Cellular signalling by primary cilia in development, organ function and disease

A novel NEK1 variant disturbs the interaction between the C-terminal fragment of NEK1 and the VDAC1 channel, causing lethal short-rib polydactyly syndrome

The NIMA-related kinase 1 (NEK1) gene belongs to the Never in Mitosis Gene A (NIMA) kinase family, a group whose members play essential roles in cell cycle regulation, specifically in cell division and ciliogenesis. Mutations in the NEK1 gene have been implicated in several diseases, including short-rib polydactyly syndrome (SRPS). SRPS is a bone growth disorder characterized by severe congenital anomalies. Here, we describe a family with a lethal form of SRPS due to a novel intronic variant in the NEK1 gene. Basing on whole-exome sequencing of fetuses with SRPS we identified a homozygous variant of the NEK1 gene at position c.3584-10T>A as the causative mutation. Bioinformatic methods and minigene splicing assays were then used to assess the harmfulness and functional impact of the variant. We found that the identified mutation leads to the synthesis of the NEK1 protein lacking 90C-terminal residues following the last coiled-coil region. Additional experiments were performed to identify proteins that interact with the C-terminal fragment of NEK1 absent in the mutated protein. We suggest that the interaction between the C-terminal fragment of NEK1 and the VDAC1 channel is essential for the VDAC1 phosphorylation, the absence of which is likely to affect ciliogenesis.

Alpha-tubulin tails regulate axoneme differentiation

The tubulin tail is a key element for microtubule (MT) functionality, but the functional redundancy of tubulin genes complicates the genetic determination of their physiological functions. Here, we removed the C-terminal tail of five alpha- and four beta-tubulin genes in the C. elegans genome. Sensory cilia typically exhibit an axoneme that longitudinally differentiates into a middle segment with doublet MTs and a distal segment with singlet MTs. However, the excision of the alpha-tubulin tail, but not the beta-tubulin tail, resulted in the ectopic formation of doublet MTs in the distal segments. Molecular dynamics simulations suggest that the alpha-tubulin tail could prevent the B-tubule from docking on the surface of A-tubule. Using recombinant tubulins, we demonstrated that removing the alpha-tubulin tail efficiently promoted doublet MTs formation in vitro. These results reveal the vital and unique contributions of tubulin tails to the structural integrity and accuracy of axoneme MT organization.

Primary cilia prevent activation of the cGAS-STING pathway during mouse decidualization

Primary cilia are antenna-like organelles that sense extracellular signals and function as signaling hubs essential for vertebrate development and homeostasis. Decidualization is crucial for pregnancy establishment and maintenance in both humans and mice. While primary cilia are present in endometrial stromal cells, their role in pregnancy remains unknown. Here, we identify TMEM67, a key component of the ciliary transition zone, as a critical regulator of mouse decidualization. Loss of primary cilia triggers RhoA-MLC2-dependent actomyosin contraction, which transmits mechanical forces to the nuclear lamina, leading to micronuclei formation. Within these micronuclei, double-stranded DNA (dsDNA) can directly bind to cyclic GMP-AMP synthase (cGAS) in situ, initiating downstream signaling. This activation of the cGAS-STING pathway reduces CCL6 production and impairs decidualization. Furthermore, pharmacological inhibition of actin polymerization or RhoA-ROCK signaling alleviates mechanical forces surrounding stromal cells, restores ciliogenesis, maintains nuclear integrity, suppresses the cGAS-STING pathway activation, and ultimately rescues decidualization. Our findings reveal a previously unrecognized mechanism by which primary cilia regulate the actin cytoskeleton to maintain nuclear integrity and prevent DNA leakage. This safeguards against aberrant activation of the cGAS-STING pathway, which would otherwise trigger detrimental immune signaling and impair decidualization.

NEK8, a NIMA-family protein kinase at the core of the ciliary INV complex

Here we describe the current knowledge about the ciliary kinase NEK8, highlighting what we know and what we don't know about its regulation, substrates and potential functions. We also review the literature about the pathological consequences of different NEK8 variants in patients of nephronophthisis, renal-hepatic-pancreatic dysplasia and autosomal dominant polycystic kidney disease, three different types of ciliopathies. NEK8 belongs to the NIMA family of serine/threonine protein kinases. Like its closest relative, NEK9, it contains a protein kinase and an RCC1 domain, but lacks the C-terminal region that is key for NEK9's regulation as a G2/M kinase. Importantly, NEK8 localizes to cilia as part of a multimeric protein complex that assembles in a fibrillar fashion at the proximal half of this signaling organelle, defining what is known as the INV compartment. NEK8 and its INV compartment partners inversin, ANKS6 and NPHP3 are necessary for left-right determination and the correct development of different organs such as the kidney, the heart and the liver. But the kinase substrates, regulatory mechanism and activating cues and thus the molecular basis of NEK8 important physiological roles remain elusive. We present the current findings regarding NEK8 and also highlight what we miss in order to progress towards the understanding of the kinase and the function of the INV complex at the cilia.

Delivery of intraflagellar transport proteins to the ciliary base and assembly into trains

Anterograde intraflagellar transport (IFT) trains, composed of IFT-B, IFT-A, and BBSome subcomplexes, are responsible for transporting ciliary proteins into the cilium. How IFT subcomplexes reach the ciliary base and assemble into IFT trains is poorly understood. Here, we perform quantitative single-molecule imaging in Caenorhabditis elegans chemosensory cilia to uncover how IFT subcomplexes arrive at the base, organize in IFT trains, and enter the cilium. We find that BBSomes reach the base via diffusion where they either associate with assembling IFT trains or with the membrane surrounding the base. In contrast, IFT-B and IFT-A reach the base via directed transport most likely on vesicles that stop at distinct locations near the base. Individual subcomplexes detach from the vesicles into a diffusive pool and associate to assembling trains. Our results show that IFT-B is first incorporated into IFT trains, followed by IFT-A, and finally BBSomes, indicating that the assembly of IFT trains is a highly regulated, step-wise process.

Polycystins recruit cargo to distinct ciliary extracellular vesicle subtypes in C. elegans

Therapeutic use of tiny extracellular vesicles (EVs) requires understanding cargo loading mechanisms. Here, we use a modular proximity labeling approach to identify the cargo of ciliary EVs associated with the transient receptor potential channel polycystin-2 PKD-2 of C. elegans. Polycystins are conserved ciliary proteins and cargo of EVs; dysfunction causes polycystic kidney disease in humans and mating deficits in C. elegans. We discover that polycystins localize with specific cargo on ciliary EVs: polycystin-associated channel-like protein PACL-1, dorsal and ventral polycystin-associated membrane C-type lectins PAMLs, and conserved tumor necrosis factor receptor-associated factor (TRAF) TRF-1 and TRF-2. Loading of these components to EVs relies on polycystin-1 LOV-1. Our modular EV-TurboID approach can be applied in both cell- and tissue-specific manners to define the composition of distinct EV subtypes, addressing a major challenge of the EV field.

SIRT2 inhibition attenuates myofibroblast transition through autophagy-mediated ciliogenesis in renal epithelial cells

Myofibroblast transition plays a crucial role in both fibrotic diseases and wound healing. Although SIRT2 regulates fibrosis, its mechanisms of action remain poorly understood. This study aimed to investigate the effects of SIRT2 inhibition on myofibroblast transition in human renal cells under quiescent conditions. HK-2 kidney proximal tubular epithelial cells were starved of serum, resulting in the formation of primary cilia. Transforming growth factor-β (TGF-β) stimulation reduced both the number of ciliated cells and ciliary length. The ciliary defects resulted from a failure in autophagy termination, leading to the accumulation of OFD1, a negative regulator of ciliogenesis, at centriolar satellites. This phenomenon was correlated with the upregulation of fibrosis-related proteins. To elucidate the role of SIRT2 in the autophagy-ciliogenesis-fibrosis axis, cells were treated with AGK2, a specific inhibitor of SIRT2. AGK2 treatment promoted the formation of both autophagosomes and autolysosomes and facilitated OFD1 degradation at the centriolar satellites, resulting in the lengthening of primary cilia. Restoration of primary cilia by AGK2 was associated with the suppression of myofibroblast transition. In conclusion, SIRT2 inhibition attenuates TGF-β-induced fibrosis by promoting autophagy-mediated ciliogenesis. This study highlights SIRT2 as a potential therapeutic target for fibrotic diseases.

