Calcium pyrophosphate dihydrate crystal-induced inhibition of neutrophil apoptosis: involvement of Bcl-2 family members.
BACKGROUND
The inflammation associated with calcium pyrophosphate dihydrate (CPPD) crystal-induced arthritis arises from the activation of neutrophils with crystals in the synovial joint. Furthermore, constitutive neutrophil apoptosis is inhibited by this interaction with CPPD so that the lifetime of the cells and the duration of the inflammatory response are extended. The objective of this study was to investigate the role of bcl-2 protein family members in the CPPD-induced prosurvival response.


METHODS
Apoptosis was measured using DNA fragmentation and Caspase 3 assays. The expression and activation levels of the bcl-2 protein family members A1, Mcl-1, Bcl-xl, Bim, Bad and Bax-alpha were measured using western blot analysis.


RESULTS
The prosurvival proteins Mcl-1 and Bcl-xl were both found to be strongly expressed but unaffected by CPPD-induced neutrophil activation over 3 h. The expression of proapoptotic proteins Bim and Bax-alpha was found to decrease over the time course of a 3 h incubation of neutrophils with CPPD crystals (but not the bacterial chemoattractant fMLP). Furthermore, expression of the unphosphorylated (active, proapoptotic) form of Bim was dominant in control cells at 0.5 h, whereas the status of this protein switched to the phosphorylated form following cell activation by both CPPD and fMLP. For CPPD (but not fMLP) this phosphorylation effect reversed over a 3 h incubation.


CONCLUSIONS
Upon stimulation by CPPD crystals, the expression of both Bim and Bax-alpha decreased after 3 h suggesting a reduced proapoptotic effect of these proteins so that the static expression of the prosurvival proteins Bcl-xl and Mcl-1 might allow for a temporary shift in the balance to a prosurvival state of the cells. Because a sudden (but transient) increase in the phosphorylated form of Bim was observed in CPPD-stimulated neutrophils it is possible that this species might act as a signaling intermediate, resulting in the observed downregulation of Bax-alpha.
Higo
Tobi
T
University of British Columbia, Vancouver, Canada.
Duronio
Vince
V
Tudan
Christopher
C
Burt
Helen M
HM
Jackson
John K
JK
D000328:Adult; D017209:Apoptosis / Q000187:drug effects*; D051017:Apoptosis Regulatory Proteins / Q000378:metabolism; D000072224:Bcl-2-Like Protein 11; D002131:Calcium Pyrophosphate / Q000494:pharmacology*; D003460:Crystallization; D015536:Down-Regulation; D006801:Humans; D008297:Male; D008565:Membrane Proteins / Q000378:metabolism; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D009504:Neutrophils / Q000187:drug effects* / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism*; D015398:Signal Transduction; D051028:bcl-2-Associated X Protein / Q000378:metabolism; D051020:bcl-X Protein / Q000378:metabolism
D051017:Apoptosis Regulatory Proteins; C000606775:BCL2L11 protein, human; D000072224:Bcl-2-Like Protein 11; D008565:Membrane Proteins; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D051028:bcl-2-Associated X Protein; D051020:bcl-X Protein; D002131:Calcium Pyrophosphate