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Medial amygdala projections regulate the metabolic responses to internal and external signals The brain is a crucial part of the complex system that controls blood glucose in response to internal signals and external stressors. However, we do not know whether distinct CNS circuits regulate metabolism in response to internal state (fed vs. fasted) and environmental cues. Here we used detailed mapping of activated neurons, circuit tracing and projection-specific neural manipulation to determine the contribution of medial amygdala (MeA) neurons and circuits to the metabolic response to internal and external signals. Fasting, refeeding and stressors that increase blood glucose significantly activate MeA neurons. MeA neurons are synaptically connected to organs crucial to metabolic control and chemogenetic activation of MeA neurons significantly increased blood glucose, independent of pancreatic hormone release, and suppressed feeding. We identified the bed nucleus of the stria terminalis (BNST) and ventromedial hypothalamus (VMH) as major downstream projections from the MeA. MeA neurons projecting to BNST and to VMH are distinct neural populations activated by metabolic and emotional stress. Targeted activation of MeA neurons projecting to VMH but not to BNST MeA neurons mimicked the glycemic responses to fasting and stress with significantly impaired glucose tolerance, increased hepatic gluconeogenesis and a more rapid recovery from hypoglycemia, without increased corticosterone or epinephrine. Conversely, targeted ablation of MeA neurons projecting to VMH significantly reduced blood glucose and blunted the hyperglycemic response to stress. These data reveal a critical role for the MeA-VMH circuit in glucose regulation in response to internal and external signals. Future work will assess how this pathway is disrupted in diabetes and its contribution to the associations between diabetes and mental health disorders. Disclosure K. Devarakonda: None. A. Alvarsson: None. M. Jimenez gonzalez: None. R. Li: None. V. E. Lehmann: None. S. Stanley: None. Funding American Diabetes Association/Pathway to Stop Diabetes (1-17-ACE-31 to S.S.); National Institutes of Health (R01NS097184, OT2OD024912); U.S. Department of Defense (W81XWH-20-1-0345, W81XWH-20-1-0156); Charles H. Revson Foundation (18-25); Swedish Society

Three-dimensional mapping of pancreatic innervation shows rapid remodeling of islet innervation in mouse and human diabetes., Understanding the detailed anatomy of the endocrine pancreas, its innervation, and the remodeling that occurs in diabetes can provide new insights into metabolic disease. Using tissue clearing and whole-organ imaging, we identified the 3D associations between islets and innervation. This technique provided detailed quantification of α and β cell volumes and pancreatic nerve fibers, their distribution and heterogeneity in healthy tissue, canonical mouse models of diabetes, and samples from normal and diabetic human pancreata. Innervation was highly enriched in the mouse endocrine pancreas, with regional differences. Islet nerve density was increased in nonobese diabetic mice, in mice treated with streptozotocin, and in pancreata of human donors with type 2 diabetes. Nerve contacts with β cells were preserved in diabetic mice and humans. In summary, our whole-organ assessment allows comprehensive examination of islet characteristics and their innervation and reveals dynamic regulation of islet innervation in diabetes.

463 million people globally suffer from diabetes. The majority are deficient in insulin-producing pancreatic beta cells, although beta cells remain in most people with diabetes. Unfortunately, although many diabetes drugs exist, none is able to increase adult human beta cell numbers. Recently, small molecules that inhibit the kinase, DYRK1A, have been suggested to induce human beta cell replication in vitro and in vivo as assessed using proliferation markers, and this is enhanced by drugs that stimulate the GLP1 receptor (GLP1R) on beta cells. DYRK1A inhibitors also enhance human beta cell differentiation and function. However, it is unknown whether any drug can actually increase human beta cell mass in vivo, reflecting: 1) the intrinsic resistance of human beta cells to regeneration; and, 2) the current technical inability to accurately assess human beta cell mass in vivo. Here, we demonstrate for the first time that combining a DYRK1A inhibitor with a GLP1R agonist increases actual human beta cell numbers and overall mass in vivo by 400-700% in diabetic and non-diabetic mice over three months. We further describe a novel application of tissue-clearing and 3D imaging for quantification of human beta cell mass. These findings should be transformative for diabetes treatment.

