Low Running Capacity Research Articles

Branched-chain amino acid supplementation and voluntary running have distinct effects on the serum metabolome of rats with high or low intrinsic aerobic capacity.

A growing body of literature associates branched-chain amino acid (BCAA) catabolism to increased fatty acid oxidation and better metabolic health. Hence, BCAA-rich diets may improve body composition and muscle protein synthesis. However, the role of individual characteristics such as a low aerobic fitness, a well-established risk factor for cardio-metabolic diseases, has not been studied. This study examined 64 female rats from the high-capacity runner (HCR) and low-capacity runner (LCR) rat model. Rats from each line (HCR or LCR) were divided into four groups; differing from diet (CTRL or BCAA) and from the opportunity to voluntarily run on a running wheel (NONRUNNER or RUNNER). Groups were matched for body mass and maximal running capacity within each line. We measured maximal running capacity and metabolism before and after the intervention of diet and voluntary running activity. After the end of the experiment, serum samples were collected for metabolome analysis. We are the first to show that BCAA supplementation has a more pronounced impact on LCRs compared to HCRs. Specifically, in LCR rats, BCAA supplementation led to reduced daily voluntary running distance and an enrichment of serine metabolism in the serum metabolome. While voluntary running increased food intake and energy expenditure, its effects on the serum metabolome were minimal in HCRs. The present research highlights the benefit achieved by combining BCAA supplementation with running activity, especially in the LCR line. Importantly, our results underscore the interconnected role of BCAAs and fatty acid metabolism in promoting overall metabolic health.

Mitochondria Transplantation: Rescuing Innate Muscle Bioenergetic Impairment in a Model of Aging and Exercise Intolerance.

Arroum, T, Hish, GA, Burghardt, KJ, Ghamloush, M, Bazzi, B, Mrech, A, Morse, PT, Britton, SL, Koch, LG, McCully, JD, Hüttemann, M, and Malek, MH. Mitochondria transplantation: Rescuing innate muscle bioenergetic impairment in a model of aging and exercise intolerance. J Strength Cond Res 38(7): 1189-1199, 2024-Mitochondria, through oxidative phosphorylation, are crucial for energy production. Disease, genetic impairment, or deconditioning can harm muscle mitochondria, affecting energy production. Endurance training enhances mitochondrial function but assumes mobility. Individuals with limited mobility lack effective treatments for mitochondrial dysfunction because of disease or aging. Mitochondrial transplantation replaces native mitochondria that have been damaged with viable, respiration-competent mitochondria. Here, we used a rodent model selectively bred for low-capacity running (LCR), which exhibits innate mitochondrial dysfunction in the hind limb muscles. Hence, the purpose of this study was to use a distinct breed of rats (i.e., LCR) that display hereditary skeletal muscle mitochondrial dysfunction to evaluate the consequences of mitochondrial transplantation. We hypothesized that the transplantation of mitochondria would effectively alleviate mitochondrial dysfunction in the hind limb muscles of rats when compared with placebo injections. In addition, we hypothesized that rats receiving the mitochondrial transplantation would experience an improvement in their functional capacity, as evaluated through incremental treadmill testing. Twelve aged LCR male rats (18 months old) were randomized into 2 groups (placebo or mitochondrial transplantation). One LCR rat of the same age and sex was used as the donor to isolate mitochondria from the hindlimb muscles. Isolated mitochondria were injected into both hindlimb muscles (quadriceps femoris, tibialis anterior (TA), and gastrocnemius complex) of a subset LCR (n = 6; LCR-M) rats. The remaining LCR (n = 5; LCR-P) subset received a placebo injection containing only the vehicle without the isolated mitochondria. Four weeks after mitochondrial transplantation, rodents were euthanized and hindlimb muscles harvested. The results indicated a significant (p < 0.05) increase in mitochondrial markers for glycolytic (plantaris and TA) and mixed (quadricep femoris) muscles, but not oxidative muscle (soleus). Moreover, we found significant (p < 0.05) epigenetic changes (i.e., hypomethylation) at the global and site-specific levels for a key mitochondrial regulator (transcription factor A mitochondrial) between the placebo and mitochondrial transplantation groups. To our knowledge, this is the first study to examine the efficacy of mitochondrial transplantation in a rodent model of aging with congenital skeletal muscle dysfunction.

Intrinsic aerobic capacity modulates Alzheimer’s disease pathological hallmarks, brain mitochondrial function and proteome during aging

