Single-nucleotide polymorphisms in the SPARC gene are not associated with susceptibility to scleroderma

Genetic Susceptibility to Interstitial Lung Disease Associated with Systemic Sclerosis

Systemic sclerosis (SSc) is a connective tissue disease that is characterized by tissue fibrosis, microvasculopathy, and autoimmunity. Interstitial lung disease (ILD) is a common complication of SSc and is one of the frequent causes of mortality in SSc. Although the exact etiology of SSc remains unknown, clinical and experimental investigations have suggested that genetic and environmental factors are relevant to the pathogenesis of SSc and SSc-ILD. More than 30 genes have been identified as susceptibility loci for SSc, most of which are involved in immune regulation and inflammation. It is thought that the key pathogenesis of SSc-ILD is caused by the release of profibrotic mediators such as transforming growth factor β1 and connective tissue growth factor from lung cells induced by a persistent damage. This review presents the genetic susceptibility to SSc-ILD, including human leukocyte antigen and non-human leukocyte antigen genes, especially focusing on connective tissue growth factor.

A single nucleotide polymorphism in osteonectin 3' untranslated region regulates bone volume and is targeted by miR-433

Osteonectin/SPARC is one of the most abundant noncollagenous extracellular matrix proteins in bone, regulating collagen fiber assembly and promoting osteoblast differentiation. Osteonectin-null and haploinsufficient mice have low-turnover osteopenia, indicating that osteonectin contributes to normal bone formation. In male idiopathic osteoporosis patients, osteonectin 3' untranslated region (UTR) single-nucleotide polymorphism (SNP) haplotypes that differed only at SNP1599 (rs1054204) were previously associated with bone mass. Haplotype A (containing SNP1599G) was more frequent in severely affected patients, whereas haplotype B (containing SNP1599C) was more frequent in less affected patients and healthy controls. We hypothesized that SNP1599 contributes to variability in bone mass by modulating osteonectin levels. Osteonectin 3' UTR reporter constructs demonstrated that haplotype A has a repressive effect on gene expression compared with B. We found that SNP1599G contributed to an miR-433 binding site, and miR-433 inhibitor relieved repression of the haplotype A, but not B, 3' UTR reporter construct. We tested our hypothesis in vivo, using a knock-in approach to replace the mouse osteonectin 3' UTR with human haplotype A or B 3' UTR. Compared with haplotype A mice, bone osteonectin levels were higher in haplotype B mice. B mice displayed higher bone formation rate and gained more trabecular bone with age. When parathyroid hormone was administered intermittently, haplotype B mice gained more cortical bone area than A mice. Cultured marrow stromal cells from B mice deposited more mineralized matrix and had higher osteocalcin mRNA compared with A mice, demonstrating a cell-autonomous effect on differentiation. Altogether, SNP1599 differentially regulates osteonectin expression and contributes to variability in bone mass, by a mechanism that may involve differential targeting by miR-433. This work validates the findings of the previous candidate gene study, and it assigns a physiological function to a common osteonectin allele, providing support for its role in the complex trait of skeletal phenotype. © 2014 American Society for Bone and Mineral Research.

Mapping QTL affecting a systemic sclerosis-like disorder in a cross between UCD-200 and red jungle fowl chickens

Systemic sclerosis (SSc) or scleroderma is a rare, autoimmune, multi-factorial disease characterized by early microvascular alterations, inflammation, and fibrosis. Chickens from the UCD-200 line develop a hereditary SSc-like disease, showing all the hallmarks of the human disorder, which makes this line a promising model to study genetic factors underlying the disease. A backcross was generated between UCD-200 chickens and its wild ancestor - the red jungle fowl and a genome-scan was performed to identify loci affecting early (21 days of age) and late (175 days of age) ischemic lesions of the comb. A significant difference in frequency of disease was observed between sexes in the BC population, where the homogametic males were more affected than females, and there was evidence for a protective W chromosome effect. Three suggestive disease predisposing loci were mapped to chromosomes 2, 12 and 14. Three orthologues of genes implicated in human SSc are located in the QTL region on chromosome 2, TGFRB1, EXOC2-IRF4 and COL1A2, as well as CCR8, which is more generally related to immune function. IGFBP3 is also located within the QTL on chromosome 2 and earlier studies have showed increased IGFBP3 serum levels in SSc patients. To our knowledge, this study is the first to reveal a potential genetic association between IGFBP3 and SSc. Another gene with an immunological function, SOCS1, is located in the QTL region on chromosome 14. These results illustrate the usefulness of the UCD-200 chicken as a model of human SSc and motivate further in-depth functional studies of the implicated candidate genes.

Genetic susceptibility to systemic sclerosis from clinical aspect to genetic factor analyses

BACKGROUND

Systemic sclerosis is a rare autoimmune disease mainly characterized by vascular alteration and fibrosis involving skin but also visceral organs such as lungs, digestive tract, and heart. This disease leads to high morbidity and mortality. Its pathogenesis remains unclear, but recent attention has focus on genetic factors.

