MicroRNA-146a Induced by Hypoxia Promotes Chondrocyte Autophagy through Bcl-2.
OBJECTIVE
There have been many studies on the etiology of osteoarthritis (OA) with regard to the function of inflammatory cytokines, the process of cartilage degradation, the function of miR-146a, hypoxia stimulation and autophagy in OA chondrocytes, but there have been no reports on the relationship between miR-146a and autophagy in cartilage, especially under hypoxia. This study aimed to confirm the relationship of miR-146a and autophagy in cartilage under hypoxia.


METHODS
Chondrocytes were treated by hypoxia gradients, and the main factors including HIF-1α, HIF-2α, miR-146a and Bcl-2 and autophagy markers ULK-1, ATG-5 were detected by quantitative PCR (Q-PCR) and western blotting. The autophagy marker LC-3 was detected by immunofluorescence. The reciprocal effects between miR-146a and Bcl-2 were confirmed by several combinations of shRNAs and adenovirus-gene systems followed by Q-PCR and western blot detection.


RESULTS
Hypoxia maintained the chondrocytes phenotype and promoted autophagy and miR-146a expression via HIF-1α, but not HIF-2α, while miR-146a did not reversely affect HIF-1α. The autophagy induced by hypoxia through HIF-1α, miR-146a and Bcl-2. Simply, hypoxia induced HIF-1α, and HIF-1α increased miR-146a, but miR-146a suppressed Bcl-2, an autophagy inhibitor. While Bcl-2 affected neither HIF-1α nor miR-146a. The absence of both HIF-1α and miR-146a or Bcl-2 over-expression inhibited hypoxia-induced autophagy.


CONCLUSIONS
HIF-1α, miR-146a and Bcl-2 play crucial roles during hypoxia-induced autophagy, Hypoxia, HIF-1α and miR-146a promote chondrocytes autophagy via depressing Bcl-2. We conclude that miR-146a may serve as a novel therapeutic target for protecting cartilage from degeneration in OA.
Fei
F
Zhang
Jing
J
Wang
Jianjun
J
Chu
Cheng
C
Yang
Hui
H
Xiao
Chenglong
C
Zhao
Zhengwang
Z
Sun
Xin
X
Gao
Guanghui
G
Chen
Zhitao
Z
Han
Weiwei
W
Zou
Tielong
T
Liu
D000818:Animals; D001343:Autophagy; D000071187:Autophagy-Related Protein 5; D000071189:Autophagy-Related Protein-1 Homolog; D002358:Cartilage, Articular / Q000166:cytology; D015687:Cell Hypoxia; D002478:Cells, Cultured; D019902:Chondrocytes / Q000166:cytology / Q000378:metabolism; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D051379:Mice; D035683:MicroRNAs / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D008856:Microscopy, Fluorescence; D008869:Microtubule-Associated Proteins / Q000235:genetics / Q000378:metabolism; D016376:Oligonucleotides, Antisense / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000378:metabolism
C495773:Atg5 protein, mouse; D000071187:Autophagy-Related Protein 5; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; C480860:Map1lc3b protein, mouse; D035683:MicroRNAs; D008869:Microtubule-Associated Proteins; C534190:Mirn146 microRNA, mouse; D016376:Oligonucleotides, Antisense; D019253:Proto-Oncogene Proteins c-bcl-2; D034741:RNA, Small Interfering; D000071189:Autophagy-Related Protein-1 Homolog; D017346:Protein Serine-Threonine Kinases; C112444:Ulk1 protein, mouse