Impaired locomotion and dopamine signaling in retinoid receptor mutant mice

Retinoids Molecular Probes by Late-stage Azide Insertion - Functional Tools to Decrypt Retinoid Metabolism

Studying the complex and intricate retinoids metabolic pathways by chemical biology approaches requires design and synthesis of biologically functional molecular probes. Only few of such molecular retinoid probes could be found in literature, most of them bearing a molecular structure quite different from natural retinoids. To provide close-to-native retinoid probes, we have developed a versatile late-stage method for the insertion of azide function at the C4 position of several retinoids. This one-step process opens straightforward access to different retinoid and carotenoid probes from commercially available precursors. We have further demonstrated that the different molecular probes retain ability of the original compound to activate genes' transcription, despite azide insertion, highlighting biological activities that were further validated in zebrafish in vivo model. The present work paves the way to future studies on vitamin A's metabolism.

Case Report: A Case of a Patient with Smith-Magenis Syndrome and Early-Onset Parkinson's Disease

Smith-Magenis Syndrome (SMS) is a rare genetic disorder, characterized by intellectual disability (ID), behavioral impairments, and sleep disturbances, as well as multiple organ anomalies in some affected individuals. The syndrome is caused by a deletion in the chromosome band around 17p11.2, including the Retinoic Acid Induced 1 (RAI1) gene, a multifaceted transcriptional regulator that modulates the expression of genes involved in cellular proliferation and neurodevelopment. This gene has a positive role in regulating BDNF and, importantly, affects several cell mechanisms and pathways such as the nigro-striatal pathway, which is crucial for motor function. Parkinson's disease (PD) is one of the most common neurodegenerative diseases in older populations. It is characterized by various physical symptoms including tremors, loss of balance, bradykinesia, and a stooping posture. We present a case study of a patient diagnosed with both SMS and early-onset PD (at the age of 49). The association between both conditions is as yet ambiguous. Genome-wide association studies (GWAS) implicate an association between the RAI1 gene and PD. Similarly, the co-existence of both SMS and PD in the patient suggests a possible association between RAI1 copy number variations (CNVs) and PD, further indicating that RAI1 has strong implications for PD pathogenesis. Our results suggest that RAI1 CNVs and the pathophysiology of PD may be related, underscoring the need for further research in this field. Therefore, caregivers of SMS patients should pay careful attention to the possibility of their patients developing EOPD and should consider starting treatment for PD as soon as the first symptoms appear.

Analysis of alcohol-metabolizing enzymes genetic variants and RAR/RXR expression in patients diagnosed with fetal alcohol syndrome: a case-control study

Understanding the mechanisms underlying alcohol metabolism and its regulation, including the effect of polymorphisms in alcohol-metabolizing enzymes, is crucial for research on Fetal Alcohol Spectrum Disorders. The aim of this study was to identify specific single nucleotide polymorphisms in key alcohol-metabolizing enzymes in a cohort of 71 children, including children with fetal alcohol syndrome, children prenatally exposed to ethanol but without fetal alcohol spectrum disorder, and controls. We hypothesized that certain genetic variants related to alcohol metabolism may be fixed in these populations, giving them a particular alcohol metabolism profile. In addition, the difference in certain isoforms of these enzymes determines their affinity for alcohol, which also affects the metabolism of retinoic acid, which is key to the proper development of the central nervous system. Our results showed that children prenatally exposed to ethanol without fetal alcohol spectrum disorder traits had a higher frequency of the ADH1B*3 and ADH1C*1 alleles, which are associated with increased alcohol metabolism and therefore a protective factor against circulating alcohol in the fetus after maternal drinking, compared to FAS children who had an allele with a lower affinity for alcohol. This study also revealed the presence of an ADH4 variant in the FAS population that binds weakly to the teratogen, allowing increased circulation of the toxic agent and direct induction of developmental abnormalities in the fetus. However, both groups showed dysregulation in the expression of genes related to the retinoic acid pathway, such as retinoic acid receptor and retinoid X receptor, which are involved in the development, regeneration, and maintenance of the nervous system. These findings highlight the importance of understanding the interplay between alcohol metabolism, the retinoic acid pathway and genetic factors in the development of fetal alcohol syndrome.

Defining a vitamin A5/X specific deficiency - vitamin A5/X as a critical dietary factor for mental health

A healthy and balanced diet is an important factor to assure a good functioning of the central and peripheral nervous system. Retinoid X receptor (RXR)-mediated signaling was identified as an important mechanism of transmitting major diet-dependent physiological and nutritional signaling such as the control of myelination and dopamine signalling. Recently, vitamin A5/X, mainly present in vegetables as provitamin A5/X, was identified as a new concept of a vitamin which functions as the nutritional precursor for enabling RXR-mediated signaling. The active form of vitamin A5/X, 9-cis-13,14-dehydroretinoic acid (9CDHRA), induces RXR-activation, thereby acting as the central switch for enabling various heterodimer-RXR-signaling cascades involving various partner heterodimers like the fatty acid and eicosanoid receptors/peroxisome proliferator-activated receptors (PPARs), the cholesterol receptors/liver X receptors (LXRs), the vitamin D receptor (VDR), and the vitamin A(1) receptors/retinoic acid receptors (RARs). Thus, nutritional supply of vitamin A5/X might be a general nutritional-dependent switch for enabling this large cascade of hormonal signaling pathways and thus appears important to guarantee an overall organism homeostasis. RXR-mediated signaling was shown to be dependent on vitamin A5/X with direct effects for beneficial physiological and neuro-protective functions mediated systemically or directly in the brain. In summary, through control of dopamine signaling, amyloid β-clearance, neuro-protection and neuro-inflammation, the vitamin A5/X - RXR - RAR - vitamin A(1)-signaling might be "one of" or even "the" critical factor(s) necessary for good mental health, healthy brain aging, as well as for preventing drug addiction and prevention of a large array of nervous system diseases. Likewise, vitamin A5/X - RXR - non-RAR-dependent signaling relevant for myelination/re-myelination and phagocytosis/brain cleanup will contribute to such regulations too. In this review we discuss the basic scientific background, logical connections and nutritional/pharmacological expert recommendations for the nervous system especially considering the ageing brain.

Human nutritional relevance and suggested nutritional guidelines for vitamin A5/X and provitamin A5/X

In the last century, vitamin A was identified that included the nutritional relevant vitamin A1 / provitamin A1, as well as the vitamin A2 pathway concept. Globally, nutritional guidelines have focused on vitamin A1 with simplified recommendations and calculations based solely on vitamin A. The vitamin A / provitamin A terminology described vitamin A with respect to acting as a precursor of 11-cis-retinal, the chromophore of the visual pigment, as well as retinoic acid(s), being ligand(s) of the nuclear hormone receptors retinoic acid receptors (RARs) α, β and γ. All-trans-retinoic acid was conclusively shown to be the endogenous RAR ligand, while the concept of its isomer 9-cis-retinoic acid, being "the" endogenous ligand of the retinoid-X receptors (RXRs), remained inconclusive. Recently, 9-cis-13,14-dihydroretinoic acid was conclusively reported as an endogenous RXR ligand, and a direct nutritional precursor was postulated in 2018 and further confirmed by Rühl, Krezel and de Lera in 2021. This was further termed vitamin A5/X / provitamin A5/X. In this review, a new vitamin A5/X / provitamin A5/X concept is conceptualized in parallel to the vitamin A(1) / provitamin A(1) concept for daily dietary intake and towards dietary guidelines, with a focus on the existing national and international regulations for the physiological and nutritional relevance of vitamin A5/X. The aim of this review is to summarize available evidence and to emphasize gaps of knowledge regarding vitamin A5/X, based on new and older studies and proposed future directions as well as to stimulate and propose adapted nutritional regulations.

