Sensory functions of motile cilia and implication for bronchiectasis

Uncovering cilia function in glial development

Primary cilia play critical roles in regulating signaling pathways that underlie several developmental processes. In the nervous system, cilia are known to regulate signals that guide neuron development. Cilia dysregulation is implicated in neurological diseases, and the underlying mechanisms remain poorly understood. Cilia research has predominantly focused on neurons and has overlooked the diverse population of glial cells in the brain. Glial cells play essential roles during neurodevelopment, and their dysfunction contributes to neurological disease; however, the relationship between cilia function and glial development is understudied. Here we review the state of the field and highlight the glial cell types where cilia are found and the ciliary functions that are linked to glial development. This work uncovers the importance of cilia in glial development and raises outstanding questions for the field. We are poised to make progress in understanding the function of glial cilia in human development and their contribution to neurological diseases.

Cilia and Cancer: From Molecular Genetics to Therapeutic Strategies

Cilia are microtubule-based organelles that project from the cell surface with motility or sensory functions. Primary cilia work as antennae to sense and transduce extracellular signals. Cilia critically control proliferation by mediating cell-extrinsic signals and by regulating cell cycle entry. Recent studies have shown that primary cilia and their associated proteins also function in autophagy and genome stability, which are important players in oncogenesis. Abnormal functions of primary cilia may contribute to oncogenesis. Indeed, defective cilia can either promote or suppress cancers, depending on the cancer-initiating mutation, and the presence or absence of primary cilia is associated with specific cancer types. Together, these findings suggest that primary cilia play important, but distinct roles in different cancer types, opening up a completely new avenue of research to understand the biology and treatment of cancers. In this review, we discuss the roles of primary cilia in promoting or inhibiting oncogenesis based on the known or predicted functions of cilia and cilia-associated proteins in several key processes and related clinical implications.

Prognostic analysis of m6A-related genes as potential biomarkers in idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a progressive, fatal lung disease with limited treatment options. N6-methyladenosine (m6A) is a reversible RNA modification and has been implicated in various biological processes. However, there are few studies on m6A in IPF. This project mainly explores the prognostic value of m6A-related genes as potential biomarkers in IPF, in order to establish a set of accurate prognostic prediction model. In this study, we used GSE28042 dataset in GEO database to screen out 218 m6A-related candidate genes with high IPF correlation and high differential expression through differentially expressed gene analysis, WGCNA and m6A correlation analysis. The genes associated with the prognosis of IPF were screened out by univariate Cox regression analysis, LASSO analysis, and multivariate Cox regression analysis, and the multivariate Cox model of prognostic risk of related genes was constructed. We found that RBM11, RBM47, RIC3, TRAF5 and ZNF14 were key genes in our model. Finally, the prognostic prediction ability and independent prognostic characteristics of the risk model were evaluated by survival analysis and independent prognostic analysis, and verified by the GSE93606 dataset, which proved that the prognostic risk model we constructed has a strong and stable prediction efficiency.

Fluorescence imaging of beta cell primary cilia

Primary cilia are slender cell-surface organelles that project into the intercellular space. In pancreatic beta cells, primary cilia coordinate a variety of cell responses including GPCR signaling, calcium influx, and insulin secretion, along with likely many underappreciated roles in islet development and differentiation. To study cilia function in islet biology, direct visualization of primary cilia by microscopic methods is often a necessary first step. Ciliary abundance, distribution, and morphology are heterogeneous among islet cells and are best visualized by fluorescence microscopy, the tools for which are readily accessible to most researchers. Here we present a collection of fluorescence imaging methods that we have adopted and optimized for the observation of primary cilia in mouse and human islets. These include conventional confocal microscopy using fixed islets and pancreas sections, live-cell imaging with cilia-targeted biosensors and probes, cilia motion recordings, and quantitative analysis of primary cilia waveform in the ex vivo environment. We discuss practical considerations and limitations of our approaches as well as new tools on the horizon to facilitate the observation of primary cilia in pancreatic islets.

