Microglia Mitigate Neuronal Activation in a Zebrafish Model of Dravet Syndrome

It has been known for a long time that epileptic seizures provoke brain neuroinflammation involving the activation of microglial cells. However, the role of these cells in this disease context and the consequences of their inflammatory activation on subsequent neuron network activity remain poorly understood so far. To fill this gap of knowledge and gain a better understanding of the role of microglia in the pathophysiology of epilepsy, we used an established zebrafish Dravet syndrome epilepsy model based on Scn1Lab sodium channel loss-of-function, combined with live microglia and neuronal Ca2+ imaging, local field potential (LFP) recording, and genetic microglia ablation. Data showed that microglial cells in scn1Lab-deficient larvae experiencing epileptiform seizures displayed morphological and biochemical changes characteristic of M1-like pro-inflammatory activation; i.e., reduced branching, amoeboid-like morphology, and marked increase in the number of microglia expressing pro-inflammatory cytokine Il1β. More importantly, LFP recording, Ca2+ imaging, and swimming behavior analysis showed that microglia-depleted scn1Lab-KD larvae displayed an increase in epileptiform seizure-like neuron activation when compared to that seen in scn1Lab-KD individuals with microglia. These findings strongly suggest that despite microglia activation and the synthesis of pro-inflammatory cytokines, these cells provide neuroprotective activities to epileptic neuronal networks, making these cells a promising therapeutic target in epilepsy.

Correction: Association of Rare Genetic Variants in Opioid Receptors with Tourette Syndrome

[This corrects the article DOI: 10.5334/tohm.464.].

Novel genome-editing-based approaches to treat motor neuron diseases: Promises and challenges

Motor neuron diseases are untreatable with common pharmacological approaches. Spinal muscular atrophy (SMA) is caused by SMN1 gene mutations leading to lowered SMN expression. Symptoms are alleviated in infants with a higher copy number of the SMN2 gene, which, however, displays a splicing defect resulting in low SMN levels. Amyotrophic lateral sclerosis (ALS) is caused by a number of mutations, with C9orf72 repeat expansions the most common genetic cause and SOD1 gain-of-function mutations the first genetic cause identified for this disease. Genetic therapies based on oligonucleotides that enhance SMN2 splicing and SMN production or lower SOD1 expression have shown promise in initial clinical trials for individuals with SMA and ALS harboring SOD1 mutations, respectively. Gene addition/silencing approaches using adeno-associated viruses (AAVs) are also currently under clinical investigation in trials for SMA and ALS. Here we provide a brief overview of these efforts and their advantages and challenges. We also review genome editing approaches aimed at correcting the disease-causing mutations or modulating the expression of genetic modifiers, e.g., by repairing SOD1 mutations or the SMN2 splicing defect or deleting C9orf72 expanded repeats. These studies have shown promising results to approach therapeutic trials that should significantly lower the progression of these deadly disorders.

Behavioral And Physiological Analysis In A Zebrafish Model Of Epilepsy

Epilepsy represents one of the most common neurological disorders, affecting an estimated 50 million people worldwide. Recent advances in genetic research have uncovered a large spectrum of genes implicated in various forms of epilepsy, highlighting the heterogeneous nature of this disorder. Appropriate animal models are essential for investigating the pathological mechanisms triggered by genetic mutations implicated in epilepsy and for developing specialized, targeted therapies. In recent years, zebrafish has emerged as a valuable vertebrate organism for modeling epilepsies, with the use of both genetic manipulation and exposure to known epileptogenic drugs, such as pentylenetetrazole (PTZ), to identify novel anti-epileptic therapeutics. Deleterious mutations in the mTOR regulator DEPDC5 have been associated with various forms of focal epilepsies and knock-down of the zebrafish orthologue causes hyperactivity associated with spontaneous seizure-like episodes, as well as enhanced electrographic activity and characteristic turn wheel swimming. Here, we described the method involved in generating the DEPDC5 loss-of-function model and illustrate the protocol for assessing motor activity at 28 and 48 h post fertilization (hpf), as well as a method for recording field activity in the zebrafish optic tectum. An illustration of the effect of the epileptogenic drug PTZ on neuronal activity over time is also provided.

