Mouse models of preterm birth: Suggested assessment and reporting guidelines

Preterm birth affects approximately 1 out of every 10 births in the United States, leading to high rates of mortality and long-term negative health consequences. To investigate the mechanisms leading to preterm birth so as to develop prevention strategies, researchers have developed numerous mouse models of preterm birth. However, the lack of standard definitions for preterm birth in mice limits our field\u27s ability to compare models and make inferences about preterm birth in humans. In this review, we discuss numerous mouse preterm birth models, propose guidelines for experiments and reporting, and suggest markers that can be used to assess whether pups are premature or mature. We argue that adoption of these recommendations will enhance the utility of mice as models for preterm birth

Antioxidant Protects against Increases in Low Molecular Weight Hyaluronan and Inflammation in Asphyxiated Newborn Pigs Resuscitated with 100% Oxygen

BACKGROUND: Newborn resuscitation with 100% oxygen is associated with oxidative-nitrative stresses and inflammation. The mechanisms are unclear. Hyaluronan (HA) is fragmented to low molecular weight (LMW) by oxidative-nitrative stresses and can promote inflammation. We examined the effects of 100% oxygen resuscitation and treatment with the antioxidant, N-acetylcysteine (NAC), on lung 3-nitrotyrosine (3-NT), LMW HA, inflammation, TNFα and IL1ß in a newborn pig model of resuscitation. METHODS & PRINCIPAL FINDINGS: Newborn pigs (n = 40) were subjected to severe asphyxia, followed by 30 min ventilation with either 21% or 100% oxygen, and were observed for the subsequent 150 minutes in 21% oxygen. One 100% oxygen group was treated with NAC. Serum, bronchoalveolar lavage (BAL), lung sections, and lung tissue were obtained. Asphyxia resulted in profound hypoxia, hypercarbia and metabolic acidosis. In controls, HA staining was in airway subepithelial matrix and no 3-NT staining was seen. At the end of asphyxia, lavage HA decreased, whereas serum HA increased. At 150 minutes after resuscitation, exposure to 100% oxygen was associated with significantly higher BAL HA, increased 3NT staining, and increased fragmentation of lung HA. Lung neutrophil and macrophage contents, and serum TNFα and IL1ß were higher in animals with LMW than those with HMW HA in the lung. Treatment of 100% oxygen animals with NAC blocked nitrative stress, preserved HMW HA, and decreased inflammation. In vitro, peroxynitrite was able to fragment HA, and macrophages stimulated with LMW HA increased TNFα and IL1ß expression. CONCLUSIONS & SIGNIFICANCE: Compared to 21%, resuscitation with 100% oxygen resulted in increased peroxynitrite, fragmentation of HA, inflammation, as well as TNFα and IL1ß expression. Antioxidant treatment prevented the expression of peroxynitrite, the degradation of HA, and also blocked increases in inflammation and inflammatory cytokines. These findings provide insight into potential mechanisms by which exposure to hyperoxia results in systemic inflammation

Utilization of Different Aquaporin Water Channels in the Mouse Cervix During Pregnancy and Parturition and in Models of Preterm and Delayed Cervical Ripening Abbreviated Title: Aquaporin Water Channels in the Cervix

Abstract Biochemical changes of cervical connective tissue, including progressive disorganization of the collagen network and increased water content, occur during gestation to allow for cervical dilatation during labor, but the mechanisms that regulate cervical fluid balance are not fully understood. We examined whether aquaporins (AQPs), a family of membrane channel proteins that facilitate water transport, help mediate fluid balance in the mouse cervix during parturition. Of the thirteen known murine AQPs, AQP0-2, 6, 7, 9, 11 and 12 were absent or at the limits of detection. By Northern blot and real-time PCR, AQP3 expression was low in nongravid (NG) and mid-pregnancy cervices with peak expression on d19 and postpartum day 1 (PP1). AQP4 expression was generally low throughout pregnancy but showed a small upward trend at the time of parturition. AQP5 and AQP8 expression were significantly increased on d12-d15 but fell to NG/baseline by d19 and PP1. By in situ hybridization and immunohistochemistry, AQP3 was preferentially expressed in basal cell layers of the cervical epithelium whereas AQP4, 5, and 8 were primarily expressed in apical cell layers. Females with LPS-induced preterm labor had similar trends in AQP4, 5, and 8 expression to mice with natural labor at term gestation. Mice with delayed cervical remodeling due to deletion of the steroid 5α-reductase type 1 gene showed significant reduction in the levels of AQP3, 4, and 8 on d19 or PP1. Together, these studies suggest that AQPs 3, 4, 5, and 8 regulate distinct aspects of cervical water balance during pregnancy and parturition.

Overall model of the role of oxidative and nitrative stresses and LMW HA in asphyxia and hyperoxia-stimulated inflammation.

<p>Exposure to 100% oxygen in asphyxiated newborn pigs results in the production of superoxide and peroxynitrite that cause the fragmentation of HMW to LMW HA. LMW HA, in turn stimulates inflammatory cytokine expression in macrophages and promotes inflammation. Strategies to prevent the formation of LMW HA, such as limiting oxygen exposure or treatment with antioxidants (the current work) will result in decreased inflammation. This model predicts that direct blockade of LMW HA should also achieve the same result.</p

Hyaluronan content in bronchoalveolar lavage and serum, and expression of enzymes regulating hyaluronan synthesis and degradation.

<p>HA content was determined in BAL (A) and in serum (B). At the end of asphyxia, the HA content of BAL decreased and that in the serum increased. Resuscitation with 21% O₂ did not increase HA either in the BAL or in the serum. However, BAL HA was significantly increased in animals resuscitated with 100% O₂, and this increase was completely inhibited by treatment with NAC (A). The changes in hyaluronan synthase 1 (<i>has1</i>), <i>has2</i> and <i>has3</i>, as well as hyaluronidase 1 (<i>hyal1</i>) and 2 (<i>hyal2</i>) were determined using quantitative RT-PCR. There were no changes in <i>has1</i> and <i>has 3</i> expression (data not shown). Expression of <i>has2</i> (C) showed a trend to increased expression after asphyxia and 21% O₂ resuscitation. However, treatment with NAC significantly inhibited has2 expression compared to 100% O₂ resuscitation alone (C). The expression of <i>hyal1</i> (D) and <i>hyal2</i> (E) remained unchanged except that 100% O₂ exposed animals treated with NAC showed significantly increased expression of both hyaluronidases.</p