PCD Genes-From Patients to Model Organisms and Back to Humans

Primary ciliary dyskinesia (PCD) is a hereditary genetic disorder caused by the lack of motile cilia or the assembxly of dysfunctional ones. This rare human disease affects 1 out of 10,000-20,000 individuals and is caused by mutations in at least 50 genes. The past twenty years brought significant progress in the identification of PCD-causative genes and in our understanding of the connections between causative mutations and ciliary defects observed in affected individuals. These scientific advances have been achieved, among others, due to the extensive motile cilia-related research conducted using several model organisms, ranging from protists to mammals. These are unicellular organisms such as the green alga Chlamydomonas, the parasitic protist Trypanosoma, and free-living ciliates, Tetrahymena and Paramecium, the invertebrate Schmidtea, and vertebrates such as zebrafish, Xenopus, and mouse. Establishing such evolutionarily distant experimental models with different levels of cell or body complexity was possible because both basic motile cilia ultrastructure and protein composition are highly conserved throughout evolution. Here, we characterize model organisms commonly used to study PCD-related genes, highlight their pros and cons, and summarize experimental data collected using these models.

Epigenetically Mediated Ciliogenesis and Cell Cycle Regulation, and Their Translational Potential

Primary cilia biogenesis has been closely associated with cell cycle progression. Cilia assemble when cells exit the cell cycle and enter a quiescent stage at the post-mitosis phase, and disassemble before cells re-enter a new cell cycle. Studies have focused on how the cell cycle coordinates with the cilia assembly/disassembly process, and whether and how cilia biogenesis affects the cell cycle. Appropriate regulation of the functions and/or expressions of ciliary and cell-cycle-associated proteins is pivotal to maintaining bodily homeostasis. Epigenetic mechanisms, including DNA methylation and histone/chromatin modifications, are involved in the regulation of cell cycle progression and cilia biogenesis. In this review, first, we discuss how epigenetic mechanisms regulate cell cycle progression and cilia biogenesis through the regulation of DNA methylation and chromatin structures, to either promote or repress the transcription of genes associated with those processes and the modification of cytoskeleton network, including microtubule and actin. Next, we discuss the crosstalk between the cell cycle and ciliogenesis, and the involvement of epigenetic regulators in this process. In addition, we discuss cilia-dependent signaling pathways in cell cycle regulation. Understanding the mechanisms of how epigenetic regulators contribute to abnormal cell cycle regulation and ciliogenesis defects would lead to developing therapeutic strategies for the treatment of a wide variety of diseases, such as cancers, polycystic kidney disease (PKD), and other ciliopathy-associated disorders.

Can cilia provide an entry gateway for SARS-CoV-2 to human ciliated cells?

A worldwide coronavirus pandemic is in full swing and, at the time of writing, there are only few treatments that have been successful in clinical trials, but no effective antiviral treatment has been approved. Because of its lethality, it is important to understand the current strain's effects and mechanisms not only in the respiratory system but also in other affected organ systems as well. Past coronavirus outbreaks caused by SARS-CoV and MERS-CoV inflicted life-threatening acute kidney injuries (AKI) on their hosts leading to significant mortality rates, which went somewhat overlooked in the face of the severe respiratory effects. Recent evidence has emphasized renal involvement in SARS-CoV-2, stressing that kidneys are damaged in patients with COVID-19. The mechanism by which this virus inflicts AKI is still unclear, but evidence from other coronavirus strains may hold some clues. Two theories exist for the proposed mechanism of AKI: 1) the AKI is a secondary effect to reduced blood and oxygen levels causing hyperinflammation and 2) the AKI is due to cytotoxic effects. Kidneys express angiotensin-converting enzyme-2 (ACE2), the confirmed SARS-CoV-2 target receptor as well as collectrin, an ACE2 homologue that localizes to the primary cilium, an organelle historically targeted by coronaviruses. Although the available literature suggests that kidney damage is leading to higher mortality rates in patients with COVID-19, especially in those with preexisting kidney and cardiovascular diseases, the pathogenesis of COVID-19 is still being investigated. Here, we present brief literature review supporting our proposed hypothesis of a possible link between SARS-CoV-2 cellular infection and cilia.

