Leptin Elongates Hypothalamic Neuronal Cilia via Transcriptional Regulation and Actin Destabilization

Bardet-Biedl syndrome: A focus on genetics, mechanisms and metabolic dysfunction

Bardet-Biedl syndrome (BBS) is a rare, monogenic, multisystem disorder characterized by retinal dystrophy, renal abnormalities, polydactyly, learning disabilities, as well as metabolic dysfunction, including obesity and an increased risk of type 2 diabetes. It is a primary ciliopathy, and causative mutations in more than 25 different genes have been described. Multiple cellular mechanisms contribute to the development of the metabolic phenotype associated with BBS, including hyperphagia as a consequence of altered hypothalamic appetite signalling as well as alterations in adipocyte biology promoting adipocyte proliferation and adipogenesis. Within this review, we describe in detail the metabolic phenotype associated with BBS and discuss the mechanisms that drive its evolution. In addition, we review current approaches to the metabolic management of patients with BBS, including the use of weight loss medications and bariatric surgery. Finally, we evaluate the potential of targeting hypothalamic appetite signalling to limit hyperphagia and induce clinically significant weight loss.

Postnatal Dynamic Ciliary ARL13B and ADCY3 Localization in the Mouse Brain

Primary cilia are hair-like structures found on nearly all mammalian cell types, including cells in the developing and adult brain. A diverse set of receptors and signaling proteins localize within cilia to regulate many physiological and developmental pathways, including the Hedgehog (Hh) pathway. Defects in cilia structure, protein localization, and function lead to genetic disorders called ciliopathies, which present with various clinical features that include several neurodevelopmental phenotypes and hyperphagia-associated obesity. Despite their dysfunction being implicated in several disease states, understanding their roles in central nervous system (CNS) development and signaling has proven challenging. We hypothesize that dynamic changes to ciliary protein composition contribute to this challenge and may reflect unrecognized diversity of CNS cilia. The proteins ARL13B and ADCY3 are established markers of cilia in the brain. ARL13B is a regulatory GTPase important for regulating cilia structure, protein trafficking, and Hh signaling, and ADCY3 is a ciliary adenylyl cyclase. Here, we examine the ciliary localization of ARL13B and ADCY3 in the perinatal and adult mouse brain. We define changes in the proportion of cilia enriched for ARL13B and ADCY3 depending on brain region and age. Furthermore, we identify distinct lengths of cilia within specific brain regions of male and female mice. ARL13B+ cilia become relatively rare with age in many brain regions, including the hypothalamic feeding centers, while ADCY3 becomes a prominent cilia marker in the mature adult brain. It is important to understand the endogenous localization patterns of these proteins throughout development and under different physiological conditions as these common cilia markers may be more dynamic than initially expected. Understanding regional- and developmental-associated cilia protein composition signatures and physiological condition cilia dynamic changes in the CNS may reveal the molecular mechanisms associated with the features commonly observed in ciliopathy models and ciliopathies, like obesity and diabetes.

The role of primary cilia in thyroid diseases

Primary cilia (PC) are non-motile and microtube-based organelles protruding from the surface of almost all thyroid follicle cells. They maintain homeostasis in thyrocytes and loss of PC can result in diverse thyroid diseases. The dysfunction of structure and function of PC are found in many patients with common thyroid diseases. The alterations are associated with the cause, development, and recovery of the diseases and are regulated by PC-mediated signals. Restoring normal PC structure and function in thyrocytes is a promising therapeutic strategy to treat thyroid diseases. This review explores the function of PC in normal thyroid glands. It summarizes the pathology caused by PC alterations in thyroid cancer (TC), autoimmune thyroid diseases (AITD), hypothyroidism, and thyroid nodules (TN) to provide comprehensive references for further study.

Regulation of the length of neuronal primary cilia and its potential effects on signalling

Primary cilia protrude from most vertebrate cell bodies and act as specialized 'signalling antennae' that can substantially lengthen or retract in minutes to hours in response to specific stimuli. Here, we review the conditions and mechanisms responsible for regulating primary cilia length (PCL) in mammalian nonsensory neurons, and propose four models of how they could affect ciliary signalling and alter cell state and suggest experiments to distinguish between them. These models include (i) the passive indicator model, where changes in PCL have no consequence; (ii) the rheostat model, in which a longer cilium enhances signalling; (iii) the local concentration model, where ciliary shortening increases the local protein concentration to facilitate signalling; and (iv) the altered composition model where changes in PCL skew signalling.

