scholarly journals Disruption of Dhcr7 and Insig1/2 in cholesterol metabolism causes defects in bone formation and homeostasis through primary cilium formation

Bone Research ◽  
2020 ◽  
Vol 8 (1) ◽  
Author(s):  
Akiko Suzuki ◽  
Kenichi Ogata ◽  
Hiroki Yoshioka ◽  
Junbo Shim ◽  
Christopher A. Wassif ◽  
...  
Keyword(s):  
Bone Formation ◽  
Primary Cilium ◽  
Hedgehog Signaling ◽  
Primary Cilia ◽  
Cholesterol Metabolism ◽  
Cholesterol Biosynthesis ◽  
Cilium Formation ◽  
Intracellular Cholesterol

AbstractHuman linkage studies suggest that craniofacial deformities result from either genetic mutations related to cholesterol metabolism or high-cholesterol maternal diets. However, little is known about the precise roles of intracellular cholesterol metabolism in the development of craniofacial bones, the majority of which are formed through intramembranous ossification. Here, we show that an altered cholesterol metabolic status results in abnormal osteogenesis through dysregulation of primary cilium formation during bone formation. We found that cholesterol metabolic aberrations, induced through disruption of either Dhcr7 (which encodes an enzyme involved in cholesterol synthesis) or Insig1 and Insig2 (which provide a negative feedback mechanism for cholesterol biosynthesis), result in osteoblast differentiation abnormalities. Notably, the primary cilia responsible for sensing extracellular cues were altered in number and length through dysregulated ciliary vesicle fusion in Dhcr7 and Insig1/2 mutant osteoblasts. As a consequence, WNT/β-catenin and hedgehog signaling activities were altered through dysregulated primary cilium formation. Strikingly, the normalization of defective cholesterol metabolism by simvastatin, a drug used in the treatment of cholesterol metabolic aberrations, rescued the abnormalities in both ciliogenesis and osteogenesis in vitro and in vivo. Thus, our results indicate that proper intracellular cholesterol status is crucial for primary cilium formation during skull formation and homeostasis.

scholarly journals SLITRK5 is a negative regulator of hedgehog signaling in osteoblasts

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Jun Sun ◽  
Dong Yeon Shin ◽  
Mark Eiseman ◽  
Alisha R. Yallowitz ◽  
Na Li ◽  
...  
Keyword(s):  
Bone Formation ◽  
Primary Cilium ◽  
Hedgehog Signaling ◽  
Osteoblast Differentiation ◽  
Transmembrane Protein ◽  
Negative Regulator ◽  
Skeletal Mineralization ◽  
Enhance Bone Formation

AbstractHedgehog signaling is essential for bone formation, including functioning as a means for the growth plate to drive skeletal mineralization. However, the mechanisms regulating hedgehog signaling specifically in bone-forming osteoblasts are largely unknown. Here, we identified SLIT and NTRK-like protein-5(Slitrk5), a transmembrane protein with few identified functions, as a negative regulator of hedgehog signaling in osteoblasts. Slitrk5 is selectively expressed in osteoblasts and loss of Slitrk5 enhanced osteoblast differentiation in vitro and in vivo. Loss of SLITRK5 in vitro leads to increased hedgehog signaling and overexpression of SLITRK5 in osteoblasts inhibits the induction of targets downstream of hedgehog signaling. Mechanistically, SLITRK5 binds to hedgehog ligands via its extracellular domain and interacts with PTCH1 via its intracellular domain. SLITRK5 is present in the primary cilium, and loss of SLITRK5 enhances SMO ciliary enrichment upon SHH stimulation. Thus, SLITRK5 is a negative regulator of hedgehog signaling in osteoblasts that may be attractive as a therapeutic target to enhance bone formation.

scholarly journals The primary cilium dampens proliferative signaling and represses a G2/M transcriptional network in quiescent myoblasts

2020 ◽  
Author(s):  
Nisha Venugopal ◽  
Ananga Ghosh ◽  
Hardik Gala ◽  
Ajoy Aloysius ◽  
Neha Vyas ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Primary Cilium ◽  
Developmental Disorders ◽  
Adult Stem Cells ◽  
Primary Cilia ◽  
Translational Repressor ◽  
Elevated Protein ◽  
Proliferative Signaling

