Antioxidant Carbon Nanoparticles Inhibit Fibroblast-Like Synoviocyte Invasiveness and Reduce Disease Severity in a Rat Model of Rheumatoid Arthritis

Reactive oxygen species have been involved in the pathogenesis of rheumatoid arthritis (RA). Our goal was to determine the effects of selectively scavenging superoxide (O2•-) and hydroxyl radicals with antioxidant nanoparticles, called poly(ethylene glycol)-functionalized hydrophilic carbon clusters (PEG-HCCs), on the pathogenic functions of fibroblast-like synoviocytes (FLS) from patients with rheumatoid arthritis (RA) and on the progression of an animal model of RA. We used human FLS from patients with RA to determine PEG-HCC internalization and effects on FLS cytotoxicity, invasiveness, proliferation, and production of proteases. We used the pristane-induced arthritis (PIA) rat model of RA to assess the benefits of PEG-HCCs on reducing disease severity. PEG-HCCs were internalized by RA-FLS, reduced their intracellular O2•-, and reduced multiple measures of their pathogenicity in vitro, including proliferation and invasion. In PIA, PEG-HCCs caused a 65% reduction in disease severity, as measured by a standardized scoring system of paw inflammation and caused a significant reduction in bone and tissue damage, and circulating rheumatoid factor. PEG-HCCs did not induce lymphopenia during PIA. Our study demonstrated a role for O2•- and hydroxyl radicals in the pathogenesis of a rat model of RA and showed efficacy of PEG-HCCs in treating a rat model of RA.

KCa1.1 and Kv1.3 channels regulate the interactions between fibroblast-like synoviocytes and T lymphocytes during rheumatoid arthritis

BACKGROUND

Fibroblast-like synoviocytes (FLS) and CCR7- effector memory T (TEM) cells are two of the major cell types implicated in the progression of rheumatoid arthritis (RA). In particular, FLS become highly invasive, whereas TEM cells proliferate and secrete proinflammatory cytokines, during RA. FLS and T cells may also interact and influence each other's phenotypes. Inhibition of the pathogenic phenotypes of both FLS and TEM cells can be accomplished by selectively blocking the predominant potassium channels that they upregulate during RA: KCa1.1 (BK, Slo1, MaxiK, KCNMA1) upregulated by FLS and Kv1.3 (KCNA3) upregulated by activated TEM cells. In this study, we investigated the roles of KCa1.1 and Kv1.3 in regulating the interactions between FLS and TEM cells and determined if combination therapies of KCa1.1- and Kv1.3-selective blockers are more efficacious than monotherapies in ameliorating disease in rat models of RA.

METHODS

We used in vitro functional assays to assess the effects of selective KCa1.1 and Kv1.3 channel inhibitors on the interactions of FLS isolated from rats with collagen-induced arthritis (CIA) with syngeneic TEM cells. We also used flow cytometric analyses to determine the effects of KCa1.1 blockers on the expression of proteins used for antigen presentation on CIA-FLS. Finally, we used the CIA and pristane-induced arthritis models to determine the efficacy of combinatorial therapies of KCa1.1 and Kv1.3 blockers in reducing disease severity compared with monotherapies.

RESULTS

We show that the interactions of FLS from rats with CIA and of rat TEM cells are regulated by KCa1.1 and Kv1.3. Inhibiting KCa1.1 on FLS reduces the ability of FLS to stimulate TEM cell proliferation and migration, and inhibiting Kv1.3 on TEM cells reduces TEM cells' ability to enhance FLS expression of KCa1.1 and major histocompatibility complex class II protein, as well as stimulates their invasion. Furthermore, we show that combination therapies of selective KCa1.1 and Kv1.3 blockers are more efficacious than monotherapies at reducing signs of disease in two rat models of RA.

CONCLUSIONS

Our results demonstrate the importance of KCa1.1 and Kv1.3 in regulating FLS and TEM cells during RA, as well as the value of combined therapies targeting both of these cell types to treat RA.

Targeting KCa1.1 Channels with a Scorpion Venom Peptide for the Therapy of Rat Models of Rheumatoid Arthritis

Fibroblast-like synoviocytes (FLSs) are a key cell type involved in rheumatoid arthritis (RA) progression. We previously identified the KCa1.1 potassium channel (Maxi-K, BK, Slo 1, KCNMA1) as a regulator of FLSs and found that KCa1.1 inhibition reduces disease severity in RA animal models. However, systemic KCa1.1 block causes multiple side effects. In this study, we aimed to determine whether the KCa1.1 β1-3-specific venom peptide blocker iberiotoxin (IbTX) reduces disease severity in animal models of RA without inducing major side effects. We used immunohistochemistry to identify IbTX-sensitive KCa1.1 subunits in joints of rats with a model of RA. Patch-clamp and functional assays were used to determine whether IbTX can regulate FLSs through targeting KCa1.1. We then tested the efficacy of IbTX in ameliorating disease in two rat models of RA. Finally, we determined whether IbTX causes side effects including incontinence or tremors in rats, compared with those treated with the small-molecule KCa1.1 blocker paxilline. IbTX-sensitive subunits of KCa1.1 were expressed by FLSs in joints of rats with experimental arthritis. IbTX inhibited KCa1.1 channels expressed by FLSs from patients with RA and by FLSs from rat models of RA and reduced FLS invasiveness. IbTX significantly reduced disease severity in two rat models of RA. Unlike paxilline, IbTX did not induce tremors or incontinence in rats. Overall, IbTX inhibited KCa1.1 channels on FLSs and treated rat models of RA without inducing side effects associated with nonspecific KCa1.1 blockade and could become the basis for the development of a new treatment of RA.

KCa1.1 channels regulate β1-integrin function and cell adhesion in rheumatoid arthritis fibroblast-like synoviocytes

Large-conductance calcium-activated potassium channel (KCa1.1; BK, Slo1, MaxiK, KCNMA1) is the predominant potassium channel expressed at the plasma membrane of rheumatoid arthritis fibroblast-like synoviocytes (RA-FLSs) isolated from the synovium of patients with RA. It is a critical regulator of RA-FLS migration and invasion and therefore represents an attractive target for the therapy of RA. However, the molecular mechanisms by which KCa1.1 regulates RA-FLS invasiveness have remained largely unknown. Here, we demonstrate that KCa1.1 regulates RA-FLS adhesion through controlling the plasma membrane expression and activation of β₁ integrins, but not α₄, α₅, or α₆ integrins. Blocking KCa1.1 disturbs calcium homeostasis, leading to the sustained phosphorylation of Akt and the recruitment of talin to β₁ integrins. Interestingly, the pore-forming α subunit of KCa1.1 coimmunoprecipitates with β₁ integrins, suggesting that this physical association underlies the functional interaction between these molecules. Together, these data outline a new signaling mechanism by which KCa1.1 regulates β₁-integrin function and therefore invasiveness of RA-FLSs.-Tanner, M. R., Pennington, M. W., Laragione, T., Gulko, P. S., Beeton, C. KCa1.1 channels regulate β₁-integrin function and cell adhesion in rheumatoid arthritis fibroblast-like synoviocytes.

Short-term low-magnesium diet reduces autoimmune arthritis severity and synovial tissue gene expression

Magnesium has been suggested to have anti-inflammatory properties in short-term, mostly in vitro studies. To examine the effect of dietary magnesium modifications in arthritis severity and joint damage DA rats were placed on one of three diet regimens before the induction of autoimmune pristane-induced arthritis (PIA): a 4 wk low-magnesium diet, normal diet, and a magnesium-supplemented diet. The diets were switched to a normal diet 14 days after the induction of PIA (typical time of disease onset). Arthritis severity was scored for 38 days, and joints were examined by histology and quantitative PCR for proinflammatory genes. Rats on the low-magnesium diet were significantly and reproducibly protected and had 70% lower median arthritis severity score, with preservation of normal joint histology without erosive changes. Rats on the normal or magnesium-supplemented diets were not protected and developed equally severe and erosive disease. While the dietary modifications were at disease onset ( day 14 postinduction), the protective effect of the short-term low-magnesium diet persisted, suggesting a lasting effect on a critical pathogenic pathway. Rats on the low-magnesium diet had significant reduction in synovial tissue expression of IL-6, RORA, and RORC, which are genes required for the development of Th17 T cells. This study revealed a novel role for dietary magnesium in the regulation of autoimmune arthritis and opens new possibilities for the treatment of autoimmune diseases such as rheumatoid arthritis and psoriatic arthritis with short courses of dietary or drug-induced modulations of magnesium levels.

