Functional characterization of the dendritically localized mRNA neuronatin in hippocampal neurons

Citalopram exposure of hESCs during neuronal differentiation identifies dysregulated genes involved in neurodevelopment and depression

Selective serotonin reuptake inhibitors (SSRIs), including citalopram, are widely used antidepressants during pregnancy. However, the effects of prenatal exposure to citalopram on neurodevelopment remain poorly understood. We aimed to investigate the impact of citalopram exposure on early neuronal differentiation of human embryonic stem cells using a multi-omics approach. Citalopram induced time- and dose-dependent effects on gene expression and DNA methylation of genes involved in neurodevelopmental processes or linked to depression, such as BDNF, GDF11, CCL2, STC1, DDIT4 and GAD2. Single-cell RNA-sequencing analysis revealed distinct clusters of stem cells, neuronal progenitors and neuroblasts, where exposure to citalopram subtly influenced progenitor subtypes. Pseudotemporal analysis showed enhanced neuronal differentiation. Our findings suggest that citalopram exposure during early neuronal differentiation influences gene expression patterns associated with neurodevelopment and depression, providing insights into its potential neurodevelopmental impact and highlighting the importance of further research to understand the long-term consequences of prenatal SSRI exposure.

Nrf2 activation rescues stress-induced depression-like behaviour and inflammatory responses in male but not female rats

BACKGROUND

Major depressive disorder (MDD) is a recurring affective disorder that is two times more prevalent in females than males. Evidence supports immune system dysfunction as a major contributing factor to MDD, notably in a sexually dimorphic manner. Nuclear factor erythroid 2-related factor 2 (Nrf2), a regulator of antioxidant signalling during inflammation, is dysregulated in many chronic inflammatory disorders; however, its role in depression and the associated sex differences have yet to be explored. Here, we investigated the sex-specific antidepressant and immunomodulatory effects of the potent Nrf2 activator dimethyl fumarate (DMF), as well as the associated gene expression profiles.

METHODS

Male and female rats were treated with vehicle or DMF (25 mg/kg) whilst subjected to 8 weeks of chronic unpredictable stress. The effect of DMF treatment on stress-induced depression- and anxiety-like behaviours, as well as deficits in recognition and spatial learning and memory were then assessed. Sex differences in hippocampal (HIP) microglial activation and gene expression response were also evaluated.

RESULTS

DMF treatment during stress exposure had antidepressant effects in male but not female rats, with no anxiolytic effects in either sex. Recognition learning and memory and spatial learning and memory were impaired in chronically stressed males and females, respectively, and DMF treatment rescued these deficits. DMF treatment also prevented stress-induced HIP microglial activation in males. Conversely, females displayed no HIP microglial activation associated with stress exposure. Last, chronic stress elicited sex-specific alterations in HIP gene expression, many of which were normalized in animals treated with DMF. Of note, most of the differentially expressed genes in males normalized by DMF were related to antioxidant, inflammatory or immune responses.

CONCLUSIONS

Collectively, these findings support a greater role of immune processes in males than females in a rodent model of depression. This suggests that pharmacotherapies that target Nrf2 have the potential to be an effective sex-specific treatment for depression.

An Alzheimer's disease risk variant in TTC3 modifies the actin cytoskeleton organization and the PI3K-Akt signaling pathway in iPSC-derived forebrain neurons

A missense variant in the tetratricopeptide repeat domain 3 (TTC3) gene (rs377155188, p.S1038C, NM_003316.4:c 0.3113C>G) was found to segregate with disease in a multigenerational family with late-onset Alzheimer's disease. This variant was introduced into induced pluripotent stem cells (iPSCs) derived from a cognitively intact individual using CRISPR genome editing, and the resulting isogenic pair of iPSC lines was differentiated into cortical neurons. Transcriptome analysis showed an enrichment for genes involved in axon guidance, regulation of actin cytoskeleton, and GABAergic synapse. Functional analysis showed that the TTC3 p.S1038C iPSC-derived neuronal progenitor cells had altered 3-dimensional morphology and increased migration, while the corresponding neurons had longer neurites, increased branch points, and altered expression levels of synaptic proteins. Pharmacological treatment with small molecules that target the actin cytoskeleton could revert many of these cellular phenotypes, suggesting a central role for actin in mediating the cellular phenotypes associated with the TTC3 p.S1038C variant.

Termination codon readthrough of NNAT mRNA regulates calcium-mediated neuronal differentiation

Termination codon readthrough (TCR) is a process in which ribosomes continue to translate an mRNA beyond a stop codon generating a C-terminally extended protein isoform. Here, we demonstrate TCR in mammalian NNAT mRNA, which encodes NNAT, a proteolipid important for neuronal differentiation. This is a programmed event driven by cis-acting RNA sequences present immediately upstream and downstream of the canonical stop codon and is negatively regulated by NONO, an RNA-binding protein known to promote neuronal differentiation. Unlike the canonical isoform NNAT, we determined that the TCR product (NNATx) does not show detectable interaction with the sarco/endoplasmic reticulum Ca2+-ATPase isoform 2 Ca2+ pump, cannot increase cytoplasmic Ca2+ levels, and therefore does not enhance neuronal differentiation in Neuro-2a cells. Additionally, an antisense oligonucleotide that targets a region downstream of the canonical stop codon reduced TCR of NNAT and enhanced the differentiation of Neuro-2a cells to cholinergic neurons. Furthermore, NNATx-deficient Neuro-2a cells, generated using CRISPR-Cas9, showed increased cytoplasmic Ca2+ levels and enhanced neuronal differentiation. Overall, these results demonstrate regulation of neuronal differentiation by TCR of NNAT. Importantly, this process can be modulated using a synthetic antisense oligonucleotide.

Circulating Neuronatin Levels Are Positively Associated with BMI and Body Fat Mass but Not with Psychological Parameters

Human genetic studies have associated Neuronatin gene variants with anorexia nervosa (AN) and obesity. Studies on the expression of the Neuronatin gene product, a proteolipid, are lacking. We investigated the relationship between circulating Neuronatin, body mass index (BMI), body composition (BC), physical activity (PA), and psychometric outcomes in patients with AN, normal weight, and obesity. Plasma Neuronatin was measured by ELISA in (1) 79 subjects of five BMI categories (AN/BMI < 17.5 kg/m2; normal weight/BMI 18.5-25 kg/m2; obesity/BMI 30-40 kg/m2; obesity/BMI 40-50 kg/m2; obesity/BMI > 50 kg/m2) with assessment of BC (bioimpedance analysis; BIA); (2) 49 women with AN (BMI 14.5 ± 1.8 kg/m2) with measurements of BC (BIA) and PA (accelerometry); (3) 79 women with obesity (BMI 48.8 ± 7.8 kg/m2) with measurements of anxiety (GAD-7), stress (PSQ-20), depression (PHQ-9) and eating behavior (EDI-2). Overall, a positive correlation was found between Neuronatin and BMI (p = 0.006) as well as total fat mass (FM; p = 0.036). In AN, Neuronatin did not correlate with BMI, FM, or PA (p > 0.05); no correlations were found between Neuronatin and psychometric outcomes in obesity (p > 0.05). The findings suggest an FM-dependent peripheral Neuronatin expression. The decreased Neuronatin expression in AN provides evidence that Neuronatin is implicated in the pathogenesis of eating disorders.