Abstract Background Reversible cell cycle arrest (quiescence/G0) is characteristic of adult stem cells and is actively controlled at multiple levels. Quiescent cells also extend a primary cilium, which functions as a signaling hub. Primary cilia have been shown to be important in multiple developmental processes, and are implicated in numerous developmental disorders. Although the association of the cilium with G0 is established, the role of the cilium in the control of the quiescence program is still poorly understood. Results Primary cilia are dynamically regulated across different states of cell cycle exit in skeletal muscle myoblasts: quiescent myoblasts elaborate a primary cilium in vivo and in vitro , but terminally differentiated myofibers do not. Myoblasts where ciliogenesis is ablated using RNAi against a key ciliary assembly protein (IFT88) can exit the cell cycle but display an altered quiescence program and impaired self-renewal. Specifically, the G0 transcriptome in IFT88 knockdown cells is aberrantly enriched for G2/M regulators, suggesting a focused repression of this network by the cilium. Cilium-ablated cells also exhibit features of activation including enhanced activity of Wnt and mitogen signaling and elevated protein synthesis via inactivation of the translational repressor 4E-BP1. Conclusions Taken together, our results show that the primary cilium integrates and dampens proliferative signaling, represses translation and G2/M genes, and is integral to the establishment of the quiescence program.

scholarly journals Galectin 3 Deficiency Alters Chondrocyte Primary Cilium Formation and Exacerbates Cartilage Destruction via Mitochondrial Apoptosis

2020 ◽  
Vol 21 (4) ◽  
pp. 1486 ◽  
Author(s):  
Narjès Hafsia ◽  
Marine Forien ◽  
Félix Renaudin ◽  
Delphine Delacour ◽  
Pascal Reboul ◽  
...  
Keyword(s):  
Primary Cilium ◽  
Primary Cilia ◽  
Mitochondrial Pathway ◽  
Cartilage Destruction ◽  
Terminal Deoxynucleotidyl Transferase ◽  
Chondrocyte Apoptosis ◽  
Cytochrome C Release ◽  
Cilium Formation ◽  
Galectin 3

Mechanical overload and aging are the main risk factors of osteoarthritis (OA). Galectin 3 (GAL3) is important in the formation of primary cilia, organelles that are able to sense mechanical stress. The objectives were to evaluate the role of GAL3 in chondrocyte primary cilium formation and in OA in mice. Chondrocyte primary cilium was detected in vitro by confocal microscopy. OA was induced by aging and partial meniscectomy of wild-type (WT) and Gal3-null 129SvEV mice (Gal3−/−). Primary chondrocytes were isolated from joints of new-born mice. Chondrocyte apoptosis was assessed by Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL), caspase 3 activity and cytochrome c release. Gene expression was assessed by qRT-PCR. GAL3 was localized at the basal body of the chondrocyte primary cilium. Primary cilia of Gal3−/− chondrocytes were frequently abnormal and misshapen. Deletion of Gal3 triggered premature OA during aging and exacerbated joint instability-induced OA. In both aging and surgery-induced OA cartilage, levels of chondrocyte catabolism and hypertrophy markers and apoptosis were more severe in Gal3−/− than WT samples. In vitro, Gal3 knockout favored chondrocyte apoptosis via the mitochondrial pathway. GAL3 is a key regulator of cartilage homeostasis and chondrocyte primary cilium formation in mice. Gal3 deletion promotes OA development.

scholarly journals The primary cilium dampens proliferative signaling and represses a G2/M transcriptional network in quiescent myoblasts

2019 ◽  
Author(s):  
Nisha Venugopal ◽  
Ananga Ghosh ◽  
Hardik Gala ◽  
Ajoy Aloysius ◽  
Neha Vyas ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Primary Cilium ◽  
Developmental Disorders ◽  
Adult Stem Cells ◽  
Primary Cilia ◽  
Translational Repressor ◽  
Elevated Protein ◽  
Proliferative Signaling

