Background/Purpose: PRKR (interferon-inducible RNA-dependent protein kinase) is an intracytoplasmic molecule that induces the production of interferon(IFN)-induced genes upon binding of double-stranded RNA viruses. PRKR is spontaneously over-expressed in PBMC from systemic lupus erythematosus (SLE) patients, and we previously demonstrated that in vitro exposure of SLE cells to 2-aminopurine (a pharmacological inhibitor of PRKR) results in a significant inhibition of IFN-induced genes and immunoglobulin production. In the present study, we wanted to further investigate the role of PRKR in the pathogenesis of SLE.

Methods: Intraperitoneal 2-aminopurine versus PBS injections were administered to (NZB x NZW)_F1 mice three times a week for a period of 2 months. In addition, PRKR-KO mice were backcrossed in B6.Sle1.Sle2.Sle3 tricongenic SLE-prone mice, resulting in the generation of PRKR-KO versus WT tricongenic animals. Exploratory studies on the role of PRKR in dendritic cell differentiation were performed using bone marrow cells from the original PRKR-KO mice versus Balb/c controls. The roles of 2-aminopurine and 6-mercaptopurine on IFN-induced gene expression were evaluated in TLR3-transfected HEK293 cells.

Results: While dsDNA antibody (Ab) titers and proteinuria significantly increase over time in PBS-treated (NZB x NZW)_F1 mice, this is not the case in 2-aminopurine treated animals. 2-aminopurine therapy also results in a significant improvement of glomerulonephritis activity scores upon histological examination of the kidneys. Our first observations in PRKR-KO versus –WT SLE-prone mice indicate that dsDNA Ab titers display a significant increase from month 2 to month 10 in PRKR-WT B6.Sle1.Sle2.Sle3 mice, and this is not observed in their PRKR-KO littermates.

IL-4 and GM-CSF exposure of bone-marrow cells results in the generation of myeloid-derived dendritic cells (moDC). We observed that the percentage of bone-marrow-derived CD11c-positive cells was significantly decreased in PRKR-KO mice, compared to Balb/c age- and gender-matched animals. Similarly, CD86-positive CD11c cells were significantly less numerous in PRKR-KO compared to Balb/c animals.

Using 2-aminopurine and PRKR siRNA, we demonstrated that PRKR is involved in TLR3 signal transduction in TLR3-transfected HEK293 cells. Thus, poly I:C-induced expression of IFNβ and IFN-induced genes is abrogated in these cells upon PRKR blockade. Intriguingly, we found that exposure of these cells to 6 mercaptopurine resulted in the same inhibitory effects on IFNβ and IFN-induced gene expressio.

Conclusion: Our data indicate that PRKR, an intracytoplasmic danger-recognition molecule that has the ability to stimulate the expression of IFN-induced genes, is involved in the pathogenesis of SLE. The role of PRKR in the pathogenesis of the disease might be mediated by an increased differentiation and maturation of moDC, a hypothesis that we will verify in our PRKR-KO versus –WT SLE prone animals. Preliminary data indicate that the activity of PRKR is modulated by 6-mercaptopurine, the active metabolite of azathioprine.

ACR Meeting Abstracts - https://acrabstracts.org/abstract/role-of-interferon-inducible-rna-dependent-protein-kinase-in-the-pathogenesis-of-systemic-lupus-erythematosus/