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Cilia both receive and send information, the latter in the form of extracellular vesicles (EVs). EVs are nano-communication devices that influence cell, tissue, and organism behavior. Mechanisms driving ciliary EV biogenesis are almost entirely unknown. Here, we show that the ciliary G-protein Rab28, associated with human autosomal recessive cone-rod dystrophy, negatively regulates EV levels in the sensory organs of Caenorhabditis elegans in a cilia specific manner. Sequential targeting of lipidated Rab28 to periciliary and ciliary membranes is highly dependent on the BBSome and the prenyl-binding protein phosphodiesterase 6 subunit delta (PDE6D), respectively, and BBSome loss causes excessive and ectopic EV production. We also find that EV defective mutants display abnormalities in sensory compartment morphogenesis. Together, these findings reveal that Rab28 and the BBSome are key in vivo regulators of EV production at the periciliary membrane and suggest that EVs may mediate signaling between cilia and glia to shape sensory organ compartments. Our data also suggest that defects in the biogenesis of cilia-related EVs may contribute to human ciliopathies.

Ciliopathies are inherited disorders caused by defects in motile and non-motile (primary) cilia. Ciliopathy syndromes and associated gene variants are often highly pleiotropic and represent exemplars for interrogating genotype-phenotype correlations. Towards understanding disease mechanisms in the context of ciliopathy mutations, we have used a leading model organism for cilia and ciliopathy research, Caenorhabditis elegans, together with gene editing, to characterise two missense variants (P74S and G155S) in mksr-2/B9D2 associated with Joubert syndrome (JBTS). B9D2 functions within the Meckel syndrome (MKS) module at the ciliary base transition zone (TZ) compartment and regulates the molecular composition and sensory/signalling functions of the cilium. Quantitative assays of cilium/TZ structure and function, together with knock-in reporters, confirm that both variant alleles are pathogenic in worms. G155S causes a more severe overall phenotype and disrupts endogenous MKSR-2 organisation at the TZ. Recapitulation of the patient biallelic genotype shows that compound heterozygous worms phenocopy worms homozygous for P74S. The P74S and G155S alleles also reveal evidence of a very close functional association between the B9D2-associated B9 complex and MKS-2/TMEM216. Together, these data establish C. elegans as a model for interpreting JBTS mutations and provide further insight into MKS module organisation. This article has an associated First Person interview with the first author of the paper.

Activation of aldosterone/mineralocorticoid receptors (MR) has been implicated in vascular dysfunction of diabetes. Underlying mechanisms are elusive. Therefore, we investigated the role of Rho kinase (ROCK) in aldosterone/MR signaling and vascular dysfunction in a model of diabetes. Diabetic obese mice (db/db) and control counterparts (db/+) were treated with MR antagonist (MRA, potassium canrenoate, 30 mg/kg/day, 4 weeks) or ROCK inhibitor, fasudil (30 mg/kg/day, 3 weeks). Plasma aldosterone was increased in db/db versus db/+. This was associated with enhanced vascular MR signaling. Norepinephrine (NE)-induced contraction was increased in arteries from db/db mice. These responses were attenuated in mice treated with canrenoate or fasudil. Db/db mice displayed hypertrophic remodeling and increased arterial stiffness, improved by MR blockade. Vascular calcium sensitivity was similar between depolarized arteries from db/+ and db/db. Vascular hypercontractility in db/db mice was associated with increased myosin light chain phosphorylation and reduced expression of PKG-1α. Vascular RhoA/ROCK signaling and expression of pro-inflammatory and pro-fibrotic markers were exaggerated in db/db mice, effects that were attenuated by MRA. Fasudil, but not MRA, improved vascular insulin sensitivity in db/db mice, evidenced by normalization of Irs1 phosphorylation. Our data identify novel pathways involving MR-RhoA/ROCK-PKG-1 that underlie vascular dysfunction and injury in diabetic mice.

