Ketone body (KB) utilization increases during fasting and exercise due to enhanced hepatic fatty acid oxidation and KB production via the rate-limiting mitochondrial enzyme hydroxymethylglutaryl-CoA synthase (HMGCS2). Since KB metabolism intersects with multiple metabolic pathways and skeletal muscle KB catabolism rises during exercise, we tested the hypothesis that liver-specific HMGCS2 knockouts (KO) would have reduced energy expenditure (EE) and changes in the mitochondrial proteome of skeletal muscle with chronic exercise through voluntary wheel running (VWR), time-restricted feeding (TRF), or both combined to boost hepatic KB production and utilization. Control (CON) and HMGCS2 knockout (KO) mice (n = 6-8 per group) underwent sedentary ad libitum feeding (SED + AL), SED + TRF, VWR + AL, and VWR + TRF for 16 wk, with whole body EE measured using indirect calorimetry. In CON mice, VWR increased total EE by 19.5% and nonresting EE by 50% under AL conditions, and total EE by 16% and nonresting EE by 47.9% under TRF conditions. However, the EE increases seen with VWR did not occur in KO mice. Proteomic analysis revealed that the loss of liver HMGCS2 significantly impacted proteins involved in metabolic processes within skeletal muscle, including reduced oxidative phosphorylation (OXPHOS) protein expression in SED KO mice compared with sedentary CON. Notably, VWR restored OXPHOS protein expression in the muscle of the liver HMGCS2 KO but did not alter it in the CON. Furthermore, muscle from liver HMGCS2 KO mice had elevated expression of glycolytic pathways in sedentary and VWR conditions. These results indicate that hepatic ketogenic deficiency (HMGCS2 KO) diminishes exercise-induced increases in EE and uniquely impacts baseline and exercise-related adaptations in the metabolic and mitochondrial proteome of skeletal muscle.

The mechanisms by which exercise modulates liver metabolism are poorly understood. Leveraging data from molecular transducers of physical activity consortium (MoTrPAC), we analyzed liver adaptations across 1, 2, 4, and 8 weeks of exercise in male and female rats using multi-omics approaches. Female livers displayed a progressive increase in oxidative phosphorylation (OXPHOS) protein complexes, while male livers showed an increased acetylation of OXPHOS, tricarboxylic acid cycle, and fatty acid oxidation enzymes. Mechanistic examination revealed that these sex-specific acetylation events are partially mediated by carnitine acetyltransferase. Exercise enhanced liver cholesterol and bile acid synthesis, reducing liver lipid metabolites in males after 8 weeks of exercise. Male rats had higher fecal cholesterol and cholic acid levels, indicating a sex-specific mechanism of lipid excretion with exercise. Eight weeks of training reduced markers related to hepatic stellate cell activation and fibrosis in both sexes. This study highlights the sexual dimorphic and temporal molecular signatures by which exercise modulates liver metabolism to provide hepatoprotective effects.

