Autophagic protein LC3B confers resistance against hypoxia-induced pulmonary hypertension.
BACKGROUND
Pulmonary hypertension (PH) is a progressive disease with unclear etiology. The significance of autophagy in PH remains unknown.


OBJECTIVE
To determine the mechanisms by which autophagic proteins regulate tissue responses during PH.


METHODS
Lungs from patients with PH, lungs from mice exposed to chronic hypoxia, and human pulmonary vascular cells were examined for autophagy using electron microscopy and Western analysis. Mice deficient in microtubule-associated protein-1 light chain-3B (LC3B(-/-)), or early growth response-1 (Egr-1(-/-)), were evaluated for vascular morphology and hemodynamics.


RESULTS
Human PH lungs displayed elevated lipid-conjugated LC3B, and autophagosomes relative to normal lungs. These autophagic markers increased in hypoxic mice, and in human pulmonary vascular cells exposed to hypoxia. Egr-1, which regulates LC3B expression, was elevated in PH, and increased by hypoxia in vivo and in vitro. LC3B(-/-) or Egr-1(-/-), but not Beclin 1(+/-), mice displayed exaggerated PH during hypoxia. In vitro, LC3B knockdown increased reactive oxygen species production, hypoxia-inducible factor-1α stabilization, and hypoxic cell proliferation. LC3B and Egr-1 localized to caveolae, associated with caveolin-1, and trafficked to the cytosol during hypoxia.


CONCLUSIONS
The results demonstrate elevated LC3B in the lungs of humans with PH, and of mice with hypoxic PH. The increased susceptibility of LC3B(-/-) and Egr-1(-/-) mice to hypoxia-induced PH and increased hypoxic proliferation of LC3B knockdown cells suggest adaptive functions of these proteins during hypoxic vascular remodeling. The results suggest that autophagic protein LC3B exerts a protective function during the pathogenesis of PH, through the regulation of hypoxic cell proliferation.
Lee
Seon-Jin
SJ
Division of Pulmonary and Critical Care Medicine, Brigham and Women’s Hospital, Harvard Medical School, Boston, Massachusetts 02115, USA.
Smith
Akaya
A
Guo
Lanping
L
Alastalo
Tero-Pekka
TP
Li
Molong
M
Sawada
Hirofumi
H
Liu
Xiaoli
X
Chen
Zhi-Hua
ZH
Ifedigbo
Emeka
E
Jin
Yang
Y
Feghali-Bostwick
Carol
C
Ryter
Stefan W
SW
Kim
Hong Pyo
HP
Rabinovitch
Marlene
M
Choi
Augustine M K
AM
D000328:Adult; D000818:Animals; D001343:Autophagy; D015415:Biomarkers / Q000378:metabolism; D015153:Blotting, Western; D015687:Cell Hypoxia; D049109:Cell Proliferation; D005260:Female; D006801:Humans; D006976:Hypertension, Pulmonary / Q000209:etiology / Q000378:metabolism*; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000378:metabolism; D008168:Lung / Q000378:metabolism / Q000648:ultrastructure; D008297:Male; D051379:Mice; D008854:Microscopy, Electron; D008869:Microtubule-Associated Proteins / Q000378:metabolism*; D008875:Middle Aged; D017382:Reactive Oxygen Species / Q000378:metabolism
D015415:Biomarkers; C497443:Hif1a protein, mouse; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; C477012:MAP1LC3A protein, human; C480860:Map1lc3b protein, mouse; D008869:Microtubule-Associated Proteins; D017382:Reactive Oxygen Species