Trpv4 Mediates Hypotonic Inhibition of Central Osmosensory Neurons via Taurine Gliotransmission

The maintenance of hydromineral homeostasis requires bidirectional detection of changes in extracellular fluid osmolality by primary osmosensory neurons (ONs) in the organum vasculosum laminae terminalis (OVLT). Hypertonicity excites ONs in part through the mechanical activation of a variant transient receptor potential vanilloid-1 channel (dn-Trpv1). However, the mechanism by which local hypotonicity inhibits ONs in the OVLT remains unknown. Here, we show that hypotonicity can reduce the basal activity of dn-Trpv1 channels and hyperpolarize acutely isolated ONs. Surprisingly, we found that mice lacking dn-Trpv1 maintain normal inhibitory responses to hypotonicity when tested in situ. In the intact setting, hypotonicity inhibits ONs through a non-cell-autonomous mechanism that involves glial release of the glycine receptor agonist taurine through hypotonicity activated anion channels (HAAC) that are activated subsequent to Ca²⁺ influx through Trpv4 channels. Our study clarifies how Trpv4 channels contribute to the inhibition of OVLT ONs during hypotonicity in situ.

Association of Rare Genetic Variants in Opioid Receptors with Tourette Syndrome

Background

Genes involved in Tourette syndrome (TS) remain largely unknown. We aimed to identify genetic factors contributing to TS in a French cohort of 120 individuals using a combination of hypothesis-driven and exome-sequencing approaches.

Methods

We first sequenced exons of SLITRK1-6 and HDC in the TS cohort and subsequently sequenced the exome of 12 individuals harboring rare variants in these genes to find additional rare variants contributing to the disorder under the hypothesis of oligogenic inheritance. We further screened three candidate genes (OPRK1, PCDH10, and NTSR2) preferentially expressed in the basal ganglia, and three additional genes involved in neurotensin and opioid signaling (OPRM1, NTS, and NTSR1), and compared variant frequencies in TS patients and 788 matched control individuals. We also investigated the impact of altering the expression of Oprk1 in zebrafish.

Results

Thirteen ultrarare missense variants of SLITRK1-6 and HDC were identified in 12 patients. Exome sequencing in these patients revealed rare possibly deleterious variants in 3,041 genes, 54 of which were preferentially expressed in the basal ganglia. Comparison of variant frequencies altering selected candidate genes in TS and control individuals revealed an excess of potentially disrupting variants in OPRK1, encoding the opioid kappa receptor, in TS patients. Accordingly, we show that downregulation of the Oprk1 orthologue in zebrafish induces a hyperkinetic phenotype in early development.

Discussion

These results support a heterogeneous and complex genetic etiology of TS, possibly involving rare variants altering the opioid pathway in some individuals, which could represent a novel therapeutic target in this disorder.

Depdc5 knockdown causes mTOR-dependent motor hyperactivity in zebrafish

Objective

DEPDC5 was identified as a major genetic cause of focal epilepsy with deleterious mutations found in a wide range of inherited forms of focal epilepsy, associated with malformation of cortical development in certain cases. Identification of frameshift, truncation, and deletion mutations implicates haploinsufficiency of DEPDC5 in the etiology of focal epilepsy. DEPDC5 is a component of the GATOR1 complex, acting as a negative regulator of mTOR signaling.

Methods

Zebrafish represents a vertebrate model suitable for genetic analysis and drug screening in epilepsy-related disorders. In this study, we defined the expression of depdc5 during development and established an epilepsy model with reduced Depdc5 expression.

