Effect of nerve growth factor and its transforming tyrosine kinase protein and low-affinity nerve growth factor receptors on apoptosis of notochordal cells.
OBJECTIVE
The disappearance of notochordal cells by apoptosis is thought to be the starting point of intervertebral disc degeneration. The aim of this study was to determine the apoptotic pathway of notochordal cells as well as the anti-apoptotic potential of caspase inhibitors.


METHODS
Rat notochordal cells were isolated, cultured, and placed in either 0 % (apoptosis-promoting condition) or 10 % (normal control) foetal bovine serum (FBS). We identified and quantified apoptotic cell deaths and caspase activities. In addition, we examined the cells for expression of nerve growth factor (NGF) and its two receptors--TrkA (survival signal) and p75 (apoptotic signal)--and downstream pathways. Finally, we analysed the degree of anti-apoptotic effects of caspase inhibitors on the cells.


RESULTS
The apoptotic rate and expressions of caspase-8 (extrinsic pathway), -9 (intrinsic pathway), and -3 (common executioner) of notochordal cells were increased in 0 % FBS compared with those in 10 % FBS. Expressions of NGF, p75 receptor and JNK downstream pathways were also increased in 0 % FBS. In contrast, expressions of the TrkA receptor and Akt and MAPK downstream pathways were decreased in 0 % FBS. Pancaspase, capase-9 and capase-8 inhibitors significantly reduced apoptotic cell death.


CONCLUSIONS
Our results suggest that notochordal cells undergo apoptosis through both the intrinsic and extrinsic pathways by activation of NGF, p75 receptor, and the JNK downstream pathway. We also found that apoptosis of notochordal cells can be attenuated by caspase inhibitors. Caspase inhibitors may play a therapeutic role in delaying the starting point of disc degeneration that is due to inappropriate or premature excessive apoptosis of notochordal cells.
Department of Orthopaedic Surgery, Uijeongbu St. Mary's Hospital, College of Medicine, The Catholic University of Korea, 65-1 Kumho-dong, Uijeongbu-si, Kyunggi-do, 480-717, Korea.
Kyung-Hwan
KH
Suhl
Jong-Beom
JB
Park
Eun-Young
EY
Park
Seung-Koo
SK
Rhee
D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D061945:Caspase Inhibitors / Q000494:pharmacology; D020169:Caspases / Q000378:metabolism; D002478:Cells, Cultured; D048670:MAP Kinase Kinase 4 / Q000378:metabolism; D008297:Male; D023421:Models, Animal; D020932:Nerve Growth Factor / Q000378:metabolism*; D009672:Notochord / Q000166:cytology* / Q000187:drug effects; D051381:Rats; D017208:Rats, Wistar; D020800:Receptor, Nerve Growth Factor / Q000378:metabolism*; D020917:Receptor, trkA / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology
D061945:Caspase Inhibitors; D020800:Receptor, Nerve Growth Factor; D020932:Nerve Growth Factor; D020917:Receptor, trkA; D048670:MAP Kinase Kinase 4; D020169:Caspases