LCRMP-1 is required for spermatogenesis and stabilises spermatid F-actin organization via the PI3K-Akt pathway

Long-form collapsin response mediator protein-1 (LCRMP-1) belongs to the CRMP family which comprises brain-enriched proteins responsible for axon guidance. However, its role in spermatogenesis remains unclear. Here we find that LCRMP-1 is abundantly expressed in the testis. To characterize its physiological function, we generate LCRMP-1-deficient mice (Lcrmp-1^-/-). These mice exhibit aberrant spermiation with apoptotic spermatids, oligospermia, and accumulation of immature testicular cells, contributing to reduced fertility. In the seminiferous epithelial cycle, LCRMP-1 expression pattern varies in a stage-dependent manner. LCRMP-1 is highly expressed in spermatids during spermatogenesis and especially localized to the spermiation machinery during spermiation. Mechanistically, LCRMP-1 deficiency causes disorganized F-actin due to unbalanced signaling of F-actin dynamics through upregulated PI3K-Akt-mTOR signaling. In conclusion, LCRMP-1 maintains spermatogenesis homeostasis by modulating cytoskeleton remodeling for spermatozoa release.

Neuronal primary cilia integrate peripheral signals with metabolic drives

Neuronal primary cilia have recently emerged as important contributors to the central regulation of energy homeostasis. As non-motile, microtubule-based organelles, primary cilia serve as signaling antennae for metabolic status. The impairment of ciliary structure or function can produce ciliopathies for which obesity is a hallmark phenotype and global ablation of cilia induces non-syndromic adiposity in mouse models. This organelle is not only a hub for metabolic signaling, but also for catecholamine neuromodulation that shapes neuronal circuitry in response to sensory input. The objective of this review is to highlight current research investigating the mechanisms of primary cilium-regulated metabolic drives for maintaining energy homeostasis.

Evaluation of ciliary-GPCR dynamics using a validated organotypic brain slice culture method

The primary cilium is a structural organelle present in most mammalian cells. Primary cilia are enriched with a unique protein repertoire distinct from that of the cytosol and the plasma membrane. Such a highly organized microenvironment creates effective machinery for translating extracellular cues into intracellular signals. G protein-coupled receptors (GPCRs) are key receptors in sensing environmental stimuli transmitted via a second messenger into a cellular response. Recent data has demonstrated that a limited number of non-olfactory GPCRs, including melanin-concentrating hormone receptor 1 (MCHR1), are preferentially localized to ciliary membranes of several mammalian cell types, including neuronal cells. Evidence was accumulated to support the functional importance of ciliary-GPCR signaling accompanying ciliary structural changes using cilia-specific cell and molecular biology techniques. Thus, cilia are now considered to function as a unique sensory platform for the integration of GPCR signaling and various cytoplasmic domains. Dissociated neurons expressing ciliary-GPCRs can be a useful tool for examining ciliary dynamics. However, losing preexisting neuronal connectivity may alter neuronal ciliary morphology, such as abnormal elongation. Brain slices prepared under ex vitro conditions are a powerful approach that maintains the cytoarchitecture, enabling researchers to have accurate control over experimental conditions and to study individual cells from subregions of the brain. Here, we present a detailed description of our novel modified method for organotypic culture of rat brain slice and a validated immunostaining protocol to characterize ciliary-GPCR dynamics in coupling with neuropeptides or aminergic activation.

Mitochondrial impairment and intracellular reactive oxygen species alter primary cilia morphology

This work shows how altering energetic status and promoting intracellular/mitochondrial ROS induces cell-dependent ciliary impairments, which is relevant in diseases characterized by these features.

Primary cilia have recently emerged as cellular signaling organelles. Their homeostasis and function require a high amount of energy. However, how energy depletion and mitochondria impairment affect cilia have barely been addressed. We first studied the spatial relationship between a mitochondria subset in proximity to the cilium in vitro, finding similar mitochondrial activity measured as mitochondrial membrane potential compared with the cellular network. Next, using common primary cilia cell models and inhibitors of mitochondrial energy production, we found alterations in cilia number and/or length due to energy depletion and mitochondrial reactive oxygen species (ROS) overproduction. Finally, by using a mouse model of type 2 diabetes mellitus, we provided in vivo evidence that cilia morphology is impaired in diabetic nephropathy, which is characterized by ROS overproduction and impaired mitochondrial metabolism. In conclusion, we showed that energy imbalance and mitochondrial ROS affect cilia morphology and number, indicating that conditions characterized by mitochondria and radicals imbalances might lead to ciliary impairment.

