The brain influences glucose homeostasis, partly by supplemental control over insulin and glucagon secretion. Without this central regulation, diabetes and its complications can ensue. Yet, the neuronal network linking to pancreatic islets has never been fully mapped. Here, we refine this map using pseudorabies virus (PRV) retrograde tracing, indicating that the pancreatic islets are innervated by efferent circuits that emanate from the hypothalamus. We found that the hypothalamic arcuate nucleus (ARC), ventromedial nucleus (VMN), and lateral hypothalamic area (LHA) significantly overlap PRV and the physiological glucose-sensing enzyme glucokinase. Then, experimentally lowering glucose sensing, specifically in the ARC, resulted in glucose intolerance due to deficient insulin secretion and no significant effect in the VMN, but in the LHA it resulted in a lowering of the glucose threshold that improved glucose tolerance and/or improved insulin sensitivity, with an exaggerated counter-regulatory response for glucagon secretion. No significant effect on insulin sensitivity or metabolic homeostasis was noted. Thus, these data reveal novel direct neuronal effects on pancreatic islets and also render a functional validation of the brain-to-islet neuronal map. They also demonstrate that distinct regions of the hypothalamus differentially control insulin and glucagon secretion, potentially in partnership to help maintain glucose homeostasis and guard against hypoglycemia.

(2015) Monomethylated-adenines potentiate glucose-induced insulin production and secretion via inhibition of phosphodiesterase activity in rat pancreatic islets, Islets, 7:2, e1073435, DOI: 10.1080DOI: 10. /19382014.2015 To link to this article: https://doi.org/10. 1080/19382014.2015 Abbreviations: 3-MA, 3-methyladenine; N6-MA, N6-methyladenine; 9-MA, 9-methyladenine; 1-MA, 1-methyladenine; 7-MA, 7-methyladenine; PKA, protein kinase-A; CREB, cAMP-response element binding protein; 9-CPA, 9-cylopentyladenine; PDE, phosphodiesterase; IBMX, 3-isobutyl-1-methylxanthine; GPR-40, G-protein coupled receptor-40; PLC, phospholipase-C; DAG, diacylglycerol; PKC, protein kinase-C; GLP-1, glucagon-like peptide-1; GIP, gastric inhibitory peptide; MMPX, 8-Methoxymethyl-3-isobutyl-1-methyl xanthine; EHNA, Erythro-9-(2-hydroxy-3-nonyl) adenine; KRBH, Krebs-Ringer bicarbonate buffer; PMSF, phenylmethylsulfonyl fluoride; TLCK, Tosyl-lysyl chloromethylketone; RIA, radioimmunoassay; BCA, bicinchoninic acid; LC3, Microtubule-associated protein-1 light chain-3; mTOR, mammalian Target of Rapamycin; PI3 0 K, phosphatidylinositol-4,5-bisphosphate 3-kinase; PDK-1, Phosphoinositide dependent kinase-1; AMPK, AMP-activated protein kinase.Monomethyladenines have effects on DNA repair, G-protein-coupled receptor antagonism and autophagy. In islet û-cells, 3-methyladenine (3-MA) has been implicated in DNA-repair and autophagy, but its mechanism of action is unclear. Here, the effect of monomethylated adenines was examined in rat islets. 3-MA, N6-methyladenine (N6-MA) and 9-methyladenine (9-MA), but not 1-or 7-monomethylated adenines, specifically potentiated glucose-induced insulin secretion (3-4 fold; p 0.05) and proinsulin biosynthesis (»2-fold; p 0.05). Using 3-MA as a 'model' monomethyladenine, it was found that 3-MA augmented [cAMP] i accumulation (2-3 fold; p 0.05) in islets within 5 minutes. The 3-, N6-and 9-MA also enhanced glucose-induced phosphorylation of the cAMP/protein kinase-A (PKA) substrate cAMP-response element binding protein (CREB). Treatment of islets with pertussis or cholera toxin indicated 3-MA mediated elevation of [cAMP] i was not mediated via G-protein-coupled receptors. Also, 3-MA did not compete with 9-cyclopentyladenine (9-CPA) for adenylate cyclase inhibition, but did for the pan-inhibitor of phosphodiesterase (PDE), 3-isobutyl-1-methylxanthine (IBMX). Competitive inhibition experiments with PDE-isoform specific inhibitors suggested 3-MA to have a preference for PDE4 in islet û-cells, but this was likely reflective of PDE4 being the most abundant PDE isoform in û-cells. In vitro enzyme assays indicated that 3-, N6-and 9-MA were capable of inhibiting most PDE isoforms found in û-cells. Thus, in addition to known inhibition of phosphatidylinositol-4,5-bisphosphate 3-kinase (PI3 0 K)/m Target of Rapamycin (mTOR) signaling, 3-MA also acts as a pan-phosphodiesterase inhibitor in pancreatic û-cells to elevate [cAMP] i and then potentiate glucose-induced insulin secretion and production in parallel.

BNip3 is a hypoxia-inducible member of the Bcl-2 family that integrates into the outer mitochondrial membrane as stable homodimers where it acts as a receptor for mitochondrial engulfment through a conserved LC3 interacting region. Hepatic BNip3 levels are constitutively elevated relative to other tissues, and dramatically increase upon nutrient deprivation or glucagon stimulation, suggesting a key role for BNip3 in the fasting response. We have determined that the fasting-induced increase in hepatic BNip3 protein levels is not solely attributable to transcriptional induction and have identified post-translational modification of BNip3 that affects protein stability and function. In a mouse model of BNip3 loss, we observe metabolic defects including increased hepatic lipid synthesis and reduced fatty acid oxidation. Consistent with BNip3's role in mitophagy, defects in liver metabolism were linked to increased mitochondrial mass, but decreased mitochondrial function, including reduced oxygen consumption and loss of mitochondrial membrane potential. Delivery of a mitophagy deficient mutant BNip3 to the BNip3 null liver indicates that defects in lipid metabolism are not simply due to the accumulation of defective mitochondria, but rather BNip3 has another role to regulate lipid metabolism based on nutrient status. Of relevance, BNip3 is epigenetically silenced in the more aggressive and common form of HCC (sub-type A) and thus this work identifies potential mechanisms by which this protein may act as a tumor suppressor. Citation Format: Michelle L. Boland, He Huang, Ramilla Shah, Almas Ali, Yingming Zhao, Christopher J. Rhodes, Kay F. Macleod. BNip3 connects energy sensing to hepatic lipid metabolism and mitophagy. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4324. doi:10.1158/1538-7445.AM2014-4324