Impact of dietary vitamin A on striatal function in adult rats

The striatum is a brain structure involved in the control of voluntary movement. Striatum contains high amounts of retinoic acid, the active metabolite of vitamin A, as well as retinoid receptors, RARβ and RXRγ. Previous studies revealed that disruption of retinoid signaling initiated during development is deleterious for striatal physiology and related motor functions. However, the alteration of retinoid signaling, and the importance of vitamin A supply during adulthood on striatal physiology and function has never been established. In the present study, we investigated the impact of vitamin A supply on striatal function. Adult Sprague-Dawley rats were fed with three specific diets, either sub-deficient, sufficient, or enriched in vitamin A (0.4, 5, and 20 international units [IU] of retinol per g of diet, respectively) for 6 months. We first validated that vitamin A sub-deficient diet in adult rats constitutes a physiological model of retinoid signaling reduction in the striatum. We then revealed subtle alterations of fine motor skills in sub-deficient rats using a new behavioral apparatus specifically designed to test forepaw reach-and-grasp skills relying on striatal function. Finally, we showed using qPCR analysis and immunofluorescence that the striatal dopaminergic system per se was not affected by vitamin A sub-deficiency at adult age. Rather, cholinergic synthesis in the striatum and μ-opioid receptor expression in striosomes sub-territories were the most affected by vitamin A sub-deficiency starting at adulthood. Taken together these results revealed that retinoid signaling alteration at adulthood is associated with motor learning deficits together with discrete neurobiological alterations in the striatum.

Blood transcriptomic signatures associated with molecular changes in the brain and clinical outcomes in Parkinson's disease

The ability to use blood to predict the outcomes of Parkinson's disease, including disease progression and cognitive and motor complications, would be of significant clinical value. We undertook bulk RNA sequencing from the caudate and putamen of postmortem Parkinson's disease (n = 35) and control (n = 40) striatum, and compared molecular profiles with clinical features and bulk RNA sequencing data obtained from antemortem peripheral blood. Cognitive and motor complications of Parkinson's disease were associated with molecular changes in the caudate (stress response) and putamen (endothelial pathways) respectively. Later and earlier-onset Parkinson's disease were molecularly distinct, and disease duration was associated with changes in caudate (oligodendrocyte development) and putamen (cellular senescence), respectively. Transcriptome patterns in the postmortem Parkinson's disease brain were also evident in antemortem peripheral blood, and correlated with clinical features of the disease. Together, these findings identify molecular signatures in Parkinson's disease patients' brain and blood of potential pathophysiologic and prognostic importance.

Retinoic Acid Prevents α-Synuclein Preformed Fibrils-Induced Toxicity via Inhibiting STAT1-PARP1 Signaling

Parkinson's disease (PD), the second-most prevalent neurodegenerative disorder, is characterized by the aberrant deposition of α-synuclein (α-Syn) aggregation in neurons. Recent reports have shown that retinoic acid (RA) ameliorates motor deficits. However, the underlying molecular mechanisms remain unclear. In this article, we investigated the effects of RA on cellular and animal models of PD. We found that RA is beneficial for neuronal survival in PD-associated models. In α-Syn preformed fibrils-treated mice, RA administration relieved the formation of intracellular inclusions, dopaminergic neuronal loss, and behavioral deficits. α-Syn preformed fibrils-treated SH-SY5Y cells manifested decreased cell viability, apoptosis, α-Syn aggregation, and autophagy defects. All these negative phenomena were alleviated by RA. More importantly, RA could inhibit the neurotoxicity via inhibiting α-Syn preformed fibrils-induced STAT1-PARP1 signaling, which could also be antagonized by IFN-γ. In conclusion, RA could hinder α-Syn preformed fibrils-induced toxicity by inhibiting STAT1-PARP1 signaling. Thus, we present new insight into RA in PD management.

Transcriptional control of nucleus accumbens neuronal excitability by retinoid X receptor alpha tunes sensitivity to drug rewards

The complex nature of the transcriptional networks underlying addictive behaviors suggests intricate cooperation between diverse gene regulation mechanisms that go beyond canonical activity-dependent pathways. Here, we implicate in this process a nuclear receptor transcription factor, retinoid X receptor alpha (RXRα), which we initially identified bioinformatically as associated with addiction-like behaviors. In the nucleus accumbens (NAc) of male and female mice, we show that although its own expression remains unaltered after cocaine exposure, RXRα controls plasticity- and addiction-relevant transcriptional programs in both dopamine receptor D1- and D2-expressing medium spiny neurons, which in turn modulate intrinsic excitability and synaptic activity of these NAc cell types. Behaviorally, bidirectional viral and pharmacological manipulation of RXRα regulates drug reward sensitivity in both non-operant and operant paradigms. Together, this study demonstrates a key role for NAc RXRα in promoting drug addiction and paves the way for future studies of rexinoid signaling in psychiatric disease states.

Rapid effects of valproic acid on the fetal brain transcriptome: Implications for brain development and autism

There is an increased incidence of autism among the children of women who take the anti-epileptic, mood stabilizing drug, valproic acid (VPA) during pregnancy; moreover, exposure to VPA in utero causes autistic-like symptoms in rodents and non-human primates. Analysis of RNAseq data obtained from fetal mouse brains 3 hr after VPA administration revealed that VPA significantly [p(FDR) ≤ 0.025] increased or decreased the expression of approximately 7,300 genes. No significant sex differences in VPA-induced gene expression were observed. Expression of genes associated with neurodevelopmental disorders such as autism as well as neurogenesis, axon growth and synaptogenesis, GABAergic, glutaminergic and dopaminergic synaptic transmission, perineuronal nets, and circadian rhythms was dysregulated by VPA. Moreover, expression of 400 autism risk genes was significantly altered by VPA as was expression of 247 genes that have been reported to play fundamental roles in the development of the nervous system, but are not linked to autism by GWAS. The goal of this study was to identify mouse genes that are: (a) significantly up- or down-regulated by VPA in the fetal brain and (b) known to be associated with autism and/or to play a role in embryonic neurodevelopmental processes, perturbation of which has the potential to alter brain connectivity in the postnatal and adult brain. The set of genes meeting these criteria provides potential targets for future hypothesis-driven approaches to elucidating the proximal underlying causes of defective brain connectivity in neurodevelopmental disorders such as autism.

Preventive Vitamin A Supplementation Improves Striatal Function in 6-Hydroxydopamine Hemiparkinsonian Rats

Background

The mechanisms leading to a loss of dopaminergic (DA) neurons from the substantia nigra pars compacta (SNc) in Parkinson's disease (PD) have multifactorial origins. In this context, nutrition is currently investigated as a modifiable environmental factor for the prevention of PD. In particular, initial studies revealed the deleterious consequences of vitamin A signaling failure on dopamine-related motor behaviors. However, the potential of vitamin A supplementation itself to prevent neurodegeneration has not been established yet.