Abstract Background: Reversible cell cycle arrest (quiescence/G0) is characteristic of adult stem cells and is actively controlled at multiple levels. Quiescent cells also extend a primary cilium, which functions as a signaling hub. Primary cilia have been shown to be important in multiple developmental processes, and are implicated in numerous developmental disorders. Although the association of the cilium with G0 is established, the role of the cilium in the control of the quiescence program is still poorly understood.Results: Primary cilia are dynamically regulated across different states of cell cycle exit in skeletal muscle myoblasts: quiescent myoblasts elaborate a primary cilium in vivo and in vitro , but terminally differentiated myofibers do not. Myoblasts where ciliogenesis is ablated using RNAi against a key ciliary assembly protein (IFT88) can exit the cell cycle but display an altered quiescence program and impaired self-renewal. Specifically, the G0 transcriptome in IFT88 knockdown cells is aberrantly enriched for G2/M regulators, suggesting a focused repression of this network by the cilium. Cilium-ablated cells also exhibit features of activation including enhanced activity of Wnt and mitogen signaling and elevated protein synthesis via inactivation of the translational repressor 4E-BP1.Conclusions: Taken together, our results show that the primary cilium integrates and dampens proliferative signaling, represses translation and G2/M genes, and is integral to the establishment of the quiescence program.

Primary Cilia of Odontoblasts: Possible Role in Molar Morphogenesis

2009 ◽  
Vol 88 (10) ◽  
pp. 910-915 ◽  
Author(s):  
B. Thivichon-Prince ◽  
M.L. Couble ◽  
A. Giamarchi ◽  
P. Delmas ◽  
B. Franco ◽  
...  
Keyword(s):  
Primary Cilium ◽  
Close Relationships ◽  
Primary Cilia ◽  
Nerve Fibers ◽  
Vertebrate Cell ◽  
Pain Transmission ◽  
Dentin Formation

A primary cilium, a sensory organelle present in almost every vertebrate cell, is regularly described in odontoblasts, projecting from the surfaces of the cells. Based on the hypothesis that the primary cilium is crucial both for dentin formation and possibly in tooth pain transmission, we have investigated the expression and localization of the main cilium components and involvement of the OFD1 gene in tooth morphogenesis. Odontoblasts in vitro express tubulin, inversin, rootletin, OFD1, BBS4, BBS6, ALMS1, KIF3A, PC1, and PC2. In vivo, cilia are aligned parallel to the dentin walls, with the top part oriented toward the pulp core. Close relationships between cilium and nerve fibers are evidenced. Calcium channels are concentrated in the vicinity of the basal body. Analysis of these data suggests a putative role of cilia in sensing the microenvironment, probably related to dentin secretion. This hypothesis is enhanced by the huge defects observed on molars from Ofd1 knockout mice, showing undifferentiated dentin-forming cells.

scholarly journals Implications of Primary Cilia and Associated Lysophosphatidic Acid Signaling in Glioblastoma Biology and Therapy

2017 ◽  
Author(s):  
◽  
Yuriy Loskutov ◽  
Keyword(s):  
Cell Proliferation ◽  
G Protein ◽  
Lysophosphatidic Acid ◽  
Primary Cilium ◽  
Primary Cilia ◽  
Rapid Progression ◽  
Current Standard ◽  
G Protein Coupled

The primary cilium is a ubiquitous organelle presented on most human cells. It serves as a crucial signaling hub for multiple pathways including growth factor and G-protein coupled receptors. Loss of primary cilia was observed in various cancers, however, the implications of this event are unclear. Several studies show that loss of cilia promotes cell proliferation, suggesting that alteration of ciliary-dependent signaling can drive the hyperproliferative phenotype of cancer cells, therefore re-establishing primary cilia or targeting altered signaling pathways could be a beneficial strategy as an anti-cancer therapy.;Glioblastoma (GBM) is one of the deadliest cancers with a median survival of 14 months. Such rapid progression of the disease is usually due to the very high growth rate of the tumor and rapid recurrence after surgical resection. Current standard of care for GBM patients includes aggressive radiation and chemotherapy, thus there is a high demand for more targeted approaches. Primary cilia formation is drastically decreased in GBM, however, the role of cilia in glioblastoma proliferation has not been explored. The overall aim of this work was to elucidate the mechanisms of increases in proliferation driven by the loss of cilia, and utilize it to target GBM. The cellular origins of GBM are currently under debate. One of the potential candidates are astrocytes, a highly abundant type of cell in the brain. Loss of primary cilia in human astrocytes stimulates proliferation in the presence of serum. Lysophosphatidic acid (LPA) was found to be a serum component responsible for this phenotype. Lysophosphatidic acid receptor 1 (LPAR1), a G-protein coupled receptor, was found to be accumulated in primary cilium in both astrocytes and GBM cells when cilium was present, while previously reported interactors of LPAR1, Galpha 12 and Galphaq, were excluded from cilium. LPAR1 signaling through Galpha12/Galphaq was previously reported to be responsible for cancer cell proliferation. Such compartmentalization in ciliated cells creates a barrier against unlimited proliferation, which is one of the hallmarks of cancer.;Inhibition of LPA signaling with the small molecule compound Ki16425 in deciliated, highly proliferative astrocytes or GBM cells/xenografts drastically suppresses their growth both in vitro and in vivo. Moreover, Ki16425 brain delivery via PEG-PLGA nanoparticles inhibited tumor progression in an intracranial glioblastoma patient-derived xenograft (PDX) model. Overall, in the current studies, a novel mechanism by which primary cilium restricts proliferation was established. Loss of primary cilia is sufficient to increase mitogenic signaling, and is important for the maintenance of a highly proliferative cancer phenotype. Clinical application of LPA inhibitors may prove beneficial to restrict glioblastoma proliferation and ensure local control of the disease.