Disease modifying anti-rheumatic activity of the alkaloid montanine on experimental arthritis and fibroblast-like synoviocytes

Montanine is an alkaloid isolated from Rhodophiala bifida bulb with potential anti-arthritic activity. In this context, we evaluated whether montanine has a disease modifying anti-rheumatic activity in two arthritis models and its effect in vitro on lymphocyte proliferation and on invasiveness of fibroblast-like synoviocytes (FLS). Antigen-induced arthritis (AIA) was performed in Balb/C mice with methylated bovine serum albumin, and nociception and leukocytes migration into the knee joint were evaluated. Collagen-induced arthritis (CIA) was performed in DBA/1J mice, and arthritis development and severity were assessed by clinical and histological scoring and articular nociception. Montanine was administered intraperitoneally twice a day. Lymphocyte proliferation stimulated by concanavalin A in 48h was performed with MTT assay, while FLS invasion in 24h was assayed in a Matrigel-coated transwell system. Administration of montanine decreased nociception (P<0.001) and leukocyte articular migration (P<0.001) in mice with AIA. In mice with CIA, treatment with montanine reduced severity of arthritis and joint damage assessed by clinical (P<0.001) and histological (P<0.05) scores and ameliorated articular nociception (P<0.05). In vitro, montanine inhibited lymphocyte proliferation stimulated with ConA (P<0.001) and decreased FLS invasion (P<0.05) by 54%, with an action independent of cytotoxicity. Our findings suggest that montanine can be further explored as an innovative pharmacological approach for autoimmune diseases such as arthritis.

Different expression of β subunits of the KCa1.1 channel by invasive and non-invasive human fibroblast-like synoviocytes

Background

Fibroblast-like synoviocytes (FLS) in rheumatoid arthritis (RA-FLS) contribute to joint inflammation and damage characteristic of the disease. RA-FLS express KCa1.1 (BK, Slo1, MaxiK, KCNMA1) as their major plasma membrane potassium channel. Blocking KCa1.1 reduces the invasive phenotype of RA-FLS and attenuates disease severity in animal models of RA. This channel has therefore emerged as a promising therapeutic target in RA. However, the pore-forming α subunit of KCa1.1 is widely distributed in the body, and blocking it induces severe side effects, thus limiting its value as a therapeutic target. On the other hand, KCa1.1 channels can also contain different accessory subunits with restricted tissue distribution that regulate channel kinetics and pharmacology. Identification of the regulatory subunits of KCa1.1 expressed by RA-FLS may therefore provide the opportunity for generating a selective target for RA treatment.

Methods

Highly invasive RA-FLS were isolated from patients with RA, and FLS from patients with osteoarthritis (OA) were used as minimally invasive controls. The β subunit expression by FLS was assessed by quantitative reverse transcription polymerase chain reactions, Western blotting, and patch-clamp electrophysiology combined with pharmacological agents. FLS were sorted by flow cytometry on the basis of their CD44 expression level for comparison of their invasiveness and with their expression of KCa1.1 α and β subunits. β1 and β3 subunit expression was reduced with small interfering RNA (siRNA) to assess their specific role in KCa1.1α expression and function and in FLS invasiveness.

Results

We identified functional β1 and β3b regulatory subunits in RA-FLS. KCa1.1 β3b subunits were expressed by 70 % of the cells and were associated with highly invasive CD44^high RA-FLS, whereas minimally invasive CD44^low RA-FLS and OA-FLS expressed either β1 subunit. Furthermore, we found that silencing the β3 but not the β1 subunit with siRNA reduced KCa1.1 channel density at the plasma membrane of RA-FLS and inhibited RA-FLS invasiveness.

Conclusions

Our findings suggest the KCa1.1 channel composed of α and β3b subunits as an attractive target for the therapy of RA.

The cation channel Trpv2 is a new suppressor of arthritis severity, joint damage, and synovial fibroblast invasion

Little is known about the regulation of arthritis severity and joint damage in rheumatoid arthritis (RA). Fibroblast-like synoviocytes (FLS) have a central role in joint damage and express increased levels of the cation channel Trpv2. We aimed at determining the role of Trpv2 in arthritis. Treatment with Trpv2-specific agonists decreased the in vitro invasiveness of FLS from RA patients and arthritic rats and mice. Trpv2 stimulation suppressed IL-1β-induced expression of MMP-2 and MMP-3. Trpv2 agonists, including the new and more potent LER13, significantly reduced disease severity in KRN serum- and collagen-induced arthritis, and reduced histologic joint damage, synovial inflammation, and synovial blood vessel numbers suggesting anti-angiogenic activity. In this first in vivo use of Trpv2 agonists we discovered a new central role for Trpv2 in arthritis. These new compounds have the potential to become new therapies for RA and other diseases associated with inflammation, invasion, and angiogenesis.

KCa1.1 inhibition attenuates fibroblast-like synoviocyte invasiveness and ameliorates disease in rat models of rheumatoid arthritis

OBJECTIVE

Fibroblast-like synoviocytes (FLS) participate in joint inflammation and damage in rheumatoid arthritis (RA) and its animal models. The purpose of this study was to define the importance of KCa1.1 (BK, Maxi-K, Slo1, KCNMA1) channel expression and function in FLS and to establish these channels as potential new targets for RA therapy.

METHODS

We compared KCa1.1 expression levels in FLS from rats with pristane-induced arthritis (PIA) and in FLS from healthy rats. We then used ex vivo functional assays combined with small interfering RNA-induced knockdown, overexpression, and functional modulation of KCa1.1 in PIA FLS. Finally, we determined the effectiveness of modulating KCa1.1 in 2 rat models of RA, moderate PIA and severe collagen-induced arthritis (CIA).

RESULTS

We found that PIA FLS expressed the KCa1.1 channel as their major potassium channel, as has been found in FLS from patients with RA. In contrast, FLS from healthy rats expressed fewer of these channels. Inhibiting the function or expression of KCa1.1 ex vivo reduced proliferation and invasive properties of, as well as protease production by, PIA FLS, whereas opening native KCa1.1 or overexpressing the channel enhanced the invasiveness of both FLS from rats with PIA and FLS from healthy rats. Treatment with a KCa1.1 channel blocker at the onset of clinical signs stopped disease progression in the PIA and CIA models, reduced joint and bone damage, and inhibited FLS invasiveness and proliferation.

CONCLUSION

Our results demonstrate a critical role of KCa1.1 channels in the regulation of FLS invasiveness and suggest that KCa1.1 channels represent potential therapeutic targets in RA.

Analyses of synovial tissues from arthritic and protected congenic rat strains reveal a new core set of genes associated with disease severity

Little is known about the genes regulating disease severity and joint damage in rheumatoid arthritis (RA). In the present study we analyzed the gene expression characteristics of synovial tissues from four different strains congenic for non-MHC loci that develop mild and nonerosive arthritis compared with severe and erosive DA rats. DA.F344(Cia3d), DA.F344(Cia5a), DA.ACI(Cia10), and DA.ACI(Cia25) rats developed mild arthritis compared with DA. We found 685 genes with significantly different expression between congenics and DA, independent of the specific congenic interval, suggesting that these genes represent a new nongenetic core group of mediators of arthritis severity. This core group includes genes not previously implicated or with unclear role in arthritis severity, such as Tnn, Clec4m, and Spond1 among others, increased in DA. The core genes also included Scd1, Selenbp1, and Slc7a10, increased in congenics. Genes implicated in nuclear receptor activity, xenobiotic and lipid metabolism were also increased in the congenics, correlating with protection. Several disease mediators were among the core genes reduced in congenics, including IL-6, IL-17, and Ccl2. Analyses of upstream regulators (genes, pathways, or chemicals) suggested reduced activation of Stat3 and TLR-related genes and chemicals in congenics. Additionally, cigarette smoking was among the upstream regulators activated in DA, while p53 was an upstream regulator activated in congenics. We observed congenic-specific differential expression and detection in each individual strain. In conclusion, this new nongenetically regulated core genes of disease severity or protection in arthritis should provide new insight into critical pathways and potential new environmental risk factor for arthritis.

Arthritis severity locus Cia4 is an early regulator of IL-6, IL-1β, and NF-κB activators' expression in pristane-induced arthritis

Cia4 is a locus on rat chromosome 7 that regulates disease severity and joint damage in models of rheumatoid arthritis, including pristane-induced arthritis (PIA). To identify molecular processes regulated by Cia4, synovial tissues from MHC-identical DA (severe erosive) and DA.F344(Cia4) congenics (mild nonerosive) rats were collected at preclinical and recent onset stages following the induction of PIA and analyzed for gene expression levels. Il6 levels were significantly higher in DA compared with congenics on day 10 (135-fold) after PIA induction (preclinical stage) and remained increased on days 14 (47.7-fold) and 18 (29.41-fold). Il6 increased before Il1b suggesting that Il6 could be driving Il1b expression and early synovial inflammation; 187 genes had significantly different expression levels and included inflammatory mediators increased in DA such Slpi (10.94-fold), Ccl7 (5.17-fold), and Litaf (2.09-fold). Syk or NF-κB activating and interacting genes, including Cd74 Ccl21, were increased in DA; 59 genes implicated in cancer-related phenotypes were increased in DA. Genes involved in cell metabolism, transport across membranes, and tissue protection such as Dgat1, Dhcr7, and Slc1a1 were increased in DA.F344(Cia4) congenics; 21 genes differentially expressed or expressed in only one of the strains were located within the Cia4 interval and could be the gene accounting for the arthritis effect. In conclusion, the Cia4 interval contains at least one new arthritis gene that regulates early Il6, Il1b expression, and other inflammatory mediators. This gene regulates the expression of cancer genes that could mediate the development of synovial hyperplasia and invasion, and cartilage and bone destruction.

