Defective regulation of L1 endogenous retroelements in primary Sjogren’s syndrome and systemic lupus erythematosus:
Role of methylating enzymes
Clio P. Mavragani1,2, Adrianos Nezos2, Irina Sagalovskiy1, Surya Seshan3, Haralampos M. Moutsopoulos4, Mary K. Crow1
1Mary Kirkland Center for Lupus Research, Hospital for Special Surgery, Weill Medical College of Cornell University, New York, NY USA, 2Department of Physiology, School of Medicine, University of Athens, Athens, Greece, 3Department of Pathology, Weill Medical College of Cornell University, New York, NY, USA, 4Department of Pathophysiology, School of Medicine, University of Athens, Athens, Greece.
To investigate whether deranged methylation mechanisms are involved in the inappropriate expression of LINE-1 (L1) retroelements in primary Sjogren’s syndrome (SS) and systemic lupus erythematosus (SLE).
MATERIALS & METHODS
•Minor salivary glands (MSG) were obtained from 35 patients with primary SS [23 without adverse predictors for lymphoma development (SS-low risk), 12 complicated by B-cell lymphoma (SS-lymphoma)] and 17 sicca controls (SC).
• Additionally, kidney biopsy specimens and peripheral blood mononuclear cells (PBMCs) were obtained from 23 and 73 lupus patients, respectively.
• Relative mRNA expression was quantified for full-length L1 transcripts, along with mediators of methylation such as DNA methyltransferase (DNMT)3A, DNMT3B, DNMT1, methyl CpG binding protein 2 (MeCP2), and lymphoid-specific helicase (LSH, encoded by HELLS).
• In an independent set of 22 MSG samples (8 SS-low risk, 11 SS-lymphoma and 3 SC), as well as PBMC derived from 53 lupus and HC, methylation levels of the L1 promoter were determined by bisulphite pyrosequencing.
•Reduced levels of L1 promoter methylation along with increased DNMT3B, DNMT1, and MeCP2, but reduced LSH levels were detected in SS-low risk patients compared to both SS-lymphoma and SC (Figure 1).
• The SS-lymphoma group was also characterized by a profound decrease of MeCP2 and DNMT3B compared to SC (Figure 1).
• A strong positive correlation was demonstrated between L1 transcripts and gene products that mediate de novo and constitutive DNA methylation, DNMT3B, DNMT1 and MeCP2, in both SS MSG and lupus renal tissues (Figures 2 and 3).
•Reduced levels of L1 promoter methylation in lupus derived PBMC compared to HC (Table 1).
• A significantly negative correlation was observed between expression of L1 and LSH in both SS MSG and SLE kidney tissues, as well as between DNMT3A transcripts and L1 expression in SLE kidney tissues and PBMCs (Figures 2 and 3, Table 2).
Our data support a contributory role of altered methylation mechanisms in the pathogenesis of systemic autoimmune disorders and related lymphoproliferative processes and suggest that LSH and DNMT3A should be investigated as candidate upstream mediators of decreased L1 promoter methylation and increased L1 expression (Figure 4- proposed model).