Endocannabinoids are conserved inhibitors of the Hedgehog pathway

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.

Perturbation of 3D nuclear architecture, epigenomic dysregulation and aging, and cannabinoid synaptopathy reconfigures conceptualization of cannabinoid pathophysiology: part 1-aging and epigenomics

Much recent attention has been directed toward the spatial organization of the cell nucleus and the manner in which three-dimensional topologically associated domains and transcription factories are epigenetically coordinated to precisely bring enhancers into close proximity with promoters to control gene expression. Twenty lines of evidence robustly implicate cannabinoid exposure with accelerated organismal and cellular aging. Aging has recently been shown to be caused by increased DNA breaks. These breaks rearrange and maldistribute the epigenomic machinery to weaken and reverse cellular differentiation, cause genome-wide DNA demethylation, reduce gene transcription, and lead to the inhibition of developmental pathways, which contribute to the progressive loss of function and chronic immune stimulation that characterize cellular aging. Both cell lineage-defining superenhancers and the superanchors that control them are weakened. Cannabis exposure phenocopies the elements of this process and reproduces DNA and chromatin breakages, reduces the DNA, RNA protein and histone synthesis, interferes with the epigenomic machinery controlling both DNA and histone modifications, induces general DNA hypomethylation, and epigenomically disrupts both the critical boundary elements and the cohesin motors that create chromatin loops. This pattern of widespread interference with developmental programs and relative cellular dedifferentiation (which is pro-oncogenic) is reinforced by cannabinoid impairment of intermediate metabolism (which locks in the stem cell-like hyper-replicative state) and cannabinoid immune stimulation (which perpetuates and increases aging and senescence programs, DNA damage, DNA hypomethylation, genomic instability, and oncogenesis), which together account for the diverse pattern of teratologic and carcinogenic outcomes reported in recent large epidemiologic studies in Europe, the USA, and elsewhere. It also accounts for the prominent aging phenotype observed clinically in long-term cannabis use disorder and the 20 characteristics of aging that it manifests. Increasing daily cannabis use, increasing use in pregnancy, and exponential dose-response effects heighten the epidemiologic and clinical urgency of these findings. Together, these findings indicate that cannabinoid genotoxicity and epigenotoxicity are prominent features of cannabis dependence and strongly indicate coordinated multiomics investigations of cannabinoid genome-epigenome-transcriptome-metabolome, chromatin conformation, and 3D nuclear architecture. Considering the well-established exponential dose-response relationships, the diversity of cannabinoids, and the multigenerational nature of the implications, great caution is warranted in community cannabinoid penetration.

Combined exposure to alcohol and cannabis during development: Mechanisms and outcomes

Exposure to substances of abuse during pregnancy can have long-lasting effects on offspring. Alcohol is one of the most widely used substances of abuse that leads to the most severe consequences. Recent studies in the United States, Canada, and the United Kingdom showed that between 1% and 7% of all children exhibit signs and symptoms of fetal alcohol spectrum disorder (FASD). Despite preventive campaigns, the rate of children with FASD has not decreased during recent decades. Alcohol consumption often accompanies exposure to such drugs as tobacco, cocaine, opioids, and cannabis. These interactions can be synergistic and exacerbate the deleterious consequences of developmental alcohol exposure. The present review focuses on interactions between alcohol and cannabis exposure and the potential consequences of these interactions.

Embryonic Ethanol but Not Cannabinoid Exposure Affects Zebrafish Cardiac Development via Agrin and Sonic Hedgehog Interaction

Recent studies demonstrate the adverse effects of cannabinoids on development, including via pathways shared with ethanol exposure. Our laboratory has shown that both the nervous system and cardiac development are dependent on agrin modulation of sonic hedgehog (shh) and fibroblast growth factor (Fgf) signaling pathways. As both ethanol and cannabinoids impact these signaling molecules, we examined their role on zebrafish heart development. Zebrafish embryos were exposed to a range of ethanol and/or cannabinoid receptor 1 and 2 agonist concentrations in the absence or presence of morpholino oligonucleotides that disrupt agrin or shh expression. In situ hybridization was employed to analyze cardiac marker gene expression. Exposure to cannabinoid receptor agonists disrupted midbrain-hindbrain boundary development, but had no effect on heart development, as assessed by the presence of cardiac edema or the altered expression of cardiac marker genes. In contrast, exposure to 1.5% ethanol induced cardiac edema and the altered expression of cardiac marker genes. Combined exposure to agrin or shh morpholino and 0.5% ethanol disrupted the cmlc2 gene expression pattern, with the restoration of the normal expression following shh mRNA overexpression. These studies provide evidence that signaling pathways critical to heart development are sensitive to ethanol exposure, but not cannabinoids, during early zebrafish embryogenesis.

The endocannabinoid system's involvement in motor development relies on cannabinoid receptors, TRP channels, and Sonic Hedgehog signaling

The endocannabinoid system (eCS) plays critical roles in locomotor function and motor development; however, the roles of non-canonical cannabinoid receptor systems such as transient receptor potential (TRP) channels and the Sonic Hedgehog (SHH) signaling pathway in conjunction with the eCS in sensorimotor development remains enigmatic. To investigate the involvement of canonical and non-canonical cannabinoid receptors, TRP channels, and the SHH pathway in the development of sensorimotor function in zebrafish, we treated developing animals with pharmacological inhibitors of the CB1R, CB2R, TRPA1/TRPV1/TRPM8, and a smoothened (SMO) agonist, along with inhibitors of the eCS catabolic enzymes fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL) during the first ~24 h of zebrafish embryogenesis. Locomotor function was examined by assessing touch-evoked escape swimming at 2 days post-fertilization. We report that FAAH inhibition had no effect on swimming while MAGL inhibition using JZL 184 reduced swimming distance and the dual FAAH/MAGL inhibitor JZL 195 impaired swimming distance and mean swimming velocity. The CB1R antagonist AM 251 prevented locomotor deficits caused by eCS perturbation but the CB2R antagonist AM 630 did not. Inhibition of TRPA1/TRPV1/TRPM8 using AMG 9090 rescued the locomotor reductions caused by FAAH/MAGL inhibition, but not by MAGL inhibition alone. The SMO agonist purmorphamine attenuated the effects of JZL 184 and JZL 195 on swimming distance, but not mean velocity. Together, these findings provide one of the first investigations examining the interactions between the eCS and its non-canonical receptor systems in vertebrate motor development.

The emerging roles of Hedgehog signaling in tumor immune microenvironment

The Hedgehog (Hh) signaling pathway is pervasively involved in human malignancies, making it an effective target for cancer treatment for decades. In addition to its direct role in regulating cancer cell attributes, recent work indicates that it has an immunoregulatory effect on tumor microenvironments. An integrated understanding of these actions of Hh signaling pathway in tumor cells and tumor microenvironments will pave the way for novel tumor treatments and further advances in anti-tumor immunotherapy. In this review, we discuss the most recent research about Hh signaling pathway transduction, with a particular emphasis on its role in modulating tumor immune/stroma cell phenotype and function, such as macrophage polarity, T cell response, and fibroblast activation, as well as their mutual interactions between tumor cells and nonneoplastic cells. We also summarize the recent advances in the development of Hh pathway inhibitors and nanoparticle formulation for Hh pathway modulation. We suggest that targeting Hh signaling effects on both tumor cells and tumor immune microenvironments could be more synergistic for cancer treatment.

