Soluble guanylate cyclase generation of cGMP regulates migration of MGE neurons

DLX genes and proteins in mammalian forebrain development

The vertebrate Dlx gene family encode homeobox transcription factors that are related to the Drosophila Distal-less (Dll) gene and are crucial for development. Over the last ∼35 years detailed information has accrued about the redundant and unique expression and function of the six mammalian Dlx family genes. DLX proteins interact with general transcriptional regulators, and co-bind with other transcription factors to enhancer elements with highly specific activity in the developing forebrain. Integration of the genetic and biochemical data has yielded a foundation for a gene regulatory network governing the differentiation of forebrain GABAergic neurons. In this Primer, we describe the discovery of vertebrate Dlx genes and their crucial roles in embryonic development. We largely focus on the role of Dlx family genes in mammalian forebrain development revealed through studies in mice. Finally, we highlight questions that remain unanswered regarding vertebrate Dlx genes despite over 30 years of research.

CXCL12 targets the primary cilium cAMP/cGMP ratio to regulate cell polarity during migration

Directed cell migration requires sustained cell polarisation. In migrating cortical interneurons, nuclear movements are directed towards the centrosome that organises the primary cilium signalling hub. Primary cilium-elicited signalling, and how it affects migration, remain however ill characterised. Here, we show that altering cAMP/cGMP levels in the primary cilium by buffering cAMP, cGMP or by locally increasing cAMP, influences the polarity and directionality of migrating interneurons, whereas buffering cAMP or cGMP in the apposed centrosome compartment alters their motility. Remarkably, we identify CXCL12 as a trigger that targets the ciliary cAMP/cGMP ratio to promote sustained polarity and directed migration. We thereby uncover cAMP/cGMP levels in the primary cilium as a major target of extrinsic cues and as the steering wheel of neuronal migration.

History of "Serve and Return" and a Synthesis of the Literature on its Impacts on Children's Health and Development

Parent/caregiver sensitivity and responsiveness are important for children's health and development. The "serve and return" metaphor was created to help providers and caregivers understand the importance of sensitive and responsive early caregiving. In this review, we explain the concept of "serve and return", outline historical and theoretical principles that culminated in this metaphor, highlight parent and child constructs associated with "serve and return" interactions, and synthesize literature on sensitive and responsive caregiving and children's health and developmental outcomes. Nurses and other healthcare professionals in public policy, clinical, community, education, and research roles need knowledge of "serve and return" interactions.

NOS1 mutations cause hypogonadotropic hypogonadism with sensory and cognitive deficits that can be reversed in infantile mice

The nitric oxide (NO) signaling pathway in hypothalamic neurons plays a key role in the regulation of the secretion of gonadotropin-releasing hormone (GnRH), which is crucial for reproduction. We hypothesized that a disruption of neuronal NO synthase (NOS1) activity underlies some forms of hypogonadotropic hypogonadism. Whole-exome sequencing was performed on a cohort of 341 probands with congenital hypogonadotropic hypogonadism to identify ultrarare variants in NOS1. The activity of the identified NOS1 mutant proteins was assessed by their ability to promote nitrite and cGMP production in vitro. In addition, physiological and pharmacological characterization was carried out in a Nos1-deficient mouse model. We identified five heterozygous NOS1 loss-of-function mutations in six probands with congenital hypogonadotropic hypogonadism (2%), who displayed additional phenotypes including anosmia, hearing loss, and intellectual disability. NOS1 was found to be transiently expressed by GnRH neurons in the nose of both humans and mice, and Nos1 deficiency in mice resulted in dose-dependent defects in sexual maturation as well as in olfaction, hearing, and cognition. The pharmacological inhibition of NO production in postnatal mice revealed a critical time window during which Nos1 activity shaped minipuberty and sexual maturation. Inhaled NO treatment at minipuberty rescued both reproductive and behavioral phenotypes in Nos1-deficient mice. In summary, lack of NOS1 activity led to GnRH deficiency associated with sensory and intellectual comorbidities in humans and mice. NO treatment during minipuberty reversed deficits in sexual maturation, olfaction, and cognition in Nos1 mutant mice, suggesting a potential therapy for humans with NO deficiency.