Cerebral hypometabolism is a hallmark of Alzheimer's Disease (AD) and it is possible that alternative fuel substrates such as lactate could be beneficial in AD. However, how efficiently lactate is metabolized in AD individuals compared to cognitively healthy (CH) older adults has never been characterized. CH ( n  = 12) and AD ( n  = 12) older adults were enrolled into the Lactate for Energy and Neurocognition (LEAN) trial at the KU ADRC (NCT05207397). Subjects underwent a single study visit “lactate clamp”, where they received stable infusions of D 2 -glucose, [3- 13 C] sodium lactate, and a variable infusion of unlabeled sodium lactate for 120 minutes to achieve 4mM blood lactate. Cognitive tests (NIH toolbox) were administered prior to infusion and at minute 90, during steady state. Breath and blood sampling were performed at 0, 60, 75, 90, and 120 minutes to calculate lactate metabolism. AD blood biomarkers were assessed at 0 and 120 minutes in EDTA plasma. Brain-derived tau (BD-tau), pTau217, pTau181, total tau, glial fibrillary acidic protein (GFAP), neurofilament light-chain (NfL), and Brain Derived Neurotrophic Factor (BDNF) were analyzed by Simoa-HDX (Quanterix). β-amyloid 42 and 40 were analyzed using Lumipulse (Fujirebio). We measured creatinine (RayBiotech) and hematocrit (Immunostics, Inc) to assess change in kidney function and blood volume. AD subjects oxidized lactate as well as CH subjects ( p  = 0.988). Processing speed ( p  <0.001) and global cognition ( p  <0.001) were improved after infusion. Interestingly, we observed reductions in plasma BD-tau ( p  <0.001), pTau217 ( p  <0.001), pTau181 ( p  <0.001), GFAP ( p  <0.001), and NfL ( p  <0.001) in both AD and CH groups after lactate infusion. Total tau and BDNF levels were unchanged by infusion ( p  = 0.133 and 0.182). Pre/post change in plasma volume and eGFR were 4% and 16.9%, respectively. Our objective was to characterize whole-body lactate metabolism in AD, an understand how lactate might affect cognition. We found that lactate infusion reduced BD-tau, phosphotau species, GFAP, and NfL which could be due to systemic or brain-based changes in proteostasis. Biomarker changes were not explained by change in plasma volume or kidney function, and only brain-specific biomarkers were affected. Additional analyses are planned to investigate the relationship of lactate and perturbations in AD biomarkers.

BackgroundRising Alzheimer's disease (AD) incidence underscores the need to identify modifiable risk factors. The "obesity paradox" suggests higher late-life body mass index (BMI) may reduce AD risk. Because BMI does not distinguish between fat and lean mass, investigating body composition and brain amyloid accumulation may clarify this relationship.ObjectiveThis study tested whether baseline body stature predicts one-year change in brain amyloid.MethodsUsing data from the Alzheimer's Prevention through Exercise trial, we examined whether baseline body stature and composition (BMI, fat mass index [FMI], lean mass index [LMI], and total fat and lean mass) predicted one-year change in brain amyloid among 106 cognitively healthy older adults enriched with elevated amyloid status.ResultsHigher baseline BMI predicted less one-year amyloid accumulation globally (β = -0.33, p = 0.001) and in five of six brain regions (p = 0.001-0.05). Higher FMI predicted less amyloid accumulation globally (β = -0.35, p < 0.001) and in all six regions (p < 0.001-0.02), while higher LMI predicted less accumulation globally and in four regions (p < 0.001-0.02). Higher total fat mass was associated with less amyloid globally and regionally (p < 0.001-0.02), whereas higher total lean mass predicted reduced accumulation only in the lateral temporal lobe (p = 0.01).ConclusionsLarger body mass predicted less amyloid accumulation in cognitively healthy older adults over one year. More research is needed to investigate whether larger body stature protects against amyloid accumulation and explore underlying mechanisms.Clinical Trial RegistrationClinicalTrials.gov, Identifier (NCT02000583).

ABSTRACT Apolipoprotein E4 (APOE4) is the strongest genetic risk factor for Alzheimer's disease (AD), yet it's unclear how this allele promotes disease. While factors like diet and sex may modify AD susceptibility in APOE4 carriers, the interaction between these factors is poorly understood. Here, we sought to determine if APOE4, sex, and diet interact to influence AD related outcomes in mice. Male and female APOE3 and APOE4 targeted replacement (TR) mice were fed a low‐fat diet or high‐fat diet from 4 to 8 months old. Serum neurodegenerative disease biomarkers, brain amyloid beta (Aβ), APOE, and tau, learning and memory, hippocampal mitochondrial function and proteomics data were collected. Serum GFAP and NfL were unaffected by APOE4, while HFD was associated with greater serum NfL and GFAP. Whole brain Aβ was significantly altered by sex, diet, and genotype. There was a main effect of genotype on levels of brain APOE with levels being lower in APOE4 mice. APOE4 TR mice also exhibited impaired learning before diet. Proteomic analysis revealed that APOE4 exerts diet‐ and sex‐dependent effects on mitochondrial pathways. This included downregulation of pyruvate metabolism in HFD males and oxidative phosphorylation in HFD females. Basal respiration was lower in APOE4 versus APOE3 TR females. We provide novel evidence that APOE4 may drive early sex‐ and diet‐dependent reductions in pathways that support brain mitochondrial energy metabolism.

