SNORD116 and growth hormone therapy impact IGFBP7 in Prader-Willi syndrome.

PURPOSE: Prader-Willi syndrome (PWS) is a neurodevelopmental disorder with hypothalamic dysfunction due to deficiency of imprinted genes located on the 15q11-q13 chromosome. Among them, the SNORD116 gene appears critical for the expression of the PWS phenotype. We aimed to clarify the role of SNORD116 in cellular and animal models with regard to growth hormone therapy (GHT), the main approved treatment for PWS. METHODS: We collected serum and induced pluripotent stem cells (iPSCs) from GH-treated PWS patients to differentiate into dopaminergic neurons, and in parallel used a Snord116 knockout mouse model. We analyzed the expression of factors potentially linked to GH responsiveness. RESULTS: We found elevated levels of circulating IGFBP7 in naive PWS patients, with IGFBP7 levels normalizing under GHT. We found elevated IGFBP7 levels in the brains of Snord116 knockout mice and in iPSC-derived neurons from a SNORD116-deleted PWS patient. High circulating levels of IGFBP7 in PWS patients may result from both increased IGFBP7 expression and decreased IGFBP7 cleavage, by downregulation of the proconvertase PC1. CONCLUSION: SNORD116 deletion affects IGFBP7 levels, while IGFBP7 decreases under GHT in PWS patients. Modulation of the IGFBP7 level, which interacts with IGF1, has implications in the pathophysiology and management of PWS under GHT.

Bardet-Biedl syndrome proteins regulate intracellular signaling and neuronal function in patient-specific iPSC-derived neurons.

Bardet-Biedl syndrome (BBS) is a rare autosomal recessive disorder caused by mutations in genes encoding components of the primary cilium and is characterized by hyperphagic obesity. To investigate the molecular basis of obesity in human BBS, we developed a cellular model of BBS using induced pluripotent stem cell-derived (iPSC-derived) hypothalamic arcuate-like neurons. BBS mutations BBS1M390R and BBS10C91fsX95 did not affect neuronal differentiation efficiency but caused morphological defects, including impaired neurite outgrowth and longer primary cilia. Single-cell RNA sequencing of BBS1M390R hypothalamic neurons identified several downregulated pathways, including insulin and cAMP signaling and axon guidance. Additional studies demonstrated that BBS1M390R and BBS10C91fsX95 mutations impaired insulin signaling in both human fibroblasts and iPSC-derived neurons. Overexpression of intact BBS10 fully restored insulin signaling by restoring insulin receptor tyrosine phosphorylation in BBS10C91fsX95 neurons. Moreover, mutations in BBS1 and BBS10 impaired leptin-mediated p-STAT3 activation in iPSC-derived hypothalamic neurons. Correction of the BBS mutation by CRISPR rescued leptin signaling. POMC expression and neuropeptide production were decreased in BBS1M390R and BBS10C91fsX95 iPSC-derived hypothalamic neurons. In the aggregate, these data provide insights into the anatomic and functional mechanisms by which components of the BBSome in CNS primary cilia mediate effects on energy homeostasis.

Loss of MAGEL2 in Prader-Willi syndrome leads to decreased secretory granule and neuropeptide production.

Prader-Willi syndrome (PWS) is a developmental disorder caused by loss of maternally imprinted genes on 15q11-q13, including melanoma antigen gene family member L2 (MAGEL2). The clinical phenotypes of PWS suggest impaired hypothalamic neuroendocrine function; however, the exact cellular defects are unknown. Here, we report deficits in secretory granule (SG) abundance and bioactive neuropeptide production upon loss of MAGEL2 in humans and mice. Unbiased proteomic analysis of Magel2pΔ/m+ mice revealed a reduction in components of SG in the hypothalamus that was confirmed in 2 PWS patient-derived neuronal cell models. Mechanistically, we show that proper endosomal trafficking by the MAGEL2-regulated WASH complex is required to prevent aberrant lysosomal degradation of SG proteins and reduction of mature SG abundance. Importantly, loss of MAGEL2 in mice, NGN2-induced neurons, and human patients led to reduced neuropeptide production. Thus, MAGEL2 plays an important role in hypothalamic neuroendocrine function, and cellular defects in this pathway may contribute to PWS disease etiology. Moreover, these findings suggest unanticipated approaches for therapeutic intervention.

Physiological consequences of transient hyperleptinemia during discrete developmental periods on body weight in mice.

