La glycylation, une modification post-traductionnelle des microtubules, est cruciale dans le maintien des cils primaires. Notre groupe a précédemment identifié un rôle inattendu de la tubuline glycylase TTLL3 dans la régulation de l'homéostasie du colon et de la tumorigénèse. Plus précisément, une diminution du nombre de cils primaires a été observée chez les souris déficientes pour la glycylase TTLL3, qui est la seule glycylase exprimée dans le côlon. Les souris TTLL3 - / - ne présentent pas d'anomalie évidente à l'état stationnaire. Cependant, lorsqu'elles sont exposées à une carcinogenèse du côlon chimiquement induite, les souris TTLL3 - / - sont plus sensibles à la formation de tumeurs. Il est important de noter que les niveaux d'expression de TTLL3 sont significativement réduits dans les carcinomes primaires et métastases colorectales chez l'homme comparativement au tissu de côlon sain, ce qui suggère un lien entre la régulation des cils primaires par TTLL3 et le développement du cancer colorectal.L'objectif de mon projet de thèse était d'explorer l’effet de la modulation des cils primaires sur la carcinogenèse du côlon. J’ai ainsi démontré que le nombre de cils primaires diminue lors de la carcinogenèse du côlon chimiquement induite chez la souris. Notamment, j'ai découvert que les cils primaires du côlon sont principalement exprimés par les cellules mésenchymateuses. Pour mieux caractériser le rôle des cils primaires dans le côlon murin, j'ai étudié les conséquences de leur perte dans les cellules mésenchymateuses intestinaux. Pour cela, j'ai utilisé deux modèles de souris KO conditionnelles, pour la kinesin-3A (Kif3A) et le transport intra-flagellaire 88 (Ift88), deux molécules essentielles pour la formation des cils. Leur délétion spécifique dans les cellules mésenchymateuses intestinaux est obtenue par croisement des souches de souris Kif3Afl/fl et Ift88fl/fl des souris transgéniques collagène VI-cre. Bien que le promoteur colllagène VI ne soit actif que dans un sous-ensemble de cellules mésenchymateuses coliques, j'ai constaté que la diminution du nombre de cils primaires dans ces derniers favorise la colite chimiquement induite et la carcinogenèse. L'analyse par séquençage ARN des cellules mésenchymateuses coliques isolés de souris mutantes suggère un déclenchement de la signalisation Wnt et Notch chez les souris ColVIcre-Kif3Afl/fl. Nous confirmons actuellement ces résultats par qPCR et immunohistochimie. / Glycylation, a posttranslational modification of microtubules, is crucial in the maintenance of PC. Our group previously identified an unexpected role of the tubulin glycylase TTLL3 in the regulation of colon homeostasis and tumorigenesis. Specifically, a decreased number of primary cilia (PC) was observed in mice deficient for the glycylase TTLL3, which is the only glycyclase expressed in the colon. TTLL3-/- mice display no obvious abnormalities in the steady state. However, when exposed to chemically induced colon carcinogenesis, TTLL3-/- mice are more susceptible to tumor formation. Importantly, TTLL3 expression levels were significantly downregulated in human primary colorectal carcinomas and metastases as compared to healthy colon tissue, suggesting a link between TTLL3 regulation of PC and colorectal cancer development.The aim of my thesis project was to explore the relation of PC and colon carcinogenesis. In fact, I could demonstrate that the number of PC decreases during chemically induced colon carcinogenesis in mice. Notably, I discovered that PC in the colon are mostly expressed by fibroblasts. To better characterize the role of PC in murine colon, I studied the consequences of a loss of PC in intestinal fibroblasts. For this, I used two independent ciliary conditional knockout mice, kinesin-3A (Kif3A) and intraflagellar transport 88 (Ift88), both essential for cilia formation. Specific deletion in intestinal fibroblasts is obtained by crossing with colVI-cre transgenic mice. Though the colVI promoter is only active in a subset of colonic mesenchymal cells I found that the decreased number of PC in colonic mesenchymal cells promotes chemically induced colitis and carcinogenesis. RNAseq on isolated colonic mesenchymal cells of mutant mice suggests a triggering of Wnt and Notch signaling in ColVIcre-Kif3aflx/flx mice. We are presently validating these findings by qPCR and immunohistochemistryTaken together, I discovered that PC are expressed by at least a subset of colonic mesenchymal cells, which has not been described before. Decreased numbers of those PC renders mice more susceptible to colitis and colitis associated carcinogenesis.

