Cilia are found on nearly every cell type in the mammalian body, and have been historically classified as either motile or immotile. Motile cilia are important for fluid and cellular movement; however, the roles of non-motile or primary cilia in most tissues remain unknown. Several genetic syndromes, called the ciliopathies, are associated with defects in cilia structure or function and have a wide range of clinical presentations. Much of what we know about the formation and maintenance of cilia comes from model systems like C. elegans and Chalmydomonas. Studies of mammalian cilia in live tissues have been hampered by difficulty visualizing them.
To facilitate analyses of mammalian cilia function we generated an inducible CiliaGFP mouse by targeting mouse cDNA encoding a cilia-localized protein somatostatin receptor 3 fused to GFP (Sstr3::GFP) into the ROSA26 locus. In this system, Sstr3::GFP is expressed from the ubiquitous ROSA26 promoter after Cre mediated deletion of an upstream Neo cassette flanked by lox P sites. Fluorescent cilia labeling was observed in a variety of live tissues and after fixation. Both cell-type specific and temporally regulated cilia labeling were obtained using multiple Cre lines. The analysis of renal cilia in anesthetized live mice demonstrates that cilia commonly lay nearly parallel to the apical surface of the tubule. In contrast, in more deeply anesthetized mice the cilia display a synchronized, repetitive oscillation that ceases upon death, suggesting a relationship to heart beat, blood pressure or glomerular filtration.
The ability to visualize cilia in live samples within the CiliaGFP mouse will greatly aid studies of ciliary function. This mouse will be useful for in vivo genetic and pharmacological screens to assess pathways regulating cilia motility, signaling, assembly, trafficking, resorption and length control and to study cilia regulated physiology in relation to ciliopathy phenotypes.
Somatostatin receptor 3; ROSA26 locus; Inducible transgene; In vivo cilia labeling; Intravital microscopy
To assess the feasibility of a randomized placebo controlled trial (RCT) of blood pressure (BP) management for extremely preterm infants.
This was a prospective pilot RCT of infants 230/7 – 266/7 weeks gestation who had protocol-defined low BP in the first 24 postnatal hours. Enrolled infants were administered a study infusion (dopamine or placebo) and a study syringe medication (hydrocortisone or placebo).
Of the 366 infants screened, 119 (33%) had low BP, 58 (16%) met all entry criteria, and 10 (3%) were enrolled. 161 (44%) infants were ineligible because they received early indomethacin. Only 17% of eligible infants were enrolled. Problems with consent included insufficient time, parent unavailability, and physician unwillingness to enroll critically ill infants. Two infants were withdrawn from the study due to the potential risk of intestinal perforation with simultaneous administration of hydrocortisone and indomethacin.
This pilot RCT was not feasible due to low eligibility and consent rates. An RCT of BP management for extremely preterm infants may require a waiver of consent for research in emergency care. The frequent use of early indomethacin and the associated risk of intestinal perforation when used with hydrocortisone may limit future investigations to only inotropic medications.
Extremely preterm infant; hypotension; hydrocortisone; dopamine; informed consent
Administration of retinoic acid, the active metabolite of vitamin A, is linked to the stimulation of nephrogenesis. The aim of this study was to determine whether early postnatal administration of retinoic acid (RA) could enhance ongoing nephrogenesis in a baboon model of premature birth. Unbiased stereological methods were employed to estimate kidney volume, renal corpuscle volume and nephron number. The percentage of abnormal glomeruli and the number of glomerular generations were also determined in the kidneys of preterm control (n=6) and preterm +RA (n=6) animals that received 500 μg/kg/day of all-trans retinoic acid following premature delivery. There was no significant difference between the preterm control and the preterm +RA groups in kidney size, nephron number (preterm control: 329,924 ± 41,752; preterm +RA: 354,041 ± 52,095; p = 0.59), renal corpuscle volume, number of glomerular generations, or the percentage of abnormal glomeruli. The proportion of abnormal glomeruli did not appear to be linked to any elements of postnatal care examined. The results of this study indicate that early postnatal administration of retinoic acid is unable to stimulate nephrogenesis in the kidney of the preterm baboon. Encouragingly, it does not appear to have any adverse effects on kidney development.