NNAT is a novel mediator of oxidative stress that suppresses ER + breast cancer

BACKGROUND

Neuronatin (NNAT) was recently identified as a novel mediator of estrogen receptor-positive (ER+) breast cancer cell proliferation and migration, which correlated with decreased tumorigenic potential and prolonged patient survival. However, despite these observations, the molecular and pathophysiological role(s) of NNAT in ER + breast cancer remains unclear. Based on high protein homology with phospholamban, we hypothesized that NNAT mediates the homeostasis of intracellular calcium [Ca2+]i levels and endoplasmic reticulum (EndoR) function, which is frequently disrupted in ER + breast cancer and other malignancies.

METHODS

To evaluate the role of NNAT on [Ca2+]i homeostasis, we used a combination of bioinformatics, gene expression and promoter activity assays, CRISPR gene manipulation, pharmacological tools and confocal imaging to characterize the association between ROS, NNAT and calcium signaling.

RESULTS

Our data indicate that NNAT localizes predominantly to EndoR and lysosome, and genetic manipulation of NNAT levels demonstrated that NNAT modulates [Ca2+]i influx and maintains Ca2+ homeostasis. Pharmacological inhibition of calcium channels revealed that NNAT regulates [Ca2+]i levels in breast cancer cells through the interaction with ORAI but not the TRPC signaling cascade. Furthermore, NNAT is transcriptionally regulated by NRF1, PPARα, and PPARγ and is strongly upregulated by oxidative stress via the ROS and PPAR signaling cascades.

CONCLUSION

Collectively, these data suggest that NNAT expression is mediated by oxidative stress and acts as a regulator of Ca2+ homeostasis to impact ER + breast cancer proliferation, thus providing a molecular link between the longstanding observation that is accumulating ROS and altered Ca2+ signaling are key oncogenic drivers of cancer.

An Alzheimer's disease risk variant in TTC3 modifies the actin cytoskeleton organization and the PI3K-Akt signaling pathway in iPSC-derived forebrain neurons

A missense variant in the tetratricopeptide repeat domain 3 ( TTC3 ) gene (rs377155188, p.S1038C, NM_003316.4:c.3113C>G) was found to segregate with disease in a multigenerational family with late onset Alzheimer's disease. This variant was introduced into induced pluripotent stem cells (iPSCs) derived from a cognitively intact individual using CRISPR genome editing and the resulting isogenic pair of iPSC lines were differentiated into cortical neurons. Transcriptome analysis showed an enrichment for genes involved in axon guidance, regulation of actin cytoskeleton, and GABAergic synapse. Functional analysis showed that the TTC3 p.S1038C iPSC-derived neuronal progenitor cells had altered 3D morphology and increased migration, while the corresponding neurons had longer neurites, increased branch points, and altered expression levels of synaptic proteins. Pharmacological treatment with small molecules that target the actin cytoskeleton could revert many of these cellular phenotypes, suggesting a central role for actin in mediating the cellular phenotypes associated with the TTC3 p.S1038C variant.

Highlights

The AD risk variant TTC3 p.S1038C reduces the expression levels of TTC3 The variant modifies the expression of AD specific genes BACE1 , INPP5F , and UNC5C Neurons with the variant are enriched for genes in the PI3K-Akt pathwayiPSC-derived neurons with the alteration have increased neurite length and branchingThe variant interferes with actin cytoskeleton and is ameliorated by Cytochalasin D.

Regulation of beige adipocyte thermogenesis by the cold-repressed ER protein NNAT

OBJECTIVE

Cold stimuli trigger the conversion of white adipose tissue into beige adipose tissue, which is capable of non-shivering thermogenesis. However, what process drives this activation of thermogenesis in beige fat is not well understood. Here, we examine the ER protein NNAT as a regulator of thermogenesis in adipose tissue.

METHODS

We investigated the regulation of adipose tissue NNAT expression in response to changes in ambient temperature. We also evaluated the functional role of NNAT in thermogenic regulation using Nnat null mice and primary adipocytes that lack or overexpress NNAT.

RESULTS

Cold exposure or treatment with a β3-adrenergic agonist reduces the expression of adipose tissue NNAT in mice. Genetic disruption of Nnat in mice enhances inguinal adipose tissue thermogenesis. Nnat null mice exhibit improved cold tolerance both in the presence and absence of UCP1. Gain-of-function studies indicate that ectopic expression of Nnat abolishes adrenergic receptor-mediated respiration in beige adipocytes. NNAT physically interacts with the ER Ca²⁺-ATPase (SERCA) in adipocytes and inhibits its activity, impairing Ca²⁺ transport and heat dissipation. We further demonstrate that NHLRC1, an E3 ubiquitin protein ligase implicated in proteasomal degradation of NNAT, is induced by cold exposure or β3-adrenergic stimulation, thus providing regulatory control at the protein level. This serves to link cold stimuli to NNAT degradation in adipose tissue, which in turn leads to enhanced SERCA activity.

CONCLUSIONS

Our study implicates NNAT in the regulation of adipocyte thermogenesis.

A Guide to Preclinical Models of Zoster-Associated Pain and Postherpetic Neuralgia

Reactivation of latent varicella-zoster virus (VZV) causes herpes zoster (HZ), which is commonly accompanied by acute pain and pruritus over the time course of a zosteriform rash. Although the rash and associated pain are self-limiting, a considerable fraction of HZ cases will subsequently develop debilitating chronic pain states termed postherpetic neuralgia (PHN). How VZV causes acute pain and the mechanisms underlying the transition to PHN are far from clear. The human-specific nature of VZV has made in vivo modeling of pain following reactivation difficult to study because no single animal can reproduce reactivated VZV disease as observed in the clinic. Investigations of VZV pathogenesis following primary infection have benefited greatly from human tissues harbored in immune-deficient mice, but modeling of acute and chronic pain requires an intact nervous system with the capability of transmitting ascending and descending sensory signals. Several groups have found that subcutaneous VZV inoculation of the rat induces prolonged and measurable changes in nociceptive behavior, indicating sensitivity that partially mimics the development of mechanical allodynia and thermal hyperalgesia seen in HZ and PHN patients. Although it is not a model of reactivation, the rat is beginning to inform how VZV infection can evoke a pain response and induce long-lasting alterations to nociception. In this review, we will summarize the rat pain models from a practical perspective and discuss avenues that have opened for testing of novel treatments for both zoster-associated pain and chronic PHN conditions, which remain in critical need of effective therapies.

Cross-tissue analysis of blood and brain epigenome-wide association studies in Alzheimer's disease

To better understand DNA methylation in Alzheimer's disease (AD) from both mechanistic and biomarker perspectives, we performed an epigenome-wide meta-analysis of blood DNA methylation in two large independent blood-based studies in AD, the ADNI and AIBL studies, and identified 5 CpGs, mapped to the SPIDR, CDH6 genes, and intergenic regions, that are significantly associated with AD diagnosis. A cross-tissue analysis that combined these blood DNA methylation datasets with four brain methylation datasets prioritized 97 CpGs and 10 genomic regions that are significantly associated with both AD neuropathology and AD diagnosis. An out-of-sample validation using the AddNeuroMed dataset showed the best performing logistic regression model includes age, sex, immune cell type proportions, and methylation risk score based on prioritized CpGs in cross-tissue analysis (AUC = 0.696, 95% CI: 0.616 - 0.770, P-value = 2.78 × 10^-5). Our study offers new insights into epigenetics in AD and provides a valuable resource for future AD biomarker discovery.