Leptin plays a role in central nervous system developmental programs and intercurrent physiological processes related to body fat regulation. The timing and neuromolecular mechanisms for these effects are relevant to the prevention and treatment of obesity. Factors implicated in a body weight "set point" including dietary fat, circulating leptin, and other adipokines tend to covary with adiposity and are difficult to disarticulate experimentally. To dissociate leptin effects from adiposity and diet, we created a transgenic mouse in which leptin expression is regulated by doxycycline exposure. Using this system, we investigated the physiological consequences of developmentally-timed transient hyperleptinemia on subsequent adiposity. We evaluated physiological effects of leptin elevation during adulthood (9 to 29 weeks old), "adolescence" (3 to 8 weeks old), and the immediate postnatal period [postnatal days 0 to 22 (P0 to P22)] on long-term adiposity and susceptibility to gain weight on high-fat diet (HFD) fed ad libitum. We found that inducing chronic hyperleptinemia in adult or "adolescent" mice did not alter body weight when excess leptin was discontinued, and upon later exposure to HFD, weight gain did not differ from controls. However, transient elevation of circulating leptin from P0 to P22 increased weight and fat gain in response to HFD, indicating greater susceptibility to obesity as adults. Thus, transient plasma leptin elevations-mimicking one aspect of transient adiposity-increased later susceptibility to diet-induced obesity, although these effects were restricted to a critical developmental (P0 to P22) time window. These findings may have clinical implications for weight management in infancy.

Deficiency in prohormone convertase PC1 impairs prohormone processing in Prader-Willi syndrome.

Prader-Willi syndrome (PWS) is caused by a loss of paternally expressed genes in an imprinted region of chromosome 15q. Among the canonical PWS phenotypes are hyperphagic obesity, central hypogonadism, and low growth hormone (GH). Rare microdeletions in PWS patients define a 91-kb minimum critical deletion region encompassing 3 genes, including the noncoding RNA gene SNORD116. Here, we found that protein and transcript levels of nescient helix loop helix 2 (NHLH2) and the prohormone convertase PC1 (encoded by PCSK1) were reduced in PWS patient induced pluripotent stem cell-derived (iPSC-derived) neurons. Moreover, Nhlh2 and Pcsk1 expression were reduced in hypothalami of fasted Snord116 paternal knockout (Snord116p-/m+) mice. Hypothalamic Agrp and Npy remained elevated following refeeding in association with relative hyperphagia in Snord116p-/m+ mice. Nhlh2-deficient mice display growth deficiencies as adolescents and hypogonadism, hyperphagia, and obesity as adults. Nhlh2 has also been shown to promote Pcsk1 expression. Humans and mice deficient in PC1 display hyperphagic obesity, hypogonadism, decreased GH, and hypoinsulinemic diabetes due to impaired prohormone processing. Here, we found that Snord116p-/m+ mice displayed in vivo functional defects in prohormone processing of proinsulin, pro-GH-releasing hormone, and proghrelin in association with reductions in islet, hypothalamic, and stomach PC1 content. Our findings suggest that the major neuroendocrine features of PWS are due to PC1 deficiency.

Induced pluripotent stem cells (iPSC) created from skin fibroblasts of patients with Prader-Willi syndrome (PWS) retain the molecular signature of PWS.

Prader-Willi syndrome (PWS) is a syndromic obesity caused by loss of paternal gene expression in an imprinted interval on 15q11.2-q13. Induced pluripotent stem cells were generated from skin cells of three large deletion PWS patients and one unique microdeletion PWS patient. We found that genes within the PWS region, including SNRPN and NDN, showed persistence of DNA methylation after iPSC reprogramming and differentiation to neurons. Genes within the PWS minimum critical deletion region remain silenced in both PWS large deletion and microdeletion iPSC following reprogramming. PWS iPSC and their relevant differentiated cell types could provide in vitro models of PWS.

Hyperphagia: current concepts and future directions proceedings of the 2nd international conference on hyperphagia.

OBJECTIVE: Hyperphagia is a central feature of inherited disorders (e.g., Prader-Willi Syndrome) in which obesity is a primary phenotypic component. Hyperphagia may also contribute to obesity as observed in the general population, thus raising the potential importance of common underlying mechanisms and treatments. Substantial gaps in understanding the molecular basis of inherited hyperphagia syndromes are present as are a lack of mechanistic of mechanistic targets that can serve as a basis for pharmacologic and behavioral treatments. DESIGN AND METHODS: International conference with 28 experts, including scientists and caregivers, providing presentations, panel discussions, and debates. RESULTS: The reviewed collective research and clinical experience provides a critical body of new and novel information on hyperphagia at levels ranging from molecular to population. Gaps in understanding and tools needed for additional research were identified. CONCLUSIONS: This report documents the full scope of important topics reviewed at a comprehensive international meeting devoted to the topic of hyperphagia and identifies key areas for future funding and research.