Exercise prevents fatty liver by modifying the compensatory response of mitochondrial metabolism to excess substrate availability

Objective

Liver mitochondria adapt to high-calorie intake. We investigated how exercise alters the early compensatory response of mitochondria, thus preventing fatty liver disease as a long-term consequence of overnutrition.

Methods

We compared the effects of a steatogenic high-energy diet (HED) for six weeks on mitochondrial metabolism of sedentary and treadmill-trained C57BL/6N mice. We applied multi-OMICs analyses to study the alterations in the proteome, transcriptome, and lipids in isolated mitochondria of liver and skeletal muscle as well as in whole tissue and examined the functional consequences by high-resolution respirometry.

Results

HED increased the respiratory capacity of isolated liver mitochondria, both in sedentary and in trained mice. However, proteomics analysis of the mitochondria and transcriptomics indicated that training modified the adaptation of the hepatic metabolism to HED on the level of respiratory complex I, glucose oxidation, pyruvate and acetyl-CoA metabolism, and lipogenesis. Training also counteracted the HED-induced glucose intolerance, the increase in fasting insulin, and in liver fat by lowering diacylglycerol species and c-Jun N-terminal kinase (JNK) phosphorylation in the livers of trained HED-fed mice, two mechanisms that can reverse hepatic insulin resistance. In skeletal muscle, the combination of HED and training improved the oxidative capacity to a greater extent than training alone by increasing respiration of isolated mitochondria and total mitochondrial protein content.

Conclusion

We provide a comprehensive insight into the early adaptations of mitochondria in the liver and skeletal muscle to HED and endurance training. Our results suggest that exercise disconnects the HED-induced increase in mitochondrial substrate oxidation from pyruvate and acetyl-CoA-driven lipid synthesis. This could contribute to the prevention of deleterious long-term effects of high fat and sugar intake on hepatic mitochondrial function and insulin sensitivity.

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High-energy diet promotes mitochondrial respiration in liver independent of training.

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High-energy diet combined with training disconnects substrate oxidation from lipid synthesis.

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High-energy diet combined with training reduces complex I formation in the liver.

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Trained skeletal muscle unburdens the liver from substrate overload.

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Comprehensive resource of mitochondrial adaptations to high-energy diet and training.

[11C]MODAG-001-towards a PET tracer targeting α-synuclein aggregates

Purpose

Deposition of misfolded alpha-synuclein (αSYN) aggregates in the human brain is one of the major hallmarks of synucleinopathies. However, a target-specific tracer to detect pathological aggregates of αSYN remains lacking. Here, we report the development of a positron emission tomography (PET) tracer based on anle138b, a compound shown to have therapeutic activity in animal models of neurodegenerative diseases.

Methods

Specificity and selectivity of [³H]MODAG-001 were tested in in vitro binding assays using recombinant fibrils. After carbon-11 radiolabeling, the pharmacokinetic and metabolic profile was determined in mice. Specific binding was quantified in rats, inoculated with αSYN fibrils and using in vitro autoradiography in human brain sections of Lewy body dementia (LBD) cases provided by the Neurobiobank Munich (NBM).

Results

[³H]MODAG-001 revealed a very high affinity towards pure αSYN fibrils (K_d = 0.6 ± 0.1 nM) and only a moderate affinity to hTau46 fibrils (K_d = 19 ± 6.4 nM) as well as amyloid-β_1–42 fibrils (K_d = 20 ± 10 nM). [¹¹C]MODAG-001 showed an excellent ability to penetrate the mouse brain. Metabolic degradation was present, but the stability of the parent compound improved after selective deuteration of the precursor. (d₃)-[¹¹C]MODAG-001 binding was confirmed in fibril-inoculated rat striata using in vivo PET imaging. In vitro autoradiography showed no detectable binding to aggregated αSYN in human brain sections of LBD cases, most likely, because of the low abundance of aggregated αSYN against background protein.

Conclusion

MODAG-001 provides a promising lead structure for future compound development as it combines a high affinity and good selectivity in fibril-binding assays with suitable pharmacokinetics and biodistribution properties.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00259-020-05133-x.

Linking bioenergetic function of mitochondria to tissue-specific molecular fingerprints

Mitochondria are dynamic organelles with diverse functions in tissues such as liver and skeletal muscle. To unravel the mitochondrial contribution to tissue-specific physiology, we performed a systematic comparison of the mitochondrial proteome and lipidome of mice and assessed the consequences hereof for respiration. Liver and skeletal muscle mitochondrial protein composition was studied by data-independent ultra-high-performance (UHP)LC-MS/MS-proteomics, and lipid profiles were compared by UHPLC-MS/MS lipidomics. Mitochondrial function was investigated by high-resolution respirometry in samples from mice and humans. Enzymes of pyruvate oxidation as well as several subunits of complex I, III, and ATP synthase were more abundant in muscle mitochondria. Muscle mitochondria were enriched in cardiolipins associated with higher oxidative phosphorylation capacity and flexibility, in particular CL(18:2)₄ and 22:6-containing cardiolipins. In contrast, protein equipment of liver mitochondria indicated a shuttling of complex I substrates toward gluconeogenesis and ketogenesis and a higher preference for electron transfer via the flavoprotein quinone oxidoreductase pathway. Concordantly, muscle and liver mitochondria showed distinct respiratory substrate preferences. Muscle respired significantly more on the complex I substrates pyruvate and glutamate, whereas in liver maximal respiration was supported by complex II substrate succinate. This was a consistent finding in mouse liver and skeletal muscle mitochondria and human samples. Muscle mitochondria are tailored to produce ATP with a high capacity for complex I-linked substrates. Liver mitochondria are more connected to biosynthetic pathways, preferring fatty acids and succinate for oxidation. The physiologic diversity of mitochondria may help to understand tissue-specific disease pathologies and to develop therapies targeting mitochondrial function.