Aberrant miR-339-5p/neuronatin signaling causes prodromal neuronal calcium dyshomeostasis in mutant presenilin mice

Mushroom spine loss and calcium dyshomeostasis are early hallmark events of age-related neurodegeneration, such as Alzheimer’s disease (AD), that are connected with neuronal hyperactivity in early pathology of cognitive brain areas. However, it remains elusive how these key events are triggered at the molecular level for the neuronal abnormality that occurs at the initial stage of disease. Here, we identify downregulated miR-339-5p and its upregulated target protein, neuronatin (Nnat), in cortex neurons from the presenilin-1 M146V knockin (PSEN1-M146V KI) mouse model of familial AD (FAD). Inhibition of miR-339-5p or overexpression of Nnat recapitulates spine loss and endoplasmic reticulum calcium overload in cortical neurons with the PSEN1 mutation. Conversely, either overexpression of miR-339-5p or knockdown of Nnat restores spine morphogenesis and calcium homeostasis. We used fiber photometry recording during the object-cognitive process to further demonstrate that the PSEN1 mutant causes defective habituation in neuronal reaction in the retrosplenial cortex and that this can be rescued by restoring the miR-339-5p/Nnat pathway. Our findings thus reveal crucial roles of the miR-339-5p/Nnat pathway in FAD that may serve as potential diagnostic and therapeutic targets for early pathogenesis.

Potential roles of imprinted genes in the teratogenic effects of alcohol on the placenta, somatic growth, and the developing brain

Despite several decades of research and prevention efforts, fetal alcohol spectrum disorders (FASD) remain the most common preventable cause of neurodevelopmental disabilities worldwide. Animal and human studies have implicated fetal alcohol-induced alterations in epigenetic programming as a chief mechanism in FASD. Several studies have demonstrated fetal alcohol-related alterations in methylation and expression of imprinted genes in placental, brain, and embryonic tissue. Imprinted genes are epigenetically regulated in a parent-of-origin-specific manner, in which only the maternal or paternal allele is expressed, and the other allele is silenced. The chief functions of imprinted genes are in placental development, somatic growth, and neurobehavior-three domains characteristically affected in FASD. In this review, we summarize the growing body of literature characterizing prenatal alcohol-related alterations in imprinted gene methylation and/or expression and discuss potential mechanistic roles for these alterations in the teratogenic effects of prenatal alcohol exposure. Future research is needed to examine potential physiologic mechanisms by which alterations in imprinted genes disrupt development in FASD, which may, in turn, elucidate novel targets for intervention. Furthermore, mechanistic alterations in imprinted gene expression and/or methylation in FASD may inform screening assays that identify individuals with FASD neurobehavioral deficits who may benefit from early interventions.

Neuronatin promotes SERCA uncoupling and its expression is altered in skeletal muscles of high-fat diet-fed mice

Neuronatin (NNAT) is a transmembrane protein in the endoplasmic reticulum involved in metabolic regulation. It shares sequence homology with sarcolipin (SLN), which negatively regulates the sarco(endo)plasmic reticulum Ca²⁺ -ATPase (SERCA) that maintains energy homeostasis in muscles. Here, we examined whether NNAT could uncouple the Ca²⁺ transport activity of SERCA from ATP hydrolysis, similarly to SLN. NNAT significantly reduced Ca²⁺ uptake without altering SERCA activity, ultimately lowering the apparent coupling ratio of SERCA. This effect of NNAT was reversed by the adenylyl cyclase activator forskolin. Furthermore, soleus muscles from high fat diet (HFD)-fed mice showed a significant downregulation in NNAT content compared with chow-fed mice, whereas an upregulation in NNAT content was observed in fast-twitch muscles from HFD- versus chow- fed mice. Therefore, NNAT is a SERCA uncoupler in cells and may function in adaptive thermogenesis.

Identification of neural oscillations and epileptiform changes in human brain organoids

Brain organoids represent a powerful tool for studying human neurological diseases, particularly those that affect brain growth and structure. However, many diseases manifest with clear evidence of physiological and network abnormality in the absence of anatomical changes, raising the question of whether organoids possess sufficient neural network complexity to model these conditions. Here, we explore the network-level functions of brain organoids using calcium sensor imaging and extracellular recording approaches that together reveal the existence of complex network dynamics reminiscent of intact brain preparations. We demonstrate highly abnormal and epileptiform-like activity in organoids derived from induced pluripotent stem cells from individuals with Rett syndrome, accompanied by transcriptomic differences revealed by single-cell analyses. We also rescue key physiological activities with an unconventional neuroregulatory drug, pifithrin-α. Together, these findings provide an essential foundation for the utilization of brain organoids to study intact and disordered human brain network formation and illustrate their utility in therapeutic discovery.

Murine neuronatin deficiency is associated with a hypervariable food intake and bimodal obesity

Neuronatin (Nnat) has previously been reported to be part of a network of imprinted genes downstream of the chromatin regulator Trim28. Disruption of Trim28 or of members of this network, including neuronatin, results in an unusual phenotype of a bimodal body weight. To better characterise this variability, we examined the key contributors to energy balance in Nnat+/-p mice that carry a paternal null allele and do not express Nnat. Consistent with our previous studies, Nnat deficient mice on chow diet displayed a bimodal body weight phenotype with more than 30% of Nnat+/-p mice developing obesity. In response to both a 45% high fat diet and exposure to thermoneutrality (30 °C) Nnat deficient mice maintained the hypervariable body weight phenotype. Within a calorimetry system, food intake in Nnat+/-p mice was hypervariable, with some mice consuming more than twice the intake seen in wild type littermates. A hyperphagic response was also seen in Nnat+/-p mice in a second, non-home cage environment. An expected correlation between body weight and energy expenditure was seen, but corrections for the effects of positive energy balance and body weight greatly diminished the effect of neuronatin deficiency on energy expenditure. Male and female Nnat+/-p mice displayed subtle distinctions in the degree of variance body weight phenotype and food intake and further sexual dimorphism was reflected in different patterns of hypothalamic gene expression in Nnat+/-p mice. Loss of the imprinted gene Nnat is associated with a highly variable food intake, with the impact of this phenotype varying between genetically identical individuals.

Strain-based and sex-biased differences in adrenal and pancreatic gene expression between KK/HlJ and C57BL/6 J mice

Background

The ever-increasing prevalence of diabetes and associated comorbidities serves to highlight the necessity of biologically relevant small-animal models to investigate its etiology, pathology and treatment. Although the C57BL/6 J model is amongst the most widely used mouse model due to its susceptibility to diet-induced obesity (DIO), there are a number of limitations namely [1] that unambiguous fasting hyperglycemia can only be achieved via dietary manipulation and/or chemical ablation of the pancreatic beta cells. [2] Heterogeneity in the obesogenic effects of hypercaloric feeding has been noted, together with sex-dependent differences, with males being more responsive. The KK mouse strain has been used to study aspects of the metabolic syndrome and prediabetes. We recently conducted a study which characterized the differences in male and female glucocentric parameters between the KK/HlJ and C57BL/6 J strains as well as diabetes-related behavioral differences (Inglis et al. 2019). In the present study, we further characterize these models by examining strain- and sex-dependent differences in pancreatic and adrenal gene expression using Affymetrix microarray together with endocrine-associated serum analysis.