Vitamin A; Preterm Birth; Papio hamadryas; Kidney; Nephron
Cytosolic carboxypeptidase 1 (CCP1) is a metallopeptidase that removes C-terminal and side-chain glutamates from tubulin. The Purkinje cell degeneration (pcd) mouse lacks CCP1 due to a mutation. Previously, elevated levels of peptides derived from cytosolic and mitochondrial proteins were found in adult pcd mouse brain, raising the possibility that CCP1 functions in the degradation of intracellular peptides. To test this hypothesis, we used a quantitative peptidomics technique to compare peptide levels in wild-type and pcd mice, examining adult heart, spleen, and brain, and presymptomatic 3 week-old amygdala and cerebellum. Contrary to adult mouse brain, young pcd brain and adult heart and spleen did not show a large increase in levels of intracellular peptides. Unexpectedly, levels of peptides derived from secretory pathway proteins were altered in adult pcd mouse brain. The pattern of changes for the intracellular and secretory pathway peptides in pcd mice was generally similar to the pattern observed in mice lacking primary cilia. Collectively, these results suggest that intracellular peptide accumulation in adult pcd mouse brain is a secondary effect and is not due to a role of CCP1 in peptide turnover.
BACKGROUND AND OBJECTIVE:
The Surfactant Positive Airway Pressure and Pulse Oximetry Randomized Trial (SUPPORT) antenatal consent study demonstrated that mothers of infants enrolled in the SUPPORT trial had significantly different demographics and exposure to antenatal steroids compared with mothers of eligible, but not enrolled infants. The objective of this analysis was to compare the outcomes of bronchopulmonary dysplasia, severe retinopathy of prematurity, severe intraventricular hemorrhage or periventricular leukomalacia (IVH/PVL), death, and death/severe IVH/PVL for infants enrolled in SUPPORT in comparison with eligible, but not enrolled infants.
Perinatal characteristics and neonatal outcomes were compared for enrolled and eligible but not enrolled infants in bivariate analyses. Models were created to test the effect of enrollment in SUPPORT on outcomes, controlling for perinatal characteristics.
There were 1316 infants enrolled in SUPPORT; 3053 infants were eligible, but not enrolled. In unadjusted analyses, enrolled infants had significantly lower rates of death before discharge, severe IVH/PVL, death/severe IVH/PVL (all < 0.001), and bronchopulmonary dysplasia (P = .003) in comparison with eligible, but not enrolled infants. The rate of severe retinopathy of prematurity was not significantly different. After adjustment for perinatal factors, enrollment in the trial was not a significant predictor of any of the tested clinical outcomes.
The results of this analysis demonstrate significant outcome differences between enrolled and eligible but not enrolled infants in a trial using antenatal consent, which were likely due to enrollment bias resulting from the antenatal consent process. Additional research and regulatory review need to be conducted to ensure that large moderate-risk trials that require antenatal consent can be conducted in such a way as to ensure the generalizability of results.
antenatal steroids; clinical research/trials; informed consent; neonatal
Clusterin associated protein 1 (CLUAP1) was initially characterized as a protein that interacts with clusterin, and whose gene is frequently upregulated in colon cancer. Although the consequences of these observations remain unclear, research of CLUAP1 homologs in C. elegans and zebrafish indicates that it is needed for cilia assembly and maintenance in these models. To begin evaluating whether Cluap1 has an evolutionarily conserved role in cilia in mammalian systems and to explore the association of Cluap1 with disease pathogenesis and developmental abnormalities, we generated Cluap1 mutant mice.
Cluap1 mutant embryos were generated and examined for gross morphological and anatomical defects using light microscopy. Reverse transcription PCR, β-galactosidase staining assays, and immunofluorescence analysis were used to determine the expression of the gene and localization of the protein in vivo and in cultured cell lines. We also used immunofluorescence analysis and qRT-PCR to examine defects in the Sonic hedgehog signaling pathway in mutant embryos.
Cluap1 mutant embryos die in mid-gestation, indicating that it is necessary for proper development. Mutant phenotypes include a failure of embryonic turning, an enlarged pericardial sac, and defects in neural tube development. Consistent with the diverse phenotypes, Cluap1 is widely expressed. Furthermore, the Cluap1 protein localizes to primary cilia, and mutant embryos were found to lack cilia at embryonic day 9.5. The phenotypes observed in Cluap1 mutant mice are indicative of defects in Sonic hedgehog signaling. This was confirmed by analyzing hedgehog signaling activity in Cluap1 mutants, which revealed that the pathway is repressed.