The influence of IMPDH activity on ciliogenesis and adipogenesis of 3T3-L1 cells while undergoing differentiation

The functional roles of primary cilia and inosine 5'-monophosphate dehydrogenase (IMPDH) are among the hot topics in today's adipogenesis research. Considering the reported interaction between IMPDH and ADP Ribosylation Factor-Like GTPase 13B (ARL13B), as a key ciliary protein, our study focused on this interaction during the ciliogenesis process while 3T3-L1 pre-adipocytes undergoing differentiation to lipid-accumulating adipocytes. Our results indicated that, in the early days of differentiation, when cilium length is long, IMPDH expression is high and its interaction with ARL13B is low. Conversely, in the last days of differentiation, the cilia length and IMPDH expression reduced while, the IMPDH/ARL13B interaction remains high relative to the initial days. In either of these two situations, IMPDH was not documented within the cilia. The extent of the interaction between IMPDH and ARL13B might account for the lack of co-localization of IMPDH and ARL13B within cilia during the process of differentiation. Although, inhibiting IMPDH in the early days of differentiation did not have a significant effect on cilia length, it did reduce adipogenesis by limiting mitotic clonal expansion through arresting cells in the G1/G0 phase. These findings provide the ground for further research to investigate the relationship between the IMPDH/ARL13B interaction and cilia length, which decline in obesity.

The impact of ciliary length on the mechanical response of osteocytes to fluid shear stress

BACKGROUND

Osteocytes are crucial for detecting mechanical stimuli and translating them into biochemical responses within the bone. The primary cilium, a cellular 'antenna,' plays a vital role in this process. However, there is a lack of direct correlation between cilium length changes and osteocyte mechanosensitivity changes. This study aims to reveal the relationship between ciliary length and nitric oxide (NO) release in osteocytes to show how primary cilia may be involved in reducing osteocyte mechanosensitivity caused by microgravity.

MATERIALS AND METHODS

We used the MLO-Y4 cell line and primary osteoblasts to adjust the ciliary length using chloral hydrate (CH) for shortening and lithium ions (Li+) for elongation. We then examined the impact of varied ciliary lengths on osteocyte response to fluid shear stress, focusing on the PC1/PC2-Ca2+-NO signaling pathway. Co-culture systems assessed downstream effects on osteoblast function, including collagen secretion and mineralization.

RESULTS

We observed a significant correlation between ciliary length and osteocyte mechanosensitivity, with longer primary cilia enhancing Ca2+ influx and NO release in response to fluid shear stress. However, contrary to expectations, calmodulin (CaM) expression did not increase with ciliary length, suggesting alternative pathways, such as PKC or Akt/PKB, may modulate p-eNOS activity. Co-cultured osteoblasts showed altered osteogenic functions regulated by osteocyte-derived signals influenced by primary cilia length.

CONCLUSION

Our findings clarify the role of primary cilia length in modulating osteocyte mechanosensitivity and their influence on osteoblast function, highlighting a complex regulatory network that may not solely rely on CaM for NO release. These insights contribute to a deeper understanding of bone mechanotransduction and could have implications for developing therapeutic targets for osteocyte-related disorders.

Cholangiocyte ciliary defects induce sustained epidermal growth factor receptor signaling

BACKGROUND AND AIMS

The primary cilium, an organelle that protrudes from cell surfaces, is essential for sensing extracellular signals. With disturbed cellular communication and chronic liver pathologies, this organelle's dysfunctions have been linked to disorders, including polycystic liver disease and cholangiocarcinoma. The goal of this study was to elucidate the relationship between primary cilia and the crucial regulator of cellular proliferation, the epidermal growth factor receptor (EGFR) signaling pathway, which has been associated with various clinical conditions.

APPROACH AND RESULTS

The study identified aberrant EGFR signaling pathways in cholangiocytes lacking functional primary cilia using liver-specific intraflagellar transport 88 knockout mice, a Pkhd1 mutant rat model, and human cell lines that did not have functional cilia. Cilia-deficient cholangiocytes showed persistent EGFR activation because of impaired receptor degradation, in contrast to their normal counterparts, where EGFR localization to the cilia promotes appropriate signaling. Using histone deacetylase 6 inhibitors to restore primary cilia accelerates EGFR degradation, thereby reducing maladaptive signaling. Importantly, experimental intervention with the histone deacetylase 6 inhibitor tubastatin A in an orthotopic rat model moved EGFR to cilia and reduced ERK phosphorylation. Concurrent administration of EGFR and histone deacetylase 6 inhibitors in cholangiocarcinoma and polycystic liver disease cells demonstrated synergistic antiproliferative effects, which were associated with the restoration of functioning primary cilia.

CONCLUSIONS

This study's findings shed light on ciliary function and robust EGFR signaling with slower receptor turnover. We could use therapies that restore the function of primary cilia to treat EGFR-driven diseases in polycystic liver disease and cholangiocarcinoma.

Multicilia dynamically transduce Sonic Hedgehog signaling to regulate choroid plexus functions

The choroid plexus is a major site for cerebrospinal fluid (CSF) production, characterized by a multiciliated epithelial monolayer that regulates CSF production. We demonstrate that defective choroid plexus ciliogenesis or intraflagellar transport yields neonatal hydrocephalus, at least in part due to increased water channel Aqp1 and ion transporter Atp1a2 expression. We demonstrate choroid plexus multicilia as sensory cilia, transducing both canonical and non-canonical Sonic Hedgehog (Shh) signaling. Interestingly, it is the non-canonical Shh signaling that represses Aqp1 and Atp1a2 expression by the Smoothened (Smo)/Gαi/cyclic AMP (cAMP) pathway. Choroid plexus multicilia exhibit unique ciliary ultrastructure, carrying features of both primary and motile cilia. Unlike most cilia that elongate during maturation, choroid plexus ciliary length decreases during development, causing a decline of Shh signaling intensity in the developing choroid plexus, a derepression of Aqp1 and Atp1a2, and, ultimately, increased CSF production. Hence, the developmental dynamics of choroid plexus multicilia dampens the Shh signaling intensity to promote CSF production.

In vivo genetic labeling of primary cilia in developing astrocytes

Astrocyte cilia are largely understudied due to the lack of available tools. Astrocyte research advanced with the establishment of Aldh1l1-Cre ERT2 , an inducible Cre line that specifically targets the astrocyte lineage. Here, we develop and compare genetic models that label astrocyte cilia in the developing prefrontal cortex (PFC) using Aldh1l1-Cre ERT2 and Cre-dependent cilia reporters. We evaluate these models by testing different tamoxifen-induction protocols and quantifying the percentage of astrocytes labeled with the cilia reporters. We show that tamoxifen dosage impacts the expression of cilia reporters in astrocytes. We validate the maximum cilia-labeling efficiency of tamoxifen using constitutively-expressed cilia reporters. The data reveal that only a subset of SOX9- positive astrocytes in the PFC possess cilia throughout development. Our work highlights the utility of Cre-Lox systems to target specific cell types and the importance of carefully validating genetic models.

HSD17B4 deficiency causes dysregulation of primary cilia and is alleviated by acetyl-CoA

Primary cilia are dynamic sensory organelles orchestrating key signaling pathways, and disruption of primary ciliogenesis is implicated in a spectrum of genetic disorders. The peroxisomal bifunctional enzyme HSD17B4 is pivotal for peroxisomal β-oxidation and acetyl-CoA synthesis, and its deficiency profoundly impairs peroxisomal metabolism. While patients with HSD17B4 deficiency exhibit ciliopathy-like symptoms due to dysfunctional primary cilia, the molecular connection between HSD17B4 and ciliopathy remains poorly understood. Here, we demonstrate that HSD17B4 deficiency impairs primary ciliogenesis and alters cilia-mediated signaling, suggesting a potential link between peroxisomal metabolism and ciliary function. Notably, elevation of acetyl-CoA rescues ciliary defects via HDAC6-mediated ciliogenesis in HSD17B4-deficient cells. Strikingly, acetate administration restores motor function, enhances primary cilia formation, and preserves the Purkinje layer in Hsd17B4-knockout mice. These findings provide insights into the functional link between HSD17B4 and primary cilia, highlighting acetyl-CoA as a potential therapeutic target for HSD17B4 deficiency and ciliopathy.