Results

In addition to strain-associated differences in insulin tolerance, we found significant elevations in KK/HlJ mouse serum leptin, insulin and aldosterone. Additionally, glucagon and corticosterone were elevated in female mice of both strains. Using 2-factor ANOVA and a significance level set at 0.05, we identified 10,269 pancreatic and 10,338 adrenal genes with an intensity cut-off of ≥2.0 for all 4 experimental groups. In the pancreas, gene expression upregulated in the KK/HlJ strain related to increased insulin secretory granule biofunction and pancreatic hyperplasia, whereas ontology of upregulated adrenal differentially expressed genes (DEGs) related to cell signaling and neurotransmission. We established a network of functionally related DEGs commonly upregulated in both endocrine tissues of KK/HlJ mice which included the genes coding for endocrine secretory vesicle biogenesis and regulation: PCSK2, PCSK1N, SCG5, PTPRN, CHGB and APLP1. We also identified genes with sex-biased expression common to both strains and tissues including the paternally expressed imprint gene neuronatin.

Conclusion

Our novel results have further characterized the commonalities and diversities of pancreatic and adrenal gene expression between the KK/HlJ and C57BL/6 J strains as well as differences in serum markers of endocrine physiology.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07495-4.

Neuronatin regulates whole-body metabolism: is thermogenesis involved?

Neuronatin (NNAT) was originally discovered in 1995 and labeled as a brain developmental gene due to its abundant expression in developing brains. Over the past 25 years, researchers have uncovered NNAT in other tissues; notably, the hypothalamus, pancreatic β‐cells, and adipocytes. Recent evidence in these tissues indicates that NNAT plays a significant role in metabolism whereby it regulates food intake, insulin secretion, and adipocyte differentiation. Furthermore, genetic deletion of Nnat in mice lowers whole‐body energy expenditure and increases susceptibility to diet‐induced obesity and glucose intolerance; however, the underlying cellular mechanisms remain unknown. Based on its sequence homology with phospholamban, NNAT has a purported role in regulating the sarco(endo)plasmic reticulum Ca²⁺ ATPase (SERCA) pump. However, NNAT also shares sequence homology with sarcolipin, which has the unique property of uncoupling the SERCA pump, increasing whole‐body energy expenditure and thus promoting adaptive thermogenesis in states of caloric excess or cold exposure. Thus, in this article, we discuss the accumulating evidence suggestive of NNAT’s role in whole‐body metabolic regulation, while highlighting its potential to mediate adaptive thermogenesis via SERCA uncoupling.

Comparing Gene Expression in the Parabrachial and Amygdala of Diestrus and Proestrus Female Rats after Orofacial Varicella Zoster Injection

The orofacial pain pathway projects to the parabrachial and amygdala, and sex steroids have been shown to affect neuronal activity in these regions. GABA positive cells in the amygdala are influenced by sex steroid metabolites to affect pain, and sex steroids have been shown to alter the expression of genes in the parabrachial, changing neuronal excitability. Mechanisms by which sex steroids affect amygdala and parabrachial signaling are unclear. The expression of genes in the parabrachial and amygdala in diestrus (low estradiol) and proestrus (high estradiol) female rats were evaluated in this study. First, varicella zoster virus was injected into the whisker pad of female rats to induce a pain response. Second, gene expression was quantitated using RNA-seq one week after injection. Genes that had the greatest change in expression and known to function in pain signaling were selected for the quantitation of protein content. Protein expression of four genes in the parabrachial and seven genes in the amygdala were quantitated by ELISA. In the parabrachial, neurexin 3 (Nrnx3) was elevated at proestrus. Nrnx3 has a role in AMPA receptor and GABA signaling. Neuronatin (Nnat) and protein phosphatase, Mg²⁺/Mn²⁺ dependent 1E (Ppm1e) were elevated in the parabrachial of diestrus animals both genes having a role in pain signaling. Epoxide hydroxylase (Ephx2) was elevated in the parabrachial at proestrus and the vitamin D receptor (Vdr) was elevated in the amygdala. Ephx2 antagonists and vitamin D have been used to treat neuropathic pain. In conclusion, sex steroids regulate genes in the parabrachial and amygdala that might result in the greater pain response observed during diestrus.

Dynamic Changes in the Localization of Neuronatin-Positive Cells during Neurogenesis in the Embryonic Rat Brain

Neuronatin (NNAT) was first identified as a gene selectively and abundantly expressed in the cytoplasm of the newborn mouse brain, and involved in neonatal neurogenesis. However, the particular roles of NNAT in the developing prenatal brain have not been identified, especially in mid to late stages. In this study, we performed immunohistochemical analyses of NNAT and SOX2 proteins, a nuclear transcription factor and neural stem/progenitor marker, in the rat brain on embryonic days 13.5, E16.5, and E20.5. NNAT signals were broadly observed across the developing brain on E13.5 and gradually more localized in later stages, eventually concentrated in the alar and basal parts of the terminal hypothalamus, the alar plate of prosomere 2 of the thalamus, and the choroid plexus in the lateral and fourth ventricles on E20.5. In particular, the mammillary body in the basal part of the terminal hypothalamus, a region with a high number of SOX2-positive cells, evidenced intense NNAT signals on E20.5. The intracellular localization of NNAT showed diverse profiles, suggesting that NNAT was involved in various cellular functions, such as cell differentiation and functional maintenance, during prenatal neurogenesis in the rat brain. Thus, the present observations suggested diverse and active roles of the NNAT protein in neurogenesis. Determining the function of this molecule may assist in the elucidation of the mechanisms involved in brain development.

Disruption of Foxg1 impairs neural plasticity leading to social and cognitive behavioral defects

The transcription factor Foxg1 is known to be continuously expressed at a high level in mature neurons in the telencephalon, but little is known about its role in neural plasticity. Mutations in human FOXG1 cause deficiencies in learning and memory and limit social ability, which is defined as FOXG1 syndrome, but its pathogenic mechanism remains unclear. To examine the role of Foxg1 in adults, we crossed Camk2a-Cre^ER with Foxg1^fl/fl mice and conditionally disrupted Foxg1 with tamoxifen in mature neurons. We found that spatial learning and memory were significantly impaired when examined by the Morris water maze test. The cKO mice also showed a significant reduction in freezing time during the contextual and cued fear conditioning test, indicating that fear conditioning memory was affected. A remarkable reduction in Schaffer-collateral long-term potentiation was also recorded. Morphologically, the dendritic arborization and spine densities of hippocampal pyramidal neurons were significantly reduced. Primary cell culture further confirmed altered dendritic complexity after Foxg1 deletion. Our results indicated that Foxg1 plays an important role in maintaining the neural plasticity, which is vital to high-grade function.

Transcriptome Analysis of Small Molecule-Mediated Astrocyte-to-Neuron Reprogramming

Chemical reprogramming of astrocytes into neurons represents a promising approach to regenerate new neurons for brain repair, but the underlying mechanisms driving this trans-differentiation process are not well understood. We have recently identified four small molecules – CHIR99021, DAPT, LDN193189, and SB431542 – that can efficiently reprogram cultured human fetal astrocytes into functional neurons. Here we employ the next generation of RNA-sequencing technology to investigate the transcriptome changes during the astrocyte-to-neuron (AtN) conversion process. We found that the four small molecules can rapidly activate the hedgehog signaling pathway while downregulating many glial genes such as FN1 and MYL9 within 24 h of treatment. Chemical reprogramming is mediated by several waves of differential gene expression, including upregulation of hedgehog, Wnt/β-catenin, and Notch signaling pathways, together with downregulation of TGF-β and JAK/STAT signaling pathways. Our gene network analyses reveal many well-connected hub genes such as repulsive guidance molecule A (RGMA), neuronatin (NNAT), neurogenin 2 (NEUROG2), NPTX2, MOXD1, JAG1, and GAP43, which may coordinate the chemical reprogramming process. Together, these findings provide critical insights into the molecular cascades triggered by a combination of small molecules that eventually leads to chemical conversion of astrocytes into neurons.