Results

Here we report a zebrafish model of Depdc5 loss-of-function that displays a measurable behavioral phenotype, including hyperkinesia, circular swimming, and increased neuronal activity. These phenotypic features persisted throughout embryonic development and were significantly reduced upon treatment with the mTORC1 inhibitor, rapamycin, as well as overexpression of human WT DEPDC5 transcript. No phenotypic rescue was obtained upon expression of epilepsy-associated DEPDC5 mutations (p.Arg487* and p.Arg485Gln), indicating that these mutations cause a loss of function of the protein.

Interpretation

This study demonstrates that Depdc5 knockdown leads to early-onset phenotypic features related to motor and neuronal hyperactivity. Restoration of phenotypic features by WT but not epilepsy-associated Depdc5 mutants, as well as by mTORC1 inhibition confirm the role of Depdc5 in the mTORC1-dependent molecular cascades, defining this pathway as a potential therapeutic target for DEPDC5-inherited forms of focal epilepsy.

Neuroleptics as therapeutic compounds stabilizing neuromuscular transmission in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a rapidly progressing, fatal disorder with no effective treatment. We used simple genetic models of ALS to screen phenotypically for potential therapeutic compounds. We screened libraries of compounds in C. elegans, validated hits in zebrafish, and tested the most potent molecule in mice and in a small clinical trial. We identified a class of neuroleptics that restored motility in C. elegans and in zebrafish, and the most potent was pimozide, which blocked T-type Ca2+ channels in these simple models and stabilized neuromuscular transmission in zebrafish and enhanced it in mice. Finally, a short randomized controlled trial of sporadic ALS subjects demonstrated stabilization of motility and evidence of target engagement at the neuromuscular junction. Simple genetic models are, thus, useful in identifying promising compounds for the treatment of ALS, such as neuroleptics, which may stabilize neuromuscular transmission and prolong survival in this disease.

Neuromuscular Junction Impairment in Amyotrophic Lateral Sclerosis: Reassessing the Role of Acetylcholinesterase

Amyotrophic Lateral Sclerosis (ALS) is a highly debilitating disease caused by progressive degeneration of motorneurons (MNs). Due to the wide variety of genes and mutations identified in ALS, a highly varied etiology could ultimately converge to produce similar clinical symptoms. A major hypothesis in ALS research is the “distal axonopathy” with pathological changes occurring at the neuromuscular junction (NMJ), at very early stages of the disease, prior to MNs degeneration and onset of clinical symptoms. The NMJ is a highly specialized cholinergic synapse, allowing signaling between muscle and nerve necessary for skeletal muscle function. This nerve-muscle contact is characterized by the clustering of the collagen-tailed form of acetylcholinesterase (ColQ-AChE), together with other components of the extracellular matrix (ECM) and specific key molecules in the NMJ formation. Interestingly, in addition to their cholinergic role AChE is thought to play several “non-classical” roles that do not require catalytic function, most prominent among these is the facilitation of neurite growth, NMJ formation and survival. In all this context, abnormalities of AChE content have been found in plasma of ALS patients, in which AChE changes may reflect the neuromuscular disruption. We review these findings and particularly the evidences of changes of AChE at neuromuscular synapse in the pre-symptomatic stages of ALS.

The most prevalent genetic cause of ALS-FTD, C9orf72 synergizes the toxicity of ATXN2 intermediate polyglutamine repeats through the autophagy pathway

