Dendrosomatic Sonic Hedgehog Signaling in Hippocampal Neurons Regulates Axon Elongation

Purmorphamine Alters Anxiety-Like Behavior and Expression of Hedgehog Cascade Components in Rat Brain after Alcohol Withdrawal

Disturbances in the Hedgehog (Hh) signaling play an important role in dysmorphogenesis of bone tissue and central nervous system during prenatal alcohol exposure, which underlies development of fetal alcohol syndrome. The involvement of Hh proteins in the mechanisms of alcohol intake in adults remains obscure. We investigated the role of the Hh cascade in voluntary ethanol drinking and development of anxiety-like behavior (ALB) during early abstinence and assessed changes in the expression of Hh pathway components in different brain regions of male Wistar rats in a model of voluntary alcohol drinking using the intermittent access to 20% ethanol in a two-bottle choice procedure. Purmorphamine (Hh cascade activator and Smoothened receptor agonist) was administered intraperitoneally at a dose of 5 mg/kg body weight prior to 16-20 sessions of alcohol access. Purmorphamine had no effect on the ethanol preference; however, rats exposed to ethanol and receiving purmorphamine demonstrated changes in the ALB during the early abstinence period. Alcohol drinking affected the content of the Sonic hedgehog (Shh) and Patched mRNAs only in the amygdala. In rats exposed to ethanol and receiving purmorphamine, the level of Shh mRNA in the amygdala correlated negatively with the time spent in the open arms of the elevated plus maze. Therefore, we demonstrated for the first time that alterations in the Hh cascade induced by administration of purmorphamine did not affect alcohol preference in voluntary alcohol drinking. It was suggested that Hh cascade is involved in the development of anxiety after alcohol withdrawal through specific changes in the Hh cascade components in the amygdala.

Haploinsufficiency of intraflagellar transport protein 172 causes autism-like behavioral phenotypes in mice through BDNF

INTRODUCTION

Primary cilia are hair-like solitary organelles growing on most mammalian cells that play fundamental roles in embryonic patterning and organogenesis. Defective cilia often cause a suite of inherited diseases called ciliopathies with multifaceted manifestations. Intraflagellar transport (IFT), a bidirectional protein trafficking along the cilium, actively facilitates the formation and absorption of primary cilia. IFT172 is the largest component of the IFT-B complex, and its roles in Bardet-Biedl Syndrome (BBS) have been appreciated with unclear mechanisms.

OBJECTIVES

We performed a battery of behavioral tests with Ift172 haploinsufficiency (Ift172+/-) and WT littermates. We use RNA sequencing to identify the genes and signaling pathways that are differentially expressed and enriched in the hippocampus of Ift172+/- mice. Using AAV-mediated sparse labeling, electron microscopic examination, patch clamp and local field potential recording, western blot, luciferase reporter assay, chromatin immunoprecipitation, and neuropharmacological approach, we investigated the underlying mechanisms for the aberrant phenotypes presented by Ift172+/- mice.

RESULTS

Ift172+/- mice displayed excessive self-grooming, elevated anxiety, and impaired cognition. RNA sequencing revealed enrichment of differentially expressed genes in pathways relevant to axonogenesis and synaptic plasticity, which were further confirmed by less spine density and synaptic number. Ift172+/- mice demonstrated fewer parvalbumin-expressing neurons, decreased inhibitory synaptic transmission, augmented theta oscillation, and sharp-wave ripples in the CA1 region. Moreover, Ift172 haploinsufficiency caused less BDNF production and less activated BDNF-TrkB signaling pathway through transcription factor Gli3. Application of 7,8-Dihydroxyflavone, a potent small molecular TrkB agonist, fully restored BDNF-TrkB signaling activity and abnormal behavioral phenotypes presented by Ift172+/- mice. With luciferase and chip assays, we provided further evidence that Gli3 may physically interact with BDNF promoter I and regulate BDNF expression.

CONCLUSIONS

Our data suggest that Ift172 per se drives neurotrophic effects and, when defective, could cause neurodevelopmental disorders reminiscent of autism-like disorders.

Dexamethasone induces developmental axon damage in the offspring hippocampus by activating miR-210-3p/miR-362-5p to target the aberrant expression of Sonic Hedgehog

Given the extensive application of dexamethasone in both clinical settings and the livestock industry, human exposure to this drug can occur through various sources and pathways. Prior research has indicated that prenatal exposure to dexamethasone (PDE) heightens the risk of cognitive and emotional disorders in offspring. Axonal development impairment is a frequent pathological underpinning for neuronal dysfunction in these disorders, yet it remains unclear if it plays a role in the neural damage induced by PDE in the offspring. Through RNA-seq and bioinformatics analysis, we found that various signaling pathways related to nervous system development, including axonal development, were altered in the hippocampus of PDE offspring. Among them, the Sonic Hedgehog (SHH) signaling pathway was the most significantly altered and crucial for axonal development. By using miRNA-seq and targeting miRNAs and glucocorticoid receptor (GR) expression, we identified miR-210-3p and miR-362-5p, which can target and suppress SHH expression. Their abnormal high expression was associated with GR activation in PDE fetal rats. Further testing of PDE offspring rats and infant peripheral blood samples exposed to dexamethasone in utero showed that SHH expression was significantly decreased in peripheral blood mononuclear cells (PBMCs) and was positively correlated with SHH expression in the hippocampus and the expression of the axonal development marker growth-associated protein-43. In summary, PDE-induced hippocampal GR-miR-210-3p/miR-362-5p-SHH signaling axis changes lead to axonal developmental damage. SHH expression in PBMCs may reflect axonal developmental damage in PDE offspring and could serve as a warning marker for fetal axonal developmental damage.

Corticospinal-specific Shh overexpression in combination with rehabilitation promotes CST axonal sprouting and skilled motor functional recovery after ischemic stroke

Ischemic stroke often leads to permanent neurological impairments, largely due to limited neuroplasticity in adult central nervous system. Here, we first showed that the expression of Sonic Hedgehog (Shh) in corticospinal neurons (CSNs) peaked at the 2nd postnatal week, when corticospinal synaptogenesis occurs. Overexpression of Shh in adult CSNs did not affect motor functions and had borderline effects on promoting the recovery of skilled locomotion following ischemic stroke. In contrast, CSNs-specific Shh overexpression significantly enhanced the efficacy of rehabilitative training, resulting in robust axonal sprouting and synaptogenesis of corticospinal axons into the denervated spinal cord, along with significantly improved behavioral outcomes. Mechanistically, combinatory treatment led to additional mTOR activation in CSNs when compared to that evoked by rehabilitative training alone. Taken together, our study unveiled a role of Shh, a morphogen involved in early development, in enhancing neuroplasticity, which significantly improved the outcomes of rehabilitative training. These results thus provide novel insights into the design of combinatory treatment for stroke and traumatic central nervous system injuries.