Mechanisms of Weight Control by Primary Cilia

A primary cilium, a hair-like protrusion of the plasma membrane, is a pivotal organelle for sensing external environmental signals and transducing intracellular signaling. An interesting linkage between cilia and obesity has been revealed by studies of the human genetic ciliopathies Bardet-Biedl syndrome and Alström syndrome, in which obesity is a principal manifestation. Mouse models of cell type-specific cilia dysgenesis have subsequently demonstrated that ciliary defects restricted to specific hypothalamic neurons are sufficient to induce obesity and hyperphagia. A potential mechanism underlying hypothalamic neuron cilia-related obesity is impaired ciliary localization of G protein-coupled receptors involved in the regulation of appetite and energy metabolism. A well-studied example of this is melanocortin 4 receptor (MC4R), mutations in which are the most common cause of human monogenic obesity. In the paraventricular hypothalamus neurons, a blockade of ciliary trafficking of MC4R as well as its downstream ciliary signaling leads to hyperphagia and weight gain. Another potential mechanism is reduced leptin signaling in hypothalamic neurons with defective cilia. Leptin receptors traffic to the periciliary area upon leptin stimulation. Moreover, defects in cilia formation hamper leptin signaling and actions in both developing and differentiated hypothalamic neurons. The list of obesity-linked ciliary proteins is expending and this supports a tight association between cilia and obesity. This article provides a brief review on the mechanism of how ciliary defects in hypothalamic neurons facilitate obesity.

Ciliary GPCR-based transcriptome as a key regulator of cilia length control

The primary cilium is a plasma membrane-protruding sensory organelle that efficiently conveys signaling cascades in a highly ordered microenvironment. Its signaling is mediated, in part, by a limited set of GPCRs preferentially enriched in the cilium membrane. This includes melanin-concentrating hormone (MCH) receptor 1 (MCHR1), which plays a role in feeding and mood. In addition to its receptor composition, the length of the cilium is a characteristic parameter that is implicated in its function. We previously found that MCH can dynamically shorten cilia length via the Gi/o and Akt pathways in both MCHR1-expressing hTERT-RPE1 cells (hRPE1 cells) and rat hippocampal neurons. However, the detailed mechanisms by which MCH regulates cilia length through ciliary MCHR1 remains unclear. In this study, we aimed to determine the transcriptome changes in MCHR1-expressing hRPE1 cells in response to MCH to identify the target molecules involved in cilia length regulation via MCHR1 activation. RNA sequencing analysis of ciliated cells subjected to MCH treatment showed upregulation of 424 genes and downregulation of 112 genes compared with static control cells. Validation by quantitative real-time PCR, knocking down, and CRISPR/Cas9-mediated knockout technology identified a molecule, PDZ and LIM domain-containing protein 5 (PDLIM5). Thus, it was considered as the most significant key factor for MCHR1-mediated shortening of cilia length. Additional analyses revealed that the actin-binding protein alpha-actinin 1/4 is a crucial downstream target of the PDLIM5 signaling pathway that exerts an effect on MCHR1-induced cilia shortening. In the endogenous MCHR1-expressing hippocampus, transcriptional upregulation of PDLIM5 and actinin 1/4, following the application of MCH, was detected when the MCHR1-positive cilia were shortened. Together, our transcriptome study based on ciliary MCHR1 function uncovered a novel and important regulatory step underlying cilia length control. These results will potentially serve as a basis for understanding the mechanism underlying the development of obesity and mood disorders.

RFX1: a promising therapeutic arsenal against cancer

Regulatory factor X1 (RFX1) is an evolutionary conserved transcriptional factor that influences a wide range of cellular processes such as cell cycle, cell proliferation, differentiation, and apoptosis, by regulating a number of target genes that are involved in such processes. On a closer look, these target genes also play a key role in tumorigenesis and associated events. Such observations paved the way for further studies evaluating the role of RFX1 in cancer. These studies were indispensable due to the failure of conventional chemotherapeutic drugs to target key cellular hallmarks such as cancer stemness, cellular plasticity, enhanced drug efflux, de-regulated DNA repair machinery, and altered pathways evading apoptosis. In this review, we compile significant evidence for the tumor-suppressive activities of RFX1 while also analyzing its oncogenic potential in some cancers. RFX1 induction decreased cellular proliferation, modulated the immune system, induced apoptosis, reduced chemoresistance, and sensitized cancer stem cells for chemotherapy. Thus, our review discusses the pleiotropic function of RFX1 in multitudinous gene regulations, decisive protein–protein interactions, and also its role in regulating key cell signaling events in cancer. Elucidation of these regulatory mechanisms can be further utilized for RFX1 targeted therapy.

The entangled relationship between cilia and actin

Primary cilia are microtubule-based sensory cell organelles that are vital for tissue and organ development. They act as an antenna, receiving and transducing signals, enabling communication between cells. Defects in ciliogenesis result in severe genetic disorders collectively termed ciliopathies. In recent years, the importance of the direct and indirect involvement of actin regulators in ciliogenesis came into focus as it was shown that F-actin polymerisation impacts ciliation. The ciliary basal body was further identified as both a microtubule and actin organising centre. In the current review, we summarize recent studies on F-actin in and around primary cilia, focusing on different actin regulators and their effect on ciliogenesis, from the initial steps of basal body positioning and regulation of ciliary assembly and disassembly. Since primary cilia are also involved in several intracellular signalling pathways such as planar cell polarity (PCP), subsequently affecting actin rearrangements, the multiple effectors of this pathway are highlighted in more detail with a focus on the feedback loops connecting actin networks and cilia proteins. Finally, we elucidate the role of actin regulators in the development of ciliopathy symptoms and cancer.

