Valproic Acid Influences MTNR1A Intracellular Trafficking and Signaling in a β-Arrestin 2-Dependent Manner

Anatomy of hypothalamic and diencephalic nuclei involved in seasonal fertility regulation in ewes

In this study, we describe in detail the anatomy of nuclei involved in seasonal fertility regulation (SFR) in ewes. For this purpose, the intergeniculate leaflet of the visual thalamus, the caudal hypothalamic arcuate nucleus, and suprachiasmatic, paraventricular and supraoptic nuclei of the rostral hypothalamus were morphometrically and qualitatively analyzed in Nissl-stained serial sections, in the three anatomical planes. In addition, data were collected on calcium-binding proteins and cell phenotypes after immunostaining alternate serial sections for calretinin, parvalbumin and calbindin. For a complete neuroanatomical study, glial architecture was assessed by immunostaining and analyzing alternate sections for glial fibrillary acidic protein (GFAP) and ionized calcium-binding adapter molecule 1 (IBA1). The results showed a strong microglial and astroglia reaction around the hypothalamic nuclei of interest and around the whole 3^rd ventricle of the ewe brain. Moreover, we correlated cytoarchitectonic coordinates of panoramic serial sections with their macroscopic localization and extension in midline sagittal-sectioned whole brain to provide guidelines for microdissecting nuclei involved in SFR.

The ubiquitin-specific protease 8 antagonizes melatonin-induced endocytic degradation of MT1 receptor to promote lung adenocarcinoma growth

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Melatonin can induce the downregulation of the MT₁ receptor.

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MT₁ receptor internalization incurred by melatonin follows the canonical endolysosomal pathway.

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The ubiquitin-specific protease 8 antagonizes the endocytic degradation of the MT₁ receptor.

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The suppression of ubiquitin-specific protease 8 potentiates the cancer-inhibitory effects of melatonin in vitro.

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Combination of USP8 inhibition and melatonin treatment effectively deters tumor growth in xenograft mouse models.

Introduction

The human genome encodes two melatonin receptors (MT₁ and MT₂) that relay melatonin signals to cellular interior. Accumulating evidence has linked melatonin to multiple health benefits, among which its anticancer effects have become well-established. However, the implications of its receptors in lung adenocarcinoma have so far remained incompletely understood.

Objectives

This study aims to investigate the response of the MT₁ receptor to melatonin treatment and its dynamic regulation by ubiquitin-specific protease 8 (USP8) in lung adenocarcinoma.

Methods

The mRNA levels of MT₁ and MT₂ receptors were analyzed with sequencing data. The expression and localization of the MT₁ receptor with melatonin treatment were investigated by immunoblotting, immunofluorescence and confocal microscopy assays. Endocytic deubiquitylases were screened to identify MT₁ association. The effects of USP8 were assessed with shRNA-mediated knockdown and small molecule inhibitor. The combined efficacy of melatonin and USP8 suppression was also evaluated using xenograft animal models.

Results

Bioinformatic analysis revealed increased expression of the MT₁ receptor in lung adenocarcinoma tissues. Melatonin treatment leads to the downregulation of the MT₁ receptor in lung adenocarcinoma cells, which is attributed to receptor endocytosis and lysosomal degradation via the canonical endo-lysosomal route. USP8 negatively regulates the endocytic degradation of the MT₁ receptor incurred by melatonin exposure and thus protects lung adenocarcinoma cell growth. USP8 suppression by knockdown or pharmacological inhibition effectively deters cancer cell proliferation and sensitizes lung adenocarcinoma cells to melatonin in vitro. Furthermore, USP8 silencing significantly potentiates the anticancer effects of melatonin in xenograft tumor models.

Conclusion

The MT₁ receptor responds to melatonin treatment and is endocytosed for lysosomal degradation that is counteracted by USP8. The inhibition of USP8 demonstrates tumor-suppressive effects and thus can be exploited as potential therapeutic strategy either as monotherapy or combined therapy with melatonin.

Melatonin Treatment and Adequate Sleep Hygiene Interventions in Children with Autism Spectrum Disorder: A Randomized Controlled Trial

Robust clinical evidence has not been available for melatonin, a drug commonly administered for treating sleep problems of children with autism spectrum disorder (ASD). In a phase 3 randomized, placebo-controlled clinical trial, we administered 1-mg melatonin (n = 65), 4-mg melatonin (n = 65), or placebo (n = 66) to196 children with ASD once daily before bedtime under adequate sleep hygiene interventions. The primary outcome was sleep onset latency (SOL) assessed with the electronic sleep diary. SOL shortened significantly in the 1- and 4-mg melatonin groups compared to the placebo group (- 22.0, - 28.0, and - 5.0 min, respectively; p < 0.0001 each). This therapeutic regimen of melatonin is a reasonable clinical approach to cope with ASD-emergent difficulties in children with ASD.