Intraflagellar Transport Proteins as Regulators of Primary Cilia Length

Primary cilia are small, antenna-like organelles that detect and transduce chemical and mechanical cues in the extracellular environment, regulating cell behavior and, in turn, tissue development and homeostasis. Primary cilia are assembled via intraflagellar transport (IFT), which traffics protein cargo bidirectionally along a microtubular axoneme. Ranging from 1 to 10 μm long, these organelles typically reach a characteristic length dependent on cell type, likely for optimum fulfillment of their specific roles. The importance of an optimal cilia length is underscored by the findings that perturbation of cilia length can be observed in a number of cilia-related diseases. Thus, elucidating mechanisms of cilia length regulation is important for understanding the pathobiology of ciliary diseases. Since cilia assembly/disassembly regulate cilia length, we review the roles of IFT in processes that affect cilia assembly/disassembly, including ciliary transport of structural and membrane proteins, ectocytosis, and tubulin posttranslational modification. Additionally, since the environment of a cell influences cilia length, we also review the various stimuli encountered by renal epithelia in healthy and diseased states that alter cilia length and IFT.

First contact: the role of respiratory cilia in host-pathogen interactions in the airways

Respiratory cilia are the driving force of the mucociliary escalator, working in conjunction with secreted airway mucus to clear inhaled debris and pathogens from the conducting airways. Respiratory cilia are also one of the first contact points between host and inhaled pathogens. Impaired ciliary function is a common pathological feature in patients with chronic airway diseases, increasing susceptibility to respiratory infections. Common respiratory pathogens, including viruses, bacteria, and fungi, have been shown to target cilia and/or ciliated airway epithelial cells, resulting in a disruption of mucociliary clearance that may facilitate host infection. Despite being an integral component of airway innate immunity, the role of respiratory cilia and their clinical significance during airway infections are still poorly understood. This review examines the expression, structure, and function of respiratory cilia during pathogenic infection of the airways. This review also discusses specific known points of interaction of bacteria, fungi, and viruses with respiratory cilia function. The emerging biological functions of motile cilia relating to intracellular signaling and their potential immunoregulatory roles during infection will also be discussed.

Novel non-cystic features of polycystic kidney disease: having new eyes or seeking new landscapes

For decades, researchers have been trying to decipher the complex pathophysiology of autosomal dominant polycystic kidney disease (ADPKD). So far these efforts have led to clinical trials with different candidate treatments, with tolvaptan being the only molecule that has gained approval for this indication. As end-stage kidney disease due to ADPKD has a substantial impact on health expenditures worldwide, it is likely that new drugs targeting kidney function will be developed. On the other hand, recent clinical observations and experimental data, including PKD knockout models in various cell types, have revealed unexpected involvement of many other organs and cell systems of variable severity. These novel non-cystic features, some of which, such as lymphopenia and an increased risk to develop infections, should be validated or further explored and might open new avenues for better risk stratification and a more tailored approach. New insights into the aberrant pathways involved with abnormal expression of PKD gene products polycystin-1 and -2 could, for instance, lead to a more directed approach towards early-onset endothelial dysfunction and subsequent cardiovascular disease. Furthermore, a better understanding of cellular pathways in PKD that can explain the propensity to develop certain types of cancer can guide post-transplant immunosuppressive and prophylactic strategies. In the following review article we will systematically discuss recently discovered non-cystic features of PKD and not well-established characteristics. Overall, this knowledge could enable us to improve the outcome of PKD patients apart from ongoing efforts to slow down cyst growth and attenuate kidney function decline.

