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Interplay between glucose and leptin signalling determines the strength of GABAergic synapses at POMC neurons.

Lee DK, Jeong JH, Chun SK, Chua S, Jo YH - Nat Commun (2015)

Bottom Line: Inhibition of AMPK activity in presynaptic terminals decreases GABA release at 10 mM glucose.High-fat feeding blunts AMPK-dependent presynaptic inhibition, whereas PLC-mediated GABAergic feedback inhibition remains responsive to leptin.Our data indicate that the interplay between glucose and leptin signalling in glutamatergic POMC neurons is critical for determining the strength of inhibitory tone towards POMC neurons.

View Article: PubMed Central - PubMed

Affiliation: Division of Endocrinology, Department of Medicine, Albert Einstein College of Medicine of Yeshiva University, 1300 Morris Park Avenue, Bronx, New York 10461, USA.

ABSTRACT
Regulation of GABAergic inhibitory inputs and alterations in POMC neuron activity by nutrients and adiposity signals regulate energy and glucose homeostasis. Thus, understanding how POMC neurons integrate these two signal molecules at the synaptic level is important. Here we show that leptin's action on GABA release to POMC neurons is influenced by glucose levels. Leptin stimulates the JAK2-PI3K pathway in both presynaptic GABAergic terminals and postsynaptic POMC neurons. Inhibition of AMPK activity in presynaptic terminals decreases GABA release at 10 mM glucose. However, postsynaptic TRPC channel opening by the PI3K-PLC signalling pathway in POMC neurons enhances spontaneous GABA release via activation of presynaptic MC3/4 and mGlu receptors at 2.5 mM glucose. High-fat feeding blunts AMPK-dependent presynaptic inhibition, whereas PLC-mediated GABAergic feedback inhibition remains responsive to leptin. Our data indicate that the interplay between glucose and leptin signalling in glutamatergic POMC neurons is critical for determining the strength of inhibitory tone towards POMC neurons.

No MeSH data available.


