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Bayne M, Alvarsson A, Devarakonda K, Li R, Jimenez-Gonzalez M, Garibay D, Conner K, Varghese M, Serasinghe MN, Chipuk JE, Hof PR, Stanley SA. Repeated hypoglycemia remodels neural inputs and disrupts mitochondrial function to blunt glucose-inhibited GHRH neuron responsiveness. JCI Insight 2020; 5:133488. [PMID: 33148883 PMCID: PMC7710320 DOI: 10.1172/jci.insight.133488] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2019] [Accepted: 09/24/2020] [Indexed: 11/29/2022] Open
Abstract
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.
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Affiliation(s)
| | | | | | | | | | | | | | - Merina Varghese
- Nash Family Department of Neuroscience and Friedman Brain Institute, and
| | - Madhavika N Serasinghe
- Tisch Cancer Institute and Department of Oncological Sciences, Icahn School of Medicine at Mount Sinai, New York, New York, USA
| | - Jerry E Chipuk
- Tisch Cancer Institute and Department of Oncological Sciences, Icahn School of Medicine at Mount Sinai, New York, New York, USA
| | - Patrick R Hof
- Nash Family Department of Neuroscience and Friedman Brain Institute, and
| | - Sarah A Stanley
- Diabetes, Obesity and Metabolism Institute.,Nash Family Department of Neuroscience and Friedman Brain Institute, and
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2
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Jin S, Diano S. Mitochondrial Dynamics and Hypothalamic Regulation of Metabolism. Endocrinology 2018; 159:3596-3604. [PMID: 30203064 PMCID: PMC6157417 DOI: 10.1210/en.2018-00667] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/17/2018] [Accepted: 09/02/2018] [Indexed: 01/22/2023]
Abstract
Mitochondria are cellular organelles that play an important role in bioenergetic processes. In the central nervous system, high energy-demanding neurons are critically dependent on mitochondria to fulfill their appropriate functions. The hypothalamus is a key brain area for maintaining glucose and energy homeostasis via the ability of hypothalamic neurons to sense, integrate, and respond to numerous metabolic signals. Mitochondrial function has emerged as an important component in the regulation of hypothalamic neurons controlling glucose and energy homeostasis. Although the underlying mechanisms are not fully understood, emerging evidence indicates that mitochondrial dysfunction in hypothalamic neurons may contribute to the development of various metabolic diseases, including obesity and type 2 diabetes mellitus (T2DM). In this review, we summarize recent studies demonstrating the link between mitochondria and hypothalamic neural control of glucose and energy homeostasis. Finally, this review provides an insight to understand how mitochondria in hypothalamic neurons may contribute to the development of metabolic disorders, such as T2DM and obesity.
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Affiliation(s)
- Sungho Jin
- Program in Integrative Cell Signaling and Neurobiology of Metabolism, Yale University School of Medicine, New Haven, Connecticut
- Department of Obstetrics, Gynecology, and Reproductive Sciences, Yale University School of Medicine, New Haven, Connecticut
| | - Sabrina Diano
- Program in Integrative Cell Signaling and Neurobiology of Metabolism, Yale University School of Medicine, New Haven, Connecticut
- Department of Obstetrics, Gynecology, and Reproductive Sciences, Yale University School of Medicine, New Haven, Connecticut
- Department of Neuroscience, Yale University School of Medicine, New Haven, Connecticut
- Department of Comparative Medicine, Yale University School of Medicine, New Haven, Connecticut
- Department of Clinical Medicine and Surgery, University of Naples “Federico II,” Naples, Italy
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Chowdhury GMI, Wang P, Ciardi A, Mamillapalli R, Johnson J, Zhu W, Eid T, Behar K, Chan O. Impaired Glutamatergic Neurotransmission in the Ventromedial Hypothalamus May Contribute to Defective Counterregulation in Recurrently Hypoglycemic Rats. Diabetes 2017; 66:1979-1989. [PMID: 28416628 PMCID: PMC5482086 DOI: 10.2337/db16-1589] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/25/2016] [Accepted: 04/10/2017] [Indexed: 12/11/2022]
Abstract
The objectives of this study were to understand the role of glutamatergic neurotransmission in the ventromedial hypothalamus (VMH) in response to hypoglycemia and to elucidate the effects of recurrent hypoglycemia (RH) on this neurotransmitter. We 1) measured changes in interstitial VMH glutamate levels by using microdialysis and biosensors, 2) identified the receptors that mediate glutamate's stimulatory effects on the counterregulatory responses, 3) quantified glutamate metabolic enzyme levels in the VMH, 4) examined astrocytic glutamate reuptake mechanisms, and 5) used 1H-[13C]-nuclear magnetic resonance (NMR) spectroscopy to evaluate the effects of RH on neuronal glutamate metabolism. We demonstrated that glutamate acts through kainic acid receptors in the VMH to augment counterregulatory responses. Biosensors showed that the normal transient rise in glutamate levels in response to hypoglycemia is absent in RH animals. More importantly, RH reduced extracellular glutamate concentrations partly as a result of decreased glutaminase expression. Decreased glutamate was also associated with reduced astrocytic glutamate transport in the VMH. NMR analysis revealed a decrease in [4-13C]glutamate but unaltered [4-13C]glutamine concentrations in the VMH of RH animals. The data suggest that glutamate release is important for proper activation of the counterregulatory response to hypoglycemia and that impairment of glutamate metabolic and resynthetic pathways with RH may contribute to counterregulatory failure.