Structural and Functional Plasticity in the Regenerating Olfactory System of the Migratory Locust

Regeneration after injury is accompanied by transient and lasting changes in the neuroarchitecture of the nervous system and, thus, a form of structural plasticity. In this review, we introduce the olfactory pathway of a particular insect as a convenient model to visualize neural regeneration at an anatomical level and study functional recovery at an electrophysiological level. The olfactory pathway of the locust (Locusta migratoria) is characterized by a multiglomerular innervation of the antennal lobe by olfactory receptor neurons. These olfactory afferents were axotomized by crushing the base of the antenna. The resulting degeneration and regeneration in the antennal lobe could be quantified by size measurements, dye labeling, and immunofluorescence staining of cell surface proteins implicated in axonal guidance during development. Within 3 days post lesion, the antennal lobe volume was reduced by 30% and from then onward regained size back to normal by 2 weeks post injury. The majority of regenerating olfactory receptor axons reinnervated the glomeruli of the antennal lobe. A few regenerating axons project erroneously into the mushroom body on a pathway that is normally chosen by second-order projection neurons. Based on intracellular responses of antennal lobe output neurons to odor stimulation, regenerated fibers establish functional synapses again. Following complete absence after nerve crush, responses to odor stimuli return to control level within 10–14 days. On average, regeneration of afferents, and re-established synaptic connections appear faster in younger fifth instar nymphs than in adults. The initial degeneration of olfactory receptor axons has a trans-synaptic effect on a second order brain center, leading to a transient size reduction of the mushroom body calyx. Odor-evoked oscillating field potentials, absent after nerve crush, were restored in the calyx, indicative of regenerative processes in the network architecture. We conclude that axonal regeneration in the locust olfactory system appears to be possible, precise, and fast, opening an avenue for future mechanistic studies. As a perspective of biomedical importance, the current evidence for nitric oxide/cGMP signaling as positive regulator of axon regeneration in connectives of the ventral nerve cord is considered in light of particular regeneration studies in vertebrate central nervous systems.

Dlx1 and Dlx2 Promote Interneuron GABA Synthesis, Synaptogenesis, and Dendritogenesis

The postnatal functions of the Dlx1&2 transcription factors in cortical interneurons (CINs) are unknown. Here, using conditional Dlx1, Dlx2, and Dlx1&2 knockouts (CKOs), we defined their roles in specific CINs. The CKOs had dendritic, synaptic, and survival defects, affecting even PV+ CINs. We provide evidence that DLX2 directly drives Gad1, Gad2, and Vgat expression, and show that mutants had reduced mIPSC amplitude. In addition, the mutants formed fewer GABAergic synapses on excitatory neurons and had reduced mIPSC frequency. Furthermore, Dlx1/2 CKO had hypoplastic dendrites, fewer excitatory synapses, and reduced excitatory input. We provide evidence that some of these phenotypes were due to reduced expression of GRIN2B (a subunit of the NMDA receptor), a high confidence Autism gene. Thus, Dlx1&2 coordinate key components of CIN postnatal development by promoting their excitability, inhibitory output, and survival.

Social Origins of Developmental Risk for Mental and Physical Illness

Adversity in early childhood exerts an enduring impact on mental and physical health, academic achievement, lifetime productivity, and the probability of interfacing with the criminal justice system. More science is needed to understand how the brain is affected by early life stress (ELS), which produces excessive activation of stress response systems broadly throughout the child's body (toxic stress). Our research examines the importance of sex, timing and type of stress exposure, and critical periods for intervention in various brain systems across species. Neglect (the absence of sensitive and responsive caregiving) or disrupted interaction with offspring induces robust, lasting consequences in mice, monkeys, and humans. Complementary assessment of internalizing disorders and brain imaging in children suggests that early adversity can interfere with white matter development in key brain regions, which may increase risk for emotional difficulties in the long term. Neural circuits that are most plastic during ELS exposure in monkeys sustain the greatest change in gene expression, offering a mechanism whereby stress timing might lead to markedly different long-term behaviors. Rodent models reveal that disrupted maternal-infant interactions yield metabolic and behavioral outcomes often differing by sex. Moreover, ELS may further accelerate or delay critical periods of development, which reflect GABA circuit maturation, BDNF, and circadian Clock genes. Such factors are associated with several mental disorders and may contribute to a premature closure of plastic windows for intervention following ELS. Together, complementary cross-species studies are elucidating principles of adaptation to adversity in early childhood with molecular, cellular, and whole organism resolution.

