Objective
To identify non-obvious therapeutic targets for rheumatoid arthritis, we performed an integrative analysis incorporating multiple ‘omics data and the ENCODE database for potential regulatory regions. This analysis identified the Limb Bud and Heart development (LBH) gene, which has risk alleles associated with RA/celiac disease and lupus, and can regulate cell proliferation in RA. We identified a novel LBH transcriptional enhancer with an RA-risk allele (rs906868 G (risk, Ref) /T) 6kb upstream of the LBH gene with a differentially methylated locus. The confluence of three regulatory elements, rs906868, an RA differentially methylated locus and a putative enhancer, led us to investigate their effect on LBH regulation in fibroblast-like synoviocytes (FLS).
Methods
We cloned the 1.4kb putative enhancer with either the rs906868 Ref allele or SNP variant into reporter constructs. The constructs were methylated in vitro and transfected into cultured FLS by nucleofection.
Results
We found that both variants increased transcription, thereby confirming the region’s enhancer function. Unexpectedly, the transcriptional activity of the Ref risk allele was significantly lower than the SNP variant and is consistent with low LBH levels as a risk factor for aggressive FLS behavior. Using RA FLS lines with homozygous Ref or SNP allele, we confirmed that homozygous Ref lines expressed lower LBH mRNA levels than the SNP lines. Methylation significantly reduced enhancer activity for both alleles, indicating that enhancer function is dependent on its methylation status.
Conclusion
This study shows how the interplay between genetics and epigenetics can affect expression of LBH in rheumatoid arthritis.