Objective

The hypothesis tested in this study is that preventive vitamin A supplementation can protect DA neurons in a rat model of PD.

Methods

The impact of a 5-week preventive supplementation with vitamin A (20 IU/g of diet) was measured on motor and neurobiological alterations induced by 6-hydroxydopamine (6-OHDA) unilateral injections in the striatum of rats. Rotarod, step test and cylinder tests were performed up to 3 weeks after the lesion. Post-mortem analyses (retinol and monoamines dosages, western blots, immunofluorescence) were performed to investigate neurobiological processes.

Results

Vitamin A supplementation improved voluntary movements in the cylinder test. In 6-OHDA lesioned rats, a marked decrease of dopamine levels in striatum homogenates was measured. Tyrosine hydroxylase labeling in the SNc and in the striatum was significantly decreased by 6-OHDA injection, without effect of vitamin A. By contrast, vitamin A supplementation increased striatal expression of D2 and RXR receptors in the striatum of 6-OHDA lesioned rats.

Conclusions

Vitamin A supplementation partially alleviates motor alterations and improved striatal function, revealing a possible beneficial preventive approach for PD.

Aluminum inhibits non-amyloid pathways via retinoic acid receptor

BACKGROUND

Aluminium neurotoxicity has been widely confirmed and mainly manifests as cognitive impairment. Al³⁺ can inhibit the expression of ADAM10, a key enzyme of the nonamyloid pathway, but its mechanism of toxicity has not been fully elucidated. Studies have shown that RARs can regulate ADAM10 expression.

METHODS

We explored whether Al³⁺ affects the expression of ADAM10 through RARs, thereby affecting the nonamyloid pathway.

RESULTS

Al³⁺ reduced the expressions of RARα, RARβ and ADAM10. The expression levels of the RARα, RARβ and ADAM10 proteins were upregulated in the RA group compared with the control group. In the RA + 200 μmol Al(mal)₃ group, the downregulation of RARα, RARβ and ADAM10 was weaker than that of the 200 μmol Al(mal)₃ group, which indicated that RA participated in and upregulated the expression of ADAM10 through RARα and RARβ.

CONCLUSION

Al³⁺ inhibits ADAM10 expression through RARα and RARβ and results in a decrease in the nonamyloid pathway.

Isotretinoin and neuropsychiatric side effects: Continued vigilance is needed

Background

Isotretinoin (13-cis-retinoic acid, marketed under the names Accutane, Roaccutane, and others) is an effective treatment for acne that has been on the market for over 30 years, although reports of neuropsychiatric side effects continue to be reported. Isotretinoin is an isomer of the active form of Vitamin A, 13-trans-retinoic acid, which has known psychiatric side effects when given in excessive doses, and is part of the family of compounds called retinoids, which have multiple functions in the central nervous system.

Methods

The literature was reviewed in pubmed and psychinfo for research related to isotretinoin and neuropsychiatric side effects including depression, suicidal thoughts, suicide, mania, anxiety, impulsivity, emotional lability, violence, aggression, and psychosis.

Results

Multiple case series have shown that successful treatment of acne with isotretinoin results in improvements in measures of quality of life and self esteem However, studies show individual cases of clinically significant depression and other neuropsychiatric events that, although not common, are persistent in the literature. Since the original cases of depression were reported to the United States Food and Drug Administration, numerous cases have been reported to regulatory agencies in the United Kingdom, France, Ireland, Denmark, Australia, Canada, and other countries, making isotretinoin one of the top five medications in the world associated with depression and other neuropsychiatric side effects. Clinicians are advised to warn patients of the risks of neuropsychiatric side effects with isotretinoin which may arise from the medication itself, and not just as a side effect of acne or youth.

Regulation of prefrontal patterning and connectivity by retinoic acid

The prefrontal cortex (PFC) and its connections with the mediodorsal thalamus are crucial for cognitive flexibility and working memory1 and are thought to be altered in disorders such as autism2,3 and schizophrenia4,5. Although developmental mechanisms that govern the regional patterning of the cerebral cortex have been characterized in rodents6-9, the mechanisms that underlie the development of PFC-mediodorsal thalamus connectivity and the lateral expansion of the PFC with a distinct granular layer 4 in primates10,11 remain unknown. Here we report an anterior (frontal) to posterior (temporal), PFC-enriched gradient of retinoic acid, a signalling molecule that regulates neural development and function12-15, and we identify genes that are regulated by retinoic acid in the neocortex of humans and macaques at the early and middle stages of fetal development. We observed several potential sources of retinoic acid, including the expression and cortical expansion of retinoic-acid-synthesizing enzymes specifically in primates as compared to mice. Furthermore, retinoic acid signalling is largely confined to the prospective PFC by CYP26B1, a retinoic-acid-catabolizing enzyme, which is upregulated in the prospective motor cortex. Genetic deletions in mice revealed that retinoic acid signalling through the retinoic acid receptors RXRG and RARB, as well as CYP26B1-dependent catabolism, are involved in proper molecular patterning of prefrontal and motor areas, development of PFC-mediodorsal thalamus connectivity, intra-PFC dendritic spinogenesis and expression of the layer 4 marker RORB. Together, these findings show that retinoic acid signalling has a critical role in the development of the PFC and, potentially, in its evolutionary expansion.

Hominini-specific regulation of CBLN2 increases prefrontal spinogenesis

The similarities and differences between nervous systems of various species result from developmental constraints and specific adaptations1-4. Comparative analyses of the prefrontal cortex (PFC), a cerebral cortex region involved in higher-order cognition and complex social behaviours, have identified true and potential human-specific structural and molecular specializations4-8, such as an exaggerated PFC-enriched anterior-posterior dendritic spine density gradient5. These changes are probably mediated by divergence in spatiotemporal gene regulation9-17, which is particularly prominent in the midfetal human cortex15,18-20. Here we analysed human and macaque transcriptomic data15,20 and identified a transient PFC-enriched and laminar-specific upregulation of cerebellin 2 (CBLN2), a neurexin (NRXN) and glutamate receptor-δ GRID/GluD-associated synaptic organizer21-27, during midfetal development that coincided with the initiation of synaptogenesis. Moreover, we found that species differences in level of expression and laminar distribution of CBLN2 are, at least in part, due to Hominini-specific deletions containing SOX5-binding sites within a retinoic acid-responsive CBLN2 enhancer. In situ genetic humanization of the mouse Cbln2 enhancer drives increased and ectopic laminar Cbln2 expression and promotes PFC dendritic spine formation. These findings suggest a genetic and molecular basis for the anterior-posterior cortical gradient and disproportionate increase in the Hominini PFC of dendritic spines and a developmental mechanism that may link dysfunction of the NRXN-GRID-CBLN2 complex to the pathogenesis of neuropsychiatric disorders.

Mechanistic aspects of carotenoid health benefits - where are we now?

