Aging selectively degrades neuronal structure and function, yet the signals that actively preserve neuronal integrity over adult life remain incompletely defined. In Caenorhabditis elegans, the PVD sensory neuron develops progressive excessive higher-order dendritic branching during normal aging that correlates with declines in proprioceptive locomotion. Using this system as a quantitative in vivo readout of neuronal healthspan, we identify the cholecystokinin-like neuropeptide NLP-12 as a protective signal that preserves PVD homeostasis across adulthood. nlp-12 loss-of-function animals show early-onset excessive branching and earlier declines in proprioceptive function, whereas nlp-12 overexpression reduces excessive branching in aged adults without extending lifespan, indicating a neuron-focused effect on healthspan. Using an NLP-12::mKate reporter and coelomocyte uptake as an in vivo proxy for secretion, we find that aging is associated with reduced extracellular delivery of NLP-12 and increased retention within the soma of the DVA interneuron, where nlp-12 is predominantly expressed. Consistent with a requirement for secretory trafficking, disrupting the NLP-12 signal peptide abolishes the rescue effects of nlp-12 reintroduction in nlp-12 mutants. Additionally, histamine-gated silencing of DVA during adulthood similarly accelerates PVD excessive branching, supporting an ongoing, adult-stage requirement for this pathway. Receptor genetics further show that the ckr-1/GPCR is required for nlp-12 overexpression-mediated neuroprotection in aged animals. Finally, human cholecystokinin can rescue the branching phenotype in nlp-12 mutants, supporting evolutionary conservation. Together, these findings implicate conserved cholecystokinin-like neuropeptide signaling as an adult maintenance mechanism that buffers age-associated decline in neuronal resilience.

Background:Genome-wide studies in late-onset Alzheimer's disease (LOAD) have uncovered many risk loci, yet identifying the causal genes and clarifying how these genetic signals connect to molecular and cellular mechanisms relevant to AD pathogenesis in vivo remains challenging. Methods:Using Caenorhabditis elegans as a model to identify LOAD-associated genes that drive neurodegenerative processes, we focused on 14 understudied genes and their homologs: ABI3/abi-1, B4GALT3/bre-4, CCDC6/T09B9.4, CLPTM1 (two homologs C36B7.6 and R166.2), CNN2/cpn-2, DMWD/wdr-20, ECHDC3/ech-2, MADD/aex-3, NCK2/nck-1, RABEP1/rabn-5, RIN3/rin-1, SLC39A13/zipt-13, TRAM1/tram-1, and USP6NL/tbc-17. We knocked down these genes by RNAi and quantified lifespan, aging-associated degeneration of two neuron classes, PVD and PLM, and associative learning and short-term memory. Results:Lifespan was unaffected by most knockdowns, and only nck-1 and tbc-17 shortened lifespan. Across neuronal assays, multiple homologs modulated aging with clear neuron-class selectivity. Knockdown of aex-3, C36B7.6, cpn-2, ech-2, rabn-5, rin-1, T09B9.4, and zipt-13 attenuated late-life PVD degeneration, whereas R166.2 and tram-1 accelerated early PVD aging. Only two genes affected PLM aging: R166.2 knockdown exacerbated degeneration, while tbc-17 knockdown attenuated it despite its lifespan-shortening effect. In PLM neurons, tbc-17 knockdown, targeting a Rab GTPase-activating protein, also preserved mitochondrial architecture during early aging and shifted heat stress-induced mitochondrial remodeling toward a pattern consistent with improved quality control. In behavioral assays, ech-2 knockdown, targeting an enoyl-CoA-hydratase, enhanced short-term memory during early stages of aging. To further assess how LOAD-linked genes interact with Aβ-driven neurodegeneration, we developed a model that combines the PVD aging assay with a background expressing human Aβ1-42 pan-neuronally. In this model, Aβ expression accelerated age-dependent PVD degeneration, whereas ech-2 knockdown abolished this Aβ-induced effect. Conclusions:Our findings show that conserved homologs of several understudied LOAD risk genes causally modulate neuronal aging in vivo in a neuron-class-selective manner, often dissociable from organismal longevity. This C. elegans framework translates human genetic associations into quantitative, aging-linked neuronal phenotypes, and our results further emphasize early endosomal and lipid-related processes as key pathways that warrant functional testing in neuronal aging. This study also provides a tractable platform to prioritize targets for cross-species validation and to test synergy with established LOAD risk genes.

