Analysis of the cAMP-regulated metabolome of skeletal muscle and adipose tissue

Abstract

Aging, obesity and physical inactivity are three major risk factors leading to non-communicable diseases, like coronary heart disease or type 2 diabetes, resulting in reduced health and quality of life. As the number of obese, aged and multimorbid patients continuously rise worldwide, the treatment of the associated diseases are major burdens for the healthcare systems. Research in aging and exercise is crucial to uncover the physiological and molecular mechanisms involved, aiming at identifying biomarkers and pathways that improve health outcomes in the elderly. Metabolomics technology is a powerful tool to analyse dynamic changes in small molecules and the associated metabolic finger-print, to elucidate pathways and patterns associated with aging or exercise. <br /> In this thesis, the influence of aging on the profile of secreted metabolites of the highly metabolic active tissues brown adipose tissue (BAT), inguinal white adipose tissue (WATi) and soleus skeletal muscle (SKM) was analysed from young and old mice. Furthermore, the influence of aging and exercise on human soleus SKM was investigated. For this, state-of-the-art untargeted metabolomics was performed to elucidate the changes in the metabolic profile under basal and cAMP-stimulated conditions. <br /> Secretomic analysis of BAT, WATi, and soleus tissues demonstrated that supernatants can serve as specimen material, revealing a broad spectrum of metabolites, including lipids, amino acids, and carbohydrates. Overall, metabolomic analyses of young compared to old murine BAT, WATi and soleus SKM revealed a strong influence of aging on the metabolic profile in all three tissues. Furthermore, cAMP stimulation could induce the secretion of various metabolites in all tissues. Nevertheless, cAMP stimulation showed greater alterations in young compared to old tissues. This shows that aging not only influences the intracellular metabolism, but furthermore, impacts the tissues’ responsiveness to stimuli and the endocrine function. Among the three tissues, BAT and soleus showed a higher impact of aging than WATi. <br /> In human studies, untargeted metabolomics of soleus biopsies from young and old, trained and untrained participants highlighted significant interindividual differences, complicating the identification of common regulatory patterns. Nevertheless, regular physical activity in young participants seems to result in distinct metabolic adaptations and different responses to acute stimulation compared to young untrained but furthermore compared to old untrained and trained soleus muscle. <br /> This thesis underscores the value of untargeted metabolomics in uncovering metabolic adaptations to aging and exercise. This collection of data greatly demands further in-depth analysis including linking metabolomics data to RNA sequencing or proteomics, and in-depth in vitro and in vivo studies of key candidates, are needed to fully understand these adaptations.