LACC1 polymorphisms in inflammatory bowel disease and juvenile idiopathic arthritis

Crohn's Disease-associated variant in laccase domain containing 1 (LACC1) modulates T cell gene expression, metabolism and T cell function

Genome wide association studies (GWAS) identify many risks for Crohn's disease (CD), including a site near the metabolism gene laccase domain containing 1 (LACC1). We previously found this site near LACC1 was associated with decreased LACC1 expression in T lymphocytes, yet the mechanism affecting gene expression and its links to T cell function and inflammatory disease were unknown. Here we identify variants in the promoter region that influence transcription of LACC1. Direct association of disease-risk variants with lower LACC1 pre-mRNA in human CD4+ T cells is confirmed by comparing transcripts from each allele from donors heterozygous for the LACC1 CD-risk allele. Using gene editing, we validate the function of this promoter region in LACC1 expression in T cells. Human CD4+ T cells with LACC1 gene knockdown show altered metabolism, including reduced oxygen consumption rate, and reduced in vitro regulatory T cell differentiation. Therefore, our study provides a mechanism linking these specific LACC1 variants to colitis by attributing promoter region variants to changes in T cell metabolism and function.

Purine metabolite inosine induced by transforming growth factor‑β promotes epithelial‑mesenchymal transition in colorectal cancer

Transforming growth factor-β (TGF-β) signaling pathway serves a pivotal role in the pathogenesis of colorectal cancer (CRC). However, the specific molecular mechanisms by which the TGF-β signaling pathway regulates CRC are still not fully understood. In the present study, metabolomics and transcriptomics were used to screen for key metabolites and regulatory genes most related to the regulation of the TGF-β signaling pathway in CRC. Additionally, reverse transcription-quantitative PCR, western blotting and Transwell assays were performed to assess the process of epithelial-mesenchymal transition (EMT). Metabolomics analysis indicated that TGF-β1 has an impact on purine metabolism, leading to an increase in the purine metabolite inosine. The increase of inosine is essential for facilitating EMT and cell migration in CRC cells. Furthermore, the integrated analysis of metabolomics and transcriptomics data revealed that TGF-β1 induces the expression of laccase domain-containing 1 (LACC1), an enzyme involved in the regulation of inosine. Knockdown of LACC1 resulted in a reduction of TGF-β1-induced alterations in inosine levels, EMT and cell migration in CRC cells. The results of the present study suggest that the TGF-β signaling pathway is involved in the regulation of purine metabolism in CRC through the modulation of LACC1 expression. Furthermore, LACC1 appears to influence EMT and cell migration by elevating the levels of the purine metabolite inosine.

LACC1 deficiency leading to juvenile arthritis and anemia

OBJECTIVE

Juvenile arthritis caused by loss-of-function LACC1 mutations is characterized by early onset of symmetric and chronic arthritis, associated with an elevation of inflammatory markers. We aimed to describe serum cytokine levels, explore the type I interferon pathway, and evaluate the efficacy of treatment in a patient presenting with polyarthritis and anemia caused by novel compound heterozygous variations in LACC1.

METHODS

Clinical data of a patient with compound heterozygous variations in LACC1 was collected. Serum cytokine levels and IFN-stimulated cytokine genes were analyzed at diagnosis, at disease flare, and after treatment. Full-length cDNA of LACC1 was checked by RNA analysis. Single-cell RNA sequencing was performed in PBMCs.

RESULTS

Two novel variants in the LACC1 gene were identified in a patient presenting with polyarthritis and anemia. LACC1-cDNA was normally expressed in the healthy control, the target production at 1384 bp was not observed in the patient. Compared to nine patient controls with non-systemic juvenile idiopathic arthritis, serum interleukin(IL)-6 level was significantly elevated in the affected patient. The median IFN score for the patient, her mother, and controls were 118, 8, and 4.9, respectively. The combined treatment of JAK inhibitors with prednisone or tocilizumab led to a complete response, including remission of joint symptoms, resolution of anemia, reduced expression of IFN-stimulated cytokine genes, and normalized levels of inflammatory markers, including CRP, ESR, SAA, and serum IL-6.

CONCLUSION

LACC1 may play a crucial role in multiple inflammatory signaling pathways. The combination therapy of JAK inhibitors and tocilizumab may be effective for a subset of refractory patients.

Lupeol alleviates autoimmune myocarditis by suppressing macrophage pyroptosis and polarization via PPARα/LACC1/NF-κB signaling pathway

BACKGROUND

Autoimmune myocarditis, with increasing incidence and limited therapeutic strategies, is in urgent need to explore its underlying mechanisms and effective drugs. Pyroptosis is a programmed cell death that may contribute to the pathogenesis of myocarditis. Nonetheless, no direct evidence validated the role of pyroptosis in autoimmune myocarditis. Lupeol (Lup), a pentacyclic triterpene, possesses various biological activities such as antidiabetic properties. However, the effects of Lup on autoimmune myocarditis and pyroptosis remain unelucidated.

