Publications by year
In Press
Weightman Potter P, Vlachaki Walker J, Robb J, Chilton J, Williamson R, Randall A, Ellacott K, Beall C (In Press). Basal fatty acid oxidation increases after recurrent low glucose in human primary astrocytes.
Diabetologia Full text.
Cruz AM, Malekizadeh Y, Vlachaki Walker JM, Weightman Potter PG, Pye K, Shaw SJ, Ellacott KLJ, Beall C (In Press). Brain permeable AMPK activator R481 raises glycemia by autonomic nervous system activation and amplifies the counterregulatory response to hypoglycemia in rats.
Abstract:
Brain permeable AMPK activator R481 raises glycemia by autonomic nervous system activation and amplifies the counterregulatory response to hypoglycemia in rats
ABSTRACTAMP-activated protein kinase (AMPK) is a critical cellular and whole body energy sensor activated by energy stress, including hypoglycemia, which is frequently experienced by people with diabetes. Previous studies using direct delivery of an AMPK activator to the ventromedial hypothalamus (VMH) in rodents increased hepatic glucose production. Moreover, recurrent glucoprivation in the hypothalamus leads to blunted AMPK activation and defective hormonal responses to subsequent hypoglycemia. These data suggest that amplifying AMPK activation may prevent or reduce frequency hypoglycemia in diabetes. We used a novel brain-permeable AMPK activator, R481, which potently increased AMPK phosphorylation in vitro. R481 significantly increased peak glucose levels during glucose tolerance tests in rats, which were attenuated by treatment with AMPK inhibitor SBI-0206965 and completely abolished by blockade of the autonomic nervous system. This occurred without altering insulin sensitivity measured by hyperinsulinemic-euglycemic clamps. Endogenous insulin secretion was not altered by R481 treatment. During hyperinsulinemic-hypoglycemic clamp studies, R481 treatment reduced exogenous glucose requirements and amplified peak glucagon levels during hypoglycemia. These data demonstrate that peripheral administration of the brain permeable AMPK activator R481 amplifies the counterregulatory response to hypoglycemia in rats, which could have clinical relevance for prevention of hypoglycemia.
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Weightman Potter PG, Walker JMV, Robb JL, Chilton JK, Williamson R, Randall A, Ellacott KLJ, Beall C (In Press). Human primary astrocytes increase basal fatty acid oxidation following recurrent low glucose to maintain intracellular nucleotide levels.
Abstract:
Human primary astrocytes increase basal fatty acid oxidation following recurrent low glucose to maintain intracellular nucleotide levels
ABSTRACTHypoglycemia is a major barrier to good glucose control in type 1 diabetes and frequent exposure to hypoglycemia can impair awareness to subsequent bouts of hypoglycemia. The neural changes that occur to reduce a person’s awareness of hypoglycemia are poorly defined. Moreover, the molecular mechanisms by which glial cells contribute to hypoglycemia sensing and glucose counterregulation require further investigation. To test whether glia, specifically astrocytes, could detect changes in glucose, we utilized human primary astrocytes (HPA) and U373 astrocytoma cells and exposed them to recurrent low glucose (RLG) in vitro. This allowed measurement, with high specificity and sensitivity, of changes in cellular metabolism following RLG. We report that the AMP-activated protein kinase (AMPK) is activated over a pathophysiologically-relevant glucose concentration range. We observed an increased dependency on fatty acid oxidation for basal mitochondrial metabolism and hallmarks of mitochondrial stress including increased proton leak and reduced coupling efficiency. Relative to glucose availability, lactate release increased during low glucose but this was not modified by RLG, nor were glucose uptake or glycogen levels. Taken together, these data indicate that astrocyte mitochondria are dysfunctional following recurrent low glucose exposure, which could have implications for hypoglycemia glucose counterregulation and/or hypoglycemia awareness.
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2019
Cruz AM, Malekizadeh Y, Walker JMV, Shaw S, Ellacott KLJ, Beall C (2019). AMP-activated protein kinase (AMPK) activator R481 improves the counterregulatory response to hypoglycaemia by amplifying glucagon release in healthy rats.