Despite significant progress in revealing molecular and cellular changes in aging nervous system, the upstream mechanisms driving these changes remain elusive. Here, we investigate the regulatory roles of non-neural tissues in neuronal aging, using the cutaneous PVD polymodal neuron in Caenorhabditis elegans as a model. We demonstrate that during normal aging, PVD neurons progressively develop excessive dendritic branching, functionally correlated with age-related proprioceptive deficits. Our study further uncovers that decreased skin collagen expression, a common age-related phenomenon across species, triggers PVD aging. Specifically, loss-of-function mutations or adulthood-specific knockdown of dpy-5 or col-120 , both genes coding for cuticular collagens secreted to the epidermal apical surface, induce early-onset excessive dendritic branching in PVD, and proprioceptive deficits. Overexpressing dpy-5 or col-120 mitigates excessive branching without affecting lifespan, suggesting that skin collagens promote healthspan rather than longevity. Notably, these collagens are not involved in aging-associated dendritic beading, another PVD neurodegenerative phenotype distinctively associated with a different mechanosensitive dysfunction. Skin collagens also specifically affect branching in select sub-classes of sensory neurons. Lastly, we identify rig-3 , a neuronal Immunoglobulin Superfamily member not expressed in PVD, functioning in the same pathway as skin collagen genes to preserve PVD dendritic integrity during aging. These findings reveal an important causative role of age-related skin collagen reduction in neuronal aging, independent of their traditionally recognized involvement in direct structural support for neurons. Our study offers new insights into understanding selective neuron vulnerability in aging and age-related diseases, emphasizing the need for multi-tissue strategies in addressing the complexities of neuronal aging.### Competing Interest StatementThe authors have declared no competing interest.

Despite advances in understanding molecular and cellular changes in the aging nervous system, the upstream drivers of these changes remain poorly defined. Here, we investigate the roles of non-neural tissues in neuronal aging, using the cutaneous PVD polymodal sensory neuron in Caenorhabditis elegans as a model. We demonstrate that during normal aging, PVD neurons progressively develop excessive dendritic branching, functionally correlated with age-related proprioceptive deficits. Our study reveals that decreased collagen expression, a common age-related phenomenon across species, triggers this process. Specifically, loss-of-function in dpy-5 or col-120, genes encoding cuticular collagens secreted to the epidermal apical surface, induces early-onset excessive dendritic branching and proprioceptive deficits. Adulthood-specific overexpression of dpy-5 or col-120 mitigates excessive branching in aged animals without extending lifespan, highlighting their specific roles in promoting neuronal health span. Notably, collagen reduction specifically drives excessive branching in select sensory neuron subclasses but does not contribute to PVD dendritic beading, another aging-associated neurodegenerative phenotype associated with distinct mechanosensitive dysfunction. Lastly, we identify that rig-3, an immunoglobulin superfamily member expressed in interneurons, acts upstream of collagen genes to maintain PVD dendritic homeostasis during aging, with collagen's regulatory role requiring daf-16/FOXO. These findings reveal that age-related collagen reduction cues neuronal aging independently of collagen's traditional structural support function, possibly involving bi-directional communication processes between neurons and non-neuronal cells. Our study also offers new insights into understanding selective neuron vulnerability in aging, emphasizing the importance of multi-tissue strategies to address the complexities of neuronal aging.

Antimicrobial peptides (AMPs) are classically known as important effector molecules in innate immunity across all multicellular organisms. However, emerging evidence begins to suggest multifunctional properties of AMPs beyond their antimicrobial activity, surprisingly including their roles in regulating neuronal function, such as sleep and memory formation. Aging, which is fundamental to neurodegeneration in both physiological and disease conditions, interestingly affects the expression pattern of many AMPs in an infection-independent manner. While it remains unclear whether these are coincidental events, or a mechanistic relationship exists, previous studies have suggested a close link between AMPs and a few key proteins involved in neurodegenerative diseases. This review discusses recent literature and advances in understanding the crosstalk between AMPs and the nervous system at both molecular and functional levels, with the aim to explore how AMPs may relate to neuronal vulnerability in aging.

