Rhythmic cilia changes support SCN neuron coherence in circadian clock

Molecular modulation of aggregation-induced luminescence for improving response sensing of DNA hydrogels

Circadian rhythms are closely associated with human health, and the detection of relevant markers is essential to avoid circadian disorders. Here, we report a biosensing platform based on aggregation-induced emission for the sensitive detection of such markers. In this platform, the structure of 4,4',4″,4‴-(ethene-1,1,2,2-tetrayl)tetrabenzaldehyde (ETBA) was modulated at the molecular level to 4',4‴,4‴″,4⁗‴-(ethene-1,1,2,2-tetrayl)tetrakis([1,1'-biphenyl]-4-carbaldehyde) (ETBCA), thereby increasing the energy levels of the highest and lowest unoccupied molecular orbitals, reducing the energy gap, and enhancing the conjugation effect, ultimately improving the fluorescence properties of the molecule. ETBCA was the starting monomer used to synthesize ETBCA-loaded nanoparticles (ETBCANPs) with higher quantum yields and longer fluorescence lifetimes, which were then loaded onto responsive DNA hydrogels for the sensitive detection of melatonin. The resulting loaded hydrogel (ETBCANPs@Hydrogel) showed superior performance compared to hydrogels loaded with ETBA nanoparticles and quantum dots, with 2.9- and 3.6-fold higher sensitivities, respectively. The ETBCANPs@Hydrogel was able to detect melatonin in saliva and urine samples with limits of detection of 18.6 pg/mL and 10.5 pg/mL, respectively, recoveries of 94.2-107.5%, and satisfactory selectivity. In summary, the fluorescence performance of aggregation-induced emission molecules can be effectively improved by modulating their molecular structure, leading to the development of hydrogels for the sensitive sensing and detection of circadian rhythm disorders.

Primary ciliary protein kinase A activity in the prefrontal cortex modulates stress in mice

Primary cilia are cellular antennae emanating from vertebrate cell surfaces to sense and transduce extracellular signals intracellularly to regulate cell behavior and function. However, their signal sensing and physiological functions in neocortical neurons remain largely unclear. Here, we show that, in response to various animal stressors, primary cilia in the mouse prefrontal cortex (PFC) exhibit consistent axonemal elongation. Selective removal of excitatory neuron primary cilia in the prefrontal but not sensory cortex leads to a reduction in animal stress sensing and response. Treatment with corticosterone, the major stress hormone, elicits an increase in primary ciliary cyclic adenosine 3',5'-monphosphate (cAMP) level in PFC excitatory neurons and a decrease in neuronal excitability dependent on primary cilia. Suppression of primary ciliary protein kinase A (PKA) activity in PFC excitatory neurons reduces animal stress. These results suggest that excitatory neurons in the PFC are involved in sensing and regulating animal stress via primary ciliary cAMP/PKA signaling.

Identification of angiotensin II-responsive circadian clock gene expression in adrenal zona glomerulosa cells and human adrenocortical H295R cells

The mammalian circadian timing system is organized in a hierarchy, with the master clock residing in the suprachiasmatic nucleus (SCN) of the hypothalamus and subsidiary peripheral clocks in peripheral tissues. Because of the diversity of peripheral tissues and cell-types in the body, the existence of autonomous clock and identification of its potential entrainment signals need to be empirically defined on a cell type-by-cell type basis. In this study, we characterized the basic circadian clock properties of the adrenal zona glomerulosa cells, or ZG cells. Using isolated adrenal explants from Per2Luc mice, dissociated ZG cells from Per2-dluc rats, and a related human adrenocortical cell line H295R, we showed that ZG cells possess genetically-encoded, self-sustained and cell-autonomous circadian clock. As to the potential entrainment signals, angiotensin II (Ang II) caused phase-dependent phase-shifts of adrenal ZG cells in cultured slices. Ang II treatment also drove initiation (or reset) of circadian clock gene expression in H295R cells with associated immediate up-regulation of PER1 and E4BP4 mRNA expression. We found that the type I Ang II receptor blocker CV11974, one of the most widely used clinical drugs for hypertensive diseases, caused attenuation of the phase resetting of H295R cells. Our in vitro data provide a basis to understand and argue for the adrenal gland ZG cells as a component of autonomous and entrainable peripheral clocks.

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.