OBJECTIVE

We first recall the main manifestations associated with systemic sclerosis and leading to its diagnosis and prognosis. Then we propose an overview on human genetics studies, as a number of genetic loci have been identified that appear to be associated with the disease.

METHODS

Articles concerning association studies with candidate genes encoding for extracellular matrix proteins, cytokines, growth factors, chemokines, and proteins involved in vascular tone and immune regulations are presented and discussed.

RESULTS/CONCLUSION

Systemic sclerosis is a multigenic complex disorder. Genetic associations are observed in distinct phenotypes such as the diffuse cutaneous form or the limited form, or in association with specific autoantibody pattern. Promising candidate genes are those involved in pathways that lead to the vascular damage and fibrosis. A better knowledge of crucial mediators involved in systemic sclerosis could in the future provide new therapeutic strategies to control the disease.

Osteonectin/SPARC polymorphisms in Caucasian men with idiopathic osteoporosis

Animal models suggest a role for osteonectin/SPARC in determination of bone mass. We found haplotypes consisting of three single nucleotide polymorphisms (SNPs) in the 3' untranslated region (UTR) of the osteonectin gene are associated with bone density in Caucasian men with idiopathic osteoporosis.

INTRODUCTION

Osteonectin is a matricellular protein regulating matrix assembly, osteoblast differentiation, and survival. Animal studies indicate that osteonectin is essential for normal bone mass. The 3' UTR is a regulatory region controlling mRNA stability, trafficking, and translation, and we determined whether osteonectin 3' UTR haplotypes could be associated with bone mass and/or idiopathic osteoporosis.

METHODS

Single strand conformation polymorphism and allele-specific PCR analysis were used to assess alleles at osteonectin cDNA bases 1046, 1599, and 1970, using genomic DNA from middle-aged Caucasian men with idiopathic, low turnover osteoporosis (n = 56) and matched controls (n = 59). Bone density was measured by DXA at spine, hip and radius. Allele and haplotype frequencies were analyzed by Chi square analysis and Fisher's exact test.

RESULTS

Five common osteonectin 3' UTR haplotypes were identified. The frequency of one haplotype (1046C-1599C-1970T) was higher in controls compared with patients, and this haplotype was also associated with higher bone densities at multiple sites in patients. In contrast, a second haplotype (1046C-1599G-1970T) was associated with lower bone densities in patients at multiple sites.

CONCLUSIONS

Osteonectin regulates skeletal remodeling and bone mass in animals, and haplotypes in the 3' UTR of this gene are associated with bone density in Caucasian men with idiopathic osteoporosis.

Genetics and genomic studies in scleroderma (systemic sclerosis)

It currently is believed that scleroderma is a complex polygenic disease that occurs in genetically predisposed individuals who have encountered specific environment exposures and/or other stochastic factors. The nature of these genetic determinants and how they interact with environmental factors are areas of active investigation. This article discusses the evidence that supports a strong genetic link to scleroderma. These studies implicate potential pathogenetic mechanisms involved in scleroderma, which, it is hoped, may translate into clinical utility, including determination of disease risk, diagnosis, prognosis, and novel therapeutics.

Genetic basis for systemic sclerosis

Among the connective tissue diseases, systemic sclerosis is an orphan disease in which diffuse connective tissue alterations lead to multi-organ involvement. Environmental factors implicated in triggering this multifactorial disease include crystalline silica, chlorine solvents, welding vapors, and various other solvents. Clustering within families indicates a role for genetic factors. Although concordance for the disease among identical twins is low, concordance for autoantibodies associated with systemic sclerosis and for fibroblast gene expression profiles is higher. Because multiplex families are rare, association and candidate gene strategies are the most appropriate methods for investigating the genetics of systemic sclerosis. The most consistent data relate to the involvement of fibrosis genes, most notably the TGF-beta regulation pathway, secreted protein acid and rich in cysteine (SPARC) genes, and the fibrillin-1 gene (FBN1). Several variants of genes for cytokines or their receptors may be involved. Data on the vasculopathy characteristic of systemic sclerosis are somewhat conflicting. Investigations into the genetics of systemic sclerosis may shed light on the complex pathophysiology of this disease, help to identify factors that predict organ involvement, and suggest new treatment strategies.

