Ehinger 2016 Mov Disord

Ehinger JK, Morota S, Hansson MJ, Gesine P, Elmér E (2016) Mitochondrial respiratory function in peripheral blood cells from Huntington’s disease patients. Mov Disord doi:10.1002/mdc3.12308.

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Ehinger JK, Morota S, Hansson MJ, Gesine P, Elmer E (2016) Mov Disord

Abstract: Patients with Huntington’s disease display symptoms from both the central nervous system and peripheral tissues. Mitochondrial dysfunction has been implicated as part of the pathogenesis of the disease and has been reported in brain tissue and extracerebral tissues, such as muscle and blood cells, but the results are inconsistent. Therefore, the authors performed a refined evaluation of mitochondrial function in 2 types of peripheral blood cells from 14 patients with Huntington’s disease and 21 control subjects. Several hypotheses were predefined, including impaired mitochondrial complex II function (primary), complex I function (secondary), and maximum oxidative phosphorylation capacity (secondary) in patient cells.

High-resolution respirometry was applied to viable platelets and mononuclear cells. Data were normalized to cell counts, citrate synthase activity, and mitochondrial DNA copy numbers.

Normalized to citrate synthase activity, platelets from patients with Huntington’s disease displayed respiratory dysfunction linked to complex I, complex II, and lower maximum oxidative phosphorylation capacity. No difference was seen in mononuclear cells or when platelet data were normalized to cell counts or mitochondrial DNA. The ratio of complex I respiration through maximum oxidative phosphorylation was significantly decreased in patients compared with controls. The corresponding ratio for complex II was unaffected.

The data indicate decreased function of mitochondrial complex I in peripheral blood cells from patients with Huntington’s disease, although this could not be uniformly confirmed. The results do not confirm a systemic complex II dysfunction and do not currently support the use of mitochondrial function in blood cells as a biomarker for the disease. • Keywords: Huntington’s disease, Mitochondria, Blood cells, Respirometry, Oxygen consumption, PBMC

• O2k-Network Lab: JP Tokyo Uchino H, SE Lund Elmer E

Coupling control and the Q-junction

Mitochondrial coupling control states are measured without simultaneous change of a selected pathway control state, i.e. coupling control is separated from pathway control. Biochemical coupling efficiencies (E-L coupling efficiencies) and P-L coupling efficiencies are, therefore, studied at a defined pathway control state that must not change between measurement of LEAK respiration L, OXPHOS capacity P, and electron transfer capacity E.

A physiologically relevant pathway control state for partial reconstitution of TCA cycle function is obtained by supply of NADH-linked substrates (e.g. pyruvate&malate PM; N-pathway) in combination with succinate (S; S-pathway), supporting convergent electron transfer through Complexes I and II into the Q-junction (NS-pathway). OXPHOS- and ET-capacities are higher in the combined NS-pathway than in the separate N- or S-pathway (Gnaiger 2020). Is the NS-pathway control state appropriate for the analysis of coupling control?

Partial additivity in OXPHOS capacity NS_P or ET capacity NS_E implies that there is competition between the N- and S-pathway, when the NS-pathway capacity is less than the arithmetic sum of the constituent pathway capacities. In mitochondria with lower OXPHOS than ET capacity (P<E; when the phosphorylation system is limiting), the competition in NS_E is increasingly pronounced in NS_P, and when respiration is further reduced by complete inhibition of the phosphorylation system (e.g. by oligomycin), competition between the N- and S-pathways is maximal in LEAK respiration. Different levels of competition imply that the ratio of the effective N- and S-pathway in the NS-pathway state may shift to the extent that the dominant pathway may fully outcompete the other in the LEAK state. Convergent electron input into the Q-junction in NS_E, therefore, may shift to single electron input through either the dominant N- or S-pathway in NS_L, which then would effectively correspond to either N_L or S_L. This has deep implications on LEAK respiration, since the N-pathway has three coupling sites (H⁺ pumps: CI, CIII, CIV) with a correspondingly higher H⁺/O₂ ratio compared to the S-pathway with two coupling sites (H⁺ pumps: CIII, CIV). A higher rate of the proton leak is implied when measuring the same rate of LEAK respiration in N_L than when observing an identical oxygen consumption rate in S_L.

When inhibiting O₂ consumption by oligomycin in the NS-pathway state, the relative contribution of the N- and S-pathways to LEAK respiration is not known. By subsequent uncoupler titrations, the relative contribution of these pathways is likely to change, thus obtaining an undefined combination of pathway control and coupling control. In conclusion, the NS-pathway state is not appropriate for studying coupling control. Coupling control is best studied in the separate N- or S-pathway (Gnaiger et al 2000; 2015).

Gnaiger E (2020) Mitochondrial pathways and respiratory control. An introduction to OXPHOS analysis. 5th ed. Bioenerg Commun 2020.2. https://doi.org/10.26124/bec:2020-0002
Gnaiger E, Boushel R, Søndergaard H, Munch-Andersen T, Damsgaard R, Hagen C, Díez-Sánchez C, Ara I, Wright-Paradis C, Schrauwen P, Hesselink M, Calbet JAL, Christiansen M, Helge JW, Saltin B (2015) Mitochondrial coupling and capacity of oxidative phosphorylation in skeletal muscle of Inuit and caucasians in the arctic winter. https://doi.org/10.1111/sms.12612
Gnaiger E, Méndez G, Hand SC (2000) High phosphorylation efficiency and depression of uncoupled respiration in mitochondria under hypoxia. Proc Natl Acad Sci U S A 97:11080-5. https://doi.org/10.1073/pnas.97.20.11080

Labels: MiParea: Respiration, Patients Pathology: Neurodegenerative

Organism: Human Tissue;cell: Blood cells, Lymphocyte, Platelet Preparation: Permeabilized cells, Intact cells

Coupling state: LEAK, ROUTINE, OXPHOS, ET Pathway: N, S, CIV, NS, Other combinations, ROX HRR: Oxygraph-2k

2016-03, JP, SE, MitoEAGLE blood cells data