Understanding the intricacies of cellular mechanisms in remyelination: The role of circadian rhythm

The term "circadian rhythm" refers to the 24-h oscillations found in various physiological processes in organisms, responsible for maintaining bodily homeostasis. Many neurological diseases mainly involve the process of demyelination, and remyelination is crucial for the treatment of neurological diseases. Current research mainly focuses on the key role of circadian clocks in the pathophysiological mechanisms of multiple sclerosis. Various studies have shown that the circadian rhythm regulates various cellular molecular mechanisms and signaling pathways involved in remyelination. The process of remyelination is primarily mediated by oligodendrocyte precursor cells (OPCs), oligodendrocytes, microglia, and astrocytes. OPCs are activated, proliferate, migrate, and ultimately differentiate into oligodendrocytes after demyelination, involving many key signaling pathway and regulatory factors. Activated microglia secretes important cytokines and chemokines, promoting OPC proliferation and differentiation, and phagocytoses myelin debris that inhibits remyelination. Astrocytes play a crucial role in supporting remyelination by secreting signals that promote remyelination or facilitate the phagocytosis of myelin debris by microglia. Additionally, cell-to-cell communication via gap junctions allows for intimate contact between astrocytes and oligodendrocytes, providing metabolic support for oligodendrocytes. Therefore, gaining a deeper understanding of the mechanisms and molecular pathways of the circadian rhythm at various stages of remyelination can help elucidate the fundamental characteristics of remyelination and provide insights into treating demyelinating disorders.

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.

Ciliary length regulation by intraflagellar transport in zebrafish

How cells regulate the size of their organelles remains a fundamental question in cell biology. Cilia, with their simple structure and surface localization, provide an ideal model for investigating organelle size control. However, most studies on cilia length regulation are primarily performed on several single-celled organisms. In contrast, the mechanism of length regulation in cilia across diverse cell types within multicellular organisms remains a mystery. Similar to humans, zebrafish contain diverse types of cilia with variable lengths. Taking advantage of the transparency of zebrafish embryos, we conducted a comprehensive investigation into intraflagellar transport (IFT), an essential process for ciliogenesis. By generating a transgenic line carrying Ift88-GFP transgene, we observed IFT in multiple types of cilia with varying lengths. Remarkably, cilia exhibited variable IFT speeds in different cell types, with longer cilia exhibiting faster IFT speeds. This increased IFT speed in longer cilia is likely not due to changes in common factors that regulate IFT, such as motor selection, BBSome proteins, or tubulin modification. Interestingly, longer cilia in the ear cristae tend to form larger IFT compared to shorter spinal cord cilia. Reducing the size of IFT particles by knocking down Ift88 slowed IFT speed and resulted in the formation of shorter cilia. Our study proposes an intriguing model of cilia length regulation via controlling IFT speed through the modulation of the size of the IFT complex. This discovery may provide further insights into our understanding of how organelle size is regulated in higher vertebrates.

Chronobiological and neuroendocrine insights into dry eye

Dry eye, a prevalent ocular surface disease, is significantly influenced by modern lifestyle factors such as night-shift work and extended screen time. Emerging evidence suggests a strong correlation between disturbances in circadian rhythm, sleep disorders, and dry eye. However, the precise underlying mechanisms remain unclear. Recent studies have underscored the crucial role of circadian rhythms and neuroendocrine regulation in maintaining ocular surface health. Advances in treatment strategies targeting neuroendocrine pathways have shown promising developments. This review explores the interplay between circadian rhythms, neuroendocrine regulation, and the ocular surface, examines the impact of circadian disruption on the pathophysiology of dry eye, and proposes intervention strategies to alleviate dry eye associated with disturbances in circadian rhythms.

The nuclear transportation of CHRONO regulates the circadian rhythm

The pace of the endogenous circadian clock is important for organisms to maintain homeostasis. CHRONO has been shown to be a core component of the mammalian clock and has recently been implicated to function in several important physiological aspects. To function properly, CHRONO needs to enter the nucleus to repress transcription. We have previously shown that the N terminus of CHRONO is required for its nuclear entry. However, how CHRONO enters the nucleus and regulates the circadian clock remains unknown. Here, we report that a novel nonclassical nuclear localization signal in the N terminus of CHRONO is responsible for its nuclear entry. Multiple nuclear transporters are identified that facilitate the nuclear import of CHRONO. We show that the Arg63 is the critical amino acid of the nuclear localization signal. Using prime editing technology, we precisely edit the Arg63 to Ala at the genomic loci and demonstrate that this mutation prolongs the circadian period, which is similar to knockdown of CHRONO. By using the CHRONO KO and R63A mutant cells, we also investigated the changes in the cytoplasmic/nuclear distribution of BMAL1. We show that BMAL1 localizes more in the cytoplasm in the deficiency of CHRONO nuclear entry. These results provide a model for CHRONO nuclear entry using a network of importins involved in the regulation of the circadian period.