PURPOSE

This study aimed to reveal the role of pyroptosis in autoimmune myocarditis and explore the protective effects of Lup, and its engaged mechanisms.

METHODS

The experimental autoimmune myocarditis (EAM) mouse model was established by immunization with a fragment of cardiac myosin in Balb/c mice. Lup and MCC950 were administered after EAM induction. The protective effects were assessed by inflammation score, cardiac injury, chronic fibrosis, and cardiac function. Mechanistically, the effects of Lup on the M1 polarization and pyroptosis of macrophages were evaluated. Transcriptome sequencing and molecular docking were subsequently employed, and the underlying mechanisms of Lup were further explored in vitro with small interfering RNA and adenovirus.

RESULTS

Administration of Lup and MCC950 alleviated EAM progression. Western blotting and immunofluorescence staining identified macrophages as the primary cells undergoing pyroptosis. Lup inhibited the expression of pyroptosis-associated proteins in macrophages during EAM in a dose-dependent manner. Furthermore, Lup suppressed pyroptosis in both bone marrow-derived macrophages (BMDMs) and THP-1-derived macrophages in vitro. In addition, Lup inhibited the M1 polarization of macrophages both in vivo and in vitro. Mechanistically, the protective effects of Lup were demonstrated via the suppression of the nuclear factor-κΒ (NF-κB) signaling pathway. Transcriptome sequencing and molecular docking revealed the potential involvement of peroxisome proliferator-associated receptor α (PPARα). Subsequently, we demonstrated that Lup activated PPARα to reduce the expression level of LACC1, thereby inhibiting the NF-κB pathway and pyroptosis.

CONCLUSION

Our findings indicated the crucial role of macrophage pyroptosis in the pathogenesis of EAM. Lup ameliorated EAM by inhibiting the M1 polarization and pyroptosis of macrophages through the PPARα/LACC1/NF-κB signaling pathway. Thus, our results provided a novel therapeutic target and agent for myocarditis.

LACC1 regulates changes in the intestinal flora in a mouse model of inflammatory bowel disease

BACKGROUND

The aim of this study was to explore the mechanism whereby LACC1 regulates the intestinal flora in a mouse model of inflammatory bowel disease (IBD).

METHODS

C57BL/6 and Lacc1-/- mice were used to establish a mouse model of IBD induced by dextran sodium sulfate (DSS). The effects of Lacc1 deletion in mice were evaluated. Changes in the body weight and stool blood were recorded daily. After 7 days of successful modeling, the mice were sacrificed, blood was collected from the eyeballs, the entire colon was dissected and separated, and the length of the colon was measured.

RESULTS

Compared with the wild-type (WT) DSS model group, the Lacc1-/- DSS model group showed a significantly higher disease activity index score (P < 0.05), significantly faster weight loss (P < 0.05), and a significantly shorter colon (P < 0.05), indicating that the colonic mucosal tissue was seriously damaged in the Lacc1-/- DSS model group (P < 0.05). Serum IL-1β, IL-6, TNF-α, and IFN-γ levels were significantly higher in the Lacc1-/- DSS model group than the WT DSS model group. Principal coordinate analysis showed that there were significant microbiome differences between the WT, Lacc1-/-, WT DSS model, and Lacc1-/- DSS model groups (P < 0.05). Linear discriminant analysis effect size analysis showed that under natural conditions, Lacc1-/- mice had significant changes in their intestinal flora compared with control mice (LDA value > 3 or < 3, P < 0.05).

CONCLUSIONS

Lacc1 deletion aggravates DSS-induced IBD in mice.

Clinical characteristics and genotype analysis of a Chinese patient with juvenile arthritis due to novel LACC1 frameshift mutation and literature review

BACKGROUND

Some juvenile idiopathic arthritis (JIA) patients have a familial aggregation of the disease, and a few have been found to have a juvenile arthritis (JA) phenotype caused by a genetic mutation. JA due to LACC1 defects is a rare condition and it was never reported in China.

METHODS

The clinical and molecular characteristics of a child with LACC1 gene mutation-related juvenile arthritis, diagnosed by high-throughput sequencing in Wuhan children's Hospital in 2021 were analyzed retrospectively; The literature and database were reviewed to summarize the clinical data and genotype characteristics of patients with JA caused by LACC1 gene mutation.