Gene-environment interactions in birth defect etiology: Challenges and opportunities

Birth defects are relatively common congenital outcomes that significantly impact affected individuals, their families, and communities. Effective development and deployment of prevention and therapeutic strategies for these conditions requires sufficient understanding of etiology, including underlying genetic and environmental causes. Tremendous progress has been made in defining the genetic basis of familial and syndromic forms of birth defects. However, the majority of birth defect cases are considered nonsyndromic and thought to result from multifactorial gene-environment interactions. While substantial advances have been made in elucidating the genetic landscape of these etiologically complex conditions, significant biological and technical constraints have stymied progress toward a refined knowledge of environmental risk factors. Defining specific gene-environment interactions in birth defect etiology is even more challenging. However, progress has been made, including demonstration of critical proofs of concept and development of new conceptual and technical approaches for resolving complex gene-environment interactions. In this review, we discuss current views of multifactorial birth defect etiology, comparing them with other diseases that also involve gene-environment interactions, including primary immunodeficiency and cancer. We describe how various model systems have illuminated mechanisms of multifactorial etiology and these models' individual strengths and weaknesses. Finally, suggestions for areas of future emphasis are proposed.

Hepatocyte Smoothened Activity Controls Susceptibility to Insulin Resistance and Nonalcoholic Fatty Liver Disease

BACKGROUND & AIMS

Nonalcoholic steatohepatitis (NASH), a leading cause of cirrhosis, strongly associates with the metabolic syndrome, an insulin-resistant proinflammatory state that disrupts energy balance and promotes progressive liver degeneration. We aimed to define the role of Smoothened (Smo), an obligatory component of the Hedgehog signaling pathway, in controlling hepatocyte metabolic homeostasis and, thereby, susceptibility to NASH.

METHODS

We conditionally deleted Smo in hepatocytes of healthy chow-fed mice and performed metabolic phenotyping, coupled with single-cell RNA sequencing (RNA-seq), to characterize the role of hepatocyte Smo in regulating basal hepatic and systemic metabolic homeostasis. Liver RNA-seq datasets from 2 large human cohorts were also analyzed to define the relationship between Smo and NASH susceptibility in people.

RESULTS

Hepatocyte Smo deletion inhibited the Hedgehog pathway and promoted fatty liver, hyperinsulinemia, and insulin resistance. We identified a plausible mechanism whereby inactivation of Smo stimulated the mTORC1-SREBP1c signaling axis, which promoted lipogenesis while inhibiting the hepatic insulin cascade. Transcriptomics of bulk and single Smo-deficient hepatocytes supported suppression of insulin signaling and also revealed molecular abnormalities associated with oxidative stress and mitochondrial dysfunction. Analysis of human bulk RNA-seq data revealed that Smo expression was (1) highest in healthy livers, (2) lower in livers with NASH than in those with simple steatosis, (3) negatively correlated with markers of insulin resistance and liver injury, and (4) declined progressively as fibrosis severity worsened.

CONCLUSIONS

The Hedgehog pathway controls insulin sensitivity and energy homeostasis in adult livers. Loss of hepatocyte Hedgehog activity induces hepatic and systemic metabolic stress and enhances susceptibility to NASH by promoting hepatic lipoxicity and insulin resistance.

Cannabinoid receptor 2 (Cb2r) mediates cannabinol (CBN) induced developmental defects in zebrafish

Of the three primary cannabinoids in cannabis: Δ⁹-Tetrahydrocannabinol (Δ⁹-THC), cannabidiol (CBD) and cannabinol (CBN), very little is known about the actions of CBN, the primary oxidative metabolite of THC. Our goal was to determine if CBN exposure during gastrulation alters embryonic development, and if so, does it act via the canonical cannabinoid receptors. Zebrafish embryos were exposed to CBN during gastrulation and exhibited dose-dependent malformations, increased mortality, decreased locomotion and a reduction in motor neuron branching. Moreover, larva showed a significant reduction in the response to sound stimuli. CBN exposure altered the development of hair cells associated with otic vesicles and the lateral line. Pharmacological block of Cb2rs with AM 630 or JTE 907 prevented many of the CBN-induced developmental defects, while block of Cb1rs with AM 251 or CP 945598 had little or no effect. Altogether we show that embryonic exposure to CBN results in alterations in embryonic growth, neuronal and hair cell development, physiology and behavior via Cb2r-mediated mechanisms.

Fusion protein strategies for cryo-EM study of G protein-coupled receptors

Single particle cryogenic-electron microscopy (cryo-EM) is used extensively to determine structures of activated G protein-coupled receptors (GPCRs) in complex with G proteins or arrestins. However, applying it to GPCRs without signaling proteins remains challenging because most receptors lack structural features in their soluble domains to facilitate image alignment. In GPCR crystallography, inserting a fusion protein between transmembrane helices 5 and 6 is a highly successful strategy for crystallization. Although a similar strategy has the potential to broadly facilitate cryo-EM structure determination of GPCRs alone without signaling protein, the critical determinants that make this approach successful are not yet clear. Here, we address this shortcoming by exploring different fusion protein designs, which lead to structures of antagonist bound A2A adenosine receptor at 3.4 Å resolution and unliganded Smoothened at 3.7 Å resolution. The fusion strategies explored here are likely applicable to cryo-EM interrogation of other GPCRs and small integral membrane proteins.

Promoting Oligodendrocyte Differentiation from Human Induced Pluripotent Stem Cells by Activating Endocannabinoid Signaling for Treating Spinal Cord Injury

Transplantation of oligodendrocyte progenitor cell (OPC) at the injury site is being developed as a potential therapeutic strategy for promoting remyelination and locomotor function recovery after spinal cord injury (SCI). To this end, the development of expandable and functional human OPCs is crucial for testing their efficacy in SCI. In mice and rats, the endocannabinoid signaling system is crucial for the survival, differentiation, and maturation of OPCs. Similar studies in humans are lacking currently. Endocannabinoids and exogenous cannabinoids exert their effects mainly via cannabinoid receptors (CB1R and CB2R). We demonstrated that these receptors were differentially expressed in iPSC-derived human NSCs and OPCs, and they could be activated by WIN55212-2 (WIN), a potent CB1R/CB2R agonist to upregulate the endocannabinoid signaling during glial induction. WIN primed NSCs generated more OLIG2 + glial progenitors and migratory PDGFRα + OPC in a CB1/CB2 dependent manner compared to unprimed NSCs. Furthermore, WIN-induced OPCs (WIN-OPCs) robustly differentiated into functional oligodendrocytes and myelinate in vitro and in vivo in a mouse spinal cord injury model. RNA-Seq revealed that WIN upregulated the biological process of positive regulation of oligodendrocyte differentiation. Mechanistically, WIN could act as a partial smoothed (SMO) inhibitor or activate CB1/CB2 to form heteromeric complexes with SMO leading to the inhibition of GLI1 in the Sonic hedgehog pathway. The partial and temporal inhibition of GLI1 during glial induction is shown to promote OPCs that differentiate faster than control's. Thus, CB1R/CB2R activation results in more efficient generation of OPCs that can mature and efficiently myelinate.