Characteristic Localization of Neuronatin in Rat Testis, Hair Follicle, Tongue, and Pancreas

Neuronatin (Nnat) is expressed in the pituitary, pancreas, and other tissues; however, the function of NNAT is still unclear. Recent studies have demonstrated that NNAT is localized in the sex-determining region Y-box 2-positive stem/progenitor cells in the developing rat pituitary primordium and is downregulated during differentiation into mature hormone-producing cells. Moreover, NNAT is widely localized in subcellular organelles, excluding the Golgi. Here, we further evaluated NNAT-positive cells and intracellular localization in embryonic and postnatal rat tissues such as the pancreas, tongue, whisker hair follicle, and testis. Immunohistochemistry revealed that NNAT was localized in undifferentiated cells (i.e., epithelial basal cells and basement cells in the papillae of the tongue and round and elongated spermatids of the testis) as well as in differentiated cells (insulin-positive cells and exocrine cells of the pancreas, taste receptor cells of the fungiform papilla, the inner root sheath of whisker hair follicles, and spermatozoa). In addition, NNAT exhibited novel intracellular localization in acrosomes in the spermatozoa. Because the endoplasmic reticulum (ER) is excluded from spermatozoa and sarco/ER Ca²⁺-ATPase isoform 2 (SERCA2) is absent from the inner root sheath, these findings suggested that NNAT localization in the ER and its interaction with SERCA2 are cell- or tissue-specific properties.

Active presynaptic ribosomes in the mammalian brain, and altered transmitter release after protein synthesis inhibition

Presynaptic neuronal activity requires the localization of thousands of proteins that are typically synthesized in the soma and transported to nerve terminals. Local translation for some dendritic proteins occurs, but local translation in mammalian presynaptic nerve terminals is difficult to demonstrate. Here, we show an essential ribosomal component, 5.8S rRNA, at a glutamatergic nerve terminal in the mammalian brain. We also show active translation in nerve terminals, in situ, in brain slices demonstrating ongoing presynaptic protein synthesis in the mammalian brain. Shortly after inhibiting translation, the presynaptic terminal exhibits increased spontaneous release, an increased paired pulse ratio, an increased vesicle replenishment rate during stimulation trains, and a reduced initial probability of release. The rise and decay rates of postsynaptic responses were not affected. We conclude that ongoing protein synthesis can limit excessive vesicle release which reduces the vesicle replenishment rate, thus conserving the energy required for maintaining synaptic transmission.

Alcohol-Related Alterations in Placental Imprinted Gene Expression in Humans Mediate Effects of Prenatal Alcohol Exposure on Postnatal Growth

BACKGROUND

A growing body of evidence in animal models has implicated alcohol-induced alterations in epigenetic programming as an important mechanism in fetal alcohol spectrum disorders (FASD). Imprinted genes, a subset of epigenetically regulated genes that are sensitive to the prenatal environment, are chiefly involved in growth and neurobehavior. We tested the hypothesis that alterations in placental imprinted gene expression mediate fetal alcohol growth restriction.

METHODS

Placental expression of 109 genes previously shown to be imprinted and expressed in the placenta was assessed using the NanoString™ nCounter Analysis System in flash-frozen samples from 34 heavy drinkers and 31 control women in Cape Town, South Africa, from whom prospective pregnancy alcohol consumption data had been obtained. Length/height, weight, and head circumference were measured at 6.5 and 12 months and at an FASD diagnostic clinic (at ages 1.1 to 4.6 years) that we organized. Imprinted gene expression between exposed and control placentas was compared using the limma R package. The relation of alcohol exposure to World Health Organization length-for-age z-scores was examined before and after inclusion of expression for each alcohol-related imprinted gene, using hierarchical mixed regression models with repeated measures.

RESULTS

Heavy drinkers averaged 8 standard drinks on 2 to 3 days/wk (vs. 0 for controls). Prenatal alcohol exposure was associated with smaller length/height and weight during the postnatal period. Heavy exposure was related to alterations in expression of 11 of 93 expressed imprinted genes, including increased expression of 5 genes found to be negatively associated with growth and decreased expression of 3 genes positively associated with growth. Alcohol-related alterations in expression of 5 genes statistically mediated the effect of prenatal alcohol exposure on length.

CONCLUSIONS

These findings identify alcohol-related alterations in placental imprinted gene expression as potential biomarkers of adverse effect in FASD and suggest that these alterations may play a mechanistic role in fetal alcohol growth restriction. Future studies are needed to determine whether alterations in imprinted gene expression also mediate FASD neurobehavioral deficits and whether such alterations are amenable to intervention.

A decrease in eukaryotic elongation factor 2 phosphorylation is required for local translation of sensorin and long-term facilitation in Aplysia

Mechanistic target of rapamycin complex 1 (mTORC1)-dependent protein synthesis is required for many forms of synaptic plasticity and memory, but the downstream pathways important for synaptic plasticity are poorly understood. Long-term facilitation (LTF) in Aplysia is a form of synaptic plasticity that is closely linked to behavioral memory and an attractive model system for examining the important downstream targets for mTORC1 in regulating synaptic plasticity. Although mTORC1-regulated protein synthesis has been strongly linked to translation initiation, translation elongation is also regulated by mTORC1 and LTF leads to an mTORC1-dependent decrease in eukaryotic elongation factor 2 (eEF2) phosphorylation. The purpose of this study is to test the hypothesis that the decrease in eEF2 phosphorylation is required for mTORC1-dependent translation and plasticity. We show that the LTF-induced decrease in eEF2 phosphorylation is blocked by expression of an eEF2 kinase (eEF2K) modified to be resistant to mTORC1 regulation. We found that expression of this modified kinase blocked LTF. LTF requires local protein synthesis of the neuropeptide sensorin and importantly, local sensorin synthesis can be measured using a dendra fluorescent protein containing the 5' and 3' untranslated regions (UTRs) of sensorin. Using this construct, we show that blocking eEF2 dephosphorylation also blocks the increase in local sensorin synthesis. These results identify decreases in eEF2 phosphorylation as a critical downstream effector of mTOR required for long-term plasticity and identify an important translational target regulated by decreases in eEF2 phosphorylation.

Neuronatin Protein in Health and Disease

Neuronatin (NNAT) was first identified as a brain-specific gene crucial for brain development. Over the years, NNAT has been studied in different developing and post-developed tissues and organs. While NNAT manifests functional and structural similarities to the phospholamban gene, its physiological and pathological roles in healthy and diseased tissues have not been precisely identified. Ca²⁺ signaling, glucose transport, insulin secretion, and inflammation modulated at different pathological conditions have been proposed to be governed by NNAT. This review describes the current findings of cellular molecular pathways known to be modified concomitantly with an alteration in NNAT expression, and it highlights the need to conduct extensive investigation regarding the role of NNAT in health and disease. J. Cell. Physiol. 232: 477-481, 2017. © 2016 Wiley Periodicals, Inc.

