Oxytocin-based therapies for treatment of Prader-Willi and Schaaf-Yang syndromes: evidence, disappointments, and future research strategies

MAGEL2 (patho-)physiology and Schaaf-Yang syndrome

Schaaf-Yang syndrome (SYS) is a complex neurodevelopmental disorder characterized by autism spectrum disorder, joint contractures, and profound hypothalamic dysfunction. SYS is caused by variants in MAGEL2, a gene within the Prader-Willi syndrome (PWS) locus on chromosome 15. In this review, we consolidate decades of research on MAGEL2 to elucidate its physiological functions. Moreover, we synthesize current knowledge on SYS, suggesting that while MAGEL2 loss-of-function seems to underlie several SYS and PWS phenotypes, additional pathomechanisms probably contribute to the distinct and severe phenotype observed in SYS. In addition, we highlight recent therapeutic advances and identify promising avenues for future investigation.

Differential DNA methylation in iPSC-derived dopaminergic neurons: a step forward on the role of SNORD116 microdeletion in the pathophysiology of addictive behavior in Prader-Willi syndrome

INTRODUCTION

A microdeletion including the SNORD116 gene (SNORD116 MD) has been shown to drive the Prader-Willi syndrome (PWS) features. PWS is a neurodevelopmental disorder clinically characterized by endocrine impairment, intellectual disability and psychiatric symptoms such as a lack of emotional regulation, impulsivity, and intense temper tantrums with outbursts. In addition, this syndrome is associated with a nutritional trajectory characterized by addiction-like behavior around food in adulthood. PWS is related to the genetic loss of expression of a minimal region that plays a potential role in epigenetic regulation. Nevertheless, the role of the SNORD116 MD in DNA methylation, as well as the impact of the oxytocin (OXT) on it, have never been investigated in human neurons.

METHODS

We studied the methylation marks in induced pluripotent stem-derived dopaminergic neurons carrying a SNORD116 MD in comparison with those from an age-matched adult healthy control. We also performed identical neuron differentiation in the presence of OXT. We performed a genome-wide DNA methylation analysis from the iPSC-derived dopaminergic neurons by reduced-representation bisulfite sequencing. In addition, we performed RNA sequencing analysis in these iPSC-derived dopaminergic neurons differentiated with or without OXT.

RESULTS

The analysis revealed that 153,826 cytosines were differentially methylated between SNORD116 MD neurons and control neurons. Among the differentially methylated genes, we determined a list of genes also differentially expressed. Enrichment analysis of this list encompassed the dopaminergic system with COMT and SLC6A3. COMT displayed hypermethylation and under-expression in SNORD116 MD, and SLC6A3 displayed hypomethylation and over-expression in SNORD116 MD. RT-qPCR confirmed significant over-expression of SLC6A3 in SNORD116 MD neurons. Moreover, the expression of this gene was significantly decreased in the case of OXT adjunction during the differentiation.

CONCLUSION

SNORD116 MD dopaminergic neurons displayed differential methylation and expression in the COMT and SLC6A3 genes, which are related to dopaminergic clearance.

The Pivotal Role of Oxytocin's Mechanism of Thermoregulation in Prader-Willi Syndrome, Schaaf-Yang Syndrome, and Autism Spectrum Disorder

Oxytocin (Oxt) regulates thermogenesis, and altered thermoregulation results in Prader-Willi syndrome (PWS), Schaaf-Yang syndrome (SYS), and Autism spectrum disorder (ASD). PWS is a genetic disorder caused by the deletion of the paternal allele of 15q11-q13, the maternal uniparental disomy of chromosome 15, or defects in the imprinting center of chromosome 15. PWS is characterized by hyperphagia, obesity, low skeletal muscle tone, and autism spectrum disorder (ASD). Oxt also increases muscle tonicity and decreases proteolysis while PWS infants are hypotonic and require assisted feeding in early infancy. This evidence inspired us to merge the results of almost 20 years of studies and formulate a new hypothesis according to which the disruption of Oxt's mechanism of thermoregulation manifests in PWS, SYS, and ASD through thermosensory abnormalities and skeletal muscle tone. This review will integrate the current literature with new updates on PWS, SYS, and ASD and the recent discoveries on Oxt's regulation of thermogenesis to advance the knowledge on these diseases.

Impaired oxytocin signaling in the central amygdala in rats with chronic heart failure

Aims

Heart failure (HF) patients often suffer from cognitive decline, depression, and mood impairments, but the molecular signals and brain circuits underlying these effects remain elusive. The hypothalamic neuropeptide oxytocin (OT) is critically involved in the regulation of mood, and OTergic signaling in the central amygdala (CeA) is a key mechanism controlling emotional responses including anxiety-like behaviors. Based on this, we used in this study a well-established ischemic rat HF model and aimed to study alterations in the hypothalamus-to-CeA OTergic circuit.