Age-related macular degeneration (AMD) is a leading cause of blindness among the elderly. Canonical disease models suggest that defective interactions between complement factor H (CFH) and cell surface heparan sulfate (HS) result in increased alternative complement pathway activity, cytolytic damage, and tissue inflammation in the retina. Although these factors are thought to contribute to increased disease risk, multiple studies indicate that noncanonical mechanisms that result from defective CFH and HS interaction may contribute to the progression of AMD as well. A total of 60 ciliated sensory neurons in the nematode Caenorhabditis elegans detect chemical, olfactory, mechanical, and thermal cues in the environment. Here, we find that a C. elegans CFH homolog localizes on CEP mechanosensory neuron cilia where it has noncanonical roles in maintaining inversin/NPHP-2 within its namesake proximal compartment and preventing inversin/NPHP-2 accumulation in distal cilia compartments in aging adults. CFH localization and maintenance of inversin/NPHP-2 compartment integrity depend on the HS 3-O sulfotransferase HST-3.1 and the transmembrane proteoglycan syndecan/SDN-1. Defective inversin/NPHP-2 localization in mouse and human photoreceptors with CFH mutations indicates that these functions and interactions may be conserved in vertebrate sensory neurons, suggesting that previously unappreciated defects in cilia structure may contribute to the progressive photoreceptor dysfunction associated with CFH loss-of-function mutations in some AMD patients.

Motile and non-motile cilia are associated with mutually-exclusive genetic disorders. Motile cilia propel sperm or extracellular fluids, and their dysfunction causes primary ciliary dyskinesia. Non-motile cilia serve as sensory/signalling antennae on most cell types, and their disruption causes single-organ ciliopathies such as retinopathies or multi-system syndromes. CFAP20 is a ciliopathy candidate known to modulate motile cilia in unicellular eukaryotes. We demonstrate that in zebrafish, cfap20 is required for motile cilia function, and in C. elegans , CFAP-20 maintains the structural integrity of non-motile cilia inner junctions, influencing sensory-dependent signalling and development. Human patients and zebrafish with CFAP20 mutations both exhibit retinal dystrophy. Hence, CFAP20 functions within a structural/functional hub centered on the inner junction that is shared between motile and non-motile cilia, and is distinct from other ciliopathy-associated domains or macromolecular complexes. Our findings suggest an uncharacterised pathomechanism for retinal dystrophy, and potentially for motile and non-motile ciliopathies in general. Motile and non-motile cilia have distinct functions and protein complexes associated with them. Here, the authors show the conserved protein CFAP20 is important for both motile and non-motile cilia and is distinct from other ciliopathy-associated domains or macromolecular complexes.

