Phylogenetic and molecular analyses identify SNORD116 targets involved in the Prader Willi syndrome

Similar metabolic pathways are affected in both Congenital Myasthenic Syndrome-22 and Prader-Willi Syndrome

Loss of prolyl endopeptidase-like (PREPL) encoding a serine hydrolase with (thio)esterase activity leads to the recessive metabolic disorder Congenital Myasthenic Syndrome-22 (CMS22). It is characterized by severe neonatal hypotonia, feeding problems, growth retardation, and hyperphagia leading to rapid weight gain later in childhood. The phenotypic similarities with Prader-Willi syndrome (PWS) are striking, suggesting that similar pathways are affected. The aim of this study was to identify changes in the hypothalamic-pituitary axis in mouse models for both disorders and to examine mitochondrial function in skin fibroblasts of patients and knockout cell lines. We have demonstrated that Prepl is downregulated in the brains of neonatal PWS-IC-p/+m mice. In addition, the hypothalamic-pituitary axis is similarly affected in both Prepl-/- and PWS-IC-p/+m mice resulting in defective orexigenic signaling and growth retardation. Furthermore, we demonstrated that mitochondrial function is altered in PREPL knockout HEK293T cells and can be rescued with the supplementation of coenzyme Q10. Finally, PREPL-deficient and PWS patient skin fibroblasts display defective mitochondrial bioenergetics. The mitochondrial dysfunction in PWS fibroblasts can be rescued by overexpression of PREPL. In conclusion, we provide the first molecular parallels between CMS22 and PWS, raising the possibility that PREPL substrates might become therapeutic targets for treating both disorders.

2'-O-methylation (Nm) in RNA: progress, challenges, and future directions

RNA 2'-O-methylation (Nm) is highly abundant in noncoding RNAs including ribosomal RNA (rRNA), transfer RNA (tRNA), and small nuclear RNA (snRNA), and occurs in the 5' cap of virtually all messenger RNAs (mRNAs) in higher eukaryotes. More recently, Nm has also been reported to occur at internal sites in mRNA. High-throughput methods have been developed for the transcriptome-wide detection of Nm. However, these methods have mostly been applied to abundant RNAs such as rRNA, and the validity of the internal mRNA Nm sites detected with these approaches remains controversial. Nonetheless, Nm in both coding and noncoding RNAs has been demonstrated to impact cellular processes, including translation and splicing. In addition, Nm modifications at the 5' cap and possibly at internal sites in mRNA serve to prevent the binding of nucleic acid sensors, thus preventing the activation of the innate immune response by self-mRNAs. Finally, Nm has been implicated in a variety of diseases including cancer, cardiovascular diseases, and neurologic syndromes. In this review, we discuss current challenges in determining the distribution, regulation, function, and disease relevance of Nm, as well as potential future directions for the field.

A comprehensive review of genetic causes of obesity

BACKGROUND

Obesity is a multifactorial chronic disease with a high, increasing worldwide prevalence. Genetic causes account for 7% of the cases in children with extreme obesity.

DATA SOURCES

This narrative review was conducted by searching for papers published in the PubMed/MEDLINE, Embase and SciELO databases and included 161 articles. The search used the following search terms: "obesity", "obesity and genetics", "leptin", "Prader-Willi syndrome", and "melanocortins". The types of studies included were systematic reviews, clinical trials, prospective cohort studies, cross-sectional and prospective studies, narrative reviews, and case reports.

RESULTS

The leptin-melanocortin pathway is primarily responsible for the regulation of appetite and body weight. However, several important aspects of the pathophysiology of obesity remain unknown. Genetic causes of obesity can be grouped into syndromic, monogenic, and polygenic causes and should be assessed in children with extreme obesity before the age of 5 years, hyperphagia, or a family history of extreme obesity. A microarray study, an analysis of the melanocortin type 4 receptor gene mutations and leptin levels should be performed for this purpose. There are three therapeutic levels: lifestyle modifications, pharmacological treatment, and bariatric surgery.

CONCLUSIONS

Genetic study technologies are in constant development; however, we are still far from having a personalized approach to genetic causes of obesity. A significant proportion of the affected individuals are associated with genetic causes; however, there are still barriers to its approach, as it continues to be underdiagnosed. Video Abstract (MP4 1041807 KB).

