Primary Cilia and Mammalian Hedgehog Signaling

Sonic Hedgehog activates prostaglandin signaling to stabilize primary cilium length

Sonic Hedgehog (SHH) is a driver of embryonic patterning that, when corrupted, triggers developmental disorders and cancers. SHH effector responses are organized through primary cilia (PC) that grow and retract with the cell cycle and in response to extracellular cues. Disruption of PC homeostasis corrupts SHH regulation, placing significant pressure on the pathway to maintain ciliary fitness. Mechanisms by which ciliary robustness is ensured in SHH-stimulated cells are not yet known. Herein, we reveal a crosstalk circuit induced by SHH activation of Phospholipase A2α that drives ciliary E-type prostanoid receptor 4 (EP4) signaling to ensure PC function and stabilize ciliary length. We demonstrate that blockade of SHH-EP4 crosstalk destabilizes PC cyclic AMP (cAMP) equilibrium, slows ciliary transport, reduces ciliary length, and attenuates SHH pathway induction. Accordingly, Ep4-/- mice display shortened neuroepithelial PC and altered SHH-dependent neuronal cell fate specification. Thus, SHH initiates coordination between distinct ciliary receptors to maintain PC function and length homeostasis for robust downstream signaling.

A novel indole derivative, 2-{3-[1-(benzylsulfonyl)piperidin-4-yl]-2-methyl-1H-indol-1-yl}-1-(pyrrolidin-1-yl)ethenone, suppresses hedgehog signaling and drug-resistant tumor growth

The Hedgehog (Hh) signaling pathway plays important roles in various physiological functions. Several malignancies, such as basal cell carcinoma (BCC) and medulloblastoma (MB), have been linked to the aberrant activation of Hh signaling. Although therapeutic drugs have been developed to inhibit Hh pathway-dependent cancer growth, drug resistance remains a major obstacle in cancer treatment. Here, we show that the newly identified, 2-{3-[1-(benzylsulfonyl)-1,2,3,6-tetrahydropyridin-4-yl]-2-methyl-1H-indol-1-yl}-1-(pyrrolidin-1-yl)ethenone analog (LKD1214) exhibits comparable potency to vismodegib in suppressing the Hh pathway activation. LKD1214 represses Smoothened (SMO) activity by blocking its ciliary translocation. Interestingly, we also identified that it has a distinctive binding interface with SMO compared with other SMO-regulating chemicals. Notably, it maintains an inhibitory activity against the SmoD477H mutant, as observed in a patient with vismodegib-resistant BCC. Furthermore, LKD1214 inhibits tumor growth in the mouse model of MB. Collectively, these findings suggest that LKD1214 has the therapeutic potential to overcome drug-resistance in Hh-dependent cancers.

TonEBP inhibits ciliogenesis by controlling aurora kinase A and regulating centriolar satellite integrity

BACKGROUND

Primary cilia on the surface of eukaryotic cells serve as sensory antennas for the reception and transmission in various cell signaling pathways. They are dynamic organelles that rapidly form during differentiation and cell cycle exit. Defects in these organelles cause a group of wide-ranging disorders called ciliopathies. Tonicity-responsive enhancer-binding protein (TonEBP) is a pleiotropic stress protein that mediates various physiological and pathological cellular responses. TonEBP is well-known for its role in adaptation to a hypertonic environment, to which primary cilia have been reported to contribute. Furthermore, TonEBP is involved in a wide variety of other signaling pathways, such as Sonic Hedgehog and WNT signaling, that promote primary ciliogenesis, suggesting a possible regulatory role. However, the functional relationship between TonEBP and primary ciliary formation remains unclear.

METHODS

TonEBP siRNAs and TonEBP-mCherry plasmids were used to examine their effects on cell ciliation rates, assembly and disassembly processes, and regulators. Serum starvation was used as a condition to induce ciliogenesis.

RESULTS

We identified a novel pericentriolar localization for TonEBP. The results showed that TonEBP depletion facilitates the formation of primary cilia, whereas its overexpression results in fewer ciliated cells. Moreover, TonEBP controlled the expression and activity of aurora kinase A, a major negative regulator of ciliogenesis. Additionally, TonEBP overexpression inhibited the loss of CP110 from the mother centrioles during the early stages of primary cilia assembly. Finally, TonEBP regulated the localization of PCM1 and AZI1, which are necessary for primary cilia formation.

CONCLUSIONS

This study proposes a novel role for TonEBP as a pericentriolar protein that regulates the integrity of centriolar satellite components. This regulation has shown to have a negative effect on ciliogenesis. Investigations into cilium assembly and disassembly processes suggest that TonEBP acts upstream of the aurora kinase A - histone deacetylase 6 signaling pathway and affects basal body formation to control ciliogenesis. Taken together, our data proposes previously uncharacterized regulation of primary cilia assembly by TonEBP.

Emerging mechanistic understanding of cilia function in cellular signalling

Primary cilia are solitary, immotile sensory organelles present on most cells in the body that participate broadly in human health, physiology and disease. Cilia generate a unique environment for signal transduction with tight control of protein, lipid and second messenger concentrations within a relatively small compartment, enabling reception, transmission and integration of biological information. In this Review, we discuss how cilia function as signalling hubs in cell-cell communication using three signalling pathways as examples: ciliary G-protein-coupled receptors (GPCRs), the Hedgehog (Hh) pathway and polycystin ion channels. We review how defects in these ciliary signalling pathways lead to a heterogeneous group of conditions known as 'ciliopathies', including metabolic syndromes, birth defects and polycystic kidney disease. Emerging understanding of these pathways' transduction mechanisms reveals common themes between these cilia-based signalling pathways that may apply to other pathways as well. These mechanistic insights reveal how cilia orchestrate normal and pathophysiological signalling outputs broadly throughout human biology.

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.

The Immune Checkpoint Protein PD-L1 Regulates Ciliogenesis and Hedgehog Signaling

The primary cilium, an antenna-like sensory organelle that protrudes from the surface of most eukaryotic cell types, has become a signaling hub of growing interest given that defects in its structure and/or function are associated with human diseases and syndromes, known as ciliopathies. With the continuously expanding role of primary cilia in health and diseases, identifying new players in ciliogenesis will lead to a better understanding of the function of this organelle. It has been shown that the primary cilium shares similarities with the immune synapse, a highly organized structure at the interface between an antigen-presenting or target cell and a lymphocyte. Studies have demonstrated a role for known cilia regulators in immune synapse formation. However, whether immune synapse regulators modulate ciliogenesis remains elusive. Here, we find that programmed death ligand 1 (PD-L1), an immune checkpoint protein and regulator of immune synapse formation, plays a role in the regulation of ciliogenesis. We found that PD-L1 is enriched at the centrosome/basal body and Golgi apparatus of ciliated cells and depleting PD-L1 enhanced ciliogenesis and increased the accumulation of ciliary membrane trafficking proteins Rab8a, BBS5, and sensory receptor protein PC-2. Moreover, PD-L1 formed a complex with BBS5 and PC-2. In addition, we found that depletion of PD-L1 resulted in the ciliary accumulation of Gli3 and the downregulation of Gli1. Our results suggest that PD-L1 is a new player in ciliogenesis, contributing to PC-2-mediated sensory signaling and the Hh signaling cascade.

EYA protein complex is required for Wntless retrograde trafficking from endosomes to Golgi

Retrograde transport of WLS (Wntless) from endosomes to trans-Golgi network (TGN) is required for efficient Wnt secretion during development. However, the molecular players connecting endosomes to TGN during WLS trafficking are limited. Here, we identified a role for Eyes Absent (EYA) proteins during retrograde trafficking of WLS to TGN in human cell lines. By using worm, fly, and zebrafish models, we found that the EYA-secretory carrier-associated membrane protein 3 (SCAMP3) axis is evolved in vertebrates. EYAs form a complex and interact with retromer on early endosomes. Retromer-bound EYA complex recruits SCAMP3 to endosomes, which is necessary for the fusion of WLS-containing endosomes to TGN. Loss of EYA complex or SCAMP3 leads to defective transport of WLS to TGN and failed Wnt secretion. EYA mutations found in patients with hearing loss form a dysfunctional EYA-retromer complex that fails to activate Wnt signaling. These findings identify the EYA complex as a component of retrograde trafficking of WLS from the endosome to TGN.