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Cruz AML, Malekizadeh Y, Vlachaki Walker J, Ellacott K, Shaw S, Beall C (2019). Amplified Glucagon Response to Hypoglycemia following AMP-Activated Protein Kinase (AMPK) Activator R481 Treatment in Healthy Rats. American Diabetes Association. 7th - 11th Jun 2019.
Abstract:
Amplified Glucagon Response to Hypoglycemia following AMP-Activated Protein Kinase (AMPK) Activator R481 Treatment in Healthy Rats
Abstract.
MacDonald AJ, Robb JL, Morrissey NA, Beall C, Ellacott KLJ (2019). Astrocytes in neuroendocrine systems: an overview.
J Neuroendocrinol,
31(5).
Abstract:
Astrocytes in neuroendocrine systems: an overview.
A class of glial cell, astrocytes, is highly abundant in the central nervous system (CNS). In addition to maintaining tissue homeostasis, astrocytes regulate neuronal communication and synaptic plasticity. There is an ever-increasing appreciation that astrocytes are involved in the regulation of physiology and behaviour in normal and pathological states, including within neuroendocrine systems. Indeed, astrocytes are direct targets of hormone action in the CNS, via receptors expressed on their surface, and are also a source of regulatory neuropeptides, neurotransmitters and gliotransmitters. Furthermore, as part of the neurovascular unit, astrocytes can regulate hormone entry into the CNS. This review is intended to provide an overview of how astrocytes are impacted by and contribute to the regulation of a diverse range of neuroendocrine systems: energy homeostasis and metabolism, reproduction, fluid homeostasis, the stress response and circadian rhythms.
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Weightman Potter P (2019). The impact of glucose variation on human astrocytes.
Abstract:
The impact of glucose variation on human astrocytes
Diabetes is a metabolic disorder dysregulating glucose homeostasis. The role of astrocytes in central glucose sensing is poorly understood. But it is recognised they take part in whole-body energy homeostasis, specifically as glucose sensors necessary for the counterregulatory response (CRR) to hypoglycaemia. Iatrogenic hypoglycaemia is the limiting factor to glycaemic control in people with type 1 or type 2 diabetes. Severe hypoglycaemia occurs approximately once per year, whereas, the incidence of minor hypoglycaemia is much greater. Hypoglycaemia impairs awareness of future hypoglycaemia and blunts the CRR, eventually causing hypoglycaemia-associated autonomic failure. The mechanisms of this process are poorly understood.
This thesis utilised isolated human astrocytes exposed to acute or recurrent low glucose (RLG) in vitro to mimic glucose variation in diabetes. Cellular responses were characterised of three key astrocyte functions. Firstly, is astrocyte metabolism altered by acute and RLG treatment? Secondly, do isolated human astrocytes become activated by low glucose treatment, and is this affected by RLG? Thirdly, are astrocytic inflammatory pathways altered by acute or RLG?
The key findings from this thesis shows for the first time that astrocytic mitochondrial oxidation is increased following RLG, with a concurrent increase in fatty acid dependency but decreased coupling efficiency; glycolytic function is also enhanced. Together, this indicates that astrocytes successfully adapt to low glucose to sustain intracellular nucleotide ratios. Contrary to previous work, these human astrocytes do not respond to low glucose by Ca2+-dependent activation. However, the astrocytes do increase inflammatory cytokine release following acute and RLG. Lastly, for the first time an RNA-sequencing approach has been used to identify low glucose-induced differential gene expression. Together these findings support the argument that astrocytes are sensitive to low glucose and may be important in glucose sensation and the CRR.
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2018
Hall BC, Beall C, Randall AD (2018). Alzheimer's disease drug Memantine inhibits Adenosine triphosphate (ATP)-sensitive potassium (KATP) channel activation in hypothalamic GT1-7 cells.
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Logie L, Beall C, Rena G (2018). Effect of metformin but not AICAR on total adenosine triphosphate (ATP) levels in primary hepatocytes.
