Biology subjects

Robb, J. L.

Publications and source records attributed to Robb, J. L..

7 recordsLinked to original sources

bioRxiv2026

Lipid droplet lipolysis in POMC neurons regulates energy homeostasis in a sex-specific manner

The hypothalamus is a central regulator of glucose and energy homeostasis, with arcuate nucleus (ARC) neurons orchestrating these processes. Agouti-related peptide (AgRP) and pro-opiomelanocortin (POMC) neurons integrate metabolic cues to control feeding behavior and systemic metabolism. Among these cues, fatty acids (FA) have emerged as key modulators of ARC neuronal activity. While neuronal sensing of circulating FA has begun to be defined, the contribution of FA derived from endogenous lipid stores to ARC neuron function and energy homeostasis remains largely unexplored. We recently identified lipid droplets (LD) as regulated FA reservoirs that control FA availability and metabolism in orexigenic AgRP neurons, thereby modulating their activity and regulating feeding. This prompted us to investigate whether LD-derived FA similarly regulate POMC neuron function. To this end, we targeted adipose triglyceride lipase (ATGL), which catalyzes the first committed step of LD lipolysis, in POMC neurons. We show that LD are present in POMC neurons under basal conditions both in vitro and in vivo, and that pharmacological or genetic inhibition of ATGL increases LD abundance. ATGL deficiency enhances spontaneous firing of POMC neurons and leads to reduced body weight, fat and lean mass in males, but not females. Consistent with enhanced glucose metabolism, ATGL loss lowers glycemia and insulinemia and increases carbohydrate utilization in chow-fed males. In contrast, ATGL deficiency does not alter metabolic adaptations to cold exposure, fasting or diet-induced obesity in either sex. Collectively, these findings establish ATGL-dependent LD lipolysis in POMC neurons as a previously unrecognized, sex-dependent regulator of energy homeostasis.

neuroscience↗

bioRxiv2025

Inhibition of histone lysine demethylase restores learning and memory in aged mice

Chromatin undergoes dramatic changes during the ageing process. In the brain, these chromatin changes are thought to underlie age-associated deficits in the activity-dependent gene transcription necessary for memory consolidation. Here, we show that the levels of a specific histone post-translational modification (PTM), trimethylation of lysine 4 on histone 3 (H3K4me3) is markedly increased in the hippocampus of aged mice and that the activity-induced increase in H3K4me3 that is observed in response to a learning stimulus in young mice, is severely blunted in the aged hippocampus. H3K4me3 typically marks open, accessible chromatin at the transcriptional start sites (TSSs) of actively transcribed genes. We identify altered H3K4me3 peaks at TSSs and show that ca. 90% of the activity-induced H3K4me3 changes at TSSs are either absent or reduced in the aged hippocampus. To understand the biological significance of these age-associated changes, we screened a library of pharmacological compounds for compounds that can alter H3K4me3 levels in hippocampal neurons. We show that treatment of aged mice with one of these, the LSD1 inhibitor ORY-1001, restored normal learning and memory in object location and recognition tasks. Furthermore, we show that ORY-1001 treatment increased long-term potentiation (LTP), a form of synaptic plasticity deficient in the aged hippocampus. These findings suggest that targeting the epigenetic machinery that regulates activity-dependent gene transcription may represent an avenue for treating age-associated cognitive impairment. HighlightsO_LIH3K4me3 levels are elevated in the naive aged mouse hippocampus C_LIO_LIActivity-dependent H3K4me3 induction is impaired in the aged mouse hippocampus C_LIO_LILSD1 inhibition restores learning and memory in aged mice C_LIO_LILSD1 inhibition restores activity-dependent Arc induction and increases LTP in the aged hippocampus C_LI O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=142 SRC="FIGDIR/small/695858v1_ufig1.gif" ALT="Figure 1"> View larger version (39K): org.highwire.dtl.DTLVardef@fccd92org.highwire.dtl.DTLVardef@11c4d93org.highwire.dtl.DTLVardef@128f8b8org.highwire.dtl.DTLVardef@e1341f_HPS_FORMAT_FIGEXP M_FIG C_FIG

neuroscience↗

bioRxiv2025

DGAT1-dependent lipid droplet synthesis in microglia attenuates neuroinflammatory responses to lipopolysaccharides.