Primary cilia biogenesis and associated retinal ciliopathies

The primary cilium is a ubiquitous microtubule-based organelle that senses external environment and modulates diverse signaling pathways in different cell types and tissues. The cilium originates from the mother centriole through a complex set of cellular events requiring hundreds of distinct components. Aberrant ciliogenesis or ciliary transport leads to a broad spectrum of clinical entities with overlapping yet highly variable phenotypes, collectively called ciliopathies, which include sensory defects and syndromic disorders with multi-organ pathologies. For efficient light detection, photoreceptors in the retina elaborate a modified cilium known as the outer segment, which is packed with membranous discs enriched for components of the phototransduction machinery. Retinopathy phenotype involves dysfunction and/or degeneration of the light sensing photoreceptors and is highly penetrant in ciliopathies. This review will discuss primary cilia biogenesis and ciliopathies, with a focus on the retina, and the role of CP110-CEP290-CC2D2A network. We will also explore how recent technologies can advance our understanding of cilia biology and discuss new paradigms for developing potential therapies of retinal ciliopathies.

Multiscale mechanics of mucociliary clearance in the lung

Mucociliary clearance (MCC) is one of the most important defence mechanisms of the human respiratory system. Its failure is implicated in many chronic and debilitating airway diseases. However, due to the complexity of lung organization, we currently lack full understanding on the relationship between these regional differences in anatomy and biology and MCC functioning. For example, it is unknown whether the regional variability of airway geometry, cell biology and ciliary mechanics play a functional role in MCC. It therefore remains unclear whether the regional preference seen in some airway diseases could originate from local MCC dysfunction. Though great insights have been gained into the genetic basis of cilia ultrastructural defects in airway ciliopathies, the scaling to regional MCC function and subsequent clinical phenotype remains unpredictable. Understanding the multiscale mechanics of MCC would help elucidate genotype-phenotype relationships and enable better diagnostic tools and treatment options. Here, we review the hierarchical and variable organization of ciliated airway epithelium in human lungs and discuss how this organization relates to MCC function. We then discuss the relevancy of these structure-function relationships to current topics in lung disease research. Finally, we examine how state-of-the-art computational approaches can help address existing open questions. This article is part of the Theo Murphy meeting issue 'Unity and diversity of cilia in locomotion and transport'.

Rare Human Diseases: Model Organisms in Deciphering the Molecular Basis of Primary Ciliary Dyskinesia

Primary ciliary dyskinesia (PCD) is a recessive heterogeneous disorder of motile cilia, affecting one per 15,000-30,000 individuals; however, the frequency of this disorder is likely underestimated. Even though more than 40 genes are currently associated with PCD, in the case of approximately 30% of patients, the genetic cause of the manifested PCD symptoms remains unknown. Because motile cilia are highly evolutionarily conserved organelles at both the proteomic and ultrastructural levels, analyses in the unicellular and multicellular model organisms can help not only to identify new proteins essential for cilia motility (and thus identify new putative PCD-causative genes), but also to elucidate the function of the proteins encoded by known PCD-causative genes. Consequently, studies involving model organisms can help us to understand the molecular mechanism(s) behind the phenotypic changes observed in the motile cilia of PCD affected patients. Here, we summarize the current state of the art in the genetics and biology of PCD and emphasize the impact of the studies conducted using model organisms on existing knowledge.

Cyclic compression increases F508 Del CFTR expression in ciliated human airway epithelium

The mechanisms by which transepithelial pressure changes observed during exercise and airway clearance can benefit lung health are challenging to study. Here, we have studied 117 mature, fully ciliated airway epithelial cell filters grown at air-liquid interface grown from 10 cystic fibrosis (CF) and 19 control subjects. These were exposed to cyclic increases in apical air pressure of 15 cmH₂O for varying times. We measured the effect on proteins relevant to lung health, with a focus on the CF transmembrane regulator (CFTR). Immunoflourescence and immunoblot data were concordant in demonstrating that air pressure increased F508Del CFTR expression and maturation. This effect was in part dependent on the presence of cilia, on Ca²⁺ influx, and on formation of nitrogen oxides. These data provide a mechanosensory mechanism by which changes in luminal air pressure, like those observed during exercise and airway clearance, can affect epithelial protein expression and benefit patients with diseases of the airways.

