Enhanced PIP3 signaling in POMC neurons causes KATP channel activation and leads to diet-sensitive obesity
Leona Plum, … , Frances M. Ashcroft, Jens C. Brüning
Leona Plum, … , Frances M. Ashcroft, Jens C. Brüning
Published July 3, 2006
Citation Information: J Clin Invest. 2006;116(7):1886-1901. https://doi.org/10.1172/JCI27123.
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Research Article Neuroscience

Enhanced PIP3 signaling in POMC neurons causes KATP channel activation and leads to diet-sensitive obesity

Abstract

Leptin and insulin have been identified as fuel sensors acting in part through their hypothalamic receptors to inhibit food intake and stimulate energy expenditure. As their intracellular signaling converges at the PI3K pathway, we directly addressed the role of phosphatidylinositol3,4,5-trisphosphate–mediated (PIP3-mediated) signals in hypothalamic proopiomelanocortin (POMC) neurons by inactivating the gene for the PIP3 phosphatase Pten specifically in this cell type. Here we show that POMC-specific disruption of Pten resulted in hyperphagia and sexually dimorphic diet-sensitive obesity. Although leptin potently stimulated Stat3 phosphorylation in POMC neurons of POMC cell–restricted Pten knockout (PPKO) mice, it failed to significantly inhibit food intake in vivo. POMC neurons of PPKO mice showed a marked hyperpolarization and a reduction in basal firing rate due to increased ATP-sensitive potassium (KATP) channel activity. Leptin was not able to elicit electrical activity in PPKO POMC neurons, but application of the PI3K inhibitor LY294002 and the KATP blocker tolbutamide restored electrical activity and leptin-evoked firing of POMC neurons in these mice. Moreover, icv administration of tolbutamide abolished hyperphagia in PPKO mice. These data indicate that PIP3-mediated signals are critical regulators of the melanocortin system via modulation of KATP channels.

Authors

Leona Plum, Xiaosong Ma, Brigitte Hampel, Nina Balthasar, Roberto Coppari, Heike Münzberg, Marya Shanabrough, Denis Burdakov, Eva Rother, Ruth Janoschek, Jens Alber, Bengt F. Belgardt, Linda Koch, Jost Seibler, Frieder Schwenk, Csaba Fekete, Akira Suzuki, Tak W. Mak, Wilhelm Krone, Tamas L. Horvath, Frances M. Ashcroft, Jens C. Brüning

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Figure 1

Generation of PPKO and reporter mice.

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Generation of PPKO and reporter mice. (A)To visualize Cre-mediated recom...
(A)To visualize Cre-mediated recombination, immunohistochemistry for β-gal was performed in hypothalamic tissues of double-heterozygous reporter mice (PomcCre-RosaArte1). Blue (DAPI), DNA; green, β-gal. (B)Western blot analysis of Pten and insulin receptor β (IR-β) subunit in hypothalamus, brain, liver, pancreas, white adipose tissue (WAT), and skeletal muscle of control (CO) and PPKO mice. (C)PIP3 formation in hypothalamic neurons of control and PPKO mice. Double immunohistochemistry of ARC neurons of COArte1 and PPKOArte1 reporter mice was performed in mice fasted overnight, which were injected intravenously with either saline or insulin and sacrificed 10 and 20 minutes after insulin stimulation. Arrows indicate 1 POMC and 1 non-POMC neuron in each panel. (D)Quantification of PIP3 levels in control and PPKO POMC neurons in the basal (fasted) state. Values are mean ± SEM of sections obtained from 3 control and 3 PPKO mice. A total of 808 POMC neurons were analyzed. At left are examples of different magnitudes of PIP3 immunoreactivity (arrowheads) as described in Methods. Blue (DAPI), DNA; red, β-gal (POMC neurons); green, PIP3. ***P ≤ 0.001 versus control. Scale bars: 100 μm (A), 20 μm (C), 10 μm (D).