Infections have been identified as possible risk factors for aging-related neurodegenerative diseases, but it remains unclear whether infection-related immune molecules have a causative role in neurodegeneration during aging. Here, we reveal an unexpected role of an epidermally expressed antimicrobial peptide, NLP-29 (neuropeptide-like protein 29), in triggering aging-associated dendrite degeneration in C. elegans. The age-dependent increase of nlp-29 expression is regulated by the epidermal tir-1/SARM-pmk-1/p38 MAPK innate immunity pathway. We further identify an orphan G protein-coupled receptor NPR-12 (neuropeptide receptor 12) acting in neurons as a receptor for NLP-29 and demonstrate that the autophagic machinery is involved cell autonomously downstream of NPR-12 to transduce degeneration signals. Finally, we show that fungal infections cause dendrite degeneration using a similar mechanism as in aging, through NLP-29, NPR-12, and autophagy. Our findings reveal an important causative role of antimicrobial peptides, their neuronal receptors, and the autophagy pathway in aging- and infection-associated dendrite degeneration.

BACKGROUND:Mitochondrial dysfunction is purported as a contributory mechanism underlying diabetic neuropathy, but a defined role for damaged mitochondria in diabetic nerves remains unclear, particularly in standard diabetes models. Experiments here used a high-fat diet in attempt to exacerbate the severity of diabetes and expedite the time-course in which mitochondrial dysfunction may occur. We hypothesized a high-fat diet in addition to diabetes would increase stress on sensory neurons and worsen mitochondrial dysfunction.METHODS:Oxidative phosphorylation proteins and proteins associated with mitochondrial function were quantified in lumbar dorsal root ganglia. Comparisons were made between non-diabetic and streptozotocin-induced (STZ) C57Bl/6 mice fed a standard or high-fat diet for 8 weeks.RESULTS:Complex III subunit Core-2 and voltage dependent anion channel were increased (by 36% and 28% respectively, p<0.05) in diabetic mice compared to nondiabetic mice fed the standard diet. There were no differences among groups in UCP2, PGC-1α, PGC-1β levels or Akt, mTor, or AMPK activation. These data suggest compensatory mitochondrial biogenesis occurs to offset potential mitochondrial dysfunction after 8 weeks of STZ-induced diabetes, but a high-fat diet does not alter these parameters.CONCLUSION:Our results indicate mitochondrial protein changes early in STZ-induced diabetes. Interestingly, a high-fat diet does not appear to affect mitochondrial proteins in either nondiabetic or STZ- diabetic mice.

Lactate, once considered a metabolic dead-end, has been recently proposed to support neuron bioenergetics. To better understand how lactate specifically influences cell energy metabolism, we studied the effects of lactate supplementation on SH-SY5Y human neuroblastoma cell bioenergetic fluxes. Lactate supplementation increased cell respiration, there was no change in respiratory coupling efficiency, and lactate itself appeared to directly support the respiratory flux increase. Conversely, lactate supplementation reduced the glycolysis flux. This apparent pro-aerobic shift in the respiration:glycolysis ratio was accompanied by post-translational modifications and compartmental redistributions of proteins that respond to and modify bioenergetic fluxes, including cAMP-response element binding protein (CREB), p38 mitogen-activated protein kinases (p38 MAPK), AMP-activated protein kinase (AMPK), peroxisome-proliferator activated receptor gamma coactivator 1 β (PGC-1β), Akt, mammalian target of rapamycin (mTOR), and forkhead box protein O1 (FOXO1). mRNA levels for PGC-1β, nuclear respiratory factor 1 (NRF1), and cytochrome c oxidase subunit 1 (COX1) increased. Some effects depended on the direct presence of lactate, while others were durable and evident several hours after lactate was removed. We conclude lactate can be used to manipulate cell bioenergetics.