Brain Organization and Human Diseases

The cortex is a highly organized structure that develops from the caudal regions of the segmented neural tube. Its spatial organization sets the stage for future functional arealization. Here, we suggest using a developmental perspective to describe and understand the etiology of common cortical malformations and their manifestation in the human brain.

Concepts in Multifactorial Etiology of Developmental Disorders: Gene-Gene and Gene-Environment Interactions in Holoprosencephaly

Many common developmental disorders are thought to arise from a complex set of genetic and environmental risk factors. These factors interact with each other to affect the strength and duration of key developmental signaling pathways, thereby increasing the possibility that they fail to achieve the thresholds required for normal embryonic patterning. One such disorder, holoprosencephaly (HPE), serves as a useful model system in understanding various forms of multifactorial etiology. Genomic analysis of HPE cases, epidemiology, and mechanistic studies of animal models have illuminated multiple potential ways that risk factors interact to produce adverse developmental outcomes. Among these are: 1) interactions between driver and modifier genes; 2) oligogenic inheritance, wherein each parent provides predisposing variants in one or multiple distinct loci; 3) interactions between genetic susceptibilities and environmental risk factors that may be insufficient on their own; and 4) interactions of multiple genetic variants with multiple non-genetic risk factors. These studies combine to provide concepts that illuminate HPE and are also applicable to additional disorders with complex etiology, including neural tube defects, congenital heart defects, and oro-facial clefting.

Δ9-Tetrahydrocannabinol inhibits Hedgehog-dependent patterning during development

Many developmental disorders are thought to arise from an interaction between genetic and environmental risk factors. The Hedgehog (HH) signaling pathway regulates myriad developmental processes, and pathway inhibition is associated with birth defects, including holoprosencephaly (HPE). Cannabinoids are HH pathway inhibitors, but little is known of their effects on HH-dependent processes in mammalian embryos, and their mechanism of action is unclear. We report that the psychoactive cannabinoid Δ9-tetrahydrocannabinol (THC) induces two hallmark HH loss-of-function phenotypes (HPE and ventral neural tube patterning defects) in Cdon mutant mice, which have a subthreshold deficit in HH signaling. THC therefore acts as a 'conditional teratogen', dependent on a complementary but insufficient genetic insult. In vitro findings indicate that THC is a direct inhibitor of the essential HH signal transducer smoothened. The canonical THC receptor, cannabinoid receptor-type 1, is not required for THC to inhibit HH signaling. Cannabis consumption during pregnancy may contribute to a combination of risk factors underlying specific developmental disorders. These findings therefore have significant public health relevance.

Cannabinoids modulate food preference and consumption in Drosophila melanogaster

Cannabinoids have an important role in regulating feeding behaviors via cannabinoid receptors in mammals. Cannabinoids also exhibit potential therapeutic functions in Drosophila melanogaster, or fruit fly that lacks cannabinoid receptors. However, it remains unclear whether cannabinoids affect food consumption and metabolism in a cannabinoid receptors-independent manner in flies. In this study, we systematically investigated pharmacological functions of various cannabinoids in modulating food preference and consumption in flies. We show that flies display preferences for consuming cannabinoids, independent of two important sensory regulators Poxn and Orco. Interestingly, phyto- and endo- cannabinoids exhibit an inhibitory effect on food intake. Unexpectedly, the non-selective CB1 receptor antagonist AM251 attenuates the suppression of food intake by endocannabinoids. Moreover, the endocannabinoid anandamide (AEA) and its metabolite inhibit food intake and promote resistance to starvation, possibly through reduced lipid metabolism. Thus, this study has provided insights into a pharmacological role of cannabinoids in feeding behaviors using an adult Drosophila model.

Understanding the complex pharmacology of cannabidiol: Mounting evidence suggests a common binding site with cholesterol

Cannabidiol is claimed to bind to a large number of protein targets based on in vitro assays. This suggests opportunities for a wide range of therapeutic applications. On the other hand, the existence of phytochemical 'nuisance compounds' suggests some measure of caution - these compounds are capable of altering membrane biophysical properties and changing protein function without directly contacting a binding site. Like cannabidiol, cholesterol alters membrane properties, but it also binds directly to membrane proteins through abundant cholesterol recognition sites. We present the evidence that cannabidiol and cholesterol may bind to the same site on some proteins. As a starting point for further research, we also used blind docking to show that cannabidiol binds to a cholesterol binding site on the CB1 receptor. Elucidation of the mechanism(s) of action of cannabidiol will assist the prioritisation of in vitro hits across targets, improve the success rate of medicinal chemistry campaigns, and ultimately benefit patient populations by focusing resources on programs with the most translational potential.

Examining the developmental toxicity of piperonyl butoxide as a Sonic hedgehog pathway inhibitor

Piperonyl butoxide (PBO) is a semisynthetic chemical present in hundreds of pesticide formulations used in agricultural, commercial, and residential settings. PBO acts as a pesticide synergist by inhibiting insect cytochrome P450 enzymes and is often present at much higher concentrations than active insecticidal ingredients. PBO was recently discovered to also inhibit Sonic hedgehog (Shh) signaling, a key molecular pathway in embryonic development and in brain and face morphogenesis. Recent animal model studies have shown that in utero PBO exposure can cause overt craniofacial malformations or more subtle neurodevelopmental abnormalities. Related adverse developmental outcomes in humans are etiologically heterogeneous, and, while studies are limited, PBO exposure during pregnancy has been linked to neurodevelopmental deficits. Contextualized in PBO's newly recognized mechanism as a Shh signaling inhibitor, these findings support more rigorous examination of the developmental toxicity of PBO and its potential contribution to etiologically complex human birth defects. In this review, we highlight environmental sources of human PBO exposure and summarize existing animal studies examining the developmental impact of prenatal PBO exposure. Also presented are critical knowledge gaps in our understanding of PBO's pharmacokinetics and potential role in gene-environment and environment-environment interactions that should be addressed to better understand the human health impact of environmental PBO exposure.

Endocannabinoid signalling in stem cells and cerebral organoids drives differentiation to deep layer projection neurons via CB1 receptors

The endocannabinoid (eCB) system, via the cannabinoid CB₁ receptor, regulates neurodevelopment by controlling neural progenitor proliferation and neurogenesis. CB₁ receptor signalling in vivo drives corticofugal deep layer projection neuron development through the regulation of BCL11B and SATB2 transcription factors. Here, we investigated the role of eCB signalling in mouse pluripotent embryonic stem cell-derived neuronal differentiation. Characterization of the eCB system revealed increased expression of eCB-metabolizing enzymes, eCB ligands and CB₁ receptors during neuronal differentiation. CB₁ receptor knockdown inhibited neuronal differentiation of deep layer neurons and increased upper layer neuron generation, and this phenotype was rescued by CB₁ re-expression. Pharmacological regulation with CB₁ receptor agonists or elevation of eCB tone with a monoacylglycerol lipase inhibitor promoted neuronal differentiation of deep layer neurons at the expense of upper layer neurons. Patch-clamp analyses revealed that enhancing cannabinoid signalling facilitated neuronal differentiation and functionality. Noteworthy, incubation with CB₁ receptor agonists during human iPSC-derived cerebral organoid formation also promoted the expansion of BCL11B⁺ neurons. These findings unveil a cell-autonomous role of eCB signalling that, via the CB₁ receptor, promotes mouse and human deep layer cortical neuron development.