BACKGROUND:Carrying a germline BRCA1 mutation increases the risk of several cancers, including breast and ovarian cancer. While BRCA1 is best known for its role in DNA damage repair, emerging evidence suggests broader functions in metabolic regulation. METHODS:To determine whether heterozygous loss of Brca1, as occurs in individuals carrying a germline mutation, modifies susceptibility to diet-induced metabolic dysfunction in a sex-dependent manner, wild-type (WT) and Brca1+/- mice of both sexes were fed a low-fat diet (LFD) or high-fat diet (HFD) and underwent longitudinal metabolic phenotyping. RESULTS:Female HFD-fed Brca1+/- mice exhibited exacerbated obesity, increased adiposity, hyperinsulinemia, and impaired glucose tolerance compared with WT controls. In contrast, male Brca1+/- mice showed modest resistance to HFD-induced weight gain and improved glucose tolerance. Human genetic analyses supported an association between BRCA1 and metabolic traits, including body mass index (BMI), type 2 diabetes and liver fat accumulation. Despite divergent systemic metabolic phenotypes, Brca1 heterozygosity increased susceptibility to HFD-induced hepatic steatosis in both sexes. In HFD-fed female Brca1+/- mice, steatosis was associated with transcriptional remodeling linked to lipid accumulation and oxidative stress responses, together with reduced mitochondrial respiratory complex IV activity, altered mitochondrial morphology, lower hepatic ATP levels. Treatment with the dual GLP‑1/GIP receptor agonist tirzepatide improved systemic metabolic dysfunction and hepatic steatosis in HFD-fed female Brca1+/- mice. CONCLUSIONS:These findings identify Brca1 heterozygosity as a modifier of metabolic disease susceptibility and expand the biological role of BRCA1 beyond tumor suppression to include the regulation of metabolic health.

Alzheimer's disease and related tauopathies are escalating public health threats, particularly in the context of obesity and metabolic dysfunction, which accelerate cerebral glucose hypometabolism, tau pathology, neurodegeneration, and cognitive decline. Ketogenic therapies reconfigure systemic fuel metabolism, with emerging evidence for neuroprotection. (R,S)-1,3-butanediol (BD) raises circulating D- and L-β-hydroxybutyrate (βOHB) concentrations. To evaluate whether BD improves cognitive function across dietary contexts, male and female tau-transgenic mice and littermate controls received 10% BD in drinking water for 20 or 30 weeks starting at 6 weeks of age. BD rapidly induced ketosis (1.5-3.0 mM βOHB) in chow-fed mice, with L-βOHB contributing to ∼75% of the circulating βOHB pool. Despite minimal effects of BD on body weight and glucose homeostasis, and no effect on histopathological tau signal, 20-week BD treatment improved memory to control levels in chow-fed female tauopathy mice. Isotope-tracing untargeted metabolomics revealed that BD-treatment differentially affected glucose-derived 13 C-enrichment of metabolites in brains of male and female mice. BD-induced cognitive benefits in tau-transgenic mice were abrogated when mice were maintained on BD for 30 weeks on standard chow or when mice were administered BD over 20 weeks while maintained on a high-fat, Western diet, Notably, BD-induced ketosis was blunted in mice consuming Western diet. Moreover, intermittent ketogenic diet-induced ketosis failed to improve cognition in Western diet-fed tauopathy mice. These results suggest BD-induced ketosis extends cognitive benefits in a manner dependent on biological sex and nutritional metabolic status. Taken together, these data contextualize the roles of βOHB as modulators of cognitive resilience in tauopathy.