Methods and Results

To study potential HF-induced changes in the hypothalamus-to-CeA OTertic circuit, we combined patch-clamp electrophysiology, immunohistochemical analysis, RNAScope assessment of OTR mRNA, brain region-specific stereotaxic injections of viral vectors and retrograde tracing, optogenetic stimulation and OT biosensors in the ischemic HF model. We found that most of OTergic innervation of the central amygdala (CeA) originated from the hypothalamic supraoptic nucleus (SON). While no differences in the numbers of SON→CeA OTertic neurons (or their OT content) was observed between sham and HF rats, we did observe a blunted content and release of OT from axonal terminals within the CeA. Moreover, we report downregulation of neuronal and astrocytic OT receptors, and impaired OTR-driven GABAergic synaptic activity within the CeA microcircuit of rats with HF.

Conclusions

Our study provides first evidence that HF rats display various perturbations in the hypothalamus-to-amygdala OTergic circuit, and lays the foundation for future translational studies targeting either the OT system or GABAergic amygdala GABA microcircuit to ameliorate depression or mood impairments in rats or patients with chronic HF.

Heralding a new era of oxytocinergic research: New tools, new problems?

According to classic neuroendocrinology, hypothalamic oxytocin cells can be categorized into parvo- and magnocellular neurons. However, research in the last decade provided ample evidence that this black-and-white model of oxytocin neurons is most likely oversimplified. Novel genetic, functional and morphological studies indicate that oxytocin neurons might be organized in functional modules and suggest the existence of five or more distinct oxytocinergic subpopulations. However, many of these novel, automated high-throughput techniques might be inherently biased and interpretation of acquired data needs to be approached with caution to enable drawing sound and reliable conclusions. In addition, the recent finding that astrocytes in various brain regions express functional oxytocin receptors represents a paradigm shift and challenges the view that oxytocin primarily acts as a direct peptidergic neurotransmitter. This review highlights the latest technical advances in oxytocinergic research, puts recent studies on the oxytocin system into context and formulates various provocative ideas based on novel findings that challenges various prevailing hypotheses and dogmas about oxytocinergic modulation.

Intranasal oxytocin as a treatment for obesity: safety and efficacy

INTRODUCTION

Known for its effect on labor and lactation and on emotional and social functions, oxytocin has recently emerged as a key modulator of feeding behavior and indeed suggested as a potential treatment for obesity. The potential positive effect of oxytocin on both metabolic and psychological-behavioral complications of hypothalamic lesions makes it a promising tool in the management of these conditions.

AREAS COVERED

The aim of the present review article is to provide an overview of the mechanism of action and clinical experience of the use of oxytocin in different forms of obesity.

EXPERT OPINION

Current evidence suggests a potential role of oxytocin in the treatment of obesity with different causes. Several challenges remain: an improved understanding of the physiological regulation, mechanisms of action of oxytocin, and interplay with other endocrine axes is fundamental to clarify its role. Further clinical trials are needed to determine the safety and efficacy of oxytocin for the treatment of different forms of obesity. Understanding the mechanism(s) of action of oxytocin on body weight regulation might also improve our understanding of obesity and reveal possible new therapeutic targets - as well as promoting advances in other fields in which oxytocin might be used.

Oxytocin's Regulation of Thermogenesis May Be the Link to Prader-Willi Syndrome

Prader-Willi Syndrome (PWS) is a genetic neurodevelopmental disorder that is caused by either the deletion of the paternal allele of 15q11-q13, maternal uniparental disomy of chromosome 15 or defects in the chromosome 15 imprinting centre and is characterized by cognitive impairment, hyperphagia and low metabolic rate with significant risk of obesity, as well as a variety of other maladaptive behaviours and autistic spectrum disorder (ASD). Many of the features seen in PWS are thought to be due to hypothalamic dysfunction resulting in hormonal abnormalities and impaired social functioning. The preponderance of evidence indicates that the Oxytocin system is dysregulated in PWS individuals and that this neuropeptide pathways may provide promising targets for therapeutic intervention although the process by which this dysregulation occurs in PWS awaits mechanistic investigation. PWS individuals present abnormalities in thermoregulation an impaired detection for temperature change and altered perception of pain indicating an altered autonomic nervous system. Recent studies indicate that Oxytocin is involved in thermoregulation and pain perception. This review will describe the update on PWS and the recent discoveries on Oxytocin regulation of thermogenesis together with the potential link between Oxytocin regulation of thermogenesis and PWS to create a new groundwork for the treatment of this condition.