Dietary intake and tissue levels of carotenoids have been associated with a reduced risk of several chronic diseases, including cardiovascular diseases, type 2 diabetes, obesity, brain-related diseases and some types of cancer. However, intervention trials with isolated carotenoid supplements have mostly failed to confirm the postulated health benefits. It has thereby been speculated that dosing, matrix and synergistic effects, as well as underlying health and the individual nutritional status plus genetic background do play a role. It appears that our knowledge on carotenoid-mediated health benefits may still be incomplete, as the underlying mechanisms of action are poorly understood in relation to human relevance. Antioxidant mechanisms - direct or via transcription factors such as NRF2 and NF-κB - and activation of nuclear hormone receptor pathways such as of RAR, RXR or also PPARs, via carotenoid metabolites, are the basic principles which we try to connect with carotenoid-transmitted health benefits as exemplified with described common diseases including obesity/diabetes and cancer. Depending on the targeted diseases, single or multiple mechanisms of actions may play a role. In this review and position paper, we try to highlight our present knowledge on carotenoid metabolism and mechanisms translatable into health benefits related to several chronic diseases.

Retinoid X Receptor α Regulates DHA-Dependent Spinogenesis and Functional Synapse Formation In Vivo

Coordinated intracellular and extracellular signaling is critical to synapse development and functional neural circuit wiring. Here, we report that unesterified docosahexaenoic acid (DHA) regulates functional synapse formation in vivo via retinoid X receptor α (Rxra) signaling. Using Rxra conditional knockout (cKO) mice and virus-mediated transient gene expression, we show that endogenous Rxra plays important roles in regulating spinogenesis and excitatory synaptic transmission in cortical pyramidal neurons. We further show that the effects of RXRA are mediated through its DNA-binding domain in a cell-autonomous and reversible manner. Moreover, unesterified DHA increases spine formation and excitatory synaptic transmission in vivo in an Rxra-dependent fashion. Rxra cKO mice generally behave normally but show deficits in behavior tasks associated with social memory. Together, these results demonstrate that unesterified DHA signals through RXRA to regulate spinogenesis and functional synapse formation, providing insight into the mechanism through which DHA promotes brain development and cognitive function.

Vitamin A5/X, a New Food to Lipid Hormone Concept for a Nutritional Ligand to Control RXR-Mediated Signaling

Vitamin A is a family of derivatives synthesized from carotenoids acquired from the diet and can be converted in animals to bioactive forms essential for life. Vitamin A1 (all-trans-retinol/ATROL) and provitamin A1 (all-trans-β,β-carotene/ATBC) are precursors of all-trans-retinoic acid acting as a ligand for the retinoic acid receptors. The contribution of ATROL and ATBC to formation of 9-cis-13,14-dihydroretinoic acid (9CDHRA), the only endogenous retinoid acting as retinoid X receptor (RXR) ligand, remains unknown. To address this point novel and already known retinoids and carotenoids were stereoselectively synthesized and administered in vitro to oligodendrocyte cell culture and supplemented in vivo (orally) to mice with a following high-performance liquid chromatography-mass spectrometry (HPLC-MS)/UV-Vis based metabolic profiling. In this study, we show that ATROL and ATBC are at best only weak and non-selective precursors of 9CDHRA. Instead, we identify 9-cis-13,14-dihydroretinol (9CDHROL) and 9-cis-13,14-dihydro-β,β-carotene (9CDHBC) as novel direct nutritional precursors of 9CDHRA, which are present endogenously in humans and the human food chain matrix. Furthermore, 9CDHROL displayed RXR-dependent promnemonic activity in working memory test similar to that reported for 9CDHRA. We also propose that the endogenous carotenoid 9-cis-β,β-carotene (9CBC) can act as weak, indirect precursor of 9CDHRA via hydrogenation to 9CDHBC and further metabolism to 9CDHROL and/or 9CDHRA. In summary, since classical vitamin A1 is not an efficient 9CDHRA precursor, we conclude that this group of molecules constitutes a new class of vitamin or a new independent member of the vitamin A family, named “Vitamin A5/X”.

Loss of retinoid X receptor gamma subunit impairs group 1 mGluR mediated electrophysiological responses and group 1 mGluR dependent behaviors

Retinoid X receptors are members of the nuclear receptor family that regulate gene expression in response to retinoic acid and related ligands. Group 1 metabotropic glutamate receptors are G-protein coupled transmembrane receptors that activate intracellular signaling cascades in response to the neurotransmitter, glutamate. These two classes of molecules have been studied independently and found to play important roles in regulating neuronal physiology with potential clinical implications for disorders such as depression, schizophrenia, Parkinson's and Alzheimer's disease. Here we show that mice lacking the retinoid X receptor subunit, RXRγ, exhibit impairments in group 1 mGluR-mediated electrophysiological responses at hippocampal Schaffer collateral-CA1 pyramidal cell synapses, including impaired group 1 mGluR-dependent long-term synaptic depression (LTD), reduced group 1 mGluR-induced calcium release, and loss of group 1 mGluR-activated voltage-sensitive currents. These animals also exhibit impairments in a subset of group 1 mGluR-dependent behaviors, including motor performance, spatial object recognition, and prepulse inhibition. Together, these observations demonstrate convergence between the RXRγ and group 1 mGluR signaling pathways that may function to coordinate their regulation of neuronal activity. They also identify RXRγ as a potential target for the treatment of disorders in which group 1 mGluR signaling has been implicated.

Potential therapeutic uses of rexinoids

The discovery of nuclear receptors, particularly retinoid X receptors (RXR), and their involvement in numerous pathways related to development sparked interest in their immunomodulatory properties. Genetic models using deletion or overexpression of RXR and the subsequent development of several small molecules that are agonists or antagonists of this receptor support a promising therapeutic role for these receptors in immunology. Bexarotene was approved in 1999 for the treatment of cutaneous T cell lymphoma. Several other small molecule RXR agonists have since been synthesized with limited preclinical development, but none have yet achieved FDA approval. Cancer treatment has recently been revolutionized with the introduction of immune checkpoint inhibitors, but their success has been restricted to a minority of patients. This review showcases the emerging immunomodulatory effects of RXR and the potential of small molecules that target this receptor as therapies for cancer and other diseases. Here we describe the essential roles that RXR and partner receptors play in T cells, dendritic cells, macrophages and epithelial cells, especially within the tumor microenvironment. Most of these effects are site and cancer type dependent but skew immune cells toward an anti-inflammatory and anti-tumor effect. This beneficial effect on immune cells supports the promise of combining rexinoids with approved checkpoint blockade therapies in order to enhance efficacy of the latter and to delay or potentially eliminate drug resistance. The data compiled in this review strongly suggest that targeting RXR nuclear receptors is a promising new avenue in immunomodulation for cancer and other chronic inflammatory diseases.