The most common genetic cause for amyotrophic lateral sclerosis and frontotemporal dementia (ALS-FTD) is repeat expansion of a hexanucleotide sequence (GGGGCC) within the C9orf72 genomic sequence. To elucidate the functional role of C9orf72 in disease pathogenesis, we identified certain molecular interactors of this factor. We determined that C9orf72 exists in a complex with SMCR8 and WDR41 and that this complex acts as a GDP/GTP exchange factor for RAB8 and RAB39, 2 RAB GTPases involved in macroautophagy/autophagy. Consequently, C9orf72 depletion in neuronal cultures leads to accumulation of unresolved aggregates of SQSTM1/p62 and phosphorylated TARDBP/TDP-43. However, C9orf72 reduction does not lead to major neuronal toxicity, suggesting that a second stress may be required to induce neuronal cell death. An intermediate size of polyglutamine repeats within ATXN2 is an important genetic modifier of ALS-FTD. We found that coexpression of intermediate polyglutamine repeats (30Q) of ATXN2 combined with C9orf72 depletion increases the aggregation of ATXN2 and neuronal toxicity. These results were confirmed in zebrafish embryos where partial C9orf72 knockdown along with intermediate (but not normal) repeat expansions in ATXN2 causes locomotion deficits and abnormal axonal projections from spinal motor neurons. These results demonstrate that C9orf72 plays an important role in the autophagy pathway while genetically interacting with another major genetic risk factor, ATXN2, to contribute to ALS-FTD pathogenesis.

Loss of C9ORF72 impairs autophagy and synergizes with polyQ Ataxin-2 to induce motor neuron dysfunction and cell death

An intronic expansion of GGGGCC repeats within the C9ORF72 gene is the most common genetic cause of amyotrophic lateral sclerosis and frontotemporal dementia (ALS-FTD). Ataxin-2 with intermediate length of polyglutamine expansions (Ataxin-2 Q30x) is a genetic modifier of the disease. Here, we found that C9ORF72 forms a complex with the WDR41 and SMCR8 proteins to act as a GDP/GTP exchange factor for RAB8a and RAB39b and to thereby control autophagic flux. Depletion of C9orf72 in neurons partly impairs autophagy and leads to accumulation of aggregates of TDP-43 and P62 proteins, which are histopathological hallmarks of ALS-FTD SMCR8 is phosphorylated by TBK1 and depletion of TBK1 can be rescued by phosphomimetic mutants of SMCR8 or by constitutively active RAB39b, suggesting that TBK1, SMCR8, C9ORF72, and RAB39b belong to a common pathway regulating autophagy. While depletion of C9ORF72 only has a partial deleterious effect on neuron survival, it synergizes with Ataxin-2 Q30x toxicity to induce motor neuron dysfunction and neuronal cell death. These results indicate that partial loss of function of C9ORF72 is not deleterious by itself but synergizes with Ataxin-2 toxicity, suggesting a double-hit pathological mechanism in ALS-FTD.

Loss of VPS13C Function in Autosomal-Recessive Parkinsonism Causes Mitochondrial Dysfunction and Increases PINK1/Parkin-Dependent Mitophagy

Autosomal-recessive early-onset parkinsonism is clinically and genetically heterogeneous. The genetic causes of approximately 50% of autosomal-recessive early-onset forms of Parkinson disease (PD) remain to be elucidated. Homozygozity mapping and exome sequencing in 62 isolated individuals with early-onset parkinsonism and confirmed consanguinity followed by data mining in the exomes of 1,348 PD-affected individuals identified, in three isolated subjects, homozygous or compound heterozygous truncating mutations in vacuolar protein sorting 13C (VPS13C). VPS13C mutations are associated with a distinct form of early-onset parkinsonism characterized by rapid and severe disease progression and early cognitive decline; the pathological features were striking and reminiscent of diffuse Lewy body disease. In cell models, VPS13C partly localized to the outer membrane of mitochondria. Silencing of VPS13C was associated with lower mitochondrial membrane potential, mitochondrial fragmentation, increased respiration rates, exacerbated PINK1/Parkin-dependent mitophagy, and transcriptional upregulation of PARK2 in response to mitochondrial damage. This work suggests that loss of function of VPS13C is a cause of autosomal-recessive early-onset parkinsonism with a distinctive phenotype of rapid and severe progression.

