Session Title: Systemic Lupus Erythematosus - Animal Models
Session Type: Abstract Submissions (ACR)
Background/Purpose: Systemic lupus erythematosus (SLE) is a multi-organ, destructive autoimmune disease characterized by pathogenic autoantibodies. Though it is accepted that dendritic cells (DCs) play an important role in disease initiation, only recently have studies implicated DCs as a major factor in SLE persistence. DCs from SLE patients exhibit elevated expression of activation markers including co-stimulatory molecules and pro-inflammatory cytokines; however, the factors that are responsible for their aberrant activation is unknown. We recently identified that caspase 8, a cysteine-aspartic acid enzyme known to function in death receptor signaling, is a novel DC-specific inhibitor of inflammatory processes. While previous studies have shown that caspase 8 functions to initiate apoptosis and/or suppress necroptosis (through inhibition of RIPK1/3 signaling) in a multitude of cells, our data suggest that caspase 8 is not essential for the survival of DCs (apoptosis/necrosis), but rather inhibits the continuous activation of DCs, thereby preventing development of systemic autoimmunity.
Methods: Mice with caspase 8 flanked by loxP sites (Casp8flox/flox. WT) were crossed with mice expressing Cre under control of the CD11c gene promoter (CreCD11c), which is expressed by dendritic cells. Flow cytometric analysis was employed to characterize DC populations in both mixed bone marrow chimeras and BrdU pulse assays. Bone marrow-derived DCs were cultured with TLR agonists +/- necrostatin-1 to block RIPK1 activity. Luminex-based assays and ELISAs were used to detect cytokine and transcription factor DNA binding levels.
Results: CreCD11cCasp8flox/flox develop splenomegaly, lymphadenopathy, autoantibodies, glomerulonephritis, immune complex deposition in the kidney, exacerbated proteinuria levels, heightened amounts of serum pro-inflammatory cytokines (IL-12, IL-1β, and IFNα/β), and early mortality. Loss of caspase 8 in DCs does not affect their survival, as CreCD11cCasp8flox/flox mice present with increased DC populations, there are equal numbers of CreCD11cCasp8flox/flox and WT DCs in mixed bone marrow chimeras, there is no change in DC turnover rates using BrdU pulse assays, and bone marrow-derived DCs display similar levels of necrotic death independent of caspase 8 or RIPK1. Loss of caspase 8 in DCs does not affect their survival, but they are highly activated, leading to elevated levels of activated lymphocytes in a paracrine manner. The increased activation potential of CreCD11cCasp8flox/flox DCs may be controlled by toll-like receptors 7 and 9 (TLR7/9) since caspase 8-deficient DCs display a hyper-responsiveness to TLR7/9 ligation with increased DNA binding activity of interferon regulatory factor (IRF) and STAT1. Additionally, blocking RIPK1 signaling dampens the TLR7/9-induced secretion of pro-inflammatory cytokines in caspase 8-deficient DCs.
Conclusion: These results demonstrate that loss of caspase 8 in DCs initiates inflammatory phenotypes by a DC survival-independent novel mechanism. These data have implications for autoimmunity by elucidating previously unknown functions of a potentially useful target for therapy.
C. M. Cuda,
A. V. Misharin,
G. K. Haines III,
H. R. Perlman,
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ACR Meeting Abstracts - https://acrabstracts.org/abstract/loss-of-caspase-8-in-dendritic-cells-induces-a-systemic-lupus-erythematosus-like-disease-that-is-independent-of-the-necroptosome/