A hallmark symptom of PWS is extreme, unrelenting hyperphagia associated with obesity. Other medical characteristics of individuals with PWS include low circulating growth hormone, short stature, adrenal insufficiency, hypothyroidism, and hypogonadism. Additionally, individuals with PWS have decreased levels of circulating fasting insulin compared to age and BMI matched controls and are also hyperghrelinemic. At a physiological level, we are endeavoring to locate a common mechanism for these characteristics. Individuals with microdeletions in the PWS locus also present with all major phenotypes of PWS, identifying a minimum critical deletion region (MCDR) that is sufficient to cause all major PWS phenotypes. The MCDR contains three paternally expressed genes all of which are non-coding: SNORD109A, SNORD116, and IPW. We are using patient-specific iPSC-derived neurons to model PWS in vitro working particularly on the molecular physiology of SNORD116. We are using the CRISPR/Cas9 system to create an allelic series that includes SNORD116, SNORD109A, and IPW on the same genetic background.
Research Outcomes: Project Summary
Our findings of reductions in NHLH2 and PC1 at both the transcript and protein levels in PWS iPSC-derived neurons in consistent with the possibility that the major neuroendocrine phenotypes of PWS are due in part to defects in prohormone processing. The deleted region of the PWS microdeletion patient studied here includes only three noncoding RNA genes: SNORD109A, SNORD116, and IPW. Mice lacking the paternal copy of Snord116 display: reduced levels of hypothalamic Nhlh2 and Pcsk1 at fasting, reductions in stomach and pancreatic islet PC1 transcript and protein levels, and endocrine phenotypes similar to PC1-null mice, including hyperpghrelinemia associated with impaired processing of proghrelin to ghrelin in the stomach, dwarfism associated with low growth hormone due to impaired processing of proGHRH to GHRH in the hypothalamus, and impaired processing of proinsulin to insulin in pancreatic islets.
In support of these findings, an elevated ratio of proinsulin to insulin at fasting was detected in the plasma of PWS patients compared to age-and BMI-matched controls, suggesting that proinsulin processing is impaired in human PWS patients as well. These data suggest a unified molecular mechanism for the seemingly disparate neuroendocrine features of PWS including: hyperphagic obesity (impaired hypothalamic POMC processing to alphaMSH; upregulation via misprocessing of proAgRP, leading to elevated bio-active AgRP), hypogonadism (impaired processing proGnRH to GnRH), short stature and low GH (impaired proGHRH processing to GHRH), hyperphrelinemia (impaired proghrelin processing to ghrelin), relative hypoinsulinemia (impaired proinsulin processing to insulin), and central adrenal insufficiency (impaired pituitary processing of POMC to ACTH, and impaired hypothalamic processing of proCRH to CRH). In support of this formulation, the phenotypes of PWS patients mirror those of individuals with hypomorphic PCSK1 mutations. These data also identify potential therapeutic interventions for individuals with PWS; agents that increase cellular PC1 levels may ameliorate the salient endocrine and neuroendocrine abnormalities of PWS.
Research Outcomes: Publications
Deficiency in prohormone convertase PC1 impairs prohormone processing in Prader-Willi syndrome. Burnett LC, LeDuc CA, Sulsona CR, Paull D, Rausch R, Eddiry S, Carli JF, Morabito MV, Skowronski AA, Hubner G, Zimmer M, Wang L, Day R, Levy B, Fennoy I, Dubern B, Poitou C, Clement K, Butler MG, Rosenbaum M, Salles JP, Tauber M, Driscoll DJ, Egli D, Leibel RL. Journal of Clinical Investigation. 2017 Jan 3;127(1):293-305.
PC1/3 Deficiency Impacts Pro-opiomelanocortin Processing in Human Embryonic Stem Cell-Derived Hypothalamic Neurons. Wang L, Sui L, Panigrahi K, Meece K, Xin Y, Kim J, Gromada J, Doege CA, Wardlaw S, Egli D, Leibel RL. Stem Cell Reports. 2017 Feb 14; 8(2): 264–277.
Induced pluripotent stem cells (iPSC) created from skin fibroblasts of patients with Prader-Willi syndrome (PWS) retain the molecular signature of PWS. Burnett LC, LeDuc CA, Sulsona CR, Paull D, Eddiry S, Levy B, Salles JP, Tauber M, Driscoll DJ, Egli D, Leibel RL. Stem Cell Research. 2016 Nov; 17(3):526-530.
Efficient Generation of Hypothalamic Neurons from Human Pluripotent Stem Cells. Wang L, Egli D, Leibel RL. Current Protocols in Human Genetics. 2016 Jul 1;90:21.5.1-21.5.14.Differentiation of hypothalamic-like neurons from human pluripotent stem cells. Wang L, Meece K, Williams DJ, Lo KA, Zimmer M, Heinrich G, Martin Carli J, Leduc CA, Sun L, Zeltser LM, Freeby M, Goland R, Tsang SH, Wardlaw SL, Egli D, Leibel RL. J Clin Invest. 2015 Feb 2;125(2):796-808.
Rudolph Leibel, MD