CXCL10 and its receptor CXCR3 regulate synovial fibroblast invasion in rheumatoid arthritis

OBJECTIVE

CXCL10 is expressed in increased levels in highly invasive fibroblast-like synoviocytes (FLS) from arthritic DA rats and from patients with rheumatoid arthritis (RA). This study was undertaken to analyze the role of CXCL10 and its receptor CXCR3 in regulation of the invasive properties of FLS.

METHODS

FLS were isolated from synovial tissue of RA patients and from DA rats and arthritis-resistant DA.F344(Cia5d) rats with pristane-induced arthritis. We used an in vitro model of invasion through Matrigel, which has been shown to correlate with articular damage in RA and in rat arthritis. FLS were cultured in the presence or absence of CXCL10, anti-CXCR3 antibody, or the CXCR3 inhibitor AMG487 and then studied for invasion, matrix metalloproteinase (MMP) production (MMPs 1-3), intracellular calcium influx, and cell morphology.

RESULTS

DA rat FLS produced higher levels of CXCL10 compared with minimally invasive FLS from DA.F344(Cia5d) rats. CXCL10 treatment increased the invasiveness of FLS from DA.F344(Cia5d) rats by 2-fold, and this increase was blocked by anti-CXCR3. Both anti-CXCR3 and AMG487 reduced invasiveness of FLS from DA rats, by as much as 77%. AMG487 significantly reduced invasiveness of RA FLS (by 58%). CXCR3 blockade reduced levels of MMP-1 by 65%, inhibited receptor signaling (64-100% reduction in intracellular calcium influx), and interfered with actin cytoskeleton reorganization and lamellipodia formation in FLS from rats and RA patients.

CONCLUSION

We describe and characterize a new autocrine/paracrine role of CXCL10/CXCR3 in the regulation of FLS invasion in rats with arthritis and in RA patients. These observations suggest that the CXCL10/CXCR3 axis is a potential new target for therapies aimed at reducing FLS invasion and its associated joint damage and pannus invasion and destruction in RA.

Increased synovial expression of nuclear receptors correlates with protection in pristane-induced arthritis: a possible novel genetically regulated homeostatic mechanism

OBJECTIVE

To use microarray analyses of gene expression to characterize the synovial molecular pathways regulated by the arthritis regulatory locus Cia25 and to determine how it operates to control disease severity and joint damage.

METHODS

Synovial tissues from DA rats and DA.ACI(Cia25) rats obtained 21 days after induction of pristane-induced arthritis were used for RNA extraction and hybridization to Illumina RatRef-12 Expression BeadChips (22,228 genes). Genes with a P value≤0.01 and a fold difference in expression≥1.5 between DA rats and DA.ACI(Cia25) rats were considered significant.

RESULTS

Interleukin-1β (IL-1β) (7.4-fold), IL-6 (67-fold), Ccl2, Cxcl10, Mmp3, Mmp14, and innate immunity genes were expressed at increased levels in DA rats and at significantly lower levels in DA.ACI(Cia25) congenic rats. DA.ACI(Cia25) rats had increased expression of 10 nuclear receptor (NR) genes, including those known to interfere with NF-κB activity and cytokine expression, such as Lxra, Pparg, and Rxrg. DA.ACI(Cia25) rats also had increased expression of NR targets, suggesting increased NR activity. While Vdr was not differentially expressed, a Vdr expression signature was detected in congenic rats, along with up-regulation of mediators of vitamin D synthesis.

CONCLUSION

This is the first description of the association between increased synovial levels of NRs and arthritis protection. The expression of NRs was inversely correlated with the expression of key mediators of arthritis, suggesting reciprocally opposing effects either via NF-κB or at the genomic level in the synovial tissue. We consider that the NR signature may have an important role in maintaining synovial homeostasis and an inflammation-free tissue. These processes are regulated by the Cia25 gene and suggest a new function for this gene.

The arthritis severity locus Cia5a regulates the expression of inflammatory mediators including Syk pathway genes and proteases in pristane-induced arthritis

Background

Cia5a is a locus on rat chromosome 10 that regulates disease severity and joint damage in two models of rheumatoid arthritis, collagen- and pristane-induced arthritis (PIA). In this study, we aimed to identify cellular and molecular processes regulated by Cia5a using microarray-based gene expression analysis of synovial tissues from MHC identical DA (severe erosive disease) and DA.F344(Cia5a) congenics (mild non-erosive disease) rats.

Results

Synovial tissues from six DA and eight DA.F344(Cia5a) rats were analyzed 21 days after the induction of PIA using the Illumina RatRef-12 BeadChip (21,922 genes) and selected data confirmed with qPCR. There was a significantly increased expression of pro-inflammatory mediators such as Il1b (5-fold), Il18 (3.9-fold), Cxcl1 (10-fold), Cxcl13 (7.5-fold) and Ccl7 (7.9-fold), and proteases like Mmp3 (23-fold), Mmp9 (32-fold), Mmp14 (4.4-fold) and cathepsins in synovial tissues from DA, with reciprocally reduced levels in congenics. mRNA levels of 47 members of the Spleen Tyrosine Kinase (Syk) pathway were significantly increased in DA synovial tissues compared with DA.F344(Cia5a), and included Syk (5.4-fold), Syk-activating receptors and interacting proteins, and genes regulated by Syk such as NFkB, and NAPDH oxidase complex genes. Nuclear receptors (NR) such as Rxrg, Pparg and Rev-erba were increased in the protected congenics, and so was the anti-inflammatory NR-target gene Scd1 (54-fold increase). Tnn (72-fold decrease) was the gene most significantly increased in DA.

Conclusions

Analyses of gene expression in synovial tissues revealed that the arthritis severity locus Cia5a regulates the expression of key mediators of inflammation and joint damage, as well as the expression of members of the Syk pathway. This expression pattern correlates with disease severity and joint damage and along with the gene accounting for Cia5a could become a useful biomarker to identify patients at increased risk for severe and erosive disease. The identification of the gene accounting for Cia5a has the potential to generate a new and important target for therapy and prognosis.

Liver X receptor regulates rheumatoid arthritis fibroblast-like synoviocyte invasiveness, matrix metalloproteinase 2 activation, interleukin-6 and CXCL10

Fibroblast-like synoviocyte (FLS) invasiveness correlates with articular damage in rheumatoid arthritis (RA), yet little is known about its regulation. In this study we aimed to determine the role of the nuclear receptor liver X receptor (LXR) in FLS invasion. FLS were isolated from synovial tissues obtained from RA patients and from DA rats with pristane-induced arthritis. Invasion was tested on Matrigel-coated chambers in the presence of the LXR agonist T0901317, or control vehicle. FLS were cultured in the presence or absence of T0901317, and supernatants were used to quantify matrix metalloproteinase 1 (MMP-1), MMP-2, MMP-3, interleukin-6 (IL-6), tumor necrosis factor-α and C-X-C motif chemokine ligand 10 (CXCL10). Nuclear factor-κB (NF-κB) (p65) and Akt activation, actin cytoskeleton, cell morphology and lamellipodia formation were also determined. The LXR agonist T0901317 significantly reduced DA FLS invasion by 99% (P ≤ 0.001), and RA FLS invasion by 96% (P ≤ 0.001), compared with control. T0901317-induced suppression of invasion was associated with reduced production of activated MMP-2, IL-6 and CXCL10 by RA FLS, and with reduction of actin filament reorganization and reduced polarized formation of lamellipodia. T0901317 also prevented both IL-1β-induced and IL-6-induced FLS invasion. NF-κB (p65) and Akt activation were not significantly affected by T0901317. This is the first description of a role for LXR in the regulation of FLS invasion and in processes and pathways implicated both in invasion as well as in inflammatory responses. These findings provide a new rationale for considering LXR agonists as therapeutic agents aimed at reducing both inflammation and FLS-mediated invasion and destruction in RA.

Identification of two new arthritis severity loci that regulate levels of autoantibodies, interleukin-1β, and joint damage in pristane- and collagen-induced arthritis

OBJECTIVE

Cia3 is a locus on rat chromosome 4 that regulates severity and joint damage in collagen- and pristane-induced arthritis (CIA and PIA). This study was undertaken to refine the Cia3 gene-containing interval toward gene identification and obtain insights into its mode of action.

METHODS

Five DA.F344(Cia3) subcongenic rat strains were generated and studied using the PIA and CIA models. Levels of antibodies against type II collagen (both allo- and autoantibodies) were measured. Joints and synovial tissue were collected 32 days after the induction of PIA (chronic stage) for histologic and quantitative polymerase chain reaction analysis of interleukin-1β (IL-1β) and matrix metalloproteinase (MMP) levels.