Optical Imaging of Cilia in the Head and Neck

Background/Objectives: Cilia are hair-like organelles with various mechanosensory and chemosensory functions. In particular, motile cilia generate directional fluid flow important for multiple processes. Motile ciliopathies have serious clinical implications, including developmental and respiratory disorders. Evaluating the most suitable imaging methods for studying ciliary structure and function has great clinical significance. Methods: Here, we provide an overview of ciliary function, imaging modalities, and applications in ciliopathic diseases. Results: Optical imaging has become a crucial tool for studying ciliary structure and function, providing high-resolution, non-invasive imaging capabilities that are valuable for in vivo applications. Optical coherence tomography (OCT) is well suited for the visualization of ciliary anatomy and quantitative studies of microfluidic flow. Conclusions: A deeper understanding of ciliary biology can lead to novel approaches in diagnosing, treating, and monitoring ciliopathies, contributing to more effective and individualized care.

The Role of Integrin β1D Mislocalization in the Pathophysiology of Calpain 3-Related Limb-Girdle Muscular Dystrophy

Limb-girdle muscular dystrophy R1 (LGMDR1) is characterized by progressive proximal muscle weakness due to mutations in the CAPN3 gene. Little is known about CAPN3's function in muscle, but its loss results in aberrant sarcomere formation. Human muscle structure was analyzed in this study, with observations including integrin β1D isoform (ITGβ1D) mislocalization, a lack of Talin-1 (TLN1) in the sarcolemma and the irregular expression of focal adhesion kinase (FAK) in LGMDR1 muscles, suggesting a lack of integrin activation with an altered sarcolemma, extracellular matrix (ECM) assembly and signaling pathway deregulation, which may cause frailty in LGMDR1 muscle fibers. Additionally, altered nuclear morphology, centrosome distribution and microtubule organization have been found in muscle cells derived from LGMDR1 patients.

Collaborative role of two distinct cilium-specific cytoskeletal systems in driving Hedgehog-responsive transcription factor trafficking

In vertebrate Hedgehog (Hh) signaling, the precise output of the final effectors, GLI (glioma-associated oncogene) transcription factors, depends on the primary cilium. Upon pathway initiation, generating the precise levels of the activator form of GLI depends on its concentration at the cilium tip. The mechanisms underlying this critical step in Hh signaling are unclear. We developed an assay to visualize GLI2, the primary GLI activator isoform, at single-particle resolution within the cilium. We found that GLI2 is a cargo of intraflagellar transport (IFT) machinery. Anterograde-biased IFT loading of GLI2 in a restricted time window following pathway activation results in the tip accumulation of GLI2. Unexpectedly, we found that the conserved Hh regulator KIF7, a nonmotile kinesin, is important for the temporal control of IFT-mediated GLI2 transport and retention of GLI2 at the cilium tip. Our findings underscore a design principle where a cilia-specific cytoskeletal transport system and an Hh pathway-specific cytoskeletal protein collaboratively regulate GLI2 trafficking for Hh signaling.

Ciliopathy-Associated Missense Mutations in IFT140 are Tolerated by the Inherent Resilience of the IFT Machinery

Genotype-phenotype correlations of rare diseases are complicated by low patient number, high phenotype variability, and compound heterozygosity. Mutations may cause instability of single proteins, and affect protein complex formation or overall robustness of a specific process in a given cell. Ciliopathies offer an interesting case for studying genotype-phenotype correlations as they have a spectrum of severity and include diverse phenotypes depending on different mutations in the same protein. For instance, mutations in the intraflagellar transport protein IFT140 cause a vast spectrum of ciliopathies ranging from isolated retinal dystrophy to severe skeletal abnormalities and multi-organ diseases such as Mainzer-Saldino and Jeune syndrome. Here, the quantitative effects of 23 missense mutations in IFT140, which forms part of the crucial IFT-A complex of the ciliary machinery, were analyzed using affinity purification coupled with mass spectrometry (AP-MS). A subset of 10 mutations led to a significant and domain-specific reduction in IFT140-IFT-A complex interaction indicating complex formation issues and potentially hampering its molecular function. Knockout of IFT140 led to loss of cilia, as shown before. However, phenotypically only mild effects concerning cilia assembly were observed for two out of four tested IFT140 missense mutations. Therefore, our results demonstrate the utility of AP-MS in discerning pathogenic MMs from polymorphisms, and we postulate that reduced function is tolerated by the evolutionarily highly conserved IFT-A system.

Kibra knockdown inhibits the aberrant Hippo pathway, suppresses renal cyst formation and ameliorates renal fibrosis in nphp1KO mice

INTRODUCTION

Nephronophthisis (NPH) is an autosomal recessive interstitial cystic kidney disease, which is the most common genetic cause of end-stage renal disease (ESRD) in childhood. The Hippo pathway is regulated by the cilium and has been suggested to be linked to NPH. The aim of the study was to investigate the involvement of Hippo pathway in the pathogenesis of nphp1 defect-associated NPH (NPH1).

METHOD

Nphp1 knockout (nphp1KO) Madin-Darby Canine Kidney (MDCK) cells and nphp1KO C57BL/6J mice were generated via CRISPR gene editing strategy. The siRNAs targeting Kibra, MST1 and LATS1 were designed. An AAV9 vector was designed for Kibra knockdown. The expression and phosphorylation of core Hippo pathway molecules were evaluated. Pathological renal changes were evaluated via light microscopy respectively with haematoxylin-eosin and Masson staining.

RESULTS

In nphp1KO MDCK cells, nphp1KO mice and NPH1 patients' kidneys, Kibra, p-MST1/2, p-LATS and p-YAP exhibited a notable increase in levels, with an even greater elevation observed in renal cyst cells, indicating the Hippo pathway activated in these nphp1-deficient contexts. Nphp1 re-expression reversed the Hippo pathway activation in cells, indicating that the Hippo pathway activation is related to nphp1 deficiency in vitro. Meanwhile, in vitro, MST1 knockdown downregulated LATS1 and YAP phosphorylation, LATS1 knockdown downregulated YAP phosphorylation, suggesting the activation of the canonical Hippo pathway in nphp1-deficient contexts. Knockdown of the upstream regulator Kibra inhibited the Hippo pathway activation in both nphp1KO MDCK cells and mice. Following Kibra knockdown, the organisation of nphp1KO MDCK cells became more compact, the intensity of the actin fibres increased. Besides, decreased renal fibrosis and cyst formation were observed in nphp1KO mice.

CONCLUSIONS

The canonical Hippo pathway is aberrantly activated in nphp1-deficient conditions. Kibra may serve as a crucial upstream regulator of nphp1 deficiency-related Hippo pathway activation. Kibra upregulation and activation of the Hippo pathway are involved in the pathogenesis of NPH1.

KEY POINTS

Canonical Hippo pathway activated in nphp1-deficient disease models and patients. Kibra was a key upstream molecule in regulating the activation of canonical Hippo pathway in nphp1-deficient disease models and patients and closely related to renal cyst formation and fibrosis in nphp1KO mice.

Microtubule Reorganization and Quiescence: an Intertwined Relationship

Quiescence is operationally defined as a reversible proliferation arrest. This cellular state is central to both organism development and homeostasis, and its dysregulation causes many pathologies. The quiescent state encompasses very diverse cellular situations depending on the cell type and its environment. Further, quiescent cell properties evolve with time, a process that is thought to be the origin of aging in multicellular organisms. Microtubules are found in all eukaryotes and are essential for cell proliferation as they support chromosome segregation and intracellular trafficking. Upon proliferation cessation and quiescence establishment, the microtubule cytoskeleton was shown to undergo significant remodeling. The purpose of this review is to examine the literature in search of evidence to determine whether the observed microtubule reorganizations are merely a consequence of quiescence establishment or if they somehow participate in this cell fate decision.