Low aerobic capacity is strongly associated with all-cause mortality and risk for Alzheimer’s disease (AD). Individuals with early dementia and AD have lower aerobic capacity compared to age-matched controls. The mechanism by which aerobic capacity influences AD risk is unknown but is likely mediated by sexual dimorphism and tissue-level differences in mitochondrial energetics. Here, we used rats selectively bred for large differences in intrinsic aerobic exercise capacity. Brain tissue from 18-month and 24-month-old female and male low-capacity runner (LCR) and high-capacity runner (HCR) rats were analyzed for markers of mitochondrial function and AD-associated pathologies. LCR rats, irrespective of sex, exhibited a greater increase in brain amyloid beta (Aβ42) and tau hyperphosphorylation (pTauthr181/total tau) with aging. In female LCR rats, brain mitochondrial respiration at states 3, 4, and FCCP-induced uncoupling, when stimulated with pyruvate/malate, was reduced at 18 and 24 months, leading to lower ATP-linked mitochondrial respiration compared to mitochondria from HCR rats. Male LCR rats also showed reduced complex II-stimulated mitochondrial respiration (succinate + rotenone) at 24 months compared to HCR rats. Differences in mitochondrial respiration were associated with tau hyperphosphorylation and Aβ42 alterations in both HCR and LCR strains. Proteomic analysis unveiled a distinct difference in the mitochondrial proteome, wherein female LCR rats displayed diminished mitochondrial translation and oxidative phosphorylation (OXPHOS) proteins at 18 months compared to female HCR rats. Conversely, male LCR rats exhibited increased OXPHOS protein abundance but reduced tricarboxylic acid (TCA) cycle proteins compared to male HCR rats. These findings underscore a robust association between intrinsic aerobic exercise capacity, brain mitochondrial function, and AD pathologies during aging.

Histone β-hydroxybutyrylation-mediated Chromatin Remodeling Upregulates β-oxidation of Fatty Acids and Attenuates Metabolic Syndrome

Center for Hypertension and Precision Medicine, Department of Physiology and Pharmacology, University of Toledo, Toledo, OH Introduction: Metabolic syndrome (MetS) is a cluster of metabolic dysregulations including high blood pressure (BP), dyslipidemia, central obesity, hyperglycemia, and insulin resistance. Regular exercise is one of the lifestyle modifications known to prevent MetS by the generation of ketone bodies. Precisely how ketone bodies operate to lower MetS is largely unknown. Previously, we demonstrated that the ketone body, β-hydroxybutyrate, is a potent anti-hypertensive metabolite. β-hydroxybutyrate has been recently recognized to epigenetically modify histones by β-hydroxybutyrylation. Using assay for transposase-accessible chromatin with sequencing and chromatin immunoprecipitation assays, we found that histone β-hydroxybutyrylation causes chromatin remodeling and exposes regions for transcription of genes for β-oxidation of fatty acids. Therefore, we hypothesized that β-hydroxybutyrate alleviates MetS via histone β-hydroxybutyrylation-mediated transcriptional upregulation of β-oxidation of fatty acids. To test this hypothesis, we examined the epigenetic effect of increasing systemic β-hydroxybutyrate in a genetic rat model of MetS inbred in our laboratory, the low-capacity runner (LCR/Tol) rats. Methods: Randomly selected two groups of six months old female LCR/Tol rats (n=5/group) were surgically implanted with radiotelemetry transmitters for BP measurement. The control group was given water, whereas the experimental group was given water containing 20% v/v of 1,3-butanediol (1,3-BD), which is a precursor of β-hydroxybutyrate for 10 weeks. Following euthanasia, sera and tissues were harvested. Histones were isolated and subjected to western blotting for quantitation of β-hydroxybutyrylation. Results: Compared to the control group, rats given 1,3-BD had a significantly increased circulating β-hydroxybutyrate (mean 1.98 mM vs 0.71 mM, p&lt;0.05), lower body weight (mean 231.6 gm vs 248.4 gm, p&lt;0.05), lower fasting glucose (mean 79.60 mg/dl vs 100.8 mg/dl, p&lt;0.05) and lower 24-hour average systolic BP (116±2 mmHg vs. 120±2 mmHg, p&lt;0.05). Interestingly, histones isolated from the experimental group with higher circulating β-hydroxybutyrate also displayed a marked increase in β-hydroxybutyrylation (mean 0.82 vs 0.22, p&lt;0.01). Further, the target transcriptional genes of histone β-hydroxybutyrylation, 3-hydroxy-3-methylglutaryl-CoA synthase 2 (Hmgcs2) and cytochrome P450 family 2 subfamily d polypeptide 4 (Cyp2d4) were both significantly upregulated in the experimental group (p&lt;0.01). However, markers of liver injury, alanine transaminase, alkaline phosphatase, aspartate transaminase, and total bile acid levels, were comparable between the two groups, indicating no liver damage. Conclusion: This is the first study to demonstrate that enhanced systemic β-hydroxybutyrate attenuates MetS by histone β-hydroxybutyrylation-mediated chromatin remodeling to upregulate the transcription of Hmgcs2 and Cyp2d4 to promote β-oxidation of fatty acids. Further, our results demonstrate that for individuals with MetS who may be unable to exercise, utilizing 1,3-BD could serve as an alternate source to combat the MetS ameliorating benefits of the ketone body β-hydroxybutyrate. Funding Sources: Authors acknowledge the National Institutes of Health for funding support to Bina Joe (R01HL1430820). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Divergence in aerobic capacity influences hepatic and systemic metabolic adaptations to bile acid sequestrant and short-term high-fat/sucrose feeding in rats.