RESULTS

Here, we report a 19-month-old Chinese male patient who presented with bilateral limb edema without a history of fever. Laboratory tests showed had moderate anemia and signs of inflammation: hemoglobin of 76 g/L, white blood cell count of 20.53 × 10⁹ , and platelet count of 1194 × 10⁹ ; MRI showed the patient had synovitis and tenosynovitis in bilateral hands and wrists. Whole-exome sequencing (WES) detected compound heterozygous variants, novel c.446_449dupTAAA and c.889T>C, in the LACC1 gene. Of the 52 patients reported in the literature (including this case), 38.9% had clinical symptoms of systemic juvenile idiopathic arthritis (sJIA), which tended to be caused by loss-of-function (LOF) mutation. Findings in this study expanded the spectrum of pathogenic variants and reveal the phenotypic heterogeneity of LACC1-JA.

CONCLUSIONS

Our study reported a rare case of juvenile arthritis, which is due to the compound heterozygous mutation of LACC1, including a new novel frameshift mutation c.446_449dupTAAA, and LACC1 C297R variant causes disease by potentially modifying the local conformation of proteins. The clinical and genetic findings in our study show that LACC1-JA is highly heterogeneous, and gene testing is required for juvenile arthritis patients with a high inflammatory response at a young onset age.

Long-term presence of autoantibodies in plasma of cured leprosy patients

Autoantibodies have been detected in leprosy patients, indicating that infection with M. leprae may lead to autoimmune disorders. However, whether autoimmune response last until patients are cured is unknown. Knowing the autoimmune response in cured leprosy patients is essential to identify whether symptoms are caused by leprosy itself or by other immune-related diseases. This knowledge is essential for the ongoing health management in cured leprosy patients where autoimmune disorders still exist. In our study, we selected six autoantibodies, including anticardiolipin antibody of IgG (ACA), anti-nuclear antibody (ANA), extractable nuclear antigen antibody (ENA), anti-streptolysin O (ASO), anti-double stranded DNA antibody (dsDNA), and rheumatoid factor (RF), that had been reported in leprosy patients as typical autoantibodies. We tested the six typical autoantibodies combined with LACC1, which encodes a protein associated with autoimmune disease such as Crohn's disease and is also the susceptible gene conferring leprosy risk, in cured leprosy patients through ELISA to assess the cured patient's immune status. We observed high positive rates of autoantibodies in cured leprosy patients, and the average plasma levels of five (ACA, ANA, ENA, ASO, and RF) out of the six autoantibodies were significantly higher in cured leprosy patients than in controls. The positive detection of autoantibodies is independent of the recovery period. Moreover, the level of these autoantibodies showed a strong positive correlation with the level of LACC1 in both controls and cured patients. This study showed that there is long-term autoimmunological activation in leprosy patients, even after decades of recovery. Autoimmune responses may influence the development and prognosis of leprosy. Special care should be given to posttreatment or cured leprosy patients regarding long-term autoimmunological activation.

Crohn's disease in a patient with systemic onset juvenile idiopathic arthritis. Association or associated side effect of treatment?

The progression of systemic-onset juvenile idiopathic arthritis (JIAs) to the different forms of presentation of inflammatory bowel disease is extremely rare. We present the first report of a patient with SJIA that progressed to Crohn's disease in which mutations have been detected in genes responsible for the adequate regulation of the innate immune system.

LACC1 bridges NOS2 and polyamine metabolism in inflammatory macrophages

The mammalian immune system uses various pattern recognition receptors to recognize invaders and host damage and transmits this information to downstream immunometabolic signalling outcomes. Laccase domain-containing 1 (LACC1) protein is an enzyme highly expressed in inflammatory macrophages and serves a central regulatory role in multiple inflammatory diseases such as inflammatory bowel diseases, arthritis and clearance of microbial infection^1-4. However, the biochemical roles required for LACC1 functions remain largely undefined. Here we elucidated a shared biochemical function of LACC1 in mice and humans, converting L-citrulline to L-ornithine (L-Orn) and isocyanic acid and serving as a bridge between proinflammatory nitric oxide synthase (NOS2) and polyamine immunometabolism. We validated the genetic and mechanistic connections among NOS2, LACC1 and ornithine decarboxylase 1 (ODC1) in mouse models and bone marrow-derived macrophages infected by Salmonella enterica Typhimurium. Strikingly, LACC1 phenotypes required upstream NOS2 and downstream ODC1, and Lacc1^-/- chemical complementation with its product L-Orn significantly restored wild-type activities. Our findings illuminate a previously unidentified pathway in inflammatory macrophages, explain why its deficiency may contribute to human inflammatory diseases and suggest that L-Orn could serve as a nutraceutical to ameliorate LACC1-associated immunological dysfunctions such as arthritis or inflammatory bowel disease.