Whole-body estrogen receptor α (ERα) knockout mice develop hepatic steatosis; however, liver-specific ERα knockout (LERKO) mice fail to recapitulate this susceptibility and maintain normal hepatic mitochondrial function. However, estrogen-mediated protection against hepatic steatosis is lost in LERKO mice following ovariectomy (OVX). Here, we tested whether loss of hepatic ERα blunts estrogen modulation of hepatic mitochondrial respiratory capacity and mitochondrial proteome following ovariectomy (OVX). Sham or ovariectomy (OVX) surgery was performed in middle-aged female mice (36-40 weeks), followed by AAV injection to generate Control (Con; GFP) or LERKO mice (Cre). All mice were placed on a high-fat diet (HFD) for 10 weeks following surgery. Half of the OVX mice received 17-beta estradiol (E2) replacement (OVX+E2) for the last 4 weeks of HFD. OVX mice had greater body mass and adiposity, which was reversed by E2 replacement in both Con and LERKO mice. While E2 replacement reduced steatosis in both Con and LERKO OVX mice, the LERKO OVX mice maintained greater hepatic triglyceride content. E2 replacement promoted greater basal and ADP-stimulated (State 3) mitochondrial respiration in Con OVX but not in LERKO OVX mice under palmitate-supported conditions. Changes in mitochondrial respiration could not be attributed to altered responses to changes in energy demand (G ATP ) or to alterations in mitochondrial H 2 O 2 production. Conversely, maximal coupled branched-chain amino acid-supported respiration was universally suppressed by E2 replacement. Proteomics analysis revealed E2-mediated reductions in hepatic mitochondrial energy transduction, with relatively minimal differences between Con and LERKO mice. In conclusion, post-ovariectomy estrogen treatment reduces steatosis in the absence of hepatic ERα; however, triglyceride levels remain higher, and mitochondrial respiratory deficits persist despite similar proteomic signatures, suggesting that ERα signaling is required for optimal estrogen hepatic responsiveness.

Alzheimer's disease (AD) progresses along a continuum for years to possibly decades prior to cognitive decline. Although AD is primarily an age-related brain pathology, increasing evidence indicates dysfunction in peripheral nerves and skeletal muscle may manifest early in the disease progression. However, the underlying cause(s) for peripheral nerve dysfunction leading to impaired skeletal muscle torque production are not understood. Sciatic nerves from 5xFAD and wild-type (WT) mice were analyzed by tandem mass tag (TMT)-labeled proteomics at 3, 4, and 7 months, identifying proteome remodeling coincides with functional declines at 4 months particularly in pathways linked to mitochondrial turnover, calcium handling, and inflammation. We hypothesized either voluntary wheel running or donepezil treatment, begun prior to neuromuscular decline, would delay manifestation of neuromuscular impairment in 5xFAD mice. Separate cohorts, using 3-month-old 5xFAD mice and WT littermates, were given voluntary wheel access for 4 weeks or treated with the acetylcholinesterase inhibitor donepezil. We assessed tibial nerve stimulated plantar flexion torque and sciatic nerve compound (motor) neuron action potential (CNAP) in vivo at 4 months. Both exercise and donepezil attenuated in vivo nerve-stimulated muscle torque and CNAP dysfunction. Further, both exercise and donepezil attenuated the proteomic remodeling of the sciatic nerve through both shared and independent mechanisms that converged on mitochondria-centric pathways. Our findings in the 5xFAD model of AD support the notion that early phenotypes of AD are evident in the periphery that may have implications for timing of interventions.

Liver-specific ERα knockout (LERKO) mice with normal ovarian function are not susceptible to steatosis and maintain mitochondrial function. Here, we tested whether loss of hepatic ERα blunts estrogen modulation of hepatic mitochondrial respiratory capacity and mitochondrial proteome following ovariectomy (OVX). Sham or OVX surgery was performed in middle-aged female mice (36-40 weeks), followed by adeno-associated virus (AAV) injection to generate Control (Con; green fluorescent protein) or LERKO mice (Cre). All mice were placed on a high-fat diet for 10 weeks following surgery. Half of the OVX mice received 17β-estradiol (E2) replacement (OVX + E2) for the last 4 weeks. OVX mice had greater body mass and adiposity, which was reversed by E2 replacement in both Con and LERKO mice. E2 replacement reduced steatosis in both Con and LERKO OVX mice, but the LERKO OVX mice maintained greater hepatic triglycerides. E2 replacement promoted greater basal and ADP-stimulated (State 3) mitochondrial respiration in Con OVX but not in LERKO OVX mice. Changes in mitochondrial respiration could not be attributed to altered responses to changes in energy demand (GATP) or to alterations in mitochondrial H2O2 production. Conversely, maximal coupled branched-chain amino acid-supported respiration was universally suppressed by E2 replacement. Proteomics analysis revealed E2-mediated reductions in hepatic mitochondrial energy transduction in both Con and LERKO mice. In conclusion, post-OVX estrogen treatment reduces steatosis in the absence of hepatic ERα; however, steatosis remains higher, and mitochondrial deficits persist despite similar proteomic changes, suggesting ERα is required for optimal response to estrogen in modulating hepatic mitochondrial respiration.

