Peptidyl Arginine Deiminase Type 4 Gene Promoter Hypo-Methylation in Rheumatoid Arthritis

Abstract

Protein citrullination is carried out by peptidylarginine deiminase type 4 (PAD4) enzyme. As a consequence of this process, post-translationally modified proteins are formed that become antigens for anti-citrullinated protein antibodies (ACPA). The study aimed at identifying whether the PADI4 gene is subject to epigenetic regulation through methylation of its promoter region, whether the degree of methylation differs in healthy individuals vs. rheumatoid arthritis (RA) patients and changes in correlation with ACPA, anti-PAD4 and disease activity. A total of 125 RA patients and 30 healthy controls were enrolled. Quantitative real-time methylation-specific PCR was used to analyze the methylation status. ACPA and anti-PAD4 antibodies were determined in serum by enzyme-linked immunosorbent immunoassay. The differences were observed in the degree of PADI4 gene promoter methylation between RA patients and HC, along with an upward trend for the methylation in RA, which was inversely proportional to the disease activity. A weak or modest negative correlation between the degree of PADI4 gene methylation and anti-PAD4, disease activity score (DAS28) and ACPA level has been found. The elevated methylation is associated with lower disease activity, lower levels of ACPA and aPAD4. The methylation degree in this area is growing up during effective treatment and might play a role in the RA pathophysiology and therefore could be a future therapeutic target.

The lack of association between PADI4_94 or PADI4_104 polymorphisms and RF, ACPA and anti-PAD4 in patients with rheumatoid arthritis

“…In addition to genetic factors associated with RA, epigenetic changes have been reported in the PADI4 gene. Increased methylation in the promoter region was associated with lower disease activity, lower levels of ACPA, and anti-PAD4 antibodies 26 .…”

Catalytic Antibodies May Contribute to Demyelination in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome

“…Without the positive charge of arginine to keep it anchored to the phospholipid bilayer in the major dense line of the myelin sheath, MBP becomes unfolded in the cytoplasm making it a prime target for immunogenic attack. 66,67 Moreover, anticitrullinated protein autoantibodies have been found to be highly specific in several autoimmune diseases, including rheumatoid arthritis, where inhibition of PAD shows therapeutic potential. 65,68 Patients with ME/CFS may also present with fluctuations in severity of the disease akin to MS where symptoms rise and fall through cycles of relapse and remission.…”

“…For example, in the cerebellum, three primary covalent modifications were found: (1) deamidation of asparagine and glutamine, (2) isomerization of aspartic acid, which leads to protein cross-linking and aggregation, and (3) deimination of arginine to citrulline, which is irreversibly catalyzed by the epigenetically controlled peptidylarginine deiminase (PAD); this is an especially important modification because citrulline, which has zero charge and is not a natural component of the MBP sequence, causes profound changes to the protein structure. Without the positive charge of arginine to keep it anchored to the phospholipid bilayer in the major dense line of the myelin sheath, MBP becomes unfolded in the cytoplasm making it a prime target for immunogenic attack. , Moreover, anticitrullinated protein autoantibodies have been found to be highly specific in several autoimmune diseases, including rheumatoid arthritis, where inhibition of PAD shows therapeutic potential. , …”

The Citrullination-Neutrophil Extracellular Trap Axis in Chronic Diseases

“…While all PAD genes were expressed in RA synovium, only PAD2 and PAD4 enzymes were found in RA patients compared to controls [ 49 ]. Unsurprisingly, methylation status of PAD4 gene was inversely correlated with RA severity and ACPA concentration [ 50 ]. Autoantibodies against PAD4 were observed in both the preclinical phase of RA [ 51 ] and RA patients [ 52 ].…”