Structural analysis of the peptidoglycan editing factor PdeF from Bacillus cereus ATCC 14579

The coding gene for peptidoglycan editing factor (pdeF) is located in the division and cell wall (dcw) cluster, and encodes a protein that has an editing function for misplaced amino acids in peptidoglycan in E. coli. In this study, we determined the crystal structure of PdeF from Bacillus cereus (BcPdeF) at a 1.60 Å resolution. BcPdeF exists as a monomer in solution and consists of two domains: a core domain containing a Pfam motif DUF152 and a smaller subdomain. The X-ray fluorescence spectrum of BcPdeF crystal elucidated that the protein has a Zn2+ ion in its active site and the metal ion was coordinated by two histidine and one cysteine residue. We also performed docking calculations of the N-acetylmuramate (MurNAc)-L-Ser-D-iGlu ligand in the BcPdeF structure and revealed the substrate binding mode of the enzyme. Furthermore, structural comparisons between BcPdeF and human fatty acid metabolism-immunity nexus (FAMIN), which also contains the DUF152 motif in its core domain, provided a structural basis how the two structurally similar proteins have completely different physiological functions.

Arf6 regulates energy metabolism in neutrophils

The small GTPase Arf6 regulates many cellular processes, including cytoskeletal remodeling, receptor endocytosis, and pathogen phagocytosis. Arf6 silencing in neutrophil (PMN)-like cells is well-known to inhibit chemotactic peptide-mediated activation of phospholipase D, the oxidative burst, and β2 integrin-dependent adhesion. In conditional knockout (cKO) mice, the migration to inflammatory sites of Arf6-deficient PMNs was diminished and associated with reduced cell surface expression of β2 integrins. In this study we assessed the impact of Arf6 depletion on the functions and gene expression profile of PMNs isolated from the mouse air pouch. Numerous genes involved in response to oxygen levels, erythrocyte and myeloid differentiation, macrophage chemotaxis, response to chemicals, apoptosis, RNA destabilization, endosome organization, and vesicle transport were differentially expressed in PMNs cKO for Arf6. Lpar6 and Lacc-1 were the most up-regulated and down-regulated genes, respectively. The deletion of Arf6 also decreased Lacc-1 protein level in PMNs, and silencing of Arf6 in THP-1 monocytic cells delayed LPS-mediated Lacc-1 expression. We report that fMLP or zymosan-induced glycolysis and oxygen consumption rate were both decreased in air pouch PMNs but not in bone marrow PMNs of Arf6 cKO mice. Reduced oxygen consumption correlated with a decrease in superoxide and ROS production. Deletion of Arf6 in PMNs also reduced phagocytosis and interfered with apoptosis. The data suggest that Arf6 regulates energy metabolism, which may contribute to impaired phagocytosis, ROS production, and apoptosis in PMN-Arf6 cKO. This study provides new information on the functions and the inflammatory pathways influenced by Arf6 in PMNs.

Association of novel rare coding variants with juvenile idiopathic arthritis

OBJECTIVE

Juvenile idiopathic arthritis (JIA) is the most common type of arthritis among children, but a few studies have investigated the contribution of rare variants to JIA. In this study, we aimed to identify rare coding variants associated with JIA for the genome-wide landscape.

METHODS

We established a rare variant calling and filtering pipeline and performed rare coding variant and gene-based association analyses on three RNA-seq datasets composed of 228 JIA patients in the Gene Expression Omnibus against different sets of controls, and further conducted replication in our whole-exome sequencing (WES) data of 56 JIA patients. Then we conducted differential gene expression analysis and assessed the impact of recurrent functional coding variants on gene expression and signalling pathway.

RESULTS

By the RNA-seq data, we identified variants in two genes reported in literature as JIA causal variants, as well as additional 63 recurrent rare coding variants seen only in JIA patients. Among the 44 recurrent rare variants found in polyarticular patients, 10 were replicated by our WES of patients with the same JIA subtype. Several genes with recurrent functional rare coding variants have also common variants associated with autoimmune diseases. We observed immune pathways enriched for the genes with rare coding variants and differentially expressed genes.

CONCLUSION

This study elucidated a novel landscape of recurrent rare coding variants in JIA patients and uncovered significant associations with JIA at the gene pathway level. The convergence of common variants and rare variants for autoimmune diseases is also highlighted in this study.