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Affiliation(s)
- Golam M I Chowdhury
- Department of Psychiatry, Yale School of Medicine, New Haven, CT
- Magnetic Resonance Research Center, Yale School of Medicine, New Haven, CT
| | - Peili Wang
- Section of Endocrinology, Department of Internal Medicine, Yale School of Medicine, New Haven, CT
| | - Alisha Ciardi
- Section of Endocrinology, Department of Internal Medicine, Yale School of Medicine, New Haven, CT
| | - Ramanaiah Mamillapalli
- Section of Endocrinology, Department of Internal Medicine, Yale School of Medicine, New Haven, CT
| | - Justin Johnson
- Section of Endocrinology, Department of Internal Medicine, Yale School of Medicine, New Haven, CT
| | - Wanling Zhu
- Section of Endocrinology, Department of Internal Medicine, Yale School of Medicine, New Haven, CT
| | - Tore Eid
- Departments of Neurosurgery and Laboratory Medicine, Yale School of Medicine, New Haven, CT
| | - Kevin Behar
- Department of Psychiatry, Yale School of Medicine, New Haven, CT
- Magnetic Resonance Research Center, Yale School of Medicine, New Haven, CT
| | - Owen Chan
- Section of Endocrinology, Department of Internal Medicine, Yale School of Medicine, New Haven, CT
- Division of Endocrinology, Metabolism, and Diabetes, Department of Internal Medicine, University of Utah, Salt Lake City, UT
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Mikeladze M, Hedrington MS, Joy N, Tate DB, Younk LM, Davis I, Davis SN. Acute Effects of Oral Dehydroepiandrosterone on Counterregulatory Responses During Repeated Hypoglycemia in Healthy Humans. Diabetes 2016; 65:3161-70. [PMID: 27486235 PMCID: PMC5033266 DOI: 10.2337/db16-0406] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/28/2013] [Accepted: 07/15/2016] [Indexed: 11/13/2022]
Abstract
We tested the hypothesis that acute administration of oral dehydroepiandrosterone (DHEA) during episodes of repeated hypoglycemia can prevent the development of hypoglycemia-associated neuroendocrine and autonomic failure in healthy humans. Twenty-seven individuals (16 men, 11 women) participated in two separate randomized, single-blind, 2-day protocols. Day 1 consisted of morning and afternoon 2-h hypoglycemic clamps (2.9 mmol/L) with 800 mg of DHEA or placebo administered before each clamp. Day 2 consisted of a single 2-h hypoglycemic clamp (2.9 mmol/L) following either DHEA (1,600 mg) or placebo. A 3-tritiated glucose was used to determine glucose kinetics during hypoglycemia on day 2. Antecedent hypoglycemia with placebo resulted in significant reductions of epinephrine, norepinephrine, glucagon, growth hormone, cortisol, endogenous glucose production, and lipolytic and symptom responses. During hypoglycemia on day 2, DHEA prevented blunting of all neuroendocrine, autonomic nervous system (ANS), metabolic, and symptom counterregulatory responses following hypoglycemia on day 1. In summary, DHEA can acutely preserve a wide range of key neuroendocrine, ANS, and metabolic counterregulatory homeostatic responses during repeated hypoglycemia. We conclude that DHEA may have acute effects to protect against hypoglycemia-associated neuroendocrine and autonomic failure in healthy humans.
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Affiliation(s)
- Maia Mikeladze
- Department of Medicine, University of Maryland, Baltimore, MD
| | | | - Nino Joy
- Department of Medicine, University of Maryland, Baltimore, MD
| | - Donna B Tate
- Department of Medicine, University of Maryland, Baltimore, MD
| | - Lisa M Younk
- Department of Medicine, University of Maryland, Baltimore, MD
| | - Ian Davis
- Department of Medicine, University of Maryland, Baltimore, MD
| | - Stephen N Davis
- Department of Medicine, University of Maryland, Baltimore, MD
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Abstract
The erythropoietin-producing hepatocellular carcinoma (Eph) receptor tyrosine kinase family plays important roles in developmental processes, adult tissue homeostasis, and various diseases. Interaction with Eph receptor-interacting protein (ephrin) ligands on the surface of neighboring cells triggers Eph receptor kinase-dependent signaling. The ephrins can also transmit signals, leading to bidirectional cell contact-dependent communication. Moreover, Eph receptors and ephrins can function independently of each other through interplay with other signaling systems. Given their involvement in many pathological conditions ranging from neurological disorders to cancer and viral infections, Eph receptors and ephrins are increasingly recognized as attractive therapeutic targets, and various strategies are being explored to modulate their expression and function. Eph receptor/ephrin upregulation in cancer cells, the angiogenic vasculature, and injured or diseased tissues also offer opportunities for Eph/ephrin-based targeted drug delivery and imaging. Thus, despite the challenges presented by the complex biology of the Eph receptor/ephrin system, exciting possibilities exist for therapies exploiting these molecules.
