Serum factors mediate changes in mitochondrial bioenergetics associated with diet and exercise interventions

Mitochondrial improvements resulting from behavioral interventions, such as diet and exercise, are systemic and apparent across multiple tissues. Here, we test the hypothesis that factors present in serum, and therefore circulating throughout the body, can mediate changes in mitochondrial function in response to intervention. To investigate this, we used stored serum from a clinical trial comparing resistance training (RT) and RT plus caloric restriction (RT + CR) to examine effects of blood borne circulating factors on myoblasts in vitro. We report that exposure to dilute serum is sufficient to mediate bioenergetic benefits of these interventions. Additionally, serum-mediated bioenergetic changes can differentiate between interventions, recapitulate sex differences in bioenergetic responses, and is linked to improvements in physical function and inflammation. Using metabolomics, we identified circulating factors associated with changes in mitochondrial bioenergetics and the effects of interventions. This study provides new evidence that circulating factors play a role in the beneficial effects of interventions that improve healthspan among older adults. Understanding the factors that drive improvements in mitochondrial function is a key step towards predicting intervention outcomes and developing strategies to countermand systemic age-related bioenergetic decline.

Blood-based bioenergetic profiling reveals differences in mitochondrial function associated with cognitive performance and Alzheimer's disease

INTRODUCTION

Despite evidence for systemic mitochondrial dysfunction early in Alzheimer's disease (AD) pathogenesis, reliable approaches monitoring these key bioenergetic alterations are lacking. We used peripheral blood mononuclear cells (PBMCs) and platelets as reporters of mitochondrial function in the context of cognitive impairment and AD.

METHODS

Mitochondrial function was analyzed using complementary respirometric approaches in intact and permeabilized cells from older adults with normal cognition, mild cognitive impairment (MCI), and dementia due to probable AD. Clinical outcomes included measures of cognitive function and brain morphology.

RESULTS

PBMC and platelet bioenergetic parameters were lowest in dementia participants. MCI platelets exhibited higher maximal respiration than normocognitives. PBMC and platelet respiration positively associated with cognitive ability and hippocampal volume, and negatively associated with white matter hyperintensities.

DISCUSSION

Our findings indicate blood-based bioenergetic profiling can be used as a minimally invasive approach for measuring systemic bioenergetic differences associated with dementia, and may be used to monitor bioenergetic changes associated with AD risk and progression.

HIGHLIGHTS

Peripheral cell bioenergetic alterations accompanied cognitive decline in older adults with mild cognitive impairment (MCI) and Alzheimer's disease (AD) and related dementia (DEM). Peripheral blood mononuclear cells (PBMC) and platelet glucose-mediated respiration decreased in participants with dementia compared to normocognitive controls (NC). PBMC fatty-acid oxidation (FAO)-mediated respiration progressively declined in MCI and AD compared to NC participants, while platelet FAO-mediated respiration exhibited an inverse-Warburg effect in MCI compared to NC participants. Positive associations were observed between bioenergetics and Modified Preclinical Alzheimer's Cognitive Composite, and bioenergetics and hippocampal volume %, while a negative association was observed between bioenergetics and white matter hyperintensities. Systemic mitochondrial dysfunction is associated with cognitive decline.

Systemic Bioenergetic Capacity Changes with Cognitive Status and Insulin Sensitivity in Older Adults

Systemic mitochondrial dysfunction is reported with AD progression, suggesting that peripheral blood cells may be used to investigate systemic mitochondrial alterations related to cognitive decline. We aimed to identify bioenergetic signatures associated with AD-related dementia and differences in insulin sensitivity associated with AD risk. We analyzed mitochondrial bioenergetics in peripheral blood cells collected from 365 older adults with varying cognitive status (normal, mild cognitive impairment, and AD) and insulin sensitivity. Normoglycemic individuals exhibited lower maximal bioenergetic capacity with AD (PBMCs: 239.6 pmol·min−1, p = 0.02; Platelets: 151.7 pmol·min−1, p = 0.06) compared to normal cognition (PBMCs: 271.5 pmol·min−1; Platelets: 171.7 pmol·min−1). Individuals with impaired insulin sensitivity exhibited lower maximal bioenergetic capacity in platelets with AD (171.6 pmol·min−1, p = 0.008) compared to normal cognition (210.6 pmol.min−1). Participants with impaired insulin sensitivity also exhibited unique bioenergetic profiles exemplified by overall higher levels of mitochondrial respiration, indicating that comorbidities such as diabetes can significantly influence bioenergetic capacity. We observed strong positive associations between maximal respiration in normoglycemic individuals with cognitive function, as measured by Modified Preclinical Alzheimer’s Cognitive Composite (mPACC5) (p = 0.06), and fatty acid oxidation in individuals with impaired insulin sensitivity with cortical thickness (p = 0.05). This study demonstrates that circulating cells may provide a cost-effective and minimally invasive way to monitor systemic bioenergetic changes associated with AD risk, progression, and insulin sensitivity. These findings also suggest that blood-based bioenergetics are related to key features of AD development and progression and should be further developed as a potential biomarker.