RESULTS

Three subcongenic strains sharing the centromeric Cia3d interval were protected and 2 subcongenic strains sharing the telomeric Cia3g interval, which did not overlap with Cia3d, were also protected, developing significantly less severe CIA and PIA. Normal joint architecture was preserved in DA.F344(Cia3) and DA.F344(Cia3d) congenic rats with PIA, while DA rats had pronounced synovial hyperplasia, angiogenesis, inflammatory infiltration, and bone or cartilage erosions. The DA.F344(Cia3d) and DA.F344(Cia3g) strains had significantly lower synovial levels of IL-1β (5-fold and nearly 2-fold, respectively [the latter not reaching statistical significance]), MMP-1 (expressed predominantly in DA rats), MMP-3 (79-fold and 8-fold, respectively), and MMP-14 (21-fold and 1.4-fold, respectively) and reduced levels of pathogenic autoantibodies against type II collagen, compared with DA rats.

CONCLUSION

We have identified 2 new arthritis severity and articular damage loci within Cia3. These loci regulate pathogenic processes in 2 different models of rheumatoid arthritis, and the identification of these genes has the potential to generate new targets for therapies aimed at reducing disease severity and articular damage, and may additionally have prognostic value.

The vitamin D receptor regulates rheumatoid arthritis synovial fibroblast invasion and morphology

Serum levels of vitamin D levels are commonly reduced in patients with rheumatoid arthritis (RA) and have been implicated in disease pathogenesis. We recently identified a new vitamin D receptor transcriptional signature in synovial tissues from rats with mild and nonerosive arthritis, suggesting a vitamin D-mediated protective effect. In the present study, we address the hypothesis that part of the vitamin D protective effect is mediated via interference with fibroblast-like synoviocyte (FLS) invasive properties, an in vitro cellular phenotype that correlates with radiographic and histological damage in pristane-induced arthritis and RA. FLSs derived from DA rats with pristane-induced arthritis and RA patients were studied in an in vitro model of invasion through a collagen-rich barrier (Matrigel) over a 24-h period, in the presence or absence of calcitriol, an active form of vitamin D. Matrix metalloprotease (MMP) expression levels were analyzed with zymography and quantitative real-time polymerase chain reaction, and the cytoskeleton was studied with immunofluorescense microscopy. Calcitriol significantly inhibited DA and RA FLS invasion by 54% and 53%, respectively. Calcitriol also reduced interleukin (IL)-1β-induced expression of MMP-1 by 95% in DA FLSs and by 73.5% in RA FLS. Calcitriol treatment reduced actin cytoskeleton reorganization, reduced polarized formation of lamellipodia and reduced colocalization of phosphorylated focal adhesion kinase (p-FAK) with lamellipodia, all consistent with reduced cell ability to move and invade. In conclusion, we identified a new effect of calcitriol in FLS invasion. This discovery suggests that the reduced serum levels of vitamin D and its metabolites commonly seen in RA might increase risk for FLS-mediated cartilage and bone invasion and erosions. Treatment with vitamin D or its analogs has the potential to become a helpful adjuvant aimed at preventing or reducing joint destruction.

KCa1.1 potassium channels regulate key proinflammatory and invasive properties of fibroblast-like synoviocytes in rheumatoid arthritis

Fibroblast-like synoviocytes (FLS) play important roles in the pathogenesis of rheumatoid arthritis (RA). Potassium channels have regulatory roles in many cell functions. We have identified the calcium- and voltage-gated KCa1.1 channel (BK, Maxi-K, Slo1, KCNMA1) as the major potassium channel expressed at the plasma membrane of FLS isolated from patients with RA (RA-FLS). We further show that blocking this channel perturbs the calcium homeostasis of the cells and inhibits the proliferation, production of VEGF, IL-8, and pro-MMP-2, and migration and invasion of RA-FLS. Our findings indicate a regulatory role of KCa1.1 channels in RA-FLS function and suggest this channel as a potential target for the treatment of RA.

CXCL10 and its receptor CXCR3 regulate synovial fibroblast invasion in rheumatoid arthritis

OBJECTIVE

CXCL10 is expressed in increased levels in highly invasive fibroblast-like synoviocytes (FLS) from arthritic DA rats and from patients with rheumatoid arthritis (RA). This study was undertaken to analyze the role of CXCL10 and its receptor CXCR3 in regulation of the invasive properties of FLS.

METHODS

FLS were isolated from synovial tissue of RA patients and from DA rats and arthritis-resistant DA.F344(Cia5d) rats with pristane-induced arthritis. We used an in vitro model of invasion through Matrigel, which has been shown to correlate with articular damage in RA and in rat arthritis. FLS were cultured in the presence or absence of CXCL10, anti-CXCR3 antibody, or the CXCR3 inhibitor AMG487 and then studied for invasion, matrix metalloproteinase (MMP) production (MMPs 1-3), intracellular calcium influx, and cell morphology.

RESULTS

DA rat FLS produced higher levels of CXCL10 compared with minimally invasive FLS from DA.F344(Cia5d) rats. CXCL10 treatment increased the invasiveness of FLS from DA.F344(Cia5d) rats by 2-fold, and this increase was blocked by anti-CXCR3. Both anti-CXCR3 and AMG487 reduced invasiveness of FLS from DA rats, by as much as 77%. AMG487 significantly reduced invasiveness of RA FLS (by 58%). CXCR3 blockade reduced levels of MMP-1 by 65%, inhibited receptor signaling (64-100% reduction in intracellular calcium influx), and interfered with actin cytoskeleton reorganization and lamellipodia formation in FLS from rats and RA patients.

CONCLUSION

We describe and characterize a new autocrine/paracrine role of CXCL10/CXCR3 in the regulation of FLS invasion in rats with arthritis and in RA patients. These observations suggest that the CXCL10/CXCR3 axis is a potential new target for therapies aimed at reducing FLS invasion and its associated joint damage and pannus invasion and destruction in RA.

mTOR regulates the invasive properties of synovial fibroblasts in rheumatoid arthritis

The invasive properties of fibroblast-like synoviocytes (FLS) correlate with radiographic and histologic damage in rheumatoid arthritis (RA) and pristane-induced arthritis (PIA). We previously determined that highly invasive FLS obtained from PIA-susceptible DA (blood type D, Agouti) rats have increased expression of genes associated with invasive cancers, including Villin-2/ezrin. Villin-2/ezrin mediates invasion via mTOR. In the present study we used the mTOR inhibitor rapamycin to assess the role of the ezrin-mTOR pathway on the invasive properties of FLS. FLS were isolated from synovial tissues from arthritic DA rats, and from RA patients. FLS were treated with rapamycin or dimethyl sulfoxide (DMSO) for 24 h and then studied in a Matrigel-invasion assay. Supernatants were assayed for matrix metalloproteinase (MMP) activity, and cell lysates were used for quantification of mTOR, p70S6K1, 4EBP1 and FAK, as well as their respective phosphorylated subsets. Actin filament and FAK localization were determined by immunofluorescence. Rapamycin decreased FLS invasion in DA and RA tissues by 93% and 82%, respectively. Rapamycin treatment reduced the phosphorylation of mTOR and its substrates, p70S6K1 and 4EBP1, confirming mTOR inhibition. In conclusion, rapamycin prevented actin reorganization in both DA and RA FLS, and inhibited the directional formation of lamellipodia. Phosphorylation of the lamellipodia marker FAK was also reduced by rapamycin. MMPs were not significantly affected by rapamycin. Rapamycin significantly reduced RA and DA rat FLS invasion via the suppression of the mTOR signaling pathway. This discovery suggests that rapamycin could have a role in RA therapy aimed at reducing the articular damage and erosive changes mediated by FLS.

Microarray analyses of peripheral blood cells identifies unique gene expression signature in psoriatic arthritis

Psoriatic arthritis (PsA) is a chronic and erosive form of arthritis of unknown cause. We aimed to characterize the PsA phenotype using gene expression profiling and comparing it with healthy control subjects and patients rheumatoid arthritis (RA). Peripheral blood cells (PBCs) of 19 patients with active PsA and 19 age- and sex-matched control subjects were used in the analyses of PsA, with blood samples collected in PaxGene tubes. A significant alteration in the pattern of expression of 313 genes was noted in the PBCs of PsA patients on Affymetrix U133A arrays: 257 genes were expressed at reduced levels in PsA, and 56 genes were expressed at increased levels, compared with controls. Downregulated genes tended to cluster to certain chromosomal regions, including those containing the psoriasis susceptibility loci PSORS1 and PSORS2. Among the genes with the most significantly reduced expression were those involved in downregulation or suppression of innate and acquired immune responses, such as SIGIRR, STAT3, SHP1, IKBKB, IL-11RA, and TCF7, suggesting inappropriate control that favors proin-flammatory responses. Several members of the MAPK signaling pathway and tumor suppressor genes showed reduced expression. Three proinflammatory genes--S100A8, S100A12, and thioredoxin--showed increased expression. Logistic regression and recursive partitioning analysis determined that one gene, nucleoporin 62 kDa, could correctly classify all controls and 94.7% of the PsA patients. Using a dataset of 48 RA samples for comparison, the combination of two genes, MAP3K3 followed by CACNA1S, was enough to correctly classify all RA and PsA patients. Thus, PBC gene expression profiling identified a gene expression signature that differentiated PsA from RA, and PsA from controls. Several novel genes were differentially expressed in PsA and may prove to be diagnostic biomarkers or serve as new targets for the development of therapies.