Potential Roles of O-GlcNAcylation in Primary Cilia- Mediated Energy Metabolism

The primary cilium, an antenna-like structure on most eukaryotic cells, functions in transducing extracellular signals into intracellular responses via the receptors and ion channels distributed along it membrane. Dysfunction of this organelle causes an array of human diseases, known as ciliopathies, that often feature obesity and diabetes; this indicates the primary cilia's active role in energy metabolism, which it controls mainly through hypothalamic neurons, preadipocytes, and pancreatic β-cells. The nutrient sensor, O-GlcNAc, is widely involved in the regulation of energy homeostasis. Not only does O-GlcNAc regulate ciliary length, but it also modifies many components of cilia-mediated metabolic signaling pathways. Therefore, it is likely that O-GlcNAcylation (OGN) plays an important role in regulating energy homeostasis in primary cilia. Abnormal OGN, as seen in cases of obesity and diabetes, may play an important role in primary cilia dysfunction mediated by these pathologies.

Functional aspects of primary cilium in signaling, assembly and microenvironment in cancer

The primary cilium is an antennae‐like structure extent outside the cell surface. It has an important role in regulating cell‐signaling transduction to affect proliferation, differentiation and migration. Evidence is accumulating that ciliary defects lead to ciliopathies and ciliary deregulation also play crucial roles in cancer formation and progression. Interestingly, restoring the cilia can suppress proliferation in some cancer cell. However, t he role of primary cilia in cancer still be debated. In this article, we review the role of the primary cilium in cancer through architecture, signaling pathways, cilia assembly and disassembly regulators, and summarized the new findings of the primary cilium in tumor microenvironments and different cancers, highlighting novel possibilities for therapeutic target in cancer.

Giant Island Mice Exhibit Widespread Gene Expression Changes in Key Metabolic Organs

Island populations repeatedly evolve extreme body sizes, but the genomic basis of this pattern remains largely unknown. To understand how organisms on islands evolve gigantism, we compared genome-wide patterns of gene expression in Gough Island mice, the largest wild house mice in the world, and mainland mice from the WSB/EiJ wild-derived inbred strain. We used RNA-seq to quantify differential gene expression in three key metabolic organs: gonadal adipose depot, hypothalamus, and liver. Between 4,000 and 8,800 genes were significantly differentially expressed across the evaluated organs, representing between 20% and 50% of detected transcripts, with 20% or more of differentially expressed transcripts in each organ exhibiting expression fold changes of at least 2×. A minimum of 73 candidate genes for extreme size evolution, including Irs1 and Lrp1, were identified by considering differential expression jointly with other data sets: 1) genomic positions of published quantitative trait loci for body weight and growth rate, 2) whole-genome sequencing of 16 wild-caught Gough Island mice that revealed fixed single-nucleotide differences between the strains, and 3) publicly available tissue-specific regulatory elements. Additionally, patterns of differential expression across three time points in the liver revealed that Arid5b potentially regulates hundreds of genes. Functional enrichment analyses pointed to cell cycling, mitochondrial function, signaling pathways, inflammatory response, and nutrient metabolism as potential causes of weight accumulation in Gough Island mice. Collectively, our results indicate that extensive gene regulatory evolution in metabolic organs accompanied the rapid evolution of gigantism during the short time house mice have inhabited Gough Island.

LUZP1, a novel regulator of primary cilia and the actin cytoskeleton, is a contributing factor in Townes-Brocks Syndrome

Primary cilia are sensory organelles crucial for cell signaling during development and organ homeostasis. Cilia arise from centrosomes and their formation and function is governed by numerous factors. Through our studies on Townes-Brocks Syndrome (TBS), a rare disease linked to abnormal cilia formation in human fibroblasts, we uncovered the leucine-zipper protein LUZP1 as an interactor of truncated SALL1, a dominantly-acting protein causing the disease. Using TurboID proximity labeling and pulldowns, we show that LUZP1 associates with factors linked to centrosome and actin filaments. Here, we show that LUZP1 is a cilia regulator. It localizes around the centrioles and to actin cytoskeleton. Loss of LUZP1 reduces F-actin levels, facilitates ciliogenesis and alters Sonic Hedgehog signaling, pointing to a key role in cytoskeleton-cilia interdependency. Truncated SALL1 increases the ubiquitin proteasome-mediated degradation of LUZP1. Together with other factors, alterations in LUZP1 may be contributing to TBS etiology.