The regulation of cilium assembly and disassembly in development and disease

The primary cilium is an antenna-like organelle assembled on most types of quiescent and differentiated mammalian cells. This immotile structure is essential for interpreting extracellular signals that regulate growth, development and homeostasis. As such, ciliary defects produce a spectrum of human diseases, termed ciliopathies, and deregulation of this important organelle also plays key roles during tumor formation and progression. Recent studies have begun to clarify the key mechanisms that regulate ciliary assembly and disassembly in both normal and tumor cells, highlighting new possibilities for therapeutic intervention. Here, we review these exciting new findings, discussing the molecular factors involved in cilium formation and removal, the intrinsic and extrinsic control of cilium assembly and disassembly, and the relevance of these processes to mammalian cell growth and disease.

Coexisting cystic lung disease as a rare extra-renal manifestation of autosomal dominant polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) classically presents with multiple bilateral renal cysts and ultimately progresses to end stage renal disease. While many of the extra-renal manifestations of ADPKD are well-documented, associated pulmonary findings are particularly rare, having only been recently been reported in a handful of studies to date. A 69-year-old female with ADPKD presented to our hospital with respiratory complaints. High resolution computed tomography revealed bronchiectasis, cystic lung disease, and interstitial fibrosis. The patient did not have concurrent risk factors or coexisting disease processes to explain the etiology of her airway and cystic lung disease, which we suggest are manifestations of ADPKD. We have not found a previous report of interstitial lung disease in this setting.

Seeing cilia: imaging modalities for ciliary motion and clinical connections

The respiratory tract is lined with multiciliated epithelial cells that function to move mucus and trapped particles via the mucociliary transport apparatus. Genetic and acquired ciliopathies result in diminished mucociliary clearance, contributing to disease pathogenesis. Recent innovations in imaging technology have advanced our understanding of ciliary motion in health and disease states. Application of imaging modalities including transmission electron microscopy, high-speed video microscopy, and micron-optical coherence tomography could improve diagnostics and be applied for precision medicine. In this review, we provide an overview of ciliary motion, imaging modalities, and ciliopathic diseases of the respiratory system including primary ciliary dyskinesia, cystic fibrosis, chronic obstructive pulmonary disease, and idiopathic pulmonary fibrosis.

Alcohol consumption impairs the ependymal cilia motility in the brain ventricles

Ependymal cilia protrude into the central canal of the brain ventricles and spinal cord to circulate the cerebral spinal fluid (CSF). Ependymal cilia dysfunction can hinder the movement of CSF leading to an abnormal accumulation of CSF within the brain known as hydrocephalus. Although the etiology of hydrocephalus was studied before, the effects of ethanol ingestion on ependymal cilia function have not been investigated in vivo. Here, we report three distinct types of ependymal cilia, type-I, type-II and type-III classified based upon their beating frequency, their beating angle, and their distinct localization within the mouse brain-lateral ventricle. Our studies show for the first time that oral gavage of ethanol decreased the beating frequency of all three types of ependymal cilia in both the third and the lateral rat brain ventricles in vivo. Furthermore, we show for the first time that hydin, a hydrocephalus-inducing gene product whose mutation impairs ciliary motility, and polycystin-2, whose ablation is associated with hydrocephalus are colocalized to the ependymal cilia. Thus, our studies reinforce the presence of three types of ependymal cilia in the brain ventricles and demonstrate the involvement of ethanol as a risk factor for the impairment of ependymal cilia motility in the brain.