The beneficial effects of aerobic exercise in aging are well established but can be limited by low aerobic capacity. Resistance exercise is also beneficial, yet little is known about how intrinsic aerobic capacity influences resistance exercise performance or related motor outcomes in advanced age. We trained 18–24-month-old rats selectively bred for low (LCR) or high (HCR) aerobic capacity to perform a unilateral forelimb resistance exercise task and assessed task engagement, force production, and response duration. Orolingual motor function was evaluated as a complementary measure of cranial motor performance. Circulating extracellular vesicles (EVs) were measured as potential systemic correlates of intrinsic aerobic capacity and resistance exercise. Task acquisition was similar between LCR and HCR rats as was task engagement across increasing force requirements. HCR rats produced greater force relative to body weight at lower force requirements, whereas LCR rats exhibited longer press–hold durations across all requirements. Licking speed and total licks were greater in HCR rats, while tongue motility declined over time in sedentary LCR rats but increased in resistance exercise-trained LCR rats. Circulating EV numbers differed between LCR and HCR groups but not as a function of exercise. Together, these findings indicate that low intrinsic aerobic capacity does not affect resistance exercise engagement and performance in aging and that resistance exercise may confer functional benefits beyond the trained musculature. Resistance exercise may therefore represent a viable alternative for preserving muscle function during aging in individuals with limited aerobic capacity.

Apolipoprotein E (APOE) is essential for lipid homeostasis and has been extensively studied in Alzheimer's disease (AD). Individuals carrying an APOE4 allele have an increased risk of AD and exhibit deficits in energy metabolism, including glucose utilization and mitochondrial dysfunction. While the role of APOE in the liver is well characterized, the impact of APOE genotype on hepatic health and metabolism remains poorly understood. We sought to investigate this using young APOE3 and APOE4-targeted replacement mice and isogenic-induced pluripotent stem cell (iPSC)-derived hepatocyte-like cells (iHLCs). Proteomic and functional assays show that APOE4 causes extensive changes to liver mitochondrial function in a sex-specific manner in mice and alters glucose and lipid metabolism. APOE4 also impairs mitochondrial function in iHLCs, shifts metabolism towards glycolysis, increases reliance on fatty acid utilization, and drives lipid accumulation. Together, these findings show that APOE genetic variation causes mitochondrial dysfunction and rewires hepatic metabolism.

Background:A recent Lancet Commission estimated that up to 45% of Alzheimer's Disease and Related Dementias (ADRD) cases could be prevented by addressing modifiable lifestyle risk factors. Meanwhile, genome-wide association studies (GWAS) have shown that common genetic variants also account for substantial ADRD risk. Whether a favorable lifestyle can offset risk in genetically predisposed individuals remains unclear. Methods:We conducted a retrospective cohort study of 105,886 participants from the All of Us Research Program enrolled between 2018-2023. Participants were over age 49, assigned male or female at birth, of European ancestry, and without ADRD at baseline. ADRD diagnoses were identified via electronic health records (EHR). Fourteen potentially modifiable risk factors for ADRD were assessed using surveys, EHR records, and wearable data. Genetic risk was quantified as a polygenic risk score (PRS) based on 81 independent GWAS loci and APOE ε4 genotype. Results:Overall, 967 incident ADRD events occurred over a median follow-up of 3.7 years. Ten out of 13 modifiable risk factors were significantly associated with ADRD. When grouped into risk factor profiles, intermediate and unfavorable modifiable risk factor scores were associated with substantially higher ADRD risk (HR 3.07, 95% CI 2.47-3.83; HR 8.01, 95% CI 6.39- 10.05, respectively) compared to a favorable lifestyle; APOE ε4 dosage and polygenic risk score were also independently associated with ADRD risk. Among individuals in the highest polygenic risk group, a favorable lifestyle reduced ADRD risk from HR 18.63 (95% CI 10.25-33.86) to 1.90 (95% CI 0.94-3.81), whereas APOE ε4 homozygotes remained at elevated risk even with a favorable lifestyle (HR 6.52, 95% CI 2.97-14.33). Conclusions:Our data suggest ADRD risk is driven more by modifiable risk factors and APOE genotype than polygenic risk score. Future genomic-informed risk assessments for ADRD should calibrate their findings to accurately identify high-risk individuals.

