G protein-coupled lactate receptor GPR81 control of ventrolateral ventromedial hypothalamic nucleus glucoregulatory neurotransmitter and 5′-AMP-activated protein kinase expression

Abstract

Astrocytes store glycogen as energy and promote neuro-metabolic stability through supply of oxidizable L-lactate. Whether lactate regulates ventromedial hypothalamic nucleus (VMN) glucostatic function as a metabolic volume transmitter is unknown. Current research investigated whether G-protein-coupled lactate receptor GPR81 controls astrocyte glycogen metabolism and glucose-regulatory neurotransmission in the ventrolateral VMN (VMNvl), where glucose-regulatory neurons reside. Female rats were pretreated by intra-VMN GPR81 or scramble siRNA infusion before insulin or vehicle injection. VMNvl cell or tissue samples were acquired by laser-catapult- or micropunch microdissection for Western blot protein or uHPLC-electrospray ionization-mass spectrometric glycogen analyses. Data show that GPR81 regulates eu- and/or hypoglycemic patterns of VMNvl astrocyte glycogen metabolic enzyme and 5'-AMP-activated protein kinase (AMPK) protein expression according to VMNvl segment. GPR81 inhibits baseline rostral and caudal VMNvl glycogen accumulation, but mediates glycogen breakdown in the former site during hypoglycemia. During euglycemia, GPR81 suppresses the transmitter marker neuronal nitric oxide synthase (nNOS) in rostral and caudal VMNvl nitrergic neurons, but stimulates (rostral VMNvl) or inhibits (caudal VMNvl) GABAergic neuron glutamate decarboxylase65/67 (GAD)protein. During hypoglycemia, GPR81 regulates AMPK activation in nitrergic and GABAergic neurons located in the rostral, but not caudal. VMNvl. VMN GPR81 knockdown amplified hypoglycemic hypercorticosteronemia, but not hyperglucagonemia. Results provide novel proof that VMNvl astrocyte and glucose-regulatory neurons express GPR81 protein. Data identify neuroanatomical subpopulations of VMNvl astrocytes and glucose-regulatory neurons that exhibit differential reactivity to GPR81 input. Heterogeneous GPR81 effects during eu- versus hypoglycemia infer that energy state may affect cellular sensitivity to or post-receptor processing of lactate transmitter signaling.

Diazepam Binding Inhibitor Control of Eu- and Hypoglycemic Patterns of Ventromedial Hypothalamic Nucleus Glucose-Regulatory Signaling

“…415190-9041-000; Carl Zeiss Microscopy LLC, White Plains, NY, U.S.A.). Separate 1-in-5 series of sections were processed for immunolabeling of VMN GABAergic or nitrergic neurons, as described ( Briski et al, 2020 ; Bheemanapally et al, 2021 ; Roy et al, 2023 ; Uddin et al, 2019 ). Briefly, after ice-cold acetone fixation (5 min), sections were blocked (1 h) with 1.5% normal goat serum (prod.…”

“…no. NBP1-39681, 1:1000; Novus Biologicals, Littleton, CO, U.S.A.; RRID:AB_2282822) primary antibody ( Bheemanapally et al, 2021 ; Briski et al, 2020 ; Roy et al, 2023 ; Uddin et al, 2019 ). Tissues were subsequently exposed to a horseradish peroxidase-labeled goat anti-rabbit secondary antiserum (prod.…”

GLUT2 regulation of p38 MAPK isoform protein expression and p38 phosphorylation in male versus female rat hypothalamic primary astrocyte Cultures

“…Astrocyte-neuron metabolic coupling assures provision of the oxidizable energy fuel L-lactate for support of nerve cell mitochondrial oxidative phosphorylation. Astrocyte-derived lactate signal volume governs hypothalamic counterregulatory neurotransmission ( Mahmood et al, 2019 ; Bheemanapally et al, 2021 ; Roy et al, 2022 ). The distinctive locations in the brain where astrocyte GLUT2 shapes neural responses to neuro-glucopenia are not known.…”

A lactate-dependent shift of glycolysis mediates synaptic and cognitive processes

“…On the other hand, the molecular link(s) between HCAR1 signaling and the phosphorylated pathway are currently unknown, and future studies will address the details of this novel signaling cascade, investigating the localization of the involved HCAR1 (e.g. neurons or astrocytes) [94][95][96] and the molecular components of the involved signaling pathway. For instance, HCAR1 are generally coupled to Gi proteins 35,36 .…”