FoxO1 regulates leptin-induced mood behavior by targeting tyrosine hydroxylase

PURPOSE

While leptin has been associated with various psycho-physiological functions, the molecular network in leptin-mediated mood regulation remains elusive.

METHODS

Anxiolytic behaviors and tyrosine hydroxylase (TH) levels were examined after leptin administration. Functional roles of STAT3 and FoxO1 in regulation of TH expression were investigated using in vivo and in vitro systems. A series of animal behavioral tests using dopaminergic neuron-specific FoxO1 KO (FoxO1 KO^DAT) were performed and investigated the roles of FoxO1 in regulation of mood behaviors.

RESULTS

Here, we show that administration of leptin induces anxiolytic-like phenotype through the activation of signal transducer and activator of transcription 3 (STAT3) and the inhibition of forkhead box protein O1 (FoxO1) in dopaminergic (DA) neurons of the midbrain. Specifically, STAT3 and FoxO1 directly bind to and exert opposing effects on tyrosine hydroxylase (TH) expression, where STAT3 acts as an enhancer and FoxO1 acts as a prominent repressor. Accordingly, suppression of the prominent suppressor FoxO1 by leptin strongly increased TH expression. Furthermore, our previous results showed that specific deletion of FoxO1 in DA neurons (FoxO1 KO^DAT) led to a profound elevation of TH activity and dopamine contents. Finally, FoxO1 KO^DAT mice exhibited enhanced leptin sensitivity as well as displayed reduced anxiety- and depression-like behaviors.

CONCLUSIONS

This work establishes a novel molecular mechanism of mood behavior regulation by leptin and suggests FoxO1 suppression by leptin might be a key for leptin-induced behavioral manifestation in DA neurons.

ALMS1 and Alström syndrome: a recessive form of metabolic, neurosensory and cardiac deficits

Alström syndrome (AS) is characterised by metabolic deficits, retinal dystrophy, sensorineural hearing loss, dilated cardiomyopathy and multi-organ fibrosis. Elucidating the function of the mutated gene, ALMS1, is critical for the development of specific treatments and may uncover pathways relevant to a range of other disorders including common forms of obesity and type 2 diabetes. Interest in ALMS1 is heightened by the recent discovery of its involvement in neonatal cardiomyocyte cell cycle arrest, a process with potential relevance to regenerative medicine. ALMS1 encodes a ~ 0.5 megadalton protein that localises to the base of centrioles. Some studies have suggested a role for this protein in maintaining centriole-nucleated sensory organelles termed primary cilia, and AS is now considered to belong to the growing class of human genetic disorders linked to ciliary dysfunction (ciliopathies). However, mechanistic details are lacking, and recent studies have implicated ALMS1 in several processes including endosomal trafficking, actin organisation, maintenance of centrosome cohesion and transcription. In line with a more complex picture, multiple isoforms of the protein likely exist and non-centrosomal sites of localisation have been reported. This review outlines the evidence for both ciliary and extra-ciliary functions of ALMS1.

[Traffic and signalisation of the leptin receptor]

Receptors are the master regulators conveying the information provided by the hormone from the extracellular environment to the intracellular milieu. As a result, the level of receptors at the cell surface can determine the signaling strength. Regulation of receptor trafficking to the cell surface or receptor retention processes in intracellular compartments are key mechanisms for leptin receptor (ObR) activity. An alteration of these mechanisms leads to the development of obesity. However, the canonical mechanism of plasma membrane receptors activation is challenged by the discovery that intracellular receptors also have their own signaling activity inside specific intracellular compartments. These intracellular receptors can trigger signaling that regulates a particular function, different from, or in continuity with, surface receptor signaling. We will address both these aspects by focusing particularly on the case of the leptin receptor (ObR), i.e., i) the regulation of its level of exposure to the cell surface and its impact on the development of obesity, and ii) the discovery of its location and signaling in some intracellular compartments.

Primary Cilia as a Signaling Platform for Control of Energy Metabolism

Obesity has become a common healthcare problem worldwide. Cilia are tiny hair-like organelles on the cell surface that are generated and anchored by the basal body. Non-motile primary cilia have been considered to be evolutionary rudiments until a few decades, but they are now considered as important signaling organelles because many receptors, channels, and signaling molecules are highly expressed in primary cilia. A potential role of primary cilia in metabolic regulation and body weight maintenance has been suspected based on rare genetic disorders termed as ciliopathy, such as Bardet-Biedl syndrome and Alström syndrome, which manifest as obesity. Recent studies have demonstrated involvement of cilia-related cellular signaling pathways in transducing metabolic information in hypothalamic neurons and in determining cellular fate during adipose tissue development. In this review, we summarize the current knowledge about cilia and cilia-associated signaling pathways in the regulation of body metabolism.