The primary cilia: Orchestrating cranial neural crest cell development

Primary cilia (hereafter "cilia") are microtubule-based antenna-like organelles projecting from the surface of vertebrate cells. Cilia can serve as cellular antennae controlling cell growth and differentiation. Absent or dysfunctional cilia frequently lead to craniofacial anomalies known as craniofacial ciliopathies. However, the detailed pathological mechanisms of craniofacial ciliopathies remain unclear. This perspective discusses our current understanding of the role of cilia in cranial neural crest cells. We also describe potential mechanisms of ciliogenesis in cranial neural crest cells, which may contribute to unraveling the complex pathogenesis of craniofacial ciliopathies.

Class I PI3Ks activate stretch-induced autophagy in trabecular meshwork cells

Elevated intraocular pressure (IOP) is the primary risk factor for glaucoma, a leading cause of irreversible blindness worldwide. IOP homeostasis is maintained through a balance between aqueous humor production and its drainage through the trabecular meshwork (TM)/Schlemm's Canal (SC) outflow pathway. Prior studies by our laboratory reported a key role of mechanical forces and primary cilia (PC)-dependent stretch-induced autophagy in IOP homeostasis. However, the precise mechanism regulating this process remains elusive. In this study, we investigated the upstream signaling pathway orchestrating autophagy activation during cyclic mechanical stretch (CMS) in primary cultured human TM cells, using biochemical and cell biological analyses. Our results indicate that TM cells express catalytic subunits of class IA PI3Ks (PIK3CA, B, and D), and that inhibition of class IA isoforms, but not class II and III, significantly prevent CMS-induced autophagy. Importantly, PIK3CA was found to localize in the PC. Furthermore, we identified a coordinated action of Class IA PI3Ks along INPP4A/B, a 4' inositol phosphatase, responsible for the formation of PI(3,4)P2 and PI(3)P and stretch-induced autophagy in TM cells. These findings contribute to a deeper understanding of the molecular mechanisms underlying IOP homeostasis.

Connecting genotype and phenotype in minor spliceosome diseases

Minor spliceosome is responsible for recognizing and excising a specific subset of divergent introns during the pre-mRNA splicing process. Mutations in the unique snRNA and protein components of the minor spliceosome are increasingly being associated with a variety of germline and somatic human disorders, collectively termed as minor spliceosomopathies. Understanding the mechanistic basis of these diseases has been challenging due to limited functional information on many minor spliceosome components. However, recently published cryo-electron microscopy (cryo-EM) structures of various minor spliceosome assembly intermediates have marked a significant advancement in elucidating the roles of these components during splicing. These structural breakthroughs have not only enhanced our comprehension of the minor spliceosome's functionality but also shed light on how disease-associated mutations disrupt its functions. Consequently, research focus is now shifting toward investigating how these splicing defects translate into broader pathological processes within gene expression pathways. Here we outline the current structural and functional knowledge of the minor spliceosome, explore the mechanistic consequences of its mutations, and discuss emerging challenges in connecting molecular dysfunctions to clinical phenotypes.

Clinical implications of proximal tubular multicilia in glomerular diseases

Introduction

Multiciliated cells (MCCs) have been identified in the proximal tubules of patients with kidney disease; however, their clinical significance is unknown. We aimed to investigate whether MCCs are associated with clinical outcomes in patients with glomerular diseases.

Methods

Between August 2012 and April 2021, 134 patients (including 126 with glomerular disease patients and 8 controls) who were hospitalized at Seoul National University Boramae Medical Center and Seoul National University Hospital were included in this study. The ratio of MCCs to total proximal tubular cells was calculated using immunohistochemistry. The relationship between the MCC ratio and kidney disease-related clinical features was then analyzed.

Results

MCCs were exclusively detected in patients with glomerular diseases (68.3 %), not those in the control group. Patients with diabetic kidney disease (88.9 %) or antineutrophil cytoplasmic antibody (ANCA)-associated glomerulonephritis (GN, 86.4 %) had higher MCC ratios. MCC-positivity and MCC ratios were significantly associated with increased age and proteinuria, and a decreased estimated glomerular filtration rate (eGFR). Patients with higher MCC ratios had a significantly higher risk of end-stage kidney disease (ESKD) and composite outcomes with death. In multivariable analysis, MCC ratios were significantly correlated with an increased risk of ESKD (hazard ratio [HR], 1.413; 95 % confidence interval [CI], 1.012-1.972) and composite outcome (HR, 1.401; 95 % CI, 1.028-1.909).

Conclusion

Higher MCC ratios were correlated with poorer prognosis; therefore, quantification of MCCs in the proximal tubules can serve as a valuable prognostic marker in clinical practice.

Tau-tubulin kinase 2 restrains microtubule-depolymerizer KIF2A to support primary cilia growth

BACKGROUND

Primary cilia facilitate cellular signalling and play critical roles in development, homeostasis, and disease. Their assembly is under the control of Tau-Tubulin Kinase 2 (TTBK2), a key enzyme mutated in patients with spinocerebellar ataxia. Recent work has implicated TTBK2 in the regulation of cilia maintenance and function, but the underlying molecular mechanisms are not understood.

METHODS

To dissect the role of TTBK2 during cilia growth and maintenance in human cells, we examined disease-related TTBK2 truncations. We used biochemical approaches, proteomics, genetic engineering, and advanced microscopy techniques to unveil molecular events triggered by TTBK2.

RESULTS

We demonstrate that truncated TTBK2 protein moieties, unable to localize to the mother centriole, create unique semi-permissive conditions for cilia assembly, under which cilia begin to form but fail to elongate. Subsequently, we link the defects in cilia growth to aberrant turnover of a microtubule-depolymerizing kinesin KIF2A, which we find restrained by TTBK2 phosphorylation.

CONCLUSIONS

Together, our data imply that the regulation of KIF2A by TTBK2 represents an important mechanism governing cilia elongation and maintenance. Further, the requirement for concentrating TTBK2 activity to the mother centriole to initiate ciliogenesis can be under specific conditions bypassed, revealing TTBK2 recruitment-independent functions of its key partner, CEP164.

Potential biomarkers and immune infiltration linking endometriosis with recurrent pregnancy loss based on bioinformatics and machine learning

Objective

Endometriosis (EMs) is a chronic inflammatory disease characterized by the presence of endometrial tissue in the non-uterine cavity, resulting in dysmenorrhea, pelvic pain, and infertility. Epidemiologic data have suggested the correlation between EMs and recurrent pregnancy loss (RPL), but the pathological mechanism is unclear. This study aims to investigate the potential biomarkers and immune infiltration in EMs and RPL, providing a basis for early detection and treatment of the two diseases.

Methods

Two RPL and six EMs transcriptomic datasets from the Gene Expression Omnibus (GEO) database were used for differential analysis via limma package, followed by weighted gene co-expression network analysis (WGCNA) for key modules screening. Protein-protein interaction (PPI) network and two machine learning algorithms were applied to identify the common core genes in both diseases. The diagnostic capabilities of the core genes were assessed by receiver operating characteristic (ROC) curves. Moreover, immune cell infiltration was estimated using CIBERSORTx, and the Cancer Genome Atlas (TCGA) database was employed to elucidate the role of key genes in endometrial carcinoma (EC).

Results

26 common differentially expressed genes (DEGs) were screened in both diseases, three of which were identified as common core genes (MAN2A1, PAPSS1, RIBC2) through the combination of WGCNA, PPI network, and machine learning-based feature selection. The area under the curve (AUC) values generated by the ROC indicates excellent diagnostic powers in both EMs and RPL. The key genes were found to be significantly associated with the infiltration of several immune cells. Interestingly, MAN2A1 and RIBC2 may play a predominant role in the development and prognostic stratification of EC.

