Fasting of mice: a review

Establishing reliable blood biomarkers for trimethylamine N-oxide status in rodents: Effects of oral choline challenge, dietary choline and fasting conditions

Circulating concentrations of the gut microbial-mammalian metabolite trimethylamine N-oxide (TMAO) are linked to atherosclerosis risk. TMAO biosynthesis begins when dietary choline is converted to trimethylamine (TMA) by gut microbial TMA lyase. TMA is transported to the liver, where flavin-containing monooxygenases convert it to TMAO. While dietary modifications regulate TMAO production, the impact of different intake methods, including oral gavage, dietary supplementation, and conditions such as fasting versus nonfasting, has not been fully explored. Twelve female Sprague-Dawley rats were divided into three diet groups (n = 4 per group): no-choline (0% choline), low-choline (0.08% choline), and high-choline (1% choline). Choline and TMAO fasting and nonfasting blood concentrations, and their kinetics following an acute choline challenge, were assessed before and after a 2-week dietary intervention with the distinct choline dietary levels. Fasting choline was under tight control, with little effect of dietary choline. Nonfasting choline was more variable, with high dietary choline reflected in higher blood choline. Greater levels of dietary choline were reflected in significantly greater levels of TMAO, particularly for nonfasting levels. Kinetic profiling demonstrated additional information regarding the appearance and clearance of these compounds from blood. These results suggest that acute oral choline gavage is likely most suitable for studies targeting acute (direct) inhibitors, whereas a choline-rich diet with assessment of fasting and nonfasting blood levels is more suitable for studying alterations to TMAO production capacity. Future research should examine the impact on atherosclerosis biomarkers and microbiome diversity to deepen the understanding of TMAO regulation and its cardiovascular implications.

Resveratrol ameliorates high‑fat diet‑induced insulin resistance via the DDIT4/mTOR pathway in skeletal muscle

Resveratrol (RSV) is a natural ingredient used in the treatment of diabetes mellitus. However, the antidiabetic mechanism of RSV is not clear. In the present study the antidiabetic mechanism of RSV was investigated using mice with high-fat diet (HFD)-induced insulin resistance (IR). C57BL/6J mice were divided into the following three groups: Control (CON), HFD, and HFD + RSV (RSV, 100 mg/kg body weight/day). Mice were administered RSV for 6 weeks; then biochemical and histological parameters, as well as gene and protein expression were detected. Compared with the CON group, the circulating levels of blood glucose, insulin, triglycerides, total cholesterol and high-density lipoprotein cholesterol, and area under the glucose curve were increased (P<0.05), the quantitative insulin sensitivity check index was decreased (P<0.05), and lipid accumulation in skeletal muscle was increased in the HFD group. RSV treatment was able to reverse this process and promote the IRS-1/PI3K/AKT/GLUT4 signaling pathway. Moreover, DNA damage-inducible transcript 4 (DDIT4) expression was upregulated, while the expression levels of mammalian target of rapamycin (mTOR) and p70 ribosomal protein S6 kinase were downregulated in the HFD + RSV group compared with the HFD group (P<0.05). Cell experiments inhibiting DDIT4 or activating mTOR also confirmed the role of these pathways. In summary, RSV ameliorated IR and glucose as well as lipid metabolism, and promoted the IRS-1/PI3K/AKT/GLUT4 signaling pathway through the DDIT4/mTOR signaling pathway in mice with HFD-induced IR.

The Prevalence of Reported Gavage Incidents in Repeated Dose Toxicity Studies Involving Rats Conducted Between 2004-2023

In animal-based toxicology studies, oral gavage is the predominant technique for administering compounds directly into the stomach. Recognised as a stressful procedure for animals, gavage is associated with accidents and 'gavage-related reflux' (GRR), which may lead to respiratory distress and/or death. This paper estimates the prevalence of incidents (deaths and/or non-fatal clinical signs) attributed to the gavage procedure in a representative sample of repeated dose toxicity test reports from the last 20 years, sourced from the ECHA CHEM database of REACH-registered chemicals. In 21% of the 300 reviewed studies, at least one death or clinical sign in rats was attributed to the gavage procedure in the study report. An additional 16% of these studies reported clinical signs associated with GRR in the animals, with no other adverse effects, but without attribution to the gavage procedure. Among those studies with incidents attributed to the gavage procedure, incidents were three times more common in 90-day studies than they were in 28-day studies. Incidents were also more likely to have occurred with the test substance rather than with the control, with highly viscous substances, and in more recently conducted studies. There was no association between the number of studies with a gavage-attributed incident and the strain, size or age of the rats, the dose volume or the testing of irritant substances. The current study suggests that incidents attributed to gavage are more prevalent than previously thought, and that a review of the gavage procedure is urgently needed.

Tangeretin enhances sedative activity of diazepam in Swiss mice through GABAA receptor interaction: In vivo and in silico approaches

The citrus peel flavonoid tangeretin (TAN) has diverse biological activities, including antioxidant, anti-inflammatory, antitumor, hepatoprotective, and neuroprotective effects. This study investigates the sedative effects of TAN, in Swiss albino mice using in vivo and in silico approaches. TAN (10 and 20 mg/kg, i.p.) was administered alone and in combination with diazepam (DZP, 2 mg/kg, i.p.) and flumazenil (FLU, 0.1 mg/kg, i.p.) to evaluate its impact on thiopental sodium (TS)-induced sleep, locomotor activity, and dark-light behavior. Results demonstrated that TAN at 10 mg/kg significantly (p < 0.05) reduced sleep onset latency and increased sleep duration, with a synergistic effect observed when combined with DZP. In locomotor activity tests, TAN dose-dependently decreased the distance traveled, while the combination with DZP further enhanced this effect. Dark-light tests revealed that TAN increased dark residence time, indicating potential anxiolytic properties. Molecular docking studies showed that TAN binds to the GABAA receptor (α1 and β2 subunits) with a binding affinity of -6.6 kcal/mol, suggesting its interaction with GABAergic pathways. Pharmacokinetic analysis indicated high intestinal absorption and compliance with Lipinski's rule of five, with a favorable safety profile (LD50 = 5000 mg/kg). Overall, TAN enhances the sedative effects of DZP through GABAA receptor modulation, highlighting its potential as a natural sedative agent. Further research should explore the long-term effects, bioavailability, blood-brain barrier permeability, and synergistic interactions of TAN, with comprehensive in vitro studies and clinical trials needed to validate its potential as a natural sedative.

Influence of food availability on water and alcohol consumption in murine models

BACKGROUND

Alcohol use disorder remains a global issue. Thus, understanding the factors that contribute to alcohol abuse, including how food availability can influence drinking behavior, is critical.

METHODS

Female and male C57Bl/6 and Swiss mice underwent a two-bottle choice Intermittent Overnight Drinking (IOD) protocol consisting of 12 sessions on alternate nights, three times per week, using lickometer devices. Mice had access to two bottles, containing either water or 10% ethanol, for 16 hours, starting 2 hours before the dark cycle. Animals were initially assigned to two groups: one with access to water, ethanol, and standard rodent chow (FOOD group), and another with access only to water and ethanol (NFOOD group). After six sessions, half of the mice in the second group were reassigned to a new group with delayed access to chow (NFOOD-FOOD group).

RESULTS

Food availability led to increased drinking, but the modulation was liquid dependent for each strain. The presence of food primarily increased ethanol intake in C57Bl/6 mice, while it enhanced water intake in Swiss mice. Microstructure analysis revealed that food heightened ethanol licks in C57Bl/6 mice, whereas it elevated water licks in Swiss mice, without altering numbers of bouts. Additionally, overnight analysis showed that C57Bl/6 mice with access to food had a peak in ethanol licks between 20:00 and 22:00, while Swiss mice exhibited an increase in water licks starting at 20:00 to 2:00, highlighting a strain-specific response to the dark cycle.

CONCLUSIONS

This study provides normative data on the temporal patterns of water and ethanol consumption in C57Bl/6 and Swiss female and male mice, contributing valuable insights to the field of voluntary drinking behaviors in murine models.

