Multinuclear MRS at 7T Uncovers Exercise Driven Differences in Skeletal Muscle Energy Metabolism Between Young and Seniors.

Marjeta Tušek Jelenc,Ladislav Valkovič,Ivan Frollo,Martin Krššák,Radka Klepochová,Patrik Krumpolec,Ivica Just,Siegfried Trattnig,Barbara Ukropcová,Jozef Ukropec

doi:10.3389/fphys.2020.00644

Abstract

Purpose: Aging is associated with changes in muscle energy metabolism. Proton (1H) and phosphorous (31P) magnetic resonance spectroscopy (MRS) has been successfully applied for non-invasive investigation of skeletal muscle metabolism. The aim of this study was to detect differences in adenosine triphosphate (ATP) production in the aging muscle by 31P-MRS and to identify potential changes associated with buffer capacity of muscle carnosine by 1H-MRS.Methods: Fifteen young and nineteen elderly volunteers were examined. 1H and 31P-MRS spectra were acquired at high field (7T). The investigation included carnosine quantification using 1H-MRS and resting and dynamic 31P-MRS, both including saturation transfer measurements of phosphocreatine (PCr), and inorganic phosphate (Pi)-to-ATP metabolic fluxes.Results: Elderly volunteers had higher time constant of PCr recovery (τPCr) in comparison to the young volunteers. Exercise was connected with significant decrease in PCr-to-ATP flux in both groups. Moreover, PCr-to-ATP flux was significantly higher in young compared to elderly both at rest and during exercise. Similarly, an increment of Pi-to-ATP flux with exercise was found in both groups but the intergroup difference was only observed during exercise. Elderly had lower muscle carnosine concentration and lower postexercise pH. A strong increase in phosphomonoester (PME) concentration was observed with exercise in elderly, and a faster Pi:PCr kinetics was found in young volunteers compared to elderly during the recovery period.Conclusion: Observations of a massive increment of PME concentration together with high Pi-to-ATP flux during exercise in seniors refer to decreased ability of the muscle to meet the metabolic requirements of exercise and thus a limited ability of seniors to effectively support the exercise load.

Highlights

With the average age of the earth’s population increasing steadily, incidence of chronic diseases, and prevalence of impairments and disabilities increases as well (Miljkovic et al, 2015)
A significant decrease in PCr-to-adenosine triphosphate (ATP) flux was observed during exercise from 5.92 ± 1.15 mM.s−1 to 2.42 ± 1.15 mM.s−1 (p = 0.0001) in the elderly group and from 6.87 ± 1.38 mM.s−1 to 3.79 ± 0.93 mM.s−1 (p = 0.0001) in the young group
The difference between the two groups was significant at rest as well as during exercise

Summary

Introduction

With the average age of the earth’s population increasing steadily, incidence of chronic diseases, and prevalence of impairments and disabilities increases as well (Miljkovic et al, 2015). The skeletal muscle represents about 40% of the total body mass, and besides its role in maintaining body posture and movement, it plays a crucial role in regulating wholebody energy metabolism (Frontera and Ochala, 2015). This close link between muscle and whole-body energy metabolism, agingrelated impairments in muscle performance, and functional state drives intensive research interests (Choi et al, 2016; Gheller et al, 2016). Phosphorous magnetic resonance spectroscopy (31P-MRS) has been successfully applied in the past for the non-invasive investigation of skeletal muscle metabolism (Valkovicet al., 2017). Muscle phosphodiester (PDE) content positively correlated with age (Satrustegui et al, 1988; Szendroedi et al, 2011); the exact mechanism(s) explaining either of these findings is currently unknown

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