mRNA expression analysis confirms CD44 splicing impairment in systemic lupus erythematosus patients

Systemic Lupus Erythematosus (SLE) is a complex chronic autoimmune disease characterized by several immunological alterations. T cells have a peculiar role in SLE pathogenesis, moving from the bloodstream to the peripheral tissues, causing organ damage. This process is possible for their increased adherence and migration capacity mediated by adhesion molecules, such as CD44. Ten different variant isoforms of this molecule have been described, and two of them, CD44v3 and CD44v6 have been found to be increased on SLE T cells compared to healthy controls, being proposed as biomarkers of disease and disease activity. The process of alternative splicing of CD44 transcripts is not fully understood. We investigated the mRNA expression of CD44v3 and CD44v6 and also analyzed possible CD44 splicing regulators (ESRP1 molecule and rs9666607 CD44 polymorphism) in a cohort of SLE patients compared to healthy controls.

This study involved 18 SLE patients and 18 healthy controls. Total RNA and DNA were extracted by peripheral blood mononuclear cells. The expression study was conducted by quantitative RT-polymerase chain reaction, using SYBR Green protocol. Genotyping of rs9666607 SNP was performed by direct sequencing.

CD44v6 mRNA expression was higher in SLE patients compared to healthy controls (p = 0.028). CD44v3/v6 mRNA ratio in healthy controls was strongly unbalanced towards isoform v3 compared to SLE patients (p = 0.002) and decreased progressively from healthy controls to the SLE patients in remission and those with active disease (p = 0.015). The expression levels of CD44v3 and CD44v6 mRNA correlated with the disease duration (p = 0.038, Pearson r = 0.493 and p = 0.038, Pearson r = 0.495, respectively). Splicing regulator ESRP1 expression positively correlated with CD44v6 expression in healthy controls (p = 0.02, Pearson r = 0.532) but not in SLE patients. The variant A allele of rs9666607 of CD44 was associated with higher level of global CD44 mRNA (p = 0.04) but not with the variant isoforms.

In SLE patients, the increase in CD44v6 protein correlates with a higher transcript level of this isoform, confirming an impairment of CD44 splicing in the disease, whose regulatory mechanisms require further investigation.