Ferulic acid lipid nano capsules versus its native form in alleviating diabetic nephropathy induced in rats through TGF-β1/Hippo pathway crosstalk modulation

Diabetic nephropathy is one of the most common leading causes of end-stage renal disease with multifactorial pathophysiological mechanisms. TGF-β1 and Hippo pathway have been reported to have significant role in different kidney diseases. In addition, ferulic acid (FA) has been proposed to have pharmacological actions in different disorders such as Alzheimer, diabetes mellitus, kidney, and cardiovascular diseases but with limited oral use due to poor absorbance and bioavailability. So, recent trends aim to include FA in nano-formulations to improve its absorbance and bioavailability and to make best use of its pharmacological actions when administered orally. Thirty Sprague Dawley male rats were divided into five groups (n = 6). After 28 days, rats were sacrificed, serum and kidney tissue were isolated, histopathological examination, serum creatinine level and oxidative status biomarkers in kidney tissue were estimated, besides ELISA measurements of TGF-β1, PTEN, COX2, and GLUT3 and the relative gene expressions of MST1 and TEAD4 by qRT-PCR. Treated groups show improvement of the investigated parameters in variable degrees. Noteworthy, FA nano-formulation shows superior action over double of the native form.

Metabolic responses to starvation in the soft-shelled turtle (Pelodiscus sinensis) revealed by integrated metabolome and transcriptome analysis

Animals frequently suffer from starvation throughout their life cycle; however, the mobilization and utilization of energy sources can differ. To clarify the fundamental mechanisms underlying energy mobilization and metabolic adjustment in response to food deprivation in the soft-shelled turtle (Pelodiscus sinensis), eighty turtles (initial body weight, 51.81 ± 0.29 g) were subjected to starvation periods of 1 d, 4 d, 8 d, 16 d, and 32 d (referred to as S1, S4, S8, S16, and S32). The results showed that the greatest absolute loss in body composition occurred in moisture, followed by protein and lipid, respectively. Hepatic glycogen contents significantly decreased after 4 days of starvation and then remained stable. Notably, plasma glucose, cholesterol, and free fatty acid contents exhibited significant decreases from S8, while plasma triacylglycerol levels dramatically declined from S4. Gluconeogenesis-related genes (pepck, g6pase) were upregulated in the starving turtles to maintain glucose homeostasis. Comparative analyses between S32 and S1 groups identified a total of 6051 differential genes and 150 differential metabolites, highlighting three overlapping metabolic pathways: glycerophospholipid metabolism, alanine, aspartate, and glutamate metabolism, and taurine and hypotaurine metabolism. Integrative analyses further revealed increased levels of specific metabolites, including phosphatidylcholine, phosphatidylethanolamine, glycerophosphocholine, L-2-aminoethyl seryl phosphate, l-serine-phosphatidylethanolamine, adenyiosuccinate, 5-phosphoribosylamine, and taurine. These metabolites are vital for amino acid-driven gluconeogenesis, cell membrane stability, and mitigating cellular damage resulting from food deprivation. In conclusion, glucose homeostasis was maintained by enhancing gluconeogenesis in P. sinensis during extended periods of starvation, and the activation of lipid and amino acid metabolism represents an adaptive metabolic strategy employed by P. sinensis to cope with starvation conditions.

Unlocking the therapeutic potential of canagliflozin in NAFLD: Insights into AMPK/SIRT1-mediated lipophagy

Nonalcoholic fatty liver disease (NAFLD) is a rising global health problem. The antidiabetic canagliflozin (CANA) has been proposed to ameliorate the metabolic abnormalities in NAFLD.

AIM

This study aimed to explore the possible anti-NAFLD effects of CANA in rats and HepG2 cells, focusing on AMPK/SIRT1-mediated lipophagy.

METHODS

Wistar rats were assigned to four groups: control group, NAFLD group, NAFLD+CANA group, and NAFLD+CANA+chloroquine (CQ) group, where CQ served as autophagy inhibitor. HepG2 cells were also divided into four groups: control group, NAFLD group, NAFLD+CANA group, and NAFLD+CANA+compound C (Comp C) group, where Comp C served as AMPK inhibitor.

RESULTS

The histopathological examination showed that CANA alleviated hepatic and intracellular lipid deposition in rats and HepG2 cells. CANA induced lipophagy by increasing LC3-II levels and lowering both p62 and perilipin 2 levels in rats and HepG2 cells, in addition to decreasing mTOR protein expression in rats' livers. These outcomes were associated with upregulation of the lipophagy regulator Rab7 and downregulation of the ER stress-related protein CHOP. CANA enhanced autophagic engulfment of lipid droplets while decreased ER stress and mitochondrial damage in rats' livers, as demonstrated by TEM. In rats, CANA improved hyperglycemia, hyperinsulinemia, dyslipidemia, and obesity. In HepG2 cells, CANA's effects were linked to increased phosphorylated AMPK level and enhanced SIRT1 level and expression. However, blocking lipophagy in rats and AMPK in HepG2 cells markedly weakened CANA's protective effects against NAFLD.

CONCLUSION

CANA ameliorated NAFLD via enhancing AMPK/SIRT1-mediated lipophagy, suggesting its potential as a therapeutic intervention for this metabolic disorder.

Functional compartmentalization of hepatic mitochondrial subpopulations during MASH progression

The role of peridroplet mitochondria (PDM) in diseased liver, such as during the progression of metabolic dysfunction-associated steatohepatitis (MASH), remains unknown. We isolated hepatic cytoplasmic mitochondria (CM) and PDM from a mouse model of diet-induced MASLD/MASH to characterize their functions from simple steatosis to advanced MASH, using chow-fed mice as controls. Our findings show an inverse relationship between hepatic CM and PDM levels from healthy to steatosis to advanced MASH. Proteomics analysis revealed these two mitochondrial populations are compositionally and functionally distinct. We found that hepatic PDM are more bioenergetically active than CM, with higher pyruvate oxidation capacity in both healthy and diseased liver. Higher respiration capacity of PDM was associated with elevated OXPHOS protein complexes and increased TCA cycle flux. In contrast, CM showed higher fatty acid oxidation capacity with MASH progression. Transmission electron microscopy revealed larger and elongated mitochondria during healthy and early steatosis, which appeared small and fragmented during MASH progression. These changes coincided with higher MFN2 protein levels in hepatic PDM and higher DRP1 protein levels in hepatic CM. These findings highlight the distinct roles of hepatic CM and PDM in MASLD progression towards MASH.

Modeling Toxoplasma gondii-gut early interactions using a human microphysiological system

Oral transmission of parasites via environmentally resistant cyst stages in contaminated food or water is a common route of human infection, but there are no effective vaccines available for any enteric parasitic infection. Our knowledge of parasite cyst stage conversion and interaction with the intestinal tract is limited. Here, we investigate infection dynamics of Toxoplasma gondii cyst-stage in murine jejunum and human intestinal microphysiological systems. We focus on parasite ingress, replication, and conversion of the cyst stage to the rapidly replicating dissemination stage. In vivo bioluminescent imaging of mice fed cysts revealed spots of infection throughout the jejunum and ileum, which were selected for further analyses. Immunostaining showed parasite migration and replication predominantly in the stroma, with minimal replication in enterocytes. We recapitulated bradyzoite infection in human intestinal microphysiological systems and showed stage conversation and migration through collagen. This integrated approach elucidates complex host-parasite interactions, highlighting the value of microphysiological systems in advancing understanding and identifying potential therapeutics.

GnIH secreted by green light exposure, regulates bone mass through the activation of Gpr147

Reproductive hormones associated with the hypothalamic-pituitary-gonadal (HPG) axis are closely linked to bone homeostasis. In this study, we demonstrate that Gonadotropin inhibitory hormone (GnIH, one of the key reproductive hormones upstream of the HPG axis) plays an indispensable role in regulating bone homeostasis and maintaining bone mass. We find that deficiency of GnIH or its receptor Gpr147 leads to a significant reduction in bone mineral density (BMD) in mice primarily by enhancement of osteoclast activation in vivo and in vitro. Mechanistically, GnIH/Gpr147 inhibits osteoclastogenesis by the PI3K/AKT, MAPK, NF-κB and Nfatc1 signaling pathways. Furthermore, GnIH treatment was able to alleviate bone loss in aging, ovariectomy (OVX) or LPS-induced mice. Moreover, the therapy using green light promotes the release of GnIH and rescues OVX-induced bone loss. In humans, serum GnIH increases and bone resorption markers decrease after green light exposure. Therefore, our study elucidates that GnIH plays an important role in maintaining bone homeostasis via modulating osteoclast differentiation and demonstrates the potential of GnIH therapy or green light therapy in preventing osteoporosis.