The development and functions of multiciliated epithelia

Multiciliated cells are epithelial cells that are in contact with bodily fluids and are required for the proper function of major organs including the brain, the respiratory system and the reproductive tracts. Their multiple motile cilia beat unidirectionally to remove particles of external origin from their surface and/or drive cells or fluids into the lumen of the organs. Multiciliated cells in the brain are produced once, almost exclusively during embryonic development, whereas in respiratory tracts and oviducts they regenerate throughout life. In this Review, we provide a cell-to-organ overview of multiciliated cells and highlight recent studies that have greatly increased our understanding of the mechanisms driving the development and function of these cells in vertebrates. We discuss cell fate determination and differentiation of multiciliated cells, and provide a comprehensive account of their locations and functions in mammals.

Multiciliated Cells in Animals

Many animal cells assemble single cilia involved in motile and/or sensory functions. In contrast, multiciliated cells (MCCs) assemble up to 300 motile cilia that beat in a coordinate fashion to generate a directional fluid flow. In the human airways, the brain, and the oviduct, MCCs allow mucus clearance, cerebrospinal fluid circulation, and egg transportation, respectively. Impairment of MCC function leads to chronic respiratory infections and increased risks of hydrocephalus and female infertility. MCC differentiation during development or repair involves the activation of a regulatory cascade triggered by the inhibition of Notch activity in MCC progenitors. The downstream events include the simultaneous assembly of a large number of basal bodies (BBs)-from which cilia are nucleated-in the cytoplasm of the differentiating MCCs, their migration and docking at the plasma membrane associated to an important remodeling of the actin cytoskeleton, and the assembly and polarization of motile cilia. The direction of ciliary beating is coordinated both within cells and at the tissue level by a combination of planar polarity cues affecting BB position and hydrodynamic forces that are both generated and sensed by the cilia. Herein, we review the mechanisms controlling the specification and differentiation of MCCs and BB assembly and organization at the apical surface, as well as ciliary assembly and coordination in MCCs.

Planar Organization of Multiciliated Ependymal (E1) Cells in the Brain Ventricular Epithelium

Cerebrospinal fluid (CSF) continuously flows through the cerebral ventricles, a process essential for brain homeostasis. Multiciliated ependymal (E1) cells line the walls of the ventricles and contribute importantly to CSF flow through ciliary beating. Key to this function is the rotational and translational planar cell polarity (PCP) of E1 cells. Defects in the PCP of E1 cells can result in abnormal CSF accumulation and hydrocephalus. Here, we integrate recent data on the roles of early CSF flow in the embryonic ventricles, PCP regulators (e.g., Vangl2 and Dishevelled), and cytoskeletal networks in the establishment, refinement, and maintenance of E1 cells' PCP. The planar organization mechanisms of E1 cells could explain how CSF flow contributes to brain function and may help in the diagnosis and prevention of hydrocephalus.

Primary ciliary dyskinesia and associated sensory ciliopathies

Primary ciliary dyskinesia (PCD) is a genetic disease of motile cilia, which belongs to a group of disorders resulting from dysfunction of cilia, collectively known as ciliopathies. Insights into the genetics and phenotypes of PCD have grown over the last decade, in part propagated by the discovery of a number of novel cilia-related genes. These genes encode proteins that segregate into structural axonemal, regulatory, as well as cytoplasmic assembly proteins. Our understanding of primary (sensory) cilia has also expanded, and an ever-growing list of diverse conditions has been linked to defective function and signaling of the sensory cilium. Recent multicenter clinical and genetic studies have uncovered the heterogeneity of motile and sensory ciliopathies, and in some cases, the overlap between these conditions. Here, we will describe the genetics and pathophysiology of ciliopathies in children, focusing on PCD, review emerging genotype-phenotype relationships, and diagnostic tools available for the clinician.

