Regulation of body weight and energy homeostasis by neuronal cell adhesion molecule 1

Susceptibility to obesity is linked to genes regulating neurotransmission, pancreatic beta-cell function and energy homeostasis. Genome-wide association studies have identified associations between body mass index and two loci near cell adhesion molecule 1 (CADM1) and cell adhesion molecule 2 (CADM2), which encode membrane proteins that mediate synaptic assembly. We found that these respective risk variants associate with increased CADM1 and CADM2 expression in the hypothalamus of human subjects. Expression of both genes was elevated in obese mice, and induction of Cadm1 in excitatory neurons facilitated weight gain while exacerbating energy expenditure. Loss of Cadm1 protected mice from obesity, and tract-tracing analysis revealed Cadm1-positive innervation of POMC neurons via afferent projections originating from beyond the arcuate nucleus. Reducing Cadm1 expression in the hypothalamus and hippocampus promoted a negative energy balance and weight loss. These data identify essential roles for Cadm1-mediated neuronal input in weight regulation and provide insight into the central pathways contributing to human obesity.</p

NetPath: a public resource of curated signal transduction pathways

NetPath, a novel community resource of curated human signaling pathways is presented and its utility demonstrated using immune signaling data

Funktionelle Untersuchung des microRNA-Signalweges in pankreatischen Beta- Zellen während der Insulinresistenz

In summary, two critical aspects of the β-cell biology have been addressed in this thesis. We have shown that loss of Ago2 from β-cells potentiated the release of β-cell secretome, besides insulin, as a result of de-repression of miR-375-targeted genes. The β-cell secretome led to the identification of several proteins that are important for optimal β-cell function. Interestingly, several proteins within the β-cell secretome were previously shown to be associated with bone physiology. Their release by the β-cells is intriguing and future investigations could shed novel light on the β-cell-bone interactions. On the other hand, we also established that silencing of miR-184 in vivo promoted the expression of its target Ago2 in the islets of several mouse models of insulin resistance. In mouse models that overexpress Ago2 (dox-Ago2) or mice genetically ablated for miR-184 (miR-184KO), increased expression of Ago2 resulted in increased β-cell proliferation. Elevated levels of Ago2 in the islets of ob/ob mice enhanced miRNA function via increased suppression of genes targeted by miR-375 such as Cadm1, Gphn, Rasd1, Ywhaz, and HuD. These target genes are implicated in cellular growth and insulin secretion pathways. Importantly, the miRNA pathway in the β-cell is able to effectively sense nutrient changes and adjusts its activity accordingly. This is demonstrated by the fact that restoration of insulin sensitivity by ketogenic diet in ob/ob mice promoted the expression of miR-184 in the islets. This in turn restored the levels of Ago2, Cadm1, and ultimately the β-cell mass. Lastly, the levels of miR-184 were found to be downregulated in the islets of T2D human donors, demonstrating the functional relevance of miR-184 in human disease. In addition, the expression of Ago2 inversely correlated to that of miR-184 in islets across the entire cohort of human subjects. These observations clearly indicate that feedback mechanisms exist within the miRNA pathway so as to adjust the optimal release of β-cell secretome, besides insulin, and β-cell proliferation according to insulin sensitivity. Future studies to further dissect this pathway in the β-cell would shed novel light into mechanisms of T2D in humans.Die hier vorgelegte Arbeit adressiert zwei kritische funktionelle Aspekte der β-Zellbiologie. Wir konnten zeigen, dass der Verlust von Ago2 in β-Zellen zur verstärkten Freisetzung von Insulin führt, bedingt durch die Derepression von miR-375-Zielgenen. Außerdem konnte gezeigt werden, dass Ago2 auch das β-Zell- Sekretom reguliert. Durch die erstmalige Identifizierung aller von β-Zellen freigesetzter/sezernierter Proteine, waren wir auch in der Lage, einige Proteine zu identifizieren, die eine wichtige Rolle für die normale Funktion von β-Zellen spielen. Besonders interessant dabei ist, dass eine Reihe von Proteinen, die von β-Zellen freigesetzt werden auch in der Physiologie von Knochenzellen eine Rolle spielen. Dieser Umstand ist überraschend und zusätzliche Untersuchungen könnten bisher unbekannte Verbindungen zwischen Knochen- und β-Zellen aufzeigen. Zusätzlich haben wir in in-vivo Experimenten gezeigt, dass die Expression von miR-184 in Langerhansschen Inseln bei verschiedenen Mausmodellen der Insulin-Resistenz reduziert ist und zur verstärkten Expression des miR-184-Zielgens Ago2 führt. Eine erhöhte Expression von Ago2, sowohl in transgenen Mäusen, bei denen entweder Ago2 überexprimiert (dox-Ago2) oder miR-184 (miR-184KO) fehlte, führte zur verstärkten β-Zellproliferation. Die verstärkte Expression von Ago2 in Langerhansschen Inseln von ob/ob Mäusen führte zur einer erhöhten Unterdrückung von miR-375 Zielgenen, wie Cadm1, Gphn, Rasd1, Ywhaz und HuD. Diese Zielgene sind an der Regulation von Zellteilung und der Ausschüttung von Insulin beteiligt. Wir konnten außerdem zeigen, dass der miRNA Signalweg massgeblich auf Veränderungen im Nährstoffhaushalt reagiert und die Aktivität entsprechend anpasst. Dies konnte durch die Gabe einer ketogenen Diät bei ob/ob Mäusen beobachtet werden, die die Insulin-Resistenz verbessert und zu einer erhöhten Expression von miR-184 führt. Infolgedessen normalisierte sich die Expression von Ago2 und Cadm1 und letztlich die β-Zellmasse. Darüber hinaus konnte eine inverse Korrelation von miR-184 und Ago2 Expression auch in humanen Langerhansschen Inseln von gesunden und Typ 2 Diabetes erkrankten Patienten beobachtet werden. Diese Beobachtungen weisen auf Rückkopplungsmechanismen im miRNA Signalweg hin, die eine Anpassung der Insulinsekretion und der Kontrolle der β-Zellteilung in Abhängigkeit von dem Grad der Insulin-Resistenz ermöglichen. Zukünftige Studien zur Aufklärung dieses Mechanismus in β-Zellen führt möglicherweise zur neuen Erkenntnissen über die Entwicklung von Typ 2-Diabetes beim Menschen