LACC1 deficiency links juvenile arthritis with autophagy and metabolism in macrophages

Juvenile idiopathic arthritis is the most common chronic rheumatic disease in children, and its etiology remains poorly understood. Here, we explored four families with early-onset arthritis carrying homozygous loss-of-expression mutations in LACC1. To understand the link between LACC1 and inflammation, we performed a functional study of LACC1 in human immune cells. We showed that LACC1 was primarily expressed in macrophages upon mTOR signaling. We found that LACC1 deficiency had no obvious impact on inflammasome activation, type I interferon response, or NF-κB regulation. Using bimolecular fluorescence complementation and biochemical assays, we showed that autophagy-inducing proteins, RACK1 and AMPK, interacted with LACC1. Autophagy blockade in macrophages was associated with LACC1 cleavage and degradation. Moreover, LACC1 deficiency reduced autophagy flux in primary macrophages. This was associated with a defect in the accumulation of lipid droplets and mitochondrial respiration, suggesting that LACC1-dependent autophagy fuels macrophage bioenergetics metabolism. Altogether, LACC1 deficiency defines a novel form of genetically inherited juvenile arthritis associated with impaired autophagy in macrophages.

A novel loss-of-function mutation in LACC1 underlies hereditary juvenile arthritis with extended intra-familial phenotypic heterogeneity

OBJECTIVE

To investigate phenotypic and molecular characteristics of a consanguineous family with autosomal-recessive, polyarticular, juvenile idiopathic arthritis (JIA) with extra-articular manifestations, including renal amyloidosis and Crohn's disease, associated with a novel homozygous truncating variant in LACC1.

METHODS

Whole exome sequencing (WES) or targeted Sanger verification were performed in 15 participants. LACC1 expression and cytokine array were analyzed in patient-derived and CRISPR/Cas9-generated LACC1-knockout macrophages (Mϕ).

RESULTS

A homozygous truncating variant (p.Glu348Ter) in LACC1 was identified in three affected and one asymptomatic family member, and predicted harmful by causing premature stop of the LACC1 protein sequences, and by absence from ethnically-matched controls and public variation databases. Expression studies in patient-derived macrophages (Mϕ) showed no endogenous p. Glu348Ter-LACC1 RNA transcription or protein expression, compatible with nonsense-mediated mRNA decay. WES analysis in the asymptomatic homozygous subject for p. Glu348Ter-LACC1 detected an exclusive heterozygous variant (p.Arg928Gln) in complement component C5. Further complement activity analysis suggested a protective role for the p. Arg928Gln-C5 variant as a phenotypic modifier of LACC1-associated disease. Finally, cytokine profile analysis indicated increased levels of pro-inflammatory cytokines in LACC1-disrupted as compared with wild-type Mϕ.

CONCLUSIONS

Our findings reinforce the role of LACC1 disruption in autosomal-recessive JIA, extend the clinical spectrum and intra-familial heterogeneity of the disease-associated phenotype, indicate a modulatory effect of complement factor C5 on phenotypic severity, and suggest an inhibitory role for wild-type LACC1 on pro-inflammatory pathways.

Inflammatory Bowel Disease in Children With Systemic Juvenile Idiopathic Arthritis

OBJECTIVE

The incidence of inflammatory bowel disease (IBD) in juvenile idiopathic arthritis (JIA) is higher than in the general pediatric population. However, reports of IBD in the systemic JIA (sJIA) subtype are limited. We sought to characterize sJIA patients diagnosed with IBD and to identify potential contributing risk factors.

METHODS

Using an internationally distributed survey, we identified 16 patients with sJIA who were subsequently diagnosed with IBD (sJIA-IBD cohort). Five hundred twenty-two sJIA patients without IBD were identified from the CARRA Legacy Registry and served as the sJIA-only cohort for comparison. Differences in demographic, clinical characteristics, and therapy were assessed using chi-square test, Fisher exact test, t-test, and univariate and multivariate logistic regression, as appropriate.

RESULTS

Of the patients with sJIA-IBD, 75% had a persistent sJIA course and 25% had a history of macrophage activation syndrome. sJIA-IBD subjects were older at sJIA diagnosis, more often non-White, had a higher rate of IBD family history, and were more frequently treated with etanercept or canakinumab compared to sJIA-only subjects. Sixty-nine percent of sJIA-IBD patients successfully discontinued sJIA medications following IBD diagnosis, and sJIA symptoms resolved in 9 of 12 patients treated with tumor necrosis factor-α (TNF-α) inhibitors.

CONCLUSION

IBD in the setting of sJIA is a rare occurrence. The favorable response of sJIA symptoms to therapeutic TNF-α inhibition suggests that the sJIA-IBD cohort may represent a mechanistically distinct sJIA subgroup. Our study highlights the importance of maintaining a high level of suspicion for IBD when gastrointestinal involvement occurs in patients with sJIA and the likely broad benefit of TNF-α inhibition in those cases.

Systemic juvenile idiopathic arthritis and macrophage activation syndrome: update on pathogenesis and treatment

PURPOSE OF REVIEW

The past decade has seen substantial progress in defining the cause and pathogenesis of the chronic childhood arthropathy systemic juvenile idiopathic arthritis (SJIA) and its related complication macrophage activation syndrome (MAS). The purpose of this review is to describe and synthesize advances in this field, particularly since 2016, with the potential to transform clinical practice.

