|
|
||||||||
RESEARCH REPORT |
1 Departments of Operative Dentistry and Endodontics, and
2 Oral Microbiology, Kyushu Dental College, 2-6-1 Manazuru, Kokurakita, Kitakyushu 803-8580, Japan;
*corresponding author, chi-aki-k{at}kyu-dent.ac.jp
| ABSTRACT |
|---|
|
|
|---|
KEY WORDS: apoptosis c-Jun c-Jun N-terminal kinase heat-shock protein 70 wound healing
| INTRODUCTION |
|---|
|
|
|---|
c-Jun N-terminal kinase (JNK), a member of the mitogen-activated protein kinases, phosphorylates the transactivation domain of c-Jun. Recently, it has been demonstrated that the JNK pathway is a compartment of signaling pathways, leading cells into apoptosis in response to several stresses, including heat shock (Bossy-Wetzel et al., 1997; Tournier et al, 2000). Other molecules, heat-shock proteins (HSPs) 70 and 27, have also been shown to play an important role in the apoptotic signaling pathway in heat-stressed conditions (Garrido et al., 2001). In particular, HSP70 exhibits anti-apoptotic action through the inhibition of the JNK cascade (Gabai et al., 1997, 2000).
Heat stress brought on by cavity preparation is recognized as one of the major causes of damage to pulp tissues. In this study, we examined whether JNK, c-Jun, HSP70, and HSP27 are associated with the induction of apoptosis during pulp wound healing after cavity preparation.
| MATERIALS & METHODS |
|---|
|
|
|---|
Immunohistochemistry
Demineralized molars were dehydrated with graded ethanol and embedded in paraffin. Serial sections (5 µm thickness) were cut and mounted on 3-aminopropyltriethoxysilane-treated object slides. Immunohistochemistry was carried out with the avidin-biotin-peroxidase complex method, with use of a VECTASTAIN® ABC kit (Vector Laboratories, Inc., Burlingame, CA, USA). Deparaffinized sections were rinsed with 1xPBS, and immersed in 0.3% H2O2/methanol for blocking endogenous peroxidase. After being blocked with normal serum solution, sections were reacted with the primary antibody at 4°C overnight. Mouse monoclonal antibodies against JNK phosphorylated on Thr-183/Tyr-185 (p-JNK, G-7) and c-Jun phosphorylated on Ser-63 (p-c-Jun, KM-1) were used at a dilution of 1:400 and 1:200 in 1xPBS, respectively. Goat polyclonal antibodies against HSP70 (K-20) and HSP27 (M-20) were used at a dilution of 1:1300 and 1:500 in 1xPBS, respectively. These antibodies were purchased from Santa Cruz Biotechnology (Santa Cruz, CA, USA). Sections were incubated with biotinylated antibodies for 30 min at room temperature, and treated with peroxidase substrate solution containing diaminobenzidine (DAB) (1 mg/mL), Tris/HCl, pH 7.5, and 0.02% H2O2. After specimens were counterstained with methyl green (Vector Laboratories, Inc., Burlingame, CA, USA), DAB signals were observed under light microscopy. Negative controls were carried out by the omission of primary antibody or with non-specific IgG.
For double-immunofluorescence staining, sections were reacted with a primary antibody against either p-JNK or p-c-Jun. Goat anti-mouse IgG-Alexa Fluor 488 (Molecular Probes, Inc., Eugene, OR, USA) was used as a secondary antibody at a dilution of 1:200 in 1xPBS for 1 hr at room temperature. Sections were subsequently reacted with a primary antibody against either HSP70 or HSP27, and labeled with donkey anti-goat IgG-Alexa Fluor 546 (Molecular Probes, Inc., Eugene, OR, USA) at a dilution of 1:200 in 1xPBS. Signals were observed under the fluorescence microscope, and analyzed by Adobe Photoshop software (Adobe Systems Inc., San Jose, CA, USA).
