TLR9 Deficiency Leads to Accelerated Renal Disease and Myeloid Lineage Abnormalities in Pristane-Induced Murine Lupus

Abstract

Systemic lupus erythematosus (SLE) is a chronic, life threatening autoimmune disorder, leading to multiple organ pathologies and kidney destruction. Analyses of numerous murine models of spontaneous SLE have revealed a critical role for endosomal Toll-like receptors (TLRs) in the production of autoantibodies and development of other clinical disease manifestations. Nevertheless, the corresponding TLR9-deficient autoimmune-prone strains consistently develop more severe disease pathology. Injection of BALB/c mice with 2,6,10,14-tetramethylpentadecane (TMPD), commonly known as pristane, also results in the development of SLE-like disease. We now show that Tlr9−/− BALB/c mice injected intraperitoneally with TMPD develop more severe autoimmunity than their TLR-sufficient cohorts. Early indications include an increased accumulation of TLR7-expressing Ly6Chi inflammatory monocytes at the site of injection, upregulation of interferon regulated gene expression in the peritoneal cavity, and an increased production of myeloid lineage precursors (CMP and GMP) in the bone marrow. TMPD-injected Tlr9−/− BALB/c mice develop higher autoantibody titers against RNA, neutrophil cytoplasmic antigens (ANCA), and myeloperoxidase (MPO) than TMPD-injected WT BALB/c mice. The TMP-injected Tlr9−/− mice, and not the WT mice, also develop a marked increase in glomerular IgG deposition and infiltrating granulocytes, much more severe glomerulonephritis, and a reduced lifespan. Together the data point to a major role for TLR7 in the response to self-antigens in this model of experimental autoimmunity. Therefore the BALB/c pristane model recapitulates other TLR7-driven spontaneous models of SLE and is negatively regulated by TLR9.

Toll‐Like Receptor 9 Deficiency Breaks Tolerance to RNA‐Associated Antigens and Up‐Regulates Toll‐Like Receptor 7 Protein in Sle1 Mice

“…We showed that Sle1TLR-9 À/À mouse serum predominantly produces a cytoplasmic HEp-2 staining pattern, similar to the anti-RNA antibody BWR4 (37). The increase in the cytoplasmic HEp-2 staining pattern and/or increased anti-RNA antibody levels are common to the few TLR-9-deficient model systems that have been examined (8,9,14). Increased levels of RNA-associated autoantibodies, such as anti-Sm, U1 snRNP-1, PM/Scl-100, and/or anti-ribosomal P, were also observed in TLR-9 À/À models that develop severe kidney disease (8)(9)(10).…”

“…Over the last decade, multiple studies have supported the notion of a fundamental role of TLR-7 in SLE disease development; however, little progress has been made to elucidate the regulatory role of TLR-9 (7)(8)(9)(10)(12)(13)(14)27,(31)(32)(33)(34)41). Moreover, the lack of data from human studies has reduced enthusiasm for understanding the cellular and molecular roles in TLR-9deficient mice.…”

“…Due to the similarities between TLR‐7 and TLR‐9 expression and shared signaling pathways, it has been predicted that the deletion of either of these receptors would be beneficial in terms of disease progression. Unexpectedly, TLR‐9 deletion caused disease exacerbation in multiple models of spontaneous and induced lupus, while TLR‐7 proved to be essential for disease development . These data suggest that the system is more complex than originally thought; however, the means by which TLR‐9 prevents progression to severe disease are largely unknown.…”

Guanabenz inhibits TLR9 signaling through a pathway that is independent of eIF2α dephosphorylation by the GADD34/PP1c complex

“…In this pathological model, glomerulonephritis and autoantibody production strictly depend on signaling through the IFN-a/b receptor (IFNAR) and the formation of "lipogranulomas," which represent a chronic inflammatory response to TMPD and are the sites of autoantibody production (25,35). Monocytes are recruited to the inflamed peritoneal cavity where they are activated by endogenous TLR7 and, potentially, TLR9 ligands and are the major sources of type I IFN in this model, which, after a period of 3 to 4 months, results in different autoimmune manifestations specific to the mouse genetic background (25,36,37). The TMPD-inducible SLE model appears, therefore, to be particularly suitable for testing GBZ inhibitory activity on endosomal TLRs in vivo, because it is inducible and type I IFN-dependent and mimics some human SLE features (38).…”

An update on lupus animal models

“…Pristane-induced lupus is driven by a strong type 1 IFN response (35), and this model is therefore well-suited to investigate the type 1 IFN signature present in many SLE patients, but much weaker in spontaneous mouse models of this disease. This model is also useful to test the impact of a specific gene on lupus development directly in a non-autoimmune strain, such the protective effect of TLR9 evaluated in BALB/c.Tlr9 −/− mice treated with pristane (36) * .…”