Lipid droplets (LD) are dynamic storage organelles for triglycerides (TG). LD act as a hub that modulates the availability of fatty acids to sustain metabolic needs and the generation of fatty-acid derived signals. Recent evidence demonstrates that LD metabolism regulates immune responses including in microglia, the resident immune cells of the central nervous system. We have previously shown that blocking LD lipolysis in microglia reduces acute pro-inflammatory responses to lipopolysaccharide (LPS) including cytokine and prostanoid synthesis. Here, we investigated the role of diacylglycerol O-acyltransferase 1 (DGAT1), a key enzyme catalyzing the final step of TG synthesis, in microglial LD biogenesis and inflammatory responses induced by LPS. We found that treatment with LPS downregulates specific enzymes in the TG synthesis pathway in primary microglia, including GPAT1, AGPAT3, AGPAT5, and DGAT1, while upregulating TMEM68, a non-canonical TG synthesizing enzyme. Pharmacological inhibition of DGAT1 significantly reduced LD formation in both oleate- and LPS-stimulated conditions, indicating that DGAT1 is essential for inflammation-induced LD synthesis. Moreover, DGAT1 inhibition selectively decreased expression of pro-inflammatory cytokines TNF- and IL-1{beta}, without affecting IL-6, CCL2, or the anti-inflammatory cytokine TGF-{beta}. These findings show, that DGAT1-dependent LD formation acts as an important modulator of microglial inflammatory signaling.

neuroscience↗

bioRxiv2023

Microglial adipose triglyceride lipase regulates neuroinflammatory and behavioural responses to LPS

Adipose triglyceride lipase (ATGL), the enzyme that catalyses the rate-limiting step of triglyceride lipolysis, regulates inflammation in peripheral tissues. ATGL has been associated with both pro- and anti-inflammatory responses in different tissues suggesting its actions are dependent on cell type. Recent studies in microglia and macrophages suggest that lipid droplets (LD), a triglyceride storing organelle, and LD lipolysis via ATGL are important components of inflammatory responses. Here, we determined the impact of ATGL inhibition and microglia-specific ATGL loss-of-function on inflammatory and behavioural responses to acute pro-inflammatory insult. First, we evaluated the impact of lipolysis inhibition on lipopolysaccharide (LPS)-induced expression and secretion of cytokines in mouse primary microglia cultures. LPS led to LD accumulation in microglia and altered the expression of lipolysis regulators. The pan-lipase inhibitor ORlistat alleviated LPS-induced expression of IL-1{beta} and IL-6. Specific inhibition of ATGL by ATGListatin had similar anti-inflammatory action on cytokines expression and secretion in both neonatal and adult microglia cultures. Second, targeted and untargeted lipidomic studies revealed that ATGL inhibition reduced LPS-induced generation of pro-inflammatory prostanoids and affected ceramide profile. Finally, the role of ATGL in neuroinflammation was assessed in a novel mouse model with inducible ATGL deletion specifically in microglia. Loss of microglial ATGL in adult male mice dampened LPS-induced expression of IL-6 and reduced LPS-induced sickness behaviour. Together, our results demonstrate that pharmacological inhibition or loss of ATGL-mediated triglyceride lipolysis reduces LPS-induced inflammation to suggest that inhibition of lipolysis plays a beneficial role in neuroinflammation.

neuroscience↗

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↗

bioRxiv2022

Role of astroglial ACBP in energy metabolism flexibility and feeding responses to metabolic challenges in male mice

Acyl-CoA Binding Protein (ACBP), also known as Diazepam Binding Inhibitor (DBI), has recently emerged as a hypothalamic and brainstem gliopeptide regulating energy balance. Previous work has shown that the ACBP-derived octadecaneuropeptide exerts strong anorectic action via POMC neuron activation and the melanocortin-4 receptor. Importantly, targeted ACBP loss-of-function in astrocytes promotes hyperphagia and diet-induced obesity while its overexpression in arcuate astrocytes reduces feeding and body weight. Despite this knowledge, the role of astroglial ACBP in adaptive feeding and metabolic responses to acute metabolic challenges has not been investigated. Using different paradigms, we found that ACBP deletion in Glial Fibrillary Acidic Protein (GFAP)-positive astrocytes does not affect diet-induced weight loss in obese male mice nor metabolic parameters in chow-fed mice (e.g. energy expenditure, body temperature) during fasting, cold exposure and at thermoneutrality. In contrast, astroglial ACBP deletion impairs meal pattern and feeding responses during refeeding after a fast and during cold exposure, thereby showing that ACBP is required to mount an appropriate feeding response in states of increased energy demand. These findings challenge the general view that astroglial ACBP exerts anorectic effects and suggest that regulation of feeding by ACBP is dependent on metabolic status.

physiology↗

bioRxiv2018

Human primary astrocytes increase basal fatty acid oxidation following recurrent low glucose to maintain intracellular nucleotide levels

Hypoglycemia 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 persons 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.

neuroscience↗