Is Caspase-11-induction Dependent on IFN-gamma in Animal-models of Sjögren's syndrome?

Objectives: In previous studies, Sjögren's syndrome (SjS)-prone-NOD mice lacking a functional IFN-gamma gene exhibited a complete lack of disease-phenotype, except for lymphocyte infiltration in the lacrimal glands (LGs). Furthermore, SjS-prone-C57BL/6.NOD-Aec1Aec2 (DC) mice at 8-weeks of age, prior to disease onset, have up-regulated levels of caspase-11, caspase-3 and Stat-1 mRNA in their submandibular glands (SMX). We hypothesized, therefore, that IFN-gamma is responsible for caspase-11 induction, potentially leading to the increased acinar cell apoptosis and manifestation of SjS-like disease phenotype.

Methods: Gene expression and transcriptional activity levels of caspase-11 and its transcriptional factors STAT1 and NF-kB were determined for the SMX and LGs by RT-PCR and an electrophoretic gel mobility shift assay (EMSA), respectively, in the disease-free C57BL/6 and NOD.IFNγ^-/- mice at 8-weeks of age in comparison with gender- and age-matched SjS-prone DC and NOD mice.

Results: In SMX glands of DC mice, gene expression of Nfkb1 (p50) revealed a 3.26-fold increase, while Nfkb2 (p52) was slightly down-regulated. In contrast, SMX glands of NOD.IFNγ^-/- mice showed a reversed gene expression pattern for NF-KB. Interestingly, NF-kB binding activity detected by EMSA in the SMX was only slightly increased (8%), while STAT1 activity was up-regulated significantly (21%, p<0.05) in DC SMX glands. Surprisingly, nuclear extract isolated from the LG was completely devoid of binding activity of these transcription factors in all strains at 8-weeks despite high expression of casp11 at mRNA level in the LG of DC and NOD.IFNγ^-/- mice.

Conclusions: Up-regulated expression of caspase-11 in the LG of NOD.IFNγ^-/- mice suggests that IFN-gamma is not required for the induction of caspase-11 expression. Potentially, other interferons, such as IFN-alpha or -beta, induce caspase-11 through toll-like-receptors (TLR) for the initiation of SjS-like autoimmune exocrinopathy prior to disease onset.

Supported by NIH grants DE013769, DE014244 & DE015152