JNK phosphorylation promotes natural degeneration of cervical endplate chondrocytes by down-regulating expression of ANK.
BACKGROUND
Endplate degeneration leads to accelerated degeneration of the intervertebral disc. The importance of endplate chondrocytes in this process is unclear. Many cellular processes in chondrocytes are controlled by activated c-Jun N-terminal kinases (JNK) and protein kinase B (AKT). However, the involvement of their pathways in the degeneration process needs to be elucidated.


OBJECTIVE
To study activation of JNK and AKT signaling pathways and their significance for degeneration of endplate chondrocytes, as well as involvement of progressive ankylosis protein (ANK) in this process.


METHODS
Rat primary chondrocytes were grown to confluence and subcultured until passage 4. Morphological appearances (microscope, hematoxylin & eosin staining, toluidine blue staining) and proliferation rates of cells (MTT test) were observed. Further, levels of type II collagen, aggrecan, phosphorylated JNK and AKT, total JNK, AKT and ANK were evaluated by qPCR, flow cytometry and Western blot assays. Furthermore, inhibition experiments with SP600125, the JNK inhibitor, were carried out in the passage 4 cells to assess the effects of the JNK pathway on natural degeneration of endplate chondrocytes.


RESULTS
The proliferative speed of endplate chondrocytes progressively decreased during passaging. Expressions of type II collagen and aggrecan were significantly decreased with cells at higher passages. Furthermore, phosphorylation of JNK, but not AKT, was significantly up-regulated and accompanied by reduced ANK expression. Inhibition of the JNK pathway increased expression of type II collagen, aggrecan and ANK and facilitated proliferation rates.


CONCLUSIONS
Phosphorylation of JNK promotes natural degeneration of cervical endplate chondrocytes, likely by down-regulating ANK expression.
Department of Orthopedic Surgery, Yijishan Hospital, Wannan Medical College, Wuhu, People's Republic of China. pumchxuhg@126.com.
H-G
HG
Xu
J-F
JF
Cheng
H-X
HX
Peng
K
K
Lv
H
H
Wang
P
P
Liu
M
M
Zhong
M-Y
MY
Zhang
D053674:Aggrecans / Q000378:metabolism; D000818:Animals; D000873:Anthracenes / Q000494:pharmacology; D015153:Blotting, Western; D049109:Cell Proliferation; D002574:Cervical Vertebrae / Q000166:cytology / Q000473:pathology; D019902:Chondrocytes / Q000502:physiology*; D024043:Collagen Type II / Q000378:metabolism; D015536:Down-Regulation; D005434:Flow Cytometry; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism*; D020935:MAP Kinase Signaling System / Q000502:physiology; D008297:Male; D028061:Phosphate Transport Proteins / Q000235:genetics*; D010766:Phosphorylation; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction / Q000502:physiology
D053674:Aggrecans; C498769:Ankh protein, mouse; D000873:Anthracenes; D024043:Collagen Type II; D028061:Phosphate Transport Proteins; C432165:pyrazolanthrone; D051057:Proto-Oncogene Proteins c-akt; D048031:JNK Mitogen-Activated Protein Kinases