RECENT FINDINGS

Newly developed MAS classification criteria have been further studied and validated in other diseases and populations, as well as a recently proposed score to distinguish MAS from familial hemophagocytic lymphohistiocytosis. There has also been substantial progress toward understanding the genetic underpinnings of SJIA and MAS, both through targeted study of specific genes and the results of a large genome-wide association study. The immunopathogenesis of SJIA has been further elucidated through several studies regarding the proinflammatory cytokines interleukin-18, interferon (IFN)γ, and how their interplay impacts emergence of MAS. Finally, big data studies integrating genomic information with immunophenotypes have potential to provide novel insights into disease mechanisms in SJIA.

SUMMARY

Collectively, these research advances have significant implications regarding the classification and diagnosis of SJIA and MAS, and support a next generation of biologic treatments including kinase inhibitors and targeted interleukin-18 or IFNγ blockade.

Using genes to triangulate the pathophysiology of granulomatous autoinflammatory disease: NOD2, PLCG2 and LACC1

The intersection of granulomatosis and autoinflammatory disease is a rare occurrence that can be generally subdivided into purely granulomatous phenotypes and disease spectra that are inclusive of granulomatous features. NOD2 (nucleotide-binding oligomerization domain-containing protein 2)-related disease, which includes Blau syndrome and early-onset sarcoidosis, is the prototypic example of granulomatous inflammation in the context of monogenic autoinflammation. Granulomatous inflammation has also been observed in two related autoinflammatory diseases caused by mutations in PLCG2 (phospholipase Cγ2). More recently, mutations in LACC1 (laccase domain-containing protein 1) have been identified as the cause of a monogenic form of systemic juvenile idiopathic arthritis, which does not itself manifest granulomatous inflammation, but the same LACC1 mutations have also been shown to cause an early-onset, familial form of a well-known granulomatous condition, Crohn's disease (CD). Rare genetic variants of PLCG2 have also been shown to cause a monogenic form of CD, and moreover common variants of all three of these genes have been implicated in polygenic forms of CD. Additionally, common variants of NOD2 and LACC1 have been implicated in susceptibility to leprosy, a granulomatous infection. Although no specific mechanistic link exists between these three genes, they form an intriguing web of susceptibility to both monogenic and polygenic autoinflammatory and granulomatous phenotypes.

Biallelic loss-of-function LACC1/FAMIN Mutations Presenting as Rheumatoid Factor-Negative Polyarticular Juvenile Idiopathic Arthritis

Juvenile idiopathic arthritis (JIA) is a complex rheumatic disease with both autoimmune and autoinflammatory components. Recently, familial cases of systemic-onset JIA have been attributed to mutations in LACC1/FAMIN. We describe three affected siblings from a Moroccan consanguineous family with an early-onset chronic, symmetric and erosive arthritis previously diagnosed as rheumatoid factor (RF)-negative polyarticular JIA. Autozygosity mapping identified four homozygous regions shared by all patients, located in chromosomes 3, 6 (n:2) and 13, containing over 330 genes. Subsequent whole exome sequencing identified two potential candidate variants within these regions (in FARS2 and LACC1/FAMIN). Genotyping of a cohort of healthy Moroccan individuals (n: 352) and bioinformatics analyses finally supported the frameshift c.128_129delGT mutation in the LACC1/FAMIN gene, leading to a truncated protein (p.Cys43Tyrfs*6), as the most probable causative gene defect. Additional targeted sequencing studies performed in patients with systemic-onset JIA (n:23) and RF-negative polyarticular JIA (n: 44) revealed no pathogenic LACC1/FAMIN mutations. Our findings support the homozygous genotype in the LACC1/FAMIN gene as the defect underlying the family here described with a recessively inherited severe inflammatory joint disease. Our evidences provide further support to the involvement of LACC1/FAMIN deficiency in different types of JIA in addition to the initially described systemic-onset JIA.

Targeted Analysis of Serum Proteins Encoded at Known Inflammatory Bowel Disease Risk Loci

BACKGROUND

Few studies have investigated the blood proteome of inflammatory bowel disease (IBD). We characterized the serum abundance of proteins encoded at 163 known IBD risk loci and tested these proteins for their biomarker discovery potential.