Two novel COLVI long chains in zebrafish that are essential for muscle development

Collagen VI (COLVI), a protein ubiquitously expressed in connective tissues, is crucial for structural integrity, cellular adhesion, migration and survival. Six different genes are recognized in mammalians, encoding six COLVI-chains that assemble as two 'short' (α1, α2) and one 'long' chain (theoretically any one of α3-6). In humans, defects in the most widely expressed heterotrimer (α123), due to mutations in the COL6A1-3 genes, cause a heterogeneous group of neuromuscular disorders, collectively termed COLVI-related muscle disorders. Little is known about the function(s) of the recently described α4-6 chains and no mutations have been detected yet. In this study, we characterized two novel COLVI long chains in zebrafish that are most homologous to the mammalian α4 chain; therefore, we named the corresponding genes col6a4a and col6a4b. These orthologues represent ancestors of the mammalian Col6a4-6 genes. By in situ hybridization and RT-qPCR, we unveiled a distinctive expression kinetics for col6a4b, compared with the other col6a genes. Using morpholino antisense oligonucleotides targeting col6a4a, col6a4b and col6a2, we modelled partial and complete COLVI deficiency, respectively. All morphant embryos presented altered muscle structure and impaired motility. While apoptosis was not drastically increased, autophagy induction was defective in all morphants. Furthermore, motoneuron axon growth was abnormal in these morphants. Importantly, some phenotypical differences emerged between col6a4a and col6a4b morphants, suggesting only partial functional redundancy. Overall, our results further confirm the importance of COLVI in zebrafish muscle development and may provide important clues for potential human phenotypes associated with deficiency of the recently described COLVI-chains.

Sqstm1 knock-down causes a locomotor phenotype ameliorated by rapamycin in a zebrafish model of ALS/FTLD

Mutations in SQSTM1, encoding for the protein SQSTM1/p62, have been recently reported in 1-3.5% of patients with amyotrophic lateral sclerosis and frontotemporal lobar degeneration (ALS/FTLD). Inclusions positive for SQSTM1/p62 have been detected in patients with neurodegenerative disorders, including ALS/FTLD. In order to investigate the pathogenic mechanisms induced by SQSTM1 mutations in ALS/FTLD, we developed a zebrafish model. Knock-down of the sqstm1 zebrafish ortholog, as well as impairment of its splicing, led to a specific phenotype, consisting of behavioral and axonal anomalies. Here, we report swimming deficits associated with shorter motor neuronal axons that could be rescued by the overexpression of wild-type human SQSTM1. Interestingly, no rescue of the loss-of-function phenotype was observed when overexpressing human SQSTM1 constructs carrying ALS/FTLD-related mutations. Consistent with its role in autophagy regulation, we found increased mTOR levels upon knock-down of sqstm1. Furthermore, treatment of zebrafish embryos with rapamycin, a known inhibitor of the mTOR pathway, yielded an amelioration of the locomotor phenotype in the sqstm1 knock-down model. Our results suggest that loss-of-function of SQSTM1 causes phenotypic features characterized by locomotor deficits and motor neuron axonal defects that are associated with a misregulation of autophagic processes.

Loss of function of C9orf72 causes motor deficits in a zebrafish model of amyotrophic lateral sclerosis

OBJECTIVE

To define the role that repeat expansions of a GGGGCC hexanucleotide sequence of the C9orf72 gene play in the pathogenesis of amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD). A genetic model for ALS was developed to determine whether loss of function of the zebrafish orthologue of C9orf72 (zC9orf72) leads to abnormalities in neuronal development.

METHODS

C9orf72 mRNA levels were quantified in brain and lymphoblasts derived from FTLD and ALS/FTLD patients and in zebrafish. Knockdown of the zC9orf72 was performed using 2 specific antisense morpholino oligonucleotides to block transcription. Quantifications of spontaneous swimming and tactile escape response, as well as measurements of axonal projections from the spinal cord, were performed.