Bronchiectasis diagnosed after renal transplantation: a retrospective multicenter study

Background

Bronchiectasis is characterized by abnormal, permanent and irreversible dilatation of the bronchi, usually responsible for daily symptoms and frequent respiratory complications. Many causes have been identified, but only limited data are available concerning the association between bronchiectasis and renal transplantation.

Methods

We conducted a retrospective multicenter study of cases of bronchiectasis diagnosed after renal transplantation in 14 renal transplantation departments (French SPIESSER group). Demographic, clinical, laboratory and CT scan data were collected.

Results

Forty-six patients were included (mean age 58.2 years, 52.2 % men). Autosomal dominant polycystic kidney disease (32.6 %) was the main underlying renal disease. Chronic cough and sputum (50.0 %) were the major symptoms leading to chest CT scan. Mean duration of symptoms before diagnosis was 1.5 years [0–12.1 years]. Microorganisms were identified in 22 patients, predominantly Haemophilus influenzae. Hypogammaglobulinemia was observed in 46.9 % patients. Bronchiectasis was usually extensive (84.8 %). The total bronchiectasis score was 7.4 ± 5.5 with a significant gradient from apex to bases. Many patients remained symptomatic (43.5 %) and/or presented recurrent respiratory tract infections (37.0 %) during follow-up. Six deaths (13 %) occurred during follow-up, but none were attributable to bronchiectasis.

Conclusions

These results highlight that the diagnosis of bronchiectasis should be considered in patients with de novo respiratory symptoms after renal transplantation. Further studies are needed to more clearly understand the mechanisms underlying bronchiectasis in this setting.

In vivo micro-scale tomography of ciliary behavior in the mammalian oviduct

Motile cilia in the mammalian oviduct play a key role in reproduction, such as transporting fertilized oocytes to the uterus for implantation. Due to their small size (~5-10 μm in length and ~300 nm in diameter), live visualization of cilia and their activity in the lumen of the oviduct through tissue layers represents a major challenge not yet overcome. Here, we report a functional low-coherence optical imaging technique that allows in vivo depth-resolved mapping of the cilia location and cilia beat frequency (CBF) in the intact mouse oviduct with micro-scale spatial resolution. We validate our approach with widely-used microscopic imaging methods, present the first in vivo mapping of the oviduct CBF in its native context, and demonstrate the ability of this approach to differentiate CBF in different locations of the oviduct at different post-conception stages. This technique opens a range of opportunities for live studies in reproductive medicine as well as other areas focused on cilia activity and related ciliopathies.

Cilia dysfunction in lung disease

A characteristic feature of the human airway epithelium is the presence of ciliated cells bearing motile cilia, specialized cell surface projections containing axonemes composed of microtubules and dynein arms, which provide ATP-driven motility. In the airways, cilia function in concert with airway mucus to mediate the critical function of mucociliary clearance, cleansing the airways of inhaled particles and pathogens. The prototypical disorder of respiratory cilia is primary ciliary dyskinesia, an inherited disorder that leads to impaired mucociliary clearance, to repeated chest infections, and to the progressive destruction of lung architecture. Numerous acquired lung diseases are also marked by abnormalities in both cilia structure and function. In this review we summarize current knowledge regarding airway ciliated cells and cilia, how they function to maintain a healthy epithelium, and how disorders of cilia structure and function contribute to inherited and acquired lung disease.

Radiologic and clinical bronchiectasis associated with autosomal dominant polycystic kidney disease

BACKGROUND

Polycystin 1 and 2, the protein abnormalities associated with autosomal dominant polycystic kidney disease (ADPKD), are also found in airway cilia and smooth muscle cells. There is evidence of increased radiologic bronchiectasis associated with ADPKD, though the clinical and functional implications of this association are unknown. We hypothesized an increased prevalence of both radiologic and clinical bronchiectasis is associated with APDKD as compared to non-ADPKD chronic kidney disease (CKD) controls.