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Potter PGW, Walker JMV, Robb JL, Chilton J, Williamson R, Randall A, Ellacott KLJ, Beall C (2018). Recurrent hypoglycaemia increases human primary astrocyte oxygen consumption, fatty acid dependency and pentose phosphate pathway activity.
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Logie L, Lees Z, Allwood JW, McDougal G, Beall C, Rena G (2018). Regulation of hepatic glucose production and AMPK by AICAR but not metformin depends on drug uptake through the equilibrative nucleoside transporter 1 (ENT1).
Diabetes, Obesity and Metabolism,
(In press) Full text.
Robb J, Hammad N, Beall C, Ellacott K (2018). The 18-kDa translocator protein (TSPO) regulates cellular metabolism in astrocytes.
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2017
Vlachaki Walker JM, Robb JL, Cruz AM, Malhi A, Weightman Potter PG, Ashford MLJ, McCrimmon RJ, Ellacott KLJ, Beall C (2017). AMP-activated protein kinase (AMPK) activator A-769662 increases intracellular calcium and ATP release from astrocytes in an AMPK-independent manner.
Diabetes, Obesity and Metabolism,
19(7), 997-1005.
Abstract:
AMP-activated protein kinase (AMPK) activator A-769662 increases intracellular calcium and ATP release from astrocytes in an AMPK-independent manner
© 2017 John Wiley. &. Sons Ltd Aim: to test the hypothesis that, given the role of AMP-activated protein kinase (AMPK) in regulating intracellular ATP levels, AMPK may alter ATP release from astrocytes, the main sources of extracellular ATP (eATP) within the brain. Materials and Methods: Measurements of ATP release were made from human U373 astrocytoma cells, primary mouse hypothalamic (HTAS) and cortical astrocytes (CRTAS) and wild-type and AMPK α1/α2 null mouse embryonic fibroblasts (MEFs). Cells were treated with drugs known to modulate AMPK activity: A-769662, AICAR and metformin, for up to 3 hours. Intracellular calcium was measured using Fluo4 and Fura-2 calcium-sensitive fluorescent dyes. Results: in U373 cells, A-769662 (100 μM) increased AMPK phosphorylation, whereas AICAR and metformin (1 mM) induced a modest increase or had no effect, respectively. Only A-769662 increased eATP levels, and this was partially blocked by AMPK inhibitor Compound C. A-769662-induced increases in eATP were preserved in AMPK α1/α2 null MEF cells. A-769662 increased intracellular calcium in U373, HTAS and CRTAS cells and chelation of intracellular calcium using BAPTA-AM reduced A-769662-induced eATP levels. A-769662 also increased ATP release from a number of other central and peripheral endocrine cell types. Conclusions: AMPK is required to maintain basal eATP levels but is not required for A-769662-induced increases in eATP. A-769662 (>50 μM) enhanced intracellular calcium levels leading to ATP release in an AMPK and purinergic receptor independent pathway.
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Walker JMV, Potter PGW, Somes A, Beall C (2017). Altered adenosine triphosphate (ATP)-induced calcium responses in glucosensing GT1-7 neurons during hypoglycaemia and in astrocytes following recurrent hypoglycaemia.
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Beall C, Hanna L, Ellacott KLJ (2017). CNS Targets of Adipokines.
Compr Physiol,
7(4), 1359-1406.
Abstract:
CNS Targets of Adipokines.
Our understanding of adipose tissue as an endocrine organ has been transformed over the last 20 years. During this time, a number of adipocyte-derived factors or adipokines have been identified. This article will review evidence for how adipokines acting via the central nervous system (CNS) regulate normal physiology and disease pathology. The reported CNS-mediated effects of adipokines are varied and include the regulation of energy homeostasis, autonomic nervous system activity, the reproductive axis, neurodevelopment, cardiovascular function, and cognition. Due to the wealth of information available and the diversity of their known functions, the archetypal adipokines leptin and adiponectin will be focused on extensively. Other adipokines with established CNS actions will also be discussed. Due to the difficulties associated with studying CNS function on a molecular level in humans, the majority of our knowledge, and as such the studies described in this paper, comes from work in experimental animal models; however, where possible the relevant data from human studies are also highlighted. © 2017 American Physiological Society. Compr Physiol 7:1359-1406, 2017.
