Mol. Hum. Reprod. Advance Access originally published online on July 30, 2007
Molecular Human Reproduction 2007 13(9):655-661; doi:10.1093/molehr/gam047
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Differential expression of the metalloproteinase MMP3 and the 
5 integrin subunit in human myometrium at labour
1National Centre for Biomedical and Engineering Science, Orbsen Building, National University of Ireland Galway, University Road, Galway, Ireland 2Department of Obstetrics and Gynaecology, National University of Ireland Galway, Clinical Science Institute, University College Hospital Galway, Newcastle Road, Galway, Ireland
3 Correspondence address. Tel: +353 91 492912; Fax: +353 91 492956; E-mail: margaret.obrien{at}nuigalway.ie
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Abstract |
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Extensive tissue remodelling occurs in the human myometrium before, during and after parturition. The aim of this study was to investigate the expression of two tissue remodelling molecules, matrix metalloproteinase 3 (MMP3) and
5 integrin (ITGA5) subunit in human myometrium, during pregnancy and labour. mRNA and protein were isolated from human pregnant labouring and non-labouring myometrial tissue, and also from human primary uterine smooth muscle cells (SMCs). Semi-quantitative RT-PCR, real-time fluorescence RT-PCR and western blotting were subsequently performed to determine the expression levels of MMP3 and ITGA5 in the myometrial tissues during pregnancy and labour, and in the primary uterine SMCs. The expression of MMP3 and ITGA5 mRNA and protein are reported for the first time during pregnancy and labour in human myometrium. Furthermore, a significant increase in expression of MMP3 mRNA (41-fold, P = 0.001), and a significant decrease in ITGA5 mRNA expression (4-fold, P < 0.001) at labour, were observed. Protein expression of these two molecules was also altered at labour, pro-MMP3 protein expression significantly increased while ITGA5 protein expression decreased, with labour onset. Expression of these molecules was also observed in primary cultured human uterine SMCs. The differential expression of these two tissue remodelling molecules at labour and their detection in uterine SMCs highlights their potential importance in myometrial function during pregnancy, labour and post-partum. Key words: integrin/labour/matrix metalloproteinase/myometrium
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Introduction |
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During pregnancy, the uterus is transformed into a large muscular organ sufficient to accommodate the fetus, placenta and amniotic fluid. This is facilitated in part by tissue remodelling and cellular hypertrophy (Fata et al., 2000). Furthermore, uterine contractility at labour involves significant remodelling to achieve the powerful synchronous contractions of labour, while to enable the postpartum uterus to return to its pre-pregnancy state, considerable extracellular matrix (ECM) degradation also occurs to enable the post-partum uterus to return to its pre-pregnancy state (Monga and Sanborn, 1995; Manase et al., 2006). Amongst the major proteolytic enzymes involved in tissue remodelling are the matrix metalloproteinases (MMPs), a family of zinc-dependent endopeptidases that degrade ECM components (Le et al., 2007; Yan and Boyd, 2007). MMP enzymatic activity is transcriptionally regulated by growth factors, hormones and cytokines, and post-translationally controlled by tissue inhibitors of metalloproteinases (Birkedal-Hansen et al., 1992; Matrisian, 1992). MMP3 degrades, amongst other substrates, collagen III, IV and V, proteoglycans, fibronectin, elastin, laminin and gelatin (Sternlicht et al., 1999). Furthermore, it mediates an ECM-degrading proteolytic cascade by activation of the zymogenic forms of other MMPs (e.g. MMPs 1, 7, 8, 9, 13) (He et al., 1989; Ogata et al., 1992; Knauper et al., 1996). MMP3 itself is also activated, from a precursor form (pro-MMP3) by proteases, notably plasmin (Okada et al., 1988).