Preimplantation Genetic Testing (PGT) and Prenatal Diagnosis of Schaaf-Yang Syndrome: A Report of Three Families and a Research on Genotype-Phenotype Correlations

Schaaf-Yang Syndrome (SYS) is a genetic disorder caused by truncating pathogenic variants in the paternal allele of the maternally imprinted, paternally expressed gene MAGEL2 and is characterized by genital hypoplasia, neonatal hypotonia, developmental delay, intellectual disability, autism spectrum disorder (ASD), and other features. In this study, eleven SYS patients from three families were enrolled and comprehensive clinical features were gathered regarding each family. Whole-exome sequencing (WES) was performed for the definitive molecular diagnosis of the disease. Identified variants were validated using Sanger sequencing. Three couples underwent PGT for monogenic diseases (PGT-M) and/or a prenatal diagnosis. Haplotype analysis was performed to deduce the embryo's genotype by using the short tandem repeats (STRs) identified in each sample. The prenatal diagnosis results showed that the fetus in each case did not carry pathogenic variants, and all the babies of the three families were born at full term and were healthy. We also performed a review of SYS cases. In addition to the 11 patients in our study, a total of 127 SYS patients were included in 11 papers. We summarized all variant sites and clinical symptoms thus far, and conducted a genotype-phenotype correlation analysis. Our results also indicated that the variation in phenotypic severity may depend on the specific location of the truncating variant, suggestive of a genotype-phenotype association.

[As early as birth, oxytocin plays a key role in both food and social behavior]

Oxytocin (OT) is a neurohormone that regulates the so-called "social brain" and is mainly studied in adulthood. During postnatal development, the mechanisms by which the OT system structures various behaviors are little studied. Here we present the dynamic process of postnatal development of the OT system as well as the OT functions in the perinatal period that are essential for shaping social behaviors. Specifically, we discuss the role of OT, in the newborn, in integrating and adapting responses to early sensory stimuli and in stimulating suckling activity. Sensory dialogue and suckling are involved in mother-infant bonds and structure future social interactions. In rodents and humans, neurodevelopmental diseases with autism spectrum disorders (ASD), such as Prader-Willi and Schaaf-Yang syndromes, are associated with sensory, feeding and behavioral deficits in infancy. We propose that in early postnatal life, OT plays a key role in stimulating the maturation of neural networks controlling feeding behavior and early social interactions from birth. Administration of OT at birth improves sensory integration of environmental factors and the relationship with the mother as well as sucking activity as we have shown in mouse models and in babies with Prader-Willi syndrome. Long-term effects have also been observed on social and cognitive behavior. Therefore, early feeding difficulties might be an early predictive marker of ASD, and OT treatment a promising option to improve feeding behavior and, in the longer term, social behavioral problems.

The efficacy of intranasal oxytocin in patients with Prader-Willi syndrome: A systematic review and meta-analysis

BACKGROUND AND AIMS

Prader-Willi Syndrome (PWS) is a rare genetic disease. Oxytocin is a neuropeptide hormone that impacts fear, and social recognition. Intranasal administration of oxytocin can be utilized to treat PWS patients. The results of published trials assessing the effects of intranasal oxytocin in PWS are variable. The current systematic review aims to investigate the efficacy of oxytocin in Prader-Willi patients.

METHODS

We conducted a systematic literature search on Pubmed, Web of Science, and Scopus from inception to March 2022 for relevant interventional randomized controlled trials (RCTs) reporting the effect of oxytocin in patients with Prader-Willi syndrome. We assessed the quality of included trials using the Cochrane tool risk of bias 1. We performed the meta-analysis with Revman software version 5.4. In addition, we visualized our results using forest plots. We assessed the heterogeneity by using the Chi-square test.

RESULTS

Relevant to hyperphagia, the data extracted in three studies comprising 92 patients did not show positive outcomes of oxytocin compared to placebo (MD = 0.18; 95% CI: -0.44, 0.80; P = 0.56). Three studies that included 94 patients revealed no significant effects regarding weight between oxytocin and placebo (MD = 0.30; 95% CI: -0.22, 0.83; P = 0.25). The Aberrant Behaviour Checklist found that group-administered oxytocin improved behaviour compared to their counterpart who received a placebo.

CONCLUSION

Oxytocin didn't have significant effects on hyperphagia or weight. To establish the impact of oxytocin in Prader-Willi patients, additional prospective, large-sample randomized controlled trials (RCTs) are needed to avoid controversy.