Intermittent fasting triggers interorgan communication to suppress hair follicle regeneration

Intermittent fasting has gained global popularity for its potential health benefits, although its impact on somatic stem cells and tissue biology remains elusive. Here, we report that commonly used intermittent fasting regimens inhibit hair follicle regeneration by selectively inducing apoptosis in activated hair follicle stem cells (HFSCs). This effect is independent of calorie reduction, circadian rhythm alterations, or the mTORC1 cellular nutrient-sensing mechanism. Instead, fasting activates crosstalk between adrenal glands and dermal adipocytes in the skin, triggering the rapid release of free fatty acids into the niche, which in turn disrupts the normal metabolism of HFSCs and elevates their cellular reactive oxygen species levels, causing oxidative damage and apoptosis. A randomized clinical trial (NCT05800730) indicates that intermittent fasting inhibits human hair growth. Our study uncovers an inhibitory effect of intermittent fasting on tissue regeneration and identifies interorgan communication that eliminates activated HFSCs and halts tissue regeneration during periods of unstable nutrient supply.

Dietary and metabolic effects on intestinal stem cells in health and disease

Diet and nutritional metabolites exhibit wide-ranging effects on health and disease partly by altering tissue composition and function. With rapidly rising rates of obesity, there is particular interest in how obesogenic diets influence tissue homeostasis and risk of tumorigenesis; epidemiologically, these diets have a positive correlation with various cancers, including colorectal cancer. The gastrointestinal tract is a highly specialized, continuously renewing tissue with a fundamental role in nutrient uptake and is, in turn, influenced by diet composition and host metabolic state. Intestinal stem cells are found at the base of the intestinal crypt and can generate all mature lineages that comprise the intestinal epithelium and are uniquely influenced by host diet, metabolic by-products and energy dynamics. Similarly, tumour growth and metabolism can also be shaped by nutrient availability and host diet. In this Review, we discuss how different diets and metabolic changes influence intestinal stem cells in homeostatic and pathological conditions, as well as tumorigenesis. We also discuss how dietary changes and composition affect the intestinal epithelium and its surrounding microenvironment.

Metabolically-Driven Active Targeting of Magnetic Nanoparticles Functionalized with Glucuronic Acid to Glioblastoma: Application to MRI-Tracked Magnetic Hyperthermia Therapy

Glioblastoma continues to pose a major global health challenge due to its incurable nature. The need for new strategies to combat this devastating tumor is therefore paramount. Nanotechnology offers unique opportunities to develop innovative and more effective therapeutic approaches. However, most nanosystems developed to treat glioblastomas, especially those based on metallic nanoparticles (NPs), have proven unsuccessful due to their inability to efficiently target these tumors, which are particularly inaccessible due to the restrictions imposed by the blood-brain tumor barrier (BBTB). Here, an innovative strategy is presented to efficiently target metallic NPs to glioblastomas through glucose transporters (GLUT) overexpressed on the endothelial cells of glioblastoma microvasculature, particularly GLUT1. Specifically, Iron Oxide Nanoparticles (IONPs) are functionalized with glucuronic acid to promote GLUT-mediated transcytosis which is drastically boosted by inducing mild hypoglycemia. This metabolically-driven active targeting strategy has yielded unprecedented efficacy in targeting metallic NPs to glioblastomas. Moreover, these IONPs, designed to act as magnetic hyperthermia (MH) mediators, are used to conduct a proof-of-concept preclinical study on MRI-tracked MH therapy following intravenous administration, resulting in significant tumor growth delay. These findings demonstrate unparalleled efficiency in glioblastoma targeting and lay the ground for developing alternative therapeutic strategies to combat glioblastoma.

Intermittent fasting shifts the diurnal transcriptome atlas of transcription factors

Intermittent fasting remains a safe and effective strategy to ameliorate various age-related diseases, but its specific mechanisms are not fully understood. Considering that transcription factors (TFs) determine the response to environmental signals, here, we profiled the diurnal expression of 600 samples across four metabolic tissues sampled every 4 over 24 h from mice placed on five different feeding regimens to provide an atlas of TFs in biological space, time, and feeding regimen. Results showed that 1218 TFs exhibited tissue-specific and temporal expression profiles in ad libitum mice, of which 974 displayed significant oscillations at least in one tissue. Intermittent fasting triggered more than 90% (1161 in 1234) of TFs to oscillate somewhere in the body and repartitioned their tissue-specific expression. A single round of fasting generally promoted TF expression, especially in skeletal muscle and adipose tissues, while intermittent fasting mainly suppressed TF expression. Intermittent fasting down-regulated aging pathway and upregulated the pathway responsible for the inhibition of mammalian target of rapamycin (mTOR). Intermittent fasting shifts the diurnal transcriptome atlas of TFs, and mTOR inhibition may orchestrate intermittent fasting-induced health improvements. This atlas offers a reference and resource to understand how TFs and intermittent fasting may contribute to diurnal rhythm oscillation and bring about specific health benefits.

Effects of time-restricted feeding (TRF)-model of intermittent fasting on adipose organ: a narrative review

Time-restricted feeding (TRF), an intermittent fasting approach involving a shortened eating window within 24 h, has gained popularity as a weight management approach. This review addresses how TRF may favor fat redistribution and the function of the adipose organ. TRF trials (mainly 16:8 model, with a duration of 5-48 weeks) reported a significant weight loss (1.2-10.2%, ~ 1.4-9.4 kg), with a considerable decrease in total fat mass (1.6-21%, ~ 0.5-7 kg) and visceral adipose compartment (VAC, 11-27%) in overweight and obese subjects. Experimental TRF in normal-fed and obesogenic-diet-fed mice and rats (with a fasting duration ranging between 9 and 21 h within 1-17 weeks) reported a significant reduction in body weight (~ 7-40%), total fat mass (~ 17-71%), and intrahepatic fat (~ 25-72%). TRF also improves VAC and subcutaneous adipose compartment (SAC) function by decreasing adipocyte size, macrophage infiltration, M1-macrophage polarity, and downregulating inflammatory genes. In conclusion, beyond its effect on body weight loss, total fat mass, and intrahepatic fat accumulation, TRF favors adipose organ fat redistribution in overweight and obese subjects by decreasing VAC and improving the function of VAC and SAC.

Omega-3 Fatty Acid and Vitamin D Supplementations Partially Reversed Metabolic Disorders and Restored Gut Microbiota in Obese Wistar Rats

Obesity is a global public health issue linked to various comorbidities in both humans and animals. This study investigated the effects of vitamin D (VD) and omega-3 fatty acids (ω3FA) on obesity, gut dysbiosis, and metabolic alterations in Wistar rats. After 13 weeks on a standard (S) or High-Fat, High-Sugar (HFHS) diet, the rats received VD, ω3FA, a combination (VD/ω3), or a control (C) for another 13 weeks. The HFHS diet led to increased weight gain, abdominal circumference, glucose intolerance, insulin resistance, and gut dysbiosis. VD supplementation improved their fasting blood glucose and reduced liver damage, while ω3FA slowed BMI progression, reduced abdominal fat, liver damage, and intestinal permeability, and modulated the gut microbiota. The combination of VD/ω3 prevented weight gain, decreased abdominal circumference, improved glucose tolerance, and reduced triglycerides. This study demonstrates that VD and ω3FA, alone or combined, offer significant benefits in preventing obesity, gut dysbiosis, and metabolic alterations, with the VD/ω3 combination showing the most promise. Further research is needed to explore the mechanisms behind these effects and their long-term potential in both animal and human obesity management.

Liver fat response to two days fasting and two days isocaloric high-carbohydrate refeeding in lean and obese women

BACKGROUND AND AIMS

Prolonged fasting, which leads to the mobilization of fat from adipose tissue, can result in the development of hepatosteatosis. However, it is not yet known whether the accumulation of fat in the liver after fasting can be affected by concurrent obesity. Therefore, this study aimed to assess how excessive adiposity influences changes in liver fat content induced by fasting and subsequent refeeding.

METHODS AND RESULTS

Ten lean women and eleven women with obesity (age: 36.4 ± 7.9 and 34.5 ± 7.9 years, BMI: 21.4 ± 1.7 and 34.5 ± 4.8 kg/m2) underwent a 60-h fasting period followed by 2 days of isocaloric high-carbohydrate refeeding. Magnetic resonance spectroscopy (MRS) examinations of liver were conducted at baseline, after 48 h of fasting, and at the end of refeeding period. Hepatic fat content (HFC) increased in lean women after fasting, whereas no statistically significant change in HFC was observed in women with obesity. Additionally, fasting led to significant reductions in liver volume in both groups, likely attributable to glycogen depletion, with subsequent restoration upon refeeding. Notably, changes in hepatic fat volume (HFV) rather than HFC inversely correlated with baseline liver fat content and HOMA-IR.