Double-staining with Terminal Deoxynucleotidyl Transferase-mediated Labeling (TUNEL) and Immunohistochemistry
For double-staining of TUNEL and immunohistochemistry, sections were first subjected to TUNEL assay by means of an In Situ Cell Death Detection Kit, AP (Roche Diagnostics, Mannheim, Germany). To avoid loss of proteins, we did not treat sections with proteinase K in this experiment. We confirmed that TUNEL-positive signals in sections both with and without proteinase K treatment were similar (data not shown). Sections were reacted with a terminal deoxynucleotidyl transferase (TdT) mixture containing fluorescein-labeled nucleotides for 1 hr at 37°C. Sections were reacted with alkaline-phosphatase-conjugated anti-fluorescein antibody for 1 hr at 37°C. Signals of alkaline phosphatase were visualized by NBT/BCIP (Roche Diagnostics, Mannheim, Germany). Following TUNEL assay, immunohistochemistry was carried out with the above ABC method with the use of antibodies against p-JNK, p-c-Jun, and HSP70. After the immunohistochemical procedures, sections were observed under light microscopy.
| RESULTS |
|---|
|
|
|---|
|
|
|
|
| DISCUSSION |
|---|
|
|
|---|
One hour after injury, JNK and c-Jun were not activated in odontoblasts, suggesting that the activation of the JNK pathway is not essential for apoptosis in odontoblasts. Other factors stimulated by direct mechanical stresses, such as the damage to odontoblastic processes and the aspiration of odontoblastic bodies into dentinal tubules, may be associated with apoptosis of odontoblasts. In contrast, we observed the appearance of pulp cells with active JNK. This result suggests that gap junctional signaling may exist between injured odontoblasts and pulp cells, and that secondary apoptosis may initiate in pulp cells through the JNK pathway in the early healing process. Pulp cells with active c-Jun 1 hr post-injury were similar in number to untreated cells, suggesting that the activation of c-Jun in pulp cells during this early phase is not associated with apoptosis.
One day after injury, JNK and c-Jun were frequently activated in pulp cells, and localized in some apoptotic pulp cells, whereas HSP70 localized only in non-apoptotic pulp cells. Furthermore, we found that HSP70 transiently translocated from the cytoplasm to nuclei of pulp cells, and co-localized with active JNK and c-Jun. HSP70 is known to translocate from the cytoplasm to the nucleus following heat-shock stress (Lepock et al., 2001). Although we need direct evidence from cell culture experiments, these results suggest that heat-shock stress from cavity preparation can induce apoptosis in pulp cells, and that JNK and c-Jun contribute to secondary apoptosis in pulp cells. It is also suggested that HSP70 plays an anti-apoptotic role by inhibiting the JNK pathway, and may contribute to the thermotolerance of pulp tissues. Pulp cells showing co-localization of these molecules may be rescued from apoptosis, and pulp cells without co-localization may enter apoptosis. We also examined the expression of HSP27, one of the survival molecules in heat-shock stress (Garrido et al., 1999). In this study, HSP27 neither translocated nor co-localized with active JNK and c-Jun in the nuclei of pulp cells, suggesting that the expression of HSP27 is independent of the regulation of pulp apoptosis. We found persistent expression of HSPs in odontoblasts throughout the pulp healing process. It is well-known that HSPs function as molecular chaperones in a variety of cells (Bukau and Horwich, 1998). Sustained expression suggests that HSPs have roles in the survival of odontoblasts for reactionary dentinogenesis.
From 4 to 14 days after injury, apoptotic cells were eliminated, and reparative dentin formation was strongly activated. In these phases, JNK and c-Jun were activated and maintained only in the nuclei of some subodontoblastic pulp cells that had migrated to the front of reparative dentin formation. The JNK pathway is also known to regulate the cell differentiation process (Ip and Davis, 1998). The activation of JNK and c-Jun in specific pulp cells close to odontoblasts suggests that these cells with active JNK and c-Jun are odontoblastic progenitor cells, and that the JNK pathway is associated with the recruitment of odontoblast-like cells from pulp cells for reparative dentinogenesis.
Taken together, the results indicate that the JNK pathway contributes to both apoptosis and the differentiation of pulp cells throughout wound healing after cavity preparation. Recently, cross-talk has been suggested to occur between the JNK cascade and the Smad cascade responding through the TGF-ß family of receptors (Mazars et al., 2001; Péron et al., 2001). To clear the crossroad of survival and apoptosis of pulp cells during the wound-healing process, we are now continuing to research the cooperation of JNK pathway members with other molecules, including Smads.
| ACKNOWLEDGMENTS |
|---|
Received April 23, 2002; Last revision September 23, 2002; Accepted November 6, 2002
| REFERENCES |
|---|
|
|
|---|
Bronckers AL, Lyaruu DM, Goei W, Litz M, Luo G, Karsenty G, et al.(1996). Nuclear DNA fragmentation during postnatal tooth development of mouse and hamster and during dentin repair in the rat. Eur J Oral Sci 104:102111.[ISI][Medline]
Bukau B, Horwich AL (1998). The Hsp70 and Hsp60 chaperone machines. Cell 92:351366.[ISI][Medline]
Gabai VL, Meriin(AQ) AB, Mosser DD, Caron AW, Rits S, Shifrin VI, et al. (1997). Hsp70 prevents activation of stress kinases. A novel pathway of cellular thermotolerance. J Biol Chem 272:1803318037.
