Why Do the Fetal Membranes Rupture Early after Fetoscopy? A Review

Iatrogenic preterm premature rupture of the fetal membranes (iPPROM) remains the Achilles' heel of keyhole fetal surgery (fetoscopy) despite significant efforts in preclinical models to develop new therapies. This limited success is partially due to incomplete understanding why the fetal membranes rupture early after fetoscopy and notable differences in membrane physiology between humans and domestic species. In this review, we summarize aspects of fetoscopy that may contribute to iPPROM, the previous efforts to develop new therapies, and limitations of preclinical models commonly used in fetal membrane research.

Histological evidence of reparative activity in chorioamniotic membrane following open fetal surgery for myelomeningocele

An increased understanding of the reparative process in fetal membrane following surgical techniques may be helpful to decrease the risks to mother and fetus and avoid adverse pregnancy outcomes. The present study discusses histological evaluation of the fetal membrane following open fetal surgery. Chorioamniotic membranes (n=10) were obtained following birth from pregnancies that underwent open fetal surgery for myelomeningocele. The collagen distribution was quantified using picrosirius-polarization method comparing the suture site with non-suture site. The differences between the collagen fiber percentages at the two sites was evaluated by the paired t-test with P<0.05. The mean gestational age of fetal surgery was 26.09±0.3 and 33.81±0.82 weeks at birth. The picrosirius red sign was more intense at the suture site, primarily associated with collagen type 1. Collagen observed in the surgical area was significantly increased (13.22±2.84%) compared with the non-surgical area (6.16±1.09%; P<0.0001). It was observed that the reparative activity at the suture site of the fetal membrane was characterized by a significant increase in collagen fibers. The findings suggest nascent collagen synthesis, tissue remodeling and repair of suture site, a mechanism likely to prevent the amniotic fluid leakage and maintain pregnancy following open fetal surgery.

Trauma induces overexpression of Cx43 in human fetal membrane defects

Objective

We developed an in vitro model to examine whether trauma induces connexin 43 (Cx43) expression and collagen organisation in the amniotic membrane (AM) of fetal membrane (FM) defects.

Method

Term human FM was traumatised in vitro. Cell morphology and Cx43 were examined in the wound edge AM by immunofluorescence (IMF) confocal microscopy and compared to control AM. Collagen microstructure was examined by second harmonic generation (SHG) imaging. Cell viability was assessed with calcein and ethidium staining.

Results

After trauma, the AM showed a dense region of cells, which had migrated towards the wound edge. In wound edge AM, Cx43 puncta was preferentially distributed in mesenchymal cells compared to epithelial cells with significant expression in the fibroblast layer than epithelial layer (p < 0.001). In the fibroblast layer, the collagen fibres were highly polarised and aligned in parallel to the axis of the wound edge AM. There was an absence of cell migration across the defect with no healing after 168 h. Cell viability of the FM after trauma was maintained during culture.

Conclusion

Cx43 overexpression in wounded AM drives structural changes in collagen that slows down efficacy of cell migration across the FM defect. © 2017 The Authors. Prenatal Diagnosis published by John Wiley & Sons, Ltd.

What's already known about this topic?

After fetal surgery, the human fetal membrane shows limited healing and overexpression of Cx43 at the wound edge.

Cx43 knockdown leads to accelerated wound healing by influencing cell migration and tissue dynamics.

What does this study add?

We developed an artificial fetal membrane model to examine Cx43 expression after trauma and changes in collagen dynamics.

We observed Cx43 overexpression and polarised collagen at the wound edge. These changes were found to be similar to human fetoscopic wounds after fetal surgery.

Increased TGF-β: a drawback of tracheal occlusion in human and experimental congenital diaphragmatic hernia?

Survivors of severe congenital diaphragmatic hernia (CDH) present significant respiratory morbidity despite lung growth induced by fetal tracheal occlusion (TO). We hypothesized that the underlying mechanisms would involve changes in lung extracellular matrix and dysregulated transforming growth factor (TGF)-β pathway, a key player in lung development and repair. Pulmonary expression of TGF-β signaling components, downstream effectors, and extracellular matrix targets were evaluated in CDH neonates who died between birth and the first few weeks of life after prenatal conservative management or TO, and in rabbit pups that were prenatally randomized for surgical CDH and TO vs. sham operation. Before tissue harvesting, lung tissue mechanics in rabbits was measured using the constant-phase model during the first 30 min of life. Human CDH and control fetal lungs were also collected from midterm onwards. Human and experimental CDH did not affect TGF-β/Smad2/3 expression and activity. In human and rabbit CDH lungs, TO upregulated TGF-β transcripts. Analysis of downstream pathways indicated increased Rho-associated kinases to the detriment of Smad2/3 activation. After TO, subtle accumulation of collagen and α-smooth muscle actin within alveolar walls was detected in rabbit pups and human CDH lungs with short-term mechanical ventilation. Despite TO-induced lung growth, mediocre lung tissue mechanics in the rabbit model was associated with increased transcription of extracellular matrix components. These results suggest that prenatal TO increases TGF-β/Rho kinase pathway, myofibroblast differentiation, and matrix deposition in neonatal rabbit and human CDH lungs. Whether this might influence postnatal development of sustainably ventilated lungs remains to be determined.

Effects of an intratracheally delivered anti-inflammatory protein (rhCC10) on physiological and lung structural indices in a juvenile model of acute lung injury

BACKGROUND

Mechanical ventilation results in acute lung trauma that can stimulate processes that alter lung development. Activation of matrix metalloproteinases (MMPs) and their tissue-produced inhibitors (TIMPs) is initiated by the inflammatory response to mechanical ventilation and are involved in breakdown of the basement membrane and parenchymal modeling.

OBJECTIVES

The aim of this study was to test the hypothesis that rhCC10, a lung anti-inflammatory mediator, would foster improved lung function, structural preservation, and a reduction in net MMP activity in a juvenile model of acute lung injury.

METHODS

Twenty-four juvenile rabbits were saline-lavage-injured and treated with 100 or 25 mg/kg surfactant (Survanta, Ross Labs) with or without rhCC10 (Claragen, Inc.; n=6 per group). Animals were ventilated for 4 h, then euthanized for in vitro surfactant function analysis, lung histomorphometry, and analysis of MMP-2, MMP-7, and MMP-9 and TIMPs 1 and 2 in the lung.

RESULTS

Apical lung expansion, reduced with the lower dose of surfactant, was partially restored with the addition of rhCC10. Alveolar septal wall thickness was reduced (p<0.05) with low-dose surfactant plus rhCC10 compared to high-dose surfactant alone. Increased within-group variance in MMP-2 and MMP-9 proteolytic activity was found with the low-dose surfactant and was abolished with rhCC10. MMP-7 was reduced (p<0.05) with rhCC10 administration, independent of surfactant dose.

CONCLUSIONS

Intratracheal administration of the anti-inflammatory rhCC10 resulted in preserved lung structure and MMP/TIMP profile after 4 h of mechanical ventilation, in a surfactant dose-dependent manner.