New Perspectives on Genomic Imprinting, an Essential and Multifaceted Mode of Epigenetic Control in the Developing and Adult Brain

Mammalian evolution entailed multiple innovations in gene regulation, including the emergence of genomic imprinting, an epigenetic regulation leading to the preferential expression of a gene from its maternal or paternal allele. Genomic imprinting is highly prevalent in the brain, yet, until recently, its central roles in neural processes have not been fully appreciated. Here, we provide a comprehensive survey of adult and developmental brain functions influenced by imprinted genes, from neural development and wiring to synaptic function and plasticity, energy balance, social behaviors, emotions, and cognition. We further review the widespread identification of parental biases alongside monoallelic expression in brain tissues, discuss their potential roles in dosage regulation of key neural pathways, and suggest possible mechanisms underlying the dynamic regulation of imprinting in the brain. This review should help provide a better understanding of the significance of genomic imprinting in the normal and pathological brain of mammals including humans.

Neuronatin is a stress-responsive protein of rod photoreceptors

Neuronatin (NNAT) is a small transmembrane proteolipid that is highly expressed in the embryonic developing brain and several other peripheral tissues. This study is the first to provide evidence that NNAT is detected in the adult retina of various adult rod-dominant mammals, including wild-type (WT) rodents, transgenic rodents expressing mutant S334ter, P23H, or T17M rhodopsin, non-human primates, humans, and cone-dominant tree shrews. Immunohistochemical and quantitative real time polymerase chain reaction (qRT-PCR) analyses were applied to detect NNAT. Confocal microscopy analysis revealed that NNAT immunofluorescence is restricted to the outer segments (OSs) of photoreceptors without evidence of staining in other retinal cell types across all mammalian species. Moreover, in tree shrew retinas, we found NNAT to be co-localized with rhodopsin, indicating its predominant expression in rods. The rod-derived expression of NNAT was further confirmed by qRT-PCR in isolated rod photoreceptor cells. We also used these cells to mimic cellular stress in transgenic retinas by treating them with the endoplasmic reticulum stress inducer, tunicamycin. Thus, our data revealed accumulation of NNAT around the nucleus as compared to dispersed localization of NNAT within control cells. This distribution coincided with the partial intracellular mislocalization of NNAT to the outer nuclear layer observed in transgenic retinas. In addition, stressed retinas demonstrated an increase of NNAT mRNA and protein levels. Therefore, our study demonstrated that NNAT is a novel stress-responsive protein with a potential structural and/or functional role in adult mammalian retinas.

Altered expression of neuropeptides in FoxG1-null heterozygous mutant mice

Foxg1 gene encodes for a transcription factor essential for telencephalon development in the embryonic mammalian forebrain. Its complete absence is embryonic lethal while Foxg1 heterozygous mice are viable but display microcephaly, altered hippocampal neurogenesis and behavioral and cognitive deficiencies. In order to evaluate the effects of Foxg1 alteration in adult brain, we performed expression profiling in total brains from Foxg1+/- heterozygous mutants and wild-type littermates. We identified statistically significant differences in expression levels for 466 transcripts (P<0.001), 29 of which showed a fold change ≥ 1.5. Among the differentially expressed genes was found a group of genes expressed in the basal ganglia and involved in the control of movements. A relevant (three to sevenfold changes) and statistically significant increase of expression, confirmed by qRT-PCR, was found in two highly correlated genes with expression restricted to the hypothalamus: Oxytocin (Oxt) and Arginine vasopressin (Avp). These neuropeptides have an important role in maternal and social behavior, and their alteration is associated with impaired social interaction and autistic behavior. In addition, Neuronatin (Nnat) levels appear significantly higher both in Foxg1+/- whole brain and in hippocampal neurons after silencing Foxg1, strongly suggesting that it is directly or indirectly repressed by Foxg1. During fetal and neonatal brain development, Nnat may regulate neuronal excitability, receptor trafficking and calcium-dependent signaling and, in the adult brain, it is predominantly expressed in parvalbumin-positive GABAergic interneurons. Overall, these results implicate the overexpression of a group of neuropeptides in the basal ganglia, hypothalamus, cortex and hippocampus in the pathogenesis FOXG1 behavioral impairments.

Expression studies of neuronatin in prenatal and postnatal rat pituitary

The pituitary gland, an indispensable endocrine organ that synthesizes and secretes pituitary hormones, develops with the support of many factors. Among them, neuronatin (NNAT), which was discovered in the neonatal mouse brain as a factor involved in neural development, has subsequently been revealed to be coded by an abundantly expressing gene in the pituitary gland but its role remains elusive. We analyze the expression profile of Nnat and the localization of its product during rat pituitary development. The level of Nnat expression was high during the embryonic period but remarkably decreased after birth. Immunohistochemistry demonstrated that NNAT appeared in the SOX2-positive stem/progenitor cells in the developing pituitary primordium on rat embryonic day 11.5 (E11.5) and later in the majority of SOX2/PROP1 double-positive cells on E13.5. Thereafter, during pituitary embryonic development, Nnat expression was observed in some stem/progenitor cells, proliferating cells and terminally differentiating cells. In postnatal pituitaries, NNAT-positive cells decreased in number, with most coexpressing Sox2 or Pit1, suggesting a similar role for NNAT to that during the embryonic period. NNAT was widely localized in mitochondria, peroxisomes and lysosomes, in addition to the endoplasmic reticulum but not in the Golgi. The present study thus demonstrated the variability in expression of NNAT-positive cells in rat embryonic and postnatal pituitaries and the intracellular localization of NNAT. Further investigations to obtain functional evidence for NNAT are a prerequisite.

van der Vaart A, Web BT, Bacanu SA, Kalsi G, Kendler KS, Miles MF, Dick D, Riley BP, Dumur C, Vladimirov VI. Integrating mRNA and miRNA Weighted Gene Co-Expression Networks with eQTLs in the Nucleus Accumbens of Subjects with Alcohol Dependence

Alcohol consumption is known to lead to gene expression changes in the brain. After performing weighted gene co-expression network analyses (WGCNA) on genome-wide mRNA and microRNA (miRNA) expression in Nucleus Accumbens (NAc) of subjects with alcohol dependence (AD; N = 18) and of matched controls (N = 18), six mRNA and three miRNA modules significantly correlated with AD were identified (Bonferoni-adj. p≤ 0.05). Cell-type-specific transcriptome analyses revealed two of the mRNA modules to be enriched for neuronal specific marker genes and downregulated in AD, whereas the remaining four mRNA modules were enriched for astrocyte and microglial specific marker genes and upregulated in AD. Gene set enrichment analysis demonstrated that neuronal specific modules were enriched for genes involved in oxidative phosphorylation, mitochondrial dysfunction and MAPK signaling. Glial-specific modules were predominantly enriched for genes involved in processes related to immune functions, i.e. cytokine signaling (all adj. p≤ 0.05). In mRNA and miRNA modules, 461 and 25 candidate hub genes were identified, respectively. In contrast to the expected biological functions of miRNAs, correlation analyses between mRNA and miRNA hub genes revealed a higher number of positive than negative correlations (χ2 test p≤ 0.0001). Integration of hub gene expression with genome-wide genotypic data resulted in 591 mRNA cis-eQTLs and 62 miRNA cis-eQTLs. mRNA cis-eQTLs were significantly enriched for AD diagnosis and AD symptom counts (adj. p = 0.014 and p = 0.024, respectively) in AD GWAS signals in a large, independent genetic sample from the Collaborative Study on Genetics of Alcohol (COGA). In conclusion, our study identified putative gene network hubs coordinating mRNA and miRNA co-expression changes in the NAc of AD subjects, and our genetic (cis-eQTL) analysis provides novel insights into the etiological mechanisms of AD.