These data indicate that the function of Cluap1 is evolutionarily conserved with regard to ciliogenesis. Further, the results implicate mammalian Cluap1 as a key regulator of hedgehog signaling and as an intraflagellar transport B complex protein. Future studies on mammalian Cluap1 utilizing this mouse model may provide insights into the role for Cluap1 in intraflagellar transport and the association with colon cancer and cystic kidney disorders.
Intraflagellar transport; Sonic hedgehog; Clusterin associated protein 1; IFT complex B
A spectrum of complex oligogenic disorders called the ciliopathies have been connected to dysfunction of cilia. Among the ciliopathies are Nephronophthisis (NPHP), characterized by cystic kidney disease and retinal degeneration, and Meckel–Gruber syndrome (MKS), a gestational lethal condition with skeletal abnormalities, cystic kidneys and CNS malformation. Mutations in multiple genes have been identified in NPHP and MKS patients, and an unexpected finding has been that mutations within the same gene can cause either disorder. Further, there is minimal genotype–phenotype correlation and despite recessive inheritance, numerous patients were identified as having a single heterozygous mutation. This has made it difficult to determine the significance of these mutations on disease pathogenesis and led to the hypothesis that clinical presentation in an individual will be determined by genetic interactions between mutations in multiple cilia-related genes. Here we utilize Caenorhabditis elegans and cilia-associated behavioral and morphologic assays to evaluate the pathogenic potential of eight previously reported human NPHP4 missense mutations. We assess the impact of these mutations on C. elegans NPHP-4 function, localization and evaluate potential interactions with mutations in MKS complex genes, mksr-2 and mksr-1. Six out of eight nphp-4 mutations analyzed alter ciliary function, and three of these modify the severity of the phenotypes caused by disruption of mksr-2 and mksr-1. Collectively, our studies demonstrate the utility of C. elegans as a tool to assess the pathogenicity of mutations in ciliopathy genes and provide insights into the complex genetic interactions contributing to the diversity of phenotypes associated with cilia disorders.
Rationale: Benefits of identifying risk factors for bronchopulmonary dysplasia in extremely premature infants include providing prognostic information, identifying infants likely to benefit from preventive strategies, and stratifying infants for clinical trial enrollment.
Objectives: To identify risk factors for bronchopulmonary dysplasia, and the competing outcome of death, by postnatal day; to identify which risk factors improve prediction; and to develop a Web-based estimator using readily available clinical information to predict risk of bronchopulmonary dysplasia or death.
Methods: We assessed infants of 23–30 weeks' gestation born in 17 centers of the Eunice Kennedy Shriver National Institute of Child Health and Human Development Neonatal Research Network and enrolled in the Neonatal Research Network Benchmarking Trial from 2000–2004.
Measurements and Main Results: Bronchopulmonary dysplasia was defined as a categorical variable (none, mild, moderate, or severe). We developed and validated models for bronchopulmonary dysplasia risk at six postnatal ages using gestational age, birth weight, race and ethnicity, sex, respiratory support, and FiO2, and examined the models using a C statistic (area under the curve). A total of 3,636 infants were eligible for this study. Prediction improved with advancing postnatal age, increasing from a C statistic of 0.793 on Day 1 to a maximum of 0.854 on Day 28. On Postnatal Days 1 and 3, gestational age best improved outcome prediction; on Postnatal Days 7, 14, 21, and 28, type of respiratory support did so. A Web-based model providing predicted estimates for bronchopulmonary dysplasia by postnatal day is available at https://neonatal.rti.org.
Conclusions: The probability of bronchopulmonary dysplasia in extremely premature infants can be determined accurately using a limited amount of readily available clinical information.
bronchopulmonary dysplasia; prematurity; low-birth-weight infant
Primary cilia are cellular protrusions which serve as mechanosensors for fluid flow. In endothelial cells (EC) they function in transducing local blood flow information into functional responses, like nitric oxide production and initiation of gene expression. Cilia are present on EC in areas of low or disturbed flow and absent in areas of high flow. In the embryonic heart high flow regime applies to the endocardial cushion area, and the absence of cilia here coincides with the process of endothelial-to-mesenchymal transition (EndoMT).