Role and Mechanism of Vitamin A Metabolism in the Pathophysiology of Parkinson's Disease

Evidence shows that altered retinoic acid signaling may contribute to the pathogenesis and pathophysiology of Parkinson's disease (PD). Retinoic acid is the bioactive derivative of the lipophilic vitamin A. Vitamin A is involved in several important homeostatic processes, such as cell differentiation, antioxidant activity, inflammation and neuronal plasticity. The role of vitamin A and its derivatives in the pathogenesis and pathophysiology of neurodegenerative diseases, and their potential as therapeutics, has drawn attention for more than 10 years. However, the literature sits in disparate fields. Vitamin A could act at the crossroad of multiple environmental and genetic factors of PD. The purpose of this review is to outline what is known about the role of vitamin A metabolism in the pathogenesis and pathophysiology of PD. We examine key biological systems and mechanisms that are under the control of vitamin A and its derivatives, which are (or could be) exploited for therapeutic potential in PD: the survival of dopaminergic neurons, oxidative stress, neuroinflammation, circadian rhythms, homeostasis of the enteric nervous system, and hormonal systems. We focus on the pivotal role of ALDH1A1, an enzyme expressed by dopaminergic neurons for the detoxification of these neurons, which is under the control of retinoic acid. By providing an integrated summary, this review will guide future studies on the potential role of vitamin A in the management of symptoms, health and wellbeing for PD patients.

scTenifoldNet: A Machine Learning Workflow for Constructing and Comparing Transcriptome-wide Gene Regulatory Networks from Single-Cell Data

We present scTenifoldNet-a machine learning workflow built upon principal-component regression, low-rank tensor approximation, and manifold alignment-for constructing and comparing single-cell gene regulatory networks (scGRNs) using data from single-cell RNA sequencing. scTenifoldNet reveals regulatory changes in gene expression between samples by comparing the constructed scGRNs. With real data, scTenifoldNet identifies specific gene expression programs associated with different biological processes, providing critical insights into the underlying mechanism of regulatory networks governing cellular transcriptional activities.

Retinoic Acid and the Gut Microbiota in Alzheimer's Disease: Fighting Back-to-Back?

BACKGROUND

There is growing evidence that the gut microbiota may play an important role in neurodegenerative diseases such as Alzheimer's disease. However, how these commensals influence disease risk and progression still has to be deciphered.

OBJECTIVE

The objective of this review was to summarize current knowledge on the interplay between gut microbiota and retinoic acid. The latter one represents one of the important micronutrients, which have been correlated to Alzheimer's disease and are used in initial therapeutic intervention studies.

METHODS

A selective overview of the literature is given with the focus on the function of retinoic acid in the healthy and diseased brain, its metabolism in the gut, and the potential influence that the bioactive ligand may have on microbiota, gut physiology and, Alzheimer's disease.

RESULTS

Retinoic acid can influence neuronal functionality by means of plasticity but also by neurogenesis and modulating proteostasis. Impaired retinoid-signaling, therefore, might contribute to the development of diseases in the brain. Despite its rather direct impact, retinoic acid also influences other organ systems such as gut by regulating the residing immune cells but also factors such as permeability or commensal microbiota. These in turn can also interfere with retinoid-metabolism and via the gutbrain- axis furthermore with Alzheimer's disease pathology within the brain.

CONCLUSION

Potentially, it is yet too early to conclude from the few reports on changed microbiota in Alzheimer's disease to a dysfunctional role in retinoid-signaling. However, there are several routes how microbial commensals might affect and might be affected by vitamin A and its derivatives.

Retinoids and developmental neurotoxicity: Utilizing toxicogenomics to enhance adverse outcome pathways and testing strategies

The use of genomic approaches in toxicological studies has greatly increased our ability to define the molecular profiles of environmental chemicals associated with developmental neurotoxicity (DNT). Integration of these approaches with adverse outcome pathways (AOPs), a framework that translates environmental exposures to adverse developmental phenotypes, can potentially inform DNT testing strategies. Here, using retinoic acid (RA) as a case example, we demonstrate that the integration of toxicogenomic profiles into the AOP framework can be used to establish a paradigm for chemical testing. RA is a critical regulatory signaling molecule involved in multiple aspects of mammalian central nervous system (CNS) development, including hindbrain formation/patterning and neuronal differentiation, and imbalances in RA signaling pathways are linked with DNT. While the mechanisms remain unresolved, environmental chemicals can cause DNT by disrupting the RA signaling pathway. First, we reviewed literature evidence of RA and other retinoid exposures and DNT to define a provisional AOP related to imbalances in RA embryonic bioavailability and hindbrain development. Next, by integrating toxicogenomic datasets, we defined a relevant transcriptomic signature associated with RA-induced developmental neurotoxicity (RA-DNT) in human and rodent models that was tested against zebrafish model data, demonstrating potential for integration into an AOP framework. Finally, we demonstrated how these approaches may be systematically utilized to identify chemical hazards by testing the RA-DNT signature against azoles, a proposed class of compounds that alters RA-signaling. The provisional AOP from this study can be expanded in the future to better define DNT biomarkers relevant to RA signaling and toxicity.

The role of the retinoids in schizophrenia: genomic and clinical perspectives

Signalling by retinoid compounds is vital for embryonic development, with particular importance for neurogenesis in the human brain. Retinoids, metabolites of vitamin A, exert influence over the expression of thousands of transcripts genome wide, and thus, act as master regulators of many important biological processes. A significant body of evidence in the literature now supports dysregulation of the retinoid system as being involved in the aetiology of schizophrenia. This includes mechanistic insights from large-scale genomic, transcriptomic and, proteomic studies, which implicate disruption of disparate aspects of retinoid biology such as transport, metabolism, and signalling. As a result, retinoids may present a valuable clinical opportunity in schizophrenia via novel pharmacotherapies and dietary intervention. Further work, however, is required to expand on the largely observational data collected thus far and confirm causality. This review will highlight the fundamentals of retinoid biology and examine the evidence for retinoid dysregulation in schizophrenia.

Manipulation of retinoic acid signaling in the nucleus accumbens shell alters rat emotional behavior

Novel targets for depression and anxiety disorders are necessary for the development of more effective pharmacotherapeutics. Our previous study found that the retinoic acid (RA) signaling pathway is the signaling pathway most enhanced in the nucleus accumbens (NAc) shell, a region important for depression, anxiety, and addiction. Genetic manipulations of RA signaling in the NAc affecting addiction-related behavior prompted our study of the role of retinoic acid signaling in depression-related and anxiety-related behavior using in vivo RNA interference. Knockdown of the retinoic acid degradation enzyme cytochrome p450 family 26 subfamily b member 1 (Cyp26b1) in the nucleus accumbens shell increased depression-related behavior while decreasing anxiety-like behavior. Knockdown of the retinoic acid binding protein, cellular RA binding protein 2 (Crabp2), also increased depression-related behavior. Knockdown of another RA binding partner fatty acid binding protein 5 (Fabp5), did not alter these behaviors. These results further support the contention that RA signaling in the NAc shell can affect emotional behavior and that targeting some components of this pathway could be a promising avenue for developing novel treatments for depression and anxiety.

Genetics and functions of the retinoic acid pathway, with special emphasis on the eye

Retinoic acid (RA) is a potent morphogen required for embryonic development. RA is formed in a multistep process from vitamin A (retinol); RA acts in a paracrine fashion to shape the developing eye and is essential for normal optic vesicle and anterior segment formation. Perturbation in RA-signaling can result in severe ocular developmental diseases—including microphthalmia, anophthalmia, and coloboma. RA-signaling is also essential for embryonic development and life, as indicated by the significant consequences of mutations in genes involved in RA-signaling. The requirement of RA-signaling for normal development is further supported by the manifestation of severe pathologies in animal models of RA deficiency—such as ventral lens rotation, failure of optic cup formation, and embryonic and postnatal lethality. In this review, we summarize RA-signaling, recent advances in our understanding of this pathway in eye development, and the requirement of RA-signaling for embryonic development (e.g., organogenesis and limb bud development) and life.