The arthritis severity locus Cia5d is a novel genetic regulator of the invasive properties of synovial fibroblasts

OBJECTIVE

The synovial fibroblast, or fibroblast-like synoviocyte (FLS), has a central role in pannus invasion and destruction of cartilage and bone in rheumatoid arthritis (RA). However, regulation of the FLS remains incompletely understood. The aim of this study was to determine whether the invasive properties of FLS are genetically regulated by arthritis severity loci.

METHODS

DA rats (arthritis susceptible) and rat strains congenic for arthritis-protective intervals were studied. Primary FLS cell lines were generated from each strain and used in a well-established FLS invasion model through a collagen-rich barrier. Cells or culture supernatants were analyzed for gene expression, activity of different matrix metalloproteinases (MMPs), cytoskeleton integrity, and cell proliferation.

RESULTS

The median number of FLS from DA.F344(Cia5d) rats that invaded through the collagen-rich barrier was reduced 86.5% compared with the median number of invading FLS from DA rats. Histologic examination showed that DA.F344(Cia5d) rats preserved a normal joint without pannus, hyperplasia, or erosions. FLS from DA.F344(Cia5d) rats produced significantly lower levels of active MMP-2 compared with FLS from DA rats, but the levels of proMMP-2 and MMP-2 messenger RNA in DA.F344(Cia5d) rats were similar to those in DA rats. Treatment of FLS from DA rats with an MMP-2 inhibitor reduced cell invasion to a level similar to that in DA.F344(Cia5d) rats, demonstrating that MMP-2 activity accounted for the difference between FLS from these 2 strains. Analysis of MMP-2-activating pathways revealed increased levels of soluble membrane type 1 (MT1)-MMP in DA rats compared with DA.F344(Cia5d) rats.

CONCLUSION

These data represent the first evidence for a genetic component in the regulation of FLS invasion. A gene located within the Cia5d interval accounts for this effect and operates via the regulation of soluble MT1-MMP production and MMP-2 activation. These observations suggest novel potential pathways for prognostication and therapy.

Genetic regulation of T regulatory, CD4, and CD8 cell numbers by the arthritis severity loci Cia5a, Cia5d, and the MHC/Cia1 in the rat

T cells have a central role in the pathogenesis of autoimmune arthritis, and several abnormalities in T cell homeostasis have been described in rheumatoid arthritis (RA). We hypothesized that T cell phenotypes, including frequencies of different subsets of T regulatory (Treg) cells and in vitro functional responses could be genetically determined. Furthermore, we considered that the genetic contribution would be accounted for by one of the arthritis regulatory quantitative trait loci (QTL), thus providing novel clues to gene mode of action. T cells were isolated from thymus, peripheral blood, and spleen from DA (arthritis-susceptible) and ACI and F344 (arthritis-resistant) strains and from F344.DA(Cia1), DA.F344(Cia5a), and DA.F344(Cia5d) rats congenic for arthritis QTL. T cell subpopulations differed significantly between DA, F344, and ACI. DA rats had an increased frequency of CD4(+) cells, and a reduction in CD8(+) and CD4(+)CD45RC(|o) Treg cells, compared with F344. The differences in CD4/CD8 and CD4(+)CD45RC(|o) Treg cells were accounted for by Cia5a. DA rats also had a reduced frequency of CD8(+)CD45RC(|o) CD25(+) Treg cells compared with F344, and that difference was explained by Cia5d. DA rats also had a significantly lower frequency of CD4(+)CD25(+) and CD8(+)CD25(+) thymocytes, and of peripheral blood CD8(+)CD45RC(|o) Treg cells, compared with F344 rats, and that difference was accounted for by the MHC. This is the first identification of arthritis severity QTL regulating numbers of CD4(+)CD45RC(|o) (Cia5a) and CD8(+)CD45RC(|o) CD25(+) (Cia5d) Treg cells. The MHC effect on CD8(+) Treg cells and CD25(+) thymocytes raises a novel potential explanation for its association with arthritis.

Contribution of genetic studies in rodent models of autoimmune arthritis to understanding and treatment of rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic and potentially debilitating autoimmune disease. While novel therapies have emerged in recent years, disease remission is rarely achieved. RA is a complex trait, and the identifying of its susceptibility and severity genes has been anticipated to generate new targets for therapeutic intervention. However, finding those genes and understanding their function has been a challenging task. Studies in rodent intercrosses and congenics generated from inbred strains have been an important complementary strategy to identify arthritis genes, and understand how they operate to regulate disease. Furthermore, these new rodent arthritis genes will be new targets for therapeutic interventions, and will identify new candidate genes or candidate pathways for association studies in RA. In this review-opinion article I discuss RA genetics, difficulties involved in gene identification, and how rodent models can facilitate (1) the discovery of both arthritis susceptibility and severity genes, (2) studies of gene-environment interactions, (3) studies of gene-gender interactions, (4) epistasis, (5) functional characterization of the specific genes, (6) development of novel therapies and (7) how the information generated from rodent studies will be useful to understanding and potentially treating RA.

Genetic regulation of T regulatory, CD4, and CD8 cell numbers by the arthritis severity loci Cia5a, Cia5d, and the MHC/Cia1 in the rat

T cells have a central role in the pathogenesis of autoimmune arthritis, and several abnormalities in T cell homeostasis have been described in rheumatoid arthritis (RA). We hypothesized that T cell phenotypes, including frequencies of different subsets of T regulatory (Treg) cells and in vitro functional responses could be genetically determined. Furthermore, we considered that the genetic contribution would be accounted for by one of the arthritis regulatory quantitative trait loci (QTL), thus providing novel clues to gene mode of action. T cells were isolated from thymus, peripheral blood, and spleen from DA (arthritis-susceptible) and ACI and F344 (arthritis-resistant) strains and from F344.DA(Cia1), DA.F344(Cia5a), and DA.F344(Cia5d) rats congenic for arthritis QTL. T cell subpopulations differed significantly between DA, F344, and ACI. DA rats had an increased frequency of CD4(+) cells, and a reduction in CD8(+) and CD4(+)CD45RC(|o) Treg cells, compared with F344. The differences in CD4/CD8 and CD4(+)CD45RC(|o) Treg cells were accounted for by Cia5a. DA rats also had a reduced frequency of CD8(+)CD45RC(|o) CD25(+) Treg cells compared with F344, and that difference was explained by Cia5d. DA rats also had a significantly lower frequency of CD4(+)CD25(+) and CD8(+)CD25(+) thymocytes, and of peripheral blood CD8(+)CD45RC(|o) Treg cells, compared with F344 rats, and that difference was accounted for by the MHC. This is the first identification of arthritis severity QTL regulating numbers of CD4(+)CD45RC(|o) (Cia5a) and CD8(+)CD45RC(|o) CD25(+) (Cia5d) Treg cells. The MHC effect on CD8(+) Treg cells and CD25(+) thymocytes raises a novel potential explanation for its association with arthritis.

The arthritis severity quantitative trait loci Cia4 and Cia6 regulate neutrophil migration into inflammatory sites and levels of TNF-alpha and nitric oxide

Neutrophils are required for the development of arthritis, and their migration into the synovial tissue coincides with the onset of clinical disease. Synovial neutrophil numbers also correlate with rheumatoid arthritis disease activity and severity. We hypothesized that certain arthritis severity genes regulate disease via the regulation of neutrophil migration into the joint. This hypothesis was tested in the synovial-like air pouch model injected with carrageenan using arthritis-susceptible DA and arthritis-resistant F344 rats. DA had nearly 3-fold higher numbers of exudate neutrophils compared with F344 (p < 0.001). Five DA.F344(QTL) strains congenic for severity loci and protected from autoimmune arthritis were studied. Only DA.F344(Cia4) (chromosome 7) and DA.F344(Cia6) (chromosome 8) congenics had significantly lower exudate neutrophil counts compared with DA. TNF-alpha levels were 2.5-fold higher in DA exudates as compared with F344 exudates, and that difference was accounted for by the Cia4 locus. Exudate levels of NO, a known inhibitor of neutrophil chemotaxis, were higher in F344, compared with DA, and that difference was accounted for by Cia6. This is the first time that non-MHC autoimmune arthritis loci are found to regulate three central components of the innate immune response implicated in disease pathogenesis, namely neutrophil migration into an inflammatory site, as well as exudate levels of TNF-alpha and NO. These observations underscore the importance of identifying the Cia4 and Cia6 genes, and suggest that they should generate useful novel targets for development of new therapies.