Circulating Hedgehog: a fresh view of a classic morphogen

Members of the Hedgehog family of morphogens mediate the intercellular communication necessary for the organisation and development of many animal tissues. They are modified by various lipid adducts, rendering them insoluble in hydrophilic environments and leading to the contentious question of how these molecules travel in the aqueous extracellular space. Seminal work carried out by Suzanne Eaton and her colleagues has shed light on how these morphogens can spread over long distances through their association with lipoprotein particles. In this Spotlight article, we discuss Suzanne's pioneering work and her contribution to our understanding of the transport and activity of morphogens, in particular Hedgehog. We also describe two other essential aspects of her work: the discovery and characterisation of endogenously present Hedgehog variants, as well as her proposition that, in addition to its role as a morphogen, Hedgehog acts as an endocrine hormone.

Understanding the role of lipids and lipoproteins in development

Lipids exert diverse functions in living organisms. They form cellular membranes, store and transport energy and play signalling roles. Some lipid species function in all of these processes, making them ideal candidates to coordinate metabolism with cellular homeostasis and animal development. This theme was central to Suzanne Eaton's research in the fruit fly, Drosophila Here, we discuss her work on membrane lipid homeostasis in changing environments and on functions for lipids in the Hedgehog signalling pathway. We further highlight lipoproteins as inter-organ carriers of lipids and lipid-linked morphogens, which communicate dietary and developmental signals throughout the organism.

Glycolysis regulates Hedgehog signalling via the plasma membrane potential

Changes in cell metabolism and plasma membrane potential have been linked to shifts between tissue growth and differentiation, and to developmental patterning. How such changes mediate these effects is poorly understood. Here, we use the developing wing of Drosophila to investigate the interplay between cell metabolism and a key developmental regulator-the Hedgehog (Hh) signalling pathway. We show that reducing glycolysis both lowers steady-state levels of ATP and stabilizes Smoothened (Smo), the 7-pass transmembrane protein that transduces the Hh signal. As a result, the transcription factor Cubitus interruptus accumulates in its full-length, transcription activating form. We show that glycolysis is required to maintain the plasma membrane potential and that plasma membrane depolarization blocks cellular uptake of N-acylethanolamides-lipoprotein-borne Hh pathway inhibitors required for Smo destabilization. Similarly, pharmacological inhibition of glycolysis in mammalian cells induces ciliary translocation of Smo-a key step in pathway activation-in the absence of Hh. Thus, changes in cell metabolism alter Hh signalling through their effects on plasma membrane potential.

Identifying environmental risk factors and gene-environment interactions in holoprosencephaly

BACKGROUND

Holoprosencephaly is the most common malformation of the forebrain (1 in 250 embryos) with severe consequences for fetal and child development. This study evaluates nongenetic factors associated with holoprosencephaly risk, severity, and gene-environment interactions.

METHODS

For this retrospective case control study, we developed an online questionnaire focusing on exposures to common and rare toxins/toxicants before and during pregnancy, nutritional factors, maternal health history, and demographic factors. Patients with holoprosencephaly were primarily ascertained from our ongoing genetic and clinical studies of holoprosencephaly. Controls included children with Williams-Beuren syndrome (WBS) ascertained through online advertisements in a WBD support group and fliers.

RESULTS

Difference in odds of exposures between cases and controls as well as within cases with varying holoprosencephaly severity were studied. Cases included children born with holoprosencephaly (n = 92) and the control group consisted of children with WBS (n = 56). Pregnancy associated risk associated with holoprosencephaly included maternal pregestational diabetes (9.2% of cases and 0 controls, p = .02), higher alcohol consumption (adjusted odds ratio [aOR], 1.73; 95% CI, 0.88-15.71), and exposure to consumer products such as aerosols or sprays including hair sprays (aOR, 2.46; 95% CI, 0.89-7.19). Significant gene-environment interactions were identified including for consumption of cheese (p < .05) and espresso drinks (p = .03).

CONCLUSION

The study identifies modifiable risk factors and gene-environment interactions that should be considered in future prevention of holoprosencephaly. Studies with larger HPE cohorts will be needed to confirm these findings.

Range of SHH signaling in adrenal gland is limited by membrane contact to cells with primary cilia

The signaling protein Sonic Hedgehog (SHH) is crucial for the development and function of many vertebrate tissues. It remains largely unclear, however, what defines the range and specificity of pathway activation. The adrenal gland represents a useful model to address this question, where the SHH pathway is activated in a very specific subset of cells lying near the SHH-producing cells, even though there is an abundance of lipoproteins that would allow SHH to travel and signal long-range. We determine that, whereas adrenal cells can secrete SHH on lipoproteins, this form of SHH is inactive due to the presence of cosecreted inhibitors, potentially explaining the absence of long-range signaling. Instead, we find that SHH-producing cells signal at short range via membrane-bound SHH, only to receiving cells with primary cilia. Finally, our data from NCI-H295R adrenocortical carcinoma cells suggest that adrenocortical tumors may evade these regulatory control mechanisms by acquiring the ability to activate SHH target genes in response to TGF-β.

Getting in shape: ATP pumps up the volume in Hh signalling

Glycolysis is a major metabolic process which ensures the break down of glucose into pyruvate via multiple enzymatic steps, but if and how this catabolism can impact on developmental patterning is unclear. In this issue, Spannl et al (2020) demonstrate a novel link between energy metabolism and tissue formation in the fly imaginal discs. They show that ATPs generated via glycolysis maintain active transport of a smoothened inhibitor, which keeps Hh signalling in check to preserve the correct shape and proportion of the developing wing.

Gene-environment interactions: aligning birth defects research with complex etiology

Developmental biologists rely on genetics-based approaches to understand the origins of congenital abnormalities. Recent advancements in genomics have made it easier than ever to investigate the relationship between genes and disease. However, nonsyndromic birth defects often exhibit non-Mendelian inheritance, incomplete penetrance or variable expressivity. The discordance between genotype and phenotype indicates that extrinsic factors frequently impact the severity of genetic disorders and vice versa. Overlooking gene-environment interactions in birth defect etiology limits our ability to identify and eliminate avoidable risks. We present mouse models of sonic hedgehog signaling and craniofacial malformations to illustrate both the importance of and current challenges in resolving gene-environment interactions in birth defects. We then prescribe approaches for overcoming these challenges, including use of genetically tractable and environmentally responsive in vitro systems. Combining emerging technologies with molecular genetics and traditional animal models promises to advance our understanding of birth defect etiology and improve the identification and protection of vulnerable populations.