Temporal control of neuronal wiring

Wiring an animal brain is a complex process involving a staggering number of cell-types born at different times and locations in the developing brain. Incorporation of these cells into precise circuits with high fidelity is critical for animal survival and behavior. Assembly of neuronal circuits is heavily dependent upon proper timing of wiring programs, requiring neurons to express specific sets of genes (sometimes transiently) at the right time in development. While cell-type specificity of genetic programs regulating wiring has been studied in detail, mechanisms regulating proper timing and coordination of these programs across cell-types are only just beginning to emerge. In this review, we discuss some temporal regulators of wiring programs and how their activity is controlled over time and space. A common feature emerges from these temporal regulators - they are induced by cell-extrinsic cues and control transcription factors capable of regulating a highly cell-type specific set of target genes. Target specificity in these contexts comes from cell-type specific transcription factors. We propose that the spatiotemporal specificity of wiring programs is controlled by the combinatorial activity of temporal programs and cell-type specific transcription factors. Going forward, a better understanding of temporal regulators will be key to understanding the mechanisms underlying brain wiring, and will be critical for the development of in vitro models like brain organoids.

Sonic hedgehog pathway as a new target of atypical antipsychotics: Revisiting of amisulpride and aripiprazole effects in a rat model of schizophrenia

OBJECTIVES

Schizophrenia is a chronic mental illness presented by cognitive deficits that precede its positive and negative symptoms. Sonic hedgehog (Shh)-pathway contributes to its pathophysiology. Shh has a role in neurogenesis as it regulates proliferation and survival of neural cells. In this study, effects of the anti-psychotics Amisulpride and/or Aripiprazole on the Shh-pathway and its relation to cognitive functions and neurogenesis in a rat model of schizophrenia were tested.

METHODS

60 male Wistar rats were allocated into the following groups: control, socially isolated, amisulpride and/or aripiprazole-treated groups. Rats were then subjected to behavioral, biochemical, and histopathological tests to assess the impact of these drugs on Shh-pathway.

KEY FINDINGS

Cognitive-dysfunction was evidenced in socially isolated group in novel object, three-chamber, and Morris water maze tests, associated by disorganised Shh-pathway proteins levels concentrations, increased glial fibrillary acidic protein (GFAP)-stained astrocytes. Treated groups favorably reversed these changes evidenced by increased Shh, transmembrane patched-1 and smoothened, glioma-associated-oncogene (GLI)-1 levels, dopamine-1 receptors and brain derived neurotrophic factor, and decreased GLI-3 protein, GFAP immune reaction in astrocytes and inflammatory markers compared to socially isolated group.

CONCLUSION

Amisulpride and/or aripiprazole have a favorable role in turning on Shh-pathway with subsequent beneficial cognitive and neurogenesis effects.

Resveratrol Inhibits Activation of Microglia after Stroke through Triggering Translocation of Smo to Primary Cilia

Activated microglia act as a double-edged sword for stroke. In the acute phase of stroke, activated microglia might deteriorate neurological function. Therefore, it is of great clinical transforming potential to explore drugs or methods that can inhibit abnormal activation of microglia in the acute phase of stroke to improve neurological function after stroke. Resveratrol has a potential effect of regulating microglial activation and anti-inflammation. However, the molecular mechanism of resveratrol-inhibiting microglial activation has not been fully clarified. Smoothened (Smo) belongs to the Hedgehog (Hh) signaling pathway. Smo activation is the critical step that transmits the Hh signal across the primary cilia to the cytoplasm. Moreover, activated Smo can improve neurological function via regulating oxidative stress, inflammation, apoptosis, neurogenesis, oligodendrogenesis, axonal remodeling, and so on. More studies have indicated that resveratrol can activate Smo. However, it is currently unknown whether resveratrol inhibits microglial activation via Smo. Therefore, in this study, N9 microglia in vitro and mice in vivo were used to investigate whether resveratrol inhibited microglial activation after oxygen-glucose deprivation/reoxygenation (OGD/R) or middle cerebral artery occlusion/reperfusion (MCAO/R) injury and improved functional outcome via triggering translocation of Smo in primary cilia. We definitively found that microglia had primary cilia; resveratrol partially inhibited activation and inflammation of microglia, improved functional outcome after OGD/R and MCAO/R injury, and triggered translocation of Smo to primary cilia. On the contrary, Smo antagonist cyclopamine canceled the above effects of resveratrol. The study suggested that Smo receptor might be a therapeutic target of resveratrol for contributing to inhibit microglial activation in the acute phase of stroke.

Ciliary signaling proteins are mislocalized in the brains of Bardet-Biedl syndrome 1-null mice

In the brain, primary cilia are found on most, if not all, central neurons. The importance of neuronal cilia is underscored by the fact that human diseases caused by primary cilia dysfunction, which are known as ciliopathies, are associated with neuropathologies, including neuropsychiatric disorders and learning and memory deficits. Neuronal cilia are enriched for certain G protein-coupled receptors and their downstream effectors, suggesting they sense and respond to neuromodulators in the extracellular milieu. GPCR ciliary localization is disrupted in neurons from mouse models of the ciliopathy Bardet-Biedl syndrome, with GPCRs failing to localize to cilia, indicating the Bardet-Biedl syndrome proteins are required for trafficking of G protein-coupled receptors into neuronal cilia. Yet, dopamine receptor 1 accumulates in cilia in the absence of Bardet-Biedl syndrome proteins, suggesting Bardet-Biedl syndrome proteins are required for normal ciliary import and export. To further explore the roles of the Bardet-Biedl syndrome proteins in neuronal cilia, we examined localization of ciliary signaling proteins in a new constitutive Bbs1 knockout mouse model. Interestingly, we find that two additional ciliary G protein-coupled receptors (Gpr161 and Gpr19) abnormally accumulate in cilia on Bardet-Biedl syndrome neurons. In addition, we find that the GPCR signaling protein β-arrestin accumulates in a subset of cilia in the brain, suggesting the presence of additional unidentified ciliary G protein-coupled receptors. These results confirm the importance of the Bardet-Biedl syndrome proteins in establishing ciliary GPCR pathways and indicate that loss of Bbs1 leads to complex changes in the localization of signaling proteins in the brain.