Emerging mechanisms of valproic acid-induced neurotoxic events in autism and its implications for pharmacological treatment

Autism spectrum disorder (ASD) is a sort of mental disorder marked by deficits in cognitive and communication abilities. To date no effective cure for this pernicious disease has been available. Valproic acid (VPA) is a broad-spectrum, antiepileptic drug, and it is also a potent teratogen. Epidemiological studies have shown that children exposed to VPA are at higher risk for ASD during the first trimester of their gestational development. Several animal and human studies have demonstrated important behavioral impairments and morphological changes in the brain following VPA treatment. However, the mechanism of VPA exposure-induced ASD remains unclear. Several factors are involved in the pathological phase of ASD, including aberrant excitation/inhibition of synaptic transmission, neuroinflammation, diminished neurogenesis, oxidative stress, etc. In this review, we aim to outline the current knowledge of the critical pathophysiological mechanisms underlying VPA exposure-induced ASD. This review will give insight toward understanding the complex nature of VPA-induced neuronal toxicity and exploring a new path toward the development of novel pharmacological treatment against ASD.

Melatonin in type 2 diabetes mellitus and obesity

Despite considerable advances in the past few years, obesity and type 2 diabetes mellitus (T2DM) remain two major challenges for public health systems globally. In the past 9 years, genome-wide association studies (GWAS) have established a major role for genetic variation within the MTNR1B locus in regulating fasting plasma levels of glucose and in affecting the risk of T2DM. This discovery generated a major interest in the melatonergic system, in particular the melatonin MT₂ receptor (which is encoded by MTNR1B). In this Review, we discuss the effect of melatonin and its receptors on glucose homeostasis, obesity and T2DM. Preclinical and clinical post-GWAS evidence of frequent and rare variants of the MTNR1B locus confirmed its importance in regulating glucose homeostasis and T2DM risk with minor effects on obesity. However, these studies did not solve the question of whether melatonin is beneficial or detrimental, an issue that will be discussed in the context of the peculiarities of the melatonergic system. Melatonin receptors might have therapeutic potential as they belong to the highly druggable G protein-coupled receptor superfamily. Clarifying the precise role of melatonin and its receptors on glucose homeostasis is urgent, as melatonin is widely used for other indications, either as a prescribed medication or as a supplement without medical prescription, in many countries in Europe and in the USA.

Melatonin ameliorates hypoglycemic stress-induced brain endothelial tight junction injury by inhibiting protein nitration of TP53-induced glycolysis and apoptosis regulator

Severe hypoglycemia has a detrimental impact on the cerebrovasculature, but the molecular events that lead to the disruption of the integrity of the tight junctions remain unclear. Here, we report that the microvessel integrity was dramatically compromised (59.41% of wild-type mice) in TP53-induced glycolysis and apoptosis regulator (TIGAR) transgenic mice stressed by hypoglycemia. Melatonin, a potent antioxidant, protects against hypoglycemic stress-induced brain endothelial tight junction injury in the dosage of 400 nmol/L in vitro. FRET (fluorescence resonance energy transfer) imaging data of endothelial cells stressed by low glucose revealed that TIGAR couples with calmodulin to promote TIGAR tyrosine nitration. A tyrosine 92 mutation interferes with the TIGAR-dependent NADPH generation (55.60% decreased) and abolishes its protective effect on tight junctions in human brain microvascular endothelial cells. We further demonstrate that the low-glucose-induced disruption of occludin and Caludin5 as well as activation of autophagy was abrogated by melatonin-mediated blockade of nitrosative stress in vitro. Collectively, we provide information on the detailed molecular mechanisms for the protective actions of melatonin on brain endothelial tight junctions and suggest that this indole has translational potential for severe hypoglycemia-induced neurovascular damage.

Epigenetic regulation of melatonin receptors in neuropsychiatric disorders

Melatonin, the primary indoleamine hormone of the mammalian pineal gland, is known to have a plethora of neuroregulatory, neuroprotective and other properties. Melatonergic signalling is mediated by its two GPCRs, MT₁ and MT₂ , which are widely expressed in the mammalian CNS. Melatonin levels and receptor expression often show a decrease during normal ageing, and this reduction may be accelerated in some disease states. Depleted melatonergic signalling has been associated with neuropsychiatric dysfunction and impairments in cognition, memory, neurogenesis and neurorestorative processes. The anticonvulsant and mood stabilizer, valproic acid (VPA), up-regulates melatonin MT₁ and/or MT₂ receptor expression in cultured cells and in the rat brain. VPA is known to affect gene expression through several mechanisms, including the modulation of intracellular kinase pathways and transcription factors, as well as the inhibition of histone deacetylase (HDAC) activity. Interestingly, other HDAC inhibitors, such as trichostatin A, which are structurally distinct from VPA, can also up-regulate melatonin receptor expression, unlike a VPA analogue, valpromide, which lacks HDAC inhibitory activity. Moreover, VPA increases histone H3 acetylation along the length of the MT₁ gene promoter in rat C6 cells. These findings indicate that an epigenetic mechanism, linked to histone hyperacetylation/chromatin remodelling and associated changes in gene transcription, is involved in the up-regulation of melatonin receptors by VPA. Epigenetic induction of MT₁ and/or MT₂ receptor expression, in areas where these receptors are lost because of ageing, injury or disease, may be a promising therapeutic avenue for the management of CNS dysfunction and other disorders. LINKED ARTICLES: This article is part of a themed section on Recent Developments in Research of Melatonin and its Potential Therapeutic Applications. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.16/issuetoc.