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Affiliation(s)
- Antonio Barquilla
- Cancer Center, Sanford-Burnham Medical Research Institute, La Jolla, California 92037; ,
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Szepietowska B, Horvath TL, Sherwin RS. Role of synaptic plasticity and EphA5-ephrinA5 interaction within the ventromedial hypothalamus in response to recurrent hypoglycemia. Diabetes 2014; 63:1140-7. [PMID: 24222347 PMCID: PMC3931406 DOI: 10.2337/db13-1259] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Hypoglycemia stimulates counterregulatory hormone release to restore euglycemia. This protective response is diminished by recurrent hypoglycemia, limiting the benefits of intensive insulin treatment in patients with diabetes. We previously reported that EphA5 receptor-ephrinA5 interactions within the ventromedial hypothalamus (VMH) influence counterregulatory hormone responses during acute hypoglycemia in nondiabetic rats. In this study, we examined whether recurrent hypoglycemia alters the capacity of the ephrinA5 ligand to activate VMH EphA5 receptors, and if so, whether these changes could contribute to pathogenesis of defective glucose counterregulation in response to a standard hypoglycemic stimulus. The expression of ephrinA5, but not EphA5 receptors within the VMH, was reduced by antecedent recurrent hypoglycemia. In addition, the number of synaptic connections was increased and astroglial synaptic coverage was reduced. Activation of VMH EphA5 receptors via targeted microinjection of ephrinA5-Fc before a hyperinsulinemic hypoglycemic clamp study caused a reduction in the glucose infusion rate in nondiabetic rats exposed to recurrent hypoglycemia. The increase in the counterregulatory response to insulin-induced hypoglycemia was associated with a 150% increase in glucagon release (P < 0.001). These data suggest that changes in ephrinA5/EphA5 interactions and synaptic plasticity within the VMH, a key glucose-sensing region in the brain, may contribute to the impairment in glucagon secretion and counterregulatory responses caused by recurrent hypoglycemia.
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Affiliation(s)
- Barbara Szepietowska
- Yale University School of Medicine, Department of Internal Medicine and Endocrinology, New Haven, CT
| | - Tamas L. Horvath
- Program in Integrative Cell Signaling and Neurobiology of Metabolism, Section of Comparative Medicine, Yale University School of Medicine, New Haven, CT
| | - Robert S. Sherwin
- Yale University School of Medicine, Department of Internal Medicine and Endocrinology, New Haven, CT
- Corresponding author: Robert S. Sherwin,
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Chan O, Sherwin R. Influence of VMH fuel sensing on hypoglycemic responses. Trends Endocrinol Metab 2013; 24:616-24. [PMID: 24063974 PMCID: PMC3909530 DOI: 10.1016/j.tem.2013.08.005] [Citation(s) in RCA: 61] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/28/2013] [Revised: 08/20/2013] [Accepted: 08/27/2013] [Indexed: 12/12/2022]
Abstract
Hypoglycemia produces complex neural and hormonal responses that restore glucose levels to normal. Glucose, metabolic substrates and their transporters, neuropeptides and neurotransmitters alter the firing rate of glucose-sensing neurons in the ventromedial hypothalamus (VMH); these monitor energy status and regulate the release of neurotransmitters that instigate a suitable counter-regulatory response. Under normal physiological conditions, these mechanisms maintain blood glucose concentrations within narrow margins. However, antecedent hypoglycemia and diabetes can lead to adaptations within the brain that impair counter-regulatory responses. Clearly, the mechanisms employed to detect and regulate the response to hypoglycemia, and the pathophysiology of defective counter-regulation in diabetes, are complex and need to be elucidated to permit the development of therapies that prevent or reduce the risk of hypoglycemia.
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Affiliation(s)
- Owen Chan
- Yale University School of Medicine, Department of Internal Medicine - Section of Endocrinology, New Haven, CT, 06520 U.S.A
| | - Robert Sherwin
- Yale University School of Medicine, Department of Internal Medicine - Section of Endocrinology, New Haven, CT, 06520 U.S.A
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