Role of Sonic Hedgehog Signaling Activation in the Prevention of Neurological Abnormalities Associated with Obsessive-Compulsive Disorder

The smoothened sonic hedgehog (Smo-Shh) pathway is one mechanism that influences neurogenesis, including brain cell differentiation and development during childhood. Shh signaling dysregulation leads to decreased target gene transcription, which contributes to increased neuronal excitation, apoptosis, and neurodegeneration, eventually leading to neurological deficits. Neuropsychiatric disorders such as OCD and related neurological dysfunctions are characterized by neurotransmitter imbalance, neuroinflammation, oxidative stress, and impaired neurogenesis, disturbing the cortico-striato-thalamo-cortical (CSTC) link neuronal network. Despite the availability of several treatments, such as selective serotonin reuptake inhibitors, some individuals may not benefit much from them. Several trials on the use of antipsychotics in the treatment of OCD have also produced inadequate findings. This evidence-based review focuses on a potential pharmacological approach to alleviating OCD and associated neuronal deficits by preventing neurochemical alterations, in which sonic hedgehog activators are neuroprotective, lowering neuronal damage while increasing neuronal maintenance and survival. As a result, stimulating SMO-Shh via its potential activators may have neuroprotective effects on neurological impairment associated with OCD. This review investigates the link between SMO-Shh signaling and the neurochemical abnormalities associated with the progression of OCD and associated neurological dysfunctions. Role of Smo-Shh signaling in serotonergic neurogenesis and in maintaining their neuronal identity. The Shh ligand activates two main transcriptional factors known as Foxa2 and Nkx2.2, which again activates another transcriptional factor, GATA (GATA2 and GATA3), in post mitotic precursor cells of serotonergic neurons-following increased expression of Pet-1 and Lmx1b after GATA regulates the expression of many serotonergic enzymes such as TPH2, SERT, VMAT, slc6a4, Htr1a, Htr1b (Serotonin receptor enzymes), and MAO that regulate and control the release of serotonin and maintain their neuronal identity after their maturation. Abbreviation: Foxa2: Forkhead box; GATA: Globin transcription factor; Lmx1b: LIM homeobox transcription factor 1 beta; TPH2: Tryptophan hydroxylase 2; Htr1a: Serotonin receptor 1a; Htr1b: Serotonin receptor 1b; SERT: Serotonin transporter; VMAT: Vesicular monoamine transporter; MAO: Monoamine oxidase.

Molecular mechanisms of developmental pathways in neurological disorders: a pharmacological and therapeutic review

Developmental signalling pathways such as Wnt/β-catenin, Notch and Sonic hedgehog play a central role in nearly all the stages of neuronal development. The term 'embryonic' might appear to be a misnomer to several people because these pathways are functional during the early stages of embryonic development and adulthood, albeit to a certain degree. Therefore, any aberration in these pathways or their associated components may contribute towards a detrimental outcome in the form of neurological disorders such as Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis and stroke. In the last decade, researchers have extensively studied these pathways to decipher disease-related interactions, which can be used as therapeutic targets to improve outcomes in patients with neurological abnormalities. However, a lot remains to be understood in this domain. Nevertheless, there is strong evidence supporting the fact that embryonic signalling is indeed a crucial mechanism as is manifested by its role in driving memory loss, motor impairments and many other processes after brain trauma. In this review, we explore the key roles of three embryonic pathways in modulating a range of homeostatic processes such as maintaining blood-brain barrier integrity, mitochondrial dynamics and neuroinflammation. In addition, we extensively investigated the effect of these pathways in driving the pathophysiology of a range of disorders such as Alzheimer's, Parkinson's and diabetic neuropathy. The concluding section of the review is dedicated to neurotherapeutics, wherein we identify and list a range of biological molecules and compounds that have shown enormous potential in improving prognosis in patients with these disorders.

Contribution of Smoothened Receptor Signaling in GABAergic Neurotransmission and Chloride Homeostasis in the Developing Rodent Brain

In the early stages of the central nervous system growth and development, γ-aminobutyric acid (GABA) plays an instructive trophic role for key events including neurogenesis, migration, synaptogenesis, and network formation. These actions are associated with increased concentration of chloride ions in immature neurons [(Cl⁻)_i] that determines the depolarizing strength of ion currents mediated by GABA_A receptors, a ligand-gated Cl⁻ permeable ion channel. During neuron maturation the (Cl⁻)_i progressively decreases leading to weakening of GABA induced depolarization and enforcing GABA function as principal inhibitory neurotransmitter. A neuron restricted potassium-chloride co-transporter KCC2 is a key molecule governing Cl⁻ extrusion and determining the resting level of (Cl⁻)_i in developing and mature mammalian neurons. Among factors controlling the functioning of KCC2 and the maturation of inhibitory circuits, is Smoothened (Smo), the transducer in the receptor complex of the developmental protein Sonic Hedgehog (Shh). Too much or too little Shh-Smo action will have mirror effects on KCC2 stability at the neuron membrane, the GABA inhibitory strength, and ultimately on the newborn susceptibility to neurodevelopmental disorders. Both canonical and non-canonical Shh-Smo signal transduction pathways contribute to the regulation of KCC2 and GABAergic synaptic activity. In this review, we discuss the recent findings of the action of Shh-Smo signaling pathways on chloride ions homeostasis through the control of KCC2 membrane trafficking, and consequently on inhibitory neurotransmission and network activity during postnatal development.

Synergistic gene regulation by thyroid hormone and glucocorticoid in the hippocampus

The hippocampus is considered the center for learning and memory in the brain, and its development and function is greatly affected by the thyroid and stress axes. Thyroid hormone (TH) and glucocorticoids (GC) are known to have a synergistic effect on developmental programs across several vertebrate species, and their effects on hippocampal structure and function are well-documented. However, there are few studies that focus on the processes and genes that are cooperatively regulated by the two hormone axes. Cross-regulation of the thyroid and stress axes in the hippocampus occurs on multiple levels such that TH can regulate the expression of the GC receptor (GR) while GC can modulate tissue sensitivity to TH by controlling the expression of TH receptor (TR) and enzymes involved in TH biosynthesis. Thyroid hormone and GC are also known to synergistically regulate the transcription of genes associated with neuronal function and development. Synergistic gene regulation by TH and GC may occur through the direct, cooperative action of TR and GR on common target genes, or by indirect mechanisms involving gene regulatory cascades activated by TR and GR. In this chapter, we describe the known physiological effects and underlying molecular mechanisms of TH and GC synergistic gene regulation in the hippocampus.