Valproic acid exposure decreases the mRNA stability of Bcl-2 via up-regulating miR-34a in the cerebellum of rat

Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by impaired social interaction, limited verbal communication and repetitive behaviors. Previous studies have shown that the level of Bcl-2 in the brain tissues of ASD patients is significantly decreased. However, the mechanisms underlie the down-regulation of Bcl-2 in ASD is still unknown. In this study, we investigated the alteration of Bcl-2 level and associated mechanisms in valproic acid (VPA) exposed ASD rats. VPA exposure resulted in ASD-like behaviors in rats, such as repetitive behavior and social interaction impairment. VPA exposure also down-regulated the expression of Bcl-2 both at mRNA and protein levels, either in cerebellar cortex or primary cerebellar cortical neuronal cells. Furthermore, VPA treatment decreased the mRNA stability of Bcl-2 instead of down-regulating its transcriptional activity. Meanwhile, VPA exposure up-regulated the expression of miR-34a in cerebellar cortex and primary cerebellar cortical neuronal cells. The mimics of miR-34a directly inhibited the expression of Bcl-2 and its antagonist blocked the down-regulation effect of VPA on Bcl-2 in primary cerebellar cortical neuronal cells. Our study implies that VPA may influence ASD through sequential up-regulating miR-34a and therefore down-regulating Bcl-2 in the brain tissues of rats.

β-arrestin signalling and bias in hormone-responsive GPCRs

G protein-coupled receptors (GPCRs) play crucial roles in the ability of target organs to respond to hormonal cues. GPCRs' activation mechanisms have long been considered as a two-state process connecting the agonist-bound receptor to heterotrimeric G proteins. This view is now challenged as mounting evidence point to GPCRs being connected to large arrays of transduction mechanisms involving heterotrimeric G proteins as well as other players. Amongst the G protein-independent transduction mechanisms, those elicited by β-arrestins upon their recruitment to the active receptors are by far the best characterized and apply to most GPCRs. These concepts, in conjunction with remarkable advances made in the field of GPCR structural biology and biophysics, have supported the notion of ligand-selective signalling also known as pharmacological bias. Interestingly, recent reports have opened intriguing prospects to the way β-arrestins control GPCR-mediated signalling in space and time within the cells. In the present paper, we review the existing evidence linking endocrine-related GPCRs to β-arrestin recruitement, signalling, pathophysiological implications and selective activation by biased ligands and/or receptor modifications. Emerging concepts surrounding β-arrestin-mediated transduction are discussed in the light of the peculiarities of endocrine systems.

FXR1P is a GSK3β substrate regulating mood and emotion processing

Inhibition of glycogen synthase kinase 3β (GSK3β) is a shared action believed to be involved in the regulation of behavior by psychoactive drugs such as antipsychotics and mood stabilizers. However, little is known about the identity of the substrates through which GSK3β affects behavior. We identified fragile X mental retardation-related protein 1 (FXR1P), a RNA binding protein associated to genetic risk for schizophrenia, as a substrate for GSK3β. Phosphorylation of FXR1P by GSK3β is facilitated by prior phosphorylation by ERK2 and leads to its down-regulation. In contrast, behaviorally effective chronic mood stabilizer treatments in mice inhibit GSK3β and increase FXR1P levels. In line with this, overexpression of FXR1P in the mouse prefrontal cortex also leads to comparable mood-related responses. Furthermore, functional genetic polymorphisms affecting either FXR1P or GSK3β gene expression interact to regulate emotional brain responsiveness and stability in humans. These observations uncovered a GSK3β/FXR1P signaling pathway that contributes to regulating mood and emotion processing. Regulation of FXR1P by GSK3β also provides a mechanistic framework that may explain how inhibition of GSK3β can contribute to the regulation of mood by psychoactive drugs in mental illnesses such as bipolar disorder. Moreover, this pathway could potentially be implicated in other biological functions, such as inflammation and cell proliferation, in which FXR1P and GSK3 are known to play a role.