The regulatory roles of small nucleolar RNAs within their host locus

Small nucleolar RNAs (snoRNAs) are a class of conserved noncoding RNAs forming complexes with proteins to catalyse site-specific modifications on ribosomal RNA. Besides this canonical role, several snoRNAs are now known to regulate diverse levels of gene expression. While these functions are carried out in trans by mature snoRNAs, evidence has also been emerging of regulatory roles of snoRNAs in cis, either within their genomic locus or as longer transcription intermediates during their maturation. Herein, we review recent findings that snoRNAs can interact in cis with their intron to regulate the expression of their host gene. We also explore the ever-growing diversity of longer host-derived snoRNA extensions and their functional impact across the transcriptome. Finally, we discuss the role of snoRNA duplications into forging these new layers of snoRNA-mediated regulation, as well as their involvement in the genomic imprinting of their host locus.

Identifying key underlying regulatory networks and predicting targets of orphan C/D box SNORD116 snoRNAs in Prader-Willi syndrome

Prader-Willi syndrome (PWS) is a rare neurodevelopmental disorder characterized principally by initial symptoms of neonatal hypotonia and failure-to-thrive in infancy, followed by hyperphagia and obesity. It is well established that PWS is caused by loss of paternal expression of the imprinted region on chromosome 15q11-q13. While most PWS cases exhibit megabase-scale deletions of the paternal chromosome 15q11-q13 allele, several PWS patients have been identified harboring a much smaller deletion encompassing primarily SNORD116. This finding suggests SNORD116 is a direct driver of PWS phenotypes. The SNORD116 gene cluster is composed of 30 copies of individual SNORD116 C/D box small nucleolar RNAs (snoRNAs). Many C/D box snoRNAs have been shown to guide chemical modifications of other RNA molecules, often ribosomal RNA (rRNA). However, SNORD116 snoRNAs are termed 'orphans' because no verified targets have been identified and their sequences show no significant complementarity to rRNA. It is crucial to identify the targets and functions of SNORD116 snoRNAs because all reported PWS cases lack their expression. To address this, we engineered two different deletions modelling PWS in two distinct human embryonic stem cell (hESC) lines to control for effects of genetic background. Utilizing an inducible expression system enabled quick, reproducible differentiation of these lines into neurons. Systematic comparisons of neuronal gene expression across deletion types and genetic backgrounds revealed a novel list of 42 consistently dysregulated genes. Employing the recently described computational tool snoGloBe, we discovered these dysregulated genes are significantly enriched for predicted SNORD116 targeting versus multiple control analyses. Importantly, our results showed it is critical to use multiple isogenic cell line pairs, as this eliminated many spuriously differentially expressed genes. Our results indicate a novel gene regulatory network controlled by SNORD116 is likely perturbed in PWS patients.

Genome-wide identification, expression analysis, and potential roles under low-temperature stress of bHLH gene family in Prunus sibirica

The basic helix-loop-helix (bHLH) family is one of the most well-known transcription factor families in plants, and it regulates growth, development, and abiotic stress responses. However, systematic analyses of the bHLH gene family in Prunus sibirica have not been reported to date. In this study, 104 PsbHLHs were identified and classified into 23 subfamilies that were unevenly distributed on eight chromosomes. Nineteen pairs of segmental replication genes and ten pairs of tandem replication genes were identified, and all duplicated gene pairs were under purifying selection. PsbHLHs of the same subfamily usually share similar motif compositions and exon-intron structures. PsbHLHs contain multiple stress-responsive elements. PsbHLHs exhibit functional diversity by interacting and coordinating with other members. Twenty PsbHLHs showed varying degrees of expression. Eleven genes up-regulated and nine genes down-regulated in -4°C. The majority of PsbHLHs were highly expressed in the roots and pistils. Transient transfection experiments demonstrated that transgenic plants with overexpressed PsbHLH42 have better cold tolerance. In conclusion, the results of this study have significant implications for future research on the involvement of bHLH genes in the development and stress responses of Prunus sibirica.

Maturation of small nucleolar RNAs: from production to function

Small Nucleolar RNAs (snoRNAs) are an abundant group of non-coding RNAs with well-defined roles in ribosomal RNA processing, folding and chemical modification. Besides their classic roles in ribosome biogenesis, snoRNAs are also implicated in several other cellular activities including regulation of splicing, transcription, RNA editing, cellular trafficking, and miRNA-like functions. Mature snoRNAs must undergo a series of processing steps tightly regulated by transiently associating factors and coordinated with other cellular processes including transcription and splicing. In addition to their mature forms, snoRNAs can contribute to gene expression regulation through their derivatives and degradation products. Here, we review the current knowledge on mechanisms of snoRNA maturation, including the different pathways of processing, and the regulatory mechanisms that control snoRNA levels and complex assembly. We also discuss the significance of studying snoRNA maturation, highlight the gaps in the current knowledge and suggest directions for future research in this area.