RESULTS

Significantly decreased expression of C9orf72 transcripts in brain and lymphoblasts was found in sporadic FTLD and ALS/FTLD patients with normal-size or expanded hexanucleotide repeats. The zC9orf72 is selectively expressed in the developing nervous system at developmental stages. Loss of function of the zC9orf72 transcripts causes both behavioral and cellular deficits related to locomotion without major morphological abnormalities. These deficits were rescued upon overexpression of human C9orf72 mRNA transcripts.

INTERPRETATION

Our results indicate C9orf72 haploinsufficiency could be a contributing factor in the spectrum of ALS/FTLD neurodegenerative disorders. Loss of function of the zebrafish orthologue of zC9orf72 expression in zebrafish is associated with axonal degeneration of motor neurons that can be rescued by expressing human C9orf72 mRNA, highlighting the specificity of the induced phenotype. These results reveal a pathogenic consequence of decreased C9orf72 levels, supporting a loss of function mechanism of disease.

Methylene blue protects against TDP-43 and FUS neuronal toxicity in C. elegans and D. rerio

The DNA/RNA-binding proteins TDP-43 and FUS are found in protein aggregates in a growing number of neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS) and related dementia, but little is known about the neurotoxic mechanisms. We have generated Caenorhabditis elegans and zebrafish animal models expressing mutant human TDP-43 (A315T or G348C) or FUS (S57Δ or R521H) that reflect certain aspects of ALS including motor neuron degeneration, axonal deficits, and progressive paralysis. To explore the potential of our humanized transgenic C. elegans and zebrafish in identifying chemical suppressors of mutant TDP-43 and FUS neuronal toxicity, we tested three compounds with potential neuroprotective properties: lithium chloride, methylene blue and riluzole. We identified methylene blue as a potent suppressor of TDP-43 and FUS toxicity in both our models. Our results indicate that methylene blue can rescue toxic phenotypes associated with mutant TDP-43 and FUS including neuronal dysfunction and oxidative stress.

TRPV1 gene required for thermosensory transduction and anticipatory secretion from vasopressin neurons during hyperthermia

Increases in core body temperature promote thermoregulatory cooling by stimulating sweat production and preemptive renal water reabsorption through the release of vasopressin (VP, antidiuretic hormone). The mechanism by which the hypothalamus orchestrates this anticipatory VP release during hyperthermia is unknown but has been linked to a central thermosensory mechanism. Here, we report that thermal stimuli spanning core body temperatures activate a calcium-permeable, ruthenium red- and SB366791-sensitive nonselective cation conductance in hypothalamic VP neurons. This response is associated with a depolarizing receptor potential and an increase in action potential firing rate, indicating that these neurons are intrinsically thermosensitive. The thermosensitivity of VP neurons isolated from trpv1 knockout (Trpv1(-/-)) mice was significantly lower than that of wild-type counterparts. Moreover, Trpv1(-/-) mice showed an impaired VP response to hyperthermia in vivo. Channels encoded by the trpv1 gene thus confer thermosensitivity in central VP neurons and contribute to the thermal control of VP release in vivo.

Neurophysiology of supraoptic neurons in C57/BL mice studied in three acute in vitro preparations

Osmotic control of arginine vasopressin (AVP) and oxytocin (OXT) release from magnocellular neurosecretory cells (MNCs) of the supraoptic (SON) and paraventricular (PVN) nuclei is essential for body fluid homeostasis. The electrical activity of MNCs, which is regulated by intrinsic and extrinsic osmosensitive factors, is a primary determinant of blood AVP and OXT levels. Although we now understand many of the cellular mechanisms that mediate the osmotic control of electrical activity and secretion from MNCs, further insight is likely to emerge from a molecular analysis of these mechanisms. An important step towards this goal could be made through the use of mouse genetic models. However, the electrophysiological properties of MNCs in mice have not been characterized, making direct comparisons with the rat model somewhat difficult. In this study, we examined the electrical properties of MNCs from the mouse SON. Extracellular recordings from neurons in superfused explants revealed modes of basal and osmotically modulated firing very similar to those observed previously in rats. Recordings in hypothalamic slices confirmed that SON neurons receive kynurenic-acid-sensitive excitatory synaptic inputs from the organum vasculosum laminae terminalis (OVLT). Current-clamp recordings from acutely dissociated SON neurons showed proportional changes in membrane cation conductance during changes in fluid osmolality. We conclude, therefore, that MNCs in the mouse SON display intrinsic osmosensitive properties and firing patterns that are very similar to those reported in the rat. Mouse MNCs therefore represent a useful model for the study of molecular factors contributing to the osmotic control of AVP and OXT release.