Expression of the hippocampal PTCH during early abstinence is associated with drinking patterns in a rat model of voluntary alcohol intake

Perinatal alcohol exposure induces fetal alcohol syndrome partially through Sonic Hedgehog (SHH) impairment; however, the relationship between SHH signaling cascade and alcohol drinking pattern in adulthood remains obscure. We studied the expression of SHH and components of respective signaling cascade [PTCH receptor (Patched), SMO co-receptor (Smoothened) and downstream transcriptional factor Glioma-associated oncogene (GLI)] during early abstinence in brain regions of rats demonstrating different drinking patterns in intermittent access two-bottle choice paradigm (IA2BC). Male Wistar rats were subjected to twenty 24-h sessions of free access to two-bottle choice (water or 20% ethanol) with 24-h withdrawal periods (water only). Control animals had access to water only. Quantitative PCR and western blotting were used to assess transcript and protein levels in the brain, respectively. During the course of the IA2BC, one part of animals demonstrated gradual escalation from low to high alcohol intake and preference of alcohol over water (group I), while the other one consumed alcohol at stable high level (group II) (Peregud et al., 2021). Three days after the last drinking session, PTCH mRNA elevated in the hippocampus of group I rats as compared to the control group. However, SHH, SMO and GLI mRNA levels in the hippocampus did not change. The protein content of PTCH in the hippocampus of group I rats was higher as compared to both control and group II. PTCH elevation is a known marker of SHH cascade activity. Thus, activated hippocampal SHH signaling cascade is a hallmark of rats demonstrating gradual escalation of alcohol intake in the IA2BC procedure.

Exploring Sonic Hedgehog Cell Signaling in Neurogenesis: Its Potential Role in Depressive Behavior

Depression is the most prevalent form of neuropsychiatric disorder affecting all age groups globally. As per the estimation of the World Health Organization (WHO), depression will develop into the foremost reason for disability globally by the year 2030. The primary neurobiological mechanism implicated in depression remains ambiguous; however, dysregulation of molecular and signaling transductions results in depressive disorders. Several theories have been developed to explain the pathogenesis of depression, however, none of them completely explained all aspects of depressive-pathogenesis. In the current review, we aimed to explore the role of the sonic hedgehog (Shh) signaling pathway in the development of the depressive disorder and its potential as the therapeutic target. Shh signaling has a crucial function in neurogenesis and neural tube patterning during the development of the central nervous system (CNS). Shh signaling performs a basic function in embryogenesis and hippocampal neurogenesis. Moreover, antidepressants are also known to enhance neurogenesis in the hippocampus, which further suggests the potential of Shh signaling. Furthermore, there is decreased expression of a glioma-associated oncogene (Gli1) and Smoothened (Smo) in depression. Moreover, antidepressants also regulate brain-derived neurotrophic factor (BDNF) and wingless protein (Wnt) signaling, therefore, Shh may be implicated in the pathogenesis of the depressive disorder. Deregulation of Shh signaling in CNS results in neurological disorders such as depression.

Restoration of early deficiency of axonal guidance signaling by guanxinning injection as a novel therapeutic option for acute ischemic stroke

Despite of its high morbidity and mortality, there is still a lack of effective treatment for ischemic stroke in part due to our incomplete understanding of molecular mechanisms of its pathogenesis. In this study, we demonstrate that SHH-PTCH1-GLI1-mediated axonal guidance signaling and its related neurogenesis, a central pathway for neuronal development, also plays a critical role in early stage of an acute stroke model. Specifically, in vivo, we evaluated the effect of GXNI on ischemic stroke mice via using the middle cerebral artery embolization model, and found that GXNI significantly alleviated cerebral ischemic reperfusion (I/R) injury by reducing the volume of cerebral infarction, neurological deficit score and cerebral edema, reversing the BBB permeability and histopathological changes. A combined approach of RNA-seq and network pharmacology analysis was used to reveal the underlying mechanisms of GXNI followed by RT-PCR, immunohistochemistry and western blotting validation. It was pointed out that axon guidance signaling pathway played the most prominent role in GXNI action with Shh, Ptch1, and Gli1 genes as the critical contributors in brain protection. In addition, GXNI markedly prevented primary cortical neuron cells from oxygen-glucose deprivation/reoxygenation damage in vitro, and promoted axon growth and synaptogenesis of damaged neurons, which further confirmed the results of in vivo experiments. Moreover, due to the inhibition of the SHH-PTCH1-GLI1 signaling pathway by cyclopropylamine, the effect of GXNI was significantly weakened. Hence, our study provides a novel option for the clinical treatment of acute ischemic stroke by GXNI via SHH-PTCH1-GLI1-mediated axonal guidance signaling, a neuronal development pathway previously considered for after-stroke recovery.

KDM5A mutations identified in autism spectrum disorder using forward genetics

Autism spectrum disorder (ASD) is a constellation of neurodevelopmental disorders with high phenotypic and genetic heterogeneity, complicating the discovery of causative genes. Through a forward genetics approach selecting for defective vocalization in mice, we identified Kdm5a as a candidate ASD gene. To validate our discovery, we generated a Kdm5a knockout mouse model (Kdm5a^-/-) and confirmed that inactivating Kdm5a disrupts vocalization. In addition, Kdm5a^-/- mice displayed repetitive behaviors, sociability deficits, cognitive dysfunction, and abnormal dendritic morphogenesis. Loss of KDM5A also resulted in dysregulation of the hippocampal transcriptome. To determine if KDM5A mutations cause ASD in humans, we screened whole exome sequencing and microarray data from a clinical cohort. We identified pathogenic KDM5A variants in nine patients with ASD and lack of speech. Our findings illustrate the power and efficacy of forward genetics in identifying ASD genes and highlight the importance of KDM5A in normal brain development and function.

Smoothened receptor signaling regulates the developmental shift of GABA polarity in rat somatosensory cortex

Sonic hedgehog (Shh) and its patched-smoothened receptor complex control a variety of functions in the developing central nervous system, such as neural cell proliferation and differentiation. Recently, Shh signaling components have been found to be expressed at the synaptic level in the postnatal brain, suggesting a potential role in the regulation of synaptic transmission. Using in utero electroporation of constitutively active and negative-phenotype forms of the Shh signal transducer smoothened (Smo), we studied the role of Smo signaling in the development and maturation of GABAergic transmission in the somatosensory cortex. Our results show that enhancing Smo activity during development accelerates the shift from depolarizing to hyperpolarizing GABA in a manner dependent on functional expression of potassium-chloride cotransporter type 2 (KCC2, also known as SLC12A5). On the other hand, blocking Smo activity maintains the GABA response in a depolarizing state in mature cortical neurons, resulting in altered chloride homeostasis and increased seizure susceptibility. This study reveals unexpected functions of Smo signaling in the regulation of chloride homeostasis, through control of KCC2 cell-surface stability, and the timing of the GABA excitatory-to-inhibitory shift in brain maturation.

