Micro-trabeculae, macro-plaques or mini-basement membranes in human term fetal membranes?

Effects of inhaled fluticasone propionate on extrinsic tongue muscles in rats

Obstructive sleep apnea (OSA) is more common in patients with asthma, and inhaled corticosteroids may contribute to OSA pathogenesis in these patients. This study tested the effects of orally inhaled fluticasone propionate (FP) on extrinsic tongue muscles. Unanesthetized rats were treated with FP or placebo for 28 days. On day 29, tongue retrusive and protrusive functions were tested via hypoglossal nerve stimulation under a state of anesthesia, followed by genioglossus (GG), styloglossus (SG) and hyoglossus (HG) muscle extraction, after euthanasia, for histology [myosin heavy chain (MHC) fibers and laminin content reflecting extracellular matrix (ECM)]. On protrusive testing, FP increased percent maximum tetanic force at 40 Hz (P = 0.03 vs. placebo) and endurance index (P = 0.029 vs. placebo). On retrusive testing, FP increased maximum twitch (P = 0.026 vs. placebo) and tetanic forces (P = 0.02 vs. placebo) with no effect on endurance index. On histology, FP increased GG cross-sectional area of MHC type IIa (P = 0.036 vs. placebo) and tended to increase type IIb (P = 0.057 vs. placebo) fibers and HG MHC IIx fibers (P = 0.065). The FP group had significantly increased laminin-stained areas, of greatest magnitude in the HG muscle. FP affects tongue protrusive and retrusive functions differently, concurrent with a shift in MHC fibers and increased ECM accumulation. These differential alterations may destabilize the tongue's "muscle hydrostat" during sleep and promote collapse.NEW & NOTEWORTHY The effects of inhaled corticosteroid on upper airway may contribute to OSA pathogenesis in asthma. In this study, we tested the effects of orally inhaled fluticasone propionate on tongue protrusive and retrusive functions and on tongue extrinsic muscle fiber composition and molecular properties. We found that fluticasone treatment: 1) increased protrusive endurance and retrusive maximum twitch and tetanic force; and 2) on histology, increased cross-sectional area of myosin heavy chain (MHC) type IIa fibers and tended to increase cross-sectional area of MHC type IIb fibers in the protrusive muscle and of MHC IIx fibers in the retrusors. It also increased laminin-stained areas, across extrinsic tongue muscles, of greatest magnitude in the retrusors; and 3) reduced protein degradation and activated pathways associated with increased protein synthesis in the protrusor. These differential effects on the protrusors and retrusors may destabilize the tongue's "muscle hydrostat" properties during sleep and promote collapse.

The concurrent emergence and causes of double volcanic hotspot tracks on the Pacific plate

Mantle plumes are buoyant upwellings of hot rock that transport heat from Earth's core to its surface, generating anomalous regions of volcanism that are not directly associated with plate tectonic processes. The best-studied example is the Hawaiian-Emperor chain, but the emergence of two sub-parallel volcanic tracks along this chain, Loa and Kea, and the systematic geochemical differences between them have remained unexplained. Here we argue that the emergence of these tracks coincides with the appearance of other double volcanic tracks on the Pacific plate and a recent azimuthal change in the motion of the plate. We propose a three-part model that explains the evolution of Hawaiian double-track volcanism: first, mantle flow beneath the rapidly moving Pacific plate strongly tilts the Hawaiian plume and leads to lateral separation between high- and low-pressure melt source regions; second, the recent azimuthal change in Pacific plate motion exposes high- and low-pressure melt products as geographically distinct volcanoes, explaining the simultaneous emergence of double-track volcanism across the Pacific; and finally, secondary pyroxenite, which is formed as eclogite melt reacts with peridotite, dominates the low-pressure melt region beneath Loa-track volcanism, yielding the systematic geochemical differences observed between Loa- and Kea-type lavas. Our results imply that the formation of double-track volcanism is transitory and can be used to identify and place temporal bounds on plate-motion changes.

Extracellular matrix, gap junctions, and retinal vascular homeostasis in diabetic retinopathy

The vascular basement membrane (BM) contains extracellular matrix (ECM) proteins that assemble in a highly organized manner to form a supportive substratum for cell attachment facilitating myriad functions that are vital to cell survival and overall retinal homeostasis. The BM provides a microenvironment in which bidirectional signaling through integrins regulates cell attachment, turnover, and functionality. In diabetic retinopathy, the BM undergoes profound structural and functional changes, and recent studies have brought to light the implications of such changes. Thickened vascular BM in the retinal capillaries actively participate in the development and progression of characteristic changes associated with diabetic retinopathy. High glucose (HG)-induced compromised cell-cell communication via gap junctions (GJ) in retinal vascular cells may disrupt homeostasis in the retinal microenvironment. In this review, the role of altered ECM synthesis, compromised GJ activity, and disturbed retinal homeostasis in the development of retinal vascular lesions in diabetic retinopathy are discussed.