High versus low aerobic capacity significantly impacts the risk for metabolic diseases. Rats selectively bred for high or low intrinsic aerobic capacity differently modify hepatic bile acid metabolism in response to high-fat diets (HFDs). Here we tested if a bile acid sequestrant would alter hepatic and whole body metabolism differently in rats with high and low aerobic capacity fed a 1-wk HFD. Male rats (8 mo of age) that were artificially selected to be high (HCR) and low-capacity runners (LCR) with divergent intrinsic aerobic capacities were transitioned from a low-fat diet (LFD, 10% fat) to an HFD (45% fat) with or without a bile acid sequestrant (BA-Seq, 2% cholestyramine resin) for 7 days while maintained in an indirect calorimetry system. HFD + BA-Seq increased fecal excretion of lipids and bile acids and prevented weight and fat mass gain in both strains. Interestingly, HCR rats had increased adaptability to enhance fecal bile acid and lipid loss, resulting in more significant energy loss than their LCR counterpart. In addition, BA-Seq induced a greater expression of hepatic CYP7A1 gene expression, the rate-limiting enzyme of bile acid synthesis in HCR rats both on HFD and HFD + BA-Seq diets. HCR displayed a more significant reduction of RQ in response to HFD than LCR, but HFD + BA-Seq lowered RQ in both groups compared with HFD alone, demonstrating a pronounced impact on metabolic flexibility. In conclusion, BA-Seq provides uniform metabolic benefits for metabolic flexibility and adiposity, but rats with higher aerobic capacity display adaptability for hepatic bile acid metabolism.NEW & NOTEWORTHY The administration of bile acid sequestrant (BA-Seq) has uniform metabolic benefits in terms of metabolic flexibility and adiposity in rats with high and low aerobic capacity. However, rats with higher aerobic capacity demonstrate greater adaptability in hepatic bile acid metabolism, resulting in increased fecal bile acid and lipid loss, as well as enhanced fecal energy loss.

Parental cardiorespiratory fitness influences early life energetics and metabolic health.

High cardiorespiratory fitness (CRF) is associated with a reduced risk of metabolic disease and is linked to superior mitochondrial respiratory function. This study investigated how intrinsic CRF affects bioenergetics and metabolic health in adulthood and early life. Adult rats selectively bred for low and high running capacity [low capacity runners (LCR) and high capacity runners (HCR), respectively] underwent metabolic phenotyping before mating. Weanlings were evaluated at 4-6 wk of age, and whole body energetics and behavior were assessed using metabolic cages. Mitochondrial respiratory function was assessed in permeabilized tissues through high-resolution respirometry. Proteomic signatures of adult and weanling tissues were determined using mass spectrometry. The adult HCR group exhibited lower body mass, improved glucose tolerance, and greater physical activity compared with the LCR group. The adult HCR group demonstrated higher mitochondrial respiratory capacities in the soleus and heart compared with the adult LCR group, which coincided with a greater abundance of proteins involved in lipid catabolism. HCR and LCR weanlings had similar body mass, but HCR weanlings displayed reduced adiposity. In addition, HCR weanlings exhibited better glucose tolerance and higher physical activity levels than LCR weanlings. Higher respiratory capacities were observed in the soleus, heart, and liver tissues of HCR weanlings compared with LCR weanlings, which were not owed to greater mitochondrial content. Proteomic analyses indicated a greater potential for lipid oxidation in the contractile muscles of HCR weanlings. In conclusion, offspring born to parents with high CRF possess an enhanced capacity for lipid catabolism and oxidative phosphorylation, thereby influencing metabolic health. These findings highlight that intrinsic CRF shapes the bioenergetic phenotype with implications for metabolic resilience in early life.NEW & NOTEWORTHY Inherited cardiorespiratory fitness (CRF) influences early life bioenergetics and metabolic health. Higher intrinsic CRF was associated with reduced adiposity and improved glucose tolerance in early life. This metabolic phenotype was accompanied by greater mitochondrial respiratory capacity in skeletal muscle, heart, and liver tissue. Proteomic profiling of these three tissues further revealed potential mechanisms linking inherited CRF to early life metabolism.

Higher mitochondrial oxidative capacity is the primary molecular differentiator in muscle of rats with high and low intrinsic cardiorespiratory fitness

ObjectiveCardiorespiratory fitness (CRF) is tightly linked with health and longevity and is implicated in metabolic flexibility and substrate metabolism. The high capacity runner (HCR) and low capacity runner (LCR) rat lines are a genetically heterogeneous rat model selected and bred for CRF that reflect CRF in humans by exhibiting differences in nutrient handling. This study aims to differentiate the intrinsic substrate preference of the HCR compared to LCR rats to better understand the intersection of mitochondrial respiration and intrinsic CRF. MethodsWe performed bulk skeletal muscle RNA-Sequencing on male and female HCR and LCR rats and assessed the effect of rat line on mitochondrial gene expression pathways using the MitoCarta3.0 database. In a separate cohort of rats, mitochondria were isolated from skeletal and cardiac muscle and maximal oxidation rates were measured using an Oroboros O2k when provided either pyruvate or fatty acid substrates. ResultsThe expression of mitochondrial genes are significantly upregulated in HCR skeletal muscle in both male and female rats. In respirometry experiments, fatty acid oxidative capacities were greater in HCR compared to LCR, and male compared to female rats, as a function of both mitochondrial quality and mitochondrial density. This effect was greater in the skeletal muscle than in the heart. Pyruvate oxidation did not differ significantly between lines. ConclusionsThe capacity for increased fatty acid oxidation in the HCR rat is a result of selection for running capacity and is likely a key contributor to the healthy metabolic phenotype of individuals with high CRF.