NADPH oxidases (Noxs) are a major source of reactive oxygen species (ROS) in vascular cells. ROS are important signalling molecules with diverse actions. Mechanisms underlying differential ROS effects may relate, in part, to subcellular localization and Nox isoform specificity. We investigated the compartmentalization of Noxs and ROS in vascular smooth muscle cells (VSMC) and questioned whether these phenomena are altered in hypertension. VSMCs isolated from mesenteric arteries of Wistar-Kyoto (WKY) and stroke-prone spontaneously hypertensive rats (SHRSP) were studied. Subcellular compartmentalization of Noxs was evaluated by immunoblotting after organelle fractionation. ROS levels were measured by chemiluminescence (O2-) and amplex red (H2O2) in the absence or presence of of ML171 (Nox1 inhibitor), GKT136901 (Nox1/4 inhibitor), mito-tempol (mitochondrial-targeted antioxidant) and 4-PBA (ER stress inhibitor). Protein oxidation was assessed using the fluorescent probe DCP-Rho1 for protein sulfenylation and the oxyblot assay for protein carbonylation. Oxidation of protein tyrosine phosphatases (PTP) was evaluated by immunoblotting and Peroxiredoxin (Prx) oxidation was assessed by one-dimensional isoelectric focusing. Vascular reactivity was assessed by myography ± DTT (reducing agent) and peroxiredoxin inhibitor (Conoidin A). Expression of Nox1, Nox2 and Nox4 was greater in total cell homogenates from SHRSP versus WKY. Nox isoforms were detected in plasma membrane, ER and nucleus in both strains, but not in the mitochondria. Basal ROS generation was increased in SHRSP cells. In WKY only Nox1 inhibition decreased Ang II-induced ROS generation. Inhibition of Nox1 and Nox4 decreased basal and Ang II-induced ROS in SHRSP. Additionally, mito-tempol and 4-PBA reduced basal ROS generation in SHRSP. Analysis of protein oxidation revealed increased protein carbonylation and PTP oxidation in SHRSP. Furthermore, oxidation of the antioxidant enzymes Prxs was increased in SHRSP. Prx2, localised in the cytosol, and mitochondrial Prx3 were more oxidised in SHRSP cells than WKY cells. Noradrenaline-induced vascular contraction was reduced by DTT and Conoidin A. Our data demonstrate that Noxs are expressed in an organelle-specific manner, with Nox1,2,4 present in plasma membrane, ER and nucleus, but not in mitochondria. In SHRSP VSMCs Nox expression, ROS generation and protein oxidation are increased. Inhibition of oxidation attenuated vascular reactivity. These findings suggest an important role for Nox1/4 in oxidative stress and post-translational modification of proteins, processes that may play an important role in vascular dysfunction in hypertension.

Primary cilia rely on compartmentalisation mechanisms that establish the organelle's protein and lipid composition. In mammalian cells, septin GTPases are reported to facilitate cilium formation, function and molecular composition by regulating a membrane diffusion barrier at the ciliary base transition zone (TZ). Here, we examined septins , within sense organs. Unexpectedly, loss of one or both septin genes ( , ) does not cause global defects in cilium structure. Instead, only a subset of ciliated neurons, including the phasmid tail neurons, are affected, with septin mutants displaying short and mispositioned ciliary axonemes due to truncated dendritic processes. Notably, nematode septins do not appear to function at the TZs, with mutants retaining normal gating function and gating complex (MKS & NPHP modules) localisations. Furthermore, double mutant analyses reveal a lack of septin gene interaction with the gating pathways. Strikingly, cell-specific rescue experiments show that UNC-61 regulates phasmid neuronal cilia via a cell non-autonomous mechanism, within supporting glial cells. In addition, UNC-61 localises close to sensory pore adherens cell junctions, and we provide evidence that septin loss disrupts their integrity. Together, our data uncovers an unexpected cell non-autonomous function for glial septins in regulating a subset of sensory neuronal cilia, via a mechanism that may involve cell-cell junctions.

