**List of abbreviations**

metabolism [174,175]; it is likely that autophagy, especially mitochondrial autophagy, be amended during such an exposure. Consistent with this, experiments performed in cells showed that mitochondrial autophagy is induced by chronic hypoxia through HIF-1 (hypoxiadependent factor-1) and BNIP3, and this regulation constitutes a preventive response that is necessary to avoid accumulation of reactive oxygen species and cell death [176]. The effects of exposition to moderate altitude (i.e., 1,500–3,000 m) have also to be definite since it concerns a larger population (athletes, general tourist population, and highlanders) compared to high

**Figure 4.** Exercise and autophagy in skeletal muscle. Adapted from Sanchez AMJ et al. 2014. Autophagy is essential to support skeletal muscle plasticity in response to endurance exercise. American Journal of Physiology – Regulatory, In‐ tegrative and Comparative Physiology 307(8): R956-R969 [21]. Essential amino acids (EAA); carbohydrate (CHO)

Research of this type is leading to a better understanding of the autophagy-mediated turnover of organelles like mitochondria in response to exercise and altitude exposure. Finding optimal training strategies represents an important objective to enhance exercise adaptations in both athletes and patients with metabolic or muscle diseases, including COPD (chronic obstructive

In summary, autophagy represents a crucial mechanism for cell homeostasis and cell survival. Autophagy constitutes a recycling process that degrades used or flawed internal structures

pulmonary disease) that can cause systemic hypoxia and loss in muscle capability.

altitude.

184 Muscle Cell and Tissue

**5. Conclusions**

4E-BP1, eukaryotic translation initiation factor 4E-binding protein 1; Aβ, amyloid β; AIDS, acquired immune deficiency syndrome; AMPK, 5'-adenosine monophosphate-activated protein kinase; Atg, autophagy-specific gene; BCL2, B-cell lymphoma 2; BNIP3, BCL2/ adenovirus E1B 19 kDa-interacting protein-3; CaMKK, Ca2+/calmodulin-dependent protein kinase; CHO, carbohydrate; CHOP, C/EBP homologous protein; CMA, chaperone-mediated autophagy; COPD, chronic obstructive pulmonary disease; DEPTOR, DEP domain-containing MTOR-interacting protein; EAA, essential amino acids; eIF2B, eukaryotic translation initiation factor 2B; eIF2α, eukaryotic initiation factor 2α; FIP200, focal adhesion kinase (FAK) familyinteracting protein of 200 kDa; FoxO, forkhead box class "other" O; Gabarapl1, GABAA receptor-associated protein-like 1; GATE-16, Golgi-associated ATPase enhancer; GSK3β, glycogen synthase kinase 3β; hsc73, heat-shock cognate protein of 73 kDa; HIF-1, hypoxiadependent factor-1; IGF-1, insulin-like growth factor-1; LAMP-2A, lysosome-associated membrane protein 2A; LC3, microtubule-associated protein 1A/ 1B light chain 3; LKB1, liver kinase B1; MAFbx/atrogin-1, muscle atrophy F-box; Mfn2, mitofusin-2; mLST8/GβL, MTORassociated protein LST8 homolog; MTOR, mechanistic/mammalian target of rapamycin; MTORC1, mechanistic/mammalian target of rapamycin complex 1; Mul1, mitochondrial E3 ubiquitin protein ligase 1; MuRF1, muscle RING-finger protein-1; OPA1, optic atrophy 1; p62/ SQSTM1, sequestosome 1; PDK1, phosphoinositide-dependent kinase-1; PE, phosphatidyle‐ thanolamine; PERK, double-stranded RNA-activated protein kinase R (PKR)-like endoplasmic reticulum kinase; PGC-1, peroxisome proliferator activator receptor γ coactivator-1; PI3K, phosphatidylinositol 3-kinase; PINK1, PTEN-induced putative kinase protein 1; PKB/Akt, protein kinase B; PPARα, peroxisome proliferator-activated receptor α; PRAS40, proline-rich Akt substrate of 40 kDa; PTEN, phosphatase and tensin homolog; Rheb, ras homologous enriched in brain; RPTOR, regulatory-associated protein of MTOR, complex 1; ROS, reactive oxygen species; S6K1, p70S6 kinase 1; TAK-1, transforming growth factor β-activated kinase 1; Trim32, tripartite motif-containing protein 32; TSC21/2, tuberous sclerosis complex 1/2; Ulk, unc-51-like kinase; Vps34, vacuolar protein sorting 34; XBP1s, X-box binding protein 1; ZNF216, zinc-finger protein 216