Sonic Hedgehog Signaling Agonist (SAG) Triggers BDNF Secretion and Promotes the Maturation of GABAergic Networks in the Postnatal Rat Hippocampus

Sonic hedgehog (Shh) signaling plays critical roles during early central nervous system development, such as neural cell proliferation, patterning of the neural tube and neuronal differentiation. While Shh signaling is still present in the postnatal brain, the roles it may play are, however, largely unknown. In particular, Shh signaling components are found at the synaptic junction in the maturing hippocampus during the first two postnatal weeks. This period is characterized by the presence of ongoing spontaneous synaptic activity at the cellular and network levels thought to play important roles in the onset of neuronal circuit formation and synaptic plasticity. Here, we demonstrate that non-canonical Shh signaling increases the frequency of the synchronized electrical activity called Giant Depolarizing Potentials (GDP) and enhances spontaneous GABA post-synaptic currents in the rodent hippocampus during the early postnatal period. This effect is mediated specifically through the Shh co-receptor Smoothened via intracellular Ca²⁺ signal and the activation of the BDNF-TrkB signaling pathway. Given the importance of these spontaneous events on neuronal network maturation and refinement, this study opens new perspectives for Shh signaling on the control of early stages of postnatal brain maturation and physiology.

Hedgehog Pathway Activation Alters Ciliary Signaling in Primary Hypothalamic Cultures

Primary cilia dysfunction has been associated with hyperphagia and obesity in both ciliopathy patients and mouse models of cilia perturbation. Neurons throughout the brain possess these solitary cellular appendages, including in the feeding centers of the hypothalamus. Several cell biology questions associated with primary neuronal cilia signaling are challenging to address in vivo. Here we utilize primary hypothalamic neuronal cultures to study ciliary signaling in relevant cell types. Importantly, these cultures contain neuronal populations critical for appetite and satiety such as pro-opiomelanocortin (POMC) and agouti related peptide (AgRP) expressing neurons and are thus useful for studying signaling involved in feeding behavior. Correspondingly, these cultured neurons also display electrophysiological activity and respond to both local and peripheral signals that act on the hypothalamus to influence feeding behaviors, such as leptin and melanin concentrating hormone (MCH). Interestingly, we found that cilia mediated hedgehog signaling, generally associated with developmental processes, can influence ciliary GPCR signaling (Mchr1) in terminally differentiated neurons. Specifically, pharmacological activation of the hedgehog-signaling pathway using the smoothened agonist, SAG, attenuated the ability of neurons to respond to ligands (MCH) of ciliary GPCRs. Understanding how the hedgehog pathway influences cilia GPCR signaling in terminally differentiated neurons could reveal the molecular mechanisms associated with clinical features of ciliopathies, such as hyperphagia-associated obesity.

Sideroflexin 3 is a Mitochondrial Protein Enriched in Neurons

Sideroflexin 1 (Sfxn1) is a mitochondrial serine transporter involved in one-carbon metabolism in blood and cancer cell lines. The expression of other Sfxn homologs varies across tissues implying that each homolog may have tissue-specific functions. RNA databases suggest that among the Sfxns, Sfxn3 may have a specific function in the brain. Here, we systematically analyzed the level, cellular distribution, and subcellular localization of Sfxn3 protein in the developing and adult rodent brain. We found that, in the cortex and hippocampus, Sfxn3 protein level is low at birth but increases during development and remains at a high level in the mature brains. Similarly, in cultured hippocampal neurons, Sfxn3 protein level is low in young neurons but increases as neurons mature. Sfxn3 protein level is much higher in neurons than in astrocytes. Within neurons, Sfxn3 localizes to mitochondria in all major neuronal compartments. Our results establish that Sfxn3 is a mitochondrial protein enriched in neurons wherein it is developmentally expressed. These findings provide a foundation for future research aimed at understanding the functions of Sfxn3 and one-carbon metabolism in neurons.

Fbxo41 Promotes Disassembly of Neuronal Primary Cilia

Neuronal primary cilia are signaling organelles with crucial roles in brain development and disease. Cilia structure is decisive for their signaling capacities but the mechanisms regulating it are poorly understood. We identify Fbxo41 as a novel Skp1/Cullin1/F-box (SCF) E3-ligase complex subunit that targets to neuronal centrioles where its accumulation promotes disassembly of primary cilia, and affects sonic hedgehog signaling, a canonical ciliary pathway. Fbxo41 targeting to centrioles requires its Coiled-coil and F-box domains. Levels of Fbxo41 at the centrioles inversely correlate with neuronal cilia length, and mutations that disrupt Fbxo41 targeting or assembly into SCF-complexes also disturb its function in cilia disassembly and signaling. Fbxo41 dependent cilia disassembly in mitotic and post-mitotic cells requires rearrangements of the actin-cytoskeleton, but requires Aurora A kinase activation only in mitotic cells, highlighting important mechanistical differences controlling cilia size between mitotic and post-mitotic cells. Phorbol esters induce recruitment of overexpressed Fbxo41 to centrioles and cilia disassembly in neurons, but disassembly can also occur in absence of Fbxo41. We propose that Fbxo41 targeting to centrosomes regulates neuronal cilia structure and signaling capacity in addition to Fbxo41-independent pathways controlling cilia size.

Sonic hedgehog expression in the postnatal brain

Beyond its role in patterning the neural tube during embryogenesis, additional functions of Sonic hedgehog (Shh) in post-embryonic and mature brains have been coming into focus. However, the question of the abundance of endogenous Shh - the ligand of the signaling pathway - and its changes over time in post-embryonic and mature brains are less well understood. Here we find that while the amounts of Shh transcript and protein in rat brains are nearly undetectable at birth, they increase continuously during postnatal development and remain at readily detectable levels in young adults. This developmental age-associated increase in Shh levels is also seen in hippocampal neurons grown in culture, in which very young neurons produce minimal amounts of Shh protein but, as neurons grow and form synapses, the amounts of Shh increase significantly. Using immunolabeling with antibodies to different residues of Shh, we observed that the N-terminal fragment and the C-terminal fragment of Shh are present in hippocampal neurons, and that these two Shh forms co-exist in most compartments of the neuron. Our findings provide a better understanding of Shh expression in the brain, laying the groundwork for further comprehending the biogenesis of Shh protein in the young and mature brain and neurons.

Pathway sensor-based functional genomics screening identifies modulators of neuronal activity

Neuronal signal transduction shapes brain function and malfunction may cause mental disorders. Despite the existence of functional genomics screens for proliferation and toxicity, neuronal signalling has been difficult to address so far. To overcome this limitation, we developed a pooled screening assay which combines barcoded activity reporters with pooled genetic perturbation in a dual-expression adeno-associated virus (AAV) library. With this approach, termed pathScreener, we comprehensively dissect signalling pathways in postmitotic neurons. This overcomes several limitations of lentiviral-based screens. By applying first a barcoded and multiplexed reporter assay, termed cisProfiler, we identified the synaptic-activity responsive element (SARE) as top performance sensor of neuronal activity. Next, we targeted more than 4,400 genes and screened for modulatory effects on SARE activity in primary cortical neurons. We identified with high replicability many known genes involved in glutamatergic synapse-to-nucleus signalling of which a subset was validated in orthogonal assays. Several others have not yet been associated with the regulation of neuronal activity such as the hedgehog signalling members Ptch2 and Ift57. This assay thus enhances the toolbox for analysing regulatory processes during neuronal signalling and may help identifying novel targets for brain disorders.

