Original Research
Effect of Acute Aerobic Exercise and Rapamycin Treatment on Autophagy in Peripheral Blood Mononuclear Cells of Adults With Prediabetes

https://doi.org/10.1016/j.jcjd.2019.04.005Get rights and content

Abstract

Objectives

Recently, a malfunction of the autophagic pathway has been implicated with impaired glucose metabolism and progression from prediabetes to type 2 diabetes. The aims of this study were to investigate the effect of exercise and rapamycin (RAPA) treatment on the autophagic process in peripheral blood mononuclear cells (PBMCs) from people with prediabetes compared with control subjects.

Methods

Two groups matched for age and sex served as participants and included 6 participants with prediabetes (42.4±11.7 years) and 6 control subjects (44.4±11.9 years). Participants exercised at 50% of maximal oxygen consumption for 60 min with 5 min of rest interspersed every 20 min. PBMCs were isolated pre-exercise, immediately postexercise and 4 h after exercise recovery. Additional PBMCs were incubated for 24 h and either exposed to bafilomycin, rapamycin with bafilomycin (RAPA), or no treatment with vehicle (dimethyl sulfoxide). Proteins and mRNA were analyzed via western blot and quantitative real-time polymerase chain reaction, respectively.

Results

Exercise increased autophagy immediately postexercise and recovered 4 h after exercise in control participants but not in participants with prediabetes. Autophagy increased in PBMCs from people with prediabetes and control participants after RAPA treatment; however, a significantly impaired autophagic response was observed in people with prediabetes when compared with control subjects.

Conclusions

Our results indicate an impairment in autophagic flux in PBMCs from people with prediabetes when compared with control subjects in response to both exercise and RAPA treatment. Future methods of autophagic upregulation should be investigated to spare malfunctions in autophagy in people with prediabetes.

Résumé

Objectifs

Récemment, il a été montré qu'un dysfonctionnement de la voie autophagique a été impliqué dans une altération du métabolisme du glucose et une progression d'un prédiabète en diabète de type 2. Les objectifs de cette étude étaient d'étudier l'effet de l'exercice et d'un traitement à la rapamycine (RAPA) sur le processus autophagique dans les cellules mononucléées du sang périphérique (CMSP) de personnes prédiabétiques comparativement aux sujets témoins.

Méthodes

Les participants étaient répartis en deux groupes appariés pour l'âge et le sexe et comprenaient 6 participants atteints de prédiabète (42.4±11.7 ans) et 6 sujets témoins (44.4±11.9 ans). Les participants ont fait de l'exercice à 50 % de la consommation maximale d'oxygène pendant 60 minutes avec 5 minutes de repos toutes les 20 minutes. Les CMSPs ont été isolées avant l'exercice, immédiatement après l'exercice physique et 4 heures après la récupération de l'exercice. D'autres CMSPs ont été incubées pendant 24 h et exposées soit à la bafilomycine, à la rapamycine avec de la bafilomycine (RAPA) ou sans traitement avec véhicule seul (diméthylsulfoxyde). Les protéines et l'ARNm ont été analysés respectivement par immunobuvardage de type Western et par réaction en chaîne par polymérase en temps réel quantitative.

Résultats

L'exercice a augmenté l'autophagie immédiatement après l'exercice puis celle-ci s'est rétablie 4 h après l'exercice chez les participants témoins, mais pas chez les participants atteints de prédiabète. L'autophagie a augmenté dans les CMSPs chez les personnes atteintes de prédiabète et chez les participants témoins après le traitement à la RAPA; cependant, une réponse autophagique significativement altérée a été observée chez les personnes atteintes de prédiabète comparativement aux sujets témoins.

Conclusions

Nos résultats indiquent une diminution du flux autophagique dans les CMSPs chez les personnes atteintes de prédiabète par rapport aux sujets témoins en réponse à l'exercice et au traitement à la RAPA. Les futures méthodes promouvant l'autophagie devraient être étudiées pour éviter des dysfonctionnements de l'autophagie chez les personnes atteintes de prédiabète.

Introduction

Type 2 diabetes is a disease with increasing prevalence that has become a global health problem that affects people of all socioeconomic classes. According to the International Diabetes Federation Atlas (1), the estimated diabetes prevalence in 2017 was 425 million, with >641 million people predicted to be living with type 2 diabetes worldwide by the year 2040. It is well established that type 2 diabetes is associated with increased risk of developing microvascular disorders, including nephropathy, neuropathy and retinopathy (2). Furthermore, individuals with type 2 diabetes have increased morbidity and mortality because of increased risk of cardiovascular disorders, such as coronary artery disease, hypertension and stroke 3, 4. However, prior to the development of type 2 diabetes, a period of prediabetic state occurs, which may be characterized by impaired glucose and insulin tolerance, mild to moderate obesity and fluctuations in normoglycemic and hyperglycemic states (5).