Lactate, once considered a metabolic dead-end, has been recently proposed to support neuron bioenergetics. To better understand how lactate specifically influences cell energy metabolism, we studied the effects of lactate supplementation on SH-SY5Y human neuroblastoma cell bioenergetic fluxes. Lactate supplementation increased cell respiration, there was no change in respiratory coupling efficiency, and lactate itself appeared to directly support the respiratory flux increase. Conversely, lactate supplementation reduced the glycolysis flux. This apparent pro-aerobic shift in the respiration:glycolysis ratio was accompanied by post-translational modifications and compartmental redistributions of proteins that respond to and modify bioenergetic fluxes, including cAMP-response element binding protein (CREB), p38 mitogen-activated protein kinases (p38 MAPK), AMP-activated protein kinase (AMPK), peroxisome-proliferator activated receptor gamma coactivator 1 β (PGC-1β), Akt, mammalian target of rapamycin (mTOR), and forkhead box protein O1 (FOXO1). mRNA levels for PGC-1β, nuclear respiratory factor 1 (NRF1), and cytochrome c oxidase subunit 1 (COX1) increased. Some effects depended on the direct presence of lactate, while others were durable and evident several hours after lactate was removed. We conclude lactate can be used to manipulate cell bioenergetics.

Mitochondrial impairment is commonly found in many diseases such as diabetes, cancer, and Alzheimer disease. We demonstrate that the enzymes responsible for the addition or removal of the O-GlcNAc modification, O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA), respectively, are critical regulators of mitochondrial function. Using a SILAC (stable isotope labeling of amino acids in cell culture)-based proteomics screen, we quantified the changes in mitochondrial protein expression in OGT- and OGA-overexpressing cells. Strikingly, overexpression of OGT or OGA showed significant decreases in mitochondria-localized proteins involved in the respiratory chain and the tricarboxylic acid cycle. Furthermore, mitochondrial morphology was altered in these cells. Both cellular respiration and glycolysis were reduced in OGT/OGA-overexpressing cells. These data demonstrate that alterations in O-GlcNAc cycling profoundly affect energy and metabolite production.

The effects of exercise and physical activity on brain function and integrity are increasingly recognized, and the ability of exercise to mitigate or delay Alzheimer's disease (AD) is currently being investigated. Past rodent studies suggest exercise may enhance or conserve respiratory chain function, which is relevant to AD as respiratory efficiency and some measures of mitochondrial mass are reduced in AD patients. In this study we evaluated the impact of high-intensity exercise on respiration-relevant genes, proteins, and pathways in the brains of aged mice. We subjected C57Bl/6 mice (n=12) to twice-daily, five-days per week treadmill exercise sessions. The mice were 19 months of age at the start of the study, and 21 months of age at its conclusion. Session intensity was adjusted as needed so that the mice consistently exercised above the lactate threshold at which lactate is produced more rapidly than it is cleared. The control group consisted of equally aged mice (n=12) that did not exercise. After two months all mice were euthanized. Brains were rapidly collected and hippocampal mRNA, hemisphere DNA, and hemisphere protein lysates were prepared and analyzed for changes in bioenergetics-relevant genes, proteins, and pathways. Since brain inflammation and hippocampal neurogenesis may correlate with bioenergetic function, we also analyzed genes and proteins that reflect neurogenesis and brain inflammation activity. 21-month old C57BL/6 mice showed increased brain PGC-1α protein, mTOR and phospho-mTOR protein, citrate synthase mRNA, and mtDNA copy number. Hippocampal VEGF-A gene expression trended higher, and a positive correlation between VEGF-A and PRC mRNA levels was observed. Brain DCX, BDNF, TNF-α, and CCL11 gene expression, as well as plasma CCL11 protein levels, were unchanged. Despite these apparent negative findings, a negative correlation between plasma CCL11 protein levels and hippocampal DCX gene expression was observed; further analysis indicated exercise may mitigate this relationship. Supra-lactate threshold exercise beneficially impacts bioenergetic-relevant parameters in the brains of aged mice. Our data further suggest supra-lactate threshold exercise may enhance neurogenesis by uncoupling it from the effects of inflammatory chemokines. This study supports the view that exercising above the lactate threshold may benefit the aging brain.