Impaired Sonic Hedgehog Responsiveness of Induced Pluripotent Stem Cell-Derived Floor Plate Cells Carrying the LRRK2-I1371V Mutation Contributes to the Ontogenic Origin of Lower Dopaminergic Neuron Yield

Lower population of dopaminergic (DA) neurons is known to increase susceptibility to Parkinson's disease (PD), and our earlier study showed a lower yield of DA neurons in Leucine-Rich Repeat Kinase Isoleucine 1371 Valine (LRRK2-I1371V) mutation-carrying PD patient-derived induced Pluripotent Stem Cells (iPSCs). Although the role of Sonic Hedgehog (SHH) in DA neurogenesis of floor plate cells (FPCs) is known, the effect of LRRK2 mutations on SHH responsiveness of FPCs impacting DA neuronal yield has not been studied. We investigated SHH responsiveness of FPCs derived from LRRK2-I1371V PD patient iPSCs with regard to the expression of SHH receptors Patched1 (Ptch1) and Smoothened (Smo), in conjunction with nuclear Gli1 (glioma-associated oncogene 1) expression, intracellular Ca2+ rise, and cytosolic cyclic adenosine monophosphate (cAMP) levels upon SHH induction. In addition, we examined the mechanistic link with LRRK2-I1371V gain-of-function by assessing membrane fluidity and Rab8A and Rab10 phosphorylation in SH-SY5Y cells and healthy control (HC) FPCs overexpressing LRRK2-I1371V as well as FPCs. Although total expression of Ptch1 and Smo was comparable, receptor expression on cell surface was significantly lower in LRRK2-I1371V FPCs than in HC FPCs, with distinctly lower nuclear expression of the downstream transcription factor Gli1. HC-FPCs transfected with LRRK2-I1371V exhibited a similarly reduced cell surface expression of Ptch1 and Smo. Intracellular Ca2+ response was significantly lower with corresponding elevated cAMP levels in LRRK2-I1371V FPCs compared with HC FPCs upon SHH stimulation. The LRRK2-I1371V mutant FPCs and LRRK2-I1371V-transfected SH-SY5Y and HC FPCs too exhibited higher autophosphorylation of phospho LRRK2 (pLRRK2) serine1292 and serine935, as well as substrate phosphorylation of Rab8A and Rab10. Concurrent increase in membrane fluidity, accompanied by a decrease in membrane cholesterol, and lower expression of lipid raft marker caveolin 1 were also observed in them. These findings suggest that impaired SHH responsiveness of LRRK2-I1371V PD FPCs indeed leads to lower yield of DA neurons during ontogeny. Reduced cell surface expression of SHH receptors is influenced by alteration in membrane fluidity owing to the increased substrate phosphorylation of Rab8A and reduced membrane protein trafficking due to pRab10, both results of the LRRK2-I1371V mutation.

Unravelling the Mysteries of the Sonic Hedgehog Pathway in Cancer Stem Cells: Activity, Crosstalk and Regulation

The Sonic Hedgehog (Shh) signalling pathway plays a critical role in normal development and tissue homeostasis, guiding cell differentiation, proliferation, and survival. Aberrant activation of this pathway, however, has been implicated in the pathogenesis of various cancers, largely due to its role in regulating cancer stem cells (CSCs). CSCs are a subpopulation of cancer cells with the ability to self-renew, differentiate, and initiate tumour growth, contributing significantly to tumorigenesis, recurrence, and resistance to therapy. This review focuses on the intricate activity of the Shh pathway within the context of CSCs, detailing the molecular mechanisms through which Shh signalling influences CSC properties, including self-renewal, differentiation, and survival. It further explores the regulatory crosstalk between the Shh pathway and other signalling pathways in CSCs, highlighting the complexity of this regulatory network. Here, we delve into the upstream regulators and downstream effectors that modulate Shh pathway activity in CSCs. This review aims to cast a specific focus on the role of the Shh pathway in CSCs, provide a detailed exploration of molecular mechanisms and regulatory crosstalk, and discuss current and developing inhibitors. By summarising key findings and insights gained, we wish to emphasise the importance of further elucidating the interplay between the Shh pathway and CSCs to develop more effective cancer therapies.

Utilization of automated cilia analysis to characterize novel INPP5E variants in patients with non-syndromic retinitis pigmentosa

INPP5E encodes inositol polyphosphate-5-phosphatase E, an enzyme involved in regulating the phosphatidylinositol (PIP) makeup of the primary cilium membrane. Pathogenic variants in INPP5E hence cause a variety of ciliopathies: genetic disorders caused by dysfunctional cilia. While the majority of these disorders are syndromic, such as the neuronal ciliopathy Joubert syndrome, in some cases patients will present with an isolated phenotype-most commonly non-syndromic retinitis pigmentosa (RP). Here, we report two novel variants in INPP5E identified in two patients with non-syndromic RP: patient 1 with compound heterozygous variants (c.1516C > T, p.(Q506*), and c.847G > A, p.(A283T)) and patient 2 with a homozygous variant (c.1073C > T, p.(P358L)). To determine whether these variants were causative for the phenotype in the patients, automated ciliary phenotyping of patient-derived dermal fibroblasts was performed for percent ciliation, cilium length, retrograde IFT trafficking, and INPP5E localization. In both patients, a decrease in ciliary length and loss of INPP5E localization in the primary cilia were seen. With these molecular findings, we can confirm functionally that the novel variants in INPP5E are causative for the RP phenotypes seen in both patients. Additionally, this study demonstrates the usefulness of utilizing ciliary phenotyping as an assistant in ciliopathy diagnosis and phenotyping.

Non-cell-autonomous regulation of mTORC2 by Hedgehog signaling maintains lipid homeostasis

Organisms must appropriately allocate energetic resources between essential cellular processes to maintain homeostasis and in turn, maximize fitness. The nutritional and homeostatic regulators of energy homeostasis have been studied in detail; however, how developmental signals might impinge on these pathways to govern cellular metabolism is poorly understood. Here, we identify a non-canonical role for Hedgehog (Hh), a classic regulator of development, in maintaining intestinal lipid homeostasis in C. elegans . We find that expression of two Hh ligands, GRD-3 and GRD-4, is controlled by the LIN-29/EGR transcription factor in the hypodermis, where the Hh secretion factor CHE-14/Dispatched also facilitates non-cell autonomous Hh signaling. We demonstrate, using C. elegans and mouse hepatocytes, that Hh metabolic regulation does not occur through the canonical Hh transcription factor, TRA-1/GLI, but rather through non-canonical signaling that engages mTOR Complex 2 (mTORC2) in the intestine. Hh mutants display impaired lipid homeostasis, including reduced lipoprotein synthesis and fat accumulation, decreased growth, and upregulation of autophagy factors, mimicking loss of mTORC2. Additionally, we found that Hh inhibits p38 MAPK signaling in parallel to mTORC2 activation and that both pathways act together to modulate of lipid homeostasis. Our findings show a non-canonical role for Hedgehog signaling in lipid metabolism via regulation of core homeostatic pathways and reveal a new mechanism by which developmental timing events govern metabolic decisions.