BACKGROUND AND AIMS:Exercise and fasting are recognized for their ability to improve brain health and mitigate neurodegeneration. However, little is known about how these interventions acutely impact mitochondrial quality control mechanisms including mitophagy. METHODS:We examined the effects of a single bout of fasting and exercise (FEx) on hippocampal mitochondrial function and proteomic remodeling in male and female mice. To assess in vivo autophagy dynamics, we combined proteomics with chloroquine (CQ) inhibition of autophagic flux. Mice were assigned to sedentary (Sed), fasting (F), exercise (Ex), or combined FEx groups and received unilateral intrahippocampal injections of CQ or PBS following treatments. Four hours later, hippocampi were collected for analysis. RESULTS:LC3-II levels significantly increased in the FEx group only following CQ treatment, indicating enhanced autophagic flux. Proteomic profiling showed sedentary males failed to mount a robust response to FEx however females exhibited upregulation of proteins involved in the TCA cycle, glutathione metabolism, and oxidative phosphorylation, suggesting greater mitochondrial adaptability. Functional assays supported these findings, females showed increased complex IV activity post-FEx. The mitochondrial DNA / nuclear DNA ratio increased after FEx regardless of sex, and upstream regulator analysis predicted activation of mitochondrial biogenesis. CONCLUSIONS:Together, these data reveal sex-specific mitochondrial remodeling in response to acute fasting and exercise. Defining these normative responses is critical for understanding how mitochondrial adaptability shapes resilience or vulnerability to neurological challenges.

OBJECTIVE:Ketone body metabolism is linked to brain health benefits, including delaying age-related cognitive decline. Exercise, particularly when combined with an overnight fast, stimulates ketone body turnover and improves brain metabolism and cognition. Yet, whether ketone metabolism is obligatory for this response is unknown. Here, we use chronic exercise via voluntary wheel running plus time-restricted feeding (VWR + TRF) to explore whether ketones mediate exercise-induced brain health benefits in middle-aged mice. METHODS:To distinguish the roles of neuronal ketone metabolism vs. hepatic ketone production, we studied middle-age female neuronal-specific SCOT knockout mice and hepatocyte-specific HMGCS2 knockout mice, respectively. VWR + TRF was compared to sedentary ad-libitum fed mice to assess the impact on whole-body metabolism, cognition, and hippocampal molecular adaptations. VWR + TRF upregulated systemic lipid oxidation in all mice during the fasting period. RESULTS:In female SCOT-Neuron-KO mice, we show impaired responses to VWR + TRF in indices of short- and long-term memory. Proteomic analysis of isolated hippocampi revealed that SCOT-Neuron-KO mice failed to globally upregulate key facilitators of synaptic function, including leucine-rich repeated transmembrane proteins, neurexins, and neuroligins. In female HMGCS2-Liver-KO mice, impaired responses to VWR + TRF in indices of short-term memory were paired with an upregulation in hippocampal ketogenesis machinery, suggesting potential in vivo evidence of cerebral ketogenesis, a mechanism mitigating an otherwise more pronounced behavioral phenotype. CONCLUSION:Together, these findings suggest that neuronal ketone body utilization is essential for, while hepatic-derived ketone bodies contribute to, the full cognitive and synaptic adaptations to VWR + TRF, supporting ketone metabolism as a key mechanistic link between metabolic state and brain health in midlife.