4-hydroxy-3-methoxycinnamic acid regulates orexigenic peptides and hepatic glucose homeostasis through phosphorylation of FoxO1

4-hydroxy-3-methoxycinnamic acid (ferulic acid, FA) is known to have numerous beneficial health effects, including anti-obesity and anti-hyperglycemic properties. However, the molecular networks that modulate the beneficial FA-induced metabolic effects have not been well elucidated. In this study, we explored the molecular mechanisms mediating the beneficial metabolic effects of FA. In mice, FA protected against high-fat diet-induced weight gain, reduced food intake and exhibited an overall improved metabolic phenotype. The food intake suppression by FA was accompanied by a specific reduction in hypothalamic orexigenic neuropeptides, including agouti-related protein and neuropeptide Y, with no significant changes in the anorexigenic peptides pro-opiomelanocortin and cocaine and amphetamine-regulated transcript. FA treatment also inhibited fat accumulation in the liver and white adipose tissue and suppressed the expression of gluconeogenic genes, including phosphoenolpyruvate carboxylase and glucose-6-phosphatase. Furthermore, we show that FA phosphorylated and inactivated the transcription factor FoxO1, which positively regulates the expression of gluconeogenic and orexigenic genes, providing evidence that FA might exert its beneficial metabolic effects through inhibition of FoxO1 function in the periphery and the hypothalamus.

Leptin, An Adipokine With Central Importance in the Global Obesity Problem

Leptin has central importance in the global obesity and cardiovascular disease problem. Leptin is principally secreted by adipocytes and acts in the hypothalamus to suppress appetite and food intake, increase energy expenditure, and regulate body weight. Based on clinical translation of specific and networked actions, leptin affects the cardiovascular system and may be a marker and driver of cardiometabolic risk factors with interventions that are actionable by cardiologists. Leptin subnetwork analysis demonstrates a statistically significant role for ethnoculturally and socioeconomically appropriate lifestyle intervention in cardiovascular disease. Emergent mechanistic components and potential diagnostic or therapeutic targets include hexokinase 3, urocortins, clusterin, sialic acid-binding immunoglobulin-like lectin 6, C-reactive protein, platelet glycoprotein VI, albumin, pentraxin 3, ghrelin, obestatin prepropeptide, leptin receptor, neuropeptide Y, and corticotropin-releasing factor receptor 1. Emergent associated symptoms include weight change, eating disorders, vascular necrosis, chronic fatigue, and chest pain. Leptin-targeted therapies are reported for lipodystrophy and leptin deficiency, but they are investigational for leptin resistance, obesity, and other chronic diseases.

Cytoskeleton-related regulation of primary cilia shortening mediated by melanin-concentrating hormone receptor 1

Primary cilia are specialized microtubule-based organelles. Their importance is highlighted by the gamut of ciliary diseases associated with various syndromes including diabetes and obesity. Primary cilia serve as signaling hubs through selective interactions with ion channels and conventional G-protein-coupled receptors (GPCRs). Melanin-concentrating hormone (MCH) receptor 1 (MCHR1), a key regulator of feeding, is selectively expressed in neuronal primary cilia in distinct regions of the mouse brain. We previously found that MCH acts on ciliary MCHR1 and induces cilia shortening through a Gi/o-dependent Akt pathway with no cell cycle progression. Many factors can participate in cilia length control. However, the mechanisms for how these molecules are relocated and coordinated to activate cilia shortening are poorly understood. In the present study, we investigated the role of cytoskeletal dynamics in regulating MCH-induced cilia shortening using clonal MCHR1-expressing hTERT-RPE1 cells. Pharmacological and biochemical approaches showed that cilia shortening mediated by MCH was associated with increased soluble cytosolic tubulin without changing the total tubulin amount. Enhanced F-actin fiber intensity was also observed in MCH-treated cells. The actions of various pharmacological agents revealed that coordinated actin machinery, especially actin polymerization, was required for MCHR1-mediated cilia shortening. A recent report indicated the existence of actin-regulated machinery for cilia shortening through GPCR agonist-dependent ectosome release. However, our live-cell imaging experiments showed that MCH progressively elicited cilia shortening without exclusion of fluorescence-positive material from the tip. Short cilia phenotypes have been associated with various metabolic disorders. Thus, the present findings may contribute toward better understanding of how the cytoskeleton is involved in the GPCR ligand-triggered cilia shortening with cell mechanical properties that underlies clinical manifestations such as obesity.