Primary cilia abnormalities participate in the occurrence of spontaneous abortion through TGF-β/SMAD2/3 signaling pathway

Spontaneous abortion is the most common complication in early pregnancy, the exact etiology of most cases cannot be determined. Emerging studies suggest that mutations in ciliary genes may be associated with progression of pregnancy loss. However, the involvement of primary cilia on spontaneous abortion and the underlying molecular mechanisms remains poorly understood. We observed the number and length of primary cilia were significantly decreased in decidua of spontaneous abortion in human and lipopolysaccharide (LPS)-induced abortion mice model, accompanied with increased expression of proinflammatory cytokines interleukin (IL)-1β, IL-6, and tumor necrosis factor (TNF)-α. The length of primary cilia in human endometrial stromal cell (hESC) was significantly shortened after TNF-α treatment. Knocking down intraflagellar transport 88 (IFT88), involved in cilia formation and maintenance, promoted the expression of TNF-α. There was a reverse regulatory relationship between cilia shortening and TNF-α expression. Further research found that shortened cilia impair decidualization in hESC through transforming growth factor (TGF)-β/SMAD2/3 signaling. Primary cilia were impaired in decidua tissue of spontaneous abortion, which might be mainly caused by inflammatory injury. Primary cilia abnormalities resulted in dysregulation of TGF-β/SMAD2/3 signaling transduction and decidualization impairment, which led to spontaneous abortion.

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.

Mebendazole preferentially inhibits cilia formation and exerts anticancer activity by synergistically augmenting DNA damage

The cilium is a microtubule-based organelle that plays a pivotal role in embryonic development and maintenance of physiological functions in the human body. In addition to their function as sensors that transduce diverse extracellular signals, including growth factors, fluid flow, and physical forces, cilia are intricately involved in cell cycle regulation and preservation of DNA integrity, as their formation and resorption dynamics are tightly linked to cell cycle progression. Recently, several studies have linked defects in specific ciliary proteins to the DNA damage response. However, it remains unclear whether and how primary cilia contribute to cancer development. Mebendazole (MBZ) is an anthelmintic drug with anticancer properties in some cancer cells. MBZ is continuously being tested for clinical studies, but the precise mechanism of its anticancer activities remains unknown. Here, using Xenopus laevis embryos as a model system, we discovered that MBZ significantly hinders cilia formation and induces DNA damage. Remarkably, primary cilium-bearing cancer cells exhibited heightened vulnerability to combined treatment with MBZ and conventional anticancer drugs. Our findings shed light on the specific influence of MBZ on cilia, rather than cytosolic microtubules, in triggering DNA damage, elucidating a previously unidentified mechanism underlying potential MBZ-mediated cancer therapy.

Foraging-induced craniofacial plasticity is associated with an early, robust and dynamic transcriptional response

Phenotypic plasticity is the ability of a single genotype to vary its phenotype in response to the environment. Plasticity of the skeletal system in response to mechanical input is widely studied, but the timing of its transcriptional regulation is not well understood. Here, we used the cichlid feeding apparatus to examine the transcriptional dynamics of skeletal plasticity over time. Using three closely related species that vary in their ability to remodel bone and a panel of 11 genes, including well-studied skeletal differentiation markers and newly characterized environmentally sensitive genes, we examined plasticity at one, two, four and eight weeks following the onset of alternate foraging challenges. We found that the plastic species exhibited environment-specific bursts in gene expression beginning at one week, followed by a sharp decline in levels, while the species with more limited plasticity exhibited consistently low levels of gene expression. This trend held across nearly all genes, suggesting that it is a hallmark of the larger plasticity regulatory network. We conclude that plasticity of the cichlid feeding apparatus is not the result of slowly accumulating gene expression difference over time, but rather is stimulated by early bursts of environment-specific gene expression followed by a return to homeostatic levels.

Dual and opposing roles for the kinesin-2 motor, KIF17, in Hedgehog-dependent cerebellar development

While the kinesin-2 motors KIF3A and KIF3B have essential roles in ciliogenesis and Hedgehog (HH) signal transduction, potential role(s) for another kinesin-2 motor, KIF17, in HH signaling have yet to be explored. Here, we investigated the contribution of KIF17 to HH-dependent cerebellar development, where Kif17 is expressed in both HH-producing Purkinje cells and HH-responding cerebellar granule neuron progenitors (CGNPs). Germline Kif17 deletion in mice results in cerebellar hypoplasia due to reduced CGNP proliferation, a consequence of decreased HH pathway activity mediated through decreased Sonic HH (SHH) protein. Notably, Purkinje cell-specific Kif17 deletion partially phenocopies Kif17 germline mutants. Unexpectedly, CGNP-specific Kif17 deletion results in the opposite phenotype-increased CGNP proliferation and HH target gene expression due to altered GLI transcription factor processing. Together, these data identify KIF17 as a key regulator of HH-dependent cerebellar development, with dual and opposing roles in HH-producing Purkinje cells and HH-responding CGNPs.

Skeletal ciliopathy: pathogenesis and related signaling pathways

Cilia are tiny organelles with conserved structures and components in eukaryotic cells. Ciliopathy is a set of diseases resulting from cilium dysfunction classified into first-order and second-order ciliopathy. With the advancement of clinical diagnosis and radiography, numerous skeletal phenotypes, including polydactyly, short limbs, short ribs, scoliosis, a narrow thorax, and numerous anomalies in bone and cartilage, have been discovered in ciliopathies. Mutation in genes encoding cilia core components or other cilia-related molecules have been found in skeletal ciliopathies. Meanwhile, various signaling pathways associated with cilia and skeleton development have been deemed to be significant for the occurrence and progression of diseases. Herein, we review the structure and key components of the cilium and summarize several skeletal ciliopathies with their presumable pathology. We also emphasize the signaling pathways involved in skeletal ciliopathies, which may assist in developing potential therapies for these diseases.

Beyond cyclopamine: Targeting Hedgehog signaling for cancer intervention

Hedgehog (Hh) signaling plays a significant role in embryogenesis and several physiological processes, such as wound healing and organ homeostasis. In a pathological setting, it is associated with oncogenesis and is responsible for disease progression and poor clinical outcomes. Hedgehog signaling mediates downstream actions via Glioma Associated Oncogene Homolog (GLI) transcription factors. Inhibiting Hh signaling is an important oncological strategy in which inhibitors of the ligands SMO or GLI have been looked at. This review briefly narrates the Hh ligands, signal transduction, the target genes involved and comprehensively describes the numerous inhibitors that have been evaluated for use in various neoplastic settings.

Locational and functional characterization of PI4KB in the mouse embryo

Phosphatidylinositol 4-kinase beta (PI4KB) is a member of the PI4K family, which is mainly enriched and functions in the Golgi apparatus. The kinase domain of PI4KB catalyzes the phosphorylation of phosphatidylinositol to form phosphatidylinositol 4-phosphate, a process that regulates various sub-cellular events, such as non-vesicular cholesterol and ceramide transport, protein glycosylation, and vesicle transport, as well as cytoplasmic division. In this study, a strain of PI4KB knockout mouse, immunofluorescence, reverse transcription polymerase chain reaction and microinjection were used to characterize the cytological location and biological function of PI4KB in the mouse embryos. we found that knocking down Pi4kb in mouse embryos resulted in embryonic lethality at around embryonic day (E) 7.5. Additionally, we observed dramatic fluctuations in PI4KB expression during the development of preimplantation embryos, with high expression in the 4-cell and morula stages. PI4KB colocalized with the Golgi marker protein TGN46 in the perinuclear and cytoplasmic regions in early blastomeres. Postimplantation, PI4KB was highly expressed in the epiblast of E7.5 embryos. Treatment of embryos with PI4KB inhibitors was found to inhibit the development of the morula into a blastocyst and the normal progression of cytoplasmic division during the formation of a 4-cell embryo. These findings suggest that PI4KB plays an important role in mouse embryogenesis by regulating various intracellular vital functions of embryonic cells.

Disruption of Fuz in mouse embryos generates hypoplastic hindbrain development and reduced cranial nerve ganglia

BACKGROUND

The brain and spinal cord formation is initiated in the earliest stages of mammalian pregnancy in a highly organized process known as neurulation. Environmental or genetic interferences can impair neurulation, resulting in clinically significant birth defects known collectively as neural tube defects. The Fuz gene encodes a subunit of the CPLANE complex, a macromolecular planar polarity effector required for ciliogenesis. Ablation of Fuz in mouse embryos results in exencephaly and spina bifida, including dysmorphic craniofacial structures due to defective cilia formation and impaired Sonic Hedgehog signaling.