Ethanol and Cannabinoids Regulate Zebrafish GABAergic Neuron Development and Behavior in a Sonic Hedgehog and Fibroblast Growth Factor-Dependent Mechanism

BACKGROUND

Ethanol (EtOH) has diverse effects on nervous system development, which includes development and survival of GABAergic neurons in a sonic hedgehog (Shh) and fibroblast growth factor (Fgf)-dependent mechanism. Cannabinoids also function as inhibitors of Shh signaling, raising the possibility that EtOH and cannabinoids may interact to broadly disrupt neuronal function during brain development.

METHODS

Zebrafish embryos were exposed to a range of EtOH and/or cannabinoid receptor 1 (CB1R) agonist concentrations at specific developmental stages, in the absence or presence of morpholino oligonucleotides that disrupt shh expression. In situ hybridization was employed to analyze glutamic acid decarboxylase (gad1) gene expression as a marker of GABAergic neuron differentiation, and zebrafish behavior was analyzed using the novel tank diving test as a measure of risk-taking behavior.

RESULTS

Combined acute subthreshold EtOH and CB1R agonist exposure results in a marked reduction in gad1 mRNA expression in zebrafish forebrain. Consistent with the EtOH and cannabinoid effects on Shh signaling, fgf8 mRNA overexpression rescues the EtOH- and cannabinoid-induced decrease in gad1 gene expression and also prevents the changes in behavior induced by EtOH and cannabinoids.

CONCLUSIONS

These studies provide evidence that forebrain GABAergic neuron development and zebrafish risk-taking behavior are sensitive to both EtOH and cannabinoid exposure in a Shh- and Fgf-dependent mechanism, and provide additional evidence that a signaling pathway involving Shh and Fgf crosstalk is a critical target of EtOH and cannabinoids in FASD.

Hedgehog signaling pathway inhibitors: an updated patent review (2015-present)

Introduction: Hedgehog (Hh) signaling plays a pivotal role in tissue development and stemness, and its deregulation is found in many different tumors. Several efforts have been devoted to discovery of Hh inhibitors, including three drugs approved by the Food and Drug Administration (FDA), targeting the upstream receptor smoothened (SMO). However, SMO mutations or SMO-independent Hh pathway activation raise the need for novel Hh inhibitors.Areas covered: This review describes Hh inhibitors with anticancer potential patented in the period 2015-present.Expert opinion: Despite the initial enthusiasm in SMO antagonists, drug-resistant mutations, and SMO-independent Hh activation limited their clinical application. A growing number of therapeutic strategies are currently focusing on downstream Hh effectors (i.e. glioma-associate oncogenes (GLI) proteins) or other signaling pathways related to Hh, in addition to drug repositioning. Given the heterogenic nature of cancers, a terrific clinical impact is expected by multi-targeting approaches able to modulate simultaneously SMO and GLI, and/or additional targets that act as regulators of Hh signaling. It is expected that these alternative strategies might be investigated in clinical trials in the next years against a wide variety of tumor types, and that they provide improved outcomes compared to current SMO antagonists or other single-agent anticancer drugs.

Cannabis Consumption Patterns Explain the East-West Gradient in Canadian Neural Tube Defect Incidence: An Ecological Study

While a known link between prenatal cannabis exposure and anencephaly exists, the relationship of prenatal cannabis exposure with neural tube defects (NTDs) generally has not been defined. Published data from Canada Health and Statistics Canada were used to assess this relationship. Both cannabis use and NTDs were shown to follow an east-west and north-south gradient. Last year cannabis consumption was significantly associated (P < .0001; cannabis use-time interaction P < .0001). These results were confirmed when estimates of termination for anomaly were used. Canada Health population data allowed the calculation of an NTD odds ratio) of 1.27 (95% confidence interval = 1.19-1.37; P < 10-11) for high-risk provinces versus the remainder with an attributable fraction in exposed populations of 16.52% (95% confidence interval = 12.22-20.62). Data show a robust positive statistical association between cannabis consumption as both a qualitative and quantitative variable and NTDs on a background of declining NTD incidence. In the context of multiple mechanistic pathways these strong statistical findings implicate causal mechanisms.

Knockdown of arylalkylamine N-acetyltransferase-like 2 in Drosophila melanogaster

Drosophila melanogaster produces fatty acid amides, and thus, provides a model to unravel the pathways for their biosynthesis. We previously demonstrated that arylalkylamine N-acetyltransferase-like 2 (AANATL2) from D. melanogaster will catalyze the formation of long-chain N-acylserotonins and N-acyldopamines in vitro. Generating silencing RNA via the UAS/GAL4 bipartite approach for targeted gene expression effectively decreased the endogenous levels of the AANATL2 transcripts in D. melanogaster, as shown by reverse transcription quantitative polymerase chain reaction. Consistent with these data, western blot analysis of the offspring of the AANATL2 knockdown flies using an anti-AANATL2 antibody revealed a significant reduction in the expression of the AANATL2 protein. Reduced expression of AANATL2 decreased the cellular levels of N-palmitoyldopamine (PALDA), providing strong evidence that AANATL2 is responsible for the biosynthesis of PALDA in vivo. This is the first time that the expression of an AANAT has been reduced in D. melanogaster to link one of these enzymes to the in vivo production of an N-acylarylalkylamide.

Comparative studies of endocannabinoid modulation of pain

Cannabinoid-based therapies have long been used to treat pain, but there remain questions about their actual mechanisms and efficacy. From an evolutionary perspective, the cannabinoid system would appear to be highly conserved given that the most prevalent endogenous cannabinoid (endocannabinoid) transmitters, 2-arachidonyl glycerol and anandamide, have been found throughout the animal kingdom, at least in the species that have been analysed to date. This review will first examine recent findings regarding the potential conservation across invertebrates and chordates of the enzymes responsible for endocannabinoid synthesis and degradation and the receptors that these transmitters act on. Next, comparisons of how endocannabinoids modulate nociception will be examined for commonalities between vertebrates and invertebrates, with a focus on the medicinal leech Hirudo verbana. Evidence is presented that there are distinct, evolutionarily conserved anti-nociceptive and pro-nociceptive effects. The combined studies across various animal phyla demonstrate the utility of using comparative approaches to understand conserved mechanisms for modulating nociception. This article is part of the Theo Murphy meeting issue 'Evolution of mechanisms and behaviour important for pain'.

Cannabinoids Exacerbate Alcohol Teratogenesis by a CB1-Hedgehog Interaction

We tested whether cannabinoids (CBs) potentiate alcohol-induced birth defects in mice and zebrafish, and explored the underlying pathogenic mechanisms on Sonic Hedgehog (Shh) signaling. The CBs, Δ⁹-THC, cannabidiol, HU-210, and CP 55,940 caused alcohol-like effects on craniofacial and brain development, phenocopying Shh mutations. Combined exposure to even low doses of alcohol with THC, HU-210, or CP 55,940 caused a greater incidence of birth defects, particularly of the eyes, than did either treatment alone. Consistent with the hypothesis that these defects are caused by deficient Shh, we found that CBs reduced Shh signaling by inhibiting Smoothened (Smo), while Shh mRNA or a CB1 receptor antagonist attenuated CB-induced birth defects. Proximity ligation experiments identified novel CB1-Smo heteromers, suggesting allosteric CB1-Smo interactions. In addition to raising concerns about the safety of cannabinoid and alcohol exposure during early embryonic development, this study establishes a novel link between two distinct signaling pathways and has widespread implications for development, as well as diseases such as addiction and cancer.