In this study we investigate the role of the primary cilium in defining the responses of EC to fluid shear stress and in EndoMT.
Methods and Results
Non-ciliated mouse embryonic EC with a mutation in Tg737/Ift88 were used to compare the response to fluid shear stress to that of ciliated EC. In vitro, non-ciliated EC undergo shear-induced EndoMT which is accompanied by downregulation of Klf4. This Tgfβ/Alk5 dependent transformation is prevented by blocking Tgfβ signaling, overexpression of Klf4, or rescue of the primary cilium. In the hearts of Tg737orpk/orpk embryos Tgfβ/Alk5 signaling was activated in areas in which EC would normally be ciliated, but now lack cilia due to the mutation. In these areas EC show increased Smad2 phosphorylation and expression of αSMA.
This study demonstrates the central role of primary cilia in rendering EC prone to shear-induced activation of Tgfβ/Alk5 signaling and EndoMT, and thereby provides a functional link between primary cilia and flow related endothelial performance.
cilia; shear stress; endothelial cells; Tg737orpk/orpk; EndoMT; Tgfβ/Alk5; Klf4
Ibuprofen-induced ductus closure improves pulmonary mechanics and increases alveolar surface area in premature baboons compared with baboons with a persistent patent ductus arteriosus (PDA). Ibuprofen-treatment has no effect on the expression of genes that regulate pulmonary inflammation but does increase the expression of alpha-ENaC (the transepithelial sodium channel that is critical for alveolar water clearance). Although ligation eliminates the PDA, it does not improve pulmonary mechanics or increase alveolar surface area. We used preterm baboons (delivered at 67% of term gestation and ventilated for 14 days) to study whether the lack of beneficial effects, following PDA ligation, might be due to alterations in pulmonary gene expression. We found no differences in Ventilation or Oxygenation Indices between animals that were ligated (n=7) on day of life 6 and those that had a persistent PDA (n=12) during the entire 14 days study. In contrast with no intervention, PDA ligation produced a significant increase in the expression of genes involved with pulmonary inflammation (COX-2, TNF-alpha, and CD14), and a significant decrease in alpha-ENaC sodium channel expression. We speculate that these changes may decrease the rate of alveolar fluid clearance and contribute to the lack of improvement in pulmonary mechanics after PDA ligation.
Estrogen receptors are present within the fetal brain suggesting that estrogens may exert an influence on cerebral development. Loss of placentally-derived estrogen in preterm birth may impair development.
Baboons were delivered at 125 days of gestation (term~185 days), randomly allocated to receive estradiol (n=10) or placebo (n=8) and ventilated for 14 days. Brains were assessed for developmental and neuropathological parameters.
Body and brain weights were not different between groups but the brain/body weight ratio was increased (p<0.05) in estradiol-treated animals. There were no differences (p>0.05) between groups in any neuropathological measure in either the forebrain or cerebellum. There were no intraventricular hemorrhages; one estradiol animal displayed ectactic vessels in the subarachnoid space.
Brief postnatal estradiol administration to primates does not pose an increased risk of injury or impaired brain development.
Postnatal estradiol; premature delivery; brain injury; brain development; baboon
Ibuprofen is an effective pharmacological intervention for closure of a patent ductus arteriosus in preterm infants, and is an alternative to surgical ligation; however it is not certain whether ibuprofen treatment is associated with adverse effects on the brain. Therefore, this study examined neuropathological outcomes of ibuprofen therapy for a patent ductus arteriosus. Fetal baboons were delivered at 125-days of gestation (dg, term ~185dg) by caesarean section, given surfactant and ventilated for 14-days with positive pressure ventilation. Baboons were randomly allocated to receive either ibuprofen (PPV + ibuprofen, n=8) or no therapy (PPV, n=5). Animals were euthanased on day 14 and brains assessed for cerebral growth, development and neuropathology. Body and brain weights, the total volume of the brain and the surface folding index (measure of brain growth) were not different (p>0.05) between PPV + ibuprofen-treated and PPV animals. There was no difference (p>0.05) in the number of myelin basic protein-immunoreactive oligodendrocytes, glial fibrillary acid protein-immunoreactive astrocytes or Iba1-immunoreactive macrophages/microglia in the forebrain. No overt cerebellar alterations were observed in either group. Ibuprofen treatment for patent ductus arteriosus closure in the preterm baboon neonate is not associated with any increased risk of neuropathology or alterations to brain growth and development.