Essential hypertension (EH) is considered one of the major contributors to the present pandemic of cardiovascular disease (CVD). EH has a largely obscure aetiology, which lies upon both environmental risk factors and underlying genetic traits. The stroke-prone spontaneously hypertensive rat (SHRSP) is an excellent model of human EH and exhibits salt sensitivity. Two quantitative trait loci (QTL) for blood pressure (BP) regulation have been identified on rat chromosome 2 (chr.2). On this basis, previous work in our laboratory focused on construction of chr.2 congenic strains, on both the SHRSP and Wistar-Kyoto (WKY) genetic backgrounds. In combination with microarray gene expression profiling in kidney from salt-loaded rats, two positional candidate genes for salt-sensitive hypertension were identified. Sphingosine-1-phosphate receptor 1 (S1pr1) and vascular adhesion molecule (Vcam1) lie on the chr.2 congenic interval implicated in salt-sensitivity. Additionally, studies on vascular smooth muscle cells (VSMC) demonstrated enhanced S1PR1-mediated sphingosine signalling in SHRSP compared to WKY. Finally, glutathione S-transferase mu 1 (Gstm1) was identified as another chr.2 candidate gene for BP regulation, lying outside the region implicated in salt-sensitivity. This project attempts to comprehensively investigate the potential role of altered S1PR1 signalling in BP regulation and salt-sensitivity, through comparative proteomic and metabolomic profiling in WKY, SHRSP and chromosome 2 congenic and transgenic stains (WKY.SPGla2a, SP.WKYGla2a, SP.WKYGla2k and Gstm1-transgenic). Characterisation of S1PR1 expression in renal and vascular tissue from 21 week-old salt-loaded rats, demonstrated below detection protein levels across parental and congenic strains. To further investigate the effect of the congenic interval and Gstm1 on salt-sensitivity and BP regulation and identify putative biomarkers, high-throughput metabolomic screening of urine and plasma was conducted in parental, SP.WKYGla2k congenic and Gstm1-transgenic strains, on a normal-salt and high-salt diet. In both urine and plasma, salt-loading affected processes implicated in CVD, including inflammatory response, free radical scavenging and lipid metabolism. In urine, oleic acid, implicated in regulation of renin levels, was increased in the SHRSP and transgenic salt-sensitive strains compared to the WKY and 2k congenic salt-resistant strains, upon salt-loading. In plasma, known biomarkers of CVD were altered in SHRSP compared to the other three strains, at normal-salt, including L-proline and linoleic acid. Upon salt-loading, glutathione disulfide and sphingosine-1-phosphate (S1P) were identified in high levels in the salt-sensitive strains. However, at normal-salt S1P was decreased in SHRSP compared to WKY and 2k congenic strains. Therefore, characterisation of the impact of S1P/S1PR1 signalling in the vasculature across the different strains was further investigated. Initially, structure, mechanical properties and vascular reactivity of mesenteric resistance arteries (MRA) were studied in 16 week-old parental and reciprocal 2a congenic strains (WKY.SPGla2a and SP.WKYGla2a). There was no significant remodelling observed across the strains. However, SHRSP vessels were stiffer and this phenotype was under the control of the congenic segment. SHRSP exhibited hypercontractility, which was mediated by RhoA/Rock signalling pathway and was corrected by the transfer of the congenic interval in SP.WKYGla2a. SHRSP also displayed endothelial dysfunction, which was related to reduced nitric oxide (NO) bioavailability and was not improved by the congenic interval. The predominant regulatory mechanisms of contraction and relaxation in MRAs from WKY and WKY.SPGla2a were demonstrated to be different compared to SHRSP. Subsequently, representation of these physiological differences in MRAs, at the molecular level, was investigated along with the effect of S1P-signalling in HTN. Comprehensive, high-throughput proteome profiling of S1P-stimulated primary mesenteric VSMCs from parental and 2a-reciprocal congenic strains, was achieved through triple stable isotope labelling (SILAC), LC-MS/MS analysis and MaxQuant quantification. Detection of few abundant phosphorylated proteins was attributed to lack of enrichment for phosphoproteome. Therefore, focus was placed on proteins whose differential expression between SHRSP and WKY was genetically regulated. These proteins mapped to pathways implicated in BP-regulation, including oxidative stress, vascular tone regulation and vascular remodelling. Glutathione S-transferase mu 1 (GSTM1) was upregulated in SHRSP, as opposed to down-regulated NAD(P)H oxidase quinone 1 (NQO1) and heme oxygenase 1 (HMOX1), suggesting different antioxidant mechanisms in health and disease. Natriuretic peptide receptor C (NPR3) which is implicated in vascular relaxation was increased in SHRSP, along with activators of RhoA contractile mechanism, such as caveolin1 (CAV1). Furthermore, RhoA/Rock signalling pathway was highly altered in SHRSP. Finally, differentially expressed proteins were related to sphingosine signalling, including superoxide dismutase 2 (SOD2) and collagen type III, alpha 1 (COL3A1). To further investigate the metabolic effect of sphingosine signalling across the strains, and assess the contribution of the congenic interval, metabolomic profiling of primary mesenteric VSMCs from parental and SP.WKYGla2a congenic strains, was performed at basal conditions and upon S1P-stimulation. A labelling-free, untargeted approach was employed, using HILIC-MS analysis and data processing through IDEOM. The effect of the congenic interval on the metabolic profile of SP.WKYGla2a was more profound under basal conditions. S1P-stimulation induced greater responses in SHRSP than WKY, indicating altered signalling. Furthermore the responses were different in each strain, suggesting a combined effect of the genetic background and the congenic interval on S1P signalling regulation. Inosine, which is implicated in purine metabolism, was significantly decreased in SHRSP compared to SP.WKYGla2a, at basal conditions, but was increased upon-S1P stimulation, implying that this S1P effect depends on the congenic interval. Moreover, tyramine, which has vasodilatory properties, was increased in stimulated SHRSP compared to basal conditions, indicating potential relation of sphingosine signalling with BP-regulation. This study has combined high-throughput proteomic and metabolomic screenings with congenic and transgenic strains to capture a clearer picture of the pathophysiological processes that underlie HTN in SHRSP. Individual metabolites and proteins or pathways and processes identified to be altered in HTN, through this work, can be used for generation of new testable hypothesis towards the development of new therapeutic approaches against HTN.