Circulating hepatokine ANGPTL8, but not ANGPTL3, is increased in low-capacity runner (LCR) rats

Metabolic syndrome, including hypertension, hyperglycemia, hypertriglyceridemia, hypercholesterolemia, and visceral adiposity, increases your risk of heart disease, stroke, and type 2 diabetes. Unfortunately, there is an increase in prevalence of metabolic syndrome among women. While lifestyle interventions (e.g., diet and exercise), are desirable for preventing morbidity and mortality, the genetic predisposition of some people to these conditions means that therapeutic interventions are also necessary. Hepatokines are liver-derived hormones which convey energy status and assist in controlling the availability of endogenous nutrients to a variety of peripheral tissues. Hepatokines, therefore, are important signaling molecules that allow the liver to communicate with other organs throughout the body. Angiopoietin-like Protein (ANGPTL3) is a secreted glycoprotein and hepatokine. ANGPTL3 directly inhibits lipoprotein lipase, an enzyme responsible for hydrolyzing circulating triglycerides. Therefore, it promotes an increase in circulating triglyceride levels without altering phospholipid secretion or uptake. Moreover, ANGPTL3 inhibition has been unequivocally associated with reduced hypercholesterolemia and atherosclerosis. Therefore, we hypothesized that circulating ANGPTL3 expression would be increased in low-capacity runner (LCR) rats. LCR is an animal model metabolic syndrome and presents vascular dysfunction. On the other hand, rats selectively bred for high intrinsic capacity (HCR), presents a healthy state and reduced inflammatory markers. Plasma was extracted from the blood of female LCR (28-week-old), as well as HCR, and control [high-response trainer (HRT)]. Western blot for ANGPTL3 expression was performed. Opposite our hypothesis, we did not observe any difference in circulating ANGPTL3 in LCR relative to HCR (arbitrary units, LCR: 7.5±1.1 vs. HCR: 7.2±0.9, p&gt;0.05) or HRT (arbitrary units, LCR: 7.5±1.1 vs. HRT: 8.2±1.5, p&gt;0.05). However, it has been established that ANGPTL8 promotes the ability of ANGPTL3 to bind and inhibit lipoprotein lipase. Therefore, we performed another Western blot for ANGPTL8 expression. We observed that ANGPTL8 is significantly increased in LCR relative to HCR (arbitrary units, LCR: 12.2±0.6 vs. HCR: 9.7±1.1, p&lt;0.05) and HRT (arbitrary units, LCR: 12.2±0.6 vs. HRT: 9.2±0.4, p&lt;0.05). Overall, these data suggest that the hepatokine ANGPTL8 may be a more physiologically relevant target for the treatment of metabolic syndrome associated with low-intrinsic exercise capacity. NHLBI (R00HL151889), NIGMS (1P20GM103641 - Pilot Project), UofSC SOM (Startup funds). This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

The acute removal of metformin induces mitochondrial remodeling and increases mitochondrial respiration

Metformin is a candidate to slow biological aging and extend healthspan, as it reduces the risk of morbidity and mortality in people with type 2 diabetes. However, it is not clear how metformin impacts individuals absent of chronic disease. This unknown is important to answer before prescribing metformin to healthy individuals to prolong the healthspan. It has been shown that metformin creates an inefficiency in energy transfer by accumulating within the mitochondria. Therefore, we hypothesized that the effects of metformin on healthspan are context specific; beneficial in the context of low energy demand/mitochondrial capacity but detrimental in the context of high energy demand/mitochondrial capacity. To test this hypothesis, we used 18-month, male rats selectively bred for low and high treadmill running capacity (LCR/HCR) as models of low and high intrinsic mitochondrial function. For both HCR and LCR, we used high-resolution respirometry (Oroboros O2K) on skeletal muscles from controls (CON), 4 weeks of metformin-treatment (MET), 4 weeks of metformin-treatment with a 48-hour metformin washout (MET-WO), and 48-hour washout with metformin added back to the respirometry chamber (MET-WO-SPIKE). A week prior to sacrifice, we labeled the rats with deuterium oxide to assess protein turnover as an indicator of mitochondrial remodeling. In gastrocnemius muscle, the HCR MET-WO had greater Complex I (CI), CI+Complex II (CII), and maximal respiration (MaxR) (115 ± 23, 164 ± 38, 157 ± 35 pmol/(s✕mg), respectively) compared to the CON (70 ± 24, p = 0.02, 114 ± 32, p = 0.01, 115 ± 40 pmol/(s✕mg), p = 0.04, respectively), and MET (63 ± 54, p = 0.007, 90 ± 50, p &lt; 0.001, 91 ± 48 pmol/(s✕mg), p = 0.002, respectively). The HCR MET-SPIKE group had greater CII (83 ± 33 pmol/(s✕mg)) and MaxR (86 ± 35 pmol/(s✕mg)) compared to the MET (p = 0.007 and p = 0.002, respectively). In the soleus, MET-WO (4.15 ± 0.33%/day) had greater mitochondrial fractional synthesis rates (FSRs) compared to MET (3.12 ± 0.62%/day, p = 0.001) in the HCRs. In the LCRs, MET-WO (4.61 ± 0.42%/day) had greater FSRs compared to CON (p &lt; 0.001, 3.07 ± 0.67%/day) and MET (3.12 ± 0.61%/day, p = 0.001). In the tibialis anterior, MET-WO (3.47 ± 0.80%/day) had greater FSRs compared to the MET (2.41 ± 0.47%/day, p = 0.04) within the HCRs with no differences in the LCR. These data show that metformin reduces mitochondrial respiration in HCR rats but not in LCR rats. The presence of metformin produced a greater subsequent response in HCR compared to LCR as shown by its acute removal revealing metformin-induced mitochondrial remodeling. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Reveal key genes and factors affecting athletes performance in endurance sports using bioinformatic technologies