Permanent deconstruction of intracellular primary cilia in differentiating granule cell neurons

Primary cilia on granule cell neuron progenitors in the developing cerebellum detect sonic hedgehog to facilitate proliferation. Following differentiation, cerebellar granule cells become the most abundant neuronal cell type in the brain. While granule cell cilia are essential during early developmental stages, they become infrequent upon maturation. Here, we provide nanoscopic resolution of cilia in situ using large-scale electron microscopy volumes and immunostaining of mouse cerebella. In many granule cells, we found intracellular cilia, concealed from the external environment. Cilia were disassembled in differentiating granule cell neurons-in a process we call cilia deconstruction-distinct from premitotic cilia resorption in proliferating progenitors. In differentiating granule cells, cilia deconstruction involved unique disassembly intermediates, and, as maturation progressed, mother centriolar docking at the plasma membrane. Unlike ciliated neurons in other brain regions, our results show the deconstruction of concealed cilia in differentiating granule cells, which might prevent mitogenic hedgehog responsiveness. Ciliary deconstruction could be paradigmatic of cilia removal during differentiation in other tissues.

Circadian cilia transcriptome in mouse brain across physiological and pathological states

Primary cilia are dynamic sensory organelles that continuously undergo structural modifications in response to environmental and cellular signals, many of which exhibit rhythmic patterns. Building on our previous findings of rhythmic cilia-related gene expression in diurnal primates (baboon), this study extends the investigation to the nocturnal mouse brain to identify circadian patterns of cilia gene expression across brain regions. We used computational techniques and transcriptomic data from four publicly available databases, to examine the circadian expression of cilia-associated genes within six brain areas: brainstem, cerebellum, hippocampus, hypothalamus, striatum, and suprachiasmatic nucleus. Our analysis reveals that a substantial proportion of cilia transcripts exhibit circadian rhythmicity across the examined regions, with notable overrepresentation in the striatum, hippocampus, and cerebellum. We also demonstrate region-specific variations in the abundance and timing of circadian cilia genes' peaks, indicating an adaptation to the distinct physiological roles of each brain region. Additionally, we show that the rhythmic patterns of cilia transcripts are shifted under various physiological and pathological conditions, including modulation of the dopamine system, high-fat diet, and epileptic conditions, indicating the adaptable nature of cilia transcripts' oscillation. While limited to a few mouse brain regions, our study provides initial insights into the distinct circadian patterns of cilia transcripts and highlights the need for future research to expand the mapping across wider brain areas to fully understand the role of cilia's spatiotemporal dynamics in brain functions.

Melatonin targets the paraventricular thalamus to promote non-rapid eye movement sleep in C3H/HeJ mice

Melatonin (MLT) is an important circadian signal for sleep regulation, but the neural circuitries underlying the sleep-promoting effects of MLT are poorly understood. The paraventricular thalamus (PVT) is a critical thalamic area for wakefulness control and expresses MLT receptors, raising a possibility that PVT neurons may mediate the sleep-promoting effects of MLT. Here, we found that MLT receptors were densely expressed on PVT neurons and exhibited circadian-dependent variations in C3H/HeJ mice. Application of exogenous MLT decreased the excitability of PVT neurons, resulting in hyperpolarization of membrane potential and reduction of action potential firing. MLT also inhibited the spontaneous activity of PVT neurons at both population and single-neuron levels in freely behaving mice. Furthermore, pharmacological manipulations revealed that local infusion of exogeneous MLT into the PVT promoted non-rapid eye movement (NREM) sleep and increased NREM sleep duration, whereas MLT receptor antagonists decreased NREM sleep. Moreover, we found that selectively knocking down endogenous MLT receptors in the PVT decreased NREM sleep and correspondingly increased wakefulness, with particular changes shortly after the onset of the dark or light phase. Taken together, these results demonstrate that PVT is an important target of MLT for promoting NREM sleep.

Excess microtubule and F-actin formation mediates shortening and loss of primary cilia in response to a hyperosmotic milieu

The primary cilium is a small organelle protruding from the cell surface that receives signals from the extracellular milieu. Although dozens of studies have reported that several genetic factors can impair the structure of primary cilia, evidence for environmental stimuli affecting primary cilia structures is limited. Here, we investigated an extracellular stress that affected primary cilia morphology and its underlying mechanisms. Hyperosmotic shock induced reversible shortening and disassembly of the primary cilia of murine intramedullary collecting duct cells. The shortening of primary cilia caused by hyperosmotic shock followed delocalization of the pericentriolar material (PCM). Excessive microtubule and F-actin formation in the cytoplasm coincided with the hyperosmotic shock-induced changes to primary cilia and the PCM. Treatment with a microtubule-disrupting agent, nocodazole, partially prevented the hyperosmotic shock-induced disassembly of primary cilia and almost completely prevented delocalization of the PCM. An actin polymerization inhibitor, latrunculin A, also partially prevented the hyperosmotic shock-induced shortening and disassembly of primary cilia and almost completely prevented delocalization of the PCM. We demonstrate that hyperosmotic shock induces reversible morphological changes in primary cilia and the PCM in a manner dependent on excessive formation of microtubule and F-actin.

