Investigation of the relationship between the onset of arthritis and uveitis in genetically predisposed SKG mice.

INTRODUCTION: Systemic rheumatic conditions are often accompanied by intraocular inflammatory disease (termed uveitis). Despite the frequent manifestation of uveitis with arthritis, very little is understood of the underlying mechanisms that mediate the eye's susceptibility to disease. The genetically susceptible SKG mouse strain develops arthritis that arises from an inherent mutation that disrupts T-cell antigen receptor signal transduction and thymic selection. The ensuing T-cell-mediated disease is further modulated through exposure to microbial triggers. The purpose of this study was to elucidate how a genetically determined shift in the T-cell repertoire toward self-reactive T cells that drive arthritis influences uveitis in SKG mice. METHODS: SKG mice (BALB/c mice that harbor the W163C point mutation in zeta-chain-associated protein kinase 70 [i.e., ZAP-70]) were housed under arthritis-resistant, specific pathogen-free conditions. Arthritis was induced by intraperitoneal injection with fungal glucans (zymosan or curdlan). Arthritis onset and severity were evaluated by clinical scoring, histopathology and infrared imaging within the joints. Periocular traits involving blepharoconjunctivitis were evaluated by clinical scoring and histology. Eyes were evaluated for signs of anterior uveitis using intravital videomicroscopy to document cell-trafficking responses within the iris vasculature and stroma and by histology to detect inflammatory infiltrate and tissue damage within the anterior and posterior eye segments. RESULTS: Exposure to zymosan resulted in the predicted arthritic, sexually dimorphic phenotype in SKG mice. The eyes of SKG mice exhibited episodic intravascular cellular responses to zymosan or curdlan as indicated by significant increases in leukocyte-endothelium interactions akin to ocular vasculitis. However, despite the significant increase in early cell-trafficking responses, cellular infiltration into the iris stroma was not observed and histopathological signs indicative of a sustained uveitis were absent. Instead, eyes of SKG mice developed blepharoconjunctivitis that coincided with arthritis and exhibited sexual dimorphism. CONCLUSIONS: This study underscores the complexity surrounding the pathogenesis of uveitis and its relationship with arthritis. The findings suggest that distinct mechanisms exist by which pathogenic autoimmune T cells target the eyes versus joints, which likely involves the environmental context but nonetheless should be taken into account in the identification and development of effective therapies for each organ.

Aberrant interleukin-1 signalling does not increase susceptibility of mice to NOD2-dependent uveitis.

BACKGROUND: NOD2 is the genetic cause of Blau syndrome, an autoinflammatory disease that manifests as coincident uveitis and arthritis. Since dysregulation of IL-1 signalling is considered a pathogenic mechanism in a number of related autoinflammatory conditions, we examined the extent to which unimpeded interleukin (IL)-1 signalling influences NOD2-dependent inflammation of the eye versus the joint. METHODS: Mice deficient for IL-1R antagonist (IL-1Ra) were administered the NOD2 agonist muramyl dipeptide (MDP) by systemic (intraperitoneal) or local (intraocular and/or intra-articular) injections. NOD2-deficient mice received an intraocular injection of recombinant IL-1ß. Uveitis was evaluated by intravital videomicroscopy and histopathology, and arthritis was assessed by near-infrared imaging and histopathology. Ocular levels of IL-1α, IL-1ß and IL-1Ra were quantified by enzyme-linked immunosorbent assay. RESULTS: IL-1Ra deficiency did not render mice more responsive to systemic exposure of MDP. Despite the increased production of IL-1R agonists IL-1α and IL-1ß in response to intraocular injection of MDP, deficiency in IL-1Ra did not predispose mice to MDP-triggered uveitis, albeit intravascular cell rolling and adherence were exacerbated. NOD2 expression was dispensable for the potential of IL-1 to elicit uveitis. However, we find that IL-1Ra does play an important protective role in arthritis induced locally by MDP injection in the joint. CONCLUSIONS: Our findings highlight the complexity of NOD2 activation and IL-1 signalling effects that can be compounded by local environmental factors of the target organ. These observations may impact how we understand the molecular mechanisms by which NOD2 influences inflammation of the eye versus joint, and consequently, treatment options for uveitis versus arthritis.

Investigation of the peptidoglycan sensing molecule, PGLYRP-2, in murine inflammatory uveitis.

BACKGROUND/AIM: Peptidoglycan (PGN) recognition proteins (PGLYRPs) are innate immune molecules that recognise bacterial cell wall PGN, and participate in several inflammatory diseases such as arthritis. We sought to elucidate the contribution of PGLYRPs in murine uveitis (intraocular inflammatory disease) elicited by PGN, and the extent to which systemically administered PGN alters uveitis compared with arthritis versus locally triggered ocular responses. METHODS: Mice deficient for PGLYRP-2, PGLYRP-3 or PGLYRP-4 were administered PGN by an intraperitoneal or intraocular injection. Arthritis was assessed by near-infrared imaging and histopathology, while uveitis was measured by intravital videomicroscopy and histopathology. RESULTS: Systemic PGN exposure predisposed to arthritis through a PGLYRP-2 dependent mechanism. By contrast, systemic PGN exposure did not predispose to uveitis, and PGLYRP-2 deficiency had no impact on the development the uveitis. When PGN was administered locally, a robust uveitis ensued, which occurred independently of PGLYRP-2. Regardless of whether PGN was administered systemically or locally, neither PGLYRP-3 nor PGLYRP-4 deficiency significantly altered ocular inflammation compared with wild-type control animals. CONCLUSIONS: Our findings highlight the complexity of PGLYRPs and how PGLYRP-2 may use different molecular pathways in the joints versus eyes. Collectively, our results support a non-essential or redundant role for PGLYRPs-2, -3, -4 in uveitis.