Selection at behavioural, developmental and metabolic genes is associated with the northward expansion of a successful tropical colonizer

What makes a species able to colonize novel environments? This question is key to understand the dynamics of adaptive radiations and ecological niche shifts, but the mechanisms that underlie expansion into novel habitats remain poorly understood at a genomic scale. Lizards from the genus Anolis are typically tropical, and the green anole (Anolis carolinensis) constitutes an exception since it expanded into temperate North America from subtropical Florida. Thus, we used the green anole as a model to investigate signatures of selection associated with colonization of a new environment, namely temperate North America. To this end, we analysed 29 whole-genome sequences, covering the entire native range of the species. We used a combination of recent methods to quantify both positive and balancing selection in northern populations, including F_ST outlier methods, machine learning and ancestral recombination graphs. We naively scanned for genes of interest and assessed the overlap between multiple tests. Strikingly, we identified many genes involved in behaviour, suggesting that the recent successful colonization of northern environments may have been linked to behavioural shifts as well as physiological adaptation. Using a candidate genes strategy, we determined that genes involved in response to cold or behaviour displayed more frequently signals of selection, while controlling for local recombination rate, gene clustering and gene length. In addition, we found signatures of balancing selection at immune genes in all investigated genetic groups, but also at genes involved in neuronal and anatomical development.

Retinoic acid signaling pathways

Retinoic acid (RA), a metabolite of retinol (vitamin A), functions as a ligand for nuclear RA receptors (RARs) that regulate development of chordate animals. RA-RARs can activate or repress transcription of key developmental genes. Genetic studies in mouse and zebrafish embryos that are deficient in RA-generating enzymes or RARs have been instrumental in identifying RA functions, revealing that RA signaling regulates development of many organs and tissues, including the body axis, spinal cord, forelimbs, heart, eye and reproductive tract. An understanding of the normal functions of RA signaling during development will guide efforts for use of RA as a therapeutic agent to improve human health. Here, we provide an overview of RA signaling and highlight its key functions during development.

Implications of de novo mutations in guiding drug discovery: A study of four neuropsychiatric disorders

Recent studies have suggested an important role of de novo mutations (DNMs) in neuropsychiatric disorders. As DNMs are not subject to elimination due to evolutionary pressure, they are likely to have greater disruptions on biological functions. While a number of sequencing studies have been performed on neuropsychiatric disorders, the implications of DNMs for drug discovery remain to be explored. In this study, we employed a gene-set analysis approach to address this issue. Four neuropsychiatric disorders were studied, including schizophrenia (SCZ), autistic spectrum disorders (ASD), intellectual disability (ID) and epilepsy. We first identified gene-sets associated with different drugs, and analyzed whether the gene-set pertaining to each drug overlaps with DNMs more than expected by chance. We also assessed which medication classes are enriched among the prioritized drugs. We discovered that neuropsychiatric drug classes were indeed significantly enriched for DNMs of all four disorders; in particular, antipsychotics and antiepileptics were the most strongly enriched drug classes for SCZ and epilepsy respectively. Interestingly, we revealed enrichment of several unexpected drug classes, such as lipid-lowering agents for SCZ and anti-neoplastic agents. By inspecting individual hits, we also uncovered other interesting drug candidates or mechanisms (e.g. histone deacetylase inhibition and retinoid signaling) that might warrant further investigations. Taken together, this study provided evidence for the usefulness of DNMs in guiding drug discovery or repositioning.

Smoking and Parkinson disease: Evidence for gene-by-smoking interactions

OBJECTIVE

To investigate whether cigarette smoking interacts with genes involved in individual susceptibility to xenobiotics for the risk of Parkinson disease (PD).

METHODS

Two French population-based case-control studies (513 patients, 1,147 controls) were included as a discovery sample to examine gene-smoking interactions based on 3,179 single nucleotide polymorphisms (SNPs) in 289 genes involved in individual susceptibility to xenobiotics. SNP-by-cigarette smoking interactions were tested in the discovery sample through an empirical Bayes (EB) approach. Nine SNPs were selected for replication in a population-based case-control study from California (410 patients, 845 controls) with standard logistic regression and the EB approach. For SNPs that replicated, we performed pooled analyses including the discovery and replication datasets and computed pooled odds ratios and confidence intervals (CIs) using random-effects meta-analysis.

RESULTS

Nine SNPs interacted with smoking in the discovery dataset and were selected for replication. Interactions of smoking with rs4240705 in the RXRA gene and rs1900586 in the SLC17A6 gene were replicated. In pooled analyses (logistic regression), the interactions between smoking and rs4240705-G and rs1900586-G were 1.66 (95% CI 1.28-2.14, p = 1.1 × 10^-4, p for heterogeneity = 0.366) and 1.61 (95% CI 1.17-2.21, p = 0.003, p for heterogeneity = 0.616), respectively. For both SNPs, while smoking was significantly less frequent in patients than controls in AA homozygotes, this inverse association disappeared in G allele carriers.

CONCLUSIONS

We identified and replicated suggestive gene-by-smoking interactions in PD. The inverse association of smoking with PD was less pronounced in carriers of minor alleles of both RXRA-rs4240705 and SLC17A6-rs1900586. These findings may help identify biological pathways involved in the inverse association between smoking and PD.

N-3 (Omega-3) Fatty Acids: Effects on Brain Dopamine Systems and Potential Role in the Etiology and Treatment of Neuropsychiatric Disorders

BACKGROUND & OBJECTIVE

A number of neuropsychiatric disorders, including Parkinson's disease, schizophrenia, attention deficit hyperactivity disorder, and, to some extent, depression, involve dysregulation of the brain dopamine systems. The etiology of these diseases is multifactorial, involving genetic and environmental factors. Evidence suggests that inadequate levels of n-3 (omega- 3) polyunsaturated fatty acids (PUFA) in the brain may represent a risk factor for these disorders. These fatty acids, which are derived from the diet, are a major component of neuronal membranes and are of particular importance in brain development and function. Low levels of n-3 PUFAs in the brain affect the brain dopamine systems and, when combined with appropriate genetic and other factors, increase the risk of developing these disorders and/or the severity of the disease. This article reviews the neurobiology of n-3 PUFAs and their effects on dopaminergic function.

CONCLUSION

Clinical studies supporting their role in the etiologies of diseases involving the brain dopamine systems and the potential of n-3 PUFAs in the treatment of these disorders are discussed.

Genetic Overlap Between Attention-Deficit/Hyperactivity Disorder and Bipolar Disorder: Evidence From Genome-wide Association Study Meta-analysis

BACKGROUND

Attention-deficit/hyperactivity disorder (ADHD) and bipolar disorder (BPD) are frequently co-occurring and highly heritable mental health conditions. We hypothesized that BPD cases with an early age of onset (≤21 years old) would be particularly likely to show genetic covariation with ADHD.

