Chronic hypoxia alters mitochondrial composition in human macrophages

Hypoxia inducible factors (HIFs) are important mediators of the cellular adaptive response during acute hypoxia. The role of HIF-1 and HIF-2 during prolonged periods of hypoxia, i.e. chronic hypoxia is less defined. Therefore, we used human THP-1 macrophages with a knockdown of either HIF-1 alpha, HIF-2 alpha, or both HIF alpha-subunits, incubated them for several days under hypoxia (1% O-2), and analyzed responses to hypoxia using 2D-DIGE coupled to MS/MS-analysis. Chronic hypoxia was defined as a time point when the early but transient accumulation of HIF alpha-subunits and mRNA expression of classical HIF target genes returned towards basal levels, with a new steady state that was constant from 72 h onwards. From roughly 800 spots, that were regulated comparing normoxia to chronic hypoxia, about 100 proteins were unambiguously assigned during MS/MS-analysis. Interestingly, a number of glycolytic proteins were up-regulated, while a number of inner mitochondrial membrane proteins were down-regulated independently of HIF-1 alpha or HIF-2 alpha. Chronic hypoxic conditions depleted the mitochondrial mass by autophagy, which occurred independently of HIF proteins. Macrophages tolerate periods of chronic hypoxia very well and adaptive responses occur, at least in part, independently of HIF-1 alpha and/or HIF-2 alpha and comprise mitophagy as a pathway of particular importance. (C) 2013 Elsevier B.V. All rights reserved.