Second harmonic generation microscopy of fetal membranes under deformation: normal and altered morphology

INTRODUCTION

Insight into the microstructure of fetal membrane and its response to deformation is important for understanding causes of preterm premature rupture of the membrane. However, the microstructure of fetal membranes under deformation has not been visualized yet. Second harmonic generation microscopy, combined with an in-situ stretching device, can provide this valuable information.

METHODS

Eight fetal membranes were marked over the cervix with methylene blue during elective caesarean section. One sample per membrane of reflected tissue, between the placenta and the cervical region, was cyclically stretched with a custom built inflation device. Samples were mounted on an in-situ stretching device and imaged with a multiphoton microscope at different deformation levels. Microstructural parameters such as thickness and collagen orientation were determined. Image entropy was evaluated for the spongy layer.

RESULTS

The spongy layer consistently shows an altered collagen structure in the cervical and cycled tissue compared with the reflected membrane, corresponding to a significantly higher image entropy. An increased thickness of collagenous layers was found in cervical and stretched samples in comparison to the reflected tissue. Significant collagen fibre alignment was found to occur already at moderate deformation in all samples.

CONCLUSIONS

For the first time, second harmonic generation microscopy has been used to visualize the microstructure of fetal membranes. Repeated mechanical loading was shown to affect the integrity of the amnion-chorion interface which might indicate an increased risk of premature rupture of fetal membrane. Moreover, mechanical loading might contribute to morphological alterations of the fetal membrane over the cervical region.

Type VII collagen associated with the basement membrane of amniotic epithelium forms giant anchoring rivets which penetrate a massive lamina reticularis

In human amnion a simple cuboidal epithelium and underlying fibroblast layer are separated by an almost acellular compact layer rich in collagen types I and III. This (>10 μm) layer, which may be a thick lamina reticularis, apparently presents an unusual set of conditions. Integration of the multilaminous tissue across it is apparently achieved by waisted structures which we have observed with the light microscope in frozen, paraffin-wax and semi-thin resin sections. We have also captured transmission and scanning electron micrographs of the structures. These structures which cross the compact layer we call "rivets". The composition of these "rivets" has been examined immunocytochemically and in three dimensions using the confocal laser scanning epi-fluorescence microscope. The rivets contain type VII collagen and an α6 integrin. They associate with type IV collagen containing structures (basement membrane lamina densa and spongy coils) and a special population of fibroblasts which may generate, maintain or anchor rivets to the underlying mesenchymal layer. Although type VII collagen is well known to anchor basal lamina to underlying mesodermal collagen fibres these "rivets" are an order of magnitude larger than any previously described type VII collagen containing anchoring structures. Intriguing possible functions of these features include nodes for growth of fibrous collagen sheets and sites of possible enzymatic degradation during regulated amnion weakening approaching term. If these sites are confirmed to be involved in amnion degradation and growth they may represent important targets for therapeutic agents that are designed to delay preterm premature rupture of the membranes a major cause of fetal morbidity and mortality.

Fetal membranes structure and prelabour rupture

In most pregnancies labour begins at term in the presence of intact fetal membranes. Without intervention the membranes usually spontaneously rupture near the end of the first stage of labour. In 10% of pregnancies that deliver at term the fetal membranes fail to maintain their structural integrity and this results in their “prelabour rupture”, defined as spontaneous rupture of membranes at least one hour before the onset of labour. In 95–98% of these cases at term, labour is precipitated within 48 hours. Although preterm birth, defined as birth prior to 37 completed weeks of pregnancy, occurs in only 7–8% of all pregnancies, 40–60% of these deliveries are preceded by prelabour rupture of the fetal membranes.

The chemical structure of the Hawaiian mantle plume

The Hawaiian-Emperor volcanic island and seamount chain is usually attributed to a hot mantle plume, located beneath the Pacific lithosphere, that delivers material sourced from deep in the mantle to the surface. The shield volcanoes of the Hawaiian islands are distributed in two curvilinear, parallel trends (termed 'Kea' and 'Loa'), whose rocks are characterized by general geochemical differences. This has led to the proposition that Hawaiian volcanoes sample compositionally distinct, concentrically zoned, regions of the underlying mantle plume. Melt inclusions, or samples of local magma 'frozen' in olivine phenocrysts during crystallization, may record complexities of mantle sources, thereby providing better insight into the chemical structure of plumes. Here we report the discovery of both Kea- and Loa-like major and trace element compositions in olivine-hosted melt inclusions in individual, shield-stage Hawaiian volcanoes--even within single rock samples. We infer from these data that one mantle source component may dominate a single lava flow, but that the two mantle source components are consistently represented to some extent in all lavas, regardless of the specific geographic location of the volcano. We therefore suggest that the Hawaiian mantle plume is unlikely to be compositionally concentrically zoned. Instead, the observed chemical variation is probably controlled by the thermal structure of the plume.