Type 5 phosphodiesterase regulates glioblastoma multiforme aggressiveness and clinical outcome

Expression of type 5 phosphodiesterase (PDE5), a cGMP-specific hydrolytic enzyme, is frequently altered in human cancer, but its specific role in tumorigenesis remains controversial. Herein, by analyzing a cohort of 69 patients affected by glioblastoma multiforme (GBM) who underwent chemo- and radiotherapy after surgical resection of the tumor, we found that PDE5 was strongly expressed in cancer cells in about 50% of the patients. Retrospective analysis indicated that high PDE5 expression in GBM cells significantly correlated with longer overall survival of patients. Furthermore, silencing of endogenous PDE5 by short hairpin lentiviral transduction (sh-PDE5) in the T98G GBM cell line induced activation of an invasive phenotype. Similarly, pharmacological inhibition of PDE5 activity strongly enhanced cell motility and invasiveness in T98G cells. This invasive phenotype was accompanied by increased secretion of metallo-proteinase 2 (MMP-2) and activation of protein kinase G (PKG). Moreover, PDE5 silencing markedly enhanced DNA damage repair and cell survival following irradiation. The enhanced radio-resistance of sh-PDE5 GBM cells was mediated by an increase of poly(ADP-ribosyl)ation (PARylation) of cellular proteins and could be counteracted by poly(ADP-ribose) polymerase (PARP) inhibitors. Conversely, PDE5 overexpression in PDE5-negative U87G cells significantly reduced MMP-2 secretion, inhibited their invasive potential and interfered with DNA damage repair and cell survival following irradiation. These studies identify PDE5 as a favorable prognostic marker for GBM, which negatively affects cell invasiveness and survival to ionizing radiation. Moreover, our work highlights the therapeutic potential of targeting PKG and/or PARP activity in this currently incurable subset of brain cancers.

Redox-guided axonal regrowth requires cyclic GMP dependent protein kinase 1: Implication for neuropathic pain

Cyclic GMP-dependent protein kinase 1 (PKG1) mediates presynaptic nociceptive long-term potentiation (LTP) in the spinal cord and contributes to inflammatory pain in rodents but the present study revealed opposite effects in the context of neuropathic pain. We used a set of loss-of-function models for in vivo and in vitro studies to address this controversy: peripheral neuron specific deletion (SNS-PKG1^-/-), inducible deletion in subsets of neurons (SLICK-PKG1^-/-) and redox-dead PKG1 mutants. In contrast to inflammatory pain, SNS-PKG1^-/- mice developed stronger neuropathic hyperalgesia associated with an impairment of nerve regeneration, suggesting specific repair functions of PKG1. Although PKG1 accumulated at the site of injury, its activity was lost in the proximal nerve due to a reduction of oxidation-dependent dimerization, which was a consequence of mitochondrial damage in injured axons. In vitro, PKG1 deficiency or its redox-insensitivity resulted in enhanced outgrowth and reduction of growth cone collapse in response to redox signals, which presented as oxidative hotspots in growing cones. At the molecular level, PKG1 deficiency caused a depletion of phosphorylated cofilin, which is essential for growth cone collapse and guidance. Hence, redox-mediated guidance required PKG1 and consequently, its deficiency in vivo resulted in defective repair and enhanced neuropathic pain after nerve injury. PKG1-dependent repair functions will outweigh its signaling functions in spinal nociceptive LTP, so that inhibition of PKG1 is no option for neuropathic pain.

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Axonal injury leads mitochondrial damage.

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The loss of signaling ROS is associated with a reduction of redox-dependent autoactivation of PKG1.

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Loss of PKG1 impairs peripheral nerve regeneration and aggravates neuropathic pain in mice.

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Oxidative hot spots are generated in spiky growth cones and trigger growth cone collapse via PKG1.

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Malfunctioning of this redox-PKG1 guided growth cone collapse leads to aberrant outgrowth.