A significant increase in the expression of MMPs 1, 2, 3 and 9 in placenta and fetal membranes or amniotic fluid occurs with the onset of term and preterm parturition, while MMP9 expression increases in human labouring myometrium (Vadillo-Ortega et al., 1995; Maymon et al., 2000; Xu et al., 2002; Park et al., 2003; Smith, 2007). During pregnancy, uterine collagen content increases 
10-fold in various mammalian species (Woessner and Brewer, 1963). After delivery, this collagen content rapidly decreases due to extracellular degradation by activated collagenases (MMP7 and 13), an important process of post-partum uterine involution (Shimizu and Maekawa, 1983). MMP3 expression has been demonstrated in human perivascular tissue within the uterus, myometrium and in myometrial smooth muscle cells (SMCs) (Dou et al., 1997; Huppertz et al., 1998; Ma and Chegini, 1999). MMP3 mRNA expression was found to be down-regulated in mouse myometrium during pregnancy, and up-regulated 24 h post-partum (Salomonis et al., 2005), while MMP3 mRNA increased during late pregnancy in rat uterine artery (Kelly et al., 2003).
Integrins are divalent cation-dependent heterodimeric, transmembrane receptors that mediate cell attachment to the ECM and signal transduction from the ECM to the cell. They are composed of and ß subunits, with their substrate specificity being determined by the composition of these various and ß subunits (Reddy and Mangale, 2003). The 5 and ß1 integrin subunits partner to form the major fibronectin receptor (Reddy and Mangale, 2003; Robinson et al., 2003). The actin cytoskeleton of the myometrial smooth muscle cell is connected to the ECM at membrane-associated dense plaques or ‘focal adhesions' (Macphee and Lye, 2000). Focal adhesions consist of clusters of integrins that mediate interactions between the extra- and intra-cellular environments. The cytoplasmic regions of integrins connect with actin cytoskeletal elements and signalling components such as focal adhesion kinase, while the extracellular regions connect to specific ECM molecules such as fibronectin (Breuiller-Fouche and Germain, 2006). At the end of pregnancy, progesterone withdrawal increases the attachment of myometrial SMCs to the ECM, through integrins at the focal adhesion (Lye et al., 2001). This activates mitogen-associated protein kinase, thus increasing contractility (Loudon et al., 2004). It is reported that expression of the 5ß1 integrin substrate, fibronectin, is increased during pregnancy up to labour and fibronectin is deposited around SMCs in myometrium during late pregnancy (Nishinaka and Fukuda, 1991; Stewart et al., 1995; Shynlova et al., 2004; Williams et al., 2005). In rat myometrium ITGA5 mRNA expression also increased throughout pregnancy, while a decrease in expression was noted after labour, which further decreased post-partum (Williams et al., 2005). ITGA5 expression has been observed in non-pregnant human myometrium (Taylor et al., 1996). However, to date, no data have been reported on the expression of ITGA5 in human myometrium, during pregnancy and at labour.
We therefore investigated the expression of MMP3 and ITGA5 mRNA and protein in human pregnant myometrium at term and during labour, utilizing RT-PCR and western blot technologies.
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Materials and Methods |
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Patient recruitment and tissue collection
Patient recruitment took place in the Department of Obstetrics and Gynaecology, University College Hospital Galway (UCHG), Ireland. The study was approved by the Research Ethics committee, UCHG, and recruitment was carried out by provision of information sheets and obtaining written informed consent. Biopsies of myometrium were excised from the midline of the upper lip of the uterine incision, during elective (pregnant non-labouring, PNL) and intrapartum (pregnant labouring, PL) caesarean section. The criteria for inclusion in the intrapartum group were regular spontaneous uterine contractions, effacement of the cervix and cervical dilatation >3 cm prior to caesarean section. Women with malignant conditions, and those receiving exogenous hormone therapy (e.g. progestagens), were excluded from the study. Immediately upon removal, biopsies were rinsed in sterile saline, snap frozen in liquid nitrogen and stored at –80°C until RNA or protein isolation.