Deep brain stimulation of the subthalamic nucleus preferentially alters the translational profile of striatopallidal neurons in an animal model of Parkinson's disease

Deep brain stimulation targeting the subthalamic nucleus (STN-DBS) is an effective surgical treatment for the motor symptoms of Parkinson's disease (PD), the precise neuronal mechanisms of which both at molecular and network levels remain a topic of debate. Here we employ two transgenic mouse lines, combining translating ribosomal affinity purification (TRAP) with bacterial artificial chromosome expression (Bac), to selectively identify changes in translational gene expression in either Drd1a-expressing striatonigral or Drd2-expressing striatopallidal medium spiny neurons (MSNs) of the striatum following STN-DBS. 6-hydroxydopamine lesioned mice received either 5 days stimulation via a DBS electrode implanted in the ipsilateral STN or 5 days sham treatment (no stimulation). Striatal polyribosomal RNA was selectively purified from either Drd2 or Drd1a MSNs using the TRAP method and gene expression profiling performed. We identified eight significantly altered genes in Drd2 MSNs (Vps33b, Ppp1r3c, Mapk4, Sorcs2, Neto1, Abca1, Penk1, and Gapdh) and two overlapping genes in Drd1a MSNs (Penk1 and Ppp1r3c) implicated in the molecular mechanisms of STN-DBS. A detailed functional analysis, using a further 728 probes implicated in STN-DBS, suggested an increased ability to receive excitation (mediated by increased dendritic spines, increased calcium influx and enhanced excitatory post synaptic potentials) accompanied by processes that would hamper the initiation of action potentials, transport of neurotransmitters from soma to axon terminals and vesicular release in Drd2-expressing MSNs. Finally, changes in expression of several genes involved in apoptosis as well as cholesterol and fatty acid metabolism were also identified. This increased understanding of the molecular mechanisms induced by STN-DBS may reveal novel targets for future non-surgical therapies for PD.

Bidirectional regulation of eEF2 phosphorylation controls synaptic plasticity by decoding neuronal activity patterns

At the sensory-motor neuron synapse of Aplysia, either spaced or continuous (massed) exposure to serotonin (5-HT) induces a form of intermediate-term facilitation (ITF) that requires new protein synthesis but not gene transcription. However, spaced and massed ITF use distinct molecular mechanisms to maintain increased synaptic strength. Synapses activated by spaced applications of 5-HT generate an ITF that depends on persistent protein kinase A (PKA) activity, whereas an ITF produced by massed 5-HT depends on persistent protein kinase C (PKC) activity. In this study, we demonstrate that eukaryotic elongation factor 2 (eEF2), which catalyzes the GTP-dependent translocation of the ribosome during protein synthesis, acts as a biochemical sensor that is tuned to the pattern of neuronal stimulation. Specifically, we find that massed training leads to a PKC-dependent increase in phosphorylation of eEF2, whereas spaced training results in a PKA-dependent decrease in phosphorylation of eEF2. Importantly, by using either pharmacological or dominant-negative strategies to inhibit eEF2 kinase (eEF2K), we were able to block massed 5-HT-dependent increases in eEF2 phosphorylation and subsequent PKC-dependent ITF. In contrast, pharmacological inhibition of eEF2K during the longer period of time required for spaced training was sufficient to reduce eEF2 phosphorylation and induce ITF. Finally, we find that the massed 5-HT-dependent increase in synaptic strength requires translation elongation, but not translation initiation, whereas the spaced 5-HT-dependent increase in synaptic strength is partially dependent on translation initiation. Thus, bidirectional regulation of eEF2 is critical for decoding distinct activity patterns at synapses by activating distinct modes of translation regulation.

MicroRNAs meet calcium: joint venture in ER proteostasis

The endoplasmic reticulum (ER) is a cellular compartment that has a key function in protein translation and folding. Maintaining its integrity is of fundamental importance for organism's physiology and viability. The dynamic regulation of intraluminal ER Ca(2+) concentration directly influences the activity of ER-resident chaperones and stress response pathways that balance protein load and folding capacity. We review the emerging evidence that microRNAs play important roles in adjusting these processes to frequently changing intracellular and environmental conditions to modify ER Ca(2+) handling and storage and maintain ER homeostasis.

Protection genes in nucleus accumbens shell affect vulnerability to nicotine self-administration across isogenic strains of adolescent rat

Classical genetic studies show the heritability of cigarette smoking is 0.4–0.6, and that multiple genes confer susceptibility and resistance to smoking. Despite recent advances in identifying genes associated with smoking behaviors, the major source of this heritability and its impact on susceptibility and resistance are largely unknown. Operant self-administration (SA) of intravenous nicotine is an established model for smoking behavior. We recently confirmed that genetic factors exert strong control over nicotine intake in isogenic rat strains. Because the processing of afferent dopaminergic signals by nucleus accumbens shell (AcbS) is critical for acquisition and maintenance of motivated behaviors reinforced by nicotine, we hypothesized that differential basal gene expression in AcbS accounts for much of the strain-to-strain variation in nicotine SA. We therefore sequenced the transcriptome of AcbS samples obtained by laser capture microdissection from 10 isogenic adolescent rat strains and compared all RNA transcript levels with behavior. Weighted gene co-expression network analysis, a systems biology method, found 12 modules (i.e., unique sets of genes that covary across all samples) that correlated (p<0.05) with amount of self-administered nicotine; 9 of 12 correlated negatively, implying a protective role. PCR confirmed selected genes from these modules. Chilibot, a literature mining tool, identified 15 genes within 1 module that were nominally associated with cigarette smoking, thereby providing strong support for the analytical approach. This is the first report demonstrating that nicotine intake by adolescent rodents is associated with the expression of specific genes in AcbS of the mesolimbic system, which controls motivated behaviors. These findings provide new insights into genetic mechanisms that predispose or protect against tobacco addiction.

Neuronatin gene: Imprinted and misfolded: Studies in Lafora disease, diabetes and cancer may implicate NNAT-aggregates as a common downstream participant in neuronal loss

Neuronatin (NNAT) is a ubiquitous and highly conserved mammalian gene involved in brain development. Its mRNA isoforms, chromosomal location, genomic DNA structure and regulation have been characterized. More recently there has been rapid progress in the understanding of its function in physiology and human disease. In particular there is fairly direct evidence implicating neuronatin in the causation of Lafora disease and diabetes. Neuronatin protein has a strong predisposition to misfold and form cellular aggregates that cause cell death by apoptosis. Aggregation of Neuronatin within cortical neurons and resulting cell death is the hallmark of Lafora disease, a progressive and fatal neurodegenerative disease. Under high glucose conditions simulating diabetes, neuronatin protein also accumulates and destroys pancreatic beta cells. The neuronatin gene is imprinted and only the paternal allele is normally expressed in the adult. However, changes in DNA methylation may cause the maternal allele to lose imprinting and trigger cell proliferation and metastasis. Neuronatin has also been shown to be translated peripherally within the dendrites of neurons, a finding of relevance in synaptic plasticity. The current understanding of the function of neuronatin raises the possibility that this gene may participate in the common downstream mechanisms associated with aberrant neuronal growth and death. A better understanding of these mechanisms may open new therapeutic targets to help modify the progression of devastating neurodegenerative conditions such as Alzheimer's and anterior horn cell disease.

Stress susceptibility-specific phenotype associated with different hippocampal transcriptomic responses to chronic tricyclic antidepressant treatment in mice

Background

The effects of chronic treatment with tricyclic antidepressant (desipramine, DMI) on the hippocampal transcriptome in mice displaying high and low swim stress-induced analgesia (HA and LA lines) were studied. These mice displayed different depression-like behavioral responses to DMI: stress-sensitive HA animals responded to DMI, while LA animals did not.