Medium-intensity activities comprise the major proportion of many sorts of sports. The energy consumption of athletes has been a research emphasis for the purpose of improving both training efficiency and competition performance. However, the evidence based on large-scale gene screen has been rarely performed. This is a bioinformatic study revealing the key factors contributed to the metabolic difference between subjects with different endurance activity capacities. A dataset comprised of high- (HCR) and low-capacity running (LCR) rats was used. Differentially expressed genes (DEGs) were identified and analysed. The Gene Ontology (GO) and Kyoto Encyclopaedia of Genes and Genomes (KEGG) pathway enrichment was obtained. The DEGs' protein–protein interaction (PPI) network was built, and the enriched terms of the PPI network were also analysed. Our findings showed that the GO terms were enriched in lipid metabolism-related terms. The KEGG signalling pathway analysis enriched in the ether lipid metabolism. Plb1, Acad1, Cd2bp2, and Pla2g7 were identified as the hub genes. This study provides a theoretical foundation showing lipid metabolism plays an important role in the performance of endurance activities. Plb1, Acad1, and Pla2g7 may be the key genes involved. The training plan and diet for athletes can be designed based on above results and expecting a better competitive performance.

Reduced contextually induced muscle thermogenesis in rats with calorie restriction and lower aerobic fitness but not monogenic obesity

ABSTRACT We have previously identified predator odor as a potent stimulus activating thermogenesis in skeletal muscle in rats. As this may prove relevant for energy balance and weight loss, the current study investigated whether skeletal muscle thermogenesis was altered with negative energy balance, obesity propensity seen in association with low intrinsic aerobic fitness, and monogenic obesity. First, weight loss subsequent to 3 wk of 50% calorie restriction suppressed the muscle thermogenic response to predator odor. Next, we compared rats bred based on artificial selection for intrinsic aerobic fitness – high- and low-capacity runners (HCR, LCR) – that display robust leanness and obesity propensity, respectively. Aerobically fit HCR showed enhanced predator odor-induced muscle thermogenesis relative to the less-fit LCR. This contrasted with the profound monogenic obesity displayed by rats homozygous for a loss of function mutation in Melanocortin 4 receptor (Mc4rK3a,4X/K314X rats), which showed no discernable deficit in thermogenesis. Taken together, these data imply that body size or obesity per se are not associated with deficient muscle thermogenesis. Rather, the physiological phenotype associated with polygenic obesity propensity may encompass pleiotropic mechanisms in the thermogenic pathway. Adaptive thermogenesis associated with weight loss also likely alters muscle thermogenic mechanisms.

Rats with high aerobic capacity display enhanced transcriptional adaptability and upregulation of bile acid metabolism in response to an acute high-fat diet.

Rats selectively bred for the high intrinsic aerobic capacity runner (HCR) or low aerobic capacity runner (LCR) show pronounced differences in susceptibility for high‐fat/high sucrose (HFHS) diet‐induced hepatic steatosis and insulin resistance, replicating the protective effect of high aerobic capacity in humans. We have previously shown multiple systemic differences in energy and substrate metabolism that impacts steatosis between HCR and LCR rats. This study aimed to investigate hepatic‐specific mechanisms of action via changes in gene transcription. Livers of HCR rats had a greater number of genes that significantly changed in response to 3‐day HFHS compared with LCR rats (171 vs. 75 genes: >1.5‐fold, p < 0.05). HCR and LCR rats displayed numerous baseline differences in gene expression while on a low‐fat control diet (CON). A 3‐day HFHS diet resulted in greater expression of genes involved in the conversion of excess acetyl‐CoA to cholesterol and bile acid (BA) synthesis compared with the CON diet in HCR, but not LCR rats. These results were associated with higher fecal BA loss and lower serum BA concentrations in HCR rats. Exercise studies in rats and mice also revealed higher hepatic expression of cholesterol and BA synthesis genes. Overall, these results suggest that high aerobic capacity and exercise are associated with upregulated BA synthesis paired with greater fecal excretion of cholesterol and BA, an effect that may play a role in protection against hepatic steatosis in rodents.