Modulation of the thermosensory system by oxytocin

Oxytocin (OT) is a neurohormone involved early in neurodevelopment and is implicated in multiple functions, including sensory modulation. Evidence of such modulation has been observed for different sensory modalities in both healthy and pathological conditions. This review summarizes the pleiotropic modulation that OT can exercise on an often overlooked sensory system: thermosensation. This system allows us to sense temperature variations and compensate for the variation to maintain a stable core body temperature. Oxytocin modulates autonomic and behavioral mechanisms underlying thermoregulation at both central and peripheral levels. Hyposensitivity or hypersensitivity for different sensory modalities, including thermosensitivity, is a common feature in autism spectrum disorder (ASD), recapitulated in several ASD mouse models. These sensory dysregulations occur early in post-natal development and are correlated with dysregulation of the oxytocinergic system. In this study, we discussed the potential link between thermosensory atypia and the dysregulation of the oxytocinergic system in ASD.

Neonatal oxytocin gives the tempo of social and feeding behaviors

The nonapeptide oxytocin (OT) is a master regulator of the social brain in early infancy, adolescence, and adult life. Here, we review the postnatal dynamic development of OT-system as well as early-life OT functions that are essential for shaping social behaviors. We specifically address the role of OT in neonates, focusing on its role in modulating/adapting sensory input and feeding behavior; both processes are involved in the establishing mother-infant bond, a crucial event for structuring all future social interactions. In patients and rodent models of Prader-Willi and Schaaf-Yang syndromes, two neurodevelopmental diseases characterized by autism-related features, sensory impairments, and feeding difficulties in early infancy are linked to an alteration of OT-system. Successful preclinical studies in mice and a phase I/II clinical trial in Prader-Willi babies constitute a proof of concept that OT-treatment in early life not only improves suckling deficit but has also a positive long-term effect on learning and social behavior. We propose that in early postnatal life, OT plays a pivotal role in stimulating and coordinating the maturation of neuronal networks controlling feeding behavior and the first social interactions. Consequently, OT therapy might be considered to improve feeding behavior and, all over the life, social cognition, and learning capabilities.

Analysis of the hypothalamic oxytocin system and oxytocin receptor-expressing astrocytes in a mouse model of Prader-Willi syndrome

Prader-Willi syndrome (PWS) is a neurodevelopmental disorder characterized by hyperphagia, obesity, developmental delay and intellectual disability. Studies suggest dysfunctional signaling of the neuropeptide oxytocin as one of the key mechanisms in PWS, and administration of oxytocin via intranasal or systemic routes yielded promising results in both humans and mouse models. However, a detailed assessment of the oxytocin system in mouse models of PWS such as the Magel2-deficient Magel2^tm1.Stw mouse, is lacking. In the present study, we performed an automated counting of oxytocin cells in the entire paraventricular nucleus of the hypothalamus of Magel2^tm1.Stw and wild-type control mice and found a significant reduction in the caudal part, which represents the parvocellular subdivision. In addition, based on the recent discovery that some astrocytes express the oxytocin receptor (OTR), we performed detailed analysis of astrocyte numbers and morphology in various brain regions, and assessed expression levels of the astrocyte marker glial fibrillary acidic protein, which was significantly decreased in the hypothalamus, but not other brain regions in Magel2^tm1.Stw mice. Finally, we analyzed the number of OTR-expressing astrocytes in various brain regions and found a significant reduction in the nucleus accumbens of Magel2^tm1.Stw mice, as well as a sex-specific difference in the lateral septum. This study suggests a role for caudal paraventricular nucleus oxytocin neurons as well as OTR-expressing astrocytes in a mouse model of PWS, provides novel information about sex-specific expression of astrocytic OTRs, and presents several new brain regions containing OTR-expressing astrocytes in the mouse brain.

Oxytocin: A Multi-Functional Biomolecule with Potential Actions in Dysfunctional Conditions; From Animal Studies and Beyond

Oxytocin is a hormone secreted from definite neuroendocrine neurons located in specific nuclei in the hypothalamus (mainly from paraventricular and supraoptic nuclei), and its main known function is the contraction of uterine and/or mammary gland cells responsible for parturition and breastfeeding. Among the actions of the peripherally secreted oxytocin is the prevention of different degenerative disorders. These actions have been proven in cell culture and in animal models or have been tested in humans based on hypotheses from previous studies. This review presents the knowledge gained from the previous studies, displays the results from oxytocin intervention and/or treatment and proposes that the well described actions of oxytocin might be connected to other numerous, diverse actions of the biomolecule.

Next Steps in Prader-Willi Syndrome Research: On the Relationship between Genotype and Phenotype

This article reviews what we know of the phenotype and genotype of Prader-Willi syndrome and hypothesizes two possible paths from phenotype to genotype. It then suggests research that may strengthen the case for one or other of these hypotheses.