CONCLUSION

We demonstrated that prolonged fasting results in accumulation of fat in the liver in lean subjects only and that this accumulation is inversely related to baseline fat content and insulin resistance. Moreover, the study underscored the importance of evaluating hepatic fat volume rather than hepatic fat content in studies that involve considerable changes in hepatic lean volume.

3D-printed Laponite/Alginate hydrogel-based suppositories for versatile drug loading and release

Traditional approaches to solid rectal therapies have halted progress, leading to a continual decline in the use of conventional suppositories. Additive manufacturing techniques have been recently explored as a suitable innovative tool for suppository fabrication. However, little advancement has been made in composition materials for 3D-printed suppository (3DPS) manufacturing and still, conventional vehicles are often used for construct fabrication, hindering the growth in the field. As a novelty, this study unveils a ground-breaking Laponite-alginate hydrogel-based 3DPS. Interestingly, this study proposes a novel approach for loading drugs into the 3DPS employing for the first time the post-printing loading. Thus, a passive loading strategy of molecular models is developed, demonstrating the versatility and capacity to load molecules of different charges and molecular sizes within the matrix systems. This novel strategy allows adapting the load of a wide range of drugs into a single ink, which simplifies and speeds up the 3DPS technological development process for drugs with different physico-chemical properties. Additionally, in this research, a displacement strategy of the three-dimensional Laponite matrices is developed in order to enhance the drug release capacity through the 3DPS and their disintegration capacity, resulting in a significant improvement of the drug diffusion through the hydrogel matrix and a rapid disintegration of the 3DPS. Finally, our study demonstrates that the obtained 3DPS have a suitable in vivo behavior, being non-obstructive and allowing the normal motility of the rats intestine.

Optimisation of Animal Handing and Timing of 2-deoxy-2-[18F]fluoro-D-glucose PET Tumour Imaging in Mice

PURPOSE

In humans, 2-deoxy-2-[18F]fluoro-D-glucose ([18F]FDG) tumour-to-background contrast continues to increase long after a typical uptake period of 45 - 60 min. Similar studies have not been performed in mice and the static imaging time point for most studies is arbitrarily set at 30 - 60 min post-injection of [18F]FDG. Ideally, static PET imaging should be performed after the initial period of rapid uptake but this period has not been defined in mice, with previous dynamic studies in mice being limited to 60 min. This study aimed to define the kinetics of [18F]FDG biodistribution over periods of 3 - 4 h in different murine tumour models, both subcutaneous and autochthonous, and to further refine fasting and warming protocols used prior to imaging.

PROCEDURES

Dynamic [18F]FDG PET-CT scans lasting 3 or 4 h were performed with C57BL/6 J and Balb/c nude mice bearing subcutaneous EL4 murine T-cell lymphoma and Colo205 human colorectal tumours, respectively, and with transgenic Eμ-Myc lymphoma mice. Prior to [18F]FDG injection, four combinations of different animal handling conditions were used: warming for 1 h at 31 °C; maintenance at room temperature (20 - 24 °C), fasting for 6 - 10 h and a fed state.

RESULTS

Tumour mean standardised uptake value (SUVmean) peaked at 147 ± 48 min post injection in subcutaneous tumours and 74 ± 31 min in autochthonous Eμ-Myc lymphomas. The tumour-to-blood ratio (TBR) peaked at 171 ± 57 and 83 ± 33 min in subcutaneous and autochthonous Eμ-Myc tumours, respectively. Fasting increased tumour [18F]FDG uptake and suppressed myocardial uptake in EL4 tumour-bearing mice. There was a good correlation between tumour SUVmean and Ki calculated using an input function (IDIF) derived from the inferior vena cava.

CONCLUSIONS

Delayed static [18F]FDG-PET imaging (> 60 min) in both autochthonous and subcutaneous tumours in improved tumour-to-background contrast and increased reproducibility.

Molecular connectomics reveals a glucagon-like peptide 1-sensitive neural circuit for satiety

Liraglutide and other glucagon-like peptide 1 receptor agonists (GLP-1RAs) are effective weight loss drugs, but how they suppress appetite remains unclear. One potential mechanism is by activating neurons that inhibit the hunger-promoting Agouti-related peptide (AgRP) neurons of the arcuate hypothalamus (Arc). To identify these afferents, we developed a method combining rabies-based connectomics with single-nucleus transcriptomics. Here, we identify at least 21 afferent subtypes of AgRP neurons in the mouse mediobasal and paraventricular hypothalamus, which are predicted by our method. Among these are thyrotropin-releasing hormone (TRH)+ Arc (TRHArc) neurons, inhibitory neurons that express the Glp1r gene and are activated by the GLP-1RA liraglutide. Activating TRHArc neurons inhibits AgRP neurons and feeding, probably in an AgRP neuron-dependent manner. Silencing TRHArc neurons causes overeating and weight gain and attenuates liraglutide's effect on body weight. Our results demonstrate a widely applicable method for molecular connectomics, comprehensively identify local inputs to AgRP neurons and reveal a circuit through which GLP-1RAs suppress appetite.

There is no need for overnight fasting of rats in regulatory toxicology studies

For many years overnight fasting of rats before the collection of clinical pathology blood samples and necropsy has been a common procedure in toxicological studies for regulatory purposes. The fasting was thought to minimize the intragroup variability for clinical pathology and organ weights. However, depriving rats of food overnight will impact animal welfare by interfering with the general metabolism and may result in physiological and behavioural changes. The effects of overnight fasting in comparison to rats that were not fasted prior to necropsy was investigated in lactating rats based on an evaluation of organ weights, haematological, and clinical biochemical parameters. The results of 92 OECD 422 studies were analysed (i.e., Combined Repeated Dose Toxicity Study with the Reproduction/Developmental Toxicity Screening Test) of which approximately half of the studies incorporated fasting prior to necropsy and the other half did not. Terminal body and organ weights from all 92 studies were evaluated. Clinical pathology was included in 78 of these 92 studies. Decreased glucose levels following fasting had been reported in the literature but were not observed when comparing 39 studies with fasted conditions versus 39 studies with non-fasted conditions. Both literature and the analysed database exhibited a reduction in liver weight, alanine aminotransferase, and alkaline phosphatase levels in overnight fasted groups. These differences between fasted and non-fasted states are considered of little account as study results are always interpreted based on the differences in parameter values between treated animals compared to control animals within a study. Contrarily to previously suggested, intragroup variability was lower in the majority of parameters in non-fasted animals. According to laboratory historical data, clinical pathology and organ weight parameters are found to be very similar in male and female rats, indicating that the results of this study may be extrapolatable to non-lactating female and male rats. Based on these comparisons, it is recommended not to fast rats prior to necropsy but to continue feeding all rats ad libitum, to minimize physiological changes in these animals, to reduce variability, improve animal welfare and thereby improve the scientific value of study results.

Pea and soy fortified with leucine stimulates muscle protein synthesis comparable to whey in a murine ageing model

PURPOSE

To meet the global dietary protein demands, a trend towards plant-based protein (PBP) sources to replace animal-derived protein is currently ongoing. However, PBPs may not have the same anabolic capacity to stimulate muscle protein synthesis (MPS) as dairy proteins. For vulnerable populations with specific medical needs, it is especially important to validate the anabolic properties of PBPs. In this study, a blend of pea and soy protein isolate, with or without additional leucine, was compared to whey protein isolate on MPS in aged mice.

METHODS

25-Months aged C57BL/6J-mice received an oral gavage with 70 mg of whey protein isolate (W), PS protein isolate (PS; ratio 51:49), PS fortified with 19% leucine (PS + L), or 0.5mL water (F). Mice were subcutaneously injected with puromycin (0.04 µmol/g body weight, t = 30 min) and sacrificed 60 min thereafter. Left m. tibialis anterior (TA) was used to analyse MPS by the SUnSET method and mTOR signal transduction proteins. Amino acid concentrations were determined in plasma and right TA. Dried blood spots (DBS) were analysed for postprandial dynamics of amino acids at 10-20-45-60-min.