Biology: Motion is Function.

In 1966 Francis Crick declared that: “The ultimate aim of the modern movement in biology is to explain all biology in terms of physics and chemistry.” This motivated us to contemplate approaches that unify biology at a fundamental level. Exploration led us to consider the features of energy, entropy, and motion. Overall, it can be considered that motion of matter is the feature of life function. No motion. No function. In initial work we evaluated the hypothesis that the scope for biologic function is mediated mechanistically by a differential for energy transfer. Maximal treadmill running capacity served as a proxy for energy transfer. The span for capacity was estimated “biologically” by application of two-way artificial selection in rats for running capacity. Consistent with our “Energy Transfer Hypothesis” (ETH), low physical health and dysfunction segregated with low running capacity and high physical health and function segregated with high running capacity. The high energy yield of aerobic metabolism is also consonant with the ETH; that is, amongst the elements of the universe, oxygen is second only to fluorine in electronegativity. Although we deem these energy findings possibly correct, they are based on correlation and do not illuminate function via fundamental principles. For consideration of life, Entropy (2nd Law of thermodynamics) can be viewed as an open system that exchanges energy with the universe operating via nonequilibrium thermodynamics. The Principle of Maximal Entropy Production (MEP) states that: If a source of free energy is present, complex systems can intercept the free energy flow, and self-organize to enhance entropy production. The development of Benard convection cells in a water heat gradient demonstrate simplistic operation of MEP. A direct step forward would be to explain the mechanism of the obligatory motion of molecules for life function. Motion may be mediated by operation of “action at a distance” for molecules as considered by the Einstein-Podolsky-Rosen Paradox and confirmed by JS Bell. Magnetism, electricity, and gravity are also examples of action at a distance. We propose that some variant of “action at a distance” as directed by the property of Maximal Entropy Production (MEP) underwrites biologic motion.

Life-long exercise training and inherited aerobic endurance capacity produce converging gut microbiome signatures in rodents.

High aerobic endurance capacity can be acquired by training and/or inherited. Aerobic exercise training (AET) and aging are linked to altered gut microbiome composition, but it is unknown if the environmental stress of exercise and host genetics that predispose for higher exercise capacity have similar effects on the gut microbiome during aging. We hypothesized that exercise training and host genetics would have conserved effects on the gut microbiome across different rodents. We studied young sedentary (Y‐SED, 2‐month‐old) mice, old sedentary (O‐SED, 26‐month‐old) mice, old mice with life‐long AET (O‐AET, 26‐month‐old), and aged rats selectively bred for high (HCR [High Capacity Runner], 21‐month‐old) and low (LCR [Low Capacity Runner], 21‐month‐old) aerobic capacity. Our results showed that O‐SED mice had lower running capacity than Y‐SED mice. The fecal microbiota of O‐SED mice had a higher relative abundance of Lachnospiraceae, Ruminococcaceae, Turicibacteriaceae, and Allobaculum, but lower Bacteroidales, Alistipes, Akkermansia, and Anaeroplasma. O‐AET mice had a higher running capacity than O‐SED mice. O‐AET mice had lower fecal levels of Lachnospiraceae, Turicibacteriaceae, and Allobaculum and higher Anaeroplasma than O‐SED mice. Similar to O‐AET mice, but despite no exercise training regime, aged HCR rats had lower Lachnospiraceae and Ruminococcaceae and expansion of certain Bacteroidales in the fecal microbiome compared to LCR rats. Our data show that environmental and genetic modifiers of high aerobic endurance capacity produce convergent gut microbiome signatures across different rodent species during aging. Therefore, we conclude that host genetics and life‐long exercise influence the composition of the gut microbiome and can mitigate gut dysbiosis and functional decline during aging.

Age and Intrinsic Fitness Affect the Female Rotator Cuff Tendon Tissue.

The risk of the development of tendon disorders or ruptures increases with age, but it is unclear whether intrinsic fitness during lifetime might also affect tendon properties. To investigate this, a contrasting rat model of high-capacity runners (HCR with high intrinsic fitness) and low-capacity runners (LCR with low intrinsic fitness) was employed. Histological and molecular changes in rotator cuff (RC) tendons from 10 weeks old (young; HCR-10 and LCR-10) and 100 weeks old (old; HCR-100 and LCR-100) female rats were investigated. Age-dependent changes of RC tendons observed in HCR and LCR were increase of weight, decrease of tenocytes and RNA content, reduction of the wavy pattern of collagen and elastic fibers, repressed expression of Col1a1, Eln, Postn, Tnmd, Tgfb3 and Egr1 and reduction of the Col1:Col3 and Col1:Eln ratio. The LCR rats showed less physical activity, increased body weight, signs of metabolic disease and a reduced life expectancy. Their RC tendons revealed increased weight (more than age-dependent) and enlargement of the tenocyte nuclei (consistent with degenerative tendons). Low intrinsic fitness led to repressed expression of a further nine genes (Col3a1, Fbn1, Dcn, Tnc, Scx, Mkx, Bmp1, Tgfb1, Esr1) as well as the rise of the Col1:Col3 and Col1:Eln ratios (related to the lesser expression of Col3a1 and Eln). The intrinsic fitness influences the female RC tendons at least as much as age. Lower intrinsic fitness accelerates aging of RC tendons and leads to further impairment; this could result in decreased healing potential and elasticity and increased stiffness.