Cia25 on rat chromosome 12 regulates severity of autoimmune arthritis induced with pristane and with collagen

BACKGROUND

A genomewide scan in a DA x ACI F2 intercross studied for collagen-induced arthritis (CIA) identified the severity quantitative trait locus Cia25 on rat chromosome 12. Cia25 co-localises with loci regulating several forms of autoimmune diseases in rats, mice and humans, suggesting a common gene.

OBJECTIVE

To characterise the effects of Cia25 on severity of arthritis in congenic rats.

METHODS

DA.ACI(Cia25) congenic rats were constructed according to a genotype-guided strategy, and tested for pristane-induced arthritis (PIA) and CIA, induced with rat type II collagen (CII). A well-established scoring system previously shown to correlate with histological damage, including cartilage and bone erosions, synovial hyperplasia and synovial inflammation, was used.

RESULTS

The introgression of ACI alleles at Cia25 into DA background, as in DA.ACI(Cia25) rats, was enough to significantly reduce arthritis severity by 60% in PIA and by 40% in CIA, both in males and females compared with DA rats of the same sex. Levels of IgG anti-CII in male DA.ACI(Cia25) rats were 83% lower than in male DA. Levels of anti-CII in females were not affected by the congenic interval.

CONCLUSIONS

Cia25 contains a gene that regulates disease severity in two distinct models of autoimmune arthritis. Although both genders were protected in arthritis studies, only male congenic rats had a dramatic reduction in levels of anti-CII, suggesting the possibility of a second arthritis gene in this interval that operates via the regulation of autoantibodies in a sex-specific manner. The identification of the gene(s) accounting for Cia25 is expected to generate novel prognostic biomarkers and targets for therapy.

The arthritis severity quantitative trait locus Cia7 regulates neutrophil migration into inflammatory sites

Neutrophils are required for the development of arthritis in rodents, and are the predominant cell in the synovial fluid of active rheumatoid arthritis. We hypothesized that neutrophil migration into the inflammed joint is genetically regulated. In addition, this genetic regulation would be accounted for by one of the arthritis loci that we have previously identified in an intercross between arthritis-susceptible DA and arthritis-resistant ACI rats studied for collagen-induced arthritis. We used the synovial-like air pouch model injected with carrageenan, and tested DA, ACI, and four congenic strains. ACI exudates had a significantly lower number of neutrophils compared with DA. Transfer of DA alleles at Cia7 into the ACI background, as in ACI.DA(Cia7) congenics, was enough to increase exudate neutrophil numbers to levels identical to DA, and this locus accounted for the difference between parental strains. None of the other congenic intervals explained the differences in exudate neutrophil counts. In conclusion, we have identified a novel function for Cia7, and determined that it regulates neutrophil migration into a synovial-like inflammatory site. Our data revealed no intrinsic defect in neutrophil responses to chemotactic agents, and suggest that Cia7 regulates an as yet unidentified factor central to neutrophil recruitment into inflammed tissues.

Cia27 is a novel non-MHC arthritis severity locus on rat chromosome 10 syntenic to the rheumatoid arthritis 17q22–q25 locus

Cia27 on rat chromosome 10 is a collagen-induced arthritis (CIA) severity quantitative trait locus originally identified in a study of (DA x ACI) F2. As an initial step towards the positional cloning of the Cia27 gene, a 17 cM (21 Mb) interval from the DA strain (arthritis-susceptible) containing the two-logarithm of odds support interval comprising Cia27 was introgressed into the ACI (arthritis-resistant) background through genotype-guided congenic breeding. ACI.DA(Cia27) congenics developed a significantly more severe form of arthritis (CIA), with a 5.9-fold increase in median arthritis severity index, a parameter known to correlate with synovial inflammation, and cartilage and bone erosions, compared with ACI (P< or =0.001). The arthritis severity enhancing effect could be detected from day 21 onwards. Rats heterozygous at the congenic interval developed a disease similar to ACI rats, suggesting that DA alleles operate in a recessive manner. Levels of autoantibodies anti-rat type II collagen did not correlate with arthritis severity. Synovial tissue mRNA levels of interleukin-1beta (IL-1beta) were significantly increased in ACI.DA(Cia27) congenics compared with ACI. These results demonstrate that Cia27 harbors a novel arthritis severity regulatory gene. The identification of this gene should facilitate the identification of the rheumatoid arthritis gene mapped to the human syntenic region on chromosome 17q22-q25.

Peripheral blood gene expression profiling in rheumatoid arthritis

We carried out gene expression profiling of peripheral blood mononuclear cells (PBMCs) in 29 patients with active rheumatoid arthritis (RA) and 21 control subjects using Affymetrix U95Av2 arrays. Using cluster analysis, we observed a significant alteration in the expression pattern of 81 genes (P<0.001) in the PBMCs of RA patients compared with controls. Many of these genes correlated with differences in monocyte counts between the two study populations, and we show that a large fraction of these genes are specifically expressed at high levels in monocytes. In addition, a logistic regression analysis was performed to identify genes that performed best in the categorization of RA and control samples. Glutaminyl cyclase, IL1RA, S100A12 (also known as calgranulin or EN-RAGE) and Grb2-associated binding protein (GAB2) were among the top discriminators. Along with previous data, the overexpression of S100A12 in RA patients emphasizes the likely importance of RAGE pathways in disease pathogenesis. The altered expression of GAB2, an intracellular adaptor molecule involved in regulating phosphatase function, is of particular interest given the recent identification of the intracellular phosphatase PTPN22 as a risk gene for RA. These data suggest that a detailed study of gene expression patterns in peripheral blood can provide insight into disease pathogenesis. However, it is also clear that substantially larger sample sizes will be required in order to evaluate fully gene expression profiling as a means of identifying disease subsets, or defining biomarkers of outcome and response to therapy in RA.

Thermal signature analysis as a novel method for evaluating inflammatory arthritis activity

OBJECTIVE

To examine the potential usefulness of a novel thermal imaging technique to evaluate and monitor inflammatory arthritis activity in small joints using rat models, and to determine whether thermal changes can be used to detect preclinical stages of synovitis.

METHODS

Three different rat strains were studied in a model of inflammatory arthritis of the ankle induced by an intra-articular (IA) injection of complete Freund's adjuvant (CFA), compared with the contralateral ankle injected with normal saline. Arthritis activity and severity scores, ankle diameters, pain related posture scores, and thermal images were obtained at 10 different times between 0 h (before induction) and day 7. The pristane induced arthritis (PIA) model was used to study preclinical synovitis. Thermal images were obtained at each time point using the TSA ImagIR system and were digitally analysed.

RESULTS

Rats developed similar ankle arthritis detected six hours after the IA injection of CFA, which persisted for seven days. All ankle clinical indices, including arthritis activity and severity scores, correlated significantly with ankle thermal imaging changes in the monoarthritis model (p<0.003). No thermal imaging changes were detected in preclinical stages of PIA. However, PIA onset coincided with increased ankle thermal signature.

CONCLUSIONS

Thermal measurements correlated significantly with arthritis activity and severity indices. The technique was highly sensitive and could measure directly two cardinal signs of inflammation (warmth and oedema, based on ankle diameter) in an area (ankle) that is less than half the size of a human interphalangeal joint, suggesting a potential use in drug trials or clinical practice.

The Non-MHC Quantitative Trait Locus Cia5 Contains Three Major Arthritis Genes That Differentially Regulate Disease Severity, Pannus Formation, and Joint Damage in Collagen- and Pristane-Induced Arthritis

Cia5 is a locus on rat chromosome 10 which regulates the severity of collagen- and pristane-induced arthritis (CIA and PIA). To refine the region toward positional identification, Cia5 subcongenic strains were generated and studied in PIA and CIA. The protective effect of the telomeric locus Cia5a was confirmed in both models. A second arthritis severity locus (Cia5d) was identified within the most centromeric portion of Cia5. DA.F344(Cia5d) rats had a significantly lower median arthritis severity index in PIA, but not in CIA, compared with DA. On histologic analyses DA.F344(Cia5a) and DA.F344(Cia5d) congenics with PIA preserved a nearly normal joint architecture compared with DA, including significant reduction in synovial hyperplasia, pannus, angiogenesis, inflammatory infiltration, bone and cartilage erosions. Cia5 and Cia5a synovial levels of IL-1beta mRNA were reduced. Although both DA.F344(Cia5) and DA.F344(Cia5a) rats were protected in CIA, the arthritis scores of DA.F344(Cia5) were significantly higher than those of DA.F344(Cia5a), suggesting the existence of a third locus where F344-derived alleles centromeric from Cia5a contribute to increased arthritis severity. The existence of the third locus was further supported by higher levels of autoantibodies against rat type II collagen in DA.F344(Cia5) congenics compared with DA.F344(Cia5a). Our results determined that Cia5 contains three major arthritis severity regulatory loci regulating central events in the pathogenesis of arthritis, and differentially influencing CIA and PIA. These loci are syntenic to regions on human chromosomes 17q and 5q implicated in the susceptibility to rheumatoid arthritis, suggesting that the identification of these genes will be relevant to human disease.