Related in: MedlinePlus

Blockade of both MC3/4Rs and mGluRs inhibits leptin’s stimulatory effectA) Representative traces showing leptin’s effect on mIPSCs in POMC neurons from mice with selective deletion of leptin receptors in POMC neurons at 5 mM glucose levels. In contrast to the control group, leptin did not enhance the frequency of mIPSCs. HP = −70mV.B, C and D) Representative recording samples showing mIPSCs in the presence of the mGluR (MCPG; B), MC3/4R (SHU9119; C) antagonists or both (D) at 5 mM glucose. In the presence of the mGluR antagonist, leptin's effect was significantly diminished compared to the control group. In the presence of the MC3/4R blocker alone or the MC3/4R and mGluR blockers, leptin no longer stimulated GABA release. Rather leptin had an inhibitory effect on mIPSCs. HP = −70mV. 100 pA, 10 s.E) Summary of leptin’s net effects on mIPSCs in mice lacking leptin receptors in POMC neurons and in the presence of the mGluR, MC3/4R antagonists or both. Pharmacological blockade of MC3/4Rs or mGluRs or both significantly attenuated or completely abolished leptin's stimulatory effect on mIPSCs (LepR−/−, n = 7 neurons; MCPG, n = 19 neurons; SHU9119, n = 9 neurons; MCPG + SHU9119, n = 10 neurons).F) Images of fluorescence microscopy showing the co-labeling of glutamatergic POMC neurons and Evans blue in the ARC. Glutamatergic neurons were found adjacent to and/or within the median eminence. More than two-third of glutamatergic POMC neurons were Evans blue-positive, suggesting that glutamatergic POMC neurons are directly exposed to blood glucose and leptin.G) Images of fluorescence microscopy showing the co-expression of pS6 (red) and vGlut2 (blue) in a subset of POMC-GFP (green) neurons in the ARC of animal injected with leptin. 40% of glutamatergic POMC neurons were pS6-positive (n = 9 out of 22 neurons). White arrow represents the POMC-GFP neuron co-expressing pS6 and vGlut2. Scale bar: 50 µmH) Percent of Evans blue-positive glutamatergic and non-glutamatergic POMC neurons. The majority of glutamatergic POMC neurons were Evans Blue-positive (n = 5 animals).*p < 0.05, **p < 0.01 vs. control (paired t-test). All data are shown as mean ± SEM.
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Figure 3: Blockade of both MC3/4Rs and mGluRs inhibits leptin’s stimulatory effectA) Representative traces showing leptin’s effect on mIPSCs in POMC neurons from mice with selective deletion of leptin receptors in POMC neurons at 5 mM glucose levels. In contrast to the control group, leptin did not enhance the frequency of mIPSCs. HP = −70mV.B, C and D) Representative recording samples showing mIPSCs in the presence of the mGluR (MCPG; B), MC3/4R (SHU9119; C) antagonists or both (D) at 5 mM glucose. In the presence of the mGluR antagonist, leptin's effect was significantly diminished compared to the control group. In the presence of the MC3/4R blocker alone or the MC3/4R and mGluR blockers, leptin no longer stimulated GABA release. Rather leptin had an inhibitory effect on mIPSCs. HP = −70mV. 100 pA, 10 s.E) Summary of leptin’s net effects on mIPSCs in mice lacking leptin receptors in POMC neurons and in the presence of the mGluR, MC3/4R antagonists or both. Pharmacological blockade of MC3/4Rs or mGluRs or both significantly attenuated or completely abolished leptin's stimulatory effect on mIPSCs (LepR−/−, n = 7 neurons; MCPG, n = 19 neurons; SHU9119, n = 9 neurons; MCPG + SHU9119, n = 10 neurons).F) Images of fluorescence microscopy showing the co-labeling of glutamatergic POMC neurons and Evans blue in the ARC. Glutamatergic neurons were found adjacent to and/or within the median eminence. More than two-third of glutamatergic POMC neurons were Evans blue-positive, suggesting that glutamatergic POMC neurons are directly exposed to blood glucose and leptin.G) Images of fluorescence microscopy showing the co-expression of pS6 (red) and vGlut2 (blue) in a subset of POMC-GFP (green) neurons in the ARC of animal injected with leptin. 40% of glutamatergic POMC neurons were pS6-positive (n = 9 out of 22 neurons). White arrow represents the POMC-GFP neuron co-expressing pS6 and vGlut2. Scale bar: 50 µmH) Percent of Evans blue-positive glutamatergic and non-glutamatergic POMC neurons. The majority of glutamatergic POMC neurons were Evans Blue-positive (n = 5 animals).*p < 0.05, **p < 0.01 vs. control (paired t-test). All data are shown as mean ± SEM.

Mentions: We sought to determine the cellular mechanisms underlying leptin-mediated enhancement of IPSCs. Leptin receptors are expressed exclusively in somas and dendrites of POMC neurons30 and activation of leptin receptors on POMC neurons induces the release of the stimulatory peptide, α-MSH27. Cowley and colleagues28 suggest the existence of an auto-regulatory loop from opioid and melanocortin peptides and show the stimulatory effect of the MC3R agonist on GABA release. We thus examined whether activation of postsynaptic leptin receptors induces synaptic upregulation by using transgenic animals with selective deletion of leptin receptors in POMC neurons (i.e. POMC-Cre::LepR−/− mice31, 32). Leptin reduced mIPSC frequency without altering the mean amplitude in POMC-Cre:: LepR−/− mice at 5 mM glucose (Fig. 3A and E; mean amplitude, control, −63.9 ± 6.0 pA; leptin, −62.4 ± 6.6 pA; n = 7 neurons). Importantly, no POMC neurons showed increased mIPSC frequency in response to leptin, which was in contrast with the net stimulatory effect of leptin on mIPSCs under the same experimental conditions (see Fig. 2A, B and Table 1). Hence these results suggest that leptin’s stimulatory effect requires activation of postsynaptic rather than presynaptic leptin receptors on POMC neurons.