The brain and peripheral organs communicate through the peripheral nervous system (PNS) comprised of autonomic (sympathetic and parasympathetic) and sensory nerves. Pancreas is densely innervated by the PNS and their cell bodies reside in several ganglia, including nodose (NG), coeliac (CG) dorsal root ganglia (DRG) and intrapancreatic ganglia. Pancreatic innervation is altered in diabetes. Until now, we have lacked the ability to identify and specifically target pancreatic nerves and modulate their function to determine the physiological roles of pancreatic nerves. Here, we delivered retrograde tracers into the pancreas and quantified pancreas-projecting neurons in NG/DRG/CG with 3D visualization and tissue clearing. Next, we assessed the efficiency of different adeno-associated virus (AAV) serotypes, delivery routes and promoters to target construct expression in defined pancreatic nerves. Specific AAV serotypes selectively target pancreas-projecting efferent CG neurons or afferent NG neurons. We utilized Cre-dependent AAV to deliver activating chemogenetic constructs into pancreatic parasympathetic nerves. Targeted activation of the pancreatic parasympathetic neurons improved glucose tolerance and increased insulin secretion. Our studies demonstrate that specific AAV serotypes can target defined pancreatic innervation. Targeted modulation of pancreatic parasympathetic nerves can clarify crucial roles of peripheral nerves in pancreatic function and pathophysiology. Disclosure M. Jimenez Gonzalez: None. R. Li: None. L.E. Pomeranz: None. G.J. Schwartz: None. S. Stanley: None. Funding American Diabetes Association (1-17-ACE-31 to S.S.); National Institutes of Health (1R01NS097184, OT2OD024912); Alexander and Alexandrine Sinsheimer Scholar Award

Background: The pancreas is a highly heterogeneous organ, with regional anatomical, developmental and functional differences. The endocrine pancreas is densely innervated, and neural signals play a significant role in glucose regulation by modulating pancreatic hormone release. However, relatively little is known about the anatomical relationships between islets and nerves across the whole pancreas. Since thin filamentous structures, such as nerves, are difficult to quantify and trace over large volumes using thin section histology, there is a need for high resolution imaging and rendering of intact pancreatic tissue in 3D. Aim: To use optical clearing, whole organ imaging, and 3D rendering to quantify islets and innervation across the whole pancreas in healthy mice, in two mouse models of diabetes, and in pancreatic samples from nondiabetic and diabetic human donors. Methods: Whole-mount staining and clearing was performed using iDISCO+ to quantify innervation, defined by the neuronal marker NF200, and beta cells in pancreata from C57Bl/6 mice, non-obese diabetic (NOD) mice, streptozotocin (STZ)-treated mice, and in pancreatic samples from nondiabetic and diabetic human donors. Z-stacked optical sections were acquired with an Ultramicroscope II at 4x or 12x magnification. Imaris was used to create digital surfaces covering the NF200+ innervation and islets to automatically determine innervation density and islet/nerve interactions. Results: Beta cell volumes were 1-4% in the human pancreas, and 1-2% in the healthy mouse pancreas, with regional variations in islet volume and insulin intensity. There were also significant differences in islet biology between the diabetes models. Innervation of the endocrine pancreas was significantly enriched compared to the surrounding exocrine pancreas, with regional variation. Islets were closely associated with pancreatic innervation and decreased in size with increasing distance from nerves in both mouse and human pancreatic tissue. Innervated islets were relatively preserved in models of diabetes. Finally, islet innervation and expression of neural markers were higher in human samples from diabetic patients and in mouse models of diabetes, with temporal and regional differences. Conclusions: 3D imaging and unbiased analysis across the whole pancreas provides comprehensive measurement of pancreatic nerve volumes and distribution. It allows detailed analysis of the anatomical relationship between nerves and islets, and reveals a close association that is maintained across species. The relative enrichment of innervated islets in diabetes and dynamic changes in islet innervation during the development of diabetes suggest further work is needed to examine the role of pancreatic nerves in preserving and protecting beta cells.

Hypoglycemia is a frequent complication of diabetes, limiting therapy and increasing morbidity and mortality. With recurrent hypoglycemia, the counter-regulatory response (CRR) to decreased blood glucose is blunted, resulting in hypoglycemia unawareness. The mechanisms leading to these blunted effects remain incompletely understood. Here, we identify, with in situ hybridization, immunohistochemistry and the tissue clearing capability of iDisco, that GHRH neurons represent a unique population of arcuate nucleus neurons activated by glucose deprivationin vivo. Repeated glucose deprivation reduces GHRH neuron activation and remodels excitatory and inhibitory inputs to GHRH neurons. We show low glucose sensing is coupled to GHRH neuron depolarization, decreased ATP production and mitochondrial fusion. Repeated hypoglycemia attenuates these responses during low glucose. By maintaining mitochondrial length with the small molecule, mdivi-1, we preserved hypoglycemia sensitivityin vitroandin vivo. Our findings present possible mechanisms for the blunting of the CRR, broaden significantly our understanding of the structure of GHRH neurons and for the fist time, propose that mitochondrial dynamics play an important role in hypoglycemia unawareness. We conclude that interventions targeting mitochondrial fission in GHRH neurons may offer a new pathway to prevent hypoglycemia unawareness in diabetic patients.