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Walker JMV, Potter PGW, Robb J, Ellacott KLJ, Beall C (2017). Exposure of Astrocytes to Recurrent Hypoglycemia in Vitro Alters Gliotransmission and Purinergic Signaling.
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Potter PGW, Cruz JMV, Cruz AM, Williamson R, Randall A, Beall C (2017). Human astrocytes are altered following chronic glucose variation: differential regulation of cytokine release and increased basal metabolism.
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Beall C, Dadak S, Walker JMV, Soutar MPM, McCrimmon RJ, Ashford MLJ (2017). Oleate induces ATP-sensitive channel (K-ATP)-dependent hyperpolarisation of mouse hypothalamic glucose-excited neurons without altering cellular energy charge.
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Dadak S, Beall C, Vlachaki Walker JM, Soutar MPM, McCrimmon RJ, Ashford MLJ (2017). Oleate induces K ATP channel-dependent hyperpolarization in mouse hypothalamic glucose-excited neurons without altering cellular energy charge.
Neuroscience,
346, 29-42.
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Logie L, Beall C, Rena G (2017). Repression of hepatic glucose production by 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR) is inhibited by 8-CPT-cAMP mediated blockade of equilibrative nucleotide transporter 1 (ENT1).
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Jeffery N, Richardson S, Beall C, Harries LW (2017). The species origin of the cellular microenvironment influences markers of beta cell fate and function in EndoC-βH1 cells.
Experimental Cell Research,
361(2), 284-291.
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2016
Walker JMV, Malhi A, Hardy H, Chilton J, Beall C (2016). A769662 regulates intracellular calcium and extracellular ATP independent of AMPK.
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Cameron AR, Morrison VL, Levin D, Mohan M, Forteath C, Beall C, McNeilly AD, Balfour DJK, Savinko T, Wong AKF, et al (2016). Anti-Inflammatory Effects of Metformin Irrespective of Diabetes Status.
Circ Res,
119(5), 652-665.
Abstract:
Anti-Inflammatory Effects of Metformin Irrespective of Diabetes Status.
RATIONALE: the diabetes mellitus drug metformin is under investigation in cardiovascular disease, but the molecular mechanisms underlying possible benefits are poorly understood. OBJECTIVE: Here, we have studied anti-inflammatory effects of the drug and their relationship to antihyperglycemic properties. METHODS AND RESULTS: in primary hepatocytes from healthy animals, metformin and the IKKβ (inhibitor of kappa B kinase) inhibitor BI605906 both inhibited tumor necrosis factor-α-dependent IκB degradation and expression of proinflammatory mediators interleukin-6, interleukin-1β, and CXCL1/2 (C-X-C motif ligand 1/2). Metformin suppressed IKKα/β activation, an effect that could be separated from some metabolic actions, in that BI605906 did not mimic effects of metformin on lipogenic gene expression, glucose production, and AMP-activated protein kinase activation. Equally AMP-activated protein kinase was not required either for mitochondrial suppression of IκB degradation. Consistent with discrete anti-inflammatory actions, in macrophages, metformin specifically blunted secretion of proinflammatory cytokines, without inhibiting M1/M2 differentiation or activation. In a large treatment naive diabetes mellitus population cohort, we observed differences in the systemic inflammation marker, neutrophil to lymphocyte ratio, after incident treatment with either metformin or sulfonylurea monotherapy. Compared with sulfonylurea exposure, metformin reduced the mean log-transformed neutrophil to lymphocyte ratio after 8 to 16 months by 0.09 U (95% confidence interval, 0.02-0.17; P=0.013) and increased the likelihood that neutrophil to lymphocyte ratio would be lower than baseline after 8 to 16 months (odds ratio, 1.83; 95% confidence interval, 1.22-2.75; P=0.00364). Following up these findings in a double-blind placebo controlled trial in nondiabetic heart failure (trial registration: NCT00473876), metformin suppressed plasma cytokines including the aging-associated cytokine CCL11 (C-C motif chemokine ligand 11). CONCLUSION: We conclude that anti-inflammatory properties of metformin are exerted irrespective of diabetes mellitus status. This may accelerate investigation of drug utility in nondiabetic cardiovascular disease groups. CLINICAL TRIAL REGISTRATION: Name of the trial registry: TAYSIDE trial (Metformin in Insulin Resistant Left Ventricular [LV] Dysfunction). URL: https://www.clinicaltrials.gov. Unique identifier: NCT00473876.