Conclusion

We identified three key genes linking EMs and RPL, emphasizing the heterogeneity of immune infiltration in the occurrence of both diseases. These findings may provide new mechanistic insights or therapeutic targets for further research of EMs and RPL.

Non-canonical CDK6 activity promotes cilia disassembly by suppressing axoneme polyglutamylation

Tubulin polyglutamylation is a posttranslational modification that occurs primarily along the axoneme of cilia. Defective axoneme polyglutamylation impairs cilia function and has been correlated with ciliopathies, including Joubert Syndrome (JBTS). However, the precise mechanisms regulating proper axoneme polyglutamylation remain vague. Here, we show that cyclin-dependent kinase 6 (CDK6), but not its paralog CDK4, localizes to the cilia base and suppresses axoneme polyglutamylation by phosphorylating RAB11 family interacting protein 5 (FIP5) at site S641, a critical regulator of cilia import of glutamylases. S641 phosphorylation disrupts the ciliary recruitment of FIP5 and its association with RAB11, thereby reducing the ciliary import of glutamylases. Encouragingly, the FDA-approved CDK4/6 inhibitor Abemaciclib can effectively restore cilia function in JBTS cells with defective glutamylation. In summary, our study elucidates the regulatory mechanisms governing axoneme polyglutamylation and suggests that developing CDK6-specific inhibitors could be a promising therapeutic strategy to enhance cilia function in ciliopathy patients.

Counterregulatory roles of GLI2 and GLI3 in osteogenic differentiation via Gli1 expression

The GLI1, GLI2 and GLI3 transcription factors mediate Hedgehog (Hh) signaling, which is crucial for bone development. During intramembranous ossification, mesenchymal stem cells (MSCs) are directly differentiated into osteoblasts. Under basal and Hh pathway-stimulated conditions, primary cilia play essential roles in proteolytic processing of GLI3 to its repressor form (GLI3R) and in activation of GLI2. Although previous studies in mice have suggested that Gli1 expression depends on GLI2 and GLI3, coordinated roles of GLI1, GLI2 and GLI3 in osteogenic differentiation are not fully understood at the cellular level. From the MSC line C3H10T1/2, we established Gli2-knockout (KO) and Gli3-KO cells, as well as constitutively GLI3R-producing (cGLI3R) cells, and expressed GLI1, GLI2 and GLI3 constructs in these cell lines. The results demonstrate at the cellular level that GLI2 and GLI3R counterregulate osteogenic differentiation via activation and repression of Gli1 expression, respectively; GLI3R, which results from GLI3 processing requiring protein kinase A-mediated phosphorylation, downregulates expression of Gli2 as well as Gli1; and GLI1 upregulates expression of Gli1 itself and Gli2, constituting a GLI1-GLI2 positive feedback loop.

Tonic ubiquitination of the central body weight regulator melanocortin receptor 4 (MC4R) promotes its constitutive exit from cilia

The G protein-coupled receptor (GPCR) melanocortin receptor 4 (MC4R) is an essential regulator of body weight homeostasis. MC4R is unusual among GPCRs in that its activity is regulated by 2 opposing physiological ligands, the agonist ⍺-MSH and the antagonist/inverse agonist AgRP. Paradoxically, while MC4R localizes and functions at the cilium of hypothalamic neurons, the ciliary levels of MC4R are very low under unrestricted feeding conditions. Here, we find that the constitutive activity of MC4R is responsible for the continuous depletion of MC4R from cilia and that inhibition of MC4R's activity via AgRP leads to a robust accumulation of MC4R in cilia. Ciliary targeting of MC4R is mediated by its partner MRAP2 and the constitutive exit of MC4R from cilia relies on the sensor of activation β-arrestin, on ubiquitination, and on the BBSome ciliary trafficking complex. Thus, while MC4R exits cilia via conventional mechanisms, it only accumulates in cilia when its activity is suppressed by AgRP.

Primary Cilia Formation Mediated by Hsa_Circ_0005185/OTUB1/RAB8A Complex Inhibits Prostate Cancer Progression by Suppressing Hedgehog Signaling Pathway

Prostate cancer (PCa) is one of the most common malignancies for male individuals globally. Androgen deprivation therapy (ADT) initially demonstrated significant efficacy in treating PCa; however, most cases of PCa eventually progress to castration-resistant prostate cancer (CRPC), which becomes increasingly challenging to manage. Notably, the loss or disruption of primary cilia in PCa cells may play a critical role in the progression of the disease, and there are no reports on the role of circular RNAs in ciliogenesis. Thus, this warrants further investigation.In this study, key circular RNAs linked to prostate cancer progression, and enzalutamide resistance is identified. Specifically, it is found that hsa_circ_0005185 interacts with OTUB1 and RAB8A, serving as a molecular scaffold. Hsa_circ_0005185 mediates the binding of the deubiquitinase OTUB1 to RAB8A, resulting in the deubiquitination of RAB8A. Consequently, the stable expression of RAB8A promotes the regeneration of primary cilia and enhances the production of GLI3R, an inhibitory factor in the Hedgehog signaling pathway, thereby suppressing AR activity and slowing the progression of CRPC.

The ignored structure in female fertility: cilia in the fallopian tubes

Cilia in the fallopian tubes (CFT) play an important role in female infertility, but have not been explored comprehensively. This review reveals the detection techniques for CFT function and morphology, and the related analysis of female infertility and other gynaecological disorders. CFT differentiate from progenitor cells, and develop into primary cilia and motile cilia. Primary cilia coordinate multiple signalling pathways, and motile cilia produce laminar flow through bidirectional intraflagellar transport, which drives the movement of oocytes and gametes. Several methods for quantitative detection and protein analysis have been used to explore the factors contributing to the decrease in ciliary beat frequency (CBF), and the cellular mechanism of ciliary cell death and shedding. In both primary and secondary ciliary disorders associated with reproductive diseases, abnormal alterations in ciliary quantity, ciliary structure, CBF and ciliary signalling pathways result in abnormal tubal laminar flow, and diminished oocyte retrieval and transport capabilities.

Multicilia dynamically transduce Shh signaling to regulate choroid plexus functions

Choroid plexus is a major site for cerebrospinal fluid (CSF) production, characterized by a multiciliated epithelial monolayer that regulates CSF production. We demonstrate that defective choroid plexus ciliogenesis or Intraflagellar transport yields neonatal hydrocephalus, at least in part, due to increased water channel Aqp1 and ion transporter Atp1a2 expression. We demonstrate choroid plexus multicilia as sensory cilia, transducing both canonical and non-canonical Shh signaling. Interestingly, it is the non-canonical Shh signaling that represses Aqp1 and Atp1a2 expression by Smo/Gαi/cAMP pathway. Choroid plexus multicilia exhibit unique ciliary ultrastructure, carrying features of both primary and motile cilia. Unlike most cilia that elongate during maturation, choroid plexus ciliary length decreases during development, causing a decline of Shh signaling intensity in developing choroid plexus, a derepression of Aqp1 and Atp1a2, and ultimately, an increased CSF production. Hence, developmental dynamics of choroid plexus multicilia dampens the Shh signaling intensity to promote CSF production.

Melanophilin-induced primary cilia promote pancreatic cancer metastasis

Pancreatic ductal adenocarcinoma (PDAC) is one of the most malignant tumors because of its high metastatic ability. The glutamine (Gln)-deficient microenvironment contributes to PDAC metastasis; however, the underlying molecular mechanisms remain unclear. Here, we demonstrated that melanophilin (MLPH) promotes PDAC metastasis by inducing the regrowth of primary cilia. Using RNA sequencing, we found that MLPH was upregulated in Gln-deficient conditions. MLPH facilitated PDAC metastasis in vitro and in vivo. Clinically, high MLPH expression is positively correlated with metastasis and poor PDAC prognosis. MLPH localized to the centrosome and facilitated the regrowth of primary cilia. The primary ciliogenesis upregulated phospholipase C γ-1 (PLCG1) to promote PDAC metastasis. Interestingly, PLCG1 was localized to the primary cilia, and depletion of PLCG1 alleviated primary ciliogenesis, suggesting a feedforward role for PLCG1 in mediating primary ciliogenesis. Thus, our study revealed a novel function of the MLPH-primary cilia-PLCG1 axis in facilitating PDAC metastasis under Gln deficiency both in vitro and in vivo.