Many signaling pathways which are classically understood for their roles in early development are also known to be involved in tissue maintenance and adult energy homeostasis. Furthermore, dysfunction of these signaling pathways results in human diseases such as cancer. An in depth understanding of how developmentally important signaling pathways function in the adult will provide mechanistic insights into disease and potential new therapeutic targets. Herein Chapter 1, the Wnt, fibroblast growth factor (FGF), and Hedgehog (Hh) signaling pathways are discussed and examples of their relevance in development, adult homeostasis, and disease are provided. Wnt signaling provides an example of this concept as it has well described roles during both development and adult metabolism.<div><br></div><div> Work included in Chapter 2, investigates the regulation of adult energy homeostasis by a member of the endocrine FGF family, FGF19. The three endocrine FGFs, FGF19 (FGF15 in mice), FGF21, and FGF23 have well described roles in the regulation of metabolic processes in adults. While FGF23 is primarily involved in the regulation of phosphate and vitamin D homeostasis,FGF19 and FGF21 have shown similar pharmacological effects on whole body metabolism. Here, the importance of adaptive thermogenesis for the pharmacological action of FGF19 is explored. UsingUCP1KO animals we show that whole-body thermogenesis is dispensable for body weight loss following FGF19 treatment.<br></div><div><br></div><div>Finally, the potential involvement of Hh signaling in mediating the hyperphagia driven obesity observed in certain ciliopathies is explored in Chapter 3. Emerging evidence suggests cilia play an important role in the regulation of feeding behavior. In mammals, the hedgehog pathway is dependent on the primary cilium as an organizing center and defects in hedgehog signaling share some clinical symptoms of ciliopathies. Here, we characterized the expression of core pathway components in the adult hypothalamus. We show that neurons within specific nuclei important for regulation of feeding behavior express Hh ligand and members of its signaling pathway. We also demonstrate that the Hh pathway is transcriptionally upregulated in response to an overnight fast. This work provides an important foundation for understanding the functional role of Hh signaling in regulation of energy homeostasis. In its entirety, this work highlights the emerging clinical relevance of developmentally critical pathways in diseases associated with dysfunction of adult tissue homeostasis, such as obesity.<br></div>

No description available.

<p>Bone loss diseases, including osteoporosis affect millions of people worldwide. Understanding the underlying mechanisms behind bone homeostasis and adaptation is essential to uncovering new therapeutic targets for the prevention and treatment of bone loss diseases. Primary cilia have been implicated in the development and mechanosensation of various tissue types, including bone. The goal of the studies outlined in this thesis is to determine the mechanosensory role of primary cilia in bone cell function, bone growth, and adaptation. This goal was achieved by exploring two specific scenarios. In the first study, mice models with conditional knockouts of MKS5, a ciliary protein, in osteocytes were utilized to demonstrate that dysfunctional primary cilia in those cells result in impaired loading-induced bone formation. The hypothesis tested is that the existence of functioning primary cilia on osteocytes is crucial for proper bone adaptation following stress. The results of this study support the hypothesis, with the conditional knockout mice showing significantly lower loading-induced bone formation compared to controls. The second study highlighted the importance of the osteoblast primary cilia in bone growth by using mice models with osteoblast-specific deletion of the cilia. The hypothesis tested is that the presence of the primary cilia is crucial for proper bone growth. The results show that conditional knockout mice have lower body weights, decreased femur length, and a significantly lower rate of bone formation, confirming that the primary cilia play a great role in bone growth and development. This study has highlighted the role of primary cilia in bone health and this topic merits further investigation. </p>