METHODS

Based on the Human Protein Atlas (HPA) antibody availability, 218 proteins from genes mapping at 163 IBD risk loci were selected. Targeted serum protein profiles from 49 Crohn's disease (CD) patients, 51 ulcerative colitis (UC) patients, and 50 sex- and age-matched healthy individuals were obtained using multiplexed antibody suspension bead array assays. Differences in relative serum abundance levels between disease groups and controls were examined. Replication was attempted for CD-UC comparisons (including disease subtypes) by including 64 additional patients (33 CD and 31 UC). Antibodies targeting a potentially novel risk protein were validated by paired antibodies, Western blot, immuno-capture mass spectrometry, and epitope mapping.

RESULTS

By univariate analysis, 13 proteins mostly related to neutrophil, T-cell, and B-cell activation and function were differentially expressed in IBD patients vs healthy controls, 3 in CD patients vs healthy controls and 2 in UC patients vs healthy controls (q < 0.01). Multivariate analyses further differentiated disease groups from healthy controls and CD subtypes from UC (P < 0.05). Extended characterization of an antibody targeting a novel, discriminative serum marker, the laccase (multicopper oxidoreductase) domain containing 1 (LACC1) protein, provided evidence for antibody on-target specificity.

CONCLUSIONS

Using affinity proteomics, we identified a set of IBD-associated serum proteins encoded at IBD risk loci. These candidate proteins hold the potential to be exploited as diagnostic biomarkers of IBD.

Biochemistry of Autoinflammatory Diseases: Catalyzing Monogenic Disease

Monogenic autoinflammatory disorders are a group of conditions defined by systemic or localized inflammation without identifiable causes, such as infection. In contrast to classical primary immunodeficiencies that manifest with impaired immune responses, these disorders are due to defects in genes that regulate innate immunity leading to constitutive activation of pro-inflammatory signaling. Through studying patients with rare autoinflammatory conditions, novel mechanisms of inflammation have been identified that bare on our understanding not only of basic signaling in inflammatory cells, but also of the pathogenesis of more common inflammatory diseases and have guided treatment modalities. Autoinflammation has further been implicated as an important component of cardiovascular, neurodegenerative, and metabolic syndromes. In this review, we will focus on a subset of inherited enzymatic deficiencies that lead to constitutive inflammation, and how these rare diseases have provided insights into diverse areas of cell biology not restricted to immune cells. In this way, Mendelian disorders of the innate immune system, and in particular loss of catalytic activity of enzymes in distinct pathways, have expanded our understanding of the interplay between many seemingly disparate cellular processes. We also explore the overlap between autoinflammation, autoimmunity, and immunodeficiency, which has been increasingly recognized in patients with dysregulated immune responses.

LACC1 Regulates TNF and IL-17 in Mouse Models of Arthritis and Inflammation

Both common and rare genetic variants of laccase domain-containing 1 (LACC1, previously C13orf31) are associated with inflammatory bowel disease, leprosy, Behcet disease, and systemic juvenile idiopathic arthritis. However, the functional relevance of these variants is unclear. In this study, we use LACC1-deficient mice to gain insight into the role of LACC1 in regulating inflammation. Following oral administration of Citrobacter rodentium, LACC1 knockout (KO) mice had more severe colon lesions compared with wildtype (WT) controls. Immunization with collagen II, a collagen-induced arthritis (CIA) model, resulted in an accelerated onset of arthritis and significantly worse arthritis and inflammation in LACC1 KO mice. Similar results were obtained in a mannan-induced arthritis model. Serum and local TNF in CIA paws and C. rodentium colons were significantly increased in LACC1 KO mice compared with WT controls. The percentage of IL-17A-producing CD4⁺ T cells was elevated in LACC1 KO mice undergoing CIA as well as aged mice compared with WT controls. Neutralization of IL-17, but not TNF, prevented enhanced mannan-induced arthritis in LACC1 KO mice. These data provide new mechanistic insight into the function of LACC1 in regulating TNF and IL-17 during inflammatory responses. We hypothesize that these effects contribute to immune-driven pathologies observed in individuals carrying LACC1 variants.

Disease-specific regulation of gene expression in a comparative analysis of juvenile idiopathic arthritis and inflammatory bowel disease

BACKGROUND

The genetic and immunological factors that contribute to differences in susceptibility and progression between sub-types of inflammatory and autoimmune diseases continue to be elucidated. Inflammatory bowel disease and juvenile idiopathic arthritis are both clinically heterogeneous and known to be due in part to abnormal regulation of gene activity in diverse immune cell types. Comparative genomic analysis of these conditions is expected to reveal differences in underlying genetic mechanisms of disease.

METHODS

We performed RNA-Seq on whole blood samples from 202 patients with oligoarticular, polyarticular, or systemic juvenile idiopathic arthritis, or with Crohn's disease or ulcerative colitis, as well as healthy controls, to characterize differences in gene expression. Gene ontology analysis combined with Blood Transcript Module and Blood Informative Transcript analysis was used to infer immunological differences. Comparative expression quantitative trait locus (eQTL) analysis was used to quantify disease-specific regulation of transcript abundance.