The Effect of Age and Intrinsic Aerobic Exercise Capacity on the Expression of Inflammation and Remodeling Markers in Rat Achilles Tendons.

Old age, adiposity, and metabolic disorders are known as risk factors for chronic tendinopathy, which is a common problem in both athletes and the general population. However, the importance of these influencing factors has not yet been well understood. This study investigated alterations in gene expression and histology of Achilles tendons of young (10 weeks) and old (100 weeks) rats bred for low (low capacity runners, LCR) and high (high capacity runners, HCR) intrinsic aerobic exercise capacity. In this rat model, LCR displayed a phenotype of reduced exercise capacity, higher body weight, and metabolic dysfunctions compared to HCR. We hypothesized that the risk factors for tendinopathy in old LCR could lead to more pronounced impairments in Achilles tendon tissue. In quantitative real-time PCR (qPCR), age-related downregulation of tenocyte markers e.g., tenomodulin, genes related to matrix modeling and remodeling (e.g., collagens, elastin, biglycan, fibronectin, tenascin C) as well as transforming growth factor beta 3 (Tgfb3) have been detected. Inflammation marker cyclooxygenase 2 (Cox2) was downregulated in old rats, while microsomal prostaglandin E synthase 2 (Ptges2) was upregulated in old HCR and old LCR. In all groups, interleukin 6 (Il6), interleukin 1 beta (Il1b), and tumor necrosis factor alpha (Tnfa) showed no significant alteration. In histological evaluation, tendons of old rats had fewer and more elongated tenocyte nuclei than young rats. Even though a higher content of glycosaminoglycans, a sign of degeneration, was found in old HCR and LCR, no further signs of tendinopathy were detectable in tendons of old rats by histological evaluation. Low intrinsic aerobic exercise capacity and the associated phenotype did not show significant effects on gene expression and tendon histology. These findings indicate that aging seems to play a prominent role in molecular and structural alterations of Achilles tendon tissue and suggests that other risk factors associated with intrinsic aerobic exercise capacity are less influential in this rat model.

Saliva biomarkers for Alzheimer’s disease risk in a rat model of low and high intrinsic exercise capacity

AbstractBackgroundIdentifying a natural‐occurring animal model for Alzheimer's Disease (AD) and a non‐invasive early AD diagnostic are significant AD research challenges. Previously, we developed rat models by selectively breeding for low and high intrinsic exercise capacity. We found that compared to High Capacity Runners (HCR), Low Capacity Runners (LCR) have a reduced lifespan and greater risk for cardiovascular disease, diabetes, and obesity.1 LCR exhibit neurodegeneration, impaired memory, and decreased hippocampal neurogenesis. Saliva is a relatively new AD‐associated research area, and as a bioanalytic,2 is an important extension of protein changes in the autonomic nervous system and immune response. Our goal is to determine whether salivary biomarkers link with exercise capacity and brain health in LCR and HCR rats.MethodWe studied three‐generations of female rats (6 months: 9 LCR, 10 HCR), (20 months: 8 LCR, and 8 HCR), and (26 months: 7 LCR, 6 HCR). We assessed exercise capacity using a treadmill running test and cognitive function using a Y‐maze. Salivary gland weight and salivary flow rate (SFR) of a submandibular gland (SMG) were measured and compared. The acinar cells proliferation of SMG was assessed by IHC using PCNA. Biomarkers for p‐tau ser610 and amyloid‐beta were investigated in hippocampus tissue, saliva, and plasma using ELISA.ResultThe LCR and HCR groups were significantly different for maximal treadmill running distance and time spent in novel arm of the Y‐Maze. The SFR and acinar cell proliferation were higher in HCR. The size and mass of SMG were bigger in LCR rats. Levels of p‐tau in saliva and plasma were markedly greater in LCR than HCR, but no differences in the hippocampus. There was no difference between the two groups in the hippocampus or saliva regarding amyloid‐beta levels. However, it was significantly increased in plasma in the LCR group compared with the HCR group.ConclusionTaken together, the findings of this study provide experimental evidence that saliva biomarkers are significantly increased in the LCR group compared with the HCR group. This is the first study using novel and unexplored preclinical rat models that combines exercise capacity with AD risk by utilizing saliva biomarkers.

Intrinsic aerobic capacity, sex, and brain aging: Determinants of Alzheimer's disease risk.