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Primary cilia are sensory organelles that are important for initiating cell division in the brain, especially through sonic hedgehog (Shh) signaling. Several lines of evidence suggest that the mitogenic effect of Shh requires primary cilia. Proliferation initiated by Shh signaling plays key roles in brain development, in neurogenesis in the adult hippocampus, and in the generation of glial cells in response to cortical injury. In spite of the likely involvement of cilia in these events, little is known about their characteristics. Centrosomes, which are associated with primary cilia, also have multiple influences on the cell cycle, and they are important in assembling microtubules for the maintenance of the cell’s cytoskeleton and cilia. The cilia of terminally differentiated neurons have been previously examined with respect to length, incidence, and receptors present. However, almost nothing is known about primary cilia in stem cells, progenitors, or differentiated glial cells. Moreover, it is not known how the properties of cilia and centrosomes may vary with cell cycle or proliferative potential, in brain or other tissues. This dissertation focuses first on neurogenesis in the hippocampal subgranular zone (SGZ). The SGZ is one of the few brain regions in mammals that gives rise to a substantial number of new neurons throughout adulthood. The neuron lineage contains a progression of identifiable precursor cell types with different proliferation rates. This present study found that primary cilia were present in every cell type in the neuronal lineage in SGZ. Cilium length and incidence were positively correlated among these cell types. Ciliary levels of adenylyl cyclase type III (ACIII) levels relative to ADP-ribosylation factor-like protein 13b (Arl13b) was higher in neurons than in precursor cells and glia, and also changed with the cell cycle. G-protein coupled receptors, SstR3, MCHR1, and Gpr161 receptors were only found in neuronal cilia. The levels and distribution of three centrosomal proteins, γ-tubulin, pericentrin and cenexin in neurons was different from the distributions in precursors and glia. The second focus of study is glial responses to injury in the neocortex, which has been widely studied as an injury model. This study found that in the normal adult somatosensory cortex, primary cilia were present in astrocytes and polydendrocytes but not in microglia. Following injury, the incidence of primary cilia decreased in astrocytes. Also, a new cell type expressing GFAP, NG2 and Olig2 was seen 3 days following injury, but was not present in normal mice. The characteristics of primary cilia and centrosome described here suggest that in stem cells and progenitors their characteristics may be well suited for proliferation, whereas in neurons, the cilia and centrosomes are important for other sensory functions.

Lung cancer is the number one cause of cancer related death worldwide, with more than 1.6 million fatalities each year. Non-small cell lung cancer (NSCLC) accounts for 80-85% of all lung cancers, with KRAS being one of the most prevalent oncogenic driver mutations. Therapeutic approaches for KRAS-mutated NSCLC have been extensively explored due to the US National Cancer Institute RAS Initiative, but methods of directly targeting KRAS or downstream effectors, such as MEK, still have poor results. Previous reports have shown that KRAS-mutated NSCLC activate distinct receptor tyrosine kinases (RTKs) depending on the epithelial or mesenchymal state. Epithelial-to-mesenchymal transition (EMT) is known to play a role in the metastasis and poor prognosis of cancer, and is induced by extracellular matrix (ECM) stiffness. Hallmarks of EMT include loss of E-Cadherin and increase in Vimentin. This research investigates the role of KRAS in EMT transition due to increased ECM stiffness in KRAS mutant NSCLC, and how this affects the efficacy of KRAS and MEK inhibition. To understand how KRAS mutations in NSCLC play a role in this stiffness induced EMT, experiments were performed to detect the gene and protein expression of EMT markers, as well as possible sources of mechanosensing, including primary cilia and receptor tyrosine kinases. We hypothesized that KRAS plays a role in activation of mechanosensors and directly correlates to EMT induced by increased mechanical forces. Results show when KRAS was inhibited and there was increased mechanical forces, either from stretch or substrate stiffness, there was a decreased activation of mechanosensors. KRAS inhibition also prevented the cells from undergoing stiffness-induced EMT. This supports our hypothesis that KRAS plays a key role in ECM stiffness induced EMT. Future studies include examining the mechanism behind this phenomenon and in vivo studies.