MATERIALS AND METHODS

A retrospective case-control study was performed at our institution involving consecutive ADPKD and non-ADPKD chronic kidney disease (CKD) patients seen over a 13 year period with both chest CT and PFT. CTs were independently reviewed by two blinded thoracic radiologists. Manually collected clinical data included symptoms, smoker status, transplant history, and PFT findings.

RESULTS

Ninety-two ADPKD and 95 non-ADPKD CKD control patients were compared. Increased prevalence of radiologic bronchiectasis, predominantly mild lower lobe disease, was found in ADPKD patients compared to CKD control (19 vs. 9%, P = 0.032, OR 2.49 (CI 1.1-5.8)). After adjustment for covariates, ADPKD was associated with increased risk of radiologic bronchiectasis (OR 2.78 (CI 1.16-7.12)). Symptomatic bronchiectasis occurred in approximately a third of ADPKD patients with radiologic disease. Smoking was associated with increased radiologic bronchiectasis in ADPKD patients (OR 3.59, CI 1.23-12.1).

CONCLUSIONS

Radiological bronchiectasis is increased in patients with ADPKD particularly those with smoking history as compared to non-ADPKD CKD controls. A third of such patients have symptomatic disease. Bronchiectasis should be considered in the differential in ADPKD patients with respiratory symptoms and smoking history.

Picking up speed: advances in the genetics of primary ciliary dyskinesia

Abnormal ciliary axonemal structure and function are linked to the growing class of genetic disorders collectively known as ciliopathies, and our understanding of the complex genetics and functional phenotypes of these conditions has rapidly expanded. While progress in genetics and biology has uncovered numerous cilia-related syndromes, primary ciliary dyskinesia (PCD) remains the sole genetic disorder of motile cilia dysfunction. The first disease-causing mutation was described just 13 y ago, and since that time, the pace of gene discovery has quickened. These mutations separate into genes that encode axonemal motor proteins, structural and regulatory elements, and cytoplasmic proteins that are involved in assembly and preassembly of ciliary elements. These findings have yielded novel insights into the processes involved in ciliary assembly, structure, and function, which will allow us to better understand the clinical manifestations of PCD. Moreover, advances in techniques for genetic screening and sequencing are improving diagnostic approaches. In this article, we will describe the structure, function, and emerging genetics of respiratory cilia, review the genotype-phenotype relationships of motor ciliopathies, and explore the implications of recent discoveries for diagnostic testing for PCD.

Deletion of airway cilia results in noninflammatory bronchiectasis and hyperreactive airways

The mechanisms for the development of bronchiectasis and airway hyperreactivity have not been fully elucidated. Although genetic, acquired diseases and environmental influences may play a role, it is also possible that motile cilia can influence this disease process. We hypothesized that deletion of a key intraflagellar transport molecule, IFT88, in mature mice causes loss of cilia, resulting in airway remodeling. Airway cilia were deleted by knockout of IFT88, and airway remodeling and pulmonary function were evaluated. In IFT88(-) mice there was a substantial loss of airway cilia on respiratory epithelium. Three months after the deletion of cilia, there was clear evidence for bronchial remodeling that was not associated with inflammation or apparent defects in mucus clearance. There was evidence for airway epithelial cell hypertrophy and hyperplasia. IFT88(-) mice exhibited increased airway reactivity to a methacholine challenge and decreased ciliary beat frequency in the few remaining cells that possessed cilia. With deletion of respiratory cilia there was a marked increase in the number of club cells as seen by scanning electron microscopy. We suggest that airway remodeling may be exacerbated by the presence of club cells, since these cells are involved in airway repair. Club cells may be prevented from differentiating into respiratory epithelial cells because of a lack of IFT88 protein that is necessary to form a single nonmotile cilium. This monocilium is a prerequisite for these progenitor cells to transition into respiratory epithelial cells. In conclusion, motile cilia may play an important role in controlling airway structure and function.