Biology subjects

Pye, K. R.

Publications and source records attributed to Pye, K. R..

3 recordsLinked to original sources

bioRxiv2023

Regulation of astrocyte metabolism by mitochondrial translocator protein 18kDa

The mitochondrial translocator protein 18kDa (TSPO) has been linked to a variety of functions from steroidogenesis to regulation of cellular metabolism and is an attractive therapeutic target for chronic CNS inflammation. Studies in the periphery using Leydig cells and hepatocytes, as well as work in microglia, indicate that the function of TSPO may vary between cells depending on their specialised roles. Astrocytes are critical for providing trophic and metabolic support in the brain as part of their role in maintaining brain homeostasis. Recent work has highlighted that TSPO expression increases in astrocytes under inflamed conditions and may drive astrocyte reactivity. However, relatively little is known about the role TSPO plays in regulating astrocyte metabolism and whether this protein is involved in immunometabolic processes in these cells. Using TSPO-deficient (TSPO-/-) mouse primary astrocytes in vitro (MPAs) and a human astrocytoma cell line (U373 cells), we performed metabolic flux analyses. We found that loss of TSPO reduced basal astrocyte respiration and increased the bioenergetic response to glucose reintroduction following glucopenia, while increasing fatty acid oxidation (FAO). Lactate production was significantly reduced in TSPO-/- astrocytes. Co-immunoprecipitation studies in U373 cells revealed that TSPO forms a complex with carnitine palmitoyltransferase 1a, which presents a mechanism wherein TSPO may regulate FAO in astrocytes. Compared to TSPO+/+ cells, inflammation induced by 3h lipopolysaccharide (LPS) stimulation of TSPO-/- MPAs revealed attenuated tumour necrosis factor release, which was enhanced in TSPO-/- MPAs at 24h LPS stimulation. Together these data suggest that while TSPO acts as a regulator of metabolic flexibility in astrocytes, loss of TSPO does not appear to modulate the metabolic response of astrocytes to inflammation, at least in response to the stimulus/time course used in this study.

neuroscience↗

bioRxiv2021

Astrocytes in the dorsal vagal complex are not activated by systemic glucoprivation and their chemogenetic activation does not elicit homeostatic glucoregulatory responses in mice

The dorsal vagal complex (DVC) is a brainstem site regulating diverse aspects of physiology including food intake and blood glucose homeostasis. Astrocytes are purported to play an active role in regulating DVC function and, by extension, physiological parameters. Previous work has demonstrated that DVC astrocytes directly sense hormones that regulate food intake and blood glucose and are critical for their effect. In addition, DVC astrocytes in ex vivo slices respond to low tissue glucose. The response of neurons, including catecholaminergic neurons, to low glucose is conditional on intact astrocyte signalling in slice preparations suggesting astrocytes are possibly the primary sensors of glucose deprivation (glucoprivation). Based on these findings we hypothesised that if DVC astrocytes act as glucoprivation sensors in vivo they would both show a response to systemic glucoprivation and drive physiological responses to restore blood glucose. We found that 2 hours of systemic glucoprivation induced neither FOS nor glial fibrillary acidic protein (GFAP)-immunoreactivity in DVC astrocytes, specifically those in the nucleus of the solitary tract (NTS). Furthermore, we found that while chemogenetic activation of DVC astrocytes suppressed food intake by reducing both meal size and meal number, this manipulation also suppressed food intake under conditions of glucoprivation. Chemogenetic activation of DVC astrocytes did not increase basal blood glucose nor protect against insulin-induced hypoglycaemia. In male mice chemogenetic DVC astrocyte activation did not alter glucose tolerance, in female mice the initial glucose excursion was reduced, suggesting enhanced glucose absorption. Taken together this suggests that as a whole-population DVC astrocytes do not function as glucoprivation sensors in vivo in mice. Instead, we propose that DVC astrocytes play an indispensable, homeostatic role to maintain the function of glucoregulatory neuronal circuitry.

neuroscience↗

bioRxiv2019

Brain permeable AMPK activator R481 raises glycemia by autonomic nervous system activation and amplifies the counterregulatory response to hypoglycemia in rats

AMP-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.

neuroscience↗