Low aerobic capacity (or cardiorespiratory fitness) is strongly associated with all-cause mortality and risk for Alzheimer's disease (AD). Individuals with early dementia and AD have lower aerobic capacity compared to age-matched controls. The mechanism by which low aerobic capacity influences AD are unknown but are suggestive of an impairment in mitochondrial energetics. Here we used rats selectively bred over several generations to have intrinsic low or high exercise capacity. Rats were bred based on low or high capacity to complete an aerobic treadmill running test resulting in rats with robustly different intrinsic aerobic capacity despite being maintained sedentary. We examined mitochondrial function, RNA sequencing, and markers of AD in brain tissue from 18-month-old male and female Low Capacity Runners (LCR) and High Capacity Runners (HCR) from generation 43 of selection. We found lower mitochondrial respiration in brains of female LCR rats for complex I-, ADP-, uncoupled-, and complex II-driven flux when compared to LCR males. Brain Complex I driven respiratory flux was reduced in LCR females when compared to HCR females. No differences were observed in complex I or citrate synthase (CS) Vmax but complex IV Vmax was lower in LCR males versus HCR males. Female LCR rats had higher Aβ42 while both male and female LCR rats had higher phosphorylated tau at threonine 181 in whole brain homogenates. RNAseq revealed a greater effect of sex on gene expression than strain (HCR vs. LCR). However, FOXO signaling, axonal guidance, ubiquitination, and protein phosphorylation pathways were greater in male LCR versus male HCR rats. Glutamate NMDA receptor subunit 3A (Grin3a) and Transcription factor 7-like 2 (TCF7L2) were identified as coordinating numerous downstream targets with IPA analysis in male LCR rats. RNA sequencing outcomes suggest downregulation of AMPK signaling in female LCR rats. These data support a strong relationship between intrinsic aerobic capacity, sex, and markers of brain mitochondrial function and AD in late-middle aged HCR and LCR rats.

Low Intrinsic Aerobic Capacity Limits Recovery Response to Hindlimb Ischemia.

Introduction: In this study, we determined the influence of intrinsic exercise capacity on the vascular adaptive responses to hind limb ischemia. High Capacity Running, HCR; Low Capacity Running, LCR, rats were used to assess intrinsic aerobic capacity effects on adaptive responses to ischemia.Methods: Muscle samples from both ischemic and non-ischemic limb in both strains were compared, histologically for the muscle-capillary relationship, and functionally using microspheres to track blood flow and muscle stimulation to test fatigability. PCR was used to identify the differences in gene expression between the phenotypes following occlusive ischemia.Results: Prior to ligation, there were not significant differences between the phenotypes in the exhaustion time with high frequency pacing. Following ligation, LCR decreased significantly in the exhaustion time compare with HCRs (437 ± 47 vs. 824 ± 56, p < 0.001). The immediate decrease in flow was significantly more severe in LCRs than HCRs (52.5 vs. 37.8%, p < 0.001). VEGF, eNOS, and ANG2 (but not ANG1) gene expression were decreased in LCRs vs. HCRs before occlusion, and increased significantly in LCRs 14D after occlusion, but not in HCRs. LCR capillary density (CD) was significantly lower at all time points after occlusion (LCR 7D = 564.76 ± 40.5, LCR 14D = 507.48 ± 54.2, both p < 0.05 vs. HCR for respective time point). NCAF increased significantly in HCR and LCR in response to ischemia.Summary: These results suggest that LCR confers increased risk for ischemic injury and is subject to delayed and less effective adaptive response to ischemic stress.

Abstract 12763: High Innate Aerobic Capacity Protects Against Angiotensin II-Induced Hypertension and Vascular Remodeling

Low aerobic capacity is associated with increased cardiovascular morbidity and mortality. A heterogeneous rat population selectively bred to segregate genes that sustain innate aerobic exercise capacity, low capacity runners (LCR) show impaired cardiac function in old age and premature death versus high capacity runners (HCR). Here we investigated whether high innate aerobic capacity offers early protection against cardiovascular disease by examining the hypertensive response of 7-month-old LCR and HCR rats to angiotensin II (Ang II, 150 μg/kg/min for 14 days). LCR and HCR rats showed no difference in basal blood pressure (105 mmHg) or vessel wall morphology, but in LCRs the mean arterial blood pressure increased to 145 mmHg versus 125 mmHg in HCRs. Congruently, LCR rats had increased aortic medial thickness and fibrosis. Aortic cytosolic and mitochondrial superoxide levels were also significantly increased in LCRs. Vascular reactivity experiments revealed impaired endothelium-dependent and -independent relaxation of mesenteric arteries of LCRs. Ang II infusion significantly increased the infiltration of macrophages into the aortic adventitia of LCRs as determined by CD68 and Mac-3 staining. Gene expression analysis by qPCR showed that markers of classically-activated macrophages CD86 and TNF-α were unchanged in rat strains but markers of alternatively-activated macrophages CD163 and Arg-1 were upregulated only in LCRs. Plasma IL-6, RANTES, CCL2 and Ang II and aortic VCAM1 levels were elevated only in LCRs whereas no difference in eNOS levels was observed between the rat strains. Aortic sections of LCRs showed increased senescence in adventitia whereas vascular smooth muscle cells (VSMC) isolated from LCR rats were more susceptible to Ang II-induced senescence. LCRs also showed increased cardiac hypertrophy and fibrosis. These data support the “outside-in” hypothesis, in which vascular inflammation initiated in adventitia progresses inwards to media and intima, causing VSMC and endothelial dysfunction, and that fibroblasts play a critical role in Ang II-induced hypertension and vascular remodeling under low innate aerobic capacity conditions, whereas high innate aerobic capacity is potentially protective against hypertension.