Cholesterol accessibility at the ciliary membrane controls hedgehog signaling

Previously we proposed that transmission of the hedgehog signal across the plasma membrane by Smoothened is triggered by its interaction with cholesterol (Luchetti et al., 2016). But how is cholesterol, an abundant lipid, regulated tightly enough to control a signaling system that can cause birth defects and cancer? Using toxin-based sensors that distinguish between distinct pools of cholesterol, we find that Smoothened activation and Hedgehog signaling are driven by a biochemically-defined, small fraction of membrane cholesterol, termed accessible cholesterol. Increasing cholesterol accessibility by depletion of sphingomyelin, which sequesters cholesterol in complexes, amplifies Hedgehog signaling. Hedgehog ligands increase cholesterol accessibility in the membrane of the primary cilium by inactivating the transporter-like protein Patched 1. Trapping this accessible cholesterol blocks Hedgehog signal transmission across the membrane. Our work shows that the organization of cholesterol in the ciliary membrane can be modified by extracellular ligands to control the activity of cilia-localized signaling proteins.

Suzanne Eaton (1959-2019): A pioneer in quantitative tissue morphogenesis

Knust and Simons commemorate the life of the eminent developmental biologist, Suzanne Eaton.

Inhalation of marijuana affects Drosophila heart function

We investigated the effect of inhalation of vaporized marijuana on cardiac function in Drosophila melanogaster, a suitable genetic model for studying human diseases. Adult flies were exposed to marijuana for variable time periods and the effects on cardiac function were studied. Short treatment protocol incremented heart-rate variability. Contractility was augmented only under prolonged exposure to cannabis and it was associated with incremented calcium transient within cardiomyocytes. Neither the activity of the major proteins responsible for calcium handling nor the calcium load of the sarcoplasmic reticulum were affected by the cannabis treatment. The observed changes manifested in the cardiomyocytes even in the absence of the canonical cannabinoid receptors described in mammals. Our results are the first evidence of the in vivo impact of phytocannabinoids in D. melanogaster. By providing a simple and affordable platform prior to mammalian models, this characterization of cardiac function under marijuana exposure opens new paths for conducting genetic screenings using vaporized compounds.This article has an associated First Person interview with the first author of the paper.

The α/β-hydrolase domain-containing 4- and 5-related phospholipase Pummelig controls energy storage in Drosophila

Triglycerides (TGs) are the main energy storage form that accommodates changing organismal energy demands. In Drosophila melanogaster, the TG lipase Brummer is centrally important for body fat mobilization. Its gene brummer (bmm) encodes the ortholog of mammalian adipose TG lipase, which becomes activated by α/β-hydrolase domain-containing 5 (ABHD5/CGI-58), one member of the paralogous gene pair, α/β-hydrolase domain-containing 4 (ABHD4) and ABHD5 In Drosophila, the pummelig (puml) gene encodes the single sequence-related protein to mammalian ABHD4/ABHD5 with unknown function. We generated puml deletion mutant flies, that were short-lived as a result of lipid metabolism changes, stored excess body fat at the expense of glycogen, and exhibited ectopic fat storage with altered TG FA profile in the fly kidneys, called Malpighian tubules. TG accumulation in puml mutants was not associated with increased food intake but with elevated lipogenesis; starvation-induced lipid mobilization remained functional. Despite its structural similarity to mammalian ABHD5, Puml did not stimulate TG lipase activity of Bmm in vitro. Rather, Puml acted as a phospholipase that localized on lipid droplets, mitochondria, and peroxisomes. Together, these results show that the ABHD4/5 family member Puml is a versatile phospholipase that regulates Drosophila body fat storage and energy metabolism.

Ethanol and cannabinoids interact to alter behavior in a zebrafish fetal alcohol spectrum disorder model

BACKGROUND

Recent work suggests that endocannabinoids (eCBs) may signal through the sonic hedgehog signaling pathway. We therefore hypothesized that combined ethanol and eCB exposure during defined stages of zebrafish embryogenesis will produce deficits comparable to human fetal alcohol spectrum disorder (FASD).

METHODS

Zebrafish embryos were exposed to ethanol or cannabinoid agonists alone or in combination at defined developmental stages and assessed for changes in brain morphology or expression of marker genes such as pax6a. Juvenile fish were then assessed for risk-taking/anxiety-like behavior using the novel tank dive test.

RESULTS

Either chronic or acute exposure to high doses of the CB1R agonist ACEA resulted in FASD phenotypes. However, acute subthreshold doses of CB1R agonist alone, or combined with 0.5% ethanol, did not induce morphological phenotypes, but did induce dysmorphogenesis when combined with acute 1% ethanol. Phenotypes were rescued using the CB1R antagonist SR141716A. In addition, JZL195, a dual inhibitor of FAAH and MAGL, two degradative enzymes for eCBs, induced FASD phenotypes in the presence of subthreshold ethanol, confirming the activation of common signaling pathways by ethanol and eCBs. We next analyzed the effects of ethanol and CB1R agonist on juvenile zebrafish behavior and show that ACEA or ethanol alone did not alter behavior, but combined ACEA and ethanol increased risk-taking behavior.

CONCLUSIONS

These studies demonstrate that pathological and behavioral phenotypes associated with FASD are induced by exposure to CB1R agonists and suggest that combined exposure to lower levels of alcohol and marijuana may be capable of inducing FASD-like morphological and behavioral impairments.

Brain endocannabinoid signaling exhibits remarkable complexity

The endocannabinoid (eCB) signaling system is one of the most extensive of the mammalian brain. Despite the involvement of only few specific ligands and receptors, the system encompasses a vast diversity of triggered mechanisms and driven effects. It mediates a wide range of phenomena, including the regulation of transmitter release, neural excitability, synaptic plasticity, impulse spread, long-term neuronal potentiation, neurogenesis, cell death, lineage segregation, cell migration, inflammation, oxidative stress, nociception and the sleep cycle. It is also known to be involved in the processes of learning and memory formation. This extensive scope of action is attained by combining numerous variables. In a properly functioning brain, the correlations of these variables are kept in a strictly controlled balance; however, this balance is disrupted in many pathological conditions. However, while this balance is known to be disrupted by drugs in the case of addicts, the stimuli and mechanisms influencing the neurodegenerating brain remain elusive. This review examines the multiple factors and phenomena affecting the eCB signaling system in the brain. It evaluates techniques of controlling the eCB system to identify the obstacles in their applications and highlights the crucial interdependent variables that may influence biomedical research outcomes.