scholarly journals TDP-43 mediates SREBF2-regulated gene expression required for oligodendrocyte myelination

2021 ◽  
Vol 220 (9) ◽  
Author(s):  
Wan Yun Ho ◽  
Jer-Cherng Chang ◽  
Kenneth Lim ◽  
Amaury Cazenave-Gassiot ◽  
Aivi T. Nguyen ◽  
...  
Keyword(s):  
Cholesterol Metabolism ◽  
Cholesterol Biosynthesis ◽  
Cholesterol Homeostasis ◽  
Cholesterol Levels ◽  
The Central Nervous System ◽  
Cholesterol Supplementation ◽  
Regulated Gene Expression ◽  
Lateral Sclerosis

Cholesterol metabolism operates autonomously within the central nervous system (CNS), where the majority of cholesterol resides in myelin. We demonstrate that TDP-43, the pathological signature protein for amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD), influences cholesterol metabolism in oligodendrocytes. TDP-43 binds directly to mRNA of SREBF2, the master transcription regulator for cholesterol metabolism, and multiple mRNAs encoding proteins responsible for cholesterol biosynthesis and uptake, including HMGCR, HMGCS1, and LDLR. TDP-43 depletion leads to reduced SREBF2 and LDLR expression, and cholesterol levels in vitro and in vivo. TDP-43–mediated changes in cholesterol levels can be restored by reintroducing SREBF2 or LDLR. Additionally, cholesterol supplementation rescues demyelination caused by TDP-43 deletion. Furthermore, oligodendrocytes harboring TDP-43 pathology from FTD patients show reduced HMGCR and HMGCS1, and coaggregation of LDLR and TDP-43. Collectively, our results indicate that TDP-43 plays a role in cholesterol homeostasis in oligodendrocytes, and cholesterol dysmetabolism may be implicated in TDP-43 proteinopathies–related diseases.

scholarly journals OR04-01 MRAP2 Regulates Energy Homeostasis by Promoting Primary Cilia Localization of MC4R

2020 ◽  
Vol 4 (Supplement_1) ◽  
Author(s):  
Adelaide A Bernard ◽  
Irene Ojeda Naharros ◽  
Florence Bourgain Guglielmetti ◽  
Xinyu Yue ◽  
Christian Vaisse
Keyword(s):  
Body Weight ◽  
Primary Cilium ◽  
Energy Homeostasis ◽  
Primary Cilia ◽  
Small Population ◽  
The Body ◽  
Melanocortin Receptor ◽  
Hypothalamic Neurons

Abstract Genetic studies in humans and mice have demonstrated that the Melanocortin 4 Receptor (MC4R) is essential for adequate regulation of food intake and body weight. MC4R is expressed in a small population of hypothalamic neurons and very little is known about its molecular and cellular dynamics in vivo. We have recently demonstrated that MC4R localizes to and functions at the primary cilia of select hypothalamic neurons to control energy homeostasis. The primary cilium is a solitary hair-like organelle that serves as an antenna sensing extracellular environment. Defective primary cilia lead to a series of conditions known as ciliopathies, that can manifest through a variety of clinical features, including hyperphagia and obesity. Here we establish that the ciliary localization and the body weight regulating activity of MC4R is dependent on a single-pass transmembrane accessory protein: the Melanocortin Receptor Associated Protein 2 (MRAP2). Specifically, we show that deleting MRAP2 specifically from MC4R neurons (MC4RMRAP2-/-) leads to early onset obesity and hyperphagia. In vitro, co-expression of MRAP2 in ciliated IMCD3 cells increases MC4R localization to the primary cilium. We further demonstrate that MRAP2 and MC4R colocalize specifically at the primary cilium in vivo, and that MC4R fails to localize to the primary cilium when MRAP2 is deleted. These findings highlight the role of the primary cilium in the control of energy homeostasis, and the importance of accessory proteins for the localization of GPCRs to the primary cilium where they exert their function, in this case being critical for the regulation of energy homeostasis.