Eight proteins, defects in which are associated with Meckel-Gruber syndrome and nephronophthisis ciliopathies, work together as two functional modules at the transition zone to establish basal body/transition zone connections with the membrane and barricade entry of non-ciliary components into this organelle.
Meckel-Gruber syndrome (MKS), nephronophthisis (NPHP), and related ciliopathies present with overlapping phenotypes and display considerable allelism between at least twelve different genes of largely unexplained function. We demonstrate that the conserved C. elegans B9 domain (MKS-1, MKSR-1, and MKSR-2), MKS-3/TMEM67, MKS-5/RPGRIP1L, MKS-6/CC2D2A, NPHP-1, and NPHP-4 proteins exhibit essential, collective functions at the transition zone (TZ), an underappreciated region at the base of all cilia characterized by Y-shaped assemblages that link axoneme microtubules to surrounding membrane. These TZ proteins functionally interact as members of two distinct modules, which together contribute to an early ciliogenic event. Specifically, MKS/MKSR/NPHP proteins establish basal body/TZ membrane attachments before or coinciding with intraflagellar transport–dependent axoneme extension and subsequently restrict accumulation of nonciliary components within the ciliary compartment. Together, our findings uncover a unified role for eight TZ-localized proteins in basal body anchoring and establishing a ciliary gate during ciliogenesis, and suggest that disrupting ciliary gate function contributes to phenotypic features of the MKS/NPHP disease spectrum.
We show that manipulation of either the microtubule or the actin cytoskeleton has unexpected influences on cilia length control.
The primary cilium is an evolutionarily conserved dynamic organelle important for regulating numerous signaling pathways, and, as such, mutations disrupting ciliogenesis result in a variety of developmental abnormalities and postnatal disorders. The length of the cilium is regulated by the cell through largely unknown mechanisms. Normal cilia length is important, as either shortened or elongated cilia have been associated with disease and developmental defects. Here we explore the importance of cytoskeletal dynamics in regulating cilia length. Using pharmacological approaches in different cell types, we demonstrate that actin depolymerization or stabilization and protein kinase A activation result in a rapid elongation of the primary cilium. The effects of pharmacological agents on cilia length are associated with a subsequent increase in soluble tubulin levels and can be impaired by depletion of soluble tubulin with taxol. In addition, subtle nocodazole treatment was able to induce ciliogenesis under conditions in which cilia are not normally formed and also increases cilia length on cells that have already established cilia. Together these data indicate that cilia length can be regulated through changes in either the actin or microtubule network and implicate a possible role for soluble tubulin levels in cilia length control.
Cell motility and migration play pivotal roles in numerous physiological and pathophysiological processes including development and tissue repair. Cell migration is regulated through external stimuli such as platelet-derived growth factor-AA (PDGF-AA), a key regulator in directional cell migration during embryonic development and a chemoattractant during postnatal migratory responses including wound healing. PDGFRα signaling is coordinated by the primary cilia in quiescent cells ; however little is known about the function of the primary cilium in cell migration. Here we used micropipette analysis to show that a normal chemosensory response to PDGF-AA in fibroblasts requires the primary cilium. In vitro and in vivo wound healing assays revealed that in ORPK mouse (IFT88Tg737Rpw) fibroblasts, where ciliary assembly is defective; chemotaxis towards PDGF-AA is absent, leading to unregulated high speed and uncontrolled directional cell displacement during wound closure, with subsequent defects in wound healing. These data suggest that in coordination with cytoskeletal reorganization, the fibroblast primary cilium functions via ciliary PDGFRα signaling to monitor directional movement during wound healing.