RESULTS

We demonstrate that knocking Fuz out during embryonic mouse development results in a hypoplastic hindbrain phenotype, displaying abnormal rhombomeres with reduced length and width. This phenotype is associated with persistent reduction of ventral neuroepithelial stiffness in a notochord adjacent area at the level of the rhombomere 5. The formation of cranial and paravertebral ganglia is also impaired in these embryos.

CONCLUSIONS

This study reveals that hypoplastic hindbrain development, identified by abnormal rhombomere morphology and persistent loss of ventral neuroepithelial stiffness, precedes exencephaly in Fuz ablated murine mutants, indicating that the gene Fuz has a critical function sustaining normal neural tube development and neuronal differentiation.

Illumination of understudied ciliary kinases

Cilia are cellular signaling hubs. Given that human kinases are central regulators of signaling, it is not surprising that kinases are key players in cilia biology. In fact, many kinases modulate ciliogenesis, which is the generation of cilia, and distinct ciliary pathways. Several of these kinases are understudied with few publications dedicated to the interrogation of their function. Recent efforts to develop chemical probes for members of the cyclin-dependent kinase like (CDKL), never in mitosis gene A (NIMA) related kinase (NEK), and tau tubulin kinase (TTBK) families either have delivered or are working toward delivery of high-quality chemical tools to characterize the roles that specific kinases play in ciliary processes. A better understanding of ciliary kinases may shed light on whether modulation of these targets will slow or halt disease onset or progression. For example, both understudied human kinases and some that are more well-studied play important ciliary roles in neurons and have been implicated in neurodevelopmental, neurodegenerative, and other neurological diseases. Similarly, subsets of human ciliary kinases are associated with cancer and oncological pathways. Finally, a group of genetic disorders characterized by defects in cilia called ciliopathies have associated gene mutations that impact kinase activity and function. This review highlights both progress related to the understanding of ciliary kinases as well as in chemical inhibitor development for a subset of these kinases. We emphasize known roles of ciliary kinases in diseases of the brain and malignancies and focus on a subset of poorly characterized kinases that regulate ciliary biology.

Primary Cilium in Neural Crest Cells Crucial for Anterior Segment Development and Corneal Avascularity

Purpose

Intraflagellar transport 46 (IFT46) is an integral subunit of the IFT-B complex, playing a key role in the assembly and maintenance of primary cilia responsible for transducing signaling pathways. Despite its predominant expression in the basal body of cilia, the precise role of Ift46 in ocular development remains undetermined. This study aimed to elucidate the impact of neural crest (NC)-specific deletion of Ift46 on ocular development.

Methods

NC-specific conditional knockout mice for Ift46 (NC-Ift46F/F) were generated by crossing Ift46F mice with Wnt1-Cre2 mice, enabling the specific deletion of Ift46 in NC-derived cells (NCCs). Sonic Hedgehog (Shh) and Notch signaling activities in NC-Ift46F/F mice were evaluated using Gli1lacZ and CBF:H2B-Venus reporter mice, respectively. Cell fate mapping was conducted using ROSAmTmG reporter mice.

Results

The deletion of Ift46 in NCCs resulted in a spectrum of ocular abnormalities, including thickened corneal stroma, hypoplasia of the anterior chamber, irregular iris morphology, and corneal neovascularization. Notably, this deletion led to reduced Shh signal activity in the periocular mesenchyme, sustained expression of key transcription factors Foxc1, Foxc2 and Pitx2, along with persistent cell proliferation. Additionally, it induced increased Notch signaling activity and the development of ectopic neovascularization within the corneal stroma.

Conclusions

The absence of primary cilia due to Ift46 deficiency in NCCs is associated with anterior segment dysgenesis (ASD) and corneal neovascularization, suggesting a potential link to Axenfeld-Rieger syndrome, a disorder characterized by ASD. This underscores the pivotal role of primary cilia in ensuring proper anterior segment development and maintaining an avascular cornea.

Hormonal regulation of cilia in the female reproductive tract

This review intends to bridge the gap between our knowledge of steroid hormone regulation of motile cilia and the potential involvement of the primary cilium focusing on the female reproductive tract functions. The review emphasizes hormonal regulation of the motile and primary cilia in the oviduct and uterus. Steroid hormones including estrogen, progesterone, and testosterone act through their cognate receptors to regulate the development and biological function of the reproductive tracts. These hormones modulate motile ciliary beating and, in some cases, primary cilia function. Dysfunction of motile or primary cilia due to genetic anomalies, hormone imbalances, or loss of steroid hormone receptors impairs mammalian fertility. However, further research on hormone modulation of ciliary function, especially in the primary cilium, and its signaling cascades will provide insights into the pathogenesis of mammalian infertility and the development of contraceptives or infertility treatments targeting primary and/or motile cilia.

Crb3 is required to organize the apical domain of multiciliated cells

Cell shape changes mainly rely on the remodeling of the actin cytoskeleton. Multiciliated cells (MCCs) of the mucociliary epidermis of Xenopus laevis embryos, as they mature, dramatically reshape their apical domain to grow cilia, in coordination with the underlying actin cytoskeleton. Crumbs (Crb) proteins are multifaceted transmembrane apical polarity proteins known to recruit actin linkers and promote apical membrane growth. Here, we identify the homeolog Crb3.L as an important player for the migration of centrioles or basal bodies (collectively centrioles/BBs) and apical domain morphogenesis in MCCs. Crb3.L is present in cytoplasmic vesicles close to the ascending centrioles/BBs, where it partially colocalizes with Rab11a. Crb3.L morpholino-mediated depletion in MCCs caused abnormal migration of centrioles/BBs, a reduction of their apical surface, disorganization of their apical actin meshwork and defective ciliogenesis. Rab11a morpholino-mediated depletion phenocopied Crb3.L loss-of-function in MCCs. Thus, the control of centrioles/BBs migration by Crb3.L might be mediated by Rab11a-dependent apical trafficking. Furthermore, we show that both phospho-activated ERM (pERM; Ezrin-Radixin-Moesin) and Crb3.L are recruited to the growing apical domain of MCCs, where Crb3.L likely anchors pERM, allowing actin-dependent expansion of the apical membrane.

Collagen VI Deficiency Impairs Tendon Fibroblasts Mechanoresponse in Ullrich Congenital Muscular Dystrophy

The pericellular matrix (PCM) is a specialized extracellular matrix that surrounds cells. Interactions with the PCM enable the cells to sense and respond to mechanical signals, triggering a proper adaptive response. Collagen VI is a component of muscle and tendon PCM. Mutations in collagen VI genes cause a distinctive group of inherited skeletal muscle diseases, and Ullrich congenital muscular dystrophy (UCMD) is the most severe form. In addition to muscle weakness, UCMD patients show structural and functional changes of the tendon PCM. In this study, we investigated whether PCM alterations due to collagen VI mutations affect the response of tendon fibroblasts to mechanical stimulation. By taking advantage of human tendon cultures obtained from unaffected donors and from UCMD patients, we analyzed the morphological and functional properties of cellular mechanosensors. We found that the length of the primary cilia of UCMD cells was longer than that of controls. Unlike controls, in UCMD cells, both cilia prevalence and length were not recovered after mechanical stimulation. Accordingly, under the same experimental conditions, the activation of the Hedgehog signaling pathway, which is related to cilia activity, was impaired in UCMD cells. Finally, UCMD tendon cells exposed to mechanical stimuli showed altered focal adhesions, as well as impaired activation of Akt, ERK1/2, p38MAPK, and mechanoresponsive genes downstream of YAP. By exploring the response to mechanical stimulation, for the first time, our findings uncover novel unreported mechanistic aspects of the physiopathology of UCMD-derived tendon fibroblasts and point at a role for collagen VI in the modulation of mechanotransduction in tendons.