Cell culture
Human primary uterine SMCs were obtained from Cambrex, Biowhittaker, UK, and cultured in medium 231 (Cascade Biologics, Inc. Mansfield, Nottinghamshire, NG12 5BR, UK).
RNA extraction
Total RNA was isolated from human myometrium using TRIzol reagent (Life Technologies Ltd., Paisley, UK) (Chomczynski, 1993). Total RNA was isolated from the uterine SMCs using the RNeasy mini RNA isolation kit (Qiagen, Crawley, West Sussex, UK). RNA samples were DNase-treated with DNA-freeTM DNA removal kit (Ambion, Spitfire Close, Huntingdon, Cambridgeshire, UK). RNA concentration was determined with the Nanodrop (Nanodrop Technologies, Wilmington, USA).
Reverse transcription
Reverse transcription was performed on RNA (500 ng) at 42°C for 60 min in a reaction volume of 20 µl containing the following: oligo dT primer (500 ng), Moloney murine leukaemia virus (M-MLV) reverse transcription buffer (Promega, Southampton Science Park, Southampton, UK), dNTPs (0.2 mM) (Promega) and 200 U M-MLV reverse transcriptase (Promega). Control RNA samples, in which no reverse transcriptase (RT) was added, were included to confirm that no genomic DNA contamination was present.
Polymerase chain reaction
1 µl of the 20 µl RT reaction was then used in the subsequent PCR. PCR was performed in a final volume of 50 µl with 1.25 U Taq DNA polymerase (Bioline Ltd., London, UK), 0.2 mM dNTPs and 0.2 µM of each sense and antisense primer. The sequences of the PCR oligonucleotide primers were:
ITGA5 Sense 5'-CCC AGA CTT CTT TGG CTC TG-3'
Antisense 5'-GCA AGA TCT GAG CCT TGT CC-3' (Accession NM_002205 [GenBank] )
MMP3 Sense 5'-CCT GCT TTG TCC TTT GAT GC-3'
Antisense 5'-TGA GTC AAT CCC TGG AAA GTC-3' (Mackenzie et al., 2004)
ACTB Sense 5'-CAA CTC CAT CAT GAA GTG TGA-3'
Antisense 5'-GCC ATG CCA ATC TCA TC-3' (Accession M10277 [GenBank] ).
cDNA amplification was carried out by an initial denaturation step of 5 min at 95°C followed by 28–40 cycles of denaturation at 94°C for 1 min, annealing at 55–60°C for 1 min and elongation at 72°C for 30 s–1 min, followed by a final extension step at 72°C for 10 min. 10 µl of each PCR product was then separated by gel electrophoresis on 1.5–2% agarose gels alongside the 100 bp DNA molecular weight ladder (Promega) for sizing.
Real-time fluorescence PCR using ABI Prism 7000 technology
Real-time PCR was performed on a 1/125 dilution of each the six PNL and six PL myometrial cDNA in triplicate for each transcript, using the Applied Biosystems ABI Prism 7000 sequence Detection System (ABI, Foster City, USA). The PCR reactions were performed in a final volume of 25 µl containing 12.5 µl Sybr Green PCR Master Mix (ABI), 5 µl diluted cDNA and 0.4 µM of each sense and antisense primer.
The final volume of 25 µl was achieved using PCR grade water (Sigma-Aldrich, Dublin, Ireland). The sequences of the real-time PCR oligonucleotide primers were:
MMP3 Sense 5'-AGC AAG GAC CTC GTT TTC ATT-3'
Antisense 5'-GTC AAT CCC TGG AAA GTC TTC A-3' (Ramon et al., 2005)
ITGA5 Sense 5'-GTC GGG GGC TTC AAC TTA GAC-3'
Antisense 5'-CCT GGC TGG CTG GTA TTA GC (Wang and Seed, 2003)
ACTB Sense 5'-GGG CAT GGG TCA GAA GGA TT-3'
Antisense 5'-AGT TGG TGA CGA TGC CGT G-3' (Accession M10 277).
cDNA amplification was performed by an initial step of 50°C for 2 min and an initial denaturation step at 95°C for 10 min, followed by 40 cycles of denaturation at 95°C for 15 s, annealing at 60°C and elongation at 72°C for 30 s each. Fluorescence data was acquired at the end of each PCR cycle. Melting curve analysis was performed by an initial denaturation step of 95°C for 15 s, cooling to 60°C for 10 s, then 95°C for 15 s. Fluorescence was measured continually during the melting curve cycle.