Les cils primaires et motiles sont des structures microtubulaires présentent à la surface de nombreux types cellulaires. Les structures ciliées contrôlent de nombreuses fonctions allant de la motilité cellulaire à l’intégration par la cellule de stimuli chimiques et mécaniques. Au cours de cette thèse, nous avons étudié le dialogue entre le cil primaire et l’autophagie, un processus d’autodigestion qui permet à la cellule de s’adapter à des situations de stress. L’hypothèse de ce dialogue reposait sur l’analyse de la littérature montrant que de nombreux médiateurs (calcium, carence en sérum, arrêt du cycle cellulaire) stimulent à la fois l’activité ciliaire et l’autophagie. Dans un premier temps de notre étude nous avons montré que l’inhibition de la ciliogenèse altère l’induction de l’autophagie en réponse à la carence en sérum dans des fibroblastes d’embryon de souris, des cellules épithéliales rénales et des lignées de neurone. Nous avons aussi montré que la carence en sérum induisait une redistribution de nombreuses protéines Atg (Autophagy-related), protéines impliquées dans la biogenèse de l’autophagosome, au niveau du cil primaire (soit au niveau du corps basal soit au niveau de l’axonème). Particulièrement la protéine Atg16L1 est co-transportée vésiculairement au corps basal avec la protéine ciliaire IFT20. L’inhibition génétique ou pharmacologique de la voie de signalisation Hedgehog inhibe à la fois le transport de la protéine Atg16L1 au corps basal et l’induction de l’autophagie en absence de sérum. Nous avons aussi montré que l’invalidation de gènes ATG est associée à une ciliogenèse accrue. Dans ces conditions nous avons conclu sur des bases morphologiques et biochimiques que ces cils primaires sont fonctionnels. La protéine IFT20 s ‘accumule dans les cellules déficientes en autophagie et est dégradée par autophagie dans les cellules sauvage en présence de sérum. Ces résultats montre que l’autophagie basale (autophagie observée en présence de sérum) est un mécanisme qui contribue au contrôle de la croissance du cil primaire. Dans une deuxième partie du travail nous avons étudié l’importance de l’autophagie dans la réponse cellulaire à stress mécanique. Le contrôle de la taille et du volume des cellules épithéliales rénales est un élément important pour maintenir la polarité planaire des cellules tubulaires. Cette propriété est dépendante du cil primaire. Au cours de l’application d’un flux de liquide (1 dyn/cm2) concomitamment à la réduction du volume et de la taille cellulaire nous avons observé une stimulation de l’autophagie. Cette réponse autophagique dépend du cil primaire. L’invalidation de l’autophagie dans des cellules épithéliales ciliées abolit le contrôle du volume et de la taille cellulaire dans les cellules épithéliales rénales. L’ensemble de ces résultats montre le dialogue qui existe en l’autophagie et le cil primaire et l’importance de ce dialogue dans l’intégration par la cellule du stress mécanique. / Motile and primary cilia are microtubule-based structures located at the cell surface of many cell types. Cilia govern cellular functions ranging from motility to integration of mechanical and chemical signaling from the environment. In this work we investigate the potential cross-talk between the primary cilium and macroautophagy. Macroautophagy or self-eating is a lysosomal degradative pathway that allows cells to adapt to various stress situations. The rational for the study was based on the survey of the literature showing that many stress situations that trigger primary cilium signaling also stimulates autophagy (serum starvation, calcium mobilization, cell cycle arrest). In the first part of the study we showed that inhibition of ciliogenesis severely impairs serum-induced autophagy in mouse embryo fibroblasts, kidney epithelial cells and neurons. We also showed that in response to serum deprivation many Autophagy-related proteins (Atg proteins) involved in autophagosome formation are co-localized with cilium subdomains (axoneme and basal body). Notably the protein Atg16L1 is co-transported to the basal body with the ciliary protein IFT20. The localization of Atg16L1 to the basal body as well as serum-induced autophagy were severely impaired by inhibiting the Hedgehog signaling pathway either genetic or pharmacological approaches. We also showed that invalidation of ATG genes induced an increase in primary cilium length in basal condition. Cilia were functional in ATG-deficient cells because of the presence of a ciliary pocket and the activation of the Hedgehog signaling pathway. Finally we identified IFT20 as a substrate for autophagy. Thus autophagy is required to regulate the level of IFT20 and consequently that of the length of the primary cilium. In the second part of the work we investigate the role of the cross-talk between autophagy and the primary cilium in regulating the size of kidney epithelial cells. Previous studies have shown that the primary cilium plays a central role in regulating cell size and cell volume. This regulation is important to keep the physiological functions of tubular renal cells by maintaining the planar polarity in kidney tubule. By applying a liquid flow of 1 dyn/cm2 to MDCK or mouse kidney epithelial cells to mimic physiological conditions, we show that the flow induces autophagy and reduction of the cell volume. In absence of cilium we observed that autophagy is not induced and that the cell size/volume is not responsive to the mechanical stress. Finally we showed that ablation of autophagy led also to an impairment of flow-dependent regulation of cell size/volume in ciliated kidney epithelial cells. In conclusion primary cilium-dependent autophagy plays a major role in controlling the epithelial kidney cell size/volume during mechanical stress induced by fluid flow.

