PADI4 gene in multiple sclerosis: A family-based association study

Role of Peptidylarginine Deiminase 4 in Central Nervous System Diseases

The deimination or citrullination of arginine residues in the polypeptide chain by peptidylarginine deiminase 4 alters the charge state of the polypeptide chain and affects the function of proteins. It is one of the main ways of protein post-translational modifications to regulate its function. Peptidylarginine deiminase 4 is widely expressed in multiple tissues and organs of the body, especially the central nervous system, and regulates the normal development of organisms. The abnormal expression and activation of peptidylarginine deiminase 4 is an important pathological mechanism for the occurrence and development of central nervous system diseases such as multiple sclerosis, Alzheimer's disease, cerebral ischemia reperfusion injury, and glioblastoma.

Some Common SNPs of the T-Cell Homeostasis-Related Genes Are Associated with Multiple Sclerosis, but Not with the Clinical Manifestations of the Disease, in the Polish Population

Purpose

Multiple sclerosis (MS) is an autoimmune disease, and genetic factors play an important role in its pathogenesis and progression. The aim of our study was to evaluate the frequencies of alleles and genetic variants of the T-cell homeostasis-related genes, in subjects with MS, as well as to investigate the association with MS clinical manifestations and disability.

Methods

94 subjects with MS and 160 healthy individuals have been genotyped for seven common single-nucleotide variants in IL-2RA, CTLA4, CD40, and PADI4 genes. The ages of onset, duration of the disease, and clinical condition of the MS subjects were analysed. We used the Chi² test confirmed with Fisher's exact test for statistical analysis.

Results

The frequency of allele T and CT/TT genotypes (rs7093069) in the IL2RA gene, as well as the T allele and CT/TT genotypes in rs12722598, were significantly higher in the control group. The significant differences between studied groups we also found for the G allele and GG/GA genotypes of rs3087243 in CTLA4 gene, which were more common among the control group. The heterozygous genotype TC (rs1883832) of CD40 gene was more common in the control subjects, and the frequency of the alleles and genotypes in the rs1748033 of the PADI4 gene did not differ between the studied groups. Between the studied genotypes, we did not observe any significant differences in the age of onset and duration of disease, including sex stratification.

Conclusion

Our results highlight the protective role of some of the T-cell homeostasis-related genetic variants in MS development, but not in its clinical manifestation.

Update on peptidylarginine deiminases and deimination in skin physiology and severe human diseases

Deimination (or citrullination) is a recently described post-translational modification, but its consequences are not yet well understood. It is catalysed by peptidylarginine deiminases (PADs). These enzymes transform arginyl residues involved in a peptidyl link into citrullyl residues in a calcium-dependent manner. Several PAD substrates have already been identified like filaggrin and keratins K1 and K10 in the epidermis, trichohyalin in hair follicles, but also ubiquitous proteins like histones. PADs act in a large panel of physiological functions as cellular differentiation or gene regulation. It has been suggested that deimination plays a role in many major diseases such as rheumatoid arthritis, multiple sclerosis, Alzheimer's disease and psoriasis. Five human genes (PADIs), encoding five highly conserved paralogous enzymes (PAD1-4 and 6), have been characterized. These genes are clustered in a single locus, at 1p35-36 in man. Only PAD1-3 are expressed in human epidermis. PADs seem to be controlled at transcriptional, translational and activity levels and they present particular substrate specificities. In this review, we shall discuss these main biochemical, genetic and functional aspects of PADs together with their pathophysiological implications.

Peptidylarginine deiminase 4 and citrullination in health and disease

Deimination is catalyzed by a family of calcium binding enzymes, called peptidylarginine deiminases (PADs). Among these, the PAD4 isoform has been more extensively studied for its role in some autoimmune diseases. PAD4 is localized in the cytoplasm of monocytes, T and B cells, neutrophils, eosinophils and NK cells and can move to the nucleus upon cell activation. PAD4 plays a physiological role in gene regulation via citrullination of histones. In rheumatoid arthritis (RA), PAD4 contributes to the generation of ACPA specific substrates and is itself a target of autoantibodies; alleles of the PADI4 gene confer susceptibility to RA in Asians but not in Caucasians. In multiple sclerosis, extensive deimination of brain proteins is observed in active lesions, but no role for the PADI4 gene in susceptibility to MS has been so far described.

The functional haplotype of peptidylarginine deiminase IV (S55G, A82V and A112G) associated with susceptibility to rheumatoid arthritis dominates apoptosis of acute T leukemia Jurkat cells

Peptidylarginine deiminase IV (PADI4) posttranslationally converts peptidylarginine to citrulline. It plays an essential role in immune cell differentiation and apoptosis. A haplotype of single-nucleotide polymorphisms (SNPs) in PADI4 is functionally relevant as a rheumatoid arthritis (RA) gene. It could increase enzyme activity leading to raised levels of citrullinated protein and stimulating autoantibody. Previously, our study showed that inducible PADI4 causes haematopoietic cell death. Herein, we further investigate whether RA risk PADI4 haplotype (SNP PADI4; S55G, A82V and A112G) and the increase of its enzymatic activity induce apoptosis. In the tetracycline (Tet)-On Jurkat T cells, ionomycin (Ion) only treatment didn't induce apoptosis however it promoted inducible PADI4-decreased cell viability and -enhanced apoptosis. Through in vitro and in vivo PADI enzyme activity assay, we demonstrated that PADI4 enzyme activity of SNP PADI4 was higher than RA non-risk PADI4 haplotype (WT PADI4). The effect of SNP PADI4-induced apoptosis was superior to WT PADI4. In addition, both Ion and SNP PADI4 synergistically provoked apoptosis were compared with both Ion and WT PADI4. Concurrently, in the conditionally inducible SNP PADI4 cells of Ion treatment-induced apoptosis, not only the expression of Bcl-xL was down-regulated and Bax up-regulated, but also cytochrome c was released from mitochondria to cytoplasm in significant amounts. Western blotting data showed the increase in apoptosomal caspase activation during programmed cell death in the inducible SNP PADI4 cells subsequent to Ion treatment. These data demonstrated that both SNP PADI4 increasing their enzyme activity could enhance apoptosis through the mitochondrial pathway and further provide a conceivable explanation in the pathogenesis of RA following the upregulation of PADI4 activity in its SNPs.

Molecular "negativity" may underlie multiple sclerosis: role of the myelin basic protein family in the pathogenesis of MS

Myelin basic protein (MBP) binds to negatively charged lipids on the cytosolic surface of oligodendrocyte membranes and is responsible for adhesion of these surfaces in the multilayered myelin sheath. The pattern of extensive posttranslational modifications of MBP is dynamic during normal central nervous system development and during myelin degeneration in multiple sclerosis (MS), affecting its interactions with the myelin membranes and other proteins. In particular, the degree of deimination (or citrullination) of MBP is correlated with the severity of MS, and may represent a primary defect that precedes neurodegeneration due to autoimmune attack. That MBP deimination also affects topological accessibility of an otherwise partially buried immunodominant epitope of the protein indicates that this modification may play a major role in the autoimmune pathogenesis of the disease. In this chapter, we describe the structural and functional consequences of MBP deimination in healthy and diseased myelin.