Statistical analysis of Real Time flourescence data
The mean cycle threshold (Ct) of each gene for every patient (performed in triplicate) for the respective reactions from their standard curves were normalized to the corresponding mean Ct value of the housekeeping gene, ß-actin (ACTB). The normalized Cts of the six PL and the six PNL myometrial tissue types (PL versus PNL) were then averaged and the values obtained compared using the statistical analysis tool, the independent samples t-test. Results were expressed as mean normalized Ct units ± SEM. A P-value of <0.05 was considered to be statistically significant. Relative fold changes were then calculated using the difference in the Ct values (x) between the pregnant at-term and the labouring myometrium for each transcript, Relative fold change = 2x. All statistical analysis was performed using the SPSS statistical package (Statistical Package for the Social Sciences, v.11, SPSS Inc., Chicago, IL, USA).
Protein isolation
Human myometrial tissue or human primary uterine SMCs were homogenized in Protein lysis buffer: 50 mM Tris (pH 7.4), 100 mM NaCl, 5 mM MgCl2, 0.1% Triton X-100, 10% glycerol with inhibitors (10 µg/ml leupeptin, 10 µg/ml aprotinin, 1 mM phenylmethylsulphonyl fluoride) ice-cold buffer (Sigma-Aldrich, Ireland). Cellular debris was removed by centrifugation at 10 000g, 4°C for 15 min. The resultant supernatant was used for western blot analysis. Protein concentrations were determined using the Pierce BCA protein assay reagent kit (Promega) as per the manufacturer's protocol, with bovine serum albumin (BSA) as a standard.
Western blot analysis
Protein samples (30 µg) were resolved by electrophoresis on 7.5–12% sodium dodecyl sulphate polyacrylamide gel electropheresis gels (Bio-Rad Labarotories Hercules, USA) and electroblotted. Membranes were blocked with phosphate-buffered saline (PBS) containing 0.05% Tween 20 (Sigma-Aldrich, Ireland) and 5% low-fat milk powder (Dawn Dairies, Westmeath, Ireland). Blots were either incubated for 60 min at room temperature with a or with a 1:10 000 dilution of ACTB clone number AC-15 mouse polyclonal IgG anti-human primary antibody (Sigma-Aldrich, Ireland) or 1:1000 dilution of primary mouse anti-human MMP3 monoclonal antibody (ab17790-Abcam, Cambridge Science Park, Cambridge, UK) or ITGA5 rabbit anti-human polyclonal antibody (sc-10 729, Santa Cruz Biotechnology, Inc, Heidelberg, Germany) (0.1% NaN3) in 1x PBS containing 3% BSA and 0.03% Tween 20 for 1 h at room temperature or overnight at 4°C. Blots were then washed and incubated for 1 h at room temperature in a 1:4000 dilution of a goat anti-mouse horseradish peroxidase-conjugated antibody (sc2005 Santa Cruz Biotechnology, Inc.) or a 1:4000 dilution of a swine anti-rabbit IgG horseradish peroxidase-conjugated antibody (P-0217, DakoCytomation Ltd, Cambridgeshire, UK) containing 1x PBS, 5% low-fat milk powder (Dawn Dairies) and 0.05% Tween 20 for 1 h at room temperature. Horse-radish peroxidase (HRP)-bound secondary antibody was detected with HRP substrate using the Pierce West-Pico or the Super Signal West Dura chemiluminescence detectection kits as per the manufacturers' protocols (Promega). The membranes were scanned with the fluorescence imager (FluorchemTM 8900, Alpha Innotech Corporation, San Leandro, California, USA) and AlphaEaseFC software was used to detect the signal; the image was processed and protein expression levels were determined by densitometric analysis compared with ACTB levels.