The bidirectional relationship between cilia and PCP signaling pathway core protein Vangl2

Vangl2, a core component of the PCP signaling pathway, serves as a scaffold protein on the cell membrane, playing a crucial role in organizing protein complexes. Cilia, dynamic structures on the cell surface, carry out a wide range of functions. Research has highlighted a bidirectional regulatory interaction between Vangl2 and cilia, underscoring their interconnected roles in cellular processes. This relationship is demonstrated by the localization of Vangl2 at the base and proximal regions of cilia, where it plays essential roles in ciliary positioning, asymmetric distribution, and ciliogenesis. In contrast, the absence of cilia can disrupt Vangl2-mediated signal transduction processes. This review offers a narrative review of recent research on Vangl2's function in cilia and examines the regulatory effects of cilia on Vangl2-mediated signaling.

Primary Cilia Regulate the Homeostasis and Regeneration of the Stem Cell Niche in the Tooth

Primary cilia, functioning as crucial hubs for signal sensing and transduction, are integral to the development and maintenance of homeostasis across various organs. However, their roles in tooth homeostasis and repair remain inadequately understood. In this study, we reveal an indispensable role for primary cilia in regulating the homeostasis and regeneration of teeth, primarily through the regulation of cell proliferation. Using cilium-deficient mice, we demonstrate that disruption of ciliary homeostasis leads to abnormal tooth morphology, stunted growth and notably impaired tooth repair. RNA sequencing reveals a dysregulation in genes associated with various biological processes such as cell proliferation, differentiation, and cycle regulation. Furthermore, we show that cilium-deficient mice display reduced cell proliferation. Our findings highlight a critical function for primary cilia in the regulation of tooth homeostasis and regeneration and have important implications for the development of tooth regeneration therapies.

Regulation of the Cilia as a Potential Treatment for Senescence and Tumors: A Review

Millions of people worldwide die from malignant tumors every year, and the current clinical treatment is still based on radiotherapy and chemotherapy. Immunotherapy-adjuvant chemotherapy is widely applied, yet resistance to various factors persists in the management of advanced malignancies. Recently researchers have gradually discovered that the integrity of primary cilia is closely related to many diseases. The phenotypic changes in primary cilia are found in some cases of progeria, tumorigenesis, and drug resistance. Primary cilia seem to mediate signaling during these diseases. Hedgehog inhibitors have emerged in recent years to treat tumors by controlling signaling proteins on primary cilia. There is evidence for the use of anti-tumor drugs to treat senescence-related disease. Considering the close relationship between aging and obesity, as well as the obesity is the phenotype of many ciliopathies. Therefore, we speculate that some anti-tumor or anti-aging drugs can treat ciliopathies. Additionally, there is evidence suggesting that anti-aging drugs for tumor treatment, in which the process may be mediated by cilia. This review elucidates for the first time that cilia may be involved in the regulation of senescence, metabolic, tumorigenesis, and tumor resistance and hypothesizes that cilia can be regulated to treat these diseases in the future.

Cilia as Wnt signaling organelles

Cilia and Wnt signaling have a complex relationship, wherein Wnt regulates cilia and, conversely, cilia may affect Wnt signaling. Recently, it was shown that Wnt receptors are present in flagella, primary cilia, and multicilia, where they transmit an intraciliary signal that is independent of β-catenin. Intraciliary Wnt signaling promotes ciliogenesis, affecting male fertility, adipogenesis, and mucociliary clearance. Wnt also stimulates the beating of motile cilia, highlighting that these nanomotors, too, are chemosensory. Intraciliary Wnt signaling employs a Wnt-protein phosphatase 1 (PP1) signaling axis, involving the canonical Wnt pathway's inhibition of glycogen synthase kinase 3 (GSK3) to repress PP1 activity. Collectively, these findings support that cilia are Wnt signaling organelles, with implications for ciliopathies and cancer.

A defined tubby domain β-barrel surface region of TULP3 mediates ciliary trafficking of diverse cargoes

The primary cilium is a paradigmatic subcellular compartment at the nexus of numerous cellular and morphogenetic pathways. The tubby family protein TULP3 acts as an adapter of the intraflagellar transport complex A in transporting integral membrane and membrane-associated lipidated proteins into cilia. However, the mechanisms by which TULP3 coordinates ciliary transport of diverse cargoes is not well understood. Here, we provide molecular insights into TULP3-mediated ciliary cargo recognition. We screened for critical TULP3 residues by proximity biotinylation-mass spectrometry, structural analysis, and testing TULP3 variants in human patients with hepatorenal fibrocystic disease and spina bifida. The TULP3 residues we identified 1) were located on one side of the β-barrel of the tubby domain away from the phosphoinositide binding site, 2) mediated ciliary trafficking of lipidated and transmembrane cargoes, and 3) determined proximity with these cargoes in vivo without affecting ciliary localization, phosphoinositide binding or hydrodynamic properties of TULP3. Overall, these findings implicate a specific region of one of the surfaces of the TULP3 β-barrel in ciliary trafficking of diverse cargoes. This region overlooks the β-strands 8-12 of the β-barrel and is away from the membrane anchoring phosphoinositide binding site. Targeting the TULP3-cargo interactions could provide therapeutics in ciliary trafficking diseases.

Syndromic Retinitis Pigmentosa

Retinitis pigmentosa (RP) is a progressive inherited retinal dystrophy, characterized by the degeneration of photoreceptors, presenting as a rod-cone dystrophy. Approximately 20-30% of patients with RP also exhibit extra-ocular manifestations in the context of a syndrome. This manuscript discusses the broad spectrum of syndromes associated with RP, pathogenic mechanisms, clinical manifestations, differential diagnoses, clinical management approaches, and future perspectives. Given the diverse clinical and genetic landscape of syndromic RP, the diagnosis may be challenging. However, an accurate and timely diagnosis is essential for optimal clinical management, prognostication, and potential treatment. Broadly, the syndromes associated with RP can be categorized into ciliopathies, inherited metabolic disorders, mitochondrial disorders, and miscellaneous syndromes. Among the ciliopathies associated with RP, Usher syndrome and Bardet-Biedl syndrome are the most well-known. Less common ciliopathies include Cohen syndrome, Joubert syndrome, cranioectodermal dysplasia, asphyxiating thoracic dystrophy, Mainzer-Saldino syndrome, and RHYNS syndrome. Several inherited metabolic disorders can present with RP including Zellweger spectrum disorders, adult Refsum disease, α-methylacyl-CoA racemase deficiency, certain mucopolysaccharidoses, ataxia with vitamin E deficiency, abetalipoproteinemia, several neuronal ceroid lipofuscinoses, mevalonic aciduria, PKAN/HARP syndrome, PHARC syndrome, and methylmalonic acidaemia with homocystinuria type cobalamin (cbl) C disease. Due to the mitochondria's essential role in supplying continuous energy to the retina, disruption of mitochondrial function can lead to RP, as seen in Kearns-Sayre syndrome, NARP syndrome, primary coenzyme Q10 deficiency, SSBP1-associated disease, and long chain 3-hydroxyacyl-CoA dehydrogenase deficiency. Lastly, Cockayne syndrome and PERCHING syndrome can present with RP, but they do not fit the abovementioned hierarchy and are thus categorized as 'Miscellaneous'. Several first-in-human clinical trials are underway or in preparation for some of these syndromic forms of RP.