Better methods are required to interpret the pathogenicity of disease-associated variants of uncertain significance (VUS), which cannot be actioned clinically. In this study, we explore the use of a tractable animal model (Caenorhabditis elegans) for in vivo interpretation of missense VUS alleles of TMEM67, a cilia gene associated with ciliopathies. CRISPR/Cas9 gene editing was used to generate homozygous knock-in C. elegans worm strains carrying TMEM67 patient variants engineered into the orthologous gene (mks-3). Quantitative phenotypic assays of sensory cilia structure and function measured if the variants affect mks-3 gene function. Results from worms were validated by a genetic complementation assay in a human TMEM67 knock-out hTERT-RPE1 cell line that tests a TMEM67 signaling function. Assays in C. elegans accurately distinguished between known benign (Asp359Glu, Thr360Ala) and known pathogenic (Glu361Ter, Gln376Pro) variants. Analysis of eight missense VUS generated evidence that three are benign (Cys173Arg, Thr176Ile, Gly979Arg) and five are pathogenic (Cys170Tyr, His782Arg, Gly786Glu, His790Arg, Ser961Tyr). Efficient genome editing and quantitative functional assays in C. elegans make it a tractable in vivo animal model that allows rapid, cost-effective interpretation of ciliopathy-associated missense VUS alleles.

ABSTRACT Purpose A molecular genetic diagnosis is essential for accurate counselling and management of patients with ciliopathies. Uncharacterized missense alleles are often classified as variants of uncertain significance (VUS) and are not clinically useful. In this study, we explore the use of a tractable animal model (C. elegans) for in vivo interpretation of missense VUS alleles of TMEM67, a gene frequently mutated as a cause of ciliopathies. Methods CRISPR/Cas9 gene editing was used to generate homozygous worm strains carrying TMEM67 patient variants. Quantitative phenotypic assays (dye filling, roaming, chemotaxis) assessed cilia structure and function. Results were validated by genetic complementation assays in a human TMEM67 knock-out hTERT-RPE1 cell line. Results Quantitative assays in C. elegans distinguished between known benign (Asp359Glu, Thr360Ala) and pathogenic (Glu361Ter, Gln376Pro) variants. Analysis of seven missense VUS alleles predicted two benign (Cys173Arg, Thr176Ile) and four pathogenic variants (Cys170Tyr, His782Arg, Gly786Glu, His790Arg). Results from one VUS (Gly979Arg) were inconclusive in worms, but additional in vitro validation suggested it was likely benign. Conclusion Efficient genome editing and quantitative functional assays in C. elegans make it a tractable in vivo animal model that allows stratification and rapid, cost-effective interpretation of ciliopathy-associated missense VUS alleles. Competing Interest Statement The authors have declared no competing interest.