Dysregulation of the Suprachiasmatic Nucleus Disturbs the Circadian Rhythm and Aggravates Epileptic Seizures by Inducing Hippocampal GABAergic Dysfunction in C57BL/6 Mice

The interplay between circadian rhythms and epilepsy has gained increasing attention. The suprachiasmatic nucleus (SCN), which acts as the master circadian pacemaker, regulates physiological and behavioral rhythms through its complex neural networks. However, the exact role of the SCN and its Bmal1 gene in the development of epilepsy remains unclear. In this study, we utilized a lithium-pilocarpine model to induce epilepsy in mice and simulated circadian disturbances by creating lesions in the SCN and specifically knocking out the Bmal1 gene in the SCN neurons. We observed that the pilocarpine-induced epileptic mice experienced increased daytime seizure frequency, irregular oscillations in core body temperature, and circadian gene alterations in both the SCN and the hippocampus. Additionally, there was enhanced activation of GABAergic projections from the SCN to the hippocampus. Notably, SCN lesions intensified seizure activity, concomitant with hippocampal neuronal damage and GABAergic signaling impairment. Further analyses using the Gene Expression Omnibus database and gene set enrichment analysis indicated reduced Bmal1 expression in patients with medial temporal lobe epilepsy, potentially affecting GABA receptor pathways. Targeted deletion of Bmal1 in SCN neurons exacerbated seizures and pathology in epilepsy, as well as diminished hippocampal GABAergic efficacy. These results underscore the crucial role of the SCN in modulating circadian rhythms and GABAergic function in the hippocampus, aggravating the severity of seizures. This study provides significant insights into how circadian rhythm disturbances can influence neuronal dysfunction and epilepsy, highlighting the therapeutic potential of targeting SCN and the Bmal1 gene within it in epilepsy management.

Molecular and structural perspectives on protein trafficking to the primary cilium membrane

The primary cilium is a dynamic subcellular compartment templated from the mother centriole or basal body. Cilia are solitary and tiny, but remarkably consequential in cellular pathways regulating proliferation, differentiation, and maintenance. Multiple transmembrane proteins such as G-protein-coupled receptors, channels, enzymes, and membrane-associated lipidated proteins are enriched in the ciliary membrane. The precise regulation of ciliary membrane content is essential for effective signal transduction and maintenance of tissue homeostasis. Surprisingly, a few conserved molecular factors, intraflagellar transport complex A and the tubby family adapter protein TULP3, mediate the transport of most membrane cargoes into cilia. Recent advances in cryogenic electron microscopy provide fundamental insights into these molecular players. Here, we review the molecular players mediating cargo delivery into the ciliary membrane through the lens of structural biology. These mechanistic insights into ciliary transport provide a framework for understanding of disease variants in ciliopathies, enable precise manipulation of cilia-mediated pathways, and provide a platform for the development of targeted therapeutics.

Ciliogenesis defects after neurulation impact brain development and neuronal activity in larval zebrafish

Cilia are slender, hair-like structures extending from cell surfaces and playing essential roles in diverse physiological processes. Within the nervous system, primary cilia contribute to signaling and sensory perception, while motile cilia facilitate cerebrospinal fluid flow. Here, we investigated the impact of ciliary loss on neural circuit development using a zebrafish line displaying ciliogenesis defects. We found that cilia defects after neurulation affect neurogenesis and brain morphology, especially in the cerebellum, and lead to altered gene expression profiles. Using whole brain calcium imaging, we measured reduced light-evoked and spontaneous neuronal activity in all brain regions. By shedding light on the intricate role of cilia in neural circuit formation and function in the zebrafish, our work highlights their evolutionary conserved role in the brain and sets the stage for future analysis of ciliopathy models.