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.

TMEM216 promotes primary ciliogenesis and Hedgehog signaling through the SUFU-GLI2/GLI3 axis

Primary cilia are enriched in signaling receptors, and defects in their formation or function can induce conditions such as polycystic kidney disease, postaxial hexadactyly, and microphthalmia. Mammalian Hedgehog (Hh) signaling is important in the development of primary cilia, and TMEM216, a transmembrane protein that localizes to the base of cilia, is also implicated in ciliogenesis in zebrafish. Here, we found that Tmem216-deficient mice had impaired Hh signaling and displayed typical ciliopathic phenotypes. These phenomena were also observed in cells deficient in TMEM216. Furthermore, TMEM216 interacted with core Hh signaling proteins, including SUFU, a negative regulator of Hh, and GLI2/GLI3, transcription factors downstream of Hh. The competition between TMEM216 and SUFU for binding to GLI2/GLI3 inhibited the cleavage of GLI2/GLI3 into their repressor forms, which resulted in the nuclear accumulation of full-length GLI2 and the decreased nuclear localization of cleaved GLI3, ultimately leading to the activation of Hh signaling. Together, these data suggest that the TMEM216-SUFU-GLI2/GLI3 axis plays a role in TMEM216 deficiency-induced ciliopathies and Hh signaling abnormalities.

Primary cilia and actin regulatory pathways in renal ciliopathies

Ciliopathies are a group of rare genetic disorders caused by defects to the structure or function of the primary cilium. They often affect multiple organs, leading to brain malformations, congenital heart defects, and anomalies of the retina or skeletal system. Kidney abnormalities are among the most frequent ciliopathic phenotypes manifesting as smaller, dysplastic, and cystic kidneys that are often accompanied by renal fibrosis. Many renal ciliopathies cause chronic kidney disease and often progress to end-stage renal disease, necessitating replacing therapies. There are more than 35 known ciliopathies; each is a rare hereditary condition, yet collectively they account for a significant proportion of chronic kidney disease worldwide. The primary cilium is a tiny microtubule-based organelle at the apex of almost all vertebrate cells. It serves as a "cellular antenna" surveying environment outside the cell and transducing this information inside the cell to trigger multiple signaling responses crucial for tissue morphogenesis and homeostasis. Hundreds of proteins and unique cellular mechanisms are involved in cilia formation. Recent evidence suggests that actin remodeling and regulation at the base of the primary cilium strongly impacts ciliogenesis. In this review, we provide an overview of the structure and function of the primary cilium, focusing on the role of actin cytoskeleton and its regulators in ciliogenesis. We then describe the key clinical, genetic, and molecular aspects of renal ciliopathies. We highlight what is known about actin regulation in the pathogenesis of these diseases with the aim to consider these recent molecular findings as potential therapeutic targets for renal ciliopathies.

Hedgehog signalling is involved in acquired resistance to KRASG12C inhibitors in lung cancer cells

Although KRASG12C inhibitors have shown promising activity in lung adenocarcinomas harbouring KRASG12C, acquired resistance to these therapies eventually occurs in most patients. Re-expression of KRAS is thought to be one of the main causes of acquired resistance. However, the mechanism through which cancer cells re-express KRAS is not fully understood. Here, we report that the Hedgehog signal is induced by KRASG12C inhibitors and mediates KRAS re-expression in cancer cells treated with a KRASG12C inhibitor. Further, KRASG12C inhibitors induced the formation of primary cilia and activated the Hedgehog-GLI-1 pathway. GLI-1 binds to the KRAS promoter region, enhancing KRAS promoter activity and KRAS expression. Inhibition of GLI using siRNA or the smoothened (Smo) inhibitor suppressed re-expression of KRAS in cells treated with a KRASG12C inhibitor. In addition, we demonstrate that KRASG12C inhibitors decreased Aurora kinase A (AURKA) levels in cancer cells, and inhibition of AURKA using siRNA or inhibitors led to increased expression levels of GLI-1 and KRAS even in the absence of KRAS inhibitor. Ectopic expression of AURKA attenuated the effect of KRASG12C inhibitors on the expression of GLI-1 and re-expression of KRAS. Together, these findings demonstrate the important role of AURKA, primary cilia, and Hedgehog signals in the re-expression of KRAS and therefore the induction of acquired resistance to KRASG12C inhibitors, and provide a rationale for targeting Hedgehog signalling to overcome acquired resistance to KRASG12C inhibitors.

Functions of cilia in cardiac development and disease

Errors in embryonic cardiac development are a leading cause of congenital heart defects (CHDs), including morphological abnormalities of the heart that are often detected after birth. In the past few decades, an emerging role for cilia in the pathogenesis of CHD has been identified, but this topic still largely remains an unexplored area. Mouse forward genetic screens and whole exome sequencing analysis of CHD patients have identified enrichment for de novo mutations in ciliary genes or non-ciliary genes, which regulate cilia-related pathways, linking cilia function to aberrant cardiac development. Key events in cardiac morphogenesis, including left-right asymmetric development of the heart, are dependent upon cilia function. Cilia dysfunction during left-right axis formation contributes to CHD as evidenced by the substantial proportion of heterotaxy patients displaying complex CHD. Cilia-transduced signaling also regulates later events during heart development such as cardiac valve formation, outflow tract septation, ventricle development, and atrioventricular septa formation. In this review, we summarize the role of motile and non-motile (primary cilia) in cardiac asymmetry establishment and later events during heart development.

Hedgehog Signaling in Cortical Development

The Hedgehog (Hh) pathway plays a crucial role in embryonic development, acting both as a morphogenic signal that organizes tissue formation and a potent mitogenic signal driving cell proliferation. Dysregulated Hh signaling leads to various developmental defects in the brain. This article aims to review the roles of Hh signaling in the development of the neocortex in the mammalian brain, focusing on its regulation of neural progenitor proliferation and neuronal production. The review will summarize studies on genetic mouse models that have targeted different components of the Hh pathway, such as the ligand Shh, the receptor Ptch1, the GPCR-like transducer Smo, the intracellular transducer Sufu, and the three Gli transcription factors. As key insights into the Hh signaling transduction mechanism were obtained from mouse models displaying neural tube defects, this review will also cover some studies on Hh signaling in neural tube development. The results from these genetic mouse models suggest an intriguing hypothesis that elevated Hh signaling may play a role in the gyrification of the brain in certain species. Additionally, the distinctive production of GABAergic interneurons in the dorsal cortex in the human brain may also be linked to the extension of Hh signaling from the ventral to the dorsal brain region. Overall, these results suggest key roles of Hh signaling as both a morphogenic and mitogenic signal during the forebrain development and imply the potential involvement of Hh signaling in the evolutionary expansion of the neocortex.

Development of an In Vitro Model for Inflammation Mediated Renal Toxicity Using 3D Renal Tubules and Co-Cultured Human Immune Cells

BACKGROUND

The emergence of various infectious diseases and the toxic effects of hyperinflammation by biotherapeutics have highlighted the need for in vitro preclinical models mimicking the human immune system. In vitro models studying the relationship between hyperinflammation and acute renal injury mainly rely on 2D culture systems, which have shown limitations in recapitulating kidney function. Herein, we developed an in vitro kidney toxicity model by co-culturing 3D engineered kidney proximal tubules cells (RPTEC/TERT1) with human peripheral blood mononuclear cells (PBMC).

METHODS

RPTEC/TERT1 were sandwich cultured to form 3D renal tubules for 16 days. The tubules were then co-cultured with PBMC using transwell (0.4 μm pores) for 24 h. Hyperinflammation of PBMC was induced during co-culture using polyinosinic-polycytidylic acid (polyI:C) and lipopolysaccharide (LPS) to investigate the effects of the induced hyperinflammation on the renal tubules.