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Yavari A, Stocker CJ, Ghaffari S, Wargent ET, Steeples V, Czibik G, Pinter K, Bellahcene M, Woods A, Martínez de Morentin PB, et al (2016). Chronic Activation of γ2 AMPK Induces Obesity and Reduces β Cell Function.
Cell Metab,
23(5), 821-836.
Abstract:
Chronic Activation of γ2 AMPK Induces Obesity and Reduces β Cell Function.
Despite significant advances in our understanding of the biology determining systemic energy homeostasis, the treatment of obesity remains a medical challenge. Activation of AMP-activated protein kinase (AMPK) has been proposed as an attractive strategy for the treatment of obesity and its complications. AMPK is a conserved, ubiquitously expressed, heterotrimeric serine/threonine kinase whose short-term activation has multiple beneficial metabolic effects. Whether these translate into long-term benefits for obesity and its complications is unknown. Here, we observe that mice with chronic AMPK activation, resulting from mutation of the AMPK γ2 subunit, exhibit ghrelin signaling-dependent hyperphagia, obesity, and impaired pancreatic islet insulin secretion. Humans bearing the homologous mutation manifest a congruent phenotype. Our studies highlight that long-term AMPK activation throughout all tissues can have adverse metabolic consequences, with implications for pharmacological strategies seeking to chronically activate AMPK systemically to treat metabolic disease.
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Haythorne E, Hamilton DL, Findlay JA, Beall C, McCrimmon RJ, Ashford MLJ (2016). Chronic exposure to KATP channel openers results in attenuated glucose sensing in hypothalamic GT1-7 neurons.
Neuropharmacology,
111, 212-222.
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Walker JV, Ashford MLJ, McCrimmon RJ, Beall C (2016). Exposure of astrocytes to recurrent low glucose delays AMPK phosphorylation and alters ATP and lactate release.
DIABETIC MEDICINE,
33, 54-54.
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2015
Beall C, Walker JMV, Ashford MLJ, McCrimmon RJ (2015). A critical role for AMP-activated protein kinase in regulation of gliotransmitter release from astrocytes.
DIABETIC MEDICINE,
32, 62-62.
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Cameron AR, Morrison V, McNeilly AD, Forteath C, Beall C, Stewart CA, Balfour DJK, Sutherland CD, Sakamoto K, Fagerholm SC, et al (2015). Anti-inflammatory effects of metformin.
DIABETIC MEDICINE,
32, 54-55.
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Cameron A, Forteath C, Beall C, Rena G (2015). Anti-inflammatory effects of metformin and their relationship to the therapeutic action of the drug. Endocrine Abstracts
Walker JV, Ashford M, McCrimmon R, Beall C (2015). Characterisation of the astrocytic response to acute and recurrent hypoglycaemia. Endocrine Abstracts
Walker JMV, Gabriel J, Ashford MLJ, McCrimmon RJ, Beall C (2015). Modulation of astrocytic lactate release during hypoglycaemia by AMP-activated protein kinase and noradrenaline.
DIABETIC MEDICINE,
32, 62-63.
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2014
Hamilton DL, Beall C, Jeromson S, Chevtzoff C, Cuthbertson DJ, Ashford MLJ (2014). Kv1.3 inhibitors have differential effects on glucose uptake and AMPK activity in skeletal muscle cell lines and mouse ex vivo skeletal muscle.
J Physiol Sci,
64(1), 13-20.
Abstract:
Kv1.3 inhibitors have differential effects on glucose uptake and AMPK activity in skeletal muscle cell lines and mouse ex vivo skeletal muscle.