MicroRNAs in the axon locally mediate the effects of chondroitin sulfate proteoglycans and cGMP on axonal growth

Axonal miRNAs locally regulate axonal growth by modulating local protein composition. Whether localized miRNAs in the axon mediate the inhibitory effect of Chondroitin sulfate proteoglycans (CSPGs) on the axon remains unknown. We showed that in cultured cortical neurons, axonal application of CSPGs inhibited axonal growth and altered axonal miRNA profiles, whereas elevation of axonal cyclic guanosine monophosphate (cGMP) levels by axonal application of sildenafil reversed the effect of CSPGs on inhibition of axonal growth and on miRNA profiles. Specifically, CSPGs elevated and reduced axonal levels of miR-29c and integrin β1 (ITGB1) proteins, respectively, while elevation of cGMP levels overcame these CSPG effects. Gain-of- and loss-of-function experiments demonstrated that miR-29c in the distal axon mediates axonal growth downstream of CSPGs and cGMP by regulating axonal protein levels of ITGB1, FAK, and RhoA. Together, our data demonstrate that axonal miRNAs play an important role in mediating the inhibitory action of CSPGs on axonal growth and that miR-29c at least partially mediates this process.

Acidic pH increases cGMP accumulation through the OGR1/phospholipase C/Ca(2+)/neuronal NOS pathway in N1E-115 neuronal cells

Neuronal NO synthase (nNOS)-mediated cGMP accumulation has been shown to affect a variety of neuronal cell activities, regardless of whether they are detrimental or beneficial, depending on the amount of their levels, under the physiological and pathological situations. In the present study, we examined the role of proton-sensing G protein-coupled receptors (GPCRs), which have been identified as new pH sensors, in the acidic pH-induced nNOS/cGMP activity in N1E-115 neuronal cells. In this cell line, ovarian cancer G protein-coupled receptor 1 (OGR1) and G protein-coupled receptor 4 (GPR4) mRNAs are expressed. An extracellular acidic pH increased cGMP accumulation, which was inhibited by nNOS-specific inhibitors. Acidic pH also activated phospholipase C/Ca(2+) pathways and Akt-induced phosphorylation of nNOS at S1412, both of which have been shown to be critical regulatory mechanisms for nNOS activation. The acidic pH-induced activation of the phospholipase C/Ca(2+) pathway, but not Akt/nNOS phosphorylation, was inhibited by small interfering RNA specific to OGR1 and YM-254890, an inhibitor of Gq/11 proteins, in association with the inhibition of cGMP accumulation. Moreover cGMP accumulation was inhibited by 2-aminoethoxydiphenyl borate, an inhibitor of inositol 1,4,5-trisphosphate channel; however, it was not by wortmannin, a phosphatidylinositol 3-kinase inhibitor, which inhibited Akt/nNOS phosphorylation. In conclusion, acidic pH stimulates cGMP accumulation preferentially through the OGR1/Gq/11 proteins/phospholipase C/Ca(2+)/nNOS in N1E-115 neuronal cells. Akt-mediated phosphorylation of nNOS, however, does not appreciably contribute to the acidification-induced accumulation of cGMP.

Nitric oxide/cyclic GMP signaling regulates motility of a microglial cell line and primary microglia in vitro

Microglia are the resident immune cells of the brain, which become rapidly activated and migrate to the site of insult in brain infection and disease. Activated microglia generate large amounts of the highly reactive messenger molecule nitric oxide (NO). NO is able to raise cyclic GMP levels via binding to soluble guanylyl cyclase. We investigated potential mechanistic links between inflammation, NO signaling, and microglial migration. To monitor cell migration, we used a scratch wound assay and compared results obtained in the BV-2 microglial line to primary microglia. Incubation with lipopolysaccharide (LPS) as stimulator of acute inflammatory processes enhanced migration of both microglial cell types. LPS activated NO production in BV-2 cells and application of an NO donor increased BV-2 cell migration while an NO scavenger reduced motility. Pharmacological inhibition of soluble guanylyl cyclase and the resulting decrease in motility can be rescued by a membrane permeant analog of cGMP. Despite differences in the threshold towards stimulation with the chemical agents, both BV-2 cells and primary microglia react in a similar way. The important role of NO/cGMP as positive regulator of microglial migration, the downstream targets of the signaling cascade, and resulting cytoskeletal changes can be conveniently investigated in a microglial cell line.