Interplay between glucose and leptin signalling determines the strength of GABAergic synapses at POMC neurons.

Lee DK, Jeong JH, Chun SK, Chua S, Jo YH - Nat Commun (2015)

Blockade of both MC3/4Rs and mGluRs inhibits leptin’s stimulatory effectA) Representative traces showing leptin’s effect on mIPSCs in POMC neurons from mice with selective deletion of leptin receptors in POMC neurons at 5 mM glucose levels. In contrast to the control group, leptin did not enhance the frequency of mIPSCs. HP = −70mV.B, C and D) Representative recording samples showing mIPSCs in the presence of the mGluR (MCPG; B), MC3/4R (SHU9119; C) antagonists or both (D) at 5 mM glucose. In the presence of the mGluR antagonist, leptin's effect was significantly diminished compared to the control group. In the presence of the MC3/4R blocker alone or the MC3/4R and mGluR blockers, leptin no longer stimulated GABA release. Rather leptin had an inhibitory effect on mIPSCs. HP = −70mV. 100 pA, 10 s.E) Summary of leptin’s net effects on mIPSCs in mice lacking leptin receptors in POMC neurons and in the presence of the mGluR, MC3/4R antagonists or both. Pharmacological blockade of MC3/4Rs or mGluRs or both significantly attenuated or completely abolished leptin's stimulatory effect on mIPSCs (LepR−/−, n = 7 neurons; MCPG, n = 19 neurons; SHU9119, n = 9 neurons; MCPG + SHU9119, n = 10 neurons).F) Images of fluorescence microscopy showing the co-labeling of glutamatergic POMC neurons and Evans blue in the ARC. Glutamatergic neurons were found adjacent to and/or within the median eminence. More than two-third of glutamatergic POMC neurons were Evans blue-positive, suggesting that glutamatergic POMC neurons are directly exposed to blood glucose and leptin.G) Images of fluorescence microscopy showing the co-expression of pS6 (red) and vGlut2 (blue) in a subset of POMC-GFP (green) neurons in the ARC of animal injected with leptin. 40% of glutamatergic POMC neurons were pS6-positive (n = 9 out of 22 neurons). White arrow represents the POMC-GFP neuron co-expressing pS6 and vGlut2. Scale bar: 50 µmH) Percent of Evans blue-positive glutamatergic and non-glutamatergic POMC neurons. The majority of glutamatergic POMC neurons were Evans Blue-positive (n = 5 animals).*p < 0.05, **p < 0.01 vs. control (paired t-test). All data are shown as mean ± SEM.
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Figure 3: Blockade of both MC3/4Rs and mGluRs inhibits leptin’s stimulatory effectA) Representative traces showing leptin’s effect on mIPSCs in POMC neurons from mice with selective deletion of leptin receptors in POMC neurons at 5 mM glucose levels. In contrast to the control group, leptin did not enhance the frequency of mIPSCs. HP = −70mV.B, C and D) Representative recording samples showing mIPSCs in the presence of the mGluR (MCPG; B), MC3/4R (SHU9119; C) antagonists or both (D) at 5 mM glucose. In the presence of the mGluR antagonist, leptin's effect was significantly diminished compared to the control group. In the presence of the MC3/4R blocker alone or the MC3/4R and mGluR blockers, leptin no longer stimulated GABA release. Rather leptin had an inhibitory effect on mIPSCs. HP = −70mV. 100 pA, 10 s.E) Summary of leptin’s net effects on mIPSCs in mice lacking leptin receptors in POMC neurons and in the presence of the mGluR, MC3/4R antagonists or both. Pharmacological blockade of MC3/4Rs or mGluRs or both significantly attenuated or completely abolished leptin's stimulatory effect on mIPSCs (LepR−/−, n = 7 neurons; MCPG, n = 19 neurons; SHU9119, n = 9 neurons; MCPG + SHU9119, n = 10 neurons).F) Images of fluorescence microscopy showing the co-labeling of glutamatergic POMC neurons and Evans blue in the ARC. Glutamatergic neurons were found adjacent to and/or within the median eminence. More than two-third of glutamatergic POMC neurons were Evans blue-positive, suggesting that glutamatergic POMC neurons are directly exposed to blood glucose and leptin.G) Images of fluorescence microscopy showing the co-expression of pS6 (red) and vGlut2 (blue) in a subset of POMC-GFP (green) neurons in the ARC of animal injected with leptin. 40% of glutamatergic POMC neurons were pS6-positive (n = 9 out of 22 neurons). White arrow represents the POMC-GFP neuron co-expressing pS6 and vGlut2. Scale bar: 50 µmH) Percent of Evans blue-positive glutamatergic and non-glutamatergic POMC neurons. The majority of glutamatergic POMC neurons were Evans Blue-positive (n = 5 animals).*p < 0.05, **p < 0.01 vs. control (paired t-test). All data are shown as mean ± SEM.
Mentions: We sought to determine the cellular mechanisms underlying leptin-mediated enhancement of IPSCs. Leptin receptors are expressed exclusively in somas and dendrites of POMC neurons30 and activation of leptin receptors on POMC neurons induces the release of the stimulatory peptide, α-MSH27. Cowley and colleagues28 suggest the existence of an auto-regulatory loop from opioid and melanocortin peptides and show the stimulatory effect of the MC3R agonist on GABA release. We thus examined whether activation of postsynaptic leptin receptors induces synaptic upregulation by using transgenic animals with selective deletion of leptin receptors in POMC neurons (i.e. POMC-Cre::LepR−/− mice31, 32). Leptin reduced mIPSC frequency without altering the mean amplitude in POMC-Cre:: LepR−/− mice at 5 mM glucose (Fig. 3A and E; mean amplitude, control, −63.9 ± 6.0 pA; leptin, −62.4 ± 6.6 pA; n = 7 neurons). Importantly, no POMC neurons showed increased mIPSC frequency in response to leptin, which was in contrast with the net stimulatory effect of leptin on mIPSCs under the same experimental conditions (see Fig. 2A, B and Table 1). Hence these results suggest that leptin’s stimulatory effect requires activation of postsynaptic rather than presynaptic leptin receptors on POMC neurons.