Knockout of Kv1.3 improves glucose homeostasis and confers resistance to obesity. Additionally, Kv1.3 inhibition enhances glucose uptake. This is thought to occur through calcium release. Kv1.3 inhibition in T-lymphocytes alters mitochondrial membrane potential, and, as many agents that induce Ca(2+) release or inhibit mitochondrial function activate AMPK, we hypothesised that Kv1.3 inhibition would activate AMPK and increase glucose uptake. We screened cultured muscle with a range of Kv1.3 inhibitors for their ability to alter glucose uptake. Only Psora4 increased glucose uptake in C2C12 myotubes. None of the inhibitors had any impact on L6 myotubes. Magratoxin activated AMPK in C2C12 myotubes and only Pap1 activated AMPK in the SOL. Kv1.3 inhibitors did not alter cellular respiration, indicating a lack of effect on mitochondrial function. In conclusion, AMPK does not mediate the effects of Kv1.3 inhibitors and they display differential effects in different skeletal muscle cell lines without impairing mitochondrial function.
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2013
Beall C, Watterson KR, McCrimmon RJ, Ashford MLJ (2013). AMPK modulates glucose-sensing in insulin-secreting cells by altered phosphotransfer to KATP channels.
J Bioenerg Biomembr,
45(3), 229-241.
Abstract:
AMPK modulates glucose-sensing in insulin-secreting cells by altered phosphotransfer to KATP channels.
Glucose-sensing (GS) behaviour in pancreatic β-cells is dependent on ATP-sensitive K(+) channel (KATP) activity, which is controlled by the relative levels of the KATP ligands ATP and ADP, responsible for closing and opening KATP, respectively. However, the mechanism by which β-cells transfer energy status from mitochondria to KATP, and hence to altered electrical excitability and insulin secretion, is presently unclear. Recent work has demonstrated a critical role for AMP-activated protein kinase (AMPK) in GS behaviour of cells. Electrophysiological recordings, coupled with measurements of gene and protein expression were made from rat insulinoma cells to investigate whether AMPK activity regulates this energy transfer process. Using the whole-cell recording configuration with sufficient intracellular ATP to keep KATP closed, raised AMPK activity induced GS electrical behaviour. This effect was prevented by the AMPK inhibitor, compound C and required a phosphotransfer process. Indeed, high levels of intracellular phosphocreatine or the presence of the adenylate kinase (AK) inhibitor AP5A blocked this action of AMPK. Using conditions that maximised AMPK-induced KATP opening, there was a significant increase in AK1, AK2 and UCP2 mRNA expression. Thus we propose that KATP opening in response to lowered glucose concentration requires AMPK activity, perhaps in concert with increased AK and UCP2 to enable mitochondrial-derived ADP signals to be transferred to plasma membrane KATP by phosphotransfer cascades.
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Beall C, Haythorne E, Fan X, Du Q, Jovanovic S, Sherwin RS, Ashford MLJ, McCrimmon RJ (2013). Continuous hypothalamic K(ATP) activation blunts glucose counter-regulation in vivo in rats and suppresses K(ATP) conductance in vitro.
Diabetologia,
56(9), 2088-2092.
Abstract:
Continuous hypothalamic K(ATP) activation blunts glucose counter-regulation in vivo in rats and suppresses K(ATP) conductance in vitro.