Facile discovery of red blood cell deformation and compromised membrane/skeleton assembly in Prader-Willi syndrome

Prader-Willi syndrome (PWS) is a rare congenital disease with genetic alterations in chromosome 15. Although genetic disorders and DNA methylation abnormalities involved in PWS have been investigated to a significant degree, other anomalies such as those in erythrocytes may occur and these have not been clearly elucidated. In the present study, we uncovered slight anemia in children with PWS that was associated with increased red blood cell (RBC) distribution width (RDW) and contrarily reduced hematocrit (HCT) values. Intriguingly, the increased ratio in RDW to HCT allowed sufficient differentiation between the PWS patients from the healthy controls and, importantly, with individuals exhibiting conventional obesity. Further morphologic examinations revealed a significant deformity in erythrocytes and mild hemolysis in PWS patients. Comprehensive mechanistic investigations unveiled compromised membrane skeletal assembly and membrane lipid composition, and revealed a reduced F-actin/G-actin ratio in PWS patients. We ascribed these phenotypic changes in erythrocytes to the observed genetic defects, including DNA methylation abnormalities. Our collective data allowed us to uncover RBC deformation in children with PWS, and this may constitute an auxiliary indicator of PWS in early childhood.

Dysregulated adipose tissue expansion and impaired adipogenesis in Prader-Willi syndrome children before obesity-onset

OBJECTIVE

Prader-Willi syndrome (PWS) is a rare genetic imprinting disorder resulting from the expression loss of genes on the paternally inherited chromosome 15q11-13. Early-onset life-thriving obesity and hyperphagia represent the clinical hallmarks of PWS. The noncoding RNA gene SNORD116 within the minimal PWS genetic lesion plays a critical role in the pathogenesis of the syndrome. Despite advancements in understanding the genetic basis for PWS, the pathophysiology of obesity development in PWS remains largely uncharacterized. Here, we aimed to investigate the signatures of adipose tissue development and expansion pathways and associated adipose biology in PWS children without obesity-onset at an early stage, mainly from the perspective of the adipogenesis process, and further elucidate the underlying molecular mechanisms.

METHODS

We collected inguinal (subcutaneous) white adipose tissues (ingWATs) from phase 1 PWS and healthy children with normal weight aged from 6 M to 2 Y. Adipose morphology and histological characteristics were assessed. Primary adipose stromal vascular fractions (SVFs) were isolated, cultured in vitro, and used to determine the capacity and function of white and beige adipogenic differentiation. High-throughput RNA-sequencing (RNA-seq) was performed in adipose-derived mesenchymal stem cells (AdMSCs) to analyze transcriptome signatures in PWS subjects. Transient repression of SNORD116 was conducted to evaluate its functional relevance in adipogenesis. The changes in alternative pre-mRNA splicing were investigated in PWS and SNORD116 deficient cells.

RESULTS

In phase 1 PWS children, impaired white adipose tissue (WAT) development and unusual fat expansion occurred long before obesity onset, which was characterized by the massive enlargement of adipocytes accompanied by increased apoptosis. White and beige adipogenesis programs were impaired and differentiated adipocyte functions were disturbed in PWS-derived SVFs, despite increased proliferation capacity, which were consistent with the results of RNA-seq analysis of PWS AdMSCs. We also experimentally validated disrupted beige adipogenesis in adipocytes with transient SNORD116 downregulation. The transcript and protein levels of PPARγ, the adipogenesis master regulator, were significantly lower in PWS than in control AdMSCs as well as in SNORD116 deficient AdMSCs/adipocytes than in scramble (Scr) cells, resulting in the inhibited adipogenic program. Additionally, through RNA-seq, we observed aberrant transcriptome-wide alterations in alternative RNA splicing patterns in PWS cells mediated by SNORD116 loss and specifically identified a changed PRDM16 gene splicing profile in vitro.