RESULTS

MPS was significantly increased by W and PS + L (p < 0.003), however not by PS. Pathway protein 4EBP1 showed significant increases with W, PS and PS + L to F (p < 0.0002). W and PS + L increased plasma and muscle free leucine equally, which was confirmed by DBS.

CONCLUSION

A PS blend fortified with leucine stimulates MPS comparable to whey protein in this acute murine ageing model. Leucine appears to be the main driver for the anabolic responses observed.

Starvation-induced metabolic rewiring affects mTORC1 composition in vivo

Lysosomes play a crucial role in metabolic adaptation to starvation, but detailed in vivo studies are scarce. Therefore, we investigated the changes of the proteome of liver lysosomes in mice starved short-term for 6h or long-term for 24h. We verified starvation-induced catabolism by weight loss, ketone body production, drop in blood glucose and an increase of 3-methylhistidine. Deactivation of mTORC1 in vivo after short-term starvation causes a depletion of mTORC1 and the associated Ragulator complex in hepatic lysosomes, resulting in diminished phosphorylation of mTORC1 target proteins. While mTORC1 lysosomal protein levels and activity in liver were restored after long-term starvation, the lysosomal levels of Ragulator remained constantly reduced. To determine whether this mTORC1 activity pattern may be organ-specific, we further investigated the key metabolic organs muscle and brain. mTORC1 inactivation, but not re-activation, occurred in muscle after a starvation of 12 h or longer. In brain, mTORC1 activity remained unchanged during starvation. As mTORC1 deactivation is known to induce autophagy, we further investigated the more than 150 non-lysosomal proteins enriched in the lysosomal fraction upon starvation. Proteasomal, cytosolic and peroxisomal proteins dominated after short-term starvation, while after long-term starvation, mainly proteasomal and mitochondrial proteins accumulated, indicating ordered autophagic protein degradation.

Transient impact of chronic social stress on effort-based reward motivation in non-food restricted mice: Involvement of corticosterone

Chronic stress has been connected to a reduced effort and motivational deficits. To study effort-based motivation in rodents, operant conditioning is often employed. However, caloric restriction is typically imposed simultaneously. Since caloric restriction is a stressor in its own right, this procedure interferes with data interpretation. Here, we investigate whether chronic social defeat stress (CSD), lasting 10 consecutive days, would alter effort-based reward motivation in mice trained under ad libitum food conditions. Utilizing operant FED3 boxes in home cages, mice were trained within eight days to nose poke for palatable food. After training completion, operant memory was retained for at least 16 days, and mice demonstrated sustained effort, as assessed with a progressive ratio schedule, to obtain reward pellets. Directly after CSD exposure (10th day), mice exhibited reduced effort for palatable food rewards, but also displayed reduced nose poking in general. The effects of CSD on effort were short-lived, with no lasting impact on effort-based reward motivation one week post-stress. As corticosterone (CORT) levels were increased at day 10 of CSD, but not at day 17, we hypothesized that CORT might mediate the acute effects of CSD on effort-based reward motivation. Indeed, CORT administration [100 μg/ml], supplied via the drinking water, mirrored the CSD-induced CORT spike and temporarily reduced reward motivation. Our findings emphasize that CSD does not result in long-term deficits in reward motivation, suggesting a resilient adaptive response in mice under unrestricted feeding conditions. This study underscores the necessity of considering temporal dynamics of stress impacts and highlights the modulating effects of CORT. These insights contribute to a deeper understanding of the resilience mechanisms in motivational impairments and pave the way for further research into factors facilitating this resilience.

The Downregulation of the Liver Lipid Metabolism Induced by Hypothyroidism in Male Mice: Metabolic Flexibility Favors Compensatory Mechanisms in White Adipose Tissue

In mammals, the maintenance of energy homeostasis relies on complex mechanisms requiring tight synchronization between peripheral organs and the brain. Thyroid hormones (THs), through their pleiotropic actions, play a central role in these regulations. Hypothyroidism, which is characterized by low circulating TH levels, slows down the metabolism, which leads to a reduction in energy expenditure as well as in lipid and glucose metabolism. The objective of this study was to evaluate whether the metabolic deregulations induced by hypothyroidism could be avoided through regulatory mechanisms involved in metabolic flexibility. To this end, the response to induced hypothyroidism was compared in males from two mouse strains, the wild-derived WSB/EiJ mouse strain characterized by a diet-induced obesity (DIO) resistance due to its high metabolic flexibility phenotype and C57BL/6J mice, which are prone to DIO. The results show that propylthiouracil (PTU)-induced hypothyroidism led to metabolic deregulations, particularly a reduction in hepatic lipid synthesis in both strains. Furthermore, in contrast to the C57BL/6J mice, the WSB/EiJ mice were resistant to the metabolic dysregulations induced by hypothyroidism, mainly through enhanced lipid metabolism in their adipose tissue. Indeed, WSB/EiJ mice compensated for the decrease in hepatic lipid synthesis by mobilizing lipid reserves from white adipose tissue. Gene expression analysis revealed that hypothyroidism stimulated the hypothalamic orexigenic circuit in both strains, but there was unchanged melanocortin 4 receptor (Mc4r) and leptin receptor (LepR) expression in the hypothyroid WSB/EiJ mice strain, which reflects their adaptability to maintain their body weight, in contrast to C57BL/6J mice. Thus, this study showed that WSB/EiJ male mice displayed a resistance to the metabolic dysregulations induced by hypothyroidism through compensatory mechanisms. This highlights the importance of metabolic flexibility in the ability to adapt to disturbed circulating TH levels.

Time and dose selective glucose metabolism for glucose homeostasis and energy conversion in the liver

Hepatic glucose metabolism serves dual purposes: maintaining glucose homeostasis and converting glucose into energy sources; however, the underlying mechanisms are unclear. We quantitatively measured liver metabolites, gene expression, and phosphorylated insulin signaling molecules in mice orally administered varying doses of glucose, and constructed a transomic network. Rapid phosphorylation of insulin signaling molecules in response to glucose intake was observed, in contrast to the more gradual changes in gene expression. Glycolytic and gluconeogenic metabolites and expression of genes involved in glucose metabolism including glucose-6-phosphate, G6pc, and Pck1, demonstrated high glucose dose sensitivity. Whereas, glucokinase expression and glycogen accumulation showed low glucose dose sensitivity. During the early phase after glucose intake, metabolic flux was geared towards glucose homeostasis regardless of the glucose dose but shifted towards energy conversion during the late phase at higher glucose doses. Our research provides a comprehensive view of time- and dose-dependent selective glucose metabolism.

Optimal fasting duration for mice as assessed by metabolic status

In the study of obesity and diabetes, mice are widely used for experimental research, and fasting is a common procedure used to reset metabolism in mouse models. The fasting duration for experimental mice varies greatly in nutritional and metabolic studies, ranging from 2 to 48 h. This study aims to assess the optimal fasting duration for mice fed low- and high-fat diets over a short period of time. C57BL/6J mice were fed a low-fat diet (LFD) or high-fat diet (HFD) and fasted for 4, 6, 8, 10, 12, or 24 h. The effects of different conditions after fasting on the metabolic level of mice were explored, and the data were collected for analysis. Our data indicate that fasting has inconsistent effects on mice fed a low-fat or high-fat diet. To compare the metabolic differences between mice in different dietary levels and thereby secure better scientific data, mice should fast for 6 h in animal experiments. Fasting for 6 h is also recommended when comparing glucose tolerance with insulin tolerance.

Integrated Ultrasound Characterization of the Diet-Induced Obesity (DIO) Model in Young Adult c57bl/6j Mice: Assessment of Cardiovascular, Renal and Hepatic Changes

Consuming an unbalanced diet and being overweight represent a global health problem in young people and adults of both sexes, and may lead to metabolic syndrome. The diet-induced obesity (DIO) model in the C57BL/6J mouse substrain that mimics the gradual weight gain in humans consuming a "Western-type" (WD) diet is of great interest. This study aims to characterize this animal model, using high-frequency ultrasound imaging (HFUS) as a complementary tool to longitudinally monitor changes in the liver, heart and kidney. Long-term WD feeding increased mice body weight (BW), liver/BW ratio and body condition score (BCS), transaminases, glucose and insulin, and caused dyslipidemia and insulin resistance. Echocardiography revealed subtle cardiac remodeling in WD-fed mice, highlighting a significant age-diet interaction for some left ventricular morphofunctional parameters. Qualitative and parametric HFUS analyses of the liver in WD-fed mice showed a progressive increase in echogenicity and echotexture heterogeneity, and equal or higher brightness of the renal cortex. Furthermore, renal circulation was impaired in WD-fed female mice. The ultrasound and histopathological findings were concordant. Overall, HFUS can improve the translational value of preclinical DIO models through an integrated approach with conventional methods, enabling a comprehensive identification of early stages of diseases in vivo and non-invasively, according to the 3Rs.