Hedgehog signaling contributes to bone cancer pain by regulating sensory neuron excitability in rats

Treating bone cancer pain continues to be a clinical challenge and underlying mechanisms of bone cancer pain remain elusive. Here, we reported that sonic hedgehog signaling plays a critical role in the development of bone cancer pain. Tibia bone cavity tumor cell implantation produces bone cancer-related mechanical allodynia, thermal hyperalgesia, and spontaneous and movement-evoked pain behaviors. Production and persistence of these pain behaviors are well correlated with tumor cell implantation-induced up-regulation and activation of sonic hedgehog signaling in primary sensory neurons and spinal cord. Spinal administration of sonic hedgehog signaling inhibitor cyclopamine prevents and reverses the induction and persistence of bone cancer pain without affecting normal pain sensitivity. Inhibiting sonic hedgehog signaling activation with cyclopamine, in vivo or in vitro, greatly suppresses tumor cell implantation-induced increase of intracellular Ca²⁺ and hyperexcitability of the sensory neurons and also the activation of GluN2B receptor and the subsequent Ca²⁺-dependent signals CaMKII and CREB in dorsal root ganglion and the spinal cord. These findings show a critical mechanism underlying the pathogenesis of bone cancer pain and suggest that targeting sonic hedgehog signaling may be an effective approach for treating bone cancer pain.

Sonic Hedgehog Signaling Pathway in Endothelial Progenitor Cell Biology for Vascular Medicine

The Hedgehog (HH) signaling pathway plays an important role in embryonic and postnatal vascular development and in maintaining the homeostasis of organs. Under physiological conditions, Sonic Hedgehog (SHH), a secreted protein belonging to the HH family, regulates endothelial cell growth, promotes cell migration and stimulates the formation of new blood vessels. The present review highlights recent advances made in the field of SHH signaling in endothelial progenitor cells (EPCs). The canonical and non-canonical SHH signaling pathways in EPCs and endothelial cells (ECs) related to homeostasis, SHH signal transmission by extracellular vesicles (EVs) or exosomes containing single-strand non-coding miRNAs and impaired SHH signaling in cardiovascular diseases are discussed. As a promising therapeutic tool, the possibility of using the SHH signaling pathway for the activation of EPCs in patients suffering from cardiovascular diseases is further explored.

Ptchd1 deficiency induces excitatory synaptic and cognitive dysfunctions in mouse

Synapse development and neuronal activity represent fundamental processes for the establishment of cognitive function. Structural organization as well as signalling pathways from receptor stimulation to gene expression regulation are mediated by synaptic activity and misregulated in neurodevelopmental disorders such as autism spectrum disorder (ASD) and intellectual disability (ID). Deleterious mutations in the PTCHD1 (Patched domain containing 1) gene have been described in male patients with X-linked ID and/or ASD. The structure of PTCHD1 protein is similar to the Patched (PTCH1) receptor; however, the cellular mechanisms and pathways associated with PTCHD1 in the developing brain are poorly determined. Here we show that PTCHD1 displays a C-terminal PDZ-binding motif that binds to the postsynaptic proteins PSD95 and SAP102. We also report that PTCHD1 is unable to rescue the canonical sonic hedgehog (SHH) pathway in cells depleted of PTCH1, suggesting that both proteins are involved in distinct cellular signalling pathways. We find that Ptchd1 deficiency in male mice (Ptchd1^-/y) induces global changes in synaptic gene expression, affects the expression of the immediate-early expression genes Egr1 and Npas4 and finally impairs excitatory synaptic structure and neuronal excitatory activity in the hippocampus, leading to cognitive dysfunction, motor disabilities and hyperactivity. Thus our results support that PTCHD1 deficiency induces a neurodevelopmental disorder causing excitatory synaptic dysfunction.

Sonic hedgehog signaling in spinal cord contributes to morphine-induced hyperalgesia and tolerance through upregulating brain-derived neurotrophic factor expression

Purpose

Preventing opioid-induced hyperalgesia and tolerance continues to be a major clinical challenge, and the underlying mechanisms of hyperalgesia and tolerance remain elusive. Here, we investigated the role of sonic hedgehog (Shh) signaling in opioid-induced hyperalgesia and tolerance.

Methods

Shh signaling expression, behavioral changes, and neurochemical alterations induced by morphine were analyzed in male adult CD-1 mice with repeated administration of morphine. To investigate the contribution of Shh to morphine-induced hyperalgesia (MIH) and tolerance, Shh signaling inhibitor cyclopamine and Shh small interfering RNA (siRNA) were used. To explore the mechanisms of Shh signaling in MIH and tolerance, brain-derived neurotrophic factor (BDNF) inhibitor K252 and anti-BDNF antibody were used.

Results

Repeated administration of morphine produced obvious hyperalgesia and tolerance. The behavioral changes were correlated with the upregulation and activation of morphine treatment-induced Shh signaling. Pharmacologic and genetic inhibition of Shh signaling significantly delayed the generation of MIH and tolerance and associated neurochemical changes. Chronic morphine administration also induced upregulation of BDNF. Inhibiting BDNF effectively delayed the generation of MIH and tolerance. The upregulation of BDNF induced by morphine was significantly suppressed by inhibiting Shh signaling. In naïve mice, exogenous activation of Shh signaling caused a rapid increase of BDNF expression, as well as thermal hyperalgesia. Inhibiting BDNF significantly suppressed smoothened agonist-induced hyperalgesia.

Conclusion

These findings suggest that Shh signaling may be a critical mediator for MIH and tolerance by regulating BDNF expression. Inhibiting Shh signaling, especially during the early phase, may effectively delay or suppress MIH and tolerance.

