TCA cycle rewiring fosters metabolic adaptation to oxygen restriction in skeletal muscle from rodents and humans

Daniele Capitanio,Denny Z H Levett,Manuela Moriggi,Anna Caretti,Chiara Fania,Valentina Bravatà,Michele Samaja,Agnese Viganò,Cecilia Gelfi,Paolo Cerretelli,Enrica Torretta,Michael P W Grocott

doi:10.1038/s41598-017-10097-4

Abstract

In mammals, hypoxic stress management is under the control of the Hypoxia Inducible Factors, whose activity depends on the stabilization of their labile α subunit. In particular, the skeletal muscle appears to be able to react to changes in substrates and O2 delivery by tuning its metabolism. The present study provides a comprehensive overview of skeletal muscle metabolic adaptation to hypoxia in mice and in human subjects exposed for 7/9 and 19 days to high altitude levels. The investigation was carried out combining proteomics, qRT-PCR mRNA transcripts analysis, and enzyme activities assessment in rodents, and protein detection by antigen antibody reactions in humans and rodents. Results indicate that the skeletal muscle react to a decreased O2 delivery by rewiring the TCA cycle. The first TCA rewiring occurs in mice in 2-day hypoxia and is mediated by cytosolic malate whereas in 10-day hypoxia the rewiring is mediated by Idh1 and Fasn, supported by glutamine and HIF-2α increments. The combination of these specific anaplerotic steps can support energy demand despite HIFs degradation. These results were confirmed in human subjects, demonstrating that the TCA double rewiring represents an essential factor for the maintenance of muscle homeostasis during adaptation to hypoxia.

Highlights

Despite a number of studies on cell models and on human subjects exposed to short and long term hypoxia the biochemical mechanisms adopted by muscle tissue to cope with oxygen restriction are not fully understood
The results demonstrate that both mice and human subjects exposed to hypoxia utilized the tricarboxylic acid (TCA) cycle rewiring to cope with oxygen deficiency introducing for the first time in mammals an alternative use of the TCA cycle to sustain energy production under conditions of limited oxygen availability
Hypoxia Inducible Factors (HIFs)-1α was quantified in total extracts from gastrocnemius muscle of normoxic (N), 2-day hypoxic (2 H) and 10-day hypoxic (10 H) mice

Summary

Introduction

Despite a number of studies on cell models and on human subjects exposed to short and long term hypoxia the biochemical mechanisms adopted by muscle tissue to cope with oxygen restriction are not fully understood. Previous proteomic studies conducted on human skeletal muscles exposed to various degrees of hypoxia, indicate that short and long term hypoxia exposures do not permanently activate HIF14, 15. The results demonstrate that both mice and human subjects exposed to hypoxia utilized the TCA cycle rewiring to cope with oxygen deficiency introducing for the first time in mammals an alternative use of the TCA cycle to sustain energy production under conditions of limited oxygen availability. These results highlight the capacity of the human body to utilize unconventional metabolic pathways to sustain energy demand and maintain tissue homeostasis

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