Statistical analysis of myometrial protein Western blots
Densitometric values for ITGA5, MMP3 were determined, averaged and normalized to the corresponding ACTB values and then expressed as normalized mean densitometric units ± SEM. Independent samples t-tests were performed on the data using the statistical package SPSS for Windows version 14 (SPSS Inc.). A P-value < 0.05 was considered to be statistically significant.
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Tissue samples for mRNA expression
Biopsies of myometrium were obtained at the time of elective (PNL) (n = 6) and intrapartum (PL) (n = 6) caesarean section. The reasons for elective caesarean section included previous caesarean section (n = 5) and placenta praevia (n = 1). The reasons for emergency caesarean section were face presentation (n = 3), suspected fetal distress (n = 2) and previous classical caesarean section (n = 1). The mean age of the women was 34.83 years (range 29–41 years), 2 were primagravida and 11 were multigravida. All women were delivered between 37 and 42 weeks' gestation. There was no significant difference between those undergoing elective or emergency caesarean section in terms of age, gestation or parity. The non-pregnant biopsy was taken from the body of the uterus of a woman undergoing a hysterectomy for menorrhagia (aged 45 years).
Tissue samples for protein expression
Biopsies of myometrium during pregnancy were obtained at elective (n = 3) and intrapartum (n = 3) caesarean section. The reasons for elective caesarean section included maternal request (n = 1) and previous caesarean section (n = 2). The reasons for emergency caesarean delivery were fetal distress (n = 1), failed induction (n = 1) and failure to progress (n = 1). The mean age of the women was 35.5 years (range, 30–41 years), 3 were primagravida and 3 were multigravida. All women were delivered between 39 and 40 weeks' gestation.
RT-PCR
RT-PCR analysis using DNA-freeTM treated RNA demonstrated expression of MMP3 both in non-labouring and labouring human myometrium, with MMP3 expression being increased during labour (Fig. 1a). RT-PCR analysis demonstrated expression of ITGA5 in non-pregnant (NP), pregnant non-labouring (PNL) and labouring (PL) human myometrium (Fig. 1b). The absence of transcripts in RT negative (RT–) reactions confirmed that all products were RNA derived and not generated from contaminating genomic DNA. In order to determine cellular expression, RT-PCR analysis was also performed using DNA-freeTM treated RNA from primary human uterine SMCs (passage 6). The expression of both MMP3 and ITGA5 mRNAs was evident in the human primary uterine SMCs (Fig. 2a and b).
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Real-time fluorescence RT-PCR
Relative quantitative expression analysis was performed on human myometrium from PNL and PL biopsies by real-time RT-PCR. In order to minimize any undue experimental error from sources such as pipetting inaccuracies, analyses of each gene was performed in triplicate. All PL and PNL myometrial biopsies demonstrated expression of MMP3, ITGA5 and ACTB mRNA. RT-PCR product specificity was confirmed using melting curve analysis. Amplification curve Cts were determined for each gene from curves generated within the initial phase of exponential amplification, per 0.5 µg total RNA in the tissues studied. ACTB expression showed no significant difference between the different tissue types. The mean Ct values for each candidate gene were compared with the corresponding mean ACTB value. The mean Ct value of each gene for each patient (PCRs were performed in triplicate) at the different pregnancy stage was normalized to that of the corresponding mean ACTB Ct value, and the resultant values were averaged.
