Background/Purpose:  Heritable epigenetic phenomena may play a role in the parent-of-origin effect observed in psoriasis and psoriatic arthritis (PsA). A previous epigenome-wide association study (EWAS) identified differentially methylated regions (DMRs) in sperm cells of PsA and psoriasis patients without PsA (PsC) compared to controls. This study aimed to assess differential methylation and expression of these regions in somatic tissues.

Methods: Genomic DNA was extracted from whole blood of PsC patients (n=24), PsA patients satisfying the CASPAR criteria (n=13), and controls (n=19). All subjects were males whose semen was previously analyzed by EWAS. DNA was bisulfite converted and the most biologically interesting and statistically significant EWAS hits (oxysterol binding protein like 5 [OSBPL5], myelin basic protein [MBP], imprinted maternally expressed transcript H19, small nucleolar RNA C/D box 115 [SNORD115], E74 like ETS transcription factor 5 [ELF5], interleukin 22 [IL22], protein tyrosine phosphatase receptor type N [PTPRN2], junctional adhesion molecule 3 [JAM3], and cysteinyl-tRNA synthetase 2 [CARS2]) were analyzed by pyrosequencing. Group-wise methylation differences were compared by Student’s t test or Wilcoxon rank sum test. Multivariable logistic regression was also performed to adjust for age and psoriasis area and severity index (PASI). Whole blood RNA was collected in Tempus and Paxgene tubes and extracted with their respective kits. Differential expression was analyzed by qRT-PCR using the ΔΔCt method with normalization to glyceraldehyde-3-phosphate dehydrogenase (GAPDH).

Results:  In whole blood, CpG sites within JAM3, MBP, and PTPRN2 were differentially methylated in PsA vs. controls. JAM3 and ELF5 were differentially methylated in PsA vs. PsC. MBP was differentially methylated in PsC vs. controls (p<0.05). After adjustment for age, MBP (OR=0.1, 95% CI 0.1-0.75, p=0.03) and PTPRN2 (two CpG sites: OR=2.1, 95% CI 1.0-4.3, p=0.04 and OR=2.2, 95% CI 1.0-4.9, p=0.049) remained significantly associated with PsA vs. controls. After adjustment for age and PASI, JAM3 (OR=26.7, 95% CI 2.6-276, p=0.006) and ELF5 (OR=31.5, 95% CI 1.6-628, p=0.02) remained significantly associated with PsA vs PsC. No CpG sites were differentially methylated in PsC vs. controls in age-adjusted analyses. All genes except for ELF5, PTPRN2, and IL22 were expressed at detectable levels in whole blood. Preliminary qRT-PCR results showed significantly higher expression of CARS2 mRNA transcripts in PsA (fold change=1.18, p=0.02) and PsC patients (fold change=1.24, p=0.046) compared to controls, but no significant differences in the levels of JAM3 and MBP between groups.

Conclusion:  Several germ line DMRs associated with PsC and PsA were differentially methylated in whole blood. The presence of these DMRs in both the germ line and whole blood suggests they may be heritable epigenetic phenomena associated with PsC and PsA. Investigation of these sites in additional somatic tissues, and in extended patient populations is necessary to strengthen the evidence that they are true heritable epigenetic variations.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/validation-of-germ-line-epigenetic-variants-associated-with-psoriatic-disease/