Genetic factors in systemic sclerosis

A number of genetic loci have been identified that appear to be associated with systemic sclerosis (SSc; scleroderma). There is mounting evidence suggesting that these genetic associations may in fact be associated with distinct phenotypes in SSc based on autoantibody pattern rather than with SSc as a single disease entity. This may ultimately have implications for approaches to therapy as well as responses to therapy. The most promising candidate genes are those involved in pathways that lead to the vascular damage and fibrosis that are the hallmarks of this disease. There is uncertainty, however, regarding the nature of the key pathological mechanisms that link these two disease processes. Recent studies have focused on Fli1 (friend leukaemia integration 1), a transcription factor that is found in immune cells, fibroblasts, and endothelial cells that regulates collagen gene function and angiogenesis. Fli1 is dysregulated in SSc skin and dermal blood vessels, and appears to play a pathological role in SSc skin fibrosis and vessel degeneration. Whether this dysregulation is due to genetic polymorphisms in the Fli1 pathway or to epigenetic mechanisms is not clear.

Evidence of potential interaction of chemokine genes in susceptibility to systemic sclerosis

OBJECTIVE

To examine genetic polymorphisms in the chemokine pathway, and to assess their interactions in relation to susceptibility to systemic sclerosis (SSc).

METHODS

To identify the risk of SSc conferred by genetic polymorphisms in the chemokine pathway, 10 single-nucleotide polymorphisms (SNPs) from 8 candidate genes were studied in 99 patients with SSc and 198 age- and sex-matched controls in a Korean population. SNPs were genotyped by polymerase chain reaction-restriction fragment length polymorphism or sequence-specific primer methods. Genetic associations between each SNP and SSc risk, calculated as odds ratios with 95% confidence intervals, were estimated using chi-square tests. Haplotypes for the 2 polymorphisms in the gene CCL5 (RANTES) were constructed, and their associations with SSc were tested. Gene-gene interactions were investigated using a recently described novel method, and the results were confirmed by conditional logistic regression. Adjustment for multiple testing was based on Bonferroni correction.

RESULTS

There was significant evidence of gene-gene interaction between polymorphisms in the genes CXCL8 (interleukin-8) and CCL5, and both of these were associated with an increased risk of SSc. This SNP-SNP interaction was confirmed by 2 independent statistical methods. The associations remained significant after Bonferroni adjustment for multiple testing. No significant association between each individual SNP or haplotype and the risk of SSc was found.

CONCLUSION

Crosstalk between the 2 chemokines CXCL8 and CCL5 may contribute to the susceptibility to SSc.

Expression of osteonectin and matrix Gla protein in scleroderma patients with and without calcinosis

OBJECTIVES

Our aim was to evaluate (i) whether the bone matrix proteins osteonectin and matrix gamma-carboxyglutamic acid protein (MGP) are up-regulated in skin biopsies from patients with systemic sclerosis (SSc) and (ii) whether there is differential expression between patients with and without dermal calcinosis, a distressing and debilitating complication of SSc.

METHODS

Skin punch biopsies were taken from the forearms of 38 SSc patients with the limited cutaneous subtype of SSc [17 without calcinosis (lcSSc) and 21 with calcinosis (lcSScCal)] and from 11 healthy control subjects. Immunohistochemistry was performed with antibodies to osteonectin and MGP. Staining was assessed semiquantitatively in the microvascular endothelium and in dermal fibroblasts. The Kruskal-Wallis one-way ANOVA was used to compare the data between patient groups.

RESULTS

Both lcSSc and lcSScCal groups showed a statistically significant increase in the percentage of microvessels with osteonectin-positive endothelial cells (EC) (especially the lcSScCal group), whereas lcSScCal alone showed an increase in the percentage of microvessels with MGP-positive EC when compared with controls. In both SSc groups, the percentage of osteonectin and MGP-stained fibroblasts was increased in the reticular dermis (for osteonectin this was more marked in the lcSScCal group). In the papillary dermis, the percentage of osteonectin-stained fibroblasts was increased in both SSc groups but the lcSScCal group alone had a higher percentage of MGP-stained fibroblasts.

CONCLUSIONS

When compared with controls, protein expression of osteonectin and MGP was greater in SSc patients generally, and osteonectin expression was significantly higher in EC and fibroblasts of the lcSScCal patients than the lcSSc patients without calcinosis.

Genetics of scleroderma: update on single nucleotide polymorphism analysis and microarrays

PURPOSE OF REVIEW

Recent family, twin, and genetic association studies suggest a genetic basis for the susceptibility to systemic sclerosis or scleroderma. The purpose of this review is to summarize the results of genetic association and gene expression profiling studies from January 2004 to May 2005.

RECENT FINDINGS

In the review period, only a handful reports on single nucleotide polymorphism analysis of candidate genes and transcriptional profiling have been published.

SUMMARY

Currently, single nucleotide polymorphism association studies in systemic sclerosis use small sample sizes and have low reproducibility. To detect associations with candidate genes that confer a modest relative risk for disease in the general population, studies are needed with much larger sample sizes that also account for the effects of population stratification. Candidate genes or pathways identified through microarrays can be explored as potential biomarkers, used for molecular phenotyping of systemic sclerosis, or targeted for future genetic association studies.