New Roles of the Primary Cilium in Autophagy

The primary cilium is a nonmotile organelle that emanates from the surface of multiple cell types and receives signals from the environment to regulate intracellular signaling pathways. The presence of cilia, as well as their length, is important for proper cell function; shortened, elongated, or absent cilia are associated with pathological conditions. Interestingly, it has recently been shown that the molecular machinery involved in autophagy, the process of recycling of intracellular material to maintain cellular and tissue homeostasis, participates in ciliogenesis. Cilium-dependent signaling is necessary for autophagosome formation and, conversely, autophagy regulates both ciliogenesis and cilium length by degrading specific ciliary proteins. Here, we will discuss the relationship that exists between the two processes at the cellular and molecular level, highlighting what is known about the effects of ciliary dysfunction in the control of energy homeostasis in some ciliopathies.

KDM3A coordinates actin dynamics with intraflagellar transport to regulate cilia stability

Cilia assembly and disassembly are coupled to actin dynamics, ensuring a coherent cellular response during environmental change. How these processes are integrated remains undefined. The histone lysine demethylase KDM3A plays important roles in organismal homeostasis. Loss-of-function mouse models of Kdm3a phenocopy features associated with human ciliopathies, whereas human somatic mutations correlate with poor cancer prognosis. We demonstrate that absence of KDM3A facilitates ciliogenesis, but these resulting cilia have an abnormally wide range of axonemal lengths, delaying disassembly and accumulating intraflagellar transport (IFT) proteins. KDM3A plays a dual role by regulating actin gene expression and binding to the actin cytoskeleton, creating a responsive "actin gate" that involves ARP2/3 activity and IFT. Promoting actin filament formation rescues KDM3A mutant ciliary defects. Conversely, the simultaneous depolymerization of actin networks and IFT overexpression mimics the abnormal ciliary traits of KDM3A mutants. KDM3A is thus a negative regulator of ciliogenesis required for the controlled recruitment of IFT proteins into cilia through the modulation of actin dynamics.

The Cilium: Cellular Antenna and Central Processing Unit

Cilia mediate an astonishing diversity of processes. Recent advances provide unexpected insights into the regulatory mechanisms of cilium formation, and reveal diverse regulatory inputs that are related to the cell cycle, cytoskeleton, proteostasis, and cilia-mediated signaling itself. Ciliogenesis and cilia maintenance are regulated by reciprocal antagonistic or synergistic influences, often acting in parallel to each other. By receiving parallel inputs, cilia appear to integrate multiple signals into specific outputs and may have functions similar to logic gates of digital systems. Some combinations of input signals appear to impose higher hierarchical control related to the cell cycle. An integrated view of these regulatory inputs will be necessary to understand ciliogenesis and its wider relevance to human biology.

The Leptin Receptor Complex: Heavier Than Expected?

Under normal physiological conditions, leptin and the leptin receptor (ObR) regulate the body weight by balancing food intake and energy expenditure. However, this adipocyte-derived hormone also directs peripheral processes, including immunity, reproduction, and bone metabolism. Leptin, therefore, can act as a metabolic switch connecting the body's nutritional status to high energy consuming processes. We provide an extensive overview of current structural insights on the leptin-ObR interface and ObR activation, coupling to signaling pathways and their negative regulation, and leptin functioning under normal and pathophysiological conditions (obesity, autoimmunity, cancer, … ). We also discuss possible cross-talk with other receptor systems on the receptor (extracellular) and signaling cascade (intracellular) levels.

Primary cilia: a link between hormone signalling and endocrine-related cancers?

Primary cilia are sensory organelles that play a role as signalling hubs. Disruption of primary cilia structure and function is increasingly recognised in a range of cancers, with a growing body of evidence suggesting that ciliary disruption contributes to tumourigenesis. This review considers the role of primary cilia in the pathogenesis of endocrine-related cancers.

The cilium: a cellular antenna with an influence on obesity risk

Primary cilia are organelles that are present on many different cell types, either transiently or permanently. They play a crucial role in receiving signals from the environment and passing these signals to other parts of the cell. In that way, they are involved in diverse processes such as adipocyte differentiation and olfactory sensation. Mutations in genes coding for ciliary proteins often have pleiotropic effects and lead to clinical conditions, ciliopathies, with multiple symptoms. In this study, we reviewed observations from ciliopathies with obesity as one of the symptoms. It shows that variation in cilia-related genes is itself not a major cause of obesity in the population but may be a part of the multifactorial aetiology of this complex condition. Both common polymorphisms and rare deleterious variants may contribute to the obesity risk. Genotype-phenotype relationships have been noticed. Among the ciliary genes, obesity differs with regard to severity and age of onset, which may relate to the influence of each gene on the balance between pro- and anti-adipogenic processes. Analysis of the function and location of the proteins encoded by these ciliary genes suggests that obesity is more linked to activities at the basal area of the cilium, including initiation of the intraflagellar transport, but less to the intraflagellar transport itself. Regarding the role of cilia, three possible mechanistic processes underlying obesity are described: adipogenesis, neuronal food intake regulation and food odour perception.