Inhibition of a cyclic nucleotide-gated channel on neuronal cilia activates unfolded protein response in intestinal cells to promote longevity

Ciliary defects are linked to ciliopathies, but impairments in the sensory cilia of Caenorhabditis elegans neurons extend lifespan, a phenomenon with previously unclear mechanisms. Our study reveals that neuronal cilia defects trigger the unfolded protein response of the endoplasmic reticulum (UPRER) within intestinal cells, a process dependent on the insulin/insulin-like growth factor 1 (IGF-1) signaling transcription factor and the release of neuronal signaling molecules. While inhibiting UPRER doesn't alter the lifespan of wild-type worms, it normalizes the extended lifespan of ciliary mutants. Notably, deactivating the cyclic nucleotide-gated (CNG) channel TAX-4 on the ciliary membrane promotes lifespan extension through a UPRER-dependent mechanism. Conversely, constitutive activation of TAX-4 attenuates intestinal UPRER in ciliary mutants. Administering a CNG channel blocker to worm larvae activates intestinal UPRER and increases adult longevity. These findings suggest that ciliary dysfunction in sensory neurons triggers intestinal UPRER, contributing to lifespan extension and implying that transiently inhibiting ciliary channel activity may effectively prolong lifespan.

Ultrastructural differences impact cilia shape and external exposure across cell classes in the visual cortex

A primary cilium is a membrane-bound extension from the cell surface that contains receptors for perceiving and transmitting signals that modulate cell state and activity. Primary cilia in the brain are less accessible than cilia on cultured cells or epithelial tissues because in the brain they protrude into a deep, dense network of glial and neuronal processes. Here, we investigated cilia frequency, internal structure, shape, and position in large, high-resolution transmission electron microscopy volumes of mouse primary visual cortex. Cilia extended from the cell bodies of nearly all excitatory and inhibitory neurons, astrocytes, and oligodendrocyte precursor cells (OPCs) but were absent from oligodendrocytes and microglia. Ultrastructural comparisons revealed that the base of the cilium and the microtubule organization differed between neurons and glia. Investigating cilia-proximal features revealed that many cilia were directly adjacent to synapses, suggesting that cilia are poised to encounter locally released signaling molecules. Our analysis indicated that synapse proximity is likely due to random encounters in the neuropil, with no evidence that cilia modulate synapse activity as would be expected in tetrapartite synapses. The observed cell class differences in proximity to synapses were largely due to differences in external cilia length. Many key structural features that differed between neuronal and glial cilia influenced both cilium placement and shape and, thus, exposure to processes and synapses outside the cilium. Together, the ultrastructure both within and around neuronal and glial cilia suggest differences in cilia formation and function across cell types in the brain.

Cell Signaling in the Circadian Pacemaker: New Insights from in vivo Imaging

BACKGROUND

"One for all, and all for one," the famous rallying cry of the Three Musketeers, in Alexandre Dumas's popular novel, certainly applies to the 20,000 cells composing the suprachiasmatic nuclei (SCN). These cells work together to form the central clock that coordinates body rhythms in tune with the day-night cycle. Like virtually every body cell, individual SCN cells exhibit autonomous circadian oscillations, but this rhythmicity only reaches a high level of precision and robustness when the cells are coupled with their neighbors. Therefore, understanding the functional network organization of SCN cells beyond their core rhythmicity is an important issue in circadian biology.

SUMMARY

The present review summarizes the main results from our recent study demonstrating the feasibility of recording SCN cells in freely moving mice and the significance of variations in intracellular calcium over several timescales.

KEY MESSAGE

We discuss how in vivo imaging at the cell level will be pivotal to interrogate the mammalian master clock, in an integrated context that preserves the SCN network organization, with intact inputs and outputs.

Age-related ciliopathy: Obesogenic shortening of melanocortin-4 receptor-bearing neuronal primary cilia

Obesity is often associated with aging. However, the mechanism of age-related obesity is unknown. The melanocortin-4 receptor (MC4R) mediates leptin-melanocortin anti-obesity signaling in the hypothalamus. Here, we discovered that MC4R-bearing primary cilia of hypothalamic neurons progressively shorten with age in rats, correlating with age-dependent metabolic decline and increased adiposity. This "age-related ciliopathy" is promoted by overnutrition-induced upregulation of leptin-melanocortin signaling and inhibited or reversed by dietary restriction or the knockdown of ciliogenesis-associated kinase 1 (CILK1). Forced shortening of MC4R-bearing cilia in hypothalamic neurons by genetic approaches impaired neuronal sensitivity to melanocortin and resulted in decreased brown fat thermogenesis and energy expenditure and increased appetite, finally developing obesity and leptin resistance. Therefore, despite its acute anti-obesity effect, chronic leptin-melanocortin signaling increases susceptibility to obesity by promoting the age-related shortening of MC4R-bearing cilia. This study provides a crucial mechanism for age-related obesity, which increases the risk of metabolic syndrome.