Heterochronic Parabiosis: Old Blood Induces Changes in Mitochondrial Structure and Function of Young Mice

Heterochronic parabiosis models have been utilized to demonstrate the role of blood-borne circulating factors in systemic effects of aging. In previous studies, heterochronic parabiosis has shown positive effects across multiple tissues in old mice. More recently, a study demonstrated old blood had a more profound negative effect on muscle performance and neurogenesis of young mice. In this study, we used heterochronic parabiosis to test the hypothesis that circulating factors mediate mitochondrial bioenergetic decline, a well-established biological hallmark of aging. We examined mitochondrial morphology, expression of mitochondrial complexes, and mitochondrial respiration from skeletal muscle of mice connected as heterochronic pairs, as well as young and old isochronic controls. Our results indicate that young heterochronic mice had significantly lower total mitochondrial content and on average had significantly smaller mitochondria compared to young isochronic controls. Expression of complex IV followed a similar pattern: young heterochronic mice had a trend for lower expression compared to young isochronic controls. Additionally, respirometric analyses indicate that young heterochronic mice had significantly lower complex I, complex I + II, and maximal mitochondrial respiration and a trend for lower complex II-driven respiration compared to young isochronic controls. Interestingly, we did not observe significant improvements in old heterochronic mice compared to old isochronic controls, demonstrating the profound deleterious effects of circulating factors from old mice on mitochondrial structure and function. We also found no significant differences between the young and old heterochronic mice, demonstrating that circulating factors can be a driver of age-related differences in mitochondrial structure and function.

Skeletal Muscle Mitochondrial Respiration Is Elevated in Female Cynomolgus Macaques Fed a Western Compared with a Mediterranean Diet

BACKGROUND

Western diets are associated with increased incidences of obesity, hypertension, diabetes, and hypercholesterolemia, whereas Mediterranean diets, richer in polyphenols, monounsaturated fats, fruits, vegetables, poultry, and fish, appear to have cardiometabolic health benefits. Previous work has included population-based studies with limited evidence for causation or animal studies focused on single macro- or micronutrients; therefore, primate animal models provide an opportunity to determine potential mechanisms underlying the effects of dietary patterns on health and disease.

OBJECTIVE

The aim of this study was to determine the effects of whole dietary patterns, either a Western or Mediterranean diet, on skeletal muscle mitochondrial bioenergetics in cynomolgus macaques.

METHODS

In this study, 22 adult female cynomolgus macaques (∼11-14 y by dentition) were fed either a Western or Mediterranean diet for 30 mo. The Western diet was designed to mimic the diet of a middle-aged American woman and the Mediterranean diet included key aspects of Mediterranean diets studied in humans, such as plant-based proteins and fat, complex carbohydrates, and fiber. Diets were matched on macronutrient composition (16% protein, 54% carbohydrate, and 31% fat) and cholesterol content. Skeletal muscle was collected for high-resolution respirometry, citrate synthase activity, and western blot measurements. Pearson correlation analysis between respirometry measures and measures of carbohydrate metabolism was also performed.

RESULTS

We found that consumption of a Western diet resulted in significantly higher mitochondrial respiration with fatty acid oxidation (FAO) (53%), FAO + complex I (52%), complex I + II (31%), max electron transport system (ETS) (31%), and ETS rotenone sensitive (31%) than did consumption of a Mediterranean diet. In addition, measures of respiration in response to fatty acids were significantly and positively correlated with both insulin resistance and plasma insulin concentrations.

CONCLUSIONS

This study highlights the importance of dietary composition in mitochondrial bioenergetics and that diet can influence skeletal muscle mitochondrial respiration independently of other factors such as macronutrient composition.