scholarly journals Disuse Osteoporosis: Clinical and Mechanistic Insights

2021 ◽  
Author(s):  
Tim Rolvien ◽  
Michael Amling
Keyword(s):  
Bone Loss ◽  
Bone Formation ◽  
Primary Cilia ◽  
Neuromuscular Disorders ◽  
Focal Adhesions ◽  
Basic Research ◽  
Disuse Osteoporosis ◽  
Cord Injury

AbstractDisuse osteoporosis describes a state of bone loss due to local skeletal unloading or systemic immobilization. This review will discuss advances in the field that have shed light on clinical observations, mechanistic insights and options for the treatment of disuse osteoporosis. Clinical settings of disuse osteoporosis include spinal cord injury, other neurological and neuromuscular disorders, immobilization after fractures and bed rest (real or modeled). Furthermore, spaceflight-induced bone loss represents a well-known adaptive process to microgravity. Clinical studies have outlined that immobilization leads to immediate bone loss in both the trabecular and cortical compartments accompanied by relatively increased bone resorption and decreased bone formation. The fact that the low bone formation state has been linked to high levels of the osteocyte-secreted protein sclerostin is one of the many findings that has brought matrix-embedded, mechanosensitive osteocytes into focus in the search for mechanistic principles. Previous basic research has primarily involved rodent models based on tail suspension, spaceflight and other immobilization methods, which have underlined the importance of osteocytes in the pathogenesis of disuse osteoporosis. Furthermore, molecular-based in vitro and in vivo approaches have revealed that osteocytes sense mechanical loading through mechanosensors that translate extracellular mechanical signals to intracellular biochemical signals and regulate gene expression. Osteocytic mechanosensors include the osteocyte cytoskeleton and dendritic processes within the lacuno-canalicular system (LCS), ion channels (e.g., Piezo1), extracellular matrix, primary cilia, focal adhesions (integrin-based) and hemichannels and gap junctions (connexin-based). Overall, disuse represents one of the major factors contributing to immediate bone loss and osteoporosis, and alterations in osteocytic pathways appear crucial to the bone loss associated with unloading.

scholarly journals The primary cilium dampens proliferative signaling and represses a G2/M transcriptional network in quiescent myoblasts

2020 ◽  
Author(s):  
Nisha Venugopal ◽  
Ananga Ghosh ◽  
Hardik Gala ◽  
Ajoy Aloysius ◽  
Neha Vyas ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Primary Cilium ◽  
Developmental Disorders ◽  
Adult Stem Cells ◽  
Primary Cilia ◽  
Translational Repressor ◽  
Elevated Protein ◽  
Proliferative Signaling

Abstract Background Reversible cell cycle arrest (quiescence/G0) is characteristic of adult stem cells and is actively controlled at multiple levels. Quiescent cells also extend a primary cilium, which functions as a signaling hub. Primary cilia have been shown to be important in multiple developmental processes, and are implicated in numerous developmental disorders. Although the association of the cilium with G0 is established, the role of the cilium in the control of the quiescence program is still poorly understood. Results Primary cilia are dynamically regulated across different states of cell cycle exit in skeletal muscle myoblasts: quiescent myoblasts elaborate a primary cilium in vivo and in vitro , but terminally differentiated myofibers do not. Myoblasts where ciliogenesis is ablated using RNAi against a key ciliary assembly protein (IFT88) can exit the cell cycle but display an altered quiescence program and impaired self-renewal. Specifically, the G0 transcriptome in IFT88 knockdown cells is aberrantly enriched for G2/M regulators, suggesting a focused repression of this network by the cilium. Cilium-ablated cells also exhibit features of activation including enhanced activity of Wnt and mitogen signaling and elevated protein synthesis via inactivation of the translational repressor 4E-BP1. Conclusions Taken together, our results show that the primary cilium integrates and dampens proliferative signaling, represses translation and G2/M genes, and is integral to the establishment of the quiescence program.

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