Exercise is known to play a fundamental role in the prevention and treatment of type 2 diabetes, in part because of improvements in insulin sensitivity and increased maximal oxygen consumption (Vo2max) (6). Additionally, exercise-induced adaptations include an increased abundance of proteins involved with insulin signalling (e.g. insulin receptor substrate 1) and glucose metabolism important in cellular homeostasis 7, 8. However, these metabolic adaptations have been reported to be impaired in patients with type 2 diabetes and patients with prediabetes, indicating a potential resistance to the beneficial effects of exercise (9).

Macroautophagy (herein referred to as autophagy) is a catabolic cellular process, which involves the degradation of protein aggregates and damaged organelles, and is crucial in maintaining cellular homeostasis (10). Autophagic flux refers to the complete process of autophagy, including the amount and rate of cargo sequestered and degraded (11). Stimulation of autophagic flux has been shown to be crucial in the development of cellular adaptations to exercise (12). However, disruption of autophagy in mice has been shown to impair endurance exercise performance and glucose metabolism during an acute exercise bout (13). Furthermore, impaired autophagic functioning may contribute to the development of prediabetes and type 2 diabetes through the development of insulin resistance (14) and other comorbidities including neurodegenerative disorders 15, 16, cardiomyopathy (17) and cancer (18). Although the beneficial effects of exercise in prediabetes and type 2 diabetes have been well established (19), little is known about the effect of exercise on autophagy in people with prediabetes and people with type 2 diabetes. It has recently been demonstrated that an acute bout of endurance exercise (1 to 2 h) is sufficient to stimulate autophagic signalling in skeletal muscle of young healthy adult men 20, 21. Recent evidence suggests that the acute autophagic response may be intact in human skeletal muscle of people with type 2 diabetes in response to 60 min of cycling exercise at 70% of Vo2max (22). This may be because of an autophagic adaptation to chronic hyperglycemic conditions; however, it is unknown if people with prediabetes exhibit this adaptive response (23). Therefore, the autophagic response to exercise in individuals with prediabetes remains to be established.

The aim of this study was to investigate the response of autophagy in response to an acute bout of exercise and subsequent recovery in peripheral blood mononuclear cells (PBMCs) of individuals with prediabetes compared with age- and sex-matched control subjects. Because PBMCs come into contact with every cell in the human body and are sensitive to various physiological, pathologic and environmental changes, they were chosen as a representation of the whole body autophagy response (24). To further elucidate the mechanism of autophagic modulation, we treated PBMCs from people with prediabetes with the known autophagy inducer, rapamycin (RAPA).

Section snippets

Human participants

The study was approved by the University of New Mexico's Human Research Review Committee (HRPO-14-200), and all participants provided written informed consent. Twelve adult participants (6 men and 6 women) between the ages of 27 and 61 years and who were free of known illness or disease were recruited. This sample size was determined via an a priori power analysis (G*Power; Universität Düsseldorf, Düsseldorf, Germany) which estimated 12 participants were required based on the variable

Clinical and metabolic characteristics

Participants with prediabetes had significantly higher A1C levels (p=0.001) than control participants but showed a similar Vo2max (p=0.36), indicating minimal differences in cardiorespiratory fitness between groups. Furthermore, no differences were observed in body mass index (p=0.47), body fat percentage (p=0.56) or waist circumference (p=0.49) between participants with prediabetes and control participants (Table 1).

Effect of aerobic exercise on markers of autophagy

The protein abundance of important autophagy markers was examined between

Discussion

In this study, we examined the impact of an acute bout of moderate intensity (50% Vo2max) endurance exercise on markers of autophagy response in PBMCs of individuals with prediabetes and age- and sex-matched control subjects. To further understand differences in autophagy between people with prediabetes and control subjects, we treated PBMCs from the same participants with prediabetes and control subjects with RAPA. Our findings suggest a minor impairment of the autophagic response in people

Acknowledgments

This research was supported in part by the University of New Mexico College of Education and the University of New Mexico Research Allocation Committee. We thank Trisha VanDusseldorp, Elizabeth Harding and Hung-Sheng Hsu for their assistance with conducting the exercise trials. We also thank Len Kravitz and Fabiano Amorim for their careful review of the manuscript.

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