METHODS

Genome-wide association study data were available for 4609 individuals with ADHD, 9650 individuals with BPD (5167 thereof with early-onset BPD), and 21,363 typically developing controls. We conducted a cross-disorder genome-wide association study meta-analysis to identify whether the observed comorbidity between ADHD and BPD could be due to shared genetic risks.

RESULTS

We found a significant single nucleotide polymorphism-based genetic correlation between ADHD and BPD in the full and age-restricted samples (r_Gfull = .64, p = 3.13 × 10^-14; r_Grestricted = .71, p = 4.09 × 10^-16). The meta-analysis between the full BPD sample identified two genome-wide significant (p_rs7089973 = 2.47 × 10^-8; p_rs11756438 = 4.36 × 10^-8) regions located on chromosomes 6 (CEP85L) and 10 (TAF9BP2). Restricting the analyses to BPD cases with an early onset yielded one genome-wide significant association (p_rs58502974 = 2.11 × 10^-8) on chromosome 5 in the ADCY2 gene. Additional nominally significant regions identified contained known expression quantitative trait loci with putative functional consequences for NT5DC1, NT5DC2, and CACNB3 expression, whereas functional predictions implicated ABLIM1 as an allele-specific expressed gene in neuronal tissue.

CONCLUSIONS

The single nucleotide polymorphism-based genetic correlation between ADHD and BPD is substantial, significant, and consistent with the existence of genetic overlap between ADHD and BPD, with potential differential genetic mechanisms involved in early and later BPD onset.

Roles of Retinoic Acid Signaling in Shaping the Neuronal Architecture of the Developing Amphioxus Nervous System

The morphogen retinoic acid (RA) patterns vertebrate nervous systems and drives neurogenesis, but how these functions evolved remains elusive. Here, we show that RA signaling plays stage- and tissue-specific roles during the formation of neural cell populations with serotonin, dopamine, and GABA neurotransmitter phenotypes in amphioxus, a proxy for the ancestral chordate. Our data suggest that RA signaling restricts the specification of dopamine-containing cells in the ectoderm and of GABA neurons in the neural tube, probably by regulating Hox1 and Hox3 gene expression, respectively. The two Hox genes thus appear to serve distinct functions rather than to participate in a combinatorial Hox code. We were further able to correlate the RA signaling-dependent mispatterning of hindbrain GABA neurons with concomitant motor impairments. Taken together, these data provide new insights into how RA signaling and Hox genes contribute to nervous system as well as to motor control development in amphioxus and hence shed light on the evolution of these functions within vertebrates.

Transcriptomic Analysis Shows Decreased Cortical Expression of NR4A1, NR4A2 and RXRB in Schizophrenia and Provides Evidence for Nuclear Receptor Dysregulation

Many genes are differentially expressed in the cortex of people with schizophrenia, implicating factors that control transcription more generally. Hormone nuclear receptors dimerize to coordinate context-dependent changes in gene expression. We hypothesized that members of two families of nuclear receptors (NR4As), and retinoid receptors (RARs and RXRs), are altered in the dorsal lateral prefrontal cortex (DLPFC) of people with schizophrenia. We used next generation sequencing and then qPCR analysis to test for changes in mRNA levels for transcripts encoding nuclear receptors: orphan nuclear receptors (3 in the NR4A, 3 in the RAR, 3 in the RXR families and KLF4) in total RNA extracted from the DLPFC from people with schizophrenia compared to controls (n = 74). We also correlated mRNA levels with demographic factors and with estimates of antipsychotic drug exposure (schizophrenia group only). We tested for correlations between levels of transcription factor family members and levels of genes putatively regulated by these transcription factors. We found significantly down regulated expression of NR4A1 (Nurr 77) and KLF4 mRNAs in people with schizophrenia compared to controls, by both NGS and qPCR (p = or <0.01). We also detected decreases in NR4A2 (Nurr1) and RXRB mRNAs by using qPCR in the larger cohort (p<0.05 and p<0.01, respectively). We detected decreased expression of RARG and NR4A2 mRNAs in females with schizophrenia (p<0.05). The mRNA levels of NR4A1, NR4A2 and NR4A3 were all negative correlated with lifetime estimates of antipsychotic exposure. These novel findings, which may be influenced by antipsychotic drug exposure, implicate the orphan and retinoid nuclear receptors in the cortical pathology found in schizophrenia. Genes down stream of these receptors can be dysregulated as well, but the direction of change is not immediately predictable based on the putative transcription factor changes.

New Insights Into the Roles of Retinoic Acid Signaling in Nervous System Development and the Establishment of Neurotransmitter Systems

Secreted chiefly from the underlying mesoderm, the morphogen retinoic acid (RA) is well known to contribute to the specification, patterning, and differentiation of neural progenitors in the developing vertebrate nervous system. Furthermore, RA influences the subtype identity and neurotransmitter phenotype of subsets of maturing neurons, although relatively little is known about how these functions are mediated. This review provides a comprehensive overview of the roles played by RA signaling during the formation of the central and peripheral nervous systems of vertebrates and highlights its effects on the differentiation of several neurotransmitter systems. In addition, the evolutionary history of the RA signaling system is discussed, revealing both conserved properties and alternate modes of RA action. It is proposed that comparative approaches should be employed systematically to expand our knowledge of the context-dependent cellular mechanisms controlled by the multifunctional signaling molecule RA.

Cerebellum Transcriptome of Mice Bred for High Voluntary Activity Offers Insights into Locomotor Control and Reward-Dependent Behaviors

The role of the cerebellum in motivation and addictive behaviors is less understood than that in control and coordination of movements. High running can be a self-rewarding behavior exhibiting addictive properties. Changes in the cerebellum transcriptional networks of mice from a line selectively bred for High voluntary running (H) were profiled relative to an unselected Control (C) line. The environmental modulation of these changes was assessed both in activity environments corresponding to 7 days of Free (F) access to running wheel and to Blocked (B) access on day 7. Overall, 457 genes exhibited a significant (FDR-adjusted P-value < 0.05) genotype-by-environment interaction effect, indicating that activity genotype differences in gene expression depend on environmental access to running. Among these genes, network analysis highlighted 6 genes (Nrgn, Drd2, Rxrg, Gda, Adora2a, and Rab40b) connected by their products that displayed opposite expression patterns in the activity genotype contrast within the B and F environments. The comparison of network expression topologies suggests that selection for high voluntary running is linked to a predominant dysregulation of hub genes in the F environment that enables running whereas a dysregulation of ancillary genes is favored in the B environment that blocks running. Genes associated with locomotor regulation, signaling pathways, reward-processing, goal-focused, and reward-dependent behaviors exhibited significant genotype-by-environment interaction (e.g. Pak6, Adora2a, Drd2, and Arhgap8). Neuropeptide genes including Adcyap1, Cck, Sst, Vgf, Npy, Nts, Penk, and Tac2 and related receptor genes also exhibited significant genotype-by-environment interaction. The majority of the 183 differentially expressed genes between activity genotypes (e.g. Drd1) were under-expressed in C relative to H genotypes and were also under-expressed in B relative to F environments. Our findings indicate that the high voluntary running mouse line studied is a helpful model for understanding the molecular mechanisms in the cerebellum that influence locomotor control and reward-dependent behaviors.