Expression of the purine biosynthetic enzyme phosphoribosyl formylglycinamidine synthase in neurons

Purines are metabolic building blocks essential for all living organisms on earth. De novo purine biosynthesis occurs in the brain and appears to play important roles in neural development. Phosphoribosyl formylglycinamidine synthase (FGAMS, also known as PFAS or FGARAT), a core enzyme involved in the de novo synthesis of purines, may play alternative roles in viral pathogenesis. To date, no thorough investigation of the endogenous expression and localization of de novo purine biosynthetic enzymes has been conducted in human neurons or in virally infected cells. In this study, we characterized expression of FGAMS using multiple neuronal models. In differentiated human SH-SY5Y neuroblastoma cells, primary rat hippocampal neurons, and in whole-mouse brain sections, FGAMS immunoreactivity was distributed within the neuronal cytoplasm. FGAMS immunolabeling in vitro demonstrated extensive distribution throughout neuronal processes. To investigate potential changes in FGAMS expression and localization following viral infection, we infected cells with the human pathogen herpes simplex virus 1. In infected fibroblasts, FGAMS immunolabeling shifted from a diffuse cytoplasmic location to a mainly perinuclear localization by 12 h post-infection. In contrast, in infected neurons, FGAMS localization showed no discernable changes in the localization of FGAMS immunoreactivity. There were no changes in total FGAMS protein levels in either cell type. Together, these data provide insight into potential purine biosynthetic mechanisms utilized within neurons during homeostasis as well as viral infection. Cover Image for this Issue: doi: 10.1111/jnc.14169.

Epigenetic modifiers promote mitochondrial biogenesis and oxidative metabolism leading to enhanced differentiation of neuroprogenitor cells

During neural development, epigenetic modulation of chromatin acetylation is part of a dynamic, sequential and critical process to steer the fate of multipotent neural progenitors toward a specific lineage. Pan-HDAC inhibitors (HDCis) trigger neuronal differentiation by generating an “acetylation” signature and promoting the expression of neurogenic bHLH transcription factors. Our studies and others have revealed a link between neuronal differentiation and increase of mitochondrial mass. However, the neuronal regulation of mitochondrial biogenesis has remained largely unexplored. Here, we show that the HDACi, sodium butyrate (NaBt), promotes mitochondrial biogenesis via the NRF-1/Tfam axis in embryonic hippocampal progenitor cells and neuroprogenitor-like PC12-NeuroD6 cells, thereby enhancing their neuronal differentiation competency. Increased mitochondrial DNA replication by several pan-HDACis indicates a common mechanism by which they regulate mitochondrial biogenesis. NaBt also induces coordinates mitochondrial ultrastructural changes and enhanced OXPHOS metabolism, thereby increasing key mitochondrial bioenergetics parameters in neural progenitor cells. NaBt also endows the neuronal cells with increased mitochondrial spare capacity to confer resistance to oxidative stress associated with neuronal differentiation. We demonstrate that mitochondrial biogenesis is under HDAC-mediated epigenetic regulation, the timing of which is consistent with its integrative role during neuronal differentiation. Thus, our findings add a new facet to our mechanistic understanding of how pan-HDACis induce differentiation of neuronal progenitor cells. Our results reveal the concept that epigenetic modulation of the mitochondrial pool prior to neurotrophic signaling dictates the efficiency of initiation of neuronal differentiation during the transition from progenitor to differentiating neuronal cells. The histone acetyltransferase CREB-binding protein plays a key role in regulating the mitochondrial biomass. By ChIP-seq analysis, we show that NaBt confers an H3K27ac epigenetic signature in several interconnected nodes of nuclear genes vital for neuronal differentiation and mitochondrial reprogramming. Collectively, our study reports a novel developmental epigenetic layer that couples mitochondrial biogenesis to neuronal differentiation.

Purine Biosynthesis Enzymes in Hippocampal Neurons

Despite reports implicating disrupted purine metabolism in causing a wide spectrum of neurological defects, the mechanistic details of purine biosynthesis in neurons are largely unknown. As an initial step in filling that gap, we examined the expression and subcellular distribution of three purine biosynthesis enzymes (PFAS, PAICS and ATIC) in rat hippocampal neurons. Using immunoblotting and high-resolution light and electron microscopic analysis, we find that all three enzymes are broadly distributed in hippocampal neurons with pools of these enzymes associated with mitochondria. These findings suggest a potential link between purine metabolism and mitochondrial function in neurons and provide an impetus for further studies.

Serotonin 5-HT6 receptors affect cognition in a mouse model of Alzheimer's disease by regulating cilia function

BACKGROUND

Serotonin receptor 5-HT6 is involved in cognition and Alzheimer's disease (AD) development. However, the mechanism of 5-HT6 in AD pathology is not clear.

METHODS

Since 5-HT6 is almost exclusively expressed in the primary cilia, using immunostaining we examined the number of cilia in the hippocampus of AD animal model APP/PS1 mice. By overexpressing and knocking down 5-HT6 in the primary cultured hippocampal neurons, we investigated the roles of 5-HT6 in alternating ciliary morphology. Furthermore, 5-HT6 antagonist was applied to confirm its roles in cognition using the Morris water maze test, Y maze, and fear conditioning.

RESULTS

In the present study, we found that the primary cilia were elongated in the hippocampus of APP/PS1 mice compared with WT mice. 5-HT6 regulated cilia length, influenced cilia and axon initial segment (AIS) morphology, and affected localization of ARL13B and AnkG. We also found that, by changing cilia morphology, the AIS was elongated, branched, and more proximal to the cell body in both WT and APP/PS1 mouse neurons. Alterations of cilia also decreased the axonal length in WT and APP/PS1 neurons. Furthermore, in the water maze test, Y maze, and fear conditioning test, 5-HT6 antagonist SB271046 recovered the cognitive impairment of APP/PS1 mice.

CONCLUSION

We suggest that 5-HT6 plays a critical role in AD development through regulating the morphology and function of neuronal primary cilia, which is possibly related to the AIS and axon alterations in AD development.

Sonic -'Jack-of-All-Trades' in Neural Circuit Formation

As reflected by the term morphogen, molecules such as Shh and Wnts were identified based on their role in early development when they instruct precursor cells to adopt a specific cell fate. Only much later were they implicated in neural circuit formation. Both in vitro and in vivo studies indicated that morphogens direct axons during their navigation through the developing nervous system. Today, the best understood role of Shh and Wnt in axon guidance is their effect on commissural axons in the spinal cord. Shh was shown to affect commissural axons both directly and indirectly via its effect on Wnt signaling. In fact, throughout neural circuit formation there is cross-talk and collaboration of Shh and Wnt signaling. Thus, although the focus of this review is on the role of Shh in neural circuit formation, a separation from Wnt signaling is not possible.

Targeting sonic hedgehog signaling in neurological disorders

Sonic hedgehog (Shh) signaling influences neurogenesis and neural patterning during the development of central nervous system. Dysregulation of Shh signaling in brain leads to neurological disorders like autism spectrum disorder, depression, dementia, stroke, Parkinson's diseases, Huntington's disease, locomotor deficit, epilepsy, demyelinating disease, neuropathies as well as brain tumors. The synthesis, processing and transport of Shh ligand as well as the localization of its receptors and signal transduction in the central nervous system has been carefully reviewed. Further, we summarize the regulation of small molecule modulators of Shh pathway with potential in neurological disorders. In conclusion, further studies are warranted to demonstrate the potential of positive and negative regulators of the Shh pathway in neurological disorders.