Orexin neurons mediate temptation-resistant voluntary exercise

Despite the well-known health benefits of physical activity, many people underexercise; what drives the prioritization of exercise over alternative options is unclear. We developed a task that enabled us to study how mice freely and rapidly alternate between wheel running and other voluntary activities, such as eating palatable food. When multiple alternatives were available, mice chose to spend a substantial amount of time wheel running without any extrinsic reward and maintained this behavior even when palatable food was added as an option. Causal manipulations and correlative analyses of appetitive and consummatory processes revealed this preference for wheel running to be instantiated by hypothalamic hypocretin/orexin neurons (HONs). The effect of HON manipulations on wheel running and eating was strongly context-dependent, being the largest in the scenario where both options were available. Overall, these data suggest that HON activity enables an eat-run arbitration that results in choosing exercise over food.

Serum measures of docosahexaenoic acid (DHA) synthesis underestimates whole body DHA synthesis in male and female mice

Females have higher docosahexaenoic acid (DHA) levels than males, proposed to be a result of higher DHA synthesis rates from α-linolenic acid (ALA). However, DHA synthesis rates are reported to be low, and have not been directly compared between sexes. Here, we apply a new compound specific isotope analysis model to determine n-3 PUFA synthesis rates in male and female mice and assess its potential translation to human populations. Male and female C57BL/6N mice were allocated to one of three 12-week dietary interventions with added ALA, eicosapentaenoic acid (EPA) or DHA. The diets included low carbon-13 (δ13C)-n-3 PUFA for four weeks, followed by high δ13C-n-3 PUFA for eight weeks (n=4 per diet, time point, sex). Following the diet switch, blood and tissues were collected at multiple time points, and fatty acid levels and δ13C were determined and fit to one-phase exponential decay modeling. Hepatic DHA synthesis rates were not different (P>.05) between sexes. However, n-3 docosapentaenoic acid (DPAn-3) synthesis from dietary EPA was 66% higher (P<.05) in males compared to females, suggesting higher synthesis downstream of DPAn-3 in females. Estimates of percent conversion of dietary ALA to serum DHA was 0.2%, in line with previous rodent and human estimates, but severely underestimates percent dietary ALA conversion to whole body DHA of 9.5%. Taken together, our data indicates that reports of low human DHA synthesis rates may be inaccurate, with synthesis being much higher than previously believed. Future animal studies and translation of this model to humans are needed for greater understanding of n-3 PUFA synthesis and metabolism, and whether the higher-than-expected ALA-derived DHA can offset dietary DHA recommendations set by health agencies.

Eating Around the Clock: Circadian Rhythms of Eating and Metabolism

The time of day that we eat is increasingly recognized as contributing as importantly to overall health as the amount or quality of the food we eat. The endogenous circadian clock has evolved to promote intake at optimal times when an organism is intended to be awake and active, but electric lights and abundant food allow eating around the clock with deleterious health outcomes. In this review, we highlight literature pertaining to the effects of food timing on health, beginning with animal models and then translation into human experiments. We emphasize the pitfalls and opportunities that technological advances bring in bettering understanding of eating behaviors and their association with health and disease. There is great promise for restricting the timing of food intake both in clinical interventions and in public health campaigns for improving health via nonpharmacological therapies.

Effects of food restriction on voluntary wheel-running behavior and body mass in selectively bred High Runner lines of mice

Food restriction can have profound effects on various aspects of behavior, physiology, and morphology. Such effects might be amplified in animals that are highly active, given that physical activity can represent a substantial fraction of the total daily energy budget. More specifically, some effects of food restriction could be associated with intrinsic, genetically based differences in the propensity or ability to perform physical activity. To address this possibility, we studied the effects of food restriction in four replicate lines of High Runner (HR) mice that have been selectively bred for high levels of voluntary wheel running. We hypothesized that HR mice would respond differently than mice from four non-selected Control (C) lines. Healthy adult females from generation 65 were housed individually with wheels and provided access to food and water ad libitum for experimental days 1-19 (Phase 1), which allowed mice to attain a plateau in daily running distances. Ad libitum food intake of each mouse was measured on days 20-22 (Phase 2). After this, each mouse experienced a 20 % food restriction for 7 days (days 24-30; Phase 3), and then a 40 % food restriction for 7 additional days (days 31-37; Phase 4). Mice were weighed on experimental days 1, 8, 9, 15, 20, and 23-37 and wheel-running activity was recorded continuously, in 1-minute bins, during the entire experiment. Repeated-measures ANOVA of daily wheel-running distance during Phases 2-4 indicated that HR mice always ran much more than C, with values being 3.29-fold higher during the ad libitum feeding trial, 3.58-fold higher with -20 % food, and 3.06-fold higher with -40 % food. Seven days of food restriction at -20 % did not significantly reduce wheel-running distance of either HR (-5.8 %, P = 0.0773) or C mice (-13.3 %, P = 0.2122). With 40 % restriction, HR mice showed a further decrease in daily wheel-running distance (P = 0.0797 vs. values at 20 % restriction), whereas C mice did not (P = 0.4068 vs. values at 20 % restriction) and recovered to levels similar to those on ad libitum food (P = 0.3634). For HR mice, daily running distances averaged 11.4 % lower at -40 % food versus baseline values (P = 0.0086), whereas for C mice no statistical difference existed (-4.8 %, P = 0.7004). Repeated-measures ANOVA of body mass during Phases 2-4 indicated a highly significant effect of food restriction (P = 0.0001), but no significant effect of linetype (P = 0.1764) and no interaction (P = 0.8524). Both HR and C mice had a significant reduction in body mass only when food rations were reduced by 40 % relative to ad libitum feeding, and even then the reductions averaged only -0.60 g for HR mice (-2.6 %) and -0.49 g (-2.0 %) for C mice. Overall, our results indicate a surprising insensitivity of body mass to food restriction in both high-activity (HR) and ordinary (C) mice, and also insensitivity of wheel running in the C lines of mice, thus calling for studies of compensatory mechanisms that allow this insensitivity.

Characterization of a Syngeneic Orthotopic Model of Cholangiocarcinoma by [18F]FDG-PET/MRI

Cholangiocarcinoma (CCA) is a type of primary liver cancer originating from the biliary tract epithelium, characterized by limited treatment options for advanced cases and low survival rates. This study aimed to establish an orthotopic mouse model for CCA and monitor tumor growth using PET/MR imaging. Murine CCA cells were implanted into the liver lobe of male C57BL/6J mice. The imaging groups included contrast-enhanced (CE) MR, CE-MR with static [18F]FDG-PET, and dynamic [18F]FDG-PET. Tumor volume and FDG uptake were measured weekly over four weeks. Early tumor formation was visible in CE-MR images, with a gradual increase in volume over time. Dynamic FDG-PET revealed an increase in the metabolic glucose rate (MRGlu) over time. Blood analysis showed pathological changes in liver-related parameters. Lung metastases were observed in nearly all animals after four weeks. The study concludes that PET-MR imaging effectively monitors tumor progression in the CCA mouse model, providing insights into CCA development and potential treatment strategies.

Molecular Connectomics Reveals a Glucagon-Like Peptide 1 Sensitive Neural Circuit for Satiety

Liraglutide and other agonists of the glucagon-like peptide 1 receptor (GLP-1RAs) are effective weight loss drugs, but how they suppress appetite remains unclear. One potential mechanism is by activating neurons which inhibit hunger-promoting Agouti-related peptide (AgRP) neurons of the arcuate hypothalamus (Arc). To identify these afferents, we developed a method combining rabies-based connectomics with single-nuclei transcriptomics. Applying this method to AgRP neurons predicted at least 21 afferent subtypes in the mouse mediobasal and paraventricular hypothalamus. Among these are Trh+ Arc neurons, inhibitory neurons which express the Glp1r gene and are activated by the GLP-1RA liraglutide. Activating Trh+ Arc neurons inhibits AgRP neurons and feeding in an AgRP neuron-dependent manner. Silencing Trh+ Arc neurons causes over-eating and weight gain and attenuates liraglutide's effect on body weight. Our results demonstrate a widely applicable method for molecular connectomics, comprehensively identify local inputs to AgRP neurons, and reveal a circuit through which GLP-1RAs suppress appetite.