Fibroblasts; Cell migration; Primary cilia; Wound healing; PDGFRα; PDGF-AA
Cell motility and migration play pivotal roles in numerous physiological and pathophysiological processes including development and tissue repair. Cell migration is regulated through external stimuli such as platelet-derived growth factor-AA (PDGF-AA), a key regulator in directional cell migration during embryonic development and a chemoattractant during postnatal migratory responses including wound healing. We previously showed that PDGFRα signaling is coordinated by the primary cilium in quiescent cells. However, little is known about the function of the primary cilium in cell migration. Here we used micropipette analysis to show that a normal chemosensory response to PDGF-AA in fibroblasts requires the primary cilium. In vitro and in vivo wound healing assays revealed that in ORPK mouse (IFT88Tg737Rpw) fibroblasts, where ciliary assembly is defective, chemotaxis towards PDGF-AA is absent, leading to unregulated high speed and uncontrolled directional cell displacement during wound closure, with subsequent defects in wound healing. These data suggest that in coordination with cytoskeletal reorganization, the fibroblast primary cilium functions via ciliary PDGFRα signaling to monitor directional movement during wound healing.
Fibroblasts; Cell migration; Primary cilia; Wound healing; PDGFRα; PDGF-AA
High frequency oscillatory ventilation (HFOV) may improve pulmonary outcome in very preterm infants but the effects on the brain are largely unknown. We hypothesized that early prolonged HFOV compared to low volume positive pressure ventilation (LV-PPV) would not increase the risk of delayed brain growth or injury in a primate model of neonatal chronic lung disease. Baboons were delivered at 127±1 days` gestation (dg; term ~185dg), ventilated for 22–29 days with either: LV-PPV (n=6) or HFOV (n=5). Gestational controls were delivered at 153dg (n=4). Brains were assessed using quantitative histology. Body, brain and cerebellar weights were lower in both groups of prematurely delivered animals compared to controls; the brain to body weight ratio was higher in HFOV compared to LV-PPV and the surface folding index was lower in LV-PPV compared to controls. In both ventilated groups compared to controls, there was an increase in astrocytes and microglia and a decrease in oligodendrocytes (p<0.05) in the forebrain and a decrease in cerebellar granule cell proliferation (p<0.01); there was no difference between ventilated groups. LV-PPV and HFOV ventilation in prematurely delivered animals is associated with decreased brain growth and an increase in subtle neuropathologies; HFOV may minimize adverse effects on brain growth.
Respect for the primary cilium has undergone a remarkable renaissance over the past decade, and it is now thought to be an essential regulator of numerous signaling pathways. The primary cilium’s functions range from the movement of cells and fluid, to sensory inputs involved with olfaction and photoreception. Disruption of cilia function is involved in multiple human syndromes collectively called ‘ciliopathies’. The cilium’s activities are mediated by targeting of receptors, channels, and their downstream effector proteins to the ciliary or basal body compartment. These combined properties of the cilium make it a critical organelle facilitating the interactions between the cell and its environment. Here we review many of the recent advances contributing to the ascendancy of the primary cilium and how the extraordinary complexity of this organelle inevitably assures many more exciting future discoveries.
Although first described 1898 and long considered a vestigial organelle of little functional importance, the primary cilium has become one of the hottest research topics in modern cell biology and physiology. Primary cilia are non-motile sensory organelles present in a single copy on the surface of most growth-arrested or differentiated mammalian cells, and defects in their assembly or function are tightly coupled to many developmental defects, diseases and disorders. In normal tissues the primary cilium coordinates a series of signal transduction pathways, including Hedgehog, Wnt, PDGFRα and integrin signaling. In the kidney the primary cilium may function as a mechano-, chemo- and osmosensing unit that probes the extracellular environment and transmits signals to the cell via e.g. polycystins, which depend on ciliary localization for appropriate function. Indeed, hypomorphic mutations in the mouse ift88 (previously called Tg737) gene, which encodes a ciliogenic intraflagellar transport (IFT) protein, result in malformation of primary cilia, and in the collecting ducts of kidney tubules this is accompanied by development of autosomal recessive polycystic kidney disease (PKD; (1)). While PKD was one of the first diseases to be linked to dysfunctional primary cilia, defects in this organelle have subsequently been associated with many other phenotypes, including cancer, obesity, diabetes as well as a number of developmental defects. Collectively, these disorders of the cilium are now referred to as the ciliopathies. In this review we provide a brief overview of the structure and function of primary cilia and some of their roles in coordinating signal transduction pathways in mammalian development, health and disease. This review was written in conjunction with the Takis Anagnostopoulos Symposium on Renal and Epithelial Physiology and Physiopathology at Faculté de Médecine Necker in Paris, June 26-27, 2008.