Permanent cilia loss during cerebellar granule cell neurogenesis involves withdrawal of cilia maintenance and centriole capping

Brain neurons utilize the primary cilium as a privileged compartment to detect and respond to extracellular ligands such as Sonic hedgehog (SHH). However, cilia in cerebellar granule cell (GC) neurons disassemble during differentiation through ultrastructurally unique intermediates, a process we refer to as cilia deconstruction. In addition, mature neurons do not reciliate despite having docked centrioles. Here, we identify molecular changes that accompany cilia deconstruction and centriole docking in GC neurons. We used single cell transcriptomic and immunocytological analyses to compare the transcript levels and subcellular localization of proteins between progenitor, differentiating, and mature GCs. Differentiating GCs lacked transcripts for key activators of premitotic cilia resorption, indicating that cilia disassembly in differentiating cells is distinct from premitotic cilia resorption. Instead, during differentiation, transcripts of many genes required for cilia maintenance-specifically those encoding components of intraflagellar transport, pericentrosomal material, and centriolar satellites-decreased. The abundance of several corresponding proteins in and around cilia and centrosomes also decreased. These changes coincided with downregulation of SHH signaling prior to differentiation, even in a mutant with excessive SHH activation. Finally, mother centrioles in maturing granule neurons recruited the cap complex protein, CEP97. These data suggest that a global, developmentally programmed decrease in cilium maintenance in differentiating GCs mediates cilia deconstruction, while capping of docked mother centrioles prevents cilia regrowth and dysregulated SHH signaling. Our study provides mechanistic insights expanding our understanding of permanent cilia loss in multiple tissue-specific contexts.

TXNDC15, an ER-localized thioredoxin-like transmembrane protein, contributes to ciliary transition zone integrity

Primary cilia have specific proteins on their membrane to fulfill their sensory functions. Preservation of the specific protein composition of cilia relies on the barrier function of the transition zone (TZ) located at the ciliary base. Defects in cilia and the TZ cause ciliopathies, which have diverse clinical manifestations, including Meckel syndrome (MKS). Many of the proteins mutated in individuals with MKS are known to constitute the MKS module of the TZ. Although TXNDC15 (also known as MKS14) is a thioredoxin-related transmembrane protein that is localized mainly in the endoplasmic reticulum (ER) and is mutated in individuals with MKS, its role at the TZ or within cilia has not been characterized. Here, we show that TXNDC15-knockout cells have defects in MKS module assembly and in ciliary membrane protein localization. These defects in TXNDC15-knockout cells were not rescued by exogenous expression of any of the TXNDC15 constructs with MKS variations in the thioredoxin domain. Furthermore, TXNDC15 with mutations of two cysteine residues within the thioredoxin domain failed to rescue defects in TXNDC15-knockout cells, suggesting that TXNDC15 controls the TZ integrity from outside the TZ via its thioredoxin domain.

Impaired Glucose Metabolism, Primary Cilium Defects, and Kidney Cystogenesis in Glycogen Storage Disease Type Ia

Key Points

Metabolism adaptations due to glucose-6 phosphate accumulation in glycogen storage disease type Ia kidneys, toward a Warburg-like metabolism, promoted cell proliferation. Metabolic perturbations directly affected primary cilium structure and cystogenesis in glycogen storage disease type Ia kidneys.

Background

Glycogen storage disease type Ia (GSDIa) is a rare metabolic disorder caused by mutations in the catalytic subunit of glucose-6 phosphatase (G6PC1). This leads to severe hypoglycemia, and most young patients with GSDIa develop CKD. The kidney pathology is characterized by the development of cysts, which typically occur at an advanced stage of CKD.

Methods

To elucidate the molecular mechanisms responsible for cyst formation, we characterized renal metabolism, molecular pathways involved in cell proliferation, and primary cilium integrity using mice in which G6pc1 was specifically deleted in the kidney from an in utero stage.

Results

GSDIa mice exhibited kidney fibrosis, high inflammation, and cyst formation, leading to kidney dysfunction. In addition, the loss of G6PC1 led to the ectopic accumulation of glycogen and lipids in the kidneys and a metabolic shift toward a Warburg-like metabolism. This metabolic adaptation was due to an excess of glucose-6 phosphate, which supports cell proliferation, driven by the mitogen-activated protein kinase/extracellular signal–regulated kinases and protein kinase B/mammalian target of rapamycin pathways. Treatment of GSDIa mice with rapamycin, a target of the mammalian target of rapamycin pathway, reduced cell proliferation and kidney damage. Our results also identified lipocalin 2 as a contributor to renal inflammation and an early biomarker of CKD progression in GSDIa mice. Its inactivation partially prevented kidney lesions in GSDIa. Importantly, primary cilium defects were observed in the kidneys of GSDIa mice.

Conclusions

Metabolic adaptations because of glucose-6 phosphate accumulation in GSDIa renal tubules, toward a Warburg-like metabolism, promoted cell proliferation and cyst formation in a similar manner to that observed in various cystic kidney diseases. This was associated with downregulation of primary cilium gene expression and, consequently, altered cilium morphology.

Advances in mechanotransduction and sonobiology: effects of audible acoustic waves and low-vibration stimulations on mammalian cells

In recent decades, research on mechanotransduction has advanced considerably, focusing on the effects of audible acoustic waves (AAWs) and low-vibration stimulation (LVS), which has propelled the field of sonobiology forward. Taken together, the current evidence demonstrates the influence of these biosignals on key cellular processes, such as growth, differentiation and migration in mammalian cells, emphasizing the determining role of specific physical parameters during stimulation, such as frequency, sound pressure level/amplitude and exposure time. These mechanical waves interact with various cellular elements, including ion channels, primary cilia, cell-cell adhesion receptors, cell-matrix and extracellular matrix proteins, and focal adhesion complexes. These components connect with the cytoskeletal fibre network, enabling the transmission of mechanical stimuli towards the nucleus. The nucleus, in turn, linked to the cytoskeleton via the linkers of the nucleoskeleton and cytoskeleton complex, acts as a mechanosensitive centre, not only responding to changes in cytoskeletal stiffness and nuclear tension but also regulating gene expression through the transcriptional co-activator YAP/TAZ and interactions between chromatin and the nuclear envelope. This intricate chain of mechanisms highlights the potential of sonobiology in various fields, including dentistry, regenerative medicine, tissue engineering and cancer research. However, progress in these fields requires the establishment of standardized measurement methodologies and biocompatible experimental setups to ensure the reproducibility of results.

Immunomodulatory potential of primary cilia in the skin

Primary cilia (PC) are essential signaling hubs for proper epithelial formation and the maintenance of skin homeostasis. Found on most cells in the human body, including skin cells, PC facilitate signal transduction that allows ciliated cells to interact with the immune system via multiple pathways, helping to maintain immune system homeostasis. PC can be altered by various microenvironmental stimuli to develop corresponding regulatory functions. Both PC and ciliary signaling pathways have been shown to be involved in the immune processes of various skin lesions. However, the mechanisms by which PC regulate cellular functions and maintain immune homeostasis in tissues are highly complex, and our understanding of them in the skin remains limited. In this paper, we discuss key ciliary signaling pathways and ciliated cells in the skin, with a focus on their immunomodulatory functions. We have compiled evidence from various cells, tissues and disease models to help explore the potential immunomodulatory effects of PC in the skin and their molecular mechanisms.

Influence of Hypoxia on the Airway Epithelium

The necessity of oxygen for metabolic processes means that hypoxia can lead to serious cell and tissue damage. On the other hand, in some situations, hypoxia occurs under physiological conditions and serves as an important regulation factor. The airway epithelium is specific in that it gains oxygen not only from the blood supply but also directly from the luminal air. Many respiratory diseases are associated with airway obstruction or excessive mucus production thus leading to luminal hypoxia. The main goal of this review is to point out how the airway epithelium reacts to hypoxic conditions. Cells detect low oxygen levels using molecular mechanisms involving hypoxia-inducible factors (HIFs). In addition, the cells of the airway epithelium appear to overexpress HIFs in hypoxic conditions. HIFs then regulate many aspects of epithelial cell functions. The effects of hypoxia include secretory cell stimulation and hyperplasia, epithelial barrier changes, and ciliogenesis impairment. All the changes can impair mucociliary clearance, exacerbate infection, and promote inflammation leading to damage of airway epithelium and subsequent airway wall remodeling. The modulation of hypoxia regulatory mechanisms may be one of the strategies for the treatment of obstructive respiratory diseases or diseases with mucus hyperproduction. Keywords: Secretory cells, Motile cilia, Epithelial barrier, Oxygenation, Obstructive respiratory diseases.