Impact of IL-1 signalling on experimental uveitis and arthritis.

BACKGROUND: Uveitis, or inflammatory eye disease, is a common extra-articular manifestation of many systemic autoinflammatory diseases involving the joints. Anakinra (recombinant interleukin (IL)-1 receptor antagonist (Ra)) is an effective therapy in several arthritic diseases; yet, few studies have investigated the extent to which IL-1 signalling or IL-1Ra influences the onset and/or severity of uveitis. OBJECTIVE: To seek possible links between arthritis and uveitis pathogenesis related to IL-1 signalling. METHODS: The eyes of IL-1Ra-deficient BALB/c mice were monitored histologically and by intravital videomicroscopy to determine if uveitis developed along with the expected spontaneous arthritis in ankles and knees. Expression levels of IL-1R and its negative regulators (IL-1Ra, IL-1RII, IL-1RAcP and single Ig IL-1R-related molecule) in eye and joint tissues were compared. Differences in uveitis induced by intraocular injection of lipopolysaccharide (LPS) in mice lacking IL-1R or IL-1Ra were assessed. RESULTS: Deficiency in IL-1Ra predisposes to spontaneous arthritis, which is exacerbated by previous systemic LPS exposure. The eye, however, does not develop inflammatory disease despite the progressive arthritis or LPS exposure. Organ-specific expression patterns for IL-1Ra and negative regulators of IL-1 activity were observed that appear to predict predisposition to inflammation in each location in IL-1Ra knockout mice. The eye is extremely sensitive to locally administered LPS, and IL-1Ra deficiency markedly exacerbates the resulting uveitis. CONCLUSION: This study demonstrates that IL-1Ra plays an important role in suppressing local responses in eyes injected with LPS and that there is discordance between murine eyes and joints in the extent to which IL-1Ra protects against spontaneous inflammation.

The NLRP3 inflammasome is active but not essential in endotoxin-induced uveitis.

OBJECTIVE: The inflammasome complex involving caspase-1 and nucleotide-binding domain, leucine-rich repeat containing protein (NLRP)3, also known as NALP3 or cryopyrin is important for host responses to microbial pathogens and several autoinflammatory diseases. We investigated the extent to which NLRP3 and caspase-1 control ocular interleukin (IL)-1ß production and severity of uveitis (intraocular inflammatory disease) in an established, acute inflammatory uveitis model, endotoxin-induced uveitis (EIU). METHODS: Expression of NLRP3, its adaptor molecule ASC, also known as PYCARD (PYD and CARD domain containing), and caspase-1 were examined by immunoblotting. IL-1ß production was measured by enzyme-linked immunosorbent assay (ELISA). Using knockout mice, roles for caspase-1 and NLRP3 were examined in uveitis induced by intraocular injection of Escherichia coli lipopolysaccharide (LPS). RESULTS: NLRP3, ASC, and caspase-1 proteins are constitutively expressed in eye tissue. During EIU, IL-1ß protein production increases; this requires the presence of both caspase-1 and NLRP3. However, severity of EIU is not altered by deficiency in either caspase-1 or NLRP3, as assessed by both intravital microscopy and histology. CONCLUSIONS: These data identify the importance of the NLRP3 inflammasome for IL-1ß production in the eye, yet indicate that its participation in EIU is nonessential.

Dectin-1 and NOD2 mediate cathepsin activation in zymosan-induced arthritis in mice.

OBJECTIVE: Activation of pattern recognition receptors (PRR) may contribute to arthritis. Here, we elucidated the role of NOD2, a genetic cause of inflammatory arthritis, and several other PRR in a murine model of inflammatory arthritis. METHODS: The roles of CR3, TLR2, MyD88, NOD1, NOD2, Dectin-1 and Dectin-2 were tested in vivo in arthritis elicited by intra-articular injections of zymosan, the fungal cell wall components curdlan, laminarin and mannan, and the bacterial cell wall peptidoglycan. RESULTS: Dectin-1, and to a lesser extent Dectin-2, contributed to arthritis. TLR2, MyD88 and CR3 played non-essential roles. Observations based on injection of curdlan, laminarin or mannan supported the dominant role of the Dectin-1 pathway in the joint. We demonstrated differential roles for NOD1 and NOD2 and identified NOD2 as a novel and essential mediator of zymosan-induced arthritis. CONCLUSIONS: Together, Dectin-1 and NOD2 are critical, sentinel receptors in the arthritogenic effects of zymosan. Our data identify a novel role for NOD2 during inflammatory responses within joints.