Non-endocannabinoid N-acylethanolamines and 2-monoacylglycerols in the intestine

This review focuses on recent findings of the physiological and pharmacological role of non-endocannabinoid N-acylethanolamines (NAEs) and 2-monoacylglycerols (2-MAGs) in the intestine and their involvement in the gut-brain signalling. Dietary fat suppresses food intake, and much research concerns the known gut peptides, for example, glucagon-like peptide-1 (GLP-1) and cholecystokinin (CCK). NAEs and 2-MAGs represent another class of local gut signals most probably involved in the regulation of food intake. We discuss the putative biosynthetic pathways and targets of NAEs in the intestine as well as their anorectic role and changes in intestinal levels depending on the dietary status. NAEs can activate the transcription factor PPARα, but studies to evaluate the role of endogenous NAEs are generally lacking. Finally, we review the role of diet-derived 2-MAGs in the secretion of anorectic gut peptides via activation of GPR119. Both PPARα and GPR119 have potential as pharmacological targets for the treatment of obesity and the former for treatment of intestinal inflammation. LINKED ARTICLES: This article is part of a themed section on 8^th European Workshop on Cannabinoid Research. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.10/issuetoc.

Multiple ligand binding sites regulate the Hedgehog signal transducer Smoothened in vertebrates

The Hedgehog (Hh) pathway plays a central role in the development of multicellular organisms, guiding cell differentiation, proliferation and survival. While many components of the vertebrate pathway were discovered two decades ago, the mechanism by which the Hh signal is transmitted across the plasma membrane remains mysterious. This fundamental task in signalling is carried out by Smoothened (SMO), a human oncoprotein and validated cancer drug target that is a member of the G-protein coupled receptor protein family. Recent structural and functional studies have advanced our mechanistic understanding of SMO activation, revealing its unique regulation by two separable but allosterically-linked ligand-binding sites. Unexpectedly, these studies have nominated cellular cholesterol as having an instructive role in SMO signalling.

Δ9-Tetrahydrocannabinol induces endocannabinoid accumulation in mouse hepatocytes: antagonism by Fabp1 gene ablation

Phytocannabinoids, such as Δ9-tetrahydrocannabinol (THC), bind and activate cannabinoid (CB) receptors, thereby "piggy-backing" on the same pathway's endogenous endocannabinoids (ECs). The recent discovery that liver fatty acid binding protein-1 (FABP1) is the major cytosolic "chaperone" protein with high affinity for both Δ9-THC and ECs suggests that Δ9-THC may alter hepatic EC levels. Therefore, the impact of Δ9-THC or EC treatment on the levels of endogenous ECs, such as N-arachidonoylethanolamide (AEA) and 2-arachidonoylglycerol (2-AG), was examined in cultured primary mouse hepatocytes from WT and Fabp1 gene-ablated (LKO) mice. Δ9-THC alone or 2-AG alone significantly increased AEA and especially 2-AG levels in WT hepatocytes. LKO alone markedly increased AEA and 2-AG levels. However, LKO blocked/diminished the ability of Δ9-THC to further increase both AEA and 2-AG. In contrast, LKO potentiated the ability of exogenous 2-AG to increase the hepatocyte level of AEA and 2-AG. These and other data suggest that Δ9-THC increases hepatocyte EC levels, at least in part, by upregulating endogenous AEA and 2-AG levels. This may arise from Δ9-THC competing with AEA and 2-AG binding to FABP1, thereby decreasing targeting of bound AEA and 2-AG to the degradative enzymes, fatty acid amide hydrolase and monoacylglyceride lipase, to decrease hydrolysis within hepatocytes.

Sonic Hedgehog Activates Phospholipase A2 to Enhance Smoothened Ciliary Translocation

The G protein-coupled receptor Smoothened (Smo) is the signal transducer of the Sonic Hedgehog (Shh) pathway. Smo signals through G protein-dependent and -independent routes, with G protein-independent canonical signaling to Gli effectors requiring Smo accumulation in the primary cilium. The mechanisms controlling Smo activation and trafficking are not yet clear but likely entail small-molecule binding to pockets in its extracellular cysteine-rich domain (CRD) and/or transmembrane bundle. Here, we demonstrate that the cytosolic phospholipase cPLA2α is activated through Gβγ downstream of Smo to release arachidonic acid. Arachidonic acid binds Smo and synergizes with CRD-binding agonists, promoting Smo ciliary trafficking and high-level signaling. Chemical or genetic cPLA2α inhibition dampens Smo signaling to Gli, revealing an unexpected contribution of G protein-dependent signaling to canonical pathway activity. Arachidonic acid displaces the Smo transmembrane domain inhibitor cyclopamine to rescue CRD agonist-induced signaling, suggesting that arachidonic acid may target the transmembrane bundle to allosterically enhance signaling by CRD agonist-bound Smo.

Endocannabinoid-mediated potentiation of nonnociceptive synapses contributes to behavioral sensitization

Endocannabinoids, such as 2-arachidonoyl glycerol (2-AG) and anandamide, can elicit long-term depression of both excitatory and inhibitory synapses. This latter effect will result in disinhibition and would therefore be expected to produce an increase in neural circuit output. However, there have been no examples directly linking endocannabinoid-mediated disinhibition to a change in a functional neurobehavioral circuit. The present study uses the well-characterized central nervous system of the medicinal leech, Hirudo verbana, to examine the functional/behavioral relevance of endocannabinoid modulation of an identified afferent synapse. Bath application of 2-AG potentiates synaptic transmission by pressure-sensitive sensory neurons (P cells) as well as the magnitude of the defensive shortening reflex elicited by P-cell stimulation. This potentiation requires activation of TRPV-like channels. Endocannabinoid/TRPV signaling was found to produce sensitization of the shortening reflex elicited by either direct stimulation of nearby nociceptive afferents (N cells) or noxious stimulation applied to skin several segments away. In both cases, heterosynaptic potentiation of P-cell synapses was observed in parallel with an increase in the magnitude of elicited shortening and both synaptic and behavioral effects were blocked by pharmacological inhibition of 2-AG synthesis or TRPV-like channel activation. Serotonin (5-HT) is known to play a critical role in sensitization in Hirudo and other animals, and the 5-HT2 receptor antagonist ritanserin also blocked behavioral sensitization and the accompanying synaptic potentiation. These findings suggest a novel, endocannabinoid-mediated contribution to behavioral sensitization that may interact with known 5-HT-dependent modulatory processes. NEW & NOTEWORTHY There is considerable interest in the analgesic potential of cannabinoids. However, there is evidence that the cannabinoid system can have both pro- and antinociceptive effects. This study examines how an endogenous cannabinoid transmitter can potentiate nonnociceptive synapses and enhance their capacity to elicit a nocifensive behavioral response.

Drosophila: An Emergent Model for Delineating Interactions between the Circadian Clock and Drugs of Abuse

Endogenous circadian oscillators orchestrate rhythms at the cellular, physiological, and behavioral levels across species to coordinate activity, for example, sleep/wake cycles, metabolism, and learning and memory, with predictable environmental cycles. The 21st century has seen a dramatic rise in the incidence of circadian and sleep disorders with globalization, technological advances, and the use of personal electronics. The circadian clock modulates alcohol- and drug-induced behaviors with circadian misalignment contributing to increased substance use and abuse. Invertebrate models, such as Drosophila melanogaster, have proven invaluable for the identification of genetic and molecular mechanisms underlying highly conserved processes including the circadian clock, drug tolerance, and reward systems. In this review, we highlight the contributions of Drosophila as a model system for understanding the bidirectional interactions between the circadian system and the drugs of abuse, alcohol and cocaine, and illustrate the highly conserved nature of these interactions between Drosophila and mammalian systems. Research in Drosophila provides mechanistic insights into the corresponding behaviors in higher organisms and can be used as a guide for targeted inquiries in mammals.