A histological study of fetoscopic membrane defects to document membrane healing

OBJECTIVE

To evaluate the rate of spontaneous healing in human fetal membranes after fetoscopy.

STUDY DESIGN

Membranes from patients that had undergone fetoscopic interventions and delivered in one of the two treatment centers were included in the study. The membranes were examined macroscopically for any remaining defects and if present, the size of the defect in chorion and amnion was measured. Subsequently, the defect was excised and stained with HE for histological evaluation. Additional immunohistochemical staining was performed with Ki-67, cytokeratin and vimentin. The proliferation index (percentage of proliferating cells) was calculated in amnion and chorion.

RESULTS

Nineteen membrane defects were included in the study. The median time interval between invasive procedures and delivery was 60 days (range 3-112). All fetoscopic defects (n=19) could be identified in the gestational sac and in none spontaneous closure had occurred. Proliferation indices as measured by inmunohistochemistry were very low (median 2.8%, range 0-7%) in the chorion and 0% in the amnion.

CONCLUSION

No evidence of spontaneous membrane healing was found after fetoscopic procedures, suggesting that the membrane defect normally persists until delivery. Absence of amniotic fluid leakage after invasive procedures may be based on mechanisms other than histologic membrane repair.

Localization and distribution of tissue type and urokinase type plasminogen activators and their inhibitors Type 1 and 2 in human and rhesus monkey fetal membranes

Fetal membranes consist of 10 distinct layers including components of amnion, chorion and decidua, the latter being of maternal origin. They form mechanically integrated sheets capable of retaining amniotic fluid and play an essential role in protecting fetal growth and development in the pregnant uterus. The extracellular matrix, substrate for plasminogen activators (PAs), is an important supportive framework of the fetal membranes. Fetal membranes from women with preterm premature rupture of membranes may differ in their protease activity compared with normal membranes. To identify the presence of PAs and their inhibitors (PAI) and their possible role in the process of fetal membrane rupture, this study investigated the distribution and localization of both protein and mRNA for tissue (t) and urokinase (u) PA and their inhibitors type 1 (PAI-1) and type 2 (PAI-2) in amniochorion of human and rhesus monkey using conventional and confocal immunofluorescence microscopy. In situ hybridization analysis showed that the distribution and localization of mRNAs for tPA, uPA, PAI-1 and PAI-2 were similar in the fetal membranes of human and rhesus monkey; no obvious species difference was observed. Evidence of tPA mRNA was detected in amniotic epithelium, trophoblast cells and nearly all cells of the decidual layer. Strong expression of uPA mRNA was noted in the decidual cells which increased in intensity as the abscission point was approached. Weak staining in chorion laeve trophoblast was also detected. In situ hybridization experiments showed PAI-1 mRNA to be concentrated mainly in the decidual cells, some of which were interposed into the maternal-facing edge of the chorion laeve. Maximal labelling of the decidua occurred towards the zone of abscission. Weak expression of PAI-1 mRNA was also noted in some cells of the chorion laeve. The distribution of PAI-2 mRNA in amniochorion was also concentrated in the cells of the decidual layer, maximum expression of the mRNA was in the level of abscission. No detectable amount of mRNAs for tPA, uPA, PAI-1 and PAI-2 was found in the fibroblast, reticular and spongy layers. Distribution of the proteins of tPA, uPA and PAI-1 in the fetal membranes of these two species was consistent with the distribution of their mRNA. Anti-PAI-2 immunofluorescence was found to be strongly concentrated in the amniotic epithelium, but PAI-2 mRNA was negative in this layer, suggesting that the epithelium-associated PAI-2 is not of epithelial origin. These findings suggest that a local fibrinolysis in fetal membranes generated by precisely balanced expression of PAs and their inhibitors via paracrine or autocrine mechanisms may play an essential role in fetal membrane development, maturation and in membrane rupture. Following an analysis of the distribution and synthesis of activators and inhibitors it was found that they may play a role in abscission during the third stage of labour.