RESULTS

Encapsulated RPTEC/TERT1 cells in Matrigel exhibited elevated renal function markers compared to 2D culture. The coexistence of PBMC and polyI:C induced a strong inflammatory response in the kidney cells. This hyperinflammation significantly reduced primary cilia formation and upregulated kidney injury markers along the 3D tubules. Similarly, treating co-cultured PBMC with LPS to induce hyperinflammation resulted in comparable inflammatory responses and potential kidney injury.

CONCLUSION

The model demonstrated similar changes in kidney injury markers following polyI:C and LPS treatment, indicating its suitability for detecting immune-associated kidney damage resulting from infections and biopharmaceutical applications.

The emerging role of the hedgehog signaling pathway in immunity response and autoimmune diseases

The Hedgehog (Hh) family is a prototypical morphogen involved in embryonic patterning, multi-lineage differentiation, self-renewal, morphogenesis, and regeneration. There are studies that have demonstrated that the Hh signaling pathway differentiates developing T cells into MHC-restricted self-antigen tolerant T cells in a concentration-dependent manner in the thymus. Whereas Hh signaling pathway is not required in the differentiation of B cells but is indispensable in maintaining the regeneration of hematopoietic stem cells (HSCs) and the viability of germinal centers (GCs) B cells. The Hh signaling pathway exerts both positive and negative effects on immune responses, which involves activating human peripheral CD4+ T cells, regulating the accumulation of natural killer T (NKT) cells, recruiting and activating macrophages, increasing CD4+Foxp3+ regulatory T cells in the inflammation sites to sustain homeostasis. Hedgehog signaling is involved in the patterning of the embryo, as well as homeostasis of adult tissues. Therefore, this review aims to highlight evidence for Hh signaling in the differentiation, function of immune cells and autoimmune disease. Targeting Hh signaling promises to be a novel, alternative or adjunct approach to treating tumors and autoimmune diseases.

Functional heterogeneity of Wnt-responsive and Hedgehog-responsive neural stem cells in the murine adult hippocampus

Neural stem cells (NSCs) in the adult hippocampus are composed of multiple subpopulations. However, their origin and functional heterogeneity are still unclear. Here, we found that the contribution of murine Wnt-responsive (Axin2+) and Hedgehog-responsive (Gli1+) embryonic neural progenitors to adult NSCs started from early and late postnatal stages, respectively. Axin2+ adult NSCs were intended to actively proliferate, whereas Gli1+ adult NSCs were relatively quiescent and responsive to external stimuli. Moreover, Gli1+ NSC-derived adult-born neurons exhibited more complex dendritic arborization and connectivity than Axin2+ NSC-derived ones. Importantly, genetic cell ablation analysis identified that Axin2+ and Gli1+ adult NSCs were involved in hippocampus-dependent learning, but only Axin2+ adult NSCs were engaged in buffering stress responses and depressive behavior. Together, our study not only defined the heterogeneous multiple origins of adult NSCs but also advanced the concept that different subpopulations of adult NSCs may function differently.

Putative Role of Cholesterol in Shaping the Structural and Functional Dynamics of Smoothened (SMO)

The smoothened (SMO) receptor belongs to the superfamily of class F G protein-coupled receptors (GPCRs) and is a potential drug target in several types of cancer. It has two ligand binding sites, respectively, in the cysteine-rich domain (CRD) and the transmembrane domain (TMD). It has been shown that cholesterol is important for its activation and function. However, the molecular-level understanding of SMO dynamics in the presence of cholesterol has not been explored in sufficient detail. In this work, we have carried out atomistic molecular dynamics simulations totaling 3.6 μs to analyze the effect of cholesterol binding to TMD and/or CRD on the structure and dynamics of the SMO receptor. Our results show that the presence of cholesterol in the CRD and TMD, respectively, alters the conformational dynamics of SMO differently. We reported that the reorganization of the D-R-E network at the extracellular end of the TMD is important for the high activity of SMO. In general, the transmembrane helices 5, 6, and 7 and helix 8 are most affected, which, in turn, leads to changes in the CRD and intracellular cytoplasmic domain (ICD) dynamics patterns depending on the presence or absence of cholesterol in the CRD and/or the TMD. We have also reported that the interaction of membrane lipids with SMO is different in different SMO states. These results agree with the experimental structural observations and data of cholesterol-bound and unbound structures of SMO and add to our molecular understanding of the SMO-cholesterol interaction.

Absence of the primary cilia formation gene Talpid3 impairs muscle stem cell function

Skeletal muscle stem cells (MuSC) are crucial for tissue homoeostasis and repair after injury. Following activation, they proliferate to generate differentiating myoblasts. A proportion of cells self-renew, re-enter the MuSC niche under the basal lamina outside the myofiber and become quiescent. Quiescent MuSC have a primary cilium, which is disassembled upon cell cycle entry. Ex vivo experiments suggest cilia are important for MuSC self-renewal, however, their requirement for muscle regeneration in vivo remains poorly understood. Talpid3 (TA3) is essential for primary cilia formation and Hedgehog (Hh) signalling. Here we use tamoxifen-inducible conditional deletion of TA3 in MuSC (iSC-KO) and show that regeneration is impaired in response to cytotoxic injury. Depletion of MuSC after regeneration suggests impaired self-renewal, also consistent with an exacerbated phenotype in TA3iSC-KO mice after repeat injury. Single cell transcriptomics of MuSC progeny isolated from myofibers identifies components of several signalling pathways, which are deregulated in absence of TA3, including Hh and Wnt. Pharmacological activation of Wnt restores muscle regeneration, while purmorphamine, an activator of the Smoothened (Smo) co-receptor in the Hh pathway, has no effect. Together, our data show that TA3 and primary cilia are important for MuSC self-renewal and pharmacological treatment can efficiently restore muscle regeneration.

Empagliflozin suppresses hedgehog pathway, alleviates ER stress, and ameliorates hepatic fibrosis in rats

Worldwide mortality from hepatic fibrosis remains high, due to hepatocellular carcinoma and end stage liver failure. The progressive nature of hepatic fibrosis from inflammation to cicatrized tissues warrants subtle intervention with pharmacological agents that hold potential. Empagliflozin (Empa), a novel hypoglycemic drug with antioxidant and anti-inflammatory properties, has lately been proposed to have additional antifibrotic activities. In the current study, we examined the antifibrotic effect of the Empa through modulating the activity of hepatic stellate cells by hedgehog (Hh) pathway. We also assessed the markers of inflammatory response and endoplasmic reticulum (ER) stress. Male Albino rats were treated with either CCl4 (0.4 mg/kg twice/week) and/or Empa (10 mg/kg/day) for eight weeks. In this study, CCl4 rats had active Hh signaling as indicated by overexpression of Patched 1, Smoothened and Glioblastoma-2. CCl4 induced ER stress as CHOP expression was upregulated and ERAD was downregulated. CCl4-induced inflammatory response was demonstrated through increased levels of TNF-α, IL-6 and mRNA levels of IL-17 while undetectable expression of IL-10. Conversely, Empa elicited immunosuppression, suppressed the expression of Hh markers, and reversed markers of ER stress. In conclusion, Empa suppressed CCl4-induced Hh signaling and proinflammatory response, meanwhile embraced ER stress in the hepatic tissues, altogether provided hepatoprotection.

Emerging principles of primary cilia dynamics in controlling tissue organization and function

Primary cilia project from the surface of most vertebrate cells and are key in sensing extracellular signals and locally transducing this information into a cellular response. Recent findings show that primary cilia are not merely static organelles with a distinct lipid and protein composition. Instead, the function of primary cilia relies on the dynamic composition of molecules within the cilium, the context-dependent sensing and processing of extracellular stimuli, and cycles of assembly and disassembly in a cell- and tissue-specific manner. Thereby, primary cilia dynamically integrate different cellular inputs and control cell fate and function during tissue development. Here, we review the recently emerging concept of primary cilia dynamics in tissue development, organization, remodeling, and function.