Primary cilia; cellular GPS; signal transduction; development; tissue homeostasis; diseases; disorders; ciliopathies
Rationale: Nitric oxide (NO) plays an important role in lung development and perinatal lung function, and pulmonary NO synthases (NOS) are decreased in bronchopulmonary dysplasia (BPD) following preterm birth. Fetal estradiol levels increase during late gestation and estradiol up-regulates NOS, suggesting that after preterm birth estradiol deprivation causes attenuated lung NOS resulting in impaired pulmonary function.
Objective: To test the effects of postnatal estradiol administration in a primate model of BPD over 14 days after delivery at 125 days of gestation (term = 185 d).
Methods: Cardiopulmonary function was assessed by echocardiography and whole body plethysmography. Lung morphometric and histopathologic analyses were performed, and NOS enzymatic activity and abundance were measured.
Measurements and Main Results: Estradiol caused an increase in blood pressure and ductus arteriosus closure. Expiratory resistance and lung compliance were also improved, and this occurred before spontaneous ductal closure. Furthermore, both oxygenation and ventilation indices were improved with estradiol, and the changes in lung function and ventilatory support requirements persisted throughout the study period. Whereas estradiol had negligible effect on indicators of lung inflammation and on lung structure assessed after the initial 14 days of ventilatory support, it caused an increase in lung neuronal and endothelial NOS enzymatic activity.
Conclusions: In a primate model of BPD, postnatal estradiol treatment had favorable cardiovascular impact, enhanced pulmonary function, and lowered requirements for ventilatory support in association with an up-regulation of lung NOS. Estradiol may be an efficacious postnatal therapy to improve lung function and outcome in preterm infants.
A patent ductus arteriosus (PDA) alters pulmonary mechanics and regional blood flow in the preterm infant. Its significance with respect to brain injury and brain development are unclear. We evaluated the effects of surgical ductal ligation on the preterm baboon brain. Baboons were delivered at 125 days of gestation (dg, term ~185dg) and ventilated for 14 days (n=12). The PDA was ligated 6 days after delivery (n=7) or left untreated (n=5). Animals were euthanized at 139dg and brains compared histologically with gestational control fetuses (n=7) at 140dg. Brain and body weights were reduced (p<0.05) in both groups of ventilated preterm animals, however, the brain to body weight ratio was increased (p<0.01) in ligated but not unligated newborns compared to gestational controls. No overt lesions were observed in either premature newborn group. Astrocyte density in the neocortex and hippocampus were greatest in the unligated newborns (p<0.01). Myelination and oligodendrocytes were reduced (p<0.05) in both premature newborn groups. The brain growth and development index was reduced and the damage index was increased in prematurely delivered baboons. Surgical ligation of the PDA does not increase the incidence of brain injury and may be beneficial if the PDA is contributing to persistent pulmonary and hemodynamic instability.
non-human primate; prematurity; cerebral injury; positive pressure ventilation; brain development
The primary cilium is a microtubule-based organelle implicated as an essential component of a number of signaling pathways. It is present on cells throughout the mammalian body; however, its functions in most tissues remain largely unknown. Herein we demonstrate that primary cilia are present on cells in murine skin and hair follicles throughout morphogenesis and during hair follicle cycling in postnatal life. Using the Cre-lox system, we disrupted cilia assembly in the ventral dermis and evaluated the effects on hair follicle development. Mice with disrupted dermal cilia have severe hypotrichosis (lack of hair) in affected areas. Histological analyses reveal that most follicles in the mutants arrest at stage 2 of hair development and have small or absent dermal condensates. This phenotype is reminiscent of that seen in the skin of mice lacking Shh or Gli2. In situ hybridization and quantitative RT-PCR analysis indicates that the hedgehog pathway is downregulated in the dermis of the cilia mutant hair follicles. Thus, these data establish cilia as a critical signaling component required for normal hair morphogenesis and suggest that this organelle is needed on cells in the dermis for reception of signals such as sonic hedgehog.
Rationale: Bronchopulmonary dysplasia (BPD) is a frequent cause of morbidity in preterm infants that is characterized by prolonged need for ventilatory support in an intensive care environment. BPD is characterized histopathologically by persistently thick, cellular distal airspace walls. In normally developing lungs, by comparison, remodeling of the immature parenchymal architecture is characterized by thinning of the future alveolar walls, a process predicated on cell loss through apoptosis.