AIMS/HYPOTHESIS: Acute systemic delivery of the sulfonylurea receptor (SUR)-1-specific ATP-sensitive K(+) channel (K(ATP)) opener, NN414, has been reported to amplify glucose counter-regulatory responses (CRRs) in rats exposed to hypoglycaemia. Thus, we determined whether continuous NN414 could prevent hypoglycaemia-induced defective counter-regulation. METHODS: Chronically catheterised male Sprague-Dawley rats received a continuous infusion of NN414 into the third ventricle for 8 days after implantation of osmotic minipumps. Counter-regulation was examined by hyperinsulinaemic-hypoglycaemic clamp on day 8 after three episodes of insulin-induced hypoglycaemia (recurrent hypoglycaemia [RH]) on days 5, 6 and 7. In a subset of rats exposed to RH, NN414 infusion was terminated on day 7 to wash out NN414 before examination of counter-regulation on day 8. To determine whether continuous NN414 exposure altered K(ATP) function, we used the hypothalamic glucose-sensing GT1-7 cell line, which expresses the SUR-1-containing K(ATP) channel. RESULTS: Continuous exposure to NN414 in the setting of RH increased, rather than decreased, the glucose infusion rate (GIR), as exemplified by attenuated adrenaline (epinephrine) secretion. Termination of NN414 on day 7 with subsequent washout for 24 h partially diminished the GIR. The same duration of exposure of GT1-7 cells to NN414 substantially reduced K(ATP) conductance, which was also reversed on washout of the agonist. The suppression of K(ATP) current was not associated with reduced channel subunit mRNA or protein levels. CONCLUSIONS/INTERPRETATION: These data indicate that continuous K(ATP) activation results in suppressed CRRs to hypoglycaemia in vivo, which in vitro is associated with the reversible conversion of KATP into a stable inactive state.
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2012
Ashford M, Beall C, McCrimmon R (2012). Hypoglycaemia: exercise for the brain?.
J Neuroendocrinol,
24(10), 1365-1366.
Abstract:
Hypoglycaemia: exercise for the brain?
Low blood sugar, or hypoglycaemia, is detected by specialised sugar sensing neurones in the brain. However, the detection of hypoglycaemia is blunted after repeated hypoglycaemia and this is a result of adaptive mechanisms kicking in within the brain; mechanisms that resemble the 'training effect' in muscle. These adaptations most likely not only increase the tolerance of the brain to stress, but also perturb the detection of hypoglycaemia, further increasing the likelihood of hypoglycaemia.
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Beall C, Hamilton DL, Gallagher J, Logie L, Wright K, Soutar MP, Dadak S, Ashford FB, Haythorne E, Du Q, et al (2012). Mouse hypothalamic GT1-7 cells demonstrate AMPK-dependent intrinsic glucose-sensing behaviour.
Diabetologia,
55(9), 2432-2444.
Abstract:
Mouse hypothalamic GT1-7 cells demonstrate AMPK-dependent intrinsic glucose-sensing behaviour.
AIMS/HYPOTHESIS: Hypothalamic glucose-excited (GE) neurons contribute to whole-body glucose homeostasis and participate in the detection of hypoglycaemia. This system appears defective in type 1 diabetes, in which hypoglycaemia commonly occurs. Unfortunately, it is at present unclear which molecular components required for glucose sensing are produced in individual neurons and how these are functionally linked. We used the GT1-7 mouse hypothalamic cell line to address these issues. METHODS: Electrophysiological recordings, coupled with measurements of gene expression and protein levels and activity, were made from unmodified GT1-7 cells and cells in which AMP-activated protein kinase (AMPK) catalytic subunit gene expression and activity were reduced. RESULTS: Hypothalamic GT1-7 neurons express the genes encoding glucokinase and ATP-sensitive K(+) channel (K(ATP)) subunits K. (. ir. ). 6.2 and Sur1 and exhibit GE-type glucose-sensing behaviour. Lowered extracellular glucose concentration hyperpolarised the cells in a concentration-dependent manner, an outcome that was reversed by tolbutamide. Inhibition of glucose uptake or metabolism hyperpolarised cells, showing that energy metabolism is required to maintain their resting membrane potential. Short hairpin (sh)RNA directed to Ampkα2 (also known as Prkaa2) reduced GT1-7 cell AMPKα2, but not AMPKα1, activity and lowered the threshold for hypoglycaemia-induced hyperpolarisation. shAmpkα1 (also known as Prkaa1) had no effect on glucose-sensing or AMPKα2 activity. Decreased uncoupling protein 2 (Ucp2) mRNA was detected in AMPKα2-reduced cells, suggesting that AMPKα2 regulates UCP2 levels. CONCLUSIONS/INTERPRETATION: We have demonstrated that GT1-7 cells closely mimic GE neuron glucose-sensing behaviour, and reducing AMPKα2 blunts their responsiveness to hypoglycaemic challenge, possibly by altering UCP2 activity. These results show that suppression of AMPKα2 activity inhibits normal glucose-sensing behaviour and may contribute to defective detection of hypoglycaemia.