Re-dicing the pancreatic β-cell: do microRNAs define cellular identity?

A role for Dicer and miRNAs in regulating pancreatic β-cell differentiation and insulin production is discussed here in the broader context of miRNA functions in cell fate specification and cellular stress responses

Atp6ap2 deletion causes extensive vacuolation that consumes the insulin content of pancreatic β cells

Pancreatic β cells store insulin within secretory granules which undergo exocytosis upon elevation of blood glucose levels. Crinophagy and autophagy are instead responsible to deliver damaged or old granules to acidic lysosomes for intracellular degradation. However, excessive consumption of insulin granules can impair β cell function and cause diabetes. Atp6ap2 is an essential accessory component of the vacuolar ATPase required for lysosomal degradative functions and autophagy. Here, we show that Cre recombinase-mediated conditional deletion of Atp6ap2 in mouse β cells causes a dramatic accumulation of large, multigranular vacuoles in the cytoplasm, with reduction of insulin content and compromised glucose homeostasis. Loss of insulin stores and gigantic vacuoles were also observed in cultured insulinoma INS-1 cells upon CRISPR/Cas9-mediated removal of Atp6ap2. Remarkably, these phenotypic alterations could not be attributed to a deficiency in autophagy or acidification of lysosomes. Together, these data indicate that Atp6ap2 is critical for regulating the stored insulin pool and that a balanced regulation of granule turnover is key to maintaining β cell function and diabetes prevention

Additional file 9: of The IL-4/STAT6 signaling axis establishes a conserved microRNA signature in human and mouse macrophages regulating cell survival via miR-342-3p

Schematic representation of genomic localization of miR-99b and miR-125a coding regions and pri-miR-99b-125a as well as common miR-125a/Spaca6-specific primer pairs. (PDF 7 kb

Regulation of body weight and energy homeostasis by neuronal cell adhesion molecule 1

Susceptibility to obesity is linked to genes regulating neurotransmission, pancreatic beta-cell function and energy homeostasis. Genome-wide association studies have identified associations between body mass index and two loci near cell adhesion molecule 1 (CADM1) and cell adhesion molecule 2 (CADM2), which encode membrane proteins that mediate synaptic assembly. We found that these respective risk variants associate with increased CADM1 and CADM2 expression in the hypothalamus of human subjects. Expression of both genes was elevated in obese mice, and induction of Cadm1 in excitatory neurons facilitated weight gain while exacerbating energy expenditure. Loss of Cadm1 protected mice from obesity, and tract-tracing analysis revealed Cadm1-positive innervation of POMC neurons via afferent projections originating from beyond the arcuate nucleus. Reducing Cadm1 expression in the hypothalamus and hippocampus promoted a negative energy balance and weight loss. These data identify essential roles for Cadm1-mediated neuronal input in weight regulation and provide insight into the central pathways contributing to human obesit

Fly Cell Atlas: a single-cell transcriptomic atlas of the adult fruit fly

Abstract The ability to obtain single cell transcriptomes for stable cell types and dynamic cell states is ushering in a new era for biology. We created the Tabula Drosophilae , a single cell atlas of the adult fruit fly which includes 580k cells from 15 individually dissected sexed tissues as well as the entire head and body. Over 100 researchers from the fly community contributed annotations to >250 distinct cell types across all tissues. We provide an in-depth analysis of cell type-related gene signatures and transcription factor markers, as well as sexual dimorphism, across the whole animal. Analysis of common cell types that are shared between tissues, such as blood and muscle cells, allowed the discovery of rare cell types and tissue-specific subtypes. This atlas provides a valuable resource for the entire Drosophila community and serves as a comprehensive reference to study genetic perturbations and disease models at single cell resolution

Fly Cell Atlas: a single-nucleus transcriptomic atlas of the adult fruit fly

The fruit fly Drosophila melanogaster has served as a premier model organism for discovering fundamental and evolutionarily conserved biological mechanisms. Combining recent advances in single-cell sequencing with powerful fly genetic tools holds great promise for making further discoveries. Li et al. present a single-cell atlas of the entire adult fly that includes 580,000 cells and more than 250 annotated cell types. Cells from the head and body recapitulated cell types from 15 dissected tissues. In-depth analyses revealed rare cell types, cell-type-specific gene signatures, and sexual dimorphism. This atlas provides a resource for the Drosophila community to study genetic perturbations and diseases at single-cell resolution. —BA