Techniques of advanced light microscopy and their applications to morphological analysis of human extra-embryonic membranes

The science of light microscopy has advanced dramatically in recent years through the introduction of new technology. A brief description of scanning light microscopes, laser illumination, the confocal principle, digital imaging, and image processing reveals a number of theoretical advantages which are particularly useful in improving epifluorescence microscope images. Examples of results from several studies of human extra-embryonic membranes conducted in our laboratory show how the application of these techniques has been used to describe structures such as microtrabeculae and rivets for the first time, to map the microscopic distribution of a wide range of proteins, and to observe the activity of placental villi at the microscopic level in an environmentally controlled microscope stage. High-sensitivity detectors have permitted the "super-resolution" detection of structures smaller than the theoretically calculated limits of light microscope resolution. Rendering images in false colour is demonstrably useful in detecting subtle variations in fluorescence intensity at different intracellular sites and at different sites within tissues of fetal membranes. Processing stacks of digital images using appropriate software allows the 3-D reconstruction of suitably sized extra-embryonic membrane components. These digital images created from optical sections through the tissue are obtained non-destructively, and the relationships in space of the components are well preserved.

Immunohistochemical localization of fibrillin in developing macaque and term human placentas and fetal membranes

The objective of this study was to examine the developmental appearance of the extracellular matrix glycoprotein fibrillin in macaque placentas and fetal membranes and to compare this distribution to that seen in term human placentas and fetal membranes. Standard immunoperoxidase methods were used on paraformaldehyde-fixed, paraffin-embedded tissues. At early gestational ages (26-30 days), fibrillin was found in cell columns and cytotrophoblastic shell, with weak staining in the villous stroma. Staining was abundant in the shell and columns at 53 days as well, and stronger staining was seen in the stroma of the chorionic plate and stem villi. Staining in the shell and remnants of the cell columns in later gestation continued to be positive, though variable. Generally, the strongest staining was present in the distal cytotrophoblastic shell. Stroma in the tips of anchoring villi was also strongly positive. Later in gestation, fibrillin was observed around the multilayered cytotrophoblast of the chorionic plate. Fibrillin was abundant in the stromal cores of human term placental villi. In early macaque amnion, fibrillin staining was abundant in a layer beneath the amniotic epithelium. Later in gestation, macaque chorioamnion staining was generally similar to human term chorioamnion staining, with the heaviest staining in portions of the compact and reticular layers. Fibrillin was sometimes localized in regions known to be rich in connective tissue microfibrils, but, in other regions known to have abundant microfibrils, fibrillin staining was weak. This suggests that some microfibrils in placenta may be composed predominantly of some other protein(s). The function of fibrillin in the various placental compartments is unknown at present. It may provide attachment points for cells while at the same time providing a strong, yet flexible, matrix to accommodate growth particularly in areas subject to shear stress.

Stromal differentiation and architecture of the human umbilical cord

In order to assess the characteristics of its stromal cells and the distribution of extracellular matrix proteins, we investigated, immunohistochemically and ultrastructurally, term, first and second trimester human umbilical cords. A differential distribution pattern of the various cytoskeletal proteins of stromal cells and extracellular matrix proteins was observed in different zones of the stroma, the subamniotic stroma, Wharton's jelly, and the vessels' adventitia. All three zones showed immunoreactivities for collagen types I, III and VI and for basement membrane molecules such as collagen type IV, laminin and heparan sulphate proteoglycan. Immunoreactivities for these extracellular matrix molecules were observed around cleft-like territories (stromal clefts) in the Wharton's jelly which were occupied by homogeneous ground substance but void of collagen fibrils and basal lamina molecules. Moreover, between the stromal clefts, slender cells were found which immunohistochemically and ultrastructurally corresponded to various stages of myofibroblastic differentiation. In earlier stages of gestation, stromal cells with a less complex expression pattern prevailed. The stromal clefts and the contractile cells together might serve as a system regulating the turgor of the cord.

The pathobiology of premature rupture of membranes

Premature rupture of membranes arises from what are likely multifaceted and multistep pathogenic pathways. Pathophysiological processes may involve both endogenous and exogenous fetal and maternal factors. This article reviews and analyzes information regarding, first, the form and function of fetal membranes; second, how membranes physically fail (rupture) at term and preterm gestations; and third, evaluates if we can reduce risks of rupture using physiological understanding and evidence-based clinical studies.

Cryofracture of human term amniochorion

By use of cryofracture and scanning electron microscopy of human amniochorion we have captured images of all the major layers of the tissue. Correlation of confocal and electron-microscope data has allowed greater understanding of how these cellular and acellular layers interconnect in order to maintain their integrity as a multilaminar tissue. This is not straightforward as mutual sliding or area change is required of concentric curved surfaces which expand and contract as does the amnion. In this paper we suggest a mechanism by which the amnion is able to slide with respect to the chorion and still maintain continuity as a structural unit. It is based on the observation of complementary gyri and sulci on surfaces facing the spongy layer which is a shear plane. Cellular detail at higher resolution of the amniotic epithelium and acellular layers provides a more complete description of structural composition than was previously available.