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Beall C, Ashford ML, McCrimmon RJ (2012). The physiology and pathophysiology of the neural control of the counterregulatory response.
Am J Physiol Regul Integr Comp Physiol,
302(2), R215-R223.
Abstract:
The physiology and pathophysiology of the neural control of the counterregulatory response.
Despite significant technological and pharmacological advancements, insulin replacement therapy fails to adequately replicate β-cell function, and so glucose control in type 1 diabetes mellitus (T1D) is frequently erratic, leading to periods of hypoglycemia. Moreover, the counterregulatory response (CRR) to falling blood glucose is impaired in diabetes, leading to an increased risk of severe hypoglycemia. It is now clear that the brain plays a significant role in the development of defective glucose counterregulation and impaired hypoglycemia awareness in diabetes. In this review, the basic intracellular glucose-sensing mechanisms are discussed, as well as the neural networks that respond to and coordinate the body's response to a hypoglycemic challenge. Subsequently, we discuss how the body responds to repeated hypoglycemia and how these adaptations may explain, at least in part, the development of impaired glucose counterregulation in diabetes.
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2010
Piipari K, Beall C, Al-Qassab H, Smith MA, Carling D, Viollet B, Ashford MLJ, Withers DJ (2010). Key Role of AMP-Activated Protein Kinase in Pancreatic Beta Cell Glucose-Sensing and Whole Body Glucose Homeostasis.
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Beall C, Piipari K, Al-Qassab H, Smith MA, Parker N, Carling D, Viollet B, Withers DJ, Ashford MLJ (2010). Loss of AMP-activated protein kinase alpha2 subunit in mouse beta-cells impairs glucose-stimulated insulin secretion and inhibits their sensitivity to hypoglycaemia.
Biochem J,
429(2), 323-333.
Abstract:
Loss of AMP-activated protein kinase alpha2 subunit in mouse beta-cells impairs glucose-stimulated insulin secretion and inhibits their sensitivity to hypoglycaemia.
AMPK (AMP-activated protein kinase) signalling plays a key role in whole-body energy homoeostasis, although its precise role in pancreatic beta-cell function remains unclear. In the present study, we therefore investigated whether AMPK plays a critical function in beta-cell glucose sensing and is required for the maintenance of normal glucose homoeostasis. Mice lacking AMPK alpha2 in beta-cells and a population of hypothalamic neurons (RIPCre alpha2KO mice) and RIPCre alpha2KO mice lacking AMPK alpha1 (alpha1KORIPCre alpha2KO) globally were assessed for whole-body glucose homoeostasis and insulin secretion. Isolated pancreatic islets from these mice were assessed for glucose-stimulated insulin secretion and gene expression changes. Cultured beta-cells were examined electrophysiologically for their electrical responsiveness to hypoglycaemia. RIPCre alpha2KO mice exhibited glucose intolerance and impaired GSIS (glucose-stimulated insulin secretion) and this was exacerbated in alpha1KORIPCre alpha2KO mice. Reduced glucose concentrations failed to completely suppress insulin secretion in islets from RIPCre alpha2KO and alpha1KORIPCre alpha2KO mice, and conversely GSIS was impaired. Beta-cells lacking AMPK alpha2 or expressing a kinase-dead AMPK alpha2 failed to hyperpolarize in response to low glucose, although KATP (ATP-sensitive potassium) channel function was intact. We could detect no alteration of GLUT2 (glucose transporter 2), glucose uptake or glucokinase that could explain this glucose insensitivity. UCP2 (uncoupling protein 2) expression was reduced in RIPCre alpha2KO islets and the UCP2 inhibitor genipin suppressed low-glucose-mediated wild-type mouse beta-cell hyperpolarization, mimicking the effect of AMPK alpha2 loss. These results show that AMPK alpha2 activity is necessary to maintain normal pancreatic beta-cell glucose sensing, possibly by maintaining high beta-cell levels of UCP2.
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