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. 2009 Nov;10(5):343-54.
doi: 10.1016/j.cmet.2009.09.008.

Dominant role of the p110beta isoform of PI3K over p110alpha in energy homeostasis regulation by POMC and AgRP neurons

Hind Al-Qassab  1 , Mark A Smith, Elaine E Irvine, Julie Guillermet-Guibert, Marc Claret, Agharul I Choudhury, Colin Selman, Kaisa Piipari, Melanie Clements, Steven Lingard, Keval Chandarana, Jimmy D Bell, Gregory S Barsh, Andrew J H Smith, Rachel L Batterham, Michael L J Ashford, Bart Vanhaesebroeck, Dominic J Withers
Affiliations

Dominant role of the p110beta isoform of PI3K over p110alpha in energy homeostasis regulation by POMC and AgRP neurons

Hind Al-Qassab et al. Cell Metab. 2009 Nov.

Abstract

PI3K signaling is thought to mediate leptin and insulin action in hypothalamic pro-opiomelanocortin (POMC) and agouti-related protein (AgRP) neurons, key regulators of energy homeostasis, through largely unknown mechanisms. We inactivated either p110alpha or p110beta PI3K catalytic subunits in these neurons and demonstrate a dominant role for the latter in energy homeostasis regulation. In POMC neurons, p110beta inactivation prevented insulin- and leptin-stimulated electrophysiological responses. POMCp110beta null mice exhibited central leptin resistance, increased adiposity, and diet-induced obesity. In contrast, the response to leptin was not blocked in p110alpha-deficient POMC neurons. Accordingly, POMCp110alpha null mice displayed minimal energy homeostasis abnormalities. Similarly, in AgRP neurons, p110beta had a more important role than p110alpha. AgRPp110alpha null mice displayed normal energy homeostasis regulation, whereas AgRPp110beta null mice were lean, with increased leptin sensitivity and resistance to diet-induced obesity. These results demonstrate distinct metabolic roles for the p110alpha and p110beta isoforms of PI3K in hypothalamic energy regulation.

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Figures

Figure 1
Figure 1
Genetic Inactivation of p110α and p110β in Hypothalami of POMCp110 Null and AgRPp110 Null Mice Recombination of p110α (A) or p110β (B) alleles in the hypothalamus (H), but not the cerebral cortex (C), of POMCp110null and AgRPp110 null mice. Unaltered expression of p85 and reduction of p110α activity (C) or p110β activity (D) in hypothalamic lysates from POMCp110 null and AgRPp110 null mice, n = 3. All values are mean ± SEM, ∗p < 0.05.
Figure 2
Figure 2
Energy Homeostasis Phenotypes in POMCp110α Null and POMCp110β Null Mice Body weight curves of male POMCp110β null (A) and POMCp110α null (B) mice on chow diet, n = 30 per genotype. (C) Fat pad mass in 40-week-old POMCp110α null and POMCp110β null mice, n = 10. (D) Fasting plasma leptin levels in control, POMCp110α null, and POMCp110β null mice, n = 8. (E) Twenty-four hour food intake under freely feeding conditions in 12-week-old male control, POMCp110α null and POMCp110β null mice, n = 10–14. Food intake after overnight fast in 16-week-old male POMCp110α null (F) and POMCp110β null (G) mice, n = 10–14. Body weight (H), percentage fat mass (I), and fasting plasma leptin levels (J) of POMCp110α null and POMCp110β null mice following 18 week exposure to HFD, n = 10–15. All values are mean ± SEM, ∗p < 0.05.
Figure 3
Figure 3
Energy Homeostasis Phenotypes in AgRPp110α Null and AgRPp110β Null Mice Body weight curves of male AgRPp110β null (A) and AgRPp110α null (B) mice on chow diet, n = 30 per genotype. (C) Percentage fat pad mass in 40-week-old AgRPp110α null and AgRPp110β null mice, n = 10. (D) Fasting plasma leptin levels in AgRPp110α null and AgRPp110β null mice, n = 8. (E) Twenty-four hour food intake under freely feeding conditions in 12-week-old male AgRPp110α null and AgRPp110β null mice, n = 10–14. Food intake after overnight fast in 16-week-old male AgRPp110α null (F) and AgRPp110β null (G) mice, n = 10–12. Body weight (H), percentage fat mass (I), and fasting plasma leptin levels (J) of AgRPp110α null and AgRPp110β null mice following 18 week exposure to HFD, n = 10–15. All values are mean ± SEM, ∗p < 0.05, ∗∗p < 0.01, ∗∗∗p < 0.001.
Figure 4
Figure 4
Response to Centrally Administered Leptin and Hypothalamic Neuropeptide Expression of POMCp110β Null and AgRPp110β Null Mice Suppression of food intake in POMCp110β null (A) and AgRPp110β null (B) mice following i.c.v. injection of leptin (0.5 μg), n = 8. Pomc, Agrp, and Npy mRNA expression in hypothalami of POMCp110β null (C) and AgRPp110β null (D) mice. All values are mean ± SEM, ∗p < 0.05, ∗∗∗p < 0.001.
Figure 5
Figure 5
PI3K Activity Underlies Leptin and Insulin Modulation of POMC Neuronal Excitability Whole-cell recordings were made from control (A, D, E, H, I, and J), p110α null (B and F), and p110β null (C and G) POMC neurons. Continuous current-clamp traces are shown in upper traces and expanded sections in lower traces, respectively. A minority population of control (A) and p110α null (B) POMC neurons were depolarized by leptin (50 nM for 2 min, as indicated by the arrows), which was associated with an increase in spike firing frequency (upward deflections). Leptin hyperpolarized a minority population of p110β null (C) but had no effect on the majority of p110β-inhibited (1 μM TGX-221) (D) POMC neurons. (E) Insulin (50 nM for 2 min, where indicated) hyperpolarized the majority of POMC neurons, which was reversed by the subsequent application of 200 μM tolbutamide. Note that there was a small reduction in input resistance following insulin application, as denoted by the reduced amplitude of the periodic downward deflections shown in the continuous trace. Genetic inactivation of p110α (F) or p110β (G) prevented insulin modulation of POMC neuron excitability. Pharmacological inhibition of p110β (1 μM TGX-221) (H) or a general PI3K inhibitor (100 nM PI-103) (I) prevented insulin modulation of POMC neuronal excitability. (J) Representative continuous current-clamp trace before and after sequential leptin and insulin (50 nM for 2 min) application as indicated by the arrows. Expanded sections are shown underneath at time points indicated by the corresponding letters in italics. Note that leptin-induced depolarization was reversed by subsequent insulin application, although a subsequent leptin administration had no effect on membrane potential.
Figure 6
Figure 6
Insulin-Induced Depolarization of AgRP Neurons Is Dependent on p110α and p110β Expression Leptin (50 nM) does not modulate the excitability of control (A) and p110α (B) or p110β (C) null AgRP neurons. (D) A minority population of AgRP neurons were depolarized by insulin (50 nM), and this was associated with an increase in spike firing frequency. A proportion of p110α (E) and p110β (F) null or PI3K-inhibited (100 nM wortmannin; G) AgRP neurons were hyperpolarized by insulin, and this effect was reversibly occluded by 200 μM tolbutamide.
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