Complex II phosphorylation is triggered by unbalanced redox homeostasis in cells lacking complex III

Abstract

A marked stimulation of complex II enzymatic activity was detected in cybrids bearing a homoplasmic MTCYB microdeletion causing disruption of both the activity and the assembly of complex III, but not in cybrids harbouring another MTCYB mutation affecting only the complex III activity. Moreover, complex II stimulation was associated with SDHA subunit tyrosine phosphorylation. Despite the lack of detectable hydrogen peroxide production, up-regulation of the levels of mitochondrial antioxidant defenses revealed a significant redox unbalance. This effect was also supported by the finding that treatment with N-acetylcysteine dampened the complex II stimulation, SDHA subunit tyrosine phosphorylation, and levels of antioxidant enzymes. In the absence of complex III, the cellular amount of succinate, but not fumarate, was markedly increased, indicating that enhanced activity of complex II is hampered due to the blockage of respiratory electron flow. Thus, we propose that complex II phosphorylation and stimulation of its activity represent a molecular mechanism triggered by perturbation of mitochondrial redox homeostasis due to severe dysfunction of respiratory complexes. Depending on the site and nature of the damage, complex II stimulation can either bypass the energetic deficit as an efficient compensatory mechanism, or be ineffectual, leaving cells to rely on glycolysis for survival.

Organization of the Respiratory Supercomplexes in Cells with Defective Complex III: Structural Features and Metabolic Consequences

“…Furthermore, the CIV assembly was also defective because some CIV subunits were recruited within the accumulated CIII subassemblies. A similar analysis was carried out by Páleníková et al (2021) [119], in cells bearing a 18-bp frame deletion in MTCYB gene that produced a protein shortened of six amino acids and induced a strong defect of CIII 2 activity/assembly as well as of CI and CIV [113,120,121]. These cells, differently from those with the 4-bp deletion, exhibited some amount of isolated CIII 2 and CI, that were associated in the enzymatically active CI+III 2 SC [113,121], in agreement with structural data demonstrating the existence of multiple interactions between the two complexes [74].…”

Reactive Oxygen Species Produced by Mutated Mitochondrial Respiratory Chains of Entire Cells Monitored Using Modified Microelectrodes

“…Furthermore, the sign of the current changes measured can also give information on the amount of redox active molecules present out of mitochondria in different cell types. More specifically, this method allows us to clearly demonstrate that mitochondria bearing the cytochrome b microdeletion indeed produces enhanced H 2 O 2 , being this finding previously supported by indirect evidences only. In view of the relatively low amount of cells required for each measurement and considering that the bioenergetics and redox homeostasis of mitochondria play a relevant role in many physiological and pathological conditions of human biology, in the author views this approach will be of widespread interest for numerous biomedical investigations.…”

“…Enhanced generation of mitochondrial ROS has been associated with various diseases, in particular those caused by mutations in the mitochondrial DNA (mtDNA) affecting subunits of respiratory complexes. The RJ206 and the Δcytb cell lines are transmitochondrial hybrid cells (cybrids) exhibiting perturbations of redox homeostasis as a consequence of specific defects in respiratory complexes I (CI) and III (CIII) ,. The Δcytb cell line bears a 18‐base pair long in‐frame microdeletion in the mitochondrial MT‐CYB gene, which was identified in a patient suffering a severe encephalomyopathy and leads to the loss of six amino acid (I300‐P305) residues in the sixth transmembrane helix of cytochrome b, a subunit of CIII.…”

“…The Δcytb cell line bears a 18‐base pair long in‐frame microdeletion in the mitochondrial MT‐CYB gene, which was identified in a patient suffering a severe encephalomyopathy and leads to the loss of six amino acid (I300‐P305) residues in the sixth transmembrane helix of cytochrome b, a subunit of CIII. Cybrids bearing this MT‐CYB microdeletion exhibited a strongly reduced CIII enzymatic activity and features of redox unbalance ,. The RJ206 cell line harbours one of the three pathogenic mutations causing the most common mitochondrial disease, Leber's hereditary optic neuropathy (LHON) .…”

Using complex II as an emerging therapeutic target for the treatment of muscle lesions

“…As an oxygen sensor (Baysal et al, 2000) and key regulator of respiratory and metabolic activities, it responds to changing inflammation-linked pathologies and abnormalities (Hollinshead and Tennant, 2016, Rasheed and Tarjan, 2018, Bezawork-Geleta et al, 2018). Under harsh conditions, such as hypoxia, CII shows an increased activity, which is stimulated by reactive oxygen species (ROS) (Acín-Pérez et al, 2014, Tretter et al, 2016, Tropeano et al, 2018). Therefore, it can be concluded that CII may be the major source for the remodeling of mitochondrial energy systems in anaerobic energy metabolism (Bezawork-Geleta et al, 2017).…”