Ligand-dependent hedgehog signaling maintains an undifferentiated, malignant osteosarcoma phenotype

TP53 and RB1 loss-of-function mutations are common in osteosarcoma. During development, combined loss of TP53 and RB1 function leads to downregulation of autophagy and the aberrant formation of primary cilia, cellular organelles essential for the transmission of canonical Hedgehog (Hh) signaling. Excess cilia formation then leads to hypersensitivity to Hedgehog (Hh) ligand signaling. In mouse and human models, we now show that osteosarcomas with mutations in TP53 and RB1 exhibit enhanced ligand-dependent Hh pathway activation through Smoothened (SMO), a transmembrane signaling molecule required for activation of the canonical Hh pathway. This dependence is mediated by hypersensitivity to Hh ligand and is accompanied by impaired autophagy and increased primary cilia formation and expression of Hh ligand in vivo. Using a conditional genetic mouse model of Trp53 and Rb1 inactivation in osteoblast progenitors, we further show that deletion of Smo converts the highly malignant osteosarcoma phenotype to benign, well differentiated bone tumors. Conversely, conditional overexpression of SHH ligand, or a gain-of-function SMO mutant in committed osteoblast progenitors during development blocks terminal bone differentiation. Finally, we demonstrate that the SMO antagonist sonidegib (LDE225) induces growth arrest and terminal differentiation in vivo in osteosarcomas that express primary cilia and Hh ligand combined with mutations in TP53. These results provide a mechanistic framework for aberrant Hh signaling in osteosarcoma based on defining mutations in the tumor suppressor, TP53.

Towards modular engineering of cell signalling: Topographically-textured microparticles induce osteogenesis via activation of canonical hedgehog signalling

Polymer microparticles possess great potential as functional building blocks for advanced bottom-up engineering of complex tissues. Tailoring the three-dimensional architectural features of culture substrates has been shown to induce osteogenesis in mesenchymal stem cells in vitro, but the molecular mechanisms underpinning this remain unclear. This study proposes a mechanism linking the activation of Hedgehog signalling to the osteoinductive effect of surface-engineered, topographically-textured polymeric microparticles. In this study, mesenchymal progenitor C3H10T1/2 cells were cultured on smooth and dimpled poly(D,l-lactide) microparticles to assess differences in viability, cellular morphology, proliferation, and expression of a range of Hedgehog signalling components and osteogenesis-related genes. Dimpled microparticles induced osteogenesis and activated the Hedgehog signalling pathway relative to smooth microparticles and 2D-cultured controls without the addition of exogenous biochemical factors. We observed upregulation of the osteogenesis markers Runt-related transcription factor2 (Runx2) and bone gamma-carboxyglutamate protein 2 (Bglap2), as well as the Hedgehog signalling components, glioma associated oncogene homolog 1 (Gli1), Patched1 (Ptch1), and Smoothened (Smo). Treatment with the Smo antagonist KAAD-cyclopamine confirmed the involvement of Smo in Gli1 target gene activation, with a significant reduction in the expression of Gli1, Runx2 and Bglap2 (p ≤ 0.001) following KAAD-cyclopamine treatment. Overall, our study demonstrates the role of the topographical microenvironment in the modulation of Hedgehog signalling, highlighting the potential for tailoring substrate topographical design to offer cell-instructive 3D microenvironments. Topographically-textured microparticles allow the modulation of Hedgehog signalling in vitro without adding exogenous biochemical agonists, thereby eliminating potential confounding artefacts in high-throughput drug screening applications.

Signaling Pathways and Therapeutic Strategies in Advanced Basal Cell Carcinoma

Non-melanoma skin cancers (NMSCs) are the most common human neoplasms world-wide. In detail, basal cell carcinoma (BCC) is the most frequent malignancy in the fair-skinned population. The incidence of BCC remains difficult to assess due to the poor registration practice; however, it has been increasing in the last few years. Approximately, 85% of sporadic BCCs carry mutations in Hedgehog pathway genes, especially in PTCH, SUFU and SMO genes, which lead to the aberrant activation of GLI transcriptional factors, typically silent in cells of adult individuals. The management of advanced BCC (aBCC), both metastatic (mBCC) and locally advanced BCC (laBCC), not candidates for surgical excision or radiotherapy, remains challenging. The discovery of mutations in the Hh signaling pathway has paved the way for the development of Hh pathway inhibiting agents, such as vismodegib and sonidegib, which have represented a breakthrough in the aBCC management. However, the use of these agents is limited by the frequent occurrence of adverse events or the development of drug resistance. In this review, we thoroughly describe the current knowledge regarding the available options for the pharmacological management of aBCCs and provide a forward-looking update on novel therapeutic strategies that could enrich the therapeutic armamentarium of BCC in the near future.

Signaling pathways and targeted therapeutic strategies for polycystic ovary syndrome

Polycystic ovary syndrome (PCOS) is the most common endocrine disorder among women of reproductive age. Although promising strides have been made in the field of PCOS over the past decades, the distinct etiologies of this syndrome are not fully elucidated. Prenatal factors, genetic variation, epigenetic mechanisms, unhealthy lifestyles, and environmental toxins all contribute to the development of this intricate and highly heterogeneous metabolic, endocrine, reproductive, and psychological disorder. Moreover, interactions between androgen excess, insulin resistance, disruption to the hypothalamic-pituitary-ovary (HPO) axis, and obesity only make for a more complex picture. In this review, we investigate and summarize the related molecular mechanisms underlying PCOS pathogenesis from the perspective of the level of signaling pathways, including PI3K/Akt, TGF-β/Smads, Wnt/β-catenin, and Hippo/YAP. Additionally, this review provides an overview of prospective therapies, such as exosome therapy, gene therapy, and drugs based on traditional Chinese medicine (TCM) and natural compounds. By targeting these aberrant pathways, these interventions primarily alleviate inflammation, insulin resistance, androgen excess, and ovarian fibrosis, which are typical symptoms of PCOS. Overall, we hope that this paper will pave the way for better understanding and management of PCOS in the future.

Pioneering therapies for post-infarction angiogenesis: Insight into molecular mechanisms and preclinical studies

Acute myocardial infarction (MI), despite significant progress in its treatment, remains a leading cause of chronic heart failure and cardiovascular events such as cardiac arrest. Promoting angiogenesis in the myocardial tissue after MI to restore blood flow in the ischemic and hypoxic tissue is considered an effective treatment strategy. The repair of the myocardial tissue post-MI involves a robust angiogenic response, with mechanisms involved including endothelial cell proliferation and migration, capillary growth, changes in the extracellular matrix, and stabilization of pericytes for neovascularization. In this review, we provide a detailed overview of six key pathways in angiogenesis post-MI: the PI3K/Akt/mTOR signaling pathway, the Notch signaling pathway, the Wnt/β-catenin signaling pathway, the Hippo signaling pathway, the Sonic Hedgehog signaling pathway, and the JAK/STAT signaling pathway. We also discuss novel therapeutic approaches targeting these pathways, including drug therapy, gene therapy, protein therapy, cell therapy, and extracellular vesicle therapy. A comprehensive understanding of these key pathways and their targeted therapies will aid in our understanding of the pathological and physiological mechanisms of angiogenesis after MI and the development and application of new treatment strategies.