Transcriptomics of Environmental Enrichment Reveals a Role for Retinoic Acid Signaling in Addiction

There exists much variability in susceptibility/resilience to addiction in humans. The environmental enrichment paradigm is a rat model of resilience to addiction-like behavior, and understanding the molecular mechanisms underlying this protective phenotype may lead to novel targets for pharmacotherapeutics to treat cocaine addiction. We investigated the differential regulation of transcript levels using RNA sequencing of the rat nucleus accumbens after environmental enrichment/isolation and cocaine/saline self-administration. Ingenuity Pathways Analysis and Gene Set Enrichment Analysis of 14,309 transcripts demonstrated that many biofunctions and pathways were differentially regulated. New functional pathways were also identified for cocaine modulation (e.g., Rho GTPase signaling) and environmental enrichment (e.g., signaling of EIF2, mTOR, ephrin). However, one novel pathway stood out above the others, the retinoic acid (RA) signaling pathway. The RA signaling pathway was identified as one likely mediator of the protective enrichment addiction phenotype, an interesting result given that nine RA signaling-related genes are expressed selectively and at high levels in the nucleus accumbens shell (NAcSh). Subsequent knockdown of Cyp26b1 (an RA degradation enzyme) in the NAcSh of rats confirmed this role by increasing cocaine self-administration as well as cocaine seeking. These results provide a comprehensive account of enrichment effects on the transcriptome and identify RA signaling as a contributing factor for cocaine addiction.

From molecules to behavior: An integrative theory of autism spectrum disorder

Autism spectrum disorder (ASD) comprises a group of neurodevelopmental disorders for which various theories have been proposed. Each theory brings valuable insights and has experimental evidence backing it, yet none provides an overarching explanation for each of the pathological aspects involved in ASD. Here we present an integrative theory of ASD, centered on a sequence of events spanning from the molecular to the behavioral level. We propose that an abnormality in the interplay between retinoic acid and sex hormones predisposes an individual to specific molecular malfunctions. In turn, this molecular syndrome generates an altered brain connectivity between the cerebellum, the midbrain dopaminergic areas, and the prefrontal cortex. Lastly, this disconnection would generate specific behavioral traits traditionally involved in ASD. Therefore, this paper represents a step forward in unifying different levels of pathological features into novel integrated testable hypotheses.

Incidence of Depression Related to Isotretinoin Treatment in 100 ACNE Vulgaris Patients

The incidence of depression in acne patients using isotretinoin was assessed in 100 patients with moderate and nodulocystic acne. All patients received 0.75–1.00 mg/kg/day of isotretinoin for 20–28 weeks after acne was assessed. All patients' acne lesions were improved at the end of the treatment period. Psychological state was evaluated at baseline, at Month 3, and Month 6 by a psychiatrist using a Turkish version of the Hamilton Depression Rating Scale. Only one patient's score increased to the clinical level of depression at Month 3 of treatment and declined to subclinical levels at Month 6. Although Hamilton scores increased at Month 3 over baseline scores, except for one patient, others' scores remained below the subclinical level for depression. At the end of Month 6, the mean score decreased below that at Month 3. These changes in means might be related to the onset of clinical effect of isotretinoin.

Genome-wide Analysis of RARβ Transcriptional Targets in Mouse Striatum Links Retinoic Acid Signaling with Huntington's Disease and Other Neurodegenerative Disorders

Retinoic acid (RA) signaling through retinoic acid receptors (RARs), known for its multiple developmental functions, emerged more recently as an important regulator of adult brain physiology. How RAR-mediated regulation is achieved is poorly known, partly due to the paucity of information on critical target genes in the brain. Also, it is not clear how reduced RA signaling may contribute to pathophysiology of diverse neuropsychiatric disorders. We report the first genome-wide analysis of RAR transcriptional targets in the brain. Using chromatin immunoprecipitation followed by high-throughput sequencing and transcriptomic analysis of RARβ-null mutant mice, we identified genomic targets of RARβ in the striatum. Characterization of RARβ transcriptional targets in the mouse striatum points to mechanisms through which RAR may control brain functions and display neuroprotective activity. Namely, our data indicate with statistical significance (FDR 0.1) a strong contribution of RARβ in controlling neurotransmission, energy metabolism, and transcription, with a particular involvement of G-protein coupled receptor (p = 5.0e^-5), cAMP (p = 4.5e^-4), and calcium signaling (p = 3.4e^-3). Many identified RARβ target genes related to these pathways have been implicated in Alzheimer's, Parkinson's, and Huntington's disease (HD), raising the possibility that compromised RA signaling in the striatum may be a mechanistic link explaining the similar affective and cognitive symptoms in these diseases. The RARβ transcriptional targets were particularly enriched for transcripts affected in HD. Using the R6/2 transgenic mouse model of HD, we show that partial sequestration of RARβ in huntingtin protein aggregates may account for reduced RA signaling reported in HD.

Fragile X Mental Retardation Protein (FMRP) controls diacylglycerol kinase activity in neurons

Fragile X syndrome (FXS) is caused by the absence of the Fragile X Mental Retardation Protein (FMRP) in neurons. In the mouse, the lack of FMRP is associated with an excessive translation of hundreds of neuronal proteins, notably including postsynaptic proteins. This local protein synthesis deregulation is proposed to underlie the observed defects of glutamatergic synapse maturation and function and to affect preferentially the hundreds of mRNA species that were reported to bind to FMRP. How FMRP impacts synaptic protein translation and which mRNAs are most important for the pathology remain unclear. Here we show by cross-linking immunoprecipitation in cortical neurons that FMRP is mostly associated with one unique mRNA: diacylglycerol kinase kappa (Dgkκ), a master regulator that controls the switch between diacylglycerol and phosphatidic acid signaling pathways. The absence of FMRP in neurons abolishes group 1 metabotropic glutamate receptor-dependent DGK activity combined with a loss of Dgkκ expression. The reduction of Dgkκ in neurons is sufficient to cause dendritic spine abnormalities, synaptic plasticity alterations, and behavior disorders similar to those observed in the FXS mouse model. Overexpression of Dgkκ in neurons is able to rescue the dendritic spine defects of the Fragile X Mental Retardation 1 gene KO neurons. Together, these data suggest that Dgkκ deregulation contributes to FXS pathology and support a model where FMRP, by controlling the translation of Dgkκ, indirectly controls synaptic proteins translation and membrane properties by impacting lipid signaling in dendritic spine.

Interstitial 1q23.3q24.1 deletion in a patient with renal malformation, congenital heart disease, and mild intellectual disability

Interstitial deletions including chromosome region 1q23.3q24.1 are rare. Only eight patients with molecularly characterized deletions have been reported to date. Their phenotype included intellectual disability/developmental delay, growth retardation, microcephaly, congenital heart disease, and renal malformations. We report on a female patient with mild developmental delay, congenital heart disease, and bilateral renal hypoplasia in whom an interstitial de novo deletion of approximately 2.7 Mb in 1q23.3q24.1 was detected by array CGH. This is the smallest deletion described in this region so far. Genotype-phenotype comparison with previously published patients allowed us to propose LMX1A and RXRG as potential candidate genes for intellectual disability, PBX1 as a probable candidate gene for renal malformation, and enabled us to narrow down a chromosome region associated with microcephaly. © 2016 Wiley Periodicals, Inc.