Hypoglycemia is a frequent complication of diabetes, limiting therapy and increasing morbidity and mortality. With recurrent hypoglycemia, the counterregulatory response (CRR) to decreased blood glucose is blunted, resulting in hypoglycemia-associated autonomic failure (HAAF). The mechanisms leading to these blunted effects are only poorly understood. Here, we report, with ISH, IHC, and the tissue-clearing capability of iDISCO+, that growth hormone releasing hormone (GHRH) neurons represent a unique population of arcuate nucleus neurons activated by glucose deprivation in vivo. Repeated glucose deprivation reduces GHRH neuron activation and remodels excitatory and inhibitory inputs to GHRH neurons. We show that low glucose sensing is coupled to GHRH neuron depolarization, decreased ATP production, and mitochondrial fusion. Repeated hypoglycemia attenuates these responses during low glucose. By maintaining mitochondrial length with the small molecule mitochondrial division inhibitor-1, we preserved hypoglycemia sensitivity in vitro and in vivo. Our findings present possible mechanisms for the blunting of the CRR, significantly broaden our understanding of the structure of GHRH neurons, and reveal that mitochondrial dynamics play an important role in HAAF. We conclude that interventions targeting mitochondrial fission in GHRH neurons may offer a new pathway to prevent HAAF in patients with diabetes., GHRH neurons in the arcuate nucleus are activated by glucose deprivation; however, repeated hypoglycemia blunts activation, remodels inputs, and disrupts mitochondrial fusion.

Genetic deletion of cyclin-dependent kinase 4 (Cdk4) is associated with pancreatic beta cell loss and glucose dysregulation in rodents. Palbociclib, one of the first selective CDK4/6 inhibitors approved for the treatment of advanced breast cancer, is currently being investigated as an adjuvant treatment in patients with early-stage breast cancer and in a variety of cancers covering a wide-range of patient populations. Hence, longer chronic toxicity studies were necessary to further examine its safety profile. The effects of different doses and duration of palbociclib administration on glucose and beta cell homeostasis in young (two months) versus aged (12 months) rats was compared. Glucose dysregulation, due to pancreatic beta cell degeneration, was observed in young rats administered the highest dose of palbociclib for 6 months. Abnormal pancreatic islet histology and activation of the endoplasmic reticulum stress response in beta cells were detected after shorter administration with high-dose palbociclib in young rats. To test the hypothesis that palbociclib-associated inhibition of beta cell proliferation will more profoundly affect younger animals that have not achieved replicative quiescence, we administered high-dose palbociclib to aged rats for 6 months. In contrast to the young rats, despite equivalent exposures to palbociclib, no evidence of impaired glucose tolerance, hypoinsulinemia, beta cell vacuolization, or beta cell loss was seen in aged rats. Palbociclib administration induces beta cell failure in young but not aged rats. Implications: Although adult humans receiving palbociclib have not displayed detectable adverse effects on glucose metabolism, the risk of beta cell failure in children remains unexplored. Mol Cancer Res; 15(11); 1531–41. ©2017 AACR.

Aims/Hypothesis Finding ways to stimulate the regeneration of endogenous pancreatic beta cells is an important goal in the treatment of diabetes. Parathyroid hormone-related protein (PTHrP), the full-length (1–139) and amino-terminal (1–36) peptides, enhance beta cell function, proliferation, and survival. Therefore, we hypothesize that PTHrP(1–36) has the potential to regenerate endogenous beta cells. Methods The partial pancreatectomy (PPx) mouse model of beta cell injury was used to test this hypothesis. Male Balb/c mice underwent either sham-operation or PPx, and were subsequently injected with PTHrP(1–36) (160μg/kg) or vehicle (veh), for 7, 30, or 90 days. The four groups of mice, sham-veh, sham-PTHrP, PPx-veh, and PPx-PTHrP were assessed for PTHrP and receptor expression, and glucose and beta cell homeostasis. Results PTHrP-receptor, but not the ligand, was significantly up-regulated in islets from mice that underwent PPx compared to sham-operated mice. This suggests that exogenous PTHrP could further enhance beta cell regeneration after PPx. PTHrP did not significantly affect body weight, blood glucose, plasma insulin, or insulin sensitivity, in either sham or PPx mice. Glucose tolerance improved in the PPx-PTHrP versus PPx-veh mice only in the early stages of treatment. As hypothesized, there was a significant increase in beta cell proliferation in PPx-PTHrP mice at days 7 and 30; however, this was normalized by day 90, compared to PPx-veh mice. Enhanced beta cell proliferation translated to a marked increase in beta cell mass at day 90, in PPx-PTHrP versus PPx-veh mice. Conclusions PTHrP(1–36) significantly enhances beta cell regeneration through increased beta cell proliferation and beta cell mass after PPx. Future studies will determine the potential of PTHrP to enhance functional beta cell mass in the setting of diabetes.