The neuronal cilium - a highly diverse and dynamic organelle involved in sensory detection and neuromodulation

Cilia are fascinating organelles that act as cellular antennae, sensing the cellular environment. Cilia gained significant attention in the late 1990s after their dysfunction was linked to genetic diseases known as ciliopathies. Since then, several breakthrough discoveries have uncovered the mechanisms underlying cilia biogenesis and function. Like most cells in the animal kingdom, neurons also harbor cilia, which are enriched in neuromodulatory receptors. Yet, how neuronal cilia modulate neuronal physiology and animal behavior remains poorly understood. By comparing ciliary biology between the sensory and central nervous systems (CNS), we provide new perspectives on the functions of cilia in brain physiology.

Circadian Disruption as a Risk Factor for Development of Cardiovascular and Metabolic Disorders - From Animal Models to Human Population

The lifestyle of human society is drifting apart from the natural environmental cycles that have influenced it since its inception. These cycles were fundamental in structuring the daily lives of people in the pre-industrial era, whether they were seasonal or daily. Factors that disrupt the regularity of human behaviour and its alignment with solar cycles, such as late night activities accompanied with food intake, greatly disturb the internal temporal organization in the body. This is believed to contribute to the rise of the so-called diseases of civilization. In this review, we discuss the connection between misalignment in daily (circadian) regulation and its impact on health, with a focus on cardiovascular and metabolic disorders. Our aim is to review selected relevant research findings from laboratory and human studies to assess the extent of evidence for causality between circadian clock disruption and pathology. Keywords: Circadian clock, Chronodisruption, Metabolism, Cardiovascular disorders, Spontaneously hypertensive rat, Human, Social jetlag, Chronotype.

Characterization of Sonic Hedgehog transcripts in the adult mouse brain: co-expression with neuronal and oligodendroglial markers

In the adult mammalian brain, astrocytes are proposed to be the major Sonic Hedgehog (Shh)-responsive cells. However, the sources of the Shh molecule mediating activation of the pathway are still poorly characterized. The present work investigates the distribution and phenotype of cells expressing Shh mRNA in the adult mouse brain. Using single-molecule fluorescent in situ hybridization (smfISH), we report much broader expression of Shh transcripts in almost all brain regions than originally reported. We identify Shh mRNA in HuC/D+ neuronal populations, including GABAergic (glutamic acid decarboxylase 67, Gad67), cholinergic (choline acetyltransferase, ChAT), dopaminergic (tyrosine hydroxylase, TH), nitrergic (neuronal nitric oxide synthase, nNOS), and in a small population of oligodendroglial cells expressing Sox10 and Olig2 mRNA transcription factors. Further analysis of Shh mRNA in cerebral cortical and hypothalamic neurons suggests that Shh is also expressed by glutamatergic neurons. Interestingly, we did not observe substantial Desert Hedgehog and Indian Hedgehog mRNA signals, nor Shh signals in S100β+ astrocytes and Iba1+ microglial cells. Collectively, the present work provides the most robust central map of Shh-expressing cells to date and underscores the importance of nitrergic neurons in regulating Shh availability to brain cells. Thus, our study provides a framework for future experiments aimed at better understanding of the functions of Shh signaling in the brain in normal and pathological states, and the characterization of novel regulatory mechanisms of the signaling pathway.

Cilia loss on distinct neuron populations differentially alters cocaine-induced locomotion and reward

BACKGROUND

Neuronal primary cilia are being recognized for their role in mediating signaling associated with a variety of neurobehaviors, including responses to drugs of abuse. They function as signaling hubs, enriched with a diverse array of G-protein coupled receptors (GPCRs), including several associated with motivation and drug-related behaviors. However, our understanding of how cilia regulate neuronal function and behavior is still limited.

AIMS

The objective of the current study was to investigate the contributions of primary cilia on specific neuronal populations to behavioral responses to cocaine.

METHODS

To test the consequences of cilia loss on cocaine-induced locomotion and reward-related behavior, we selectively ablated cilia from dopaminergic or GAD2-GABAergic neurons in mice.

RESULTS

Cilia ablation on either population of neurons failed to significantly alter acute locomotor responses to cocaine at a range of doses. With repeated administration, mice lacking cilia on GAD2-GABAergic neurons showed no difference in locomotor sensitization to cocaine compared to wild-type (WT) littermates, whereas mice lacking cilia on dopaminergic neurons exhibited reduced locomotor sensitization to cocaine at 10 and 30 mg/kg. Mice lacking cilia on GAD2-GABAergic neurons showed no difference in cocaine conditioned place preference (CPP), whereas mice lacking cilia on dopaminergic neurons exhibited reduced CPP compared to WT littermates.