BACKGROUND:Elevated circulating lipids increase oxidative stress and impair vascular function, but their effects on sympathetic-vascular control in humans are not well understood. We tested the hypothesis that intravenous lipid infusion enhances sympathetic-vascular transduction and beat-to-beat arterial pressure variability in humans, and that these effects are mediated, in part, by oxidative stress. METHODS:In a randomized, double-blind, placebo-controlled crossover study, healthy adults underwent 2 hours of intravenous lipid infusion (20% Intralipid) with coinfusion of ascorbic acid or saline control. Endothelial function was assessed by brachial artery flow-mediated dilation, and muscle sympathetic nerve activity (MSNA) was recorded using microneurography. Sympathetic-vascular transduction was quantified by signal-averaging beat-to-beat mean arterial pressure (MAP) and brachial vascular conductance responses after spontaneous MSNA bursts. RESULTS:Plasma malondialdehyde increased during lipid+saline (peak: 48±12 versus BL: 42±11 ng/mL; P<0.01) and decreased with lipid+ascorbic acid (nadir: 34±12 versus baseline: 45±14 ng/mL; P<0.01). Lipid+saline reduced flow-mediated dilation (4.1±2.7 versus baseline: 6.8±3.2%; P<0.01), increased beat-to-beat MAP variability (1.7±0.5 versus baseline: 1.5±0.4 mm Hg; P=0.01), and augmented responses to large MSNA bursts for MAP (4.7±2.0 versus baseline: 3.4±1.4%; P=0.03) and vascular conductance (-9.3±3.4 versus BL: -6.7±3.7%; P=0.01). Despite lipid-mediated increases in MSNA burst amplitude, coinfusion of ascorbic acid was not associated with an increase in beat-to-beat MAP variability (1.6±0.4 versus baseline: 1.5±0.4 mm Hg; P=0.23) and MAP (4.4±0.9 versus baseline: 4.1±0.8%; P=0.37) and vascular conductance (-6.8±4.6 versus baseline: -9.4±5.5%; P<0.01) responses to large MSNA bursts, although reductions in flow-mediated dilation were observed (5.0±3.0 versus baseline: 8.1±3.8%; P<0.01). CONCLUSIONS:Lipid infusion enhances sympathetic-vascular transduction and arterial pressure variability, consistent with a redox-sensitive mechanism, while impairing endothelial function via pathways that ascorbic acid does not fully reverse. REGISTRATION:URL: https://www.clinicaltrials.gov; Unique identifier: NCT04832009.

Apolipoprotein E (APOE) genetic variation is the strongest genetic risk factor for Alzheimer’s Disease (AD). Prior studies on APOE genotype-dependent changes have largely focused on amyloid beta (Aβ) aggregation and lipid metabolism. There is an increased interest in the relationship between metabolic function and APOE genetic variation. We examined how APOE genotype affects brain metabolism in young APOE3 and APOE4 targeted replacement (TR) mice. In addition, we examined cell type-specific differences using induced pluripotent stem cell (iPSC)-derived astrocytes and neurons. We found sex and APOE genotype dependent changes to brain metabolism where APOE4 mice show signs of metabolic stress. Using proteomics and stable isotope tracing, we found that APOE4 iAstrocytes and iNeurons exhibit mitochondrial dysfunction, altered citric acid cycle (TCA) cycle, and a metabolic shift from oxidative metabolism towards glycolysis. Taken together, this data indicates APOE4 causes early changes to metabolism within the central nervous system, and this has implications for early intervention to prevent AD. These metabolic alterations may contribute to the inflammatory changes observed in APOE4 cells, linking disrupted energy metabolism with immune activation in the brain. While this study establishes a relationship between APOE genotype and dysregulated bioenergetics, additional studies are needed to investigate underlying mechanisms.