Brain bioenergetic function declines in some neurodegenerative diseases, this may influence other pathologies and administering bioenergetic intermediates could have therapeutic value. To test how one intermediate, oxaloacetate (OAA) affects brain bioenergetics, insulin signaling, inflammation and neurogenesis, we administered intraperitoneal OAA, 1-2 g/kg once per day for 1-2 weeks, to C57Bl/6 mice. OAA altered levels, distributions or post-translational modifications of mRNA and proteins (proliferator-activated receptor-gamma coactivator 1α, PGC1 related co-activator, nuclear respiratory factor 1, transcription factor A of the mitochondria, cytochrome oxidase subunit 4 isoform 1, cAMP-response element binding, p38 MAPK and adenosine monophosphate-activated protein kinase) in ways that should promote mitochondrial biogenesis. OAA increased Akt, mammalian target of rapamycin and P70S6K phosphorylation. OAA lowered nuclear factor κB nucleus-to-cytoplasm ratios and CCL11 mRNA. Hippocampal vascular endothelial growth factor mRNA, doublecortin mRNA, doublecortin protein, doublecortin-positive neuron counts and neurite length increased in OAA-treated mice. (1)H-MRS showed OAA increased brain lactate, GABA and glutathione thereby demonstrating metabolic changes are detectable in vivo. In mice, OAA promotes brain mitochondrial biogenesis, activates the insulin signaling pathway, reduces neuroinflammation and activates hippocampal neurogenesis.

In aged mice, we assessed how intensive exercise affects brain bioenergetics, inflammation, and neurogenesis-relevant parameters. After 8 weeks of a supra-lactate threshold treadmill exercise intervention, 21-month-old C57BL/6 mice showed increased brain peroxisome proliferator-activated receptor gamma coactivator-1α protein, mammalian target of rapamycin and phospho-mammalian target of rapamycin protein, citrate synthase messenger RNA, and mitochondrial DNA copy number. Hippocampal vascular endothelial growth factor A (VEGF-A) gene expression trended higher, and a positive correlation between VEGF-A and PRC messenger RNA levels was observed. Brain doublecortin, brain-derived neurotrophic factor, tumor necrosis factor-α, and CCL11 gene expression, as well as plasma CCL11 protein levels, were unchanged. Despite these apparent negative findings, a negative correlation between plasma CCL11 protein levels and hippocampal doublecortin gene expression was observed; further analysis indicated exercise may mitigate this relationship. Overall, our data suggest supra-lactate threshold exercise activates a partial mitochondrial biogenesis in aged mice, and a gene (VEGF-A) known to support neurogenesis. Our data are consistent with another study that found systemic inflammation in general, and CCL11 protein specifically, suppresses hippocampal neurogenesis. Our study supports the view that intense exercise above the lactate threshold may benefit the aging brain; future studies to address the extent to which exercise-generated lactate mediates the observed effects are warranted.

Diet composition may affect energy metabolism in a tissue-specific manner. Using C57Bl/6J mice, we tested the effect of ketosis-inducing and non-inducing high fat diets on genes relevant to brain bioenergetic infrastructures, and on proteins that constitute and regulate that infrastructure. At the end of a one-month study period the two high fat diets appeared to differentially affect peripheral insulin signaling, but brain insulin signaling was not obviously altered. Some bioenergetic infrastructure parameters were similarly impacted by both high fat diets, while other parameters were only impacted by the ketogenic diet. For both diets, mRNA levels for CREB, PGC1α, and NRF2 increased while NRF1, TFAM, and COX4I1 mRNA levels decreased. PGC1β mRNA increased and TNFα mRNA decreased only with the ketogenic diet. Brain mtDNA levels fell in both the ketogenic and non-ketogenic high fat diet groups, although TOMM20 and COX4I1 protein levels were maintained, and mRNA and protein levels of the mtDNA-encoded COX2 subunit were also preserved. Overall, the pattern of changes observed in mice fed ketogenic and non-ketogenic high fat diets over a one month time period suggests these interventions enhance some aspects of the brain's aerobic infrastructure, and may enhance mtDNA transcription efficiency. Further studies to determine which diet effects are due to changes in brain ketone body levels, fatty acid levels, glucose levels, altered brain insulin signaling, or other factors such as adipose tissue-associated hormones are indicated.