Increasing Ciliary ARL13B Expression Drives Active and Inhibitor-Resistant Smoothened and GLI into Glioma Primary Cilia

ADP-ribosylation factor-like protein 13B (ARL13B), a regulatory GTPase and guanine exchange factor (GEF), enriches in primary cilia and promotes tumorigenesis in part by regulating Smoothened (SMO), GLI, and Sonic Hedgehog (SHH) signaling. Gliomas with increased ARL13B, SMO, and GLI2 expression are more aggressive, but the relationship to cilia is unclear. Previous studies have showed that increasing ARL13B in glioblastoma cells promoted ciliary SMO accumulation, independent of exogenous SHH addition. Here, we show that SMO accumulation is due to increased ciliary, but not extraciliary, ARL13B. Increasing ARL13B expression promotes the accumulation of both activated SMO and GLI2 in glioma cilia. ARL13B-driven increases in ciliary SMO and GLI2 are resistant to SMO inhibitors, GDC-0449, and cyclopamine. Surprisingly, ARL13B-induced changes in ciliary SMO/GLI2 did not correlate with canonical changes in downstream SHH pathway genes. However, glioma cell lines whose cilia overexpress WT but not guanine exchange factor-deficient ARL13B, display reduced INPP5e, a ciliary membrane component whose depletion may favor SMO/GLI2 enrichment. Glioma cells overexpressing ARL13B also display reduced ciliary intraflagellar transport 88 (IFT88), suggesting that altered retrograde transport could further promote SMO/GLI accumulation. Collectively, our data suggest that factors increasing ARL13B expression in glioma cells may promote both changes in ciliary membrane characteristics and IFT proteins, leading to the accumulation of drug-resistant SMO and GLI. The downstream targets and consequences of these ciliary changes require further investigation.

Cross-species analysis of SHH medulloblastoma models reveals significant inhibitory effects of trametinib on tumor progression

Sonic Hedgehog (SHH) medulloblastomas (MBs) exhibit an intermediate prognosis and extensive intertumoral heterogeneity. While SHH pathway antagonists are effective in post-pubertal patients, younger patients exhibit significant side effects, and tumors that harbor mutations in downstream SHH pathway genes will be drug resistant. Thus, novel targeted therapies are needed. Here, we performed preclinical testing of the potent MEK inhibitor (MEKi) trametinib on tumor properties across 2 human and 3 mouse SHH MB models in vitro and in 3 orthotopic MB xenograft models in vivo. Trametinib significantly reduces tumorsphere size, stem/progenitor cell proliferation, viability, and migration. RNA-sequencing on human and mouse trametinib treated cells corroborated these findings with decreased expression of cell cycle, stem cell pathways and SHH-pathway related genes concomitant with increases in genes associated with cell death and ciliopathies. Importantly, trametinib also decreases tumor growth and increases survival in vivo. Cell cycle related E2F target gene sets are significantly enriched for genes that are commonly downregulated in both trametinib treated tumorspheres and primary xenografts. However, IL6/JAK STAT3 and TNFα/NFκB signaling gene sets are specifically upregulated following trametinib treatment in vivo indicative of compensatory molecular changes following long-term MEK inhibition. Our study reveals a novel role for trametinib in effectively attenuating SHH MB tumor progression and warrants further investigation of this potent MEK1/2 inhibitor either alone or in combination with other targeted therapies for the treatment of SHH MB exhibiting elevated MAPK pathway activity.

Brain mosaicism of hedgehog signalling and other cilia genes in hypothalamic hamartoma

Hypothalamic hamartoma (HH) is a rare benign developmental brain lesion commonly associated with a well characterized epilepsy phenotype. Most individuals with HH are non-syndromic without additional developmental anomalies nor a family history of disease. Nonetheless, HH is a feature of Pallister-Hall (PHS) and Oro-Facial-Digital Type VI (OFD VI) syndromes, both characterized by additional developmental anomalies. Initial genetic of analysis HH began with syndromic HH, where germline inherited or de novo variants in GLI3, encoding a central transcription factor in the sonic hedgehog (Shh) signalling pathway, were identified in most individuals with PHS. Following these discoveries in syndromic HH, the hypothesis that post-zygotic mosaicism in related genes may underly non-syndromic HH was tested. We discuss the identified mosaic variants within individuals with non-syndromic HH, review the analytical methodologies and diagnostic yields, and explore understanding of the functional role of the implicated genes with respect to Shh signalling, and cilia development and function. We also outline future challenges in studying non-syndromic HH and suggest potential novel strategies to interrogate brain mosaicism in HH.

Cellular and molecular mechanisms of Hedgehog signalling

The Hedgehog signalling pathway has crucial roles in embryonic tissue patterning, postembryonic tissue regeneration, and cancer, yet aspects of Hedgehog signal transmission and reception have until recently remained unclear. Biochemical and structural studies surprisingly reveal a central role for lipids in Hedgehog signalling. The signal - Hedgehog protein - is modified by cholesterol and palmitate during its biogenesis, thereby necessitating specialized proteins such as the transporter Dispatched and several lipid-binding carriers for cellular export and receptor engagement. Additional lipid transactions mediate response to the Hedgehog signal, including sterol activation of the transducer Smoothened. Access of sterols to Smoothened is regulated by the apparent sterol transporter and Hedgehog receptor Patched, whose activity is blocked by Hedgehog binding. Alongside these lipid-centric mechanisms and their relevance to pharmacological pathway modulation, we discuss emerging roles of Hedgehog pathway activity in stem cells or their cellular niches, with translational implications for regeneration and restoration of injured or diseased tissues.

Sonic hedgehog signaling in craniofacial development

Mutations in SHH and several other genes encoding components of the Hedgehog signaling pathway have been associated with holoprosencephaly syndromes, with craniofacial anomalies ranging in severity from cyclopia to facial cleft to midfacial and mandibular hypoplasia. Studies in animal models have revealed that SHH signaling plays crucial roles at multiple stages of craniofacial morphogenesis, from cranial neural crest cell survival to growth and patterning of the facial primordia to organogenesis of the palate, mandible, tongue, tooth, and taste bud formation and homeostasis. This article provides a summary of the major findings in studies of the roles of SHH signaling in craniofacial development, with emphasis on recent advances in the understanding of the molecular and cellular mechanisms regulating the SHH signaling pathway activity and those involving SHH signaling in the formation and patterning of craniofacial structures.

Transcriptional regulation by the NSL complex enables diversification of IFT functions in ciliated versus nonciliated cells

Members of the NSL histone acetyltransferase complex are involved in multiorgan developmental syndromes. While the NSL complex is known for its importance in early development, its role in fully differentiated cells remains enigmatic. Using a kidney-specific model, we discovered that deletion of NSL complex members KANSL2 or KANSL3 in postmitotic podocytes led to catastrophic kidney dysfunction. Systematic comparison of two primary differentiated cell types reveals the NSL complex as a master regulator of intraciliary transport genes in both dividing and nondividing cells. NSL complex ablation led to loss of cilia and impaired sonic hedgehog pathway in ciliated fibroblasts. By contrast, nonciliated podocytes responded with altered microtubule dynamics and obliterated podocyte functions. Finally, overexpression of wild-type but not a double zinc finger (ZF-ZF) domain mutant of KANSL2 rescued the transcriptional defects, revealing a critical function of this domain in NSL complex assembly and function. Thus, the NSL complex exhibits bifurcation of functions to enable diversity of specialized outcomes in differentiated cells.

Hedgehog signaling in tissue homeostasis, cancers, and targeted therapies

The past decade has seen significant advances in our understanding of Hedgehog (HH) signaling pathway in various biological events. HH signaling pathway exerts its biological effects through a complex signaling cascade involved with primary cilium. HH signaling pathway has important functions in embryonic development and tissue homeostasis. It plays a central role in the regulation of the proliferation and differentiation of adult stem cells. Importantly, it has become increasingly clear that HH signaling pathway is associated with increased cancer prevalence, malignant progression, poor prognosis and even increased mortality. Understanding the integrative nature of HH signaling pathway has opened up the potential for new therapeutic targets for cancer. A variety of drugs have been developed, including small molecule inhibitors, natural compounds, and long non-coding RNA (LncRNA), some of which are approved for clinical use. This review outlines recent discoveries of HH signaling in tissue homeostasis and cancer and discusses how these advances are paving the way for the development of new biologically based therapies for cancer. Furthermore, we address status quo and limitations of targeted therapies of HH signaling pathway. Insights from this review will help readers understand the function of HH signaling in homeostasis and cancer, as well as opportunities and challenges of therapeutic targets for cancer.