The non-major histocompatibility complex quantitative trait locus Cia10 contains a major arthritis gene and regulates disease severity, pannus formation, and joint damage

OBJECTIVE

To construct rats congenic for the chromosome 2 arthritis-regulatory quantitative trait locus Cia10, originally identified in a (DA x ACI)F(2) intercross rat strain that had been assessed for collagen-induced arthritis (CIA), and to determine the effect of this congenic interval on arthritis severity, joint histologic structure, and cytokine transcription in rats with pristane-induced arthritis (PIA).

METHODS

A 52.6-MB interval derived from the ACI (CIA- and PIA-resistant) strain and containing the Cia10 interval was introgressed into the DA (arthritis-susceptible) background through genotype-guided congenic breeding. Homozygous male and female DA.ACI(Cia10) congenic rats were studied for their susceptibility to and severity of PIA, and were compared with same-sex DA rats. Histologic analyses were done on hind paws collected on day 32 following the pristane injection. Levels of interleukin-1beta (IL-1beta) and tumor necrosis factor alpha (TNFalpha) messenger RNA (mRNA) were measured with real-time polymerase chain reaction on synovial tissues from day-32 ankles.

RESULTS

Both male and female DA.ACI(Cia10) congenic rats developed a significantly milder form of arthritis, with a 95% and 92% reduction in the arthritis severity index compared with DA male and female controls, respectively (males P < or = 0.001 and females P = 0.003). DA.ACI(Cia10) congenic rat synovial tissue was more likely to preserve its normal histologic architecture, including minimal to no cartilage and bone erosions, synovial hyperplasia, and pannus formation, and reduced numbers of vessels (angiogenesis), when compared with DA synovial tissue. There was a 2.7- and 2.4-fold reduction in the amount of IL-1beta and TNFalpha mRNA, respectively, in the synovial tissue of DA.ACI(Cia10) congenic rats compared with DA rats. Sequencing analyses of complementary DNA for the Cia10-predicted candidate gene Ptpn8, the rat homolog of the rheumatoid arthritis (RA)-susceptibility gene PTPN22, revealed no polymorphisms between the DA and ACI strains.

CONCLUSION

This study determined that Cia10 harbors a major autoimmune arthritis-regulatory gene. This gene regulates clinical disease severity, histologic damage, and the levels of at least two central proinflammatory cytokines. We are in the process of narrowing down the critical region for positional cloning of the Cia10 gene. The identification of this gene will provide novel targets or pathways for focused candidate-gene studies in RA.

Identification of two novel female-specific non-major histocompatibility complex loci regulating collagen-induced arthritis severity and chronicity, and evidence of epistasis

OBJECTIVE

To identify additional sex-specific and epistatic quantitative trait loci (QTL) regulating collagen-induced arthritis (CIA) severity overall, as well as within different stages during the disease course, in an intercross between major histocompatibility complex-identical inbred rat strains DA/Bkl (susceptible) and ACI/Hsd (resistant).

METHODS

Arthritic male (DA x ACI)F2 intercross offspring (n = 143) were analyzed separately from the females (n = 184). Phenotypic extremes (maximum arthritis scores [MAS]) were genotyped and used for QTL analysis. All 327 rats were genotyped with the simple sequence-length polymorphism (SSLP) markers closest to the peak of Cia7 and Cia10, the major loci previously identified in this intercross, and with SSLPs covering chromosomes 12 and 18. Phenotypes studied were disease onset, arthritis severity scores on days 14-39, MAS, mean and cumulative arthritis scores, delayed-type hypersensitivity, and antibody responses to rat type II collagen.

RESULTS

A new female-specific arthritis-severity recessive locus was identified on rat chromosome 12 (Cia25), with a maximum effect observed on day 28 (logarithm of odds [LOD] 4.7). The homozygous DA genotype at Cia25 was associated with a 45% higher median arthritis score in females. Sequencing analyses of the Cia25 candidate gene Ncf1 revealed polymorphisms between DA and ACI. The previously identified locus, Cia10, was found to be male-specific. A 2-locus interaction model analysis identified a novel recessive chromosome 18 QTL, Cia26, which was dependent on Cia7, with its maximum effect observed at later stages during the disease course (peak LOD score of 3.6 for arthritis scores on day 39).

CONCLUSION

This study identified 2 novel female-specific loci, and 1 male-specific locus. Cia25 regulates MAS and disease severity during the mid-to-late stages of the disease course and may be accounted for by Ncf1 polymorphisms. Cia26 is in epistasis with Cia7 and regulates later stages of disease, suggesting an involvement in disease perpetuation and/or chronicity.

Modulation of multiple experimental arthritis models by collagen-induced arthritis quantitative trait loci isolated in congenic rat lines: different effects of non-major histocompatibility complex quantitative trait loci in males and females

OBJECTIVE

Collagen-induced arthritis (CIA) is a model of inflammatory arthritis with many similarities to rheumatoid arthritis (RA). We previously mapped in F(2) offspring of CIA-susceptible DA and CIA-resistant F344 rats, 5 quantitative trait loci (QTLs) for which F344 alleles were associated with reduced CIA severity. In the present study, we sought to characterize the independent arthritis-modulating effects of these 5 QTLs.

METHODS

CIA-regulatory regions were transferred from the F344 genome to the DA background or vice versa by repeated backcrossing. The arthritis-modulating effects of the transferred alleles were determined by comparing the severity of experimentally induced arthritis in congenic rats with that in DA rats.

RESULTS

Congenic lines with either the F344 major histocompatibility complex (MHC) on the DA background or the DA MHC on the F344 background were resistant to CIA, confirming both MHC and non-MHC contributions to the genetic regulation of CIA. F344 alleles at the Cia3 and Cia5 regions of chromosomes 4 and 10 reduced CIA severity relative to that observed in DA rats. F344 Cia4 and Cia6 regions of chromosomes 7 and 8 failed to significantly alter CIA severity. Arthritis-modifying effects of Cia4 and Cia6 were, however, detected in pristane-induced and/or Freund's incomplete adjuvant oil-induced arthritis. The arthritis-modifying effects of the non-MHC CIA-regulatory loci differed in males and females.

CONCLUSION

These congenic lines confirmed the existence and location of genes that regulate the severity of experimental arthritis in rats. Mechanisms responsible for the sex-specificity of individual arthritis-regulatory loci may explain some of the sex differences observed in RA and other autoimmune diseases in humans.

Genetic factors involved in central nervous system/immune interactions

Analysis of several inbred rat strains has led us to hypothesize that HPA axis abnormalities may contribute, in part, to susceptibility to both autoimmune disease and addiction. In this article we review the evidence for this hypothesis and describe our ongoing efforts to genetically characterize these traits. We have mapped the locations of 23 loci that regulate autoimmune disease in rats, and are currently constructing QTL congenic lines in which a genomic region from the resistant strain is transferred to the susceptible strain or vice versa. These QTL congenic lines will be valuable to test whether genes encoding autoimmune regulation also control neuroendocrine traits. Further genetic dissection and identification of the underlying genes will be necessary to infer a mechanistic link between autoimmune and neuroendocrine traits.

Evaluation of quantitative trait loci regulating severity of mycobacterial adjuvant-induced arthritis in monocongenic and polycongenic rats: identification of a new regulatory locus on rat chromosome 10 and evidence of overlap with rheumatoid arthritis susceptibility loci

OBJECTIVE

To evaluate the regulatory potential of genetic loci controlling Mycobacterium butyricum adjuvant-induced arthritis (Mbt-AIA) using mono- and polycongenic rats.

METHODS

Of 4 quantitative trait loci (QTLs) that regulate Mbt-AIA, F344 alleles at 3 of these loci, Aia1, Aia2, and Aia3, are associated with lower arthritis severity, whereas F344 alleles at Aia4 are associated with greater arthritis severity. In this study, we constructed congenic lines by transferring 1 or more of the F344 genomic segments containing Aia1, Aia2, and Aia3 onto the DA genome. We comparatively evaluated their responses to Mbt-AIA with the responses of parental DA and F344 rats.

RESULTS

Aia1, encompassing the rat major histocompatibility complex, reduced arthritis severity in monocongenic rats of both sexes. The arthritis-lowering effects of Aia2 and Aia3 were sex-influenced and were therefore observed in only males and only females, respectively. Polycongenic rats containing F344 genomic regions at Aia1, Aia2, and Aia3 developed Mbt-AIA of relatively greater severity than did F344 rats, implying that in DA and F344 rats, there could be other Mbt-AIA loci in addition to Aia1, Aia2, Aia3, and Aia4. To test the possibility that some of these Mbt-AIA-regulatory loci may colocalize with other arthritis QTLs, we evaluated Mbt-AIA in DA.F344 monocongenic rats containing collagen-induced arthritis QTLs. Cia5 (the QTL region on chromosome 10), but not Cia5a, Cia4, or Cia6, also regulated Mbt-AIA, and was named Aia5.