Sonic hedgehog pathway activation increases mitochondrial abundance and activity in hippocampal neurons

Activation of the Sonic hedgehog signaling pathway affects multiple aspects of mitochondria in hippocampal neurons. It increases mitochondrial mass significantly, reduces fission, and promotes elongation. It also protects neurons against stress.

Mitochondria are essential organelles whose biogenesis, structure, and function are regulated by many signaling pathways. We present evidence that, in hippocampal neurons, activation of the Sonic hedgehog (Shh) signaling pathway affects multiple aspects of mitochondria. Mitochondrial mass was increased significantly in neurons treated with Shh. Using biochemical and fluorescence imaging analyses, we show that Shh signaling activity reduces mitochondrial fission and promotes mitochondrial elongation, at least in part, via suppression of the mitochondrial fission protein dynamin-like GTPase Drp1. Mitochondria from Shh-treated neurons were more electron-dense, as revealed by electron microscopy, and had higher membrane potential and respiratory activity. We further show that Shh protects neurons against a variety of stresses, including the mitochondrial poison rotenone, amyloid β-peptide, hydrogen peroxide, and high levels of glutamate. Collectively our data suggest a link between Shh pathway activity and the physiological properties of mitochondria in hippocampal neurons.

Sonic Hedgehog Signaling and Hippocampal Neuroplasticity

Sonic hedgehog (Shh) is a secreted protein that controls the patterning of neural progenitor cells, and their neuronal and glial progeny, during development. Emerging findings suggest that Shh also has important roles in the formation and plasticity of neuronal circuits in the hippocampus, a brain region of fundamental importance in learning and memory. Shh mediates activity-dependent and injury-induced hippocampal neurogenesis. Activation of Shh receptors in the dendrites of hippocampal neurons engages a trans-neuronal signaling pathway that accelerates axon outgrowth and enhances glutamate release from presynaptic terminals. Impaired Shh signaling may contribute to the pathogenesis of several developmental and adult-onset neurological disorders that affect the hippocampus, suggesting a potential for therapeutic interventions that target Shh pathways.

Selective depletion of tumour suppressors Deleted in Colorectal Cancer (DCC) and neogenin by environmental and endogenous serine proteases: linking diet and cancer

BACKGROUND

The related tumour suppressor proteins Deleted in Colorectal Cancer (DCC) and neogenin are absent or weakly expressed in many cancers, whereas their insertion into cells suppresses oncogenic behaviour. Serine proteases influence the initiation and progression of cancers although the mechanisms are unknown.

METHODS

The effects of environmental (bacterial subtilisin) and endogenous mammalian (chymotrypsin) serine proteases were examined on protein expression in fresh, normal tissue and human neuroblastoma and mammary adenocarcinoma lines. Cell proliferation and migration assays (chemoattraction and wound closure) were used to examine cell function. Cells lacking DCC were transfected with an ectopic dcc plasmid.

RESULTS

Subtilisin and chymotrypsin selectively depleted DCC and neogenin from cells at nanomolar concentrations without affecting related proteins. Cells showed reduced adherence and increased migration, but after washing they re-attached within 24 h, with recovery of protein expression. These effects are induced by chymotryptic activity as they are prevented by chymostatin and the soybean Bowman-Birk inhibitor typical of many plant protease inhibitors.

CONCLUSIONS

Bacillus subtilis, which secretes subtilisin is widely present in soil, the environment and the intestinal contents, while subtilisin itself is used in meat processing, animal feed probiotics and many household cleaning agents. With chymotrypsin present in chyme, blood and tissues, these proteases may contribute to cancer development by depleting DCC and neogenin. Blocking their activity by Bowman-Birk inhibitors may explain the protective effects of a plant diet. Our findings identify a potential non-genetic contribution to cancer cell behaviour which may explain both the association of processed meats and other factors with cancer incidence and the protection afforded by plant-rich diets, with significant implications for cancer prevention.

Dependence receptor involvement in subtilisin-induced long-term depression and in long-term potentiation

The serine protease subtilisin induces a form of long-term depression (LTD) which is accompanied by a reduced expression of the axo-dendritic guidance molecule Unco-ordinated-5C (Unc-5C). One objective of the present work was to determine whether a loss of Unc-5C function contributed to subtilisin-induced LTD by using Unc-5C antibodies in combination with the pore-forming agents Triton X-100 (0.005%) or streptolysin O in rat hippocampal slices. In addition we have assessed the effect of subtilisin on the related dependence receptor Deleted in Colorectal Cancer (DCC) and used antibodies to this protein for functional studies. Field excitatory postsynaptic potentials (fEPSPs) were analyzed in rat hippocampal slices and protein extracts were used for Western blotting. Subtilisin produced a greater loss of DCC than of Unc-5C, but the antibodies had no effect on resting excitability or fEPSPs and did not modify subtilisin-induced LTD. However, antibodies to DCC but not Unc-5C did reduce the amplitude of theta-burst long-term potentiation (LTP). In addition, two inhibitors of endocytosis - dynasore and tat-gluR2(3Y) - were tested and, although the former compound had no effect on neurophysiological responses, tat-gluR2(3Y) did reduce the amplitude of subtilisin-induced LTD without affecting the expression of DCC or Unc-5C but with some loss of PostSynaptic Density Protein-95. The results support the view that the dependence receptor DCC may be involved in LTP and suggest that the endocytotic removal of a membrane protein or proteins may contribute to subtilisin-induced LTD, although it appears that neither Unc-5C nor DCC are involved in this process.

Probing extracellular Sonic hedgehog in neurons

The bioactivity of Sonic hedgehog (Shh) depends on specific lipid modifications; a palmitate at its N-terminus and a cholesterol at its C-terminus. This dual-lipid modification makes Shh molecules lipophilic, which prevents them from diffusing freely in extracellular space. Multiple lines of evidence indicate that Shh proteins are carried by various forms of extracellular vesicles (EVs). It also has been shown, for instance, that in some tissues Shh proteins are transported to neighboring cells directly via filopodia. We have previously reported that Shh proteins are expressed in hippocampal neurons. In this study we show that, in the hippocampus and cerebellum of postnatal day (P)2 rats, Shh is mostly found near or on the membrane surface of small neurites or filopodia. We also examined cultured hippocampal neurons where we observed noticeable and widespread Shh-immunolabeled vesicles located outside neurons. Through immunoelectron microscopy and biochemical analysis, we find Shh-containing EVs with a wide range of sizes. Unlike robust Shh activity in EVs isolated from cells overexpressing an N-terminal Shh fragment construct, we did not detect measurable Shh activity in EVs purified from the medium of cultured hippocampal neurons. These results suggest the complexity of the transcellular Shh signaling mechanisms in neurons.