AgRP's Role in Energy Homeostasis

This blog has featured various posting on the building blocks and involved in Energy Homeostasis. This is key to future therapies for Obesity and Diabetes.
Here researchers study: Yongheng Cao1, Masanori Nakata, Shiki Okamoto, Eisuke Takano, Toshihiko Yada, Yasuhiko Minokoshi, Yukio Hirata, Kazunori Nakajima, Kristy Iskandar, Yoshitake Hayashi, Wataru Ogawa, Gregory S. Barsh, Hiroshi Hosoda, Kenji Kangawa, Hiroshi Itoh, Tetsuo Noda, Masato Kasuga, Jun Nakae.PDK1-Foxo1 in Agouti-Related Peptide Neurons Regulates Energy Homeostasis by Modulating Food Intake and Energy Expenditure. PLoS ONE 6(4): e18324. doi:10.1371/journal.pone.0018324.

IHC Protocol: For immunofluorescence analyses, mice were transcardially perfused with saline followed by 4% paraformaldehyde in 0.1 M phosphate-buffered saline, pH 7.4 (PBS). The brains were dissected and immersed in 4% paraformaldehyde at 4°C overnight and then soaked in 30% sucrose overnight. Frozen, free-floating coronal sections (4 µm thick) were cut through the arcuate nucleus with a microtome (Leica Microsystems). The sections were washed extensively in PBS for 20 min to quench endogenous peroxidase activity. For double staining of PDK1 and AGRP, the sections were stained with a Renaissance Tyramide Signal Amplification kit (#NEL701, Perkin Elmer, Waltham, MA) according to the manufacturer's protocol. The primary antibodies were Ab-241 (Signalway Antibody, Pearland, TX) for PDK1 and GT15023 (Neuromics, Edina, MN) for AGRP; the secondary antibodies were Alexa FluorR 594 chicken anti-rabbit IgG and Alexa FluorR 488 donkey anti-goat IgG (Molecular Probes, Eugene, OR). For double staining of Foxo1 and AGRP, we used an anti-FOXO1A antibody (ab12161, abcamR, Cambridge, UK), respectively. For double staining of FLAG and AGRP, the sections were stained using a Renaissance Tyramide Signal Amplification kit according to the manufacturer's protocol. The primary antibodies were the OctA-Probe (D-8: sc-807, Santa Cruz Biotechnology, Inc, Santa Cruz, CA); the secondary antibodies were Alexa FluorR 594 chicken anti-rabbit IgG and Alexa FluorR 488 donkey anti-goat IgG (Invitrogen, Carlsbad, CA).

Images: Functional defects of AGRP neurons in AGRPPdk1−/− mice. (A) Numbers of AGRP positive cells in the arcuate nuclei of AGRPPdk1+/+ (gray bar) and AGRPPdk1−/− (blue bar) mice. AGRP cell counts indifferent regions of the arcuate nucleus showed different numbers of AGRP neurons in AGRPPdk1+/+ (n = 3) and AGRPPdk1−/− mice (n = 3). (B) Representative Immunofluorescence images of AGRP in the hypothalamic regions of AGRPPdk1+/+ (left panel) and AGRPPdk1−/− mice (right panel). Green, AGRP; blue, DAPI. Scale bars indicate 100 µm. (C) Expression in the fed-state of hypothalamic neuropeptide genes in control (gray bar) and AGRPPdk1−/−(blue bar) mice. Data were normalized to β-actin expression and represent the mean ± SEM of six mice per genotype.

doi:10.1371/journal.pone.0018324.g002

Key Findings:PDK1 and Foxo1 signaling pathways play important roles in the control of energy homeostasis through AGRP-independent mechanisms. data indicated that PDK1 was indispensable for the orexigenic activity of AGRP neurons. Hypothalamic AGRP neurons express AGRP, NPY, the neurotransmitter GABA, and potentially other undiscovered molecules. In AGRPPdk1−/− mice, the expression of Agrp and Npy tended to be lower than that observed in control mice although the difference was not significant. Interestingly, the Δ256Foxo1AGRPPdk1−/− mice exhibited significantly increased food intake compared to AGRPPdk1−/− mice in spite of significantly decreased expression of Agrp and Npy. Therefore, changes in the expression levels of Agrp and Npy may not explain the changes in food intake in AGRPPdk1−/− mice.

Featured and Related Reagents:
Agouti-Related Protein-Cat#: GT15023
Agouti-Related Protein (Human)-Goat
Agouti-Related Protein (Mouse)-Monoclonal
Neuropeptide and Neuropeptide Receptor Antibodies
Diabetes and Obesity Research Antibodies
Diabetes and Obesity Research