Mitochondrial complex II is essential for hypoxia-induced pulmonary vasoconstriction of intra- but not of pre-acinar arteries.
OBJECTIVE
Alveolar hypoxia acutely elicits contraction of pulmonary arteries, leading to a rise in pulmonary arterial pressure (PAP) and shifting blood to better ventilated areas of the lung. The molecular mechanisms underlying this hypoxic pulmonary vasoconstriction (HPV) are still incompletely understood. Here, we investigated the role of succinate dehydrogenase (SDH; synonymous to mitochondrial complex II) in HPV, with particular emphasis on regional differences along the vascular bed and consequences for PAP and perfusion-to-ventilation matching, using mutant mice heterozygous for the SDHD subunit of complex II (SDHD(+/-)).


RESULTS
Western blots revealed reduced protein content of complex II subunits SDHA, SDHB, and SDHC in lungs of SDHD(+/-) mice, despite unaffected mRNA content as determined by real-time PCR. Hypoxic pulmonary vasoconstriction of small (20-50 µm) intra-acinar and larger (51-100 µm) pre-acinar arteries was evaluated by videomorphometric analysis of precision-cut lung slices. The hypoxic response was detectable in pre-acinar arteries but absent from intra-acinar arteries of SDHD(+/-) mice. In isolated perfused lungs, basal PAP and its hypoxia-induced increase were indistinguishable between both mouse strains. Arterial oxygenation was measured after provocation of regional ventilatory failure by tracheal fluid instillation in anaesthetized mice, and it declined more in SDHD(+/-) than in wild-type mice.


CONCLUSIONS
SDHD is required for the formation of a stable mitochondrial complex II and it is selectively important for HPV of intra-acinar vessels. This specialized vascular segment participates in perfusion-to-ventilation matching but does not significantly contribute to the acute hypoxic rise in PAP that results from more proximal vasoconstriction.
Institute of Anatomy and Cell Biology, Excellence Cluster Cardio-Pulmonary System, Justus-Liebig-University, Aulweg 123, 35385 Giessen, Germany. renate.paddenberg@anatomie.med.uni-giessen.de
Renate
R
Paddenberg
Martina
M
Tiefenbach
Petra
P
Faulhammer
Anna
A
Goldenberg
Barbara
B
Gries
Uwe
U
Pfeil
Katrin S
KS
Lips
José I
JI
Piruat
José
J
López-Barneo
Ralph T
RT
Schermuly
Norbert
N
Weissmann
Wolfgang
W
Kummer
D000818:Animals; D001794:Blood Pressure / Q000502:physiology; D042963:Electron Transport Complex II / Q000235:genetics / Q000502:physiology; D006579:Heterozygote; D000860:Hypoxia / Q000503:physiopathology*; D008168:Lung / Q000098:blood supply* / Q000378:metabolism; D008565:Membrane Proteins / Q000235:genetics / Q000502:physiology; D051379:Mice; D008817:Mice, Mutant Strains; D023421:Models, Animal; D011651:Pulmonary Artery / Q000503:physiopathology*; D012333:RNA, Messenger / Q000378:metabolism; D013385:Succinate Dehydrogenase / Q000235:genetics / Q000502:physiology*; D014661:Vasoconstriction / Q000502:physiology*
D008565:Membrane Proteins; D012333:RNA, Messenger; D042963:Electron Transport Complex II; C574938:SDHD protein, mouse; D013385:Succinate Dehydrogenase