Neurophysiological characterization of mammalian osmosensitive neurones

In mammals, the osmolality of the extracellular fluid is maintained near a predetermined set-point through a negative feedback regulation of thirst, diuresis, salt appetite and natriuresis. This homeostatic control is believed to be mediated by osmosensory neurones which synaptically regulate the electrical activity of command neurones that mediate each of these osmoregulatory effector responses. Our present understanding of the molecular, cellular and network basis that underlies the central control of osmoregulation is largely derived from studies on primary osmosensory neurones in the organum vasculosum lamina terminalis (OVLT) and effector neurones in the supraoptic nucleus (SON), which release hormones that regulate diuresis and natriuresis. Primary osmosensory neurones in the OVLT exhibit changes in action potential firing rate that vary in proportion with ECF osmolality. This effect results from the intrinsic depolarizing receptor potential which these cells generate via a molecular transduction complex that may comprise various members of the transient receptor potential vanilloid (TRPV) family of cation channel proteins, notably TRPV1 and TRPV4. Osmotically evoked changes in the firing rate of OVLT neurones then regulate the electrical activity of downstream neurones in the SON through graded changes in glutamate release.

Hes6 inhibits astrocyte differentiation and promotes neurogenesis through different mechanisms

The mechanisms regulating the generation of cell diversity in the mammalian cerebral cortex are beginning to be elucidated. In that regard, Hairy/Enhancer of split (Hes) 1 and 5 are basic helix-loop-helix (bHLH) factors that inhibit the differentiation of pluripotent cortical progenitors into neurons. In contrast, a related Hes family member termed Hes6 promotes neurogenesis. It is shown here that knockdown of endogenous Hes6 causes supernumerary cortical progenitors to differentiate into cells that exhibit an astrocytic morphology and express the astrocyte marker protein GFAP. Conversely, exogenous Hes6 expression in cortical progenitors inhibits astrocyte differentiation. The negative effect of Hes6 on astrocyte differentiation is independent of its ability to promote neuronal differentiation. We also show that neither its proneuronal nor its anti-gliogenic functions appear to depend on Hes6 ability to bind to DNA via the basic arm of its bHLH domain. Both of these activities require Hes6 to be localized to nuclei, but only its anti-gliogenic function depends on two short peptides, LNHLL and WRPW, that are conserved in all Hes6 proteins. These findings suggest that Hes6 is an important regulator of the neurogenic phase of cortical development by promoting the neuronal fate while suppressing astrocyte differentiation. They suggest further that separate molecular mechanisms underlie the proneuronal and anti-gliogenic activities of Hes6 in cortical progenitor cells.

Transient receptor potential vanilloid 1 is required for intrinsic osmoreception in organum vasculosum lamina terminalis neurons and for normal thirst responses to systemic hyperosmolality

