MYOMETRIAL ACTIVATION – COORDINATION, CONNECTIVITY AND CONTRACTILITY

Etiology behind canine uterine inertia: Role of uterine expression of MLCK4, MYH2, and PKC genes

Dystocia is an obstetrical emergency, and primary uterine inertia (PUI) is the major etiological reason among the more prevalent maternal causes in dogs. The present study involved the relative expression analysis of genes associated with myometrial contraction in medium-sized dog breeds with uterine inertia. Dogs without any progress in the parturition process even after four hours of the onset of labor and the absence of uterine contractions were considered to have complete primary uterine inertia (CPUI, n = 9). Dogs that had expelled at least one fetus and made no further progress in parturition in the absence of active uterine contraction were considered to be experiencing partial primary uterine inertia (PPUI, n = 6). Dogs with the fetal cause of dystocia (FCD), i.e., obstructive dystocia, were taken as the third (n = 7) group. Uterine tissue samples were collected during cesarean section in each group, RNA was isolated, and the relative expression of myometrial ACTA2, ACTG2, MLCK4, MYH2, and PKC genes was analyzed. The MLCK4 gene expression was downregulated in CPUI (P ≤ 0.05) and PPUI (P ≤ 0.01) when compared to FCD. The MYH2 gene expression was downregulated in PPUI in comparison to CPUI (P ≤ 0.01) and FCD (P ≤ 0.05). The PKC gene expression was upregulated in PPUI in comparison to FCD and CPUI (P ≤ 0.05). The downregulation of MLCK4 and MYH2 gene expressions recorded in PPUI indicated the possibility of myometrial defects. The possibility of myometrial defects was also observed in CPUI, but to a lesser degree, suggesting other etiologies.

Uterine expression of smooth muscle alpha- and gamma-actin and smooth muscle myosin in bitches diagnosed with uterine inertia and obstructive dystocia

Primary uterine inertia (PUI) is the most common type of dystocia in dogs. We hypothesized that PUI develops because of lower than normal expression of the basic contractile elements in the uterus, i.e., smooth muscle (SM) α- and γ-actin and SM-myosin, and that the expression of these proteins is influenced by the number of fetuses present in utero. Full-thickness inter-placental uterine biopsies were collected during Cesarean sections from dogs with PUI (n = 11), and from bitches with obstructive dystocia (OD) still presenting strong labor contractions (designated as the control group, n = 7). Relative gene expression was determined by semi-quantitative real-time (TaqMan) PCR, and protein localization by immunohistochemistry. Gene expression between PUI and OD bitches, and between PUI bitches carrying small, large, or average number of fetuses according to their breed, were compared. Uterine SM-γ-actin and SM-myosin mRNA levels were significantly higher in PUI than in OD dogs, while SM-α-actin did not differ. PUI bitches carrying large litters had lower uterine SM-γ-actin gene expression than those with small litters (P = 0.008). Immunostaining for SM-actin isoforms and SM-myosin was present in the myometrium, and localization pattern and staining intensity appeared similar in the PUI and OD groups. All proteins stained in blood vessels, and SM-γ-actin was also present in endometrial luminal and glandular epithelium. In conclusion, higher uterine SM-γ-actin and SM-myosin gene expression in PUI bitches, compared with OD dogs, might be an indication of abnormal progression with labor. Whether this is the cause of PUI due to an intrinsic error of the myometrium not becoming committed to labor, or the consequence of inadequate endocrine or mechanical stimuli, is not clear. Litter size was previously shown to be one of the risk factors for the development of uterine inertia in dogs, and our findings suggest possible differing uterine pathophysiology of PUI with respect to litter size.

Activator protein 1 is a key terminal mediator of inflammation-induced preterm labor in mice

Activation of uterine inflammatory pathways leads to preterm labor (PTL), associated with high rates of neonatal mortality and morbidity. The transcription factors nuclear factor κB (NFκB) and activator protein 1 (AP-1) regulate key proinflammatory and procontractile genes involved in normal labor and PTL. Here we show that NFκB activation normally occurs in the mouse myometrium at gestation day E18, prior to labor, whereas AP-1 and JNK activation occurs at labor onset. Where labor was induced using the progesterone receptor antagonist RU486, NFkB and AP-1/JNK activation both occurred at the time of labor (20 h compared to 60 h in DMSO-treated controls). Using an LPS (Escherichia coli: serotype O111)-induced PTL model that selectively activates AP-1 but not NFkB, we show that myometrial AP-1 activation drives production of cytokines (Il-6, Il-8, and Il-1β), metalloproteinases (Mmp3 and Mmp10), and procontractile proteins (Cox-2 and Cx43) resulting in PTL after 7 h. Protein levels of CX43 and IL-1β, and IL-1β cleavage, were increased following LPS-induced activation of AP-1. Inhibition of JNK by SP600125 (30 mg/kg) delayed PTL by 6 h (7.5 vs. 13.5 h P<0.05). Our data reveal that NFκB activation is not a functional requirement for infection/inflammation-induced preterm labor and that AP-1 activation is sufficient to drive inflammatory pathways that cause PTL.

The Th1:th2 dichotomy of pregnancy and preterm labour

Pregnancy is a unique immunological state in which a balance of immune tolerance and suppression is needed to protect the fetus without compromising the mother. It has long been established that a bias from the T helper 1 cytokine profile towards the T helper 2 profile contributes towards successful pregnancy maintenance. The majority of publications that report on aberrant Th1:Th2 balance focus on early pregnancy loss and preeclampsia. Over the last few decades, there has been an increased awareness of the role of infection and inflammation in preterm labour, and the search for new biomarkers to predict preterm labour continues. In this paper, we explore the evidence for an aberrant Th1:Th2 profile associated with preterm labour. We also consider the potential for its use in screening women at high risk of preterm labour and for prophylactic therapeutic measures for the prevention of preterm labour and associated neonatal adverse outcomes.