CREB3 mediates the transcriptional regulation of PGC-1α, a master regulator of energy homeostasis and mitochondrial biogenesis

Lipid metabolism hinges on a balance between lipogenesis and fatty acid oxidation (FAO). Disruptions in this balance can induce endoplasmic reticulum (ER) stress triggering the unfolded protein response (UPR) and contribute to metabolic diseases. The UPR protein, Luman or CREB3, has recently been implicated in metabolic regulation-CREB3 knockout mice exhibit resistance to diet-induced obesity and altered insulin sensitivity. Here, we show that CREB3 activated PPARGC1A transcription from a 1 kb promoter region. An increase in CREB3 expression correlated inversely with endogenous PPARGC1A mRNA levels and genes involved in FAO. As PGC-1α encoded by PPARGC1A is a master regulator of mitochondrial biogenesis and energy homeostasis, these findings demonstrate that CREB3 is a transcriptional regulator of PGC-1α, underlining the potential role of CREB3 in energy metabolism.

Genomic Convergence in Hibernating Mammals Elucidates the Genetics of Metabolic Regulation in the Hypothalamus

Elucidating the genetic basis of mammalian metabolism could help define mechanisms central to health and disease. Here, we define conserved cis-regulatory elements (CREs) and programs for mammalian metabolic control. We delineate gene expression and chromatin responses in the mouse hypothalamus for 7 steps of the Fed-to-Fasted-to-Refed (FFR) response process. Comparative genomics of hibernating versus non-hibernating lineages then illuminates cis-elements showing convergent changes in hibernators. Hibernators accumulated loss-of-function effects for specific CREs regulating hypothalamic FFR responses. Multi-omics approaches pinpoint key CREs, genes, regulatory programs, and cell types in the divergence of hibernating and homeothermic lineages. The refeeding period after extended fasting is revealed as one critical period of chromatin remodeling with convergent genomic changes. This genetic framework is a step toward harnessing hibernator adaptations in medicine.

Time of day and circadian disruption influence host response and parasite growth in a mouse model of cerebral malaria

Malaria is a disease caused by infection with parasite Plasmodium spp. We studied the circadian regulation of host responses to the parasite, in a mouse model of cerebral malaria. The course of the disease was markedly affected by time of infection, with decreased parasitemia and increased inflammation upon infection in the middle of the night. At this time, there were fewer reticulocytes, which are target cells of the parasites. We next investigated the effects of desynchronization of host clocks on the infection: after 10 weeks of recurrent jet lags, mice showed decreased parasite growth and lack of parasite load rhythmicity, paralleled by a loss of glucose rhythm. Accordingly, disrupting host metabolic rhythms impacted parasite load rhythmicity. In summary, our findings of a circadian modulation of malaria parasite growth and infection shed light on aspects of the disease relevant to human malaria and could contribute to new therapeutic or prophylactic measures.

Mitochondrial ACSS1-K635 acetylation knock-in mice exhibit altered metabolism, cell senescence, and nonalcoholic fatty liver disease

Acetyl-CoA synthetase short-chain family member 1 (ACSS1) uses acetate to generate mitochondrial acetyl-CoA and is regulated by deacetylation by sirtuin 3. We generated an ACSS1-acetylation (Ac) mimic mouse, where lysine-635 was mutated to glutamine (K635Q). Male Acss1K635Q/K635Q mice were smaller with higher metabolic rate and blood acetate and decreased liver/serum ATP and lactate levels. After a 48-hour fast, Acss1K635Q/K635Q mice presented hypothermia and liver aberrations, including enlargement, discoloration, lipid droplet accumulation, and microsteatosis, consistent with nonalcoholic fatty liver disease (NAFLD). RNA sequencing analysis suggested dysregulation of fatty acid metabolism, cellular senescence, and hepatic steatosis networks, consistent with NAFLD. Fasted Acss1K635Q/K635Q mouse livers showed increased fatty acid synthase (FASN) and stearoyl-CoA desaturase 1 (SCD1), both associated with NAFLD, and increased carbohydrate response element-binding protein binding to Fasn and Scd1 enhancer regions. Last, liver lipidomics showed elevated ceramide, lysophosphatidylethanolamine, and lysophosphatidylcholine, all associated with NAFLD. Thus, we propose that ACSS1-K635-Ac dysregulation leads to aberrant lipid metabolism, cellular senescence, and NAFLD.

Transient loss of satiety effects of leptin in middle-aged male mice

Extensive research is undertaken in rodents to determine the mechanism underlying obesity-induced leptin resistance. While body weight is generally tightly controlled in these studies, the effect of age of experimental animals has received less attention. Specifically, there has been little investigation into leptin regulation of food intake in middle-aged animals, which is a period of particular relevance for weight gain in humans. We investigated whether the satiety effects of leptin remained constant in young (3 months), middle-aged (12 months) or aged (18-22 months) male mice. Although mean body weight increased with age, leptin concentrations did not significantly increase in male mice beyond 12 months of age. Exogenous leptin administration led to a significant reduction in food intake in young mice but had no effect on food intake in middle-aged male mice. This loss of the satiety effect of leptin appeared to be transient, with leptin administration leading to the greatest inhibition of food intake in the aged male mice. Subsequently, we investigated whether these differences were due to changes in leptin transport into the brain with ageing. No change in leptin clearance from the blood or transport into the brain was observed, suggesting the emergence of central resistance to leptin in middle age. These studies demonstrate the presence of dynamic and age-specific changes in the satiety effects of leptin in male mice and highlight the requirement for age to be carefully considered when undertaking metabolic studies in rodents.

Metabolic programming of organ-specific natural killer cell responses

Cells of the mammalian innate immune system have evolved to protect the host from various environmental or internal insults and injuries which perturb the homeostatic state of the organism. Among the lymphocytes of the innate immune system are natural killer (NK) cells, which circulate and survey host tissues for signs of stress, including infection or transformation. NK cells rapidly eliminate damaged cells in the blood or within tissues through secretion of cytolytic machinery and production of proinflammatory cytokines. To perform these effector functions while traversing between the blood and tissues, patrolling NK cells require sufficient fuel to meet their energetic demands. Here, we highlight the ability of NK cells to metabolically adapt across tissues, during times of nutrient deprivation and within tumor microenvironments. Whether at steady state, or during viral infection and cancer, NK cells readily shift their nutrient uptake and usage in order to maintain metabolism, survival, and function.

Hippocampal neuroimmune response in mice undergoing serial daily torpor induced by calorie restriction

Hibernating animals demonstrate a remarkable ability to withstand extreme physiological brain changes without triggering adverse neuroinflammatory responses. While hibernators may offer valuable insights into the neuroprotective mechanisms inherent to hibernation, studies using such species are constrained by the limited availability of molecular tools. Laboratory mice may serve as an alternative, entering states of hypometabolism and hypothermia similar to the torpor observed in hibernation when faced with energy shortage. Notably, prolonged calorie restriction (CR) induces serial daily torpor patterns in mice, comparable to species that utilize daily hibernation. Here, we examined the neuroinflammatory response in the hippocampus of male C57BL/6 mice undergoing serial daily torpor induced by a 30% CR for 4 weeks. During daily torpor episodes, CR mice exhibited transient increases in TNF-α mRNA expression, which normalized upon arousal. Concurrently, the CA1 region of the hippocampus showed persistent morphological changes in microglia, characterized by reduced cell branching, decreased cell complexity and altered shape. Importantly, these morphological changes were not accompanied by evident signs of astrogliosis or oxidative stress, typically associated with detrimental neuroinflammation. Collectively, the adaptive nature of the brain's inflammatory response to CR-induced torpor in mice parallels observations in hibernators, highlighting its value for studying the mechanisms of brain resilience during torpor. Such insights could pave the way for novel therapeutic interventions in stroke and neurodegenerative disorders in humans.