Primary cilia are non-motile organelles having 9+0 microtubules that project from the basal body of the cell. While the main purpose of motile cilia in mammalian cells is to move fluid or mucus over the cell surface, the purpose of primary cilia has remained elusive for the most part. Primary cilia are shortened in the kidney tubules of Tg737orpk mice, which have polycystic kidney disease due to ciliary defects. The product of the Tg737 gene is polaris, which is directly involved in a microtubule-dependent transport process called intraflagellar transport (IFT). In order to determine the importance of polaris in the development of neuronal cilia, cilium length and numerical density of cilia were quantitatively assessed in six different brain regions on postnatal days 14 and 31 in Tg737orpk mutant and wildtype mice. Our results indicate that the polaris mutation leads to shortening of cilia as well as decreased percentage of ciliated neurons in all brain regions that were quantitatively assessed. Maintainance of cilia was especially affected in the ventromedial nucleus of the hypothalamus. Furthermore, the polaris mutation curtailed cilium length more severely on postnatal day 31 than postnatal day 14. These data suggests that even after ciliogenesis, intraflagellar transport is necessary in order to maintain neuronal cilia. Regional heterogeneity in the effect of this gene mutation on neuronal cilia suggests that the functions of some brain regions might be more compromised than others.

Indiana University-Purdue University Indianapolis (IUPUI) / Primary cilia are solitary cellular appendages that function as signaling centers for cells in adult energy homeostasis. Here in chapter 1, I introduce cilia and how dysfunction of these conserved organelles results in ciliopathies, such as Bardet-Biedl Syndrome (BBS), which present with childhood obesity. Furthermore, conditional loss of primary cilia from neurons in the hypothalamus leads to hyperphagia and obesity in mouse models of ciliopathies. Classically, cilia coordinate signaling often through specific G-protein coupled receptors (GPCRs) as is the case in both vision and olfaction. In addition, neurons throughout the brain including hypothalamic neurons possess primary cilia whose dysfunction contributes to ciliopathy-associated obesity. How neuronal cilia regulate the signaling of GPCRs remains unclear and many fundamental cell biology questions remain about cilia mediated signaling. For example, how cilia coordinate signaling to influence neuronal activity is unknown. To begin to address some of these cell biology questions around neuronal cilia, chapter 2, describes the development and use of a system for primary neuronal cultures from the hypothalamus. Using this system, we found that activation of the cilia regulated hedgehog pathway, which is critical in development, influenced the ability of neurons to respond to GPCR ligands. This result highlights the role of the developmentally critical hedgehog pathway on terminally differentiated hypothalamic neurons. One challenge facing the cilia field is our ability to assess cilia in large numbers without potential bias. This is especially true in tissues like the brain, where cilia appear to have region-specific characteristics. Work included in Chapter 3 describes the use of a computer-assisted artificial intelligence (Ai) approach to analyze cilia composition and morphology in a less biased and high throughput manner. Cilia length and intensities are important parameters for evaluation of cilia signaling. Evidence suggests that activation of some ciliary GPCRs results in shortening of cilia whereas deviations from normal cilia length in mutant phenotypes affects normal physiological processes such as decreased mucociliary clearance. Therefore, to analyze a large number of cilia, we describe the use of the Ai module from in vitro and in vivo samples in a reproducible manner that minimizes user bias. Using this approach, we identified that Mchr1 expression is significantly stronger in the cilia of paraventricular nucleus than that in the arcuate nucleus of adult mice. Work in Chapter 4 continues to explore the integration between hedgehog pathway and ciliary GPCR signaling in the central nervous system, and its relevance with energy homeostasis. We evaluated the hedgehog ligand in the plasma of mice in acute and long-term metabolic changes and identified that the activity of the ligand changed under altered metabolic conditions. We also developed a genetic mouse model where hedgehog signaling was constitutively active in neuronal cilia. These mice become hyperphagic and obese. These results further emphasize the potential role of the hedgehog signaling pathway in regulation of feeding behavior in adult vertebrates. Overall, results from this work will provide a better understanding of the defects not only underlying ciliopathy-associated obesity but may also reveal more common mechanisms of centrally mediated obesity. In addition, the tools I have developed will help in understanding how neuronal cilia are used for intercellular communications and ultimately how they regulate behaviors like feeding.