Molecular pathology of systemic lupus erythematosus in Asians

2017-02-08T01:11:48Z (GMT) by Chai, Hwa Chia
Systemic lupus erythematosus (SLE) is a prototypic autoimmune disease affecting various parts of the body. Polymorphisms in genes involved in toll-like receptor (TLR)/interferon (IFN) signalling pathways have been reported previously to be associated with SLE in many populations. This study aimed to investigate the role of seven single nucleotide polymorphisms (SNPs) within TNFAIP3 (rs2230936 and rs3757173), STAT4 (rs7574865, rs10168266, and rs7601754), and IRF5 (rs4728142 and rs729302), that are involved in upstream and downstream pathway of type I IFN production, in the Malaysian SLE. Genotyping of 360 Malaysian SLE patients and 430 normal healthy individuals revealed that STAT4 rs7574865 and rs10168266 with their minor T alleles [p=0.001, odds ratio (OR)=1.40 and p=5.75x10-4, OR=1.43, respectively] and TNFAIP3 rs3757173 with its C allele (p=0.017, OR=1.66) were associated with elevated risk of SLE in the Malaysian patients, as well as in the Malays and Chinese. The minor G allele of TNFAIP3 rs2230926 was found to reduce the SLE risk (p=0.021, OR=0.53) in the Malaysian patients, particularly in the Malays. No association was observed for STAT4 rs7601754 and SNPs in IRF5 gene. Besides having haplotype TT (p=1 x 10-4, OR=1.53) and CG (p=0.02, OR=0.76) being significantly associated with SLE susceptibility, STAT4 rs7574865 and rs10168266 also formed the best model for high-risk group in multifactor dimensionality reduction (MDR) test. In conclusion, polymorphisms in STAT4 and TNFAIP3 genes could be potential genetic risk factors for SLE development in the Malaysian individuals. Genotyping analysis of two recently reported HLA variants demonstrated that the frequency for minor allele G and its homozygous GG of HLA-DRB1/HLA-DQA1 rs9271366 significantly higher in the Malaysian SLE patients (p=5.78 x 10-5, OR=1.63 and p=0.001, OR=3.30, respectively), as well as in the Malays and Chinese. Whereas, the minor allele T (p=1.93 x 10-5, OR=0.58) and the heterozygous CT (p=3.65 x 10-4, OR=0.54) of HLA-DQB1/HLA-DQA2 rs9275328 conferred protection to SLE in the Malaysians, including the Malays and Chinese. Both SNPs did not show associations with SLE in the Indians. Haplotype GC and AT were significantly associated with SLE (p<5.0 x 10-4) after 10000 permutations. The MDR test clustered the genotype combinations of GG and CC, and AG and CC of rs9271366 and rs9275328, accordingly, as high-risk group. These results consolidated the importance of HLA gene, which involved in the immune complex processing, in the Malaysian SLE. The seeking of potential SLE/lupus nephritis (LN)-associated protein biomarkers was attempted using two-dimensional difference gel electrophoresis (2D-DIGE) and liquid chromatography tandem mass spectrometry (LC-MS/MS) approaches. A total of 30 spots from 18 high-abundant (HAP)-depleted plasma proteins, 26 spots from 11 plasma HAPs, and 59 spots from 25 urinary proteins were identified to have differential expressions. Serum constitutional and transport proteins, including haptoglobin and histidine-rich glycoprotein, occupied the largest portion among both plasma and urinary proteins (~28%). Several proteins were newly discovered in the present study, such as afamin, hemopexin, retinol-binding protein 4, and vitamin D-binding protein. Group-specific proteins were also determined for each group of SLE/LN, for instance up-regulation of plasma alpha-1-antitrypsin and down-regulation of serum amyloid P-component were unique to SLE without kidney involvement, while decreased urinary protein AMBP was specific to LN class V. These proteins may have prospective diagnostic value to discriminate the types of SLE and classes of LN. Most differentially expressed plasma proteins returned to normal levels upon LN remission, while most urinary proteins remained at their abnormal levels. Interactions between SLE/LN-associated proteins analysed using IPA software summarized the networks or pathways responsible for the pathogenesis of each patient group. Network functions in cellular movement, inflammatory response, and cancer was associated with SLE without kidney involvement, whereas the top scored network generated for LN class II involved in cellular movement, haematological system development and function, and immune cell trafficking. Abnormal lipid metabolism, small molecule biochemistry, molecular transport, and vitamin and mineral metabolism were responsible for the development of LN class III. LN class IV was related to network implicated in cell cycle, cell death and survival, and tumor morphology. Connective tissue disorders, inflammatory disease, and skeletal and muscular disorders might increase the susceptibility to LN class V. Interestingly, networks having functions in immune and inflammatory responses were not as important as expected. Mycophenolate mofetil (MMF) is one of the promising immunosuppressants with less toxicity used in the treatment of LN. After 8 months of MMF treatment, LN class III patients showed level changes in 18 protein fragments derived from 10 plasma proteins, such as angiotensinogen, and 6 protein fragments from 4 urinary proteins, such as lysosomal alpha-glucosidase. The results might have uncovered the mechanism of action of MMF other than that has been described previously.