CONCLUSIONS

Combined with previous findings using amphetamine, our results show that behavioral effects of cilia ablation are cell- and drug type-specific, and that neuronal cilia contribute to modulation of both the locomotor-inducing and rewarding properties of cocaine.

The miR-669a-5p/G3BP/HDAC6/AKAP12 Axis Regulates Primary Cilia Length

Primary cilia are conserved organelles in most mammalian cells, acting as "antennae" to sense external signals. Maintaining a physiological cilium length is required for cilium function. MicroRNAs (miRNAs) are potent gene expression regulators, and aberrant miRNA expression is closely associated with ciliopathies. However, how miRNAs modulate cilium length remains elusive. Here, using the calcium-shock method and small RNA sequencing, a miRNA is identified, namely, miR-669a-5p, that is highly expressed in the cilia-enriched noncellular fraction. It is shown that miR-669a-5p promotes cilium elongation but not cilium formation in cultured cells. Mechanistically, it is demonstrated that miR-669a-5p represses ras-GTPase-activating protein SH3-domain-binding protein (G3BP) expression to inhibit histone deacetylase 6 (HDAC6) expression, which further upregulates A-kinase anchor protein 12 (AKAP12) expression. This effect ultimately blocks cilia disassembly and leads to greater cilium length, which can be restored to wild-type lengths by either upregulating HDAC6 or downregulating AKAP12. Collectively, these results elucidate a previously unidentified miR-669a-5p/G3BP/HDAC6/AKAP12 signaling pathway that regulates cilium length, providing potential pharmaceutical targets for treating ciliopathies.

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.

Circadian Rhythm Alteration of the Core Clock Genes and the Lipid Metabolism Genes Induced by High-Fat Diet (HFD) in the Liver Tissue of the Chinese Soft-Shelled Turtle (Trionyx sinensis)

Physiology disorders of the liver, as it is an important tissue in lipid metabolism, can cause fatty liver disease. The mechanism might be regulated by 17 circadian clock genes and 18 fat metabolism genes, together with a high-fat diet (HFD). Due to their rich nutritional and medicinal value, Chinese soft-shelled turtles (Trionyx sinensis) are very popular among the Chinese people. In the study, we aimed to investigate the influence of an HFD on the daily expression of both the core clock genes and the lipid metabolism genes in the liver tissue of the turtles. The two diets were formulated with 7.98% lipid (the CON group) and 13.86% lipid (the HFD group) to feed 180 juvenile turtles, which were randomly divided into two groups with three replicates per group and 30 turtles in each replicate for six weeks, and the diet experiment was administrated with a photophase regimen of a 24 h light/dark (12L:12D) cycle. At the end of the experiment, the liver tissue samples were collected from nine turtles per group every 3 h (zeitgeber time: ZT 0, 3, 6, 9, 12, 15, 18, 21 and 24) for 24 h to investigate the daily expression and correlation analysis of these genes. The results showed that 11 core clock genes [i.e., circadian locomotor output cycles kaput (Clock), brain and muscle arnt-like protein 1 and 2 (Bmal1/2), timeless (Tim), cryptochrome 1 (Cry2), period2 (Per2), nuclear factor IL-3 gene (Nfil3), nuclear receptor subfamily 1, treatment D, member 1 and 2 (Nr1d1/2) and retinoic acid related orphan receptor α/β/γ β and γ (Rorβ/γ)] exhibited circadian oscillation, but 6 genes did not, including neuronal PAS domain protein 2 (Npas2), Per1, Cry1, basic helix-loop-helix family, member E40 (Bhlhe40), Rorα and D-binding protein (Dbp), and 16 lipid metabolism genes including fatty acid synthase (Fas), diacylglycerol acyltransferase 1 (Dgat1), 3-hydroxy-3-methylglutaryl-CoA reductase (Hmgcr), Low-density lipoprotein receptor-related protein 1-like (Ldlr1), Lipin 1 (Lipin1), Carnitine palmitoyltransferase 1A (Cpt1a), Peroxisome proliferator activation receptor α, β and γ (Pparα/β/γ), Sirtuin 1 (Sirt1), Apoa (Apoa1), Apolipoprotein B (Apob), Pyruvate Dehydrogenase kinase 4 (Pdk4), Acyl-CoA synthase long-chain1 (Acsl1), Liver X receptors α (Lxrα) and Retinoid X receptor, α (Rxra) also demonstrated circadian oscillations, but 2 genes did not, Scd and Acaca, in the liver tissues of the CON group. However, in the HFD group, the circadian rhythms' expressional patterns were disrupted for the eight core clock genes, Clock, Cry2, Per2, Nfil3, Nr1d1/2 and Rorβ/γ, and the peak expression of Bmal1/2 and Tim showed delayed or advanced phases. Furthermore, four genes (Cry1, Per1, Dbp and Rorα) displayed no diurnal rhythm in the CON group; instead, significant circadian rhythms appeared in the HFD group. Meanwhile, the HFD disrupted the circadian rhythm expressions of seven fat metabolism genes (Fas, Cpt1a, Sirt1, Apoa1, Apob, Pdk4 and Acsl1). Meanwhile, the other nine genes in the HFD group also showed advanced or delayed expression peaks compared to the CON group. Most importantly of all, there were remarkably positive or negative correlations between the core clock genes and the lipid metabolism genes, and their correlation relationships were altered by the HFD. To sum up, circadian rhythm alterations of the core clock genes and the lipid metabolism genes were induced by the high-fat diet (HFD) in the liver tissues of T. sinensis. This result provides experimental and theoretical data for the mass breeding and production of T. sinensis in our country.