Motile Cilia in Female and Male Reproductive Tracts and Fertility

Motile cilia are evolutionarily conserved organelles. In humans, multiciliated cells (MCCs), assembling several hundred motile cilia on their apical surface, are components of the monolayer epithelia lining lower and upper airways, brain ventricles, and parts of the reproductive tracts, the fallopian tube and uterus in females, and efferent ductules in males. The coordinated beating of cilia generates a force that enables a shift of the tubular fluid, particles, or cells along the surface of the ciliated epithelia. Uncoordinated or altered cilia motion or cilia immotility may result in subfertility or even infertility. Here, we summarize the current knowledge regarding the localization and function of MCCs in the human reproductive tracts, discuss how cilia and cilia beating-generated fluid flow directly and indirectly contribute to the processes in these organs, and how lack or improper functioning of cilia influence human fertility.

Hedgehog Signaling Pathway in Fibrosis and Targeted Therapies

Hedgehog (Hh) signaling is a well-established developmental pathway; it is crucial for early embryogenesis, cell differentiation, and damage-driven regeneration. It is being increasingly recognized that dysregulated Hh signaling is also involved in fibrotic diseases, which are characterized by excessive extracellular matrix deposition that compromises tissue architecture and function. As in-depth insights into the mechanisms of Hh signaling are obtained, its complex involvement in fibrosis is gradually being illuminated. Notably, some Hh-targeted inhibitors are currently under exploration in preclinical and clinical trials as a means to prevent fibrosis progression. In this review, we provide a concise overview of the biological mechanisms involved in Hh signaling. We summarize the latest advances in our understanding of the roles of Hh signaling in fibrogenesis across the liver, kidneys, airways, and lungs, as well as other tissues and organs, with an emphasis on both the shared features and, more critically, the distinct functional variations observed across these tissues and organs. We thus highlight the context dependence of Hh signaling, as well as discuss the current status and the challenges of Hh-targeted therapies for fibrosis.

C. elegans PPEF-type phosphatase (Retinal degeneration C ortholog) functions in diverse classes of cilia to regulate nematode behaviors

Primary (non-motile) cilia represent structurally and functionally diverse organelles whose roles as specialized cellular antenna are central to animal cell signaling pathways, sensory physiology and development. An ever-growing number of ciliary proteins, including those found in vertebrate photoreceptors, have been uncovered and linked to human disorders termed ciliopathies. Here, we demonstrate that an evolutionarily-conserved PPEF-family serine-threonine phosphatase, not functionally linked to cilia in any organism but associated with rhabdomeric (non-ciliary) photoreceptor degeneration in the Drosophila rdgC (retinal degeneration C) mutant, is a bona fide ciliary protein in C. elegans. The nematode protein, PEF-1, depends on transition zone proteins, which make up a 'ciliary gate' in the proximal-most region of the cilium, for its compartmentalization within cilia. Animals lacking PEF-1 protein function display structural defects to several types of cilia, including potential degeneration of microtubules. They also exhibit anomalies to cilium-dependent behaviors, including impaired responses to chemical, temperature, light, and noxious CO2 stimuli. Lastly, we demonstrate that PEF-1 function depends on conserved myristoylation and palmitoylation signals. Collectively, our findings broaden the role of PPEF proteins to include cilia, and suggest that the poorly-characterized mammalian PPEF1 and PPEF2 orthologs may also have ciliary functions and thus represent ciliopathy candidates.

Loss of Sc5d results in micrognathia due to a failure in osteoblast differentiation

INTRODUCTION

Mutations in genes related to cholesterol metabolism, or maternal diet and health status, affect craniofacial bone formation. However, the precise role of intracellular cholesterol metabolism in craniofacial bone development remains unclear.

OBJECTIVE

The aim of this study is to determine how cholesterol metabolism aberrations affect craniofacial bone development.

METHODS

Mice with a deficiency in Sc5d, which encodes an enzyme involved in cholesterol synthesis, were analyzed with histology, micro computed tomography (microCT), and cellular and molecular biological methods.

RESULTS

Sc5d null mice exhibited mandible hypoplasia resulting from defects in osteoblast differentiation. The activation of the hedgehog and WNT/β-catenin signaling pathways, which induce expression of osteogenic genes Col1a1 and Spp1, was compromised in the mandible of Sc5d null mice due to a failure in the formation of the primary cilium, a cell surface structure that senses extracellular cues. Treatments with an inducer of hedgehog or WNT/β-catenin signaling or with simvastatin, a drug that restores abnormal cholesterol production, partially rescued the defects in osteoblast differentiation seen in Sc5d mutant cells.

CONCLUSION

Our results indicate that loss of Sc5d results in mandibular hypoplasia through defective primary cilia-mediated hedgehog and WNT/β-catenin signaling pathways.

Large-scale genomic investigation of pediatric cholestasis reveals a novel hepatorenal ciliopathy caused by PSKH1 mutations

PURPOSE

Pediatric cholestasis is the phenotypic expression of clinically and genetically heterogeneous disorders of bile acid synthesis and flow. Although a growing number of monogenic causes of pediatric cholestasis have been identified, the majority of cases remain undiagnosed molecularly.

METHODS

In a cohort of 299 pediatric participants (279 families) with intrahepatic cholestasis, we performed exome sequencing as a first-tier diagnostic test.

RESULTS

A likely causal variant was identified in 135 families (48.56%). These comprise 135 families that harbor variants spanning 37 genes with established or tentative links to cholestasis. In addition, we propose a novel candidate gene (PSKH1) (HGNC:9529) in 4 families. PSKH1 was particularly compelling because of strong linkage in 3 consanguineous families who shared a novel hepatorenal ciliopathy phenotype. Two of the 4 families shared a founder homozygous variant, whereas the third and fourth had different homozygous variants in PSKH1. PSKH1 encodes a putative protein serine kinase of unknown function. Patient fibroblasts displayed abnormal cilia that are long and show abnormal transport. A homozygous Pskh1 mutant mouse faithfully recapitulated the human phenotype and displayed abnormally long cilia. The phenotype could be rationalized by the loss of catalytic activity observed for each recombinant PSKH1 variant using in vitro kinase assays.

CONCLUSION

Our results support the use of genomics in the workup of pediatric cholestasis and reveal PSKH1-related hepatorenal ciliopathy as a novel candidate monogenic form.

Rare homozygous cilia gene variants identified in consanguineous congenital heart disease patients

Congenital heart defects (CHD) appear in almost one percent of live births. Asian countries have the highest birth prevalence of CHD in the world. Recessive genotypes may represent a CHD risk factor in Asian populations with a high degree of consanguineous marriages. Genetic analysis of consanguineous families may represent a relatively unexplored source for investigating CHD etiology. To obtain insight into the contribution of recessive genotypes in CHD we analysed a cohort of forty-nine Pakistani CHD probands, originating from consanguineous unions. The majority (82%) of patient's malformations were septal defects. We identified protein altering, rare homozygous variants (RHVs) in the patient's coding genome by whole exome sequencing. The patients had a median of seven damaging RHVs each, and our analysis revealed a total of 758 RHVs in 693 different genes. By prioritizing these genes based on variant severity, loss-of-function intolerance and specific expression in the developing heart, we identified a set of 23 candidate disease genes. These candidate genes were significantly enriched for genes known to cause heart defects in recessive mouse models (P < 2.4e-06). In addition, we found a significant enrichment of cilia genes in both the initial set of 693 genes (P < 5.4e-04) and the 23 candidate disease genes (P < 5.2e-04). Functional investigation of ADCY6 in cell- and zebrafish-models verified its role in heart development. Our results confirm a significant role for cilia genes in recessive forms of CHD and suggest important functions of cilia genes in cardiac septation.