Bottom Line: Inhibition of AMPK activity in presynaptic terminals decreases GABA release at 10 mM glucose.High-fat feeding blunts AMPK-dependent presynaptic inhibition, whereas PLC-mediated GABAergic feedback inhibition remains responsive to leptin.Our data indicate that the interplay between glucose and leptin signalling in glutamatergic POMC neurons is critical for determining the strength of inhibitory tone towards POMC neurons.

View Article: PubMed Central - PubMed

Affiliation: Division of Endocrinology, Department of Medicine, Albert Einstein College of Medicine of Yeshiva University, 1300 Morris Park Avenue, Bronx, New York 10461, USA.

ABSTRACT
Regulation of GABAergic inhibitory inputs and alterations in POMC neuron activity by nutrients and adiposity signals regulate energy and glucose homeostasis. Thus, understanding how POMC neurons integrate these two signal molecules at the synaptic level is important. Here we show that leptin's action on GABA release to POMC neurons is influenced by glucose levels. Leptin stimulates the JAK2-PI3K pathway in both presynaptic GABAergic terminals and postsynaptic POMC neurons. Inhibition of AMPK activity in presynaptic terminals decreases GABA release at 10 mM glucose. However, postsynaptic TRPC channel opening by the PI3K-PLC signalling pathway in POMC neurons enhances spontaneous GABA release via activation of presynaptic MC3/4 and mGlu receptors at 2.5 mM glucose. High-fat feeding blunts AMPK-dependent presynaptic inhibition, whereas PLC-mediated GABAergic feedback inhibition remains responsive to leptin. Our data indicate that the interplay between glucose and leptin signalling in glutamatergic POMC neurons is critical for determining the strength of inhibitory tone towards POMC neurons.

No MeSH data available.


Related in: MedlinePlus