The role of Rpgrip1l, a component of the primary cilium, in adipocyte development and function.

Genetic variants within the FTO (α-ketoglutarate-dependent dioxygenase) gene have been strongly associated with a modest increase in adiposity as a result of increased food intake. These risk alleles are associated with decreased expression of both FTO and neighboring RPGRIP1L (retinitis pigmentosa GTPase regulator-interacting protein 1 like). RPGRIP1L encodes a protein that is critical to the function of the primary cilium, which conveys extracellular information to the cell. Rpgrip1l+/- mice exhibit increased adiposity, in part, as a result of hyperphagia. Here, we describe the effects of Rpgrip1l in adipocytes that may contribute to the adiposity phenotype observed in these animals and possibly in humans who segregate for FTO risk alleles. Loss of Rpgrip1l in 3T3-L1 preadipocytes increased the number of cells that are capable of differentiating into mature adipocytes. Knockout of Rpgrip1l in mature adipocytes using Adipoq-Cre did not increase adiposity in mice that were fed chow or a high-fat diet. We also did not observe any effects of Rpgrip1l knockdown in mature 3T3-L1 adipocytes. Thus, to the extent that Rpgrip1l affects cell-autonomous adipose tissue function, it may do so as a result of the effects conveyed in preadipocytes in which the primary cilium is functionally important. We propose that decreased RPGRIP1L expression in preadipocytes in humans who segregate for FTO obesity risk alleles may increase the storage capacity of adipose tissue.-Martin Carli, J. F., LeDuc, C. A., Zhang, Y., Stratigopoulos, G., Leibel, R. L. The role of Rpgrip1l, a component of the primary cilium, in adipocyte development and function.

Loss of the imprinted, non-coding Snord116 gene cluster in the interval deleted in the Prader Willi syndrome results in murine neuronal and endocrine pancreatic developmental phenotypes.

Global neurodevelopmental delay is a prominent characteristic of individuals with Prader-Willi syndrome (PWS). The neuromolecular bases for these delays are unknown. We identified neuroanatomical changes in the brains of mice deficient for a gene in the minimal critical deletion region for PWS (Snord116p-/m+). In Snord116p-/m+ mice, reduced primary forebrain neuron cell body size is apparent in embryonic day 15.5 fetuses, and persists until postnatal day 30 in cerebellar Purkinje neurons. Snord116 is a snoRNA gene cluster of unknown function that can localize to the nucleolus. In cerebellar Purkinje neurons from postnatal day 30 Snord116p-/m+ mice the reduction in neuronal cell body size was associated with decreased neuronal nucleolar size. We also identified developmental changes in the endocrine pancreas of Snord116p-/m+ animals that persist into adulthood. Mice lacking Snord116 have smaller pancreatic islets; within the islet the percentage of δ-cells is increased, while the percentage of α-cells is reduced. The α-cell markers, Sst and Hhex, are upregulated in Snord116p-/m+ isolated islets while Ins1, Ins2, Pdx1, Nkx6-1, and Pax6 are downregulated. There is a 3-fold increase in the percentage of polyhormonal cells in the neonatal pancreata of Snord116p-/m+ mice, due primarily to an increase in cells co-positive with somatostatin. Snord116 may play a role in islet cell lineage specification. The Snord116 gene cluster is important for developmental processes in the brain as well as the endocrine pancreas.

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.

Genome-wide meta-analysis uncovers novel loci influencing circulating leptin levels.

Leptin is an adipocyte-secreted hormone, the circulating levels of which correlate closely with overall adiposity. Although rare mutations in the leptin (LEP) gene are well known to cause leptin deficiency and severe obesity, no common loci regulating circulating leptin levels have been uncovered. Therefore, we performed a genome-wide association study (GWAS) of circulating leptin levels from 32,161 individuals and followed up loci reaching P<10(-6) in 19,979 additional individuals. We identify five loci robustly associated (P<5 × 10(-8)) with leptin levels in/near LEP, SLC32A1, GCKR, CCNL1 and FTO. Although the association of the FTO obesity locus with leptin levels is abolished by adjustment for BMI, associations of the four other loci are independent of adiposity. The GCKR locus was found associated with multiple metabolic traits in previous GWAS and the CCNL1 locus with birth weight. Knockdown experiments in mouse adipose tissue explants show convincing evidence for adipogenin, a regulator of adipocyte differentiation, as the novel causal gene in the SLC32A1 locus influencing leptin levels. Our findings provide novel insights into the regulation of leptin production by adipose tissue and open new avenues for examining the influence of variation in leptin levels on adiposity and metabolic health.