Frontiers in Physiology | www.frontiersin.org 1 January 2022 | Volume 12 | Article 791588 ORIGINAL RESEARCH published: 04 January 2022 doi: 10.3389/fphys.2021.791588 Edited by: Ryan Ceddia, Vanderbilt University Medical Center, United States Reviewed by: Paul Trayhurn, University of Liverpool, United Kingdom Jean-François Mauger, University of Ottawa, Canada *Correspondence: Gijs H. Goossens g.goossens@maastrichtuniversity.nl Specialty section: This article was submitted to Metabolic Physiology, a section of the journal Frontiers in Physiology Received: 08 October 2021 Accepted: 30 November 2021 Published: 04 January 2022 Citation: Van Meijel RLJ, Wang P, Bouwman F, Blaak EE, Mariman ECM and Goossens GH (2022) The Effects of Mild Intermittent Hypoxia Exposure on the Abdominal Subcutaneous Adipose Tissue Proteome in Overweight and Obese Men: A First- in-Human Randomized, Single-Blind, and Cross-Over Study. Front. Physiol. 12:791588. doi: 10.3389/fphys.2021.791588 The Effects of Mild Intermittent Hypoxia Exposure on the Abdominal Subcutaneous Adipose Tissue Proteome in Overweight and Obese Men: A First-in-Human Randomized, Single-Blind, and Cross-Over Study Rens L. J. Van Meijel 1 , Ping Wang 2 , Freek Bouwman 1 , Ellen E. Blaak 1 , Edwin C. M. Mariman 1 and Gijs H. Goossens 1 * 1 Department of Human Biology, NUTRIM School of Nutrition and Translational Research in Metabolism, Maastricht University Medical Center + , Maastricht, Netherlands, 2 Department of Clinical Genetics, Maastricht University Medical Center + , Maastricht, Netherlands Adipose tissue (AT) oxygen tension (pO 2 ) has been implicated in AT dysfunction and metabolic perturbations in both rodents and humans. Compelling evidence suggests that hypoxia exposure alters metabolism, at least partly through effects on AT. However, it remains to be elucidated whether mild intermittent hypoxia (MIH) exposure impacts the AT proteome. We performed a randomized, single-blind, and cross-over study to investigate the effects of seven consecutive days of MIH (FiO 2 15%, 3x2h/d) compared to normoxia (FiO 2 21%) exposure on the AT proteome in overweight/obese men. In vivo AT insulin sensitivity was determined by the gold standard hyperinsulinemic-euglycemic clamp, and abdominal subcutaneous AT biopsies were collected under normoxic fasting conditions following both exposure regimens (day 8). AT proteins were isolated and quantified using liquid chromatography-mass spectrometry. After correction for blood contamination, 1,022 AT protein IDs were identified, of which 123 were differentially expressed following MIH (p < 0.05). We demonstrate for the first time that MIH exposure, which markedly reduces in vivo AT oxygen tension, impacts the human AT proteome. Although we cannot exclude that a single differentially expressed protein might be a false positive finding, several functional pathways were altered by MIH exposure, also after adjustment for multiple testing. Specifically, differentially expressed proteins were involved in redox systems, cell-adhesion, actin cytoskeleton organization, extracellular matrix composition, and energy metabolism. The MIH-induced change in AT TMOD3 expression was strongly related to altered in vivo AT insulin sensitivity, thus linking MIH-induced effects on the AT proteome to metabolic changes in overweight/obese humans. Keywords: adipose tissue, proteomics, mild intermittent hypoxia, obesity, RCT