These values, MMP3 mean normalized Ct values (per 0.5 µg total RNA)±SEM were: PL (n = 6) 31.8582 ± 1.08840; PNL (n = 6) 37.2167 ± 0.58237, P = 0.001. These data are graphically represented in Fig. 3a. The relative fold change was calculated from the difference in the mean normalized Ct values (x) between the PL and PNL myometrium, Relative fold change = 2x, i.e. 37.2167–31.8582, 25.3585. This resulted in a 41-fold up-regulation of MMP3 mRNA expression at labour (P = 0.001) (Fig. 3b).
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The ITGA5 mean normalized Ct values (per 0.5 µg total RNA) ± SEM were: PL (n = 6) 28.9333 ± 0.307; PNL (n = 6) 26.9367 ± 0.22658, P < 0.001. These data are graphically represented in Fig. 4a. A statistically significant 4-fold down-regulation in ITGA5 mRNA expression at labour was calculated from the difference in the Ct values (x) between the PL and PNL myometrium (P < 0.001) (Fig. 4b).
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Western blot analysis
Western blotting demonstrated the expression of MMP3 and ITGA5 protein in PNL and PL human myometrium and alterations in the levels of these proteins in myometrium at labour in comparison with the ACTB control (Figs 5 and 6). A single band of
60 kDa was observed with the MMP3 antibody (which can detect both the pro- and active forms of MMP3); this corresponds to the size of the previously observed 59 kDa pro-MMP3 protein (Fig. 5a) (Watari et al., 1999; Mackenzie et al., 2004). A single band of 150 kDa was demonstrated for ITGA5 (Fig. 6a). An increase in pro-MMP3 protein expression and a decrease in ITGA5 protein expression was observed at labour (Figs 5a and 6a). The ACTB protein levels did not significantly differ amongst the PNL and PL myometrial samples.
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Quantitative densitometric analysis was performed where protein expression was normalized to ACTB protein from the same blot, PL (n = 3) and PNL (n = 3). The averaged densitometric units normalized to (per 30 µg total protein) ± SEM for pro-MMP3 were: PL (n = 3) 49.6667 ± 1.76383; PNL (n = 3) 38 ± 2.64575, P = 0.021. A graphical representation of these quantitative data is presented in Fig. 5b. Statistical analysis revealed a significant 77% increase in pro-MMP3 protein expression in human myometrial tissues at labour (P = 0.021).
The averaged densitometric units normalized to ACTB (per 30 µg total protein) ± SEM for ITGA5 were: PL (n = 3) 0.4033 ± 0.09404; PNL (n = 3) 0.6413 ± 0.03692, P = 0.067. A graphical representation of these quantitative data is presented in Fig. 6b. The protein expression level was found to be decreased at labour, by 60%, however, the reduction was found not to be statistically significant (P = 0.067).
Western blotting confirmed expression of MMP3 and ITGA5 protein in human primary uterine SMCs (Fig. 7a and b). A single band of 60 kDa indicated the presence of pro-MMP3 protein, while a faint band of 47 kDa suggested activated MMP3 protein in the SMCs (Fig. 7a) (Galazka et al., 1996). A single band (150 kDa) was evident on the ITGA5 western indicating the expression of this protein in the uterine SMCs (Fig. 7b).
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Discussion |
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This study investigated the expression of the ECM-related and tissue remodelling molecules, ITGA5 and MMP3, at the mRNA and protein levels in human myometrium during pregnancy and labour. MMP3 expression was previously observed in non-pregnant human myometrium (Dou et al., 1997); however, this is the first report of its expression in human myometrium during pregnancy and labour and its subsequent up-regulation at labour.