RESULTS

A pattern of differentially expressed genes and pathways reveals a gradient of disease spanning from healthy controls to oligoarticular, polyarticular, and systemic juvenile idiopathic arthritis (JIA); Crohn's disease; and ulcerative colitis. Transcriptional risk scores also provide good discrimination of controls, JIA, and IBD. Most eQTL are found to have similar effects across disease sub-types, but we also identify disease-specific eQTL at loci associated with disease by GWAS.

CONCLUSION

JIA and IBD are characterized by divergent peripheral blood transcriptomes, the genetic regulation of which displays limited disease specificity, implying that disease-specific genetic influences are largely independent of, or downstream of, eQTL effects.

Functional Analyses of the Crohn's Disease Risk Gene LACC1

BACKGROUND

Genetic variation in the Laccase (multicopper oxidoreductase) domain-containing 1 (LACC1) gene has been shown to affect the risk of Crohn's disease, leprosy and, more recently, ulcerative colitis and juvenile idiopathic arthritis. LACC1 function appears to promote fatty-acid oxidation, with concomitant inflammasome activation, reactive oxygen species production, and anti-bacterial responses in macrophages. We sought to contribute to elucidating LACC1 biological function by extensive characterization of its expression in human tissues and cells, and through preliminary analyses of the regulatory mechanisms driving such expression.

METHODS

We implemented Western blot, quantitative real-time PCR, immunofluorescence microscopy, and flow cytometry analyses to investigate fatty acid metabolism-immune nexus (FAMIN; the LACC1 encoded protein) expression in subcellular compartments, cell lines and relevant human tissues. Gene-set enrichment analyses were performed to initially investigate modulatory mechanisms of LACC1 expression. A small-interference RNA knockdown in vitro model system was used to study the effect of FAMIN depletion on peroxisome function.

RESULTS

FAMIN expression was detected in macrophage-differentiated THP-1 cells and several human tissues, being highest in neutrophils, monocytes/macrophages, myeloid and plasmacytoid dendritic cells among peripheral blood cells. Subcellular co-localization was exclusively confined to peroxisomes, with some additional positivity for organelle endomembrane structures. LACC1 co-expression signatures were enriched for genes involved in peroxisome proliferator-activated receptors (PPAR) signaling pathways, and PPAR ligands downregulated FAMIN expression in in vitro model systems.

CONCLUSION

FAMIN is a peroxisome-associated protein with primary role(s) in macrophages and other immune cells, where its metabolic functions may be modulated by PPAR signaling events. However, the precise molecular mechanisms through which FAMIN exerts its biological effects in immune cells remain to be elucidated.

Genetic Risk for Inflammatory Bowel Disease Is a Determinant of Crohn's Disease Development in Chronic Granulomatous Disease

BACKGROUND

Approximately, one-third to one-half of children with chronic granulomatous disease (CGD) develop gastrointestinal inflammation characteristic of idiopathic inflammatory bowel disease (IBD), usually Crohn's disease. We hypothesized that the overall IBD genetic risk, determined by IBD genetic risk score (GRS), might in part determine IBD development in CGD.

METHODS

We reviewed medical records to establish IBD diagnoses in CGD subjects seen at NIAID. IBD risk single nucleotide polymorphism genotypes were determined using the Immunochip, and GRS were estimated by Mangrove.

RESULTS

Among 157 white patients with CGD, 55 were confirmed, 78 excluded, and 24 were uncertain for IBD. Two hundred one established, independent European IBD risk single nucleotide polymorphisms passed quality control. After sample quality control and removing non-IBD CGD patients with perianal disease, mean GRS for 40 unrelated patients with CGD-IBD was higher than 53 CGD non-IBD patients (in log2-scale 0.08 ± 1.62 versus -0.67 ± 1.64, P = 0.026) but lower than 239 IBD Genetics Consortium (IBDGC) young-onset Crohn's disease cases (0.76 ± 1.60, P = 0.025). GRS for non-IBD CGD was similar to 609 IBDGC controls (-0.69 ± 1.60, P = 0.95). Seven established IBD single nucleotide polymorphisms were nominally significant among CGD-IBD versus CGD non-IBD, including those near LACC1 (P = 0.005), CXCL14 (P = 0.007), and TNFSF15 (P = 0.016).

CONCLUSIONS

The weight of the common IBD risk alleles are significant determinants of IBD in CGD. However, IBD risk gene burden among CGD children with IBD is significantly lower than that in nonsyndromic pediatric Crohn's disease, congruent with the concept that defective superoxide production in CGD is also a major IBD risk factor. Individual IBD genes might interact with the CGD defect to cause IBD in CGD.