Respiratory chain efficiency, some measures of mitochondrial mass, and glucose utilization decline during Alzheimer's disease (AD). Increased inflammation and age-related reductions in hippocampal neurogenesis, parameters that may also reflect bioenergetic dysfunction, might further exacerbate AD. How to most effectively promote brain bioenergetic function is unclear. We explored how oxaloacetate (OAA), a metabolism intermediate whose reduction to malate oxidizes NADH to NAD+, impacts brain bioenergetic infrastructures, neurogenesis, and inflammation. We injected 0, 1, or 2 g/kg/day of OAA into the intraperitoneal (IP) cavities of five-month old C57Bl/6 mice (n=15 mice per group). After two weeks hippocampal mRNA, hemisphere DNA, and hemisphere protein lysates were analyzed for changes in bioenergetics-relevant genes, proteins, and pathways. We also analyzed genes and proteins that reflect neurogenesis and brain inflammation activity. We used magnetic resonance spectroscopy (MRS) at 9.4 tesla to quantify mouse (n=8) brain metabolites before and after 2 g/kg/day of IP OAA. OAA at 1 and 2 g/kg/day induced changes consistent with mitochondrial biogenesis or activation of pathways that promote mitochondrial biogenesis. Phospho-AMPK increased with 1 g/kg/day. mRNA for PGC1a, PRC, TFAM, NRF1, and ND1 increased with 2 g/kg/day, as did phospho-CREB, phospho-MTOR, and phospho-AKT. COX4 mRNA, COX4 protein, and total CREB protein increased with both treatments. Nuclear translocation of PGC1a (at 1 and 2 g/kg/day) and PRC (at 2 g/kg/day) occurred. Mitochondrial DNA levels and mRNA for COX2, PGC1b, or SIRT1, though, were unchanged. Hippocampal mRNA for TNFa and CCL11 (markers of inflammation) were reduced by 2 g/kg/day, and hippocampal mRNA for doublecortin (marker of immature neurons) increased with both treatments. MRS revealed several metabolite changes; after one week of the 2 g/kg/day treatment lactate, GABA, and glutathione were higher than their pre-treatment values. OAA administered to mice IP alters brain bioenergetics, neurogenesis, and inflammation-relevant parameters. Our data suggest OAA induces at least a partial mitochondrial biogenesis, reduces inflammation, and may enhance neurogenesis activity and glucose utilization. This preclinical study supports testing OAA in AD subjects, although determining how much OAA needs to be delivered to the human brain and how best to get it there may prove challenging.

Alzheimer's disease (AD) is a progressive neurodegenerative disease that affects a staggering percentage of the aging population and causes memory loss and cognitive decline. Mitochondrial abnormalities can be observed systemically and in brains of patients suffering from AD, and may account for part of the disease phenotype. In this review, we summarize some of the key findings that indicate mitochondrial dysfunction is present in AD-affected subjects, including cytochrome oxidase deficiency, endophenotype data, and altered mitochondrial morphology. Special attention is given to recently described perturbations in mitochondrial autophagy, fission–fusion dynamics, and biogenesis. We also briefly discuss how mitochondrial dysfunction may influence amyloidosis in Alzheimer's disease, why mitochondria are a valid therapeutic target, and strategies for addressing AD-specific mitochondrial dysfunction.