CONCLUSIONS

Imbalance in the WAT expansion pathway and developmental disruption are primary defects in PWS displaying aberrant adipocyte hypertrophy and impaired adipogenesis process, in which SNORD116 deficiency plays a part. Our findings suggest that dysregulated adiposity specificity existing at an early phase is a potential pathological mechanism exacerbating hyperphagic obesity onset in PWS. This mechanistic evidence on adipose biology in young PWS patients expands knowledge regarding the pathogenesis of PWS obesity and may aid in developing a new therapeutic strategy targeting disturbed adipogenesis and driving AT plasticity to combat abnormal adiposity and associated metabolic disorders for PWS patients.

Hypogonadism in Males With Genetic Neurodevelopmental Syndromes

Genetic syndromes that affect the nervous system may also disrupt testicular function, and the mechanisms for these effects may be interrelated. Most often neurological signs and symptoms predominate and hypogonadism remains undetected and untreated, while in other cases, a thorough evaluation of a hypogonadal male reveals previously unrecognized ataxia, movement disorder, muscle weakness, tremor, or seizures, leading to a syndromic diagnosis. Androgen deficiency in patients with neurological diseases may aggravate muscle weakness and fatigue and predispose patients to osteoporosis and obesity. The purpose of this mini review is to provide a current understanding of the clinical, biochemical, histologic, and genetic features of syndromes in which male hypogonadism and neurological dysfunction may coexist and may be encountered by the clinical endocrinologist.

Reference Genes across Nine Brain Areas of Wild Type and Prader-Willi Syndrome Mice: Assessing Differences in Igfbp7, Pcsk1, Nhlh2 and Nlgn3 Expression

Prader−Willi syndrome (PWS) is a complex neurodevelopmental disorder caused by the deletion or inactivation of paternally expressed imprinted genes at the chromosomal region 15q11−q13. The PWS-critical region (PWScr) harbors tandemly repeated non-protein coding IPW-A exons hosting the intronic SNORD116 snoRNA gene array that is predominantly expressed in brain. Paternal deletion of PWScr is associated with key PWS symptoms in humans and growth retardation in mice (PWScr model). Dysregulation of the hypothalamic−pituitary axis (HPA) is thought to be causally involved in the PWS phenotype. Here we performed a comprehensive reverse transcription quantitative PCR (RT-qPCR) analysis across nine different brain regions of wild-type (WT) and PWScr mice to identify stably expressed reference genes. Four methods (Delta Ct, BestKeeper, Normfinder and Genorm) were applied to rank 11 selected reference gene candidates according to their expression stability. The resulting panel consists of the top three most stably expressed genes suitable for gene-expression profiling and comparative transcriptome analysis of WT and/or PWScr mouse brain regions. Using these reference genes, we revealed significant differences in the expression patterns of Igfbp7, Nlgn3 and three HPA associated genes: Pcsk1, Pcsk2 and Nhlh2 across investigated brain regions of wild-type and PWScr mice. Our results raise a reasonable doubt on the involvement of the Snord116 in posttranscriptional regulation of Nlgn3 and Nhlh2 genes. We provide a valuable tool for expression analysis of specific genes across different areas of the mouse brain and for comparative investigation of PWScr mouse models to discover and verify different regulatory pathways affecting this complex disorder.

Dietary Conjugated Linoleic Acid Reduces Body Weight and Fat in Snord116m+/p- and Snord116m-/p- Mouse Models of Prader-Willi Syndrome

Prader–Willi Syndrome (PWS) is a human genetic condition that affects up to 1 in 10,000 live births. Affected infants present with hypotonia and developmental delay. Hyperphagia and increasing body weight follow unless drastic calorie restriction is initiated. Recently, our laboratory showed that one of the genes in the deleted locus causative for PWS, Snord116, maintains increased expression of hypothalamic Nhlh2, a basic helix–loop–helix transcription factor. We have previously also shown that obese mice with a deletion of Nhlh2 respond to a conjugated linoleic acid (CLA) diet with weight and fat loss. In this study, we investigated whether mice with a paternal deletion of Snord116 (Snord116^m+/p−) would respond similarly. We found that while Snord116^m+/p− mice and mice with a deletion of both Snord116 alleles were not significantly obese on a high-fat diet, they did lose body weight and fat on a high-fat/CLA diet, suggesting that the genotype did not interfere with CLA actions. There were no changes in food intake or metabolic rate, and only moderate differences in exercise performance. RNA-seq and microbiome analyses identified hypothalamic mRNAs, and differentially populated gut bacteria, that support future mechanistic analyses. CLA may be useful as a food additive to reduce obesity in humans with PWS.