Permanent deconstruction of intracellular primary cilia in differentiating granule cell neurons

Primary cilia on granule cell neuron progenitors in the developing cerebellum detect sonic hedgehog to facilitate proliferation. Following differentiation, cerebellar granule cells become the most abundant neuronal cell type in the brain. While essential during early developmental stages, the fate of granule cell cilia is unknown. Here, we provide nanoscopic resolution of ciliary dynamics in situ by studying developmental changes in granule cell cilia using large-scale electron microscopy volumes and immunostaining of mouse cerebella. We found that many granule cell primary cilia were intracellular and concealed from the external environment. Cilia were disassembed in differentiating granule cell neurons in a process we call cilia deconstruction that was distinct from pre-mitotic cilia resorption in proliferating progenitors. In differentiating granule cells, ciliary loss involved unique disassembly intermediates, and, as maturation progressed, mother centriolar docking at the plasma membrane. Cilia did not reform from the docked centrioles, rather, in adult mice granule cell neurons remained unciliated. Many neurons in other brain regions require cilia to regulate function and connectivity. In contrast, our results show that granule cell progenitors had concealed cilia that underwent deconstruction potentially to prevent mitogenic hedgehog responsiveness. The ciliary deconstruction mechanism we describe could be paradigmatic of cilia removal during differentiation in other tissues.

Circadian oscillation in primary cilium length by clock genes regulates fibroblast cell migration

Various mammalian cells have autonomous cellular clocks that are produced by the transcriptional cycle of clock genes. Cellular clocks provide circadian rhythms for cellular functions via transcriptional and cytoskeletal regulation. The vast majority of mammalian cells possess a primary cilium, an organelle protruding from the cell surface. Here, we investigated the little-known relationship between circadian rhythm and primary cilia. The length and number of primary cilia showed circadian dynamics both in vitro and in vivo. The circadian rhythm of primary cilium length was abolished by SR9011 and Bmal1 knockout. A centrosomal protein, pericentrin, transiently accumulates in centriolar satellites, the base of primary cilia at the shortest cilia phase, and induces elongation of primary cilia at the longest cilia phase in the circadian rhythm of primary cilia. In addition, rhythmic cell migration during wound healing depends on the length of primary cilia and affects the rate of wound healing. Our findings demonstrate that the circadian dynamics of primary cilium length by clock genes control fibroblast migration and could provide new insights into chronobiology.

Spatiotemporal Mapping of Brain Cilia Reveals Region-Specific Oscillation of Length and Orientation

In this study, we conducted high-throughput spatiotemporal analysis of primary cilia length and orientation across 22 mouse brain regions. We developed automated image analysis algorithms, which enabled us to examine over 10 million individual cilia, generating the largest spatiotemporal atlas of cilia. We found that cilia length and orientation display substantial variations across different brain regions and exhibit fluctuations over a 24-hour period, with region-specific peaks during light-dark phases. Our analysis revealed unique orientation patterns of cilia at 45 degree intervals, suggesting that cilia orientation within the brain is not random but follows specific patterns. Using BioCycle, we identified circadian rhythms of cilia length in five brain regions: nucleus accumbens core, somatosensory cortex, and three hypothalamic nuclei. Our findings present novel insights into the complex relationship between cilia dynamics, circadian rhythms, and brain function, highlighting cilia crucial role in the brain's response to environmental changes and regulation of time-dependent physiological processes.

A super Sonic circadian synchronizer

Sonic Hedgehog signaling and primary cilia control the core mammalian circadian clock.