CONCLUSION

F344 genomic regions at Aia1, Aia2, and Aia3 and the newly identified Aia5 contain genes that reduce Mbt-AIA severity in DA rats. These Mbt-AIA-regulatory loci overlap rheumatoid arthritis-susceptibility loci in humans.

The IDDM13 region containing the insulin-like growth factor binding protein-5 (IGFBP5) gene on chromosome 2q33-q36 and the genetic susceptibility to rheumatoid arthritis

We considered that the constitutive over-expression by cultured rheumatoid arthritis (RA) fibroblast-lineage synoviocytes of genes like IGFBP5 could indicate new candidate susceptibility genes. IGFBP5 is located in a region where an insulin-dependent diabetes mellitus (IDDM) susceptibility locus, IDDM13 (2q33-q36), has been mapped. Previous evidence that non-MHC IDDM loci overlap RA susceptibility loci made IGFBP5 and its region an interesting candidate locus which was tested for linkage. Forty-nine sibships (2-4 affected siblings per sibship) with RA were genotyped with microsatellite markers covering an 11.2 cM interval in the IGFBP5/IDDM13 region. Both the two-point LOD scores and a 'nonparametric' allele-sharing analysis revealed no evidence for linkage (max LOD = 0.54, P = 0.5, respectively). Adjustments for the presence of 'shared-epitope' alleles did not significantly change the LOD scores. These results suggest that, despite the involvement of the 2q33-q36 chromosomal region in another organ-specific autoimmune disease, it is unlikely that this region harbors a RA susceptibility locus.

Genetic dissection of collagen-induced arthritis in Chromosome 10 quantitative trait locus speed congenic rats: evidence for more than one regulatory locus and sex influences

Rat Chromosome 10 (RNO10) harbors Cia5, a non-MHC quantitative trait locus (QTL) that regulates the severity of type II collagen-induced arthritis (CIA) in DAxF344 and DAxBN F2 rats. CIA is an animal model with many features that resemble rheumatoid arthritis. To facilitate analysis of Cia5 independently of the other CIA regulatory loci on other chromosomes, DA recombinant QTL speed congenic rats, DA.F344(Cia5), were generated. These QTL congenic rats have a large chromosomal segment containing Cia5 (interval size < or =80.1 cM) from CIA-resistant F344 rats introgressed into their genome. Phenotypic analyses of these rats for susceptibility and severity of CIA confirmed that Cia5 is an important disease-modifying locus. CIA severity was significantly lower in the Cia5 congenic rats than in DA controls. We also generated DA Cia5 speed sub-congenic rats, DA.F344(Cia5a), which had a smaller segment of the F344 genome, Cia5a, comprising only the distal q-telomeric end (interval size < or = 22.5 cM) of Cia5, introgressed into their genome. DA.F344(Cia5a) sub-congenic rats also exhibited reduced CIA disease severity compared with the parental DA rats. The regulatory effects in both congenic strains were sex influenced. The disease-ameliorating effect of the larger fragment, Cia5, was greater in males than in females, but the effect of the smaller fragment, Cia5a, was greater in females. We also present an improved genetic linkage map covering the Cia5/Cia5a region, which we have integrated with two rat radiation hybrid maps. Comparative homology analysis of this genomic region with mouse and human chromosomes was also undertaken. Regulatory loci for multiple autoimmune/inflammatory diseases in rats (RNO10), mice (MMU11), and humans (HSA17 and HSA5q23-q31) map to chromosomal segments homologous to Cia5 and Cia5a.

An integrated genetic linkage map with 1,137 markers constructed from five F2 crosses of autoimmune disease-prone and -resistant inbred rat strains

The rat (Rattus norvegicus) is an important experimental model for many human diseases including arthritis, diabetes, and other autoimmune and chronic inflammatory diseases. The rat genetic linkage map, however, is less well developed than those of mouse and human. Integrated rat genetic linkage maps have been previously reported by Pravenec et al. (1996, Mamm. Genome 7: 117-127) (500 markers mapped in one cross), Bihoreau et al. (1997, Genome Res. 7: 434-440) (767 markers mapped in three crosses), Wei et al. (1998, Mamm. Genome 9: 1002-1007) (562 markers mapped in two crosses), Brown et al. (1998, Mamm. Genome 9: 521-530) (678 markers mapped in four crosses), and Nordquist et al. (1999, Rat Genome 5: 15-20) (330 markers mapped in two crosses). The densest linkage map combined with a radiation hybrid map, reported by Steen et al. (1999, Genome Res. 9: AP1-AP8), includes 4736 markers mapped in two crosses. Here, we present an integrated linkage map with 1137 markers. We have constructed this map by genotyping F2 progeny of five crosses: F344/NHsd x LEW/NHsd (673 markers), DA/Bkl x F344/NHsd (531 markers), BN/SsN x LEW/N (714 markers), DA/Bkl x BN/SsNHsd (194 markers), and DA/Bkl x ACI/SegHsd (245 markers). These inbred rat strains vary in susceptibility/resistance to multiple autoimmune diseases and are used extensively for many types of investigation. The integrated map includes 360 loci mapped in three or more crosses. The map contains 196 new SSLP markers developed by our group, as well as many SSLP markers developed by other groups. Two hundred forty genes are incorporated in the map. This integrated map should allow comparison of rat genetic maps from different groups and thereby facilitate genetic studies of rat autoimmune and related disease models.

Identification of a new quantitative trait locus on chromosome 7 controlling disease severity of collagen-induced arthritis in rats

Autoimmune diseases, such as rheumatoid arthritis, Crohn's disease, and multiple sclerosis, are regulated by multiple genes. Major histocompatibility complex (MHC) genes have the strongest effects, but non-MHC genes also contribute to disease susceptibility/severity. In this paper, we describe a new non-MHC quantitative trait locus, Cia8, on rat Chromosome (Chr) 7 that controls collagen-induced arthritis severity in F2 progeny of DA and F344 inbred rats, and present an updated localization of Cia4 on the same chromosome. We also describe the location of mouse and human genes, orthologous to the genes in the genomic intervals containing Cia4 and Cia8, and provide evidence that the segment of rat Chr 7 containing Cia4 and Cia8 is homologous to segments of mouse Chr 10 and 15 and human Chr 8, 12, and 19.

Identification of a new non-major histocompatibility complex genetic locus on chromosome 2 that controls disease severity in collagen-induced arthritis in rats

OBJECTIVE

To identify novel non-major histocompatibility complex (non-MHC) genetic loci controlling the severity of homologous rat type II collagen-induced arthritis (CIA).

METHODS

We conducted a genome-wide scan to identify CIA regulatory quantitative trait loci (QTL) in an F2 cross between DA (CIA highly susceptible) and ACI (CIA resistant) inbred rats immunized with homologous rat type II collagen (RII). These strains share the MHC/RT1av1 haplotype required for susceptibility to RII-induced CIA.

RESULTS

F2 females had higher median arthritis scores than did males. Relative resistance in the males was determined by inheriting either a DA or an ACI Y chromosome and was independent of the source of the X chromosome. In addition, a major QTL was localized on chromosome 2 (Cia7, logarithm of odds score 4.6). Cia7 is in a region that shows linkage conservation with chromosomal regions that regulate autoimmune diabetes and experimental autoimmune encephalomyelitis in mice and multiple sclerosis in humans.

CONCLUSION

Sex chromosomes and Cia7 play an important role in regulating CIA in response to RII. This rat model should facilitate positional cloning and functional characterization of regulatory genes that may play a role in several forms of autoimmune disease, including rheumatoid arthritis.

Localization of quantitative trait loci regulating adjuvant-induced arthritis in rats: evidence for genetic factors common to multiple autoimmune diseases

Adjuvant-induced arthritis (AIA) in rats is a widely used autoimmune experimental model with many features similar to rheumatoid arthritis (RA). To identify potential genetic regulatory mechanisms in RA, we conducted genome-wide linkage analysis in F2 progeny of arthritis-susceptible Dark Agouti (DA) and relatively resistant Fischer 344 (F344) inbred rats. We compared the data with our previously reported investigation of collagen-induced arthritis (CIA), which was expanded in the follow-up study reported in this work. We found two quantitative trait loci (QTLs) in common, i.e., Aia1/Cia1 on chromosome 20, which includes the MHC, and Aia3/Cia3 on chromosome 4. We also identified a second unique QTL in AIA, Aia2, on chromosome 4. Interestingly, the QTL region on chromosome 4 (Aia3/Cia3), like the MHC, appears to be involved in several other autoimmune diseases in rats, including insulin-dependent diabetes, thyroiditis, and experimental autoimmune uveitis. Moreover, an analysis of conserved synteny among rats, mice, and humans suggested that Aia2 and Aia3/Cia3, like Aia1/Cia1, contain candidate genes for several autoimmune/inflammatory diseases in mice and humans, including diabetes, systemic lupus erythematosus, inflammatory bowel disease, asthma/atopy, multiple sclerosis, and RA. The rat models appear to provide a powerful complementary approach to identify and characterize candidate genes that may contribute to autoimmune diseases in several species.