Jim C Oates1, Gary S Gilkeson. 1. 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
Abstract
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. CONCLUSION: 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.
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/lprmice have increased spontaneous apoptosis of leukocytes. These conflicting observations have stimulated interest in apoptosis in this SLE model. MRL/lprmice 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/lprmice 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. CONCLUSION: These results suggest that NO plays a role in spleen lymphocyte apoptosis in MRL/lprmice, possibly via inhibition of PKC, despite a Fas defect.
Authors: Chinedu Njoku; Sally E Self; Philip Ruiz; Ann F Hofbauer; Gary S Gilkeson; Jim C Oates Journal: J Investig Med Date: 2008-10 Impact factor: 2.895