Extensive research has demonstrated endurance exercise to be neuroprotective. Whether these neuroprotective benefits are mediated, in part, by hepatic ketone production remains unclear. To investigate the role of hepatic ketone production on brain health during exercise, healthy 6-month-old female rats underwent viral knockdown of the rate-limiting enzyme in the liver that catalyses the first reaction in ketogenesis: 3-hydroxymethylglutaryl-CoA synthase 2 (HMGCS2). Rats were then subjected to either a bout of acute exercise or 4 weeks of chronic treadmill running (5 days/week) and cognitive behavioural testing. Acute exercise elevated ketone plasma concentration 1 h following exercise. Hepatic HMGCS2 knockdown, verified by protein expression, reduced ketone plasma concentration 1 h after acute exercise and 48 h after chronic exercise. Proteomic analysis and enrichment of the frontal cortex revealed hepatic HMGCS2 knockdown reduced markers of mitochondrial function 1 h after acute exercise. HMGCS2 knockdown significantly reduced state 3 complex I + II respiration in isolated mitochondria from the frontal cortex after chronic exercise. Spatial memory and protein markers of synaptic plasticity were significantly reduced by HMGCS2 knockdown. These deficiencies were prevented by chronic endurance exercise training. In summary, these are the first data to propose that hepatic ketogenesis is required to maintain cognition and mitochondrial function, irrespective of training status, and that endurance exercise can overcome neuropathology caused by insufficient hepatic ketogenesis. These results establish a mechanistic link between liver and brain health that enhance our understanding of how peripheral tissue metabolism influences brain health. KEY POINTS: Decades of literature demonstrate endurance exercise to be neuroprotective. Whether neuroprotective benefits are mediated, in part, by hepatic ketone production remains unclear. This study provides the first set of data that suggest hepatic ketogenesis is required to maintain cognition, synaptic plasticity and mitochondrial function. These data indicate endurance exercise can protect against cognitive decline caused by compromised hepatic ketogenesis. These results establish a mechanistic link between liver and brain function, prompting further investigation of how hepatic metabolism influences brain health.

The mechanisms by which exercise modulate liver metabolism, a central regulator of systemic metabolism, are poorly understood. Leveraging data from MoTrPAC, we analyzed liver adaptations across 1, 2, 4, and 8 weeks of exercise in male and female rats using multi-omic approaches. Female livers displayed a progressive increase in oxidative phosphorylation (OXPHOS) complexes (at the protein level), while male livers showed an increase in acetylation of OXPHOS, TCA cycle, and fatty acid oxidation enzymes. Exercise also enhanced liver cholesterol and bile acid synthesis, reducing liver lipid metabolites in males after 8 weeks of exercise. Male rats had higher fecal cholesterol and cholic acid levels, indicating a sex-specific mechanism of lipid excretion with exercise. Moreover, 8 weeks of training reduced markers related to hepatic stellate cell activation and fibrosis in both sexes. This study highlights the sexual dimorphic and temporal molecular signatures by which exercise modulates liver metabolism to provide hepatoprotective effects.

The role of BRCA1 in cellular metabolism is not fully characterized and what we do understand has been primarily demonstrated in vitro. Our studies aimed to characterize the role of BRCA1 in metabolic pathways in a whole body system. In vivo studies using C57BL/6 wild-type and transgenic humanized BRCA1 mice demonstrate the effect of human BRCA1 on the whole body metabolic phenotype and start to elucidate the mechanism by which this occurs. Promethion metabolic chambers and glucose tolerance tests measured a number of metabolic outputs of male and female mice that were either wild-type (normal mouse Brca1 gene) or humanized BRCA1 mice (knockout Brca1/knock-in human BRCA1 gene). Humanized BRCA1 mice are more lean, hyperactive, display higher energy expenditure, and demonstrate a sexual dimorphism in lean mass and glucose tolerance when compared with wild-type mice on the same genetic background. To begin to elucidate the mechanisms behind the observed metabolic phenotype, we performed mass spectrometry, SuperArray, and Western blot analysis using skeletal muscle, a metabolic organ that significantly impacts energy metabolism. Proteomic and genomic analysis revealed changes in a number of metabolic pathways that may be implicated in the observed whole body metabolic phenotype. We concluded that substituting BRCA1 for Brca1 in an in vivo model altered the overall metabolic profile of humanized BRCA1 mice. Thus, the Brca1/BRCA1 gene appears to have a significant impact on metabolic pathways, and these effects differ from mouse to human.NEW & NOTEWORTHY This is the first in vivo evidence demonstrating the complex effects of BRCA1 expression in whole body metabolism.