Gabai VL, Meriin AB, Yaglom JA, Wei JY, Mosser DD, Sherman MY (2000). Suppression of stress kinase JNK is involved in HSP72-mediated protection of myogenic cells from transient energy deprivation. HSP72 alleviates the stress-induced inhibition of JNK dephosphorylation. J Biol Chem 275:3808838094.
Garrido C, Bruey JM, Fromentin A, Hammann A, Arrigo AP, Solary E (1999). HSP27 inhibits cytochrome c-dependent activation of procaspase-9. FASEB J 13:20612070.
Garrido C, Gurbuxani S, Ravagnan L, Kroemer G (2001). Heat shock proteins: endogenous modulators of apoptotic cell death. Biochem Biophys Res Commun 286:433442.[ISI][Medline]
Ip YT, Davis RJ (1998). Signal transduction by the c-Jun N-terminal kinase (JNK)from inflammation to development. Curr Opin Cell Biol 10:205219.[ISI][Medline]
Kitamura C, Kimura K, Nakayama T, Terashita M (1999). Temporal and spatial expression of c-jun and jun-B proto-oncogenes in pulp cells involved with reparative dentinogenesis after cavity preparation of rat molars. J Dent Res 78:673680.
Kitamura C, Kimura K, Nakayama T, Toyoshima K, Terashita M (2001). Primary and secondary induction of apoptosis in odontoblasts after cavity preparation of rat molars. J Dent Res 80:15301534.
Lepock JR, Frey HE, Heynen ML, Senisterra GA, Warters RL (2001). The nuclear matrix is a thermolabile cellular structure. Cell Stress Chaperones 6:136147.[ISI][Medline]
Mazars A, Lallemand F, Prunier C, Marais J, Ferrand N, Pessah M, et al. (2001). Evidence for a role of the JNK cascade in Smad7-mediated apoptosis. J Biol Chem 276:3679736803.
Mitsiadis TA, Fried K, Goridis C (1999). Reactivation of Delta-Notch signaling after injury: complementary expression patterns of ligand and receptor in dental pulp. Exp Cell Res 246:312318.[ISI][Medline]
Péron P, Rahmani M, Zagar Y, Durand-Schneider AM, Lardeux B, Bernuau D (2001). Potentiation of Smad transactivation by Jun proteins during a combined treatment with epidermal growth factor and transforming growth factor-beta in rat hepatocytes. Role of phosphatidylinositol 3-kinase-induced AP-1 activation. J Biol Chem 276:1052410531.
Smith AJ, Cassidy N, Perry H, Bègue-Kirn C, Ruch JV, Lesot H (1995). Reactionary dentinogenesis. Int J Dev Biol 39:273280.[ISI][Medline]
Tournier C, Hess P, Yang DD, Xu J, Turner TK, Nimnual A, et al. (2000). Requirement of JNK for stress-induced activation of the cytochrome c-mediated death pathway. Science 288:870874.
Vermelin L, Lecolle S, Septier D, Lasfargues JJ, Goldberg M (1996). Apoptosis in human and rat dental pulp. Eur J Oral Sci 104:547553.[ISI][Medline]
This article has been cited by other articles:
![]() |
Y. Ueno, C. Kitamura, M. Terashita, and T. Nishihara Re-oxygenation Improves Hypoxia-induced Pulp Cell Arrest J. Dent. Res., September 1, 2006; 85(9): 824 - 828. [Abstract] [Full Text] [PDF] |
||||
![]() |
T. Amano, T. Muramatsu, K. Amemiya, K. Kubo, and M. Shimono Responses of Rat Pulp Cells to Heat Stress in vitro. J. Dent. Res., May 1, 2006; 85(5): 432 - 435. [Abstract] [Full Text] [PDF] |
||||
![]() |
G. Spagnuolo, K. Galler, G. Schmalz, C. Cosentino, S. Rengo, and H. Schweikl Inhibition of Phosphatidylinositol 3-Kinase Amplifies TEGDMA-induced Apoptosis in Primary Human Pulp Cells J. Dent. Res., September 1, 2004; 83(9): 703 - 707. [Abstract] [Full Text] [PDF] |
||||
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| IADR Journals | Advances in Dental Research ® |
| Journal of Dental Research ® | Critical Reviews (1990-2004) |