The effects of exercise are not limited to muscle, and its ability to mitigate some chronic diseases is under study. A more complete understanding of how exercise impacts non-muscle tissues might facilitate design of clinical trials and exercise mimetics. Here, we focused on lactate's ability to mediate changes in liver and brain bioenergetic-associated parameters. In one group of experiments, C57BL/6 mice underwent 7weeks of treadmill exercise sessions at intensities intended to exceed the lactate threshold. Over time, the mice dramatically increased their lactate threshold. To ensure that plasma lactate accumulated during the final week, the mice were run to exhaustion. In the liver, mRNA levels of gluconeogenesis-promoting genes increased. While peroxisome proliferator-activated receptor-gamma co-activator 1 alpha (PGC-1) expression increased, there was a decrease in PGC-1 expression, and overall gene expression changes favored respiratory chain down-regulation. In the brain, PGC-1 and PGC-1 were unchanged, but PGC-1-related co-activator expression and mitochondrial DNA copy number increased. Brain tumor necrosis factor alpha expression fell, whereas vascular endothelial growth factor A expression rose. In another group of experiments, exogenously administered lactate was found to reproduce some but not all of these observed liver and brain changes. Our data suggest that lactate, an exercise byproduct, could mediate some of the effects exercise has on the liver and the brain, and that lactate itself can act as a partial exercise mimetic.

Alzheimer's disease (AD) patients have reduced brain acetylcholine and reversing this deficit yields clinical benefits. In this study we explored how increased cholinergic tone impacts cell bioenergetics, which are also perturbed in AD. We treated SH-SY5Y neuroblastoma cells with carbachol, a cholinergic agonist, and tested for bioenergetic flux and bioenergetic infrastructure changes. Carbachol rapidly increased both oxidative phosphorylation and glycolysis fluxes. ATP levels rose slightly, as did cell energy demand, and AMPK phosphorylation occurred. At least some of these effects depended on muscarinic receptor activation, ER calcium release, and ER calcium re-uptake. Our data show that increasing cholinergic signaling enhances cell bioenergetics, and reveal mechanisms that mediate this effect. Phenomena we observed could potentially explain why cholinesterase inhibitor therapy increases AD brain glucose utilization and N-acetyl aspartate levels. The question of whether cholinesterase inhibitors have a disease modifying effect in AD has long been debated; our data suggest a theoretical mechanism through which such an effect could potentially arise.

•  What is the central question of this study? Although exercise is shown to benefit different organs, little research has focused on the mitochondrial response to exercise training in the liver and brain. Also, why and how exercise‐induced muscle activation modifies non‐muscle tissues is not fully understood. •  What is the main finding and its importance? We found a dissociated mitochondrial biogenesis, in which some components for gluconeogenesis are enhanced while others for oxidative phosphorylation are minimized, in the livers of exercised mice. These observations suggest that mitochondrial biogenesis is not necessarily an all‐or‐none process, but rather can be strategically tailored to meet a specific tissue's particular physiological needs. Also, this is the first manuscript to show the possible role of exercise‐induced lactate production in mediating exercise's effects on non‐muscle tissues.

Background: Although some reciprocal glycolysis-respiration relationships are well recognized, the relationship between reduced glycolysis flux and mitochondrial respiration has not been critically characterized.Methods: We concomitantly measured the extracellular acidification rate (ECAR) and oxygen consumption rate (OCR) of SH-SY5Y neuroblastoma cells under free and restricted glycolysis flux conditions.Results: Under conditions of fixed energy demand ECAR and OCR values showed a reciprocal relationship. In addition to observing an expected Crabtree effect in which increasing glucose availability raised the ECAR and reduced the OCR, a novel reciprocal relationship was documented in which reducing the ECAR via glucose deprivation or glycolysis inhibition increased the OCR. Substituting galactose for glucose, which reduces net glycolysis ATP yield without blocking glycolysis flux, similarly reduced the ECAR and increased the OCR. We further determined how reduced ECAR conditions affect proteins that associate with energy sensing and energy response pathways. ERK phosphorylation, SIRT1, and HIF1a decreased while AKT, p38, and AMPK phosphorylation increased.Conclusions: These data document a novel intracellular glycolysis-respiration effect in which restricting glycolysis flux increases mitochondrial respiration.General significance: Since this effect can be used to manipulate cell bioenergetic infrastructures, this particular glycolysis-respiration effect can practically inform the development of new mitochondrial medicine approaches. (C) 2013 Elsevier B.V. All rights reserved.