Recent studies have indicated that members of the transient receptor potential vanilloid (TRPV) family of cation channels are required for the generation of normal osmoregulatory responses, yet the mechanism of osmosensory transduction in primary osmoreceptor neurons of the CNS remains to be defined. Indeed, despite ample evidence suggesting that the organum vasculosum lamina terminalis (OVLT) serves as the primary locus of the brain for the detection of osmotic stimuli, evidence that neurons in the OVLT are intrinsically osmosensitive has remained elusive. Here we show that murine OVLT neurons are intrinsically sensitive to increases in the osmolality of the extracellular fluid. Hypertonic conditions provoked increases in membrane cation conductance that resulted in the generation of an inward current, depolarizing osmoreceptor potentials, and enhanced action potential discharge. Moreover, we found that this osmosensory signal transduction cascade was absent in OVLT neurons from TRPV1 knock-out (TRPV1-/-) mice and that responses of wild type (WT) OVLT neurons could be blocked by ruthenium red, an inhibitor of TRPV channels. Finally, TRPV1-/- mice showed significantly attenuated water intake in response to systemic hypertonicity compared with WT controls. These findings indicate that OVLT neurons act as primary osmoreceptors and that a product of the trpv1 gene is required for osmosensory transduction.

Overexpression of the serine elastase inhibitor elafin protects transgenic mice from hypoxic pulmonary hypertension

BACKGROUND

Increased serine elastase activity has been implicated in the vascular remodeling associated with chronic hypoxia-related pulmonary hypertension in rats.

METHODS AND RESULTS

In this study we determined the time course of hypoxia-induced serine elastase activity in the murine lung and related this to initiation of a proteolytic cascade characterized by an increase in matrix metalloproteinases (MMPs). We then used transgenic mice in which overexpression of the selective serine elastase inhibitor elafin was targeted to the cardiovascular system to determine whether upregulation of a naturally occurring serine elastase inhibitor suppresses MMPs and the hemodynamic and structural response to chronic hypoxia (air at 380 mm Hg). In nontransgenic but not in elafin-transgenic mice, we documented a transient increase in serine elastase activity after 12 hours of hypoxic exposure attributed to a 30-kDa protein as determined by elastin zymography and fluorophosphonate/fluorophosphate-biotin labeling. Two days after hypoxia, the pro-forms of MMP-2 and MMP-9 were induced in the nontransgenic mice, but MMP-9 was suppressed in elafin-transgenic mice. Acute hypoxic vasoconstriction was similar in nontransgenic and elafin-transgenic littermates. Chronic hypoxia for 26 days resulted in >1-fold increase in right ventricular pressure (P<0.004) in nontransgenic compared with control or elafin-transgenic littermates. In the latter mice, normalization of the right ventricular pressure was associated with reduced muscularization and preservation of the number of distal vessels (P<0.04 for both comparisons).

CONCLUSIONS

Modulation of the severity of chronic hypoxia-induced pulmonary vascular disease could be a function of endogenously expressed serine elastase inhibitors.

Suppressed smooth muscle proliferation and inflammatory cell invasion after arterial injury in elafin-overexpressing mice

Elastases degrade the extracellular matrix, releasing growth factors and chemotactic peptides, inducing glycoproteins such as tenascin, and thereby promoting vascular cell proliferation and migration. Administration of serine elastase inhibitors reduces experimentally induced vascular disease. The ability to mount an intrinsic anti-elastase response may, therefore, protect against intimal/medial thickening after vascular injury. To investigate this, we showed that wire-induced endothelial denudation of the carotid artery is associated with transient elevation in elastase activity and confirmed that this is abolished in transgenic mice overexpressing the serine elastase inhibitor, elafin, targeted to the cardiovascular system. Ten days after injury, nontransgenic littermates show vessel enlargement, intimal thickening, increased medial area and cellularity, and 2-fold increase in tenascin. Injured vessels in transgenic mice become enlarged but are otherwise similar to sham-operated controls. Injury-induced vessel wall thickening, which is observed only in nontransgenic mice, is related to foci of neutrophils and macrophages, in addition to smooth muscle cells that fail to stain for alpha-actin and are likely dedifferentiated. Our study therefore suggests that a major determinant of the vascular response to injury is the early transient induction of serine elastase activity, which leads to cellular proliferation and inflammatory cell migration.