stretch Regulates Temporal and Spatial Expression of Fibronectin Protein and Its Alpha 5 Integrin Receptor in Myometrium of Unilaterally Pregnant Rats1

Abstract

The adaptive growth of the uterus during pregnancy is a critical event that involves increased synthesis of extracellular matrix (ECM) proteins and dynamic remodeling of smooth muscle cell (SMC)-ECM interactions. We have previously found a dramatic increase in the expression of the mRNAs that encode fibronectin (FN) and its alpha5-integrin receptor (ITGA5) in pregnant rat myometrium near to term. Since the myometrium at term is exposed to considerable mechanical stretching of the uterine wall by the growing fetus(es), the objective of the present study was to examine its role in the regulation of FN and ITGA5 expression at late gestation and during labor. Using myometrial tissues from unilaterally pregnant rats, we investigated the temporal changes in Itga5 gene expression in gravid and empty uterine horns by Northern blotting and real-time PCR, in combination with immunoblotting and immunofluorescence analyses of the temporal/spatial distributions of the 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 time-points examined, the Itga5 mRNA levels were increased in the 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 consistently 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 horn. ITGA5 and FN immunostaining in the gravid horn exhibited a continuous layer of variable thickness associated directly with the surfaces of individual SMCs. In contrast to the effects of stretch, P4 does not appear to regulate ITGA5 expression. We speculate that the reinforcement of the 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.

Enhanced focal adhesion assembly reflects increased mechanosensation and mechanotransduction at maternal–conceptus interface and uterine wall during ovine pregnancy

“…2) was utilized to evaluate differences in apical integrin expression in the LE of gravid and non-gravid uterine horns as well as differences in placentomal and interplacentomal epithelial cells in the gravid horns at days 40, 80, and 120 of pregnancy. Furthermore, since induction of focal adhesions in uterine myometrium has a force-dependent component (MacPhee & Lye 2000, Williams et al 2005, Li et al 2007, Shynlova et al 2007, we first evaluated the timing and pattern of focal adhesion organization in uterine myometrium to provide an index of mechanosensory input in the form of stretch of the uterine wall imposed by the growing conceptus.…”

“…By contrast, highly organized focal adhesions in myometrial cells from the rodent uterus are transient and restricted to a period during late pregnancy when both hormones of pregnancy and mechanical stretch upregulate the expression of the ECM mechanosensor FN (Shynlova et al 2004) and other focal adhesion constituents, including the a 5 b 1 integrin receptor and its ECM mechanosensory ligand FN, the cytoskeletal mechanosensors TLN1 and ACTN, and signal generators including PTK2 and activated MAPK1 (MacPhee et al 2001, Williams et al 2005, Li et al 2007, Shynlova et al 2007). These changes contribute to firm linkage between cytoskeletal proteins within myometrial cells and the ECM that contributes to contractile activity sufficient to expel term fetuses at labor.…”

The preterm parturition syndrome and its implications for understanding the biology, risk assessment, diagnosis, treatment and prevention of preterm birth

“…The following mechanisms of disease have been implicated: 1) intrauterine infection/inflammation ; 2) uterine ischaemia [293][294][295][296][297][298][299][300][301][302][303][304][305][306][307]; 3) uterine overdistension [308][309][310][311][312][313][314][315][316][317][318][319][320][321][322][323][324][325][326][327]; 4) abnormal allogenic recognition [328][329][330][331][332][333][334][335]; 5) allergic-like reaction [336][337][338][339][340]; 6) cervical disease [341,…”

Decreased Expression of the Rat Myometrial Relaxin Receptor (RXFP1) in Late Pregnancy Is Partially Mediated by the Presence of the Conceptus1

“…In particular, using the unilaterally pregnant rat model, they reported significantly higher oxytocin receptor (OTR), connexin-43, connexin-26, and fibronectin expression in the gravid uterine horn or artificially stretched horn compared with the nongravid horn, despite exposure to the same systemic endocrine environment [20][21][22]. Mechanical stretch also appears largely responsible for the up-regulation in OTR and prostaglandin H synthase 2 in the myometrium of the gravid horn in sheep around GD 130 and during labor [23] as well as in the gravid uterus of the tammar wallaby [24].…”