Objectives: We hypothesized that minimizing lung injury, using high-frequency nasal ventilation to provide positive distending pressure with minimal assisted tidal volume displacement, would increase apoptosis and decrease proliferation among mesenchymal cells in the distal airspace walls compared with a conventional mode of support (intermittent mandatory ventilation).
Methods: Accordingly, we compared two groups of preterm lambs: one group managed by high-frequency nasal ventilation and a second group managed by intermittent mandatory ventilation. Each group was maintained for 3 days.
Measurements and Main Results: Oxygenation and ventilation targets were sustained with lower airway pressures and less supplemental oxygen in the high-frequency nasal ventilation group, in which alveolarization progressed. Thinning of the distal airspace walls was accompanied by more apoptosis, and less proliferation, among mesenchymal cells of the high-frequency nasal ventilation group, based on morphometric, protein abundance, and mRNA expression indices of apoptosis and proliferation.
Conclusions: Our study shows that high-frequency nasal ventilation preserves the balance between mesenchymal cell apoptosis and proliferation in the distal airspace walls, such that alveolarization progresses.
alveolar formation; bronchopulmonary dysplasia; chronic lung disease of prematurity; morphometry; stereology
The Oak Ridge Polycystic Kidney (ORPK) mouse was described nearly 14 years ago as a model for human recessive Polycystic Kidney Disease. The ORPK mouse arose through integration of a transgene into an intron of the ift88 gene resulting in a hypomorphic allele (Ift88Tg737Rpw). The Ift88Tg737Rpw mutation impairs intraflagellar transport (IFT), a process required for assembly of motile and immotile cilia. Historically, the primary immotile cilium was thought to have minimal importance for human health; however, a rapidly expanding number of human disorders have now been attributed to ciliary defects. Importantly, many of these phenotypes are present and can be analyzed using the ORPK mouse. In this review, we highlight the research conducted using the OPRK mouse and the phenotypes shared with human cilia disorders. Further, we describe an additional follicular dysplasia phenotype in the ORPK mouse, which alongside the ectodermal dysplasias seen in human Ellis-van Creveld and Sensenbrenner’s syndromes, suggests an unappreciated role for primary cilia in the skin and hair follicle.
Cilia; ciliopathies; hair follicle; skin; IFT88
Rationale: The incidence of bronchopulmonary dysplasia (BPD), a chronic lung disease of newborns, is paradoxically rising despite medical advances. We demonstrated elevated bombesin-like peptide levels in infants that later developed BPD. In the 140-day hyperoxic baboon model of BPD, anti-bombesin antibody 2A11 abrogated lung injury.
Objectives: To test the hypothesis that bombesin-like peptides mediate BPD in extremely premature baboons (born at Gestational Day 125 and given oxygen pro re nata [PRN], called the 125-day PRN model), similar to “modern-day BPD.”
Methods: The 125-day animals were treated with 2A11 on Postnatal Day 1 (P1), P3, and P6. On P14 and P21, lungs were inflation-fixed for histopathologic analyses of alveolarization. Regulation of angiogenesis by bombesin was evaluated using cultured pulmonary microvascular endothelial cells.
Measurements and Main Results: In 125-day PRN animals, urine bombesin-like peptide levels at P2–3 are directly correlated with impaired lung function at P14. Gastrin-releasing peptide (the major pulmonary bombesin-like peptide) mRNA was elevated eightfold at P1 and remained high thereafter. At P14, 2A11 reduced alveolar wall thickness and increased the percentage of secondary septa containing endothelial cells. At P21, 2A11-treated 125-day PRN animals had improved alveolarization according to mean linear intercepts and number of branch points per millimeter squared. Bombesin promoted tubulogenesis of cultured pulmonary microvascular endothelial cells, but cocultured fetal lung mesenchymal cells abrogated this effect.
Conclusions: Early bombesin-like peptide overproduction in 125-day PRN animals predicted alveolarization defects weeks later. Bombesin-like peptide blockade improved septation, with the greatest effects at P21. This could have implications for preventing BPD in premature infants.
bombesin; gastrin-releasing peptide; mechanical ventilation; prematurity; antibody treatment