Results

To investigate the effects of DMI treatment on gene expression profiling, whole-genome Illumina Expression BeadChip arrays and qPCR were used. Total RNA isolated from hippocampi was used. Expression profiling was then performed and data were analyzed bioinformatically to assess the influence of stress susceptibility-specific phenotypes on hippocampal transcriptomic responses to chronic DMI. DMI treatment affected the expression of 71 genes in HA mice and 41 genes in LA mice. We observed the upregulation of Igf2 and the genes involved in neurogenesis (HA: Sema3f, Ntng1, Gbx2, Efna5, and Rora; LA: Otx2, Rarb, and Drd1a) in both mouse lines. In HA mice, we observed the upregulation of genes involved in neurotransmitter transport, the termination of GABA and glycine activity (Slc6a11, Slc6a9), glutamate uptake (Slc17a6), and the downregulation of neuropeptide Y (Npy) and corticotropin releasing hormone-binding protein (Crhbp). In LA mice, we also observed the upregulation of other genes involved in neuroprotection (Ttr, Igfbp2, Prlr) and the downregulation of genes involved in calcium signaling and ion binding (Adcy1, Cckbr, Myl4, Slu7, Scrp1, Zfp330).

Conclusions

Several antidepressant treatment responses are similar in individuals with different sensitivities to stress, including the upregulation of Igf2 and the genes involved in neurogenesis. However, the findings also reveal that many responses to antidepressant treatments, involving the action of individual genes engaged in neurogenesis, neurotransmitter transport and neuroprotection, depend on constitutive hippocampal transcriptomic profiles and might be genotype dependent. The results suggest that, when and if this becomes feasible, antidepressant treatment should take into consideration individual sensitivity to stress.

The protein p17 signaling pathways in cancer

P17 is a novel neuronal protein expressed under physiological conditions only at very low levels in other tissues. Accumulating data indicate its crucial involvement in tumorigenic effects. Using molecular, cellular, and biocomputational methods, the current study unraveled p17 mode of action. Data indicate that mitochondria-associated p17 interacts with the proteins TMEM115, YPEL3, ERP44, CDK5RAP, and NNAT. Moreover, p17 drives the cell cycle into the G0/G1 phase and enhances survival of proliferating cells. Interference with p17 activities thus might become a novel option to influence also the tumor suppressor protein p53 signaling pathways for the treatment of tumors.

Loss of neuronatin promotes "browning" of primary mouse adipocytes while reducing Glut1-mediated glucose disposal

Failure of white adipose tissue to appropriately store excess metabolic substrate seems to underpin obesity-associated type 2 diabetes. Encouraging "browning" of white adipose has been suggested as a therapeutic strategy to help dispose of excess stored lipid and ameliorate the resulting insulin resistance. Genetic variation at the DNA locus encoding the novel proteolipid neuronatin has been associated with obesity, and we recently observed that neuronatin expression is reduced in subcutaneous adipose tissue from obese humans. Thus, to explore the function of neuronatin further, we used RNAi to silence its expression in murine primary adipocyte cultures and examined the effects on adipocyte phenotype. We found that primary adipocytes express only the longer isoform of neuronatin. Loss of neuronatin led to increased mitochondrial biogenesis, indicated by greater intensity of MitoTracker Green staining. This was accompanied by increased expression of UCP1 and the key genes in mitochondrial oxidative phosphorylation, PGC-1α, Cox8b, and Cox4 in primary subcutaneous white adipocytes, indicative of a "browning" effect. In addition, phosphorylation of AMPK and ACC was increased, suggestive of increased fatty acid utilization. Similar, but less pronounced, effects of neuronatin silencing were also noted in primary brown adipocytes. In contrast, loss of neuronatin caused a reduction in both basal and insulin-stimulated glucose uptake and glycogen synthesis, likely mediated by a reduction in Glut1 protein upon silencing of neuronatin. In contrast, loss of neuronatin had no effect on insulin signaling. In conclusion, neuronatin appears to be a novel regulator of browning and metabolic substrate disposal in white adipocytes.

Increased hippocampal NgR1 signaling machinery in aged rats with deficits of spatial cognition

Myelin-associated inhibitor/NgR1 signaling has important roles in modulation of synaptic plasticity, with demonstrated effects on cognitive function. We have previously demonstrated that NgR1 and its ligands are upregulated in the hippocampus of aged rats with impaired spatial learning and memory, but it is unknown whether increased expression of these proteins indicates a potential increase in pathway signaling because NgR1 requires co-receptors for signal transduction through RhoA. Two co-receptor complexes have been identified to date, comprised of NgR1 and LINGO-1, and either p75 or TROY. In this study, we assessed the expression of LINGO-1, p75 and TROY, and the downstream effector RhoA in mature adult (12 months) and aged (26 months) male Fischer 344/Brown Norway hybrid rats classified as cognitively impaired or cognitively intact by Morris water maze testing. The hippocampal distribution of NgR1 and its co-receptors was assessed to determine whether receptor/co-receptor interaction, and therefore signaling through this pathway, is possible. Protein expression of LINGO-1, p75, TROY and RhoA was significantly elevated in cognitively impaired, but not intact, aged rats compared with mature adults, and expression levels correlated significantly with water maze performance. Co-localization of NgR1 with LINGO-1, p75 and TROY was observed in hippocampal neurons of aged, cognitively impaired rats. Further, expression profiles of NgR1 pathway components were demonstrated to classify rats as cognitively intact or cognitively impaired with high accuracy. Together, this suggests that hippocampal induction of this pathway is a conserved phenomenon in cognitive decline that may impair learning and memory by suppressing neuronal plasticity.

High-content RNAi screening identifies the Type 1 inositol triphosphate receptor as a modifier of TDP-43 localization and neurotoxicity

Cytosolic aggregation of the nuclear RNA-binding protein (RBP) TDP-43 (43 kDa TAR DNA-binding domain protein) is a suspected direct or indirect cause of motor neuron deterioration in amyotrophic lateral sclerosis (ALS). In this study, we implemented a high-content, genome-wide RNAi screen to identify pathways controlling TDP-43 nucleocytoplasmic shuttling. We identified ∼60 genes whose silencing increased the cytosolic localization of TDP-43, including nuclear pore complex components and regulators of G2/M cell cycle transition. In addition, we identified the type 1 inositol-1,4,5-trisphosphate (IP3) receptor (ITPR1), an IP3-gated, endoplasmic reticulum (ER)-resident Ca(2+) channel, as a strong modulator of TDP-43 nucleocytoplasmic shuttling. Knockdown or chemical inhibition of ITPR1 induced TDP-43 nuclear export in immortalized cells and primary neurons and strongly potentiated the recruitment of TDP-43 to Ubiquilin-positive autophagosomes, suggesting that diminished ITPR1 function leads to autophagosomal clearance of TDP-43. The functional significance of the TDP-43-ITPR1 genetic interaction was tested in Drosophila, where mutant alleles of ITPR1 were found to significantly extended lifespan and mobility of flies expressing TDP-43 under a motor neuron driver. These combined findings implicate IP3-gated Ca(2+) as a key regulator of TDP-43 nucleoplasmic shuttling and proteostasis and suggest pharmacologic inhibition of ITPR1 as a strategy to combat TDP-43-induced neurodegeneration in vivo.