Transcription factor RFX1 is ubiquitinated by E3 ligase STUB1 in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a chronic autoimmune disease caused by complex interactions between genes and the environment. The expression level of transcription factor regulatory factor X 1 (RFX1) is reduced in T cells from SLE patients. RFX1 can regulate epigenetic modifications of CD70 and CD11a and plays an important role in the development of SLE. However, the mechanisms that mediate reduction of RFX1 in SLE are unclear. Here, we demonstrate that RFX1 protein expression can be tightly regulated by polyubiquitination-mediated proteosomal degradation via STIP1 homology and U-box containing protein 1 (STUB1). The E3 ligase STUB1 is upregulated in CD4(+)T cells of SLE patients compared to healthy subjects. Overexpression of STUB1 in CD4(+)T cells leads to upregulation of levels of CD70 and CD11a in T cells. The modulation of STUB1 activity may provide a novel therapeutic approach for SLE.

Leptin signalling pathways in hypothalamic neurons

Leptin is the most critical hormone in the homeostatic regulation of energy balance among those so far discovered. Leptin primarily acts on the neurons of the mediobasal part of hypothalamus to regulate food intake, thermogenesis, and the blood glucose level. In the hypothalamic neurons, leptin binding to the long form leptin receptors on the plasma membrane initiates multiple signaling cascades. The signaling pathways known to mediate the actions of leptin include JAK-STAT signaling, PI3K-Akt-FoxO1 signaling, SHP2-ERK signaling, AMPK signaling, and mTOR-S6K signaling. Recent evidence suggests that leptin signaling in hypothalamic neurons is also linked to primary cilia function. On the other hand, signaling molecules/pathways mitigating leptin actions in hypothalamic neurons have been extensively investigated in an effort to treat leptin resistance observed in obesity. These include SOCS3, tyrosine phosphatase PTP1B, and inflammatory signaling pathways such as IKK-NFκB and JNK signaling, and ER stress-mitochondrial signaling. In this review, we discuss leptin signaling pathways in the hypothalamus, with a particular focus on the most recently discovered pathways.

Modulation of primary cilia length by melanin-concentrating hormone receptor 1

Melanin-concentrating hormone (MCH) receptor 1 (MCHR1) is a class A G-protein-coupled receptor (GPCR). The MCH-MCHR1 system has been implicated in the regulation of feeding, emotional processing, and sleep in rodents. Recent work revealed that MCHR1 is selectively expressed in neuronal primary cilia of the central nervous system. Cilia have various chemosensory functions in many types of cell, and ciliary dysfunction is associated with ciliopathies such as polycystic kidney disease and obesity. Although dynamic modulation of neuronal cilia length is observed in obese mice, the functional interaction of neuronal ciliary GPCR and its endogenous ligand has not yet been elucidated. We report here that MCH treatment significantly reduced cilia length in hTERT-RPE1 cells (hRPE1 cells) transfected with MCHR1. Quantitative analyses indicated that MCH-induced cilia shortening progressed in a dose-dependent manner with an EC50 lower than 1nM when cells were treated for 6h. Although the assembly and disassembly of primary cilia are tightly coupled to the cell cycle, cell cycle reentry was not a determinant of MCH-induced cilia shortening. We confirmed that MCH elicited receptor internalization, Ca(2+) mobilization, ERK and Akt phosphorylation, and inhibition of cyclic AMP accumulation in MCHR1-expressing hRPE1 cells. Among these diverse pathways, we revealed that Gi/o-dependent Akt phosphorylation was an important component in the initial stage of MCH-induced cilia length shortening. Furthermore, induction of fewer cilia by Kif3A siRNA treatment significantly decreased the MCH-mediated phosphorylation of Akt, indicating the functional importance of the MCHR1-Akt pathway in primary cilia. Taken together, the present data suggest that the MCH-MCHR1 axis may modulate the sensitivity of cells to external environments by controlling the cilia length. Therefore, further characterization of MCHR1 as a ciliary GPCR will provide a potential molecular mechanism to link cilia length control with obesity.

Bardet-Biedl syndrome: Is it only cilia dysfunction?

Bardet-Biedl syndrome (BBS) is a genetically heterogeneous, pleiotropic disorder, characterized by both congenital and late onset defects. From the analysis of the mutational burden in patients to the functional characterization of the BBS proteins, this syndrome has become a model for both understanding oligogenic patterns of inheritance and the biology of a particular cellular organelle: the primary cilium. Here we briefly review the genetics of BBS to then focus on the function of the BBS proteins, not only in the context of the cilium but also highlighting potential extra-ciliary roles that could be relevant to the etiology of the disorder. Finally, we provide an overview of how the study of this rare syndrome has contributed to the understanding of cilia biology and how this knowledge has informed on the cellular basis of different clinical manifestations that characterize BBS and the ciliopathies.