The expression of MMP3 mRNA was found to be significantly increased in the human myometrium at labour. A single band of 60 kDa was observed on myometrial tissue western blots, with a monoclonal antibody to both the pro-MMP and the active forms, suggesting that only the non-activated pro-MMP3 form was present. A significant increase in pro-MMP3 protein was also detected at labour. MMP3 mRNA and protein were found to be expressed in human primary uterine SMCs; both the pro-MMP3 (60 kDa) and a weaker band of the correct size (47 kDa) were visible on the western blot, suggesting the presence of both pro- and active MMP3 protein (Galazka et al., 1996). MMPs are induced in tissues that normally undergo extensive remodelling, e.g. the endometrium during the menstrual cycle, the wound environment and in tissue responses to various inflammatory conditions (Mignatti and Rifkin, 1996; Salamonsen and Woolley, 1996; Hulboy et al., 1997). Certainly, substantial remodelling occurs in the myometrial environment, in the lower uterine segment during late pregnancy and labour. The ECM molecules surrounding myometrial SMCs include structural proteins (fibrillar collagens and elastin), substrate adhesion molecules (fibronectin, laminin and collagen IV) and proteoglycans (Shynlova et al., 2004), all of which are MMP3 substrates (Sternlicht et al., 1999). The myometrial biopsies utilized in these studies were obtained from the lower uterine segment and the increased production of pro-MMP3 at labour suggests a significant role for this metalloproteinase in the adaptation of this region for birth. Another study observed an increase in MMP3 gene expression 24 h post-partum (Salomonis et al., 2005). MMP3 therefore may also play a role in the extensive post-partum remodelling where ECM degradation during involution enables the uterus to return to its pre-pregnancy state. Other MMPs, MMPs 7 and 9 are already known to contribute to uterine collagen extracellular degradation at this time (Shimizu and Maekawa, 1983).
MMP3 also has the ability to activate other MMP enzymes, e.g. MMPs 1, 7, 8, 9 and 13 (some of which play important roles in cervical ripening and placental membrane degradation). This may serve an important function in the overall MMP activation in the myometrium and also perhaps in other uterine or placental tissues. The induction of MMP3 expression at labour, its effects on multiple ECM components and its role in cascade initiation all suggest a significant role for MMP3 in uterine function during this critical time. Further investigation is necessary to monitor MMP3 expression throughout pregnancy and post-partum and also to study the regulation of its expression and activation whether by prostaglandins, growth factors or cytokines. The activation of other MMPs by MMP3 also merits further investigation.
Integrins are crucial to the control of cell-ECM interactions where they serve as a link between the ECM and the cytoskeleton. Integrins also contribute to the remodelling of the uterus before parturition. Other investigators have observed an increase in rat ITGA5 thoughout pregnancy and labour which decreases post-partum (Williams et al., 2005). An increase in expression of its substrate, the ECM component fibronectin, was also evident throughout pregnancy (Nishinaka and Fukuda, 1991; Stewart et al., 1995; Shynlova et al., 2004). ITGA5 expression was previously demonstrated in non-pregnant human myometrium (Taylor et al., 1996), though to our knowledge, this is the first study to report the expression of an integrin subunit, specifically ITGA5, in human myometrium during pregnancy and labour, and its subsequent down-regulation at labour.
Integrins contribute to ECM remodelling during pregnancy to facilitate the constant cell growth, to form links between the cell cytoskeleton and the ECM and to trigger signalling pathways during pregnancy and labour. The decrease of ITGA5 mRNA in human myometrium at labour onset suggests its expression levels may be returning to its pre-pregnancy levels, after labour-associated contractility has been activated.
This report reveals for the first time MMP3 and ITGA5 expression in the human myometrium during pregnancy and labour, and also their differential expression at labour. These data suggests key functions for these ECM-related molecules in tissue remodelling in the myometrium, and highlights the importance of ECM organization in the human uterus during pregnancy and labour.
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The authors are grateful to the medical and midwifery staff at University College Hospital Galway for their assistance with patient recruitment and tissue collection and to the research nurse Mary Quinn for help with acquiring patient data. This study was funded by the Health Research Board of Ireland and the Higher Education Authority of Ireland's Programme for Research in Third Level Institutions (PRTLI).
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References |
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Submitted on May 11, 2007; resubmitted on June 18, 2007; accepted on June 25, 2007.
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