A cell based, high throughput assay for quantitative analysis of Hedgehog pathway activation using a Smoothened activation sensor

The Hedgehog (Hh) signalling cascade plays an important role in development and disease. In the absence of Hh ligand, activity of the key signal transducer Smoothened (Smo) is downregulated by the Hh receptor Patched (Ptc). However, the mechanisms underlying this inhibition, and especially its release upon ligand stimulation, are still poorly understood, in part because tools for following Smo activation at the subcellular level were long lacking. To address this deficit we have developed a high throughput cell culture assay based on a fluorescent sensor for Drosophila Smo activation. We have screened a small molecule inhibitor library, and observed increased Smo sensor fluorescence with compounds aimed at two major target groups, the MAPK signalling cascade and polo and aurora kinases. Biochemical validation for selected inhibitors (dobrafenib, tak-733, volasertib) confirmed the screen results and revealed differences in the mode of Smo activation. Furthermore, monitoring Smo activation at the single cell level indicated that individual cells exhibit different threshold responses to Hh stimulation, which may be mechanistically relevant for the formation of graded Hh responses. Together, these results thus provide proof of principle that our assay may become a valuable tool for dissecting the cell biological basis of Hh pathway activation.

Contributions of Noncanonical Smoothened Signaling During Embryonic Development

The Sonic Hedgehog (Shh) signaling pathway is active during embryonic development in metazoans, and provides instructional cues necessary for proper tissue patterning. The pathway signal transducing component, Smoothened (Smo), is a G protein-coupled receptor (GPCR) that has been demonstrated to signal through at least two effector routes. The first is a G protein–independent canonical route that signals to Gli transcriptional effectors to establish transcriptional programs specifying cell fate during early embryonic development. The second, commonly referred to as the noncanonical Smo signal, induces rapid, transcription-independent responses that are essential for establishing and maintaining distinct cell behaviors during development. Herein, we discuss contributions of this noncanonical route during embryonic development. We also highlight important open questions regarding noncanonical Smo signal route selection during development, and consider implications of noncanonical signal corruption in disease.

Hedgehog Signal Transduction: Key Players, Oncogenic Drivers, and Cancer Therapy

The Hedgehog (Hh) signaling pathway governs complex developmental processes, including proliferation and patterning within diverse tissues. These activities rely on a tightly regulated transduction system that converts graded Hh input signals into specific levels of pathway activity. Uncontrolled activation of Hh signaling drives tumor initiation and maintenance. However, recent entry of pathway-specific inhibitors into the clinic reveals mixed patient responses and thus prompts further exploration of pathway activation and inhibition. In this review, we share emerging insights into regulated and oncogenic Hh signaling, supplemented with updates on the development and use of Hh pathway-targeted therapies.

Comparative biology of pain: What invertebrates can tell us about how nociception works

The inability to adequately treat chronic pain is a worldwide health care crisis. Pain has both an emotional and a sensory component, and this latter component, nociception, refers specifically to the detection of damaging or potentially damaging stimuli. Nociception represents a critical interaction between an animal and its environment and exhibits considerable evolutionary conservation across species. Using comparative approaches to understand the basic biology of nociception could promote the development of novel therapeutic strategies to treat pain, and studies of nociception in invertebrates can provide especially useful insights toward this goal. Both vertebrates and invertebrates exhibit segregated sensory pathways for nociceptive and nonnociceptive information, injury-induced sensitization to nociceptive and nonnociceptive stimuli, and even similar antinociceptive modulatory processes. In a number of invertebrate species, the central nervous system is understood in considerable detail, and it is often possible to record from and/or manipulate single identifiable neurons through either molecular genetic or physiological approaches. Invertebrates also provide an opportunity to study nociception in an ethologically relevant context that can provide novel insights into the nature of how injury-inducing stimuli produce persistent changes in behavior. Despite these advantages, invertebrates have been underutilized in nociception research. In this review, findings from invertebrate nociception studies are summarized, and proposals for how research using invertebrates can address questions about the fundamental mechanisms of nociception are presented.

Prenatal ethanol exposure in mice phenocopies Cdon mutation by impeding Shh function in the etiology of optic nerve hypoplasia

Septo-optic dysplasia (SOD) is a congenital disorder characterized by optic nerve, pituitary and midline brain malformations. The clinical presentation of SOD is highly variable with a poorly understood etiology. The majority of SOD cases are sporadic, but in rare instances inherited mutations have been identified in a small number of transcription factors, some of which regulate the expression of Sonic hedgehog (Shh) during mouse forebrain development. SOD is also associated with young maternal age, suggesting that environmental factors, including alcohol consumption at early stages of pregnancy, might increase the risk of developing this condition. Here, we address the hypothesis that SOD is a multifactorial disorder stemming from interactions between mutations in Shh pathway genes and prenatal ethanol exposure. Mouse embryos with mutations in the Shh co-receptor, Cdon, were treated in utero with ethanol or saline at embryonic day 8 (E8.0) and evaluated for optic nerve hypoplasia (ONH), a prominent feature of SOD. We show that both Cdon^-/- mutation and prenatal ethanol exposure independently cause ONH through a similar pathogenic mechanism that involves selective inhibition of Shh signaling in retinal progenitor cells, resulting in their premature cell-cycle arrest, precocious differentiation and failure to properly extend axons to the optic nerve. The ONH phenotype was not exacerbated in Cdon^-/- embryos treated with ethanol, suggesting that an intact Shh signaling pathway is required for ethanol to exert its teratogenic effects. These results support a model whereby mutations in Cdon and prenatal ethanol exposure increase SOD risk through spatiotemporal perturbations in Shh signaling activity.

Cholesterol activates the G-protein coupled receptor Smoothened to promote Hedgehog signaling

Cholesterol is necessary for the function of many G-protein coupled receptors (GPCRs). We find that cholesterol is not just necessary but also sufficient to activate signaling by the Hedgehog (Hh) pathway, a prominent cell-cell communication system in development. Cholesterol influences Hh signaling by directly activating Smoothened (SMO), an orphan GPCR that transmits the Hh signal across the membrane in all animals. Unlike many GPCRs, which are regulated by cholesterol through their heptahelical transmembrane domains, SMO is activated by cholesterol through its extracellular cysteine-rich domain (CRD). Residues shown to mediate cholesterol binding to the CRD in a recent structural analysis also dictate SMO activation, both in response to cholesterol and to native Hh ligands. Our results show that cholesterol can initiate signaling from the cell surface by engaging the extracellular domain of a GPCR and suggest that SMO activity may be regulated by local changes in cholesterol abundance or accessibility.

Metabolism meets development at Wiston House

It is becoming increasingly clear that cellular metabolite levels regulate the activity of signaling pathways, and conversely that signaling pathways affect cellular physiology and growth via metabolic pathways. Thus, metabolism and signaling mutually influence each other. The Company of Biologists' Workshop ‘Metabolism in Development and Disease’ brought together people studying signaling and development with people studying metabolism, particularly in a cancer context. This Meeting Review discusses examples of talks that illustrated this principle.