Nitric oxide induces apoptosis in spleen lymphocytes from MRL/lpr mice.
BACKGROUND
MRL/MpJ-Tnfrsf6lpr(MRL/lpr) mice, a murine model of systemic lupus erythematosus (SLE), have defective expression of Fas, substantially reducing signaling for apoptosis via this mechanism. However, it is known that MRL/lpr mice have increased spontaneous apoptosis of leukocytes. These conflicting observations have stimulated interest in apoptosis in this SLE model. MRL/lpr mice overproduce nitric oxide (NO) as autoimmune disease progresses. In vitro administration of NO may induce or decrease apoptosis depending on the cell type. Therefore, we hypothesized that NO induces MRL/lpr spleen lymphocyte apoptosis independent of Fas receptor engagement.


METHODS
Percentages of apoptotic spleen lymphocytes from MRL/lpr and BALB/cJ mice were determined ex vivo after in vivo treatment with NG-monomethyl-L-arginine (NMMA), a nitric oxide synthase (NOS) inhibitor. After culture in varying concentrations of a slow-acting NO donor, the following were determined in spleen lymphocytes: (1) levels of apoptosis, (2) the effect of phorbol myristate acid (PMA) on levels of NO-induced apoptosis, and (3) protein kinase C (PKC) activity.


RESULTS
Spleen lymphocytes from MRL/lpr mice with active disease had increased levels of ex vivo apoptosis when compared with BALB/cJ controls. This increase was reduced by pharmacologic inhibition of NOS in MRL/lpr but not in BALB/cJ mice. Exogenous administration of NO in vitro reduced PKC activity and induced apoptosis in MRL/lpr spleen lymphocytes, an effect that could be reduced via coadministration of PMA in vitro.


CONCLUSIONS
These results suggest that NO plays a role in spleen lymphocyte apoptosis in MRL/lpr mice, possibly via inhibition of PKC, despite a Fas defect.
Medical University of South Carolina, Department of Medicine, Division of Rheumatology, 96 Jonathan Lucas Street, Suite 912, PO Box 250637, Charleston, SC 29425, USA. oatesjc@musc.edu
Jim C
JC
Oates
Gary S
GS
Gilkeson
D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D004195:Disease Models, Animal; D004791:Enzyme Inhibitors / Q000494:pharmacology / Q000627:therapeutic use; D005260:Female; D008180:Lupus Erythematosus, Systemic / Q000188:drug therapy / Q000378:metabolism* / Q000473:pathology; D008214:Lymphocytes / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D051379:Mice; D008807:Mice, Inbred BALB C; D019463:Mice, Inbred MRL lpr; D009569:Nitric Oxide / Q000037:antagonists & inhibitors / Q000378:metabolism*; D013154:Spleen / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D019323:omega-N-Methylarginine / Q000494:pharmacology / Q000627:therapeutic use
D004791:Enzyme Inhibitors; D019323:omega-N-Methylarginine; D009569:Nitric Oxide