Dissociable encoding of motivated behavior by parallel thalamo-striatal projections

The successful pursuit of goals requires the coordinated execution and termination of actions that lead to positive outcomes. This process relies on motivational states that are guided by internal drivers, such as hunger or fear. However, the mechanisms by which the brain tracks motivational states to shape instrumental actions are not fully understood. The paraventricular nucleus of the thalamus (PVT) is a midline thalamic nucleus that shapes motivated behaviors via its projections to the nucleus accumbens (NAc)1,2,3,4,5,6,7,8 and monitors internal state via interoceptive inputs from the hypothalamus and brainstem.3,9,10,11,12,13,14 Recent studies indicate that the PVT can be subdivided into two major neuronal subpopulations, namely PVTD2(+) and PVTD2(-), which differ in genetic identity, functionality, and anatomical connectivity to other brain regions, including the NAc.4,15,16 In this study, we used fiber photometry to investigate the in vivo dynamics of these two distinct PVT neuronal types in mice performing a foraging-like behavioral task. We discovered that PVTD2(+) and PVTD2(-) neurons encode the execution and termination of goal-oriented actions, respectively. Furthermore, activity in the PVTD2(+) neuronal population mirrored motivation parameters such as vigor and satiety. Similarly, PVTD2(-) neurons also mirrored some of these parameters, but to a much lesser extent. Importantly, these features were largely preserved when activity in PVT projections to the NAc was selectively assessed. Collectively, our results highlight the existence of two parallel thalamo-striatal projections that participate in the dynamic regulation of goal pursuits and provide insight into the mechanisms by which the brain tracks motivational states to shape instrumental actions.

Anti-apoptotic MCL-1 promotes long-chain fatty acid oxidation through interaction with ACSL1

MCL-1 is essential for promoting the survival of many normal cell lineages and confers survival and chemoresistance in cancer. Beyond apoptosis regulation, MCL-1 has been linked to modulating mitochondrial metabolism, but the mechanism(s) by which it does so are unclear. Here, we show in tissues and cells that MCL-1 supports essential steps in long-chain (but not short-chain) fatty acid β-oxidation (FAO) through its binding to specific long-chain acyl-coenzyme A (CoA) synthetases of the ACSL family. ACSL1 binds to the BH3-binding hydrophobic groove of MCL-1 through a non-conventional BH3-domain. Perturbation of this interaction, via genetic loss of Mcl1, mutagenesis, or use of selective BH3-mimetic MCL-1 inhibitors, represses long-chain FAO in cells and in mouse livers and hearts. Our findings reveal how anti-apoptotic MCL-1 facilitates mitochondrial metabolism and indicate that disruption of this function may be associated with unanticipated cardiac toxicities of MCL-1 inhibitors in clinical trials.

The landscape of fetus metabolism in maternal hyperglycemia

Maternal hyperglycemia contributes to abnormal fetal development; yet, how it affects fetal metabolism is poorly understood. Perez-Ramirez and colleagues recently provided a comprehensive metabolic atlas of fetal organs isolated from normal and diabetic pregnant mice, identifying novel metabolites and alterations in tissue glucose utilization throughout mid-to-late gestation by maternal hyperglycemia.

Hyperglycemia and circadian disruption lead to retinal dysfunction in a stabilized colony of the fat sand rat Psammomys obesus

PURPOSE

The Fat Sand Rat (Psammomys obesus) recapitulates several features of human pre-proliferative diabetic retinopathy, but data are restricted to wild animals, incompatible with stringent biomedical research criteria. To overcome this barrier, we characterized retinal changes in a colony of P. obsesus maintained under strictly controlled housing conditions.

METHODS

Animals were maintained on low or high caloric energy diets, and raised under either standard (12 h light/12 h dark) or shortened (5 h light/5 h dark) photoperiods. Visual responses were tested by electroretinography, while structural/molecular changes were assayed by immunochemistry and molecular biology (RNAseq and qPCR).

RESULTS

Whereas high calorie diet alone did not induce hyperglycemia, coupled with short photoperiod >80 % animals developed severe hyper-insulinemia by 15 weeks, and 16 % animals further developed hyperglycemia. In these groups, electroretinography showed significant declines in visual responses in both hyper-insulinemic and hyperglycemic animals, especially in photopic (cone) responses. Transcriptomics analysis of hyperglycemic compared to low caloric controls revealed major upregulation in pathways involved in glial activation, extracellular matrix remodeling, inflammation, cytokine production, partial ischemic responses and angiogenesis. Western blotting against rhodopsin and cone opsin also showed decreased levels in both groups, overall decreases being greater for cones than rods in hyperglycemic animals.

CONCLUSIONS

P. obesus maintained in rigorously monitored captive conditions, albeit showing attenuated responses to dietary overload compared to wild counterparts, nevertheless do develop some retinal features of diabetic retinopathy-like degeneration. Such a colony with known sanitary status opens their broader use for biomedical research.

POMC-specific knockdown of MeCP2 leads to adverse phenotypes in mice chronically exposed to high fat diet

Methyl-CpG binding protein 2 (MeCP2) is an epigenetic factor associated with the neurodevelopmental disorders Rett Syndrome and MECP2 duplication syndrome. Previous studies have demonstrated that knocking out MeCP2 globally in the central nervous system leads to an obese phenotype and hyperphagia, however it is not clear if the hyperphagia is the result of an increased preference for food reward or due to an increase in motivation to obtain food reward. We show that mice deficient in MeCP2 specifically in pro-opiomelanocortin (POMC) neurons have an increased preference for high fat diet as measured by conditioned place preference but do not have a greater motivation to obtain food reward using a progressive ratio task, relative to wildtype littermate controls. We also demonstrate that POMC-Cre MeCP2 knockout (KO) mice have increased body weight after long-term high fat diet exposure as well as elevated plasma leptin and corticosterone levels compared to wildtype mice. Taken together, these results are the first to show that POMC-specific loss-of-function Mecp2 mutations leads to dissociable effects on the rewarding/motivational properties of food as well as changes to hormones associated with body weight homeostasis and stress.

Fasting-activated ventrolateral medulla neurons regulate T cell homing and suppress autoimmune disease in mice

Dietary fasting markedly influences the distribution and function of immune cells and exerts potent immunosuppressive effects. However, the mechanisms through which fasting regulates immunity remain obscure. Here we report that catecholaminergic (CA) neurons in the ventrolateral medulla (VLM) are activated during fasting in mice, and we demonstrate that the activity of these CA neurons impacts the distribution of T cells and the development of autoimmune disease in an experimental autoimmune encephalomyelitis (EAE) model. Ablation of VLM CA neurons largely reversed fasting-mediated T cell redistribution. Activation of these neurons drove T cell homing to bone marrow in a CXCR4/CXCL12 axis-dependent manner, which may be mediated by a neural circuit that stimulates corticosterone secretion. Similar to fasting, the continuous activation of VLM CA neurons suppressed T cell activation, proliferation, differentiation and cytokine production in autoimmune mouse models and substantially alleviated disease symptoms. Collectively, our study demonstrates neuronal control of inflammation and T cell distribution, suggesting a neural mechanism underlying fasting-mediated immune regulation.

Effects of prenatal dexamethasone exposure on adult C57BL/6J mouse metabolism and oxidative stress

Prenatal glucocorticoid exposure has been shown to alter hypothalamic-pituitary-adrenal axis function resulting in altered fetal development that can persist through adulthood. Fetal exposure to excess dexamethasone, a synthetic glucocorticoid, has been shown to alter adult behaviour and metabolism. This study investigated the effects prenatal dexamethasone exposure had on adult offspring cardiac and liver metabolism and oxidative stress. Pregnant C57BL/6 mice received a dose of 0.4 mg/kg dexamethasone on gestational days 15-17. Once pups were approximately 7 months old, glucose uptake was determined using positron emission tomography and insulin resistance (IR) was determined by homeostatic model assessment (HOMA) IR calculation. Oxidative stress was assessed by measuring 4-hydroxynonenal protein adduct formation and total reactive oxygen species. Female dexamethasone group had significantly increased glucose uptake when insulin stimulated compared to vehicle-treated mice. HOMA IR revealed no evidence of IR in either male or female offspring. There was also no change in oxidative stress markers in either cardiac or liver tissues of male or female offspring. These data suggest that prenatal dexamethasone exposure in male mice does not alter oxidative stress or metabolism. However, prenatal dexamethasone exposure increased glucocorticoids, cardiac glucose uptake, and pAkt signaling in female heart tissues in adult mice, suggesting there are sex differences in prenatal dexamethasone exposure.