High activity levels in immune-related genes are associated with the malfunction of immune cells isolated from people with primary Sjogren’s syndrome, a small study revealed.
Such increased gene activity levels correlate with disease severity, the researchers found.
Titled “Identification of novel genes associated with dysregulation of B cells in patients with primary Sjögren’s syndrome,” the study was published in the journal Arthritis Research & Therapy.
Sjogren’s syndrome is an autoimmune disease in which the immune system mistakenly attacks salivary glands and those responsible for tear production (lachrymal glands), resulting in dry mouth and eyes. This autoimmune attack is led by malfunctioning B-cells — immune cells that typically generate antibodies to fight infections — leading to the overproduction of autoantibodies that target these glands.
However, the underlying mechanism describing how B-cells malfunction in people with primary Sjogren’s syndrome (pSS) remains unclear.
To address this question, a team led by researchers at the Keio University School of Medicine, in Japan, assessed gene activity (expression) in B-cells isolated from pSS patients and compared it with that of healthy people (controls).
Gene expression is the process in which the instructions contained in DNA are converted into a functional product, such as a protein. The first step of gene expression is to copy the DNA information to a molecule known as messenger RNA (mRNA) in a process called transcription. Measuring mRNAs from a cell provides information on gene expression.
Here, the team isolated B-cells from six pSS patients and six healthy controls. The cells were then separated into four subtypes based on their level of maturity, from early-stage B-cells that had not been activated to memory B-cells formed at the end of an immune response, which houses long-term immunity.
All of the patients were female and had dryness symptoms, pSS-related autoantibodies, and a biopsy-proven infection of the salivary glands. The healthy controls did not have immunological conditions, and the patients had not received immunosuppressive therapy. Clinical information was collected from medical records.
Two experiments were conducted on the participants’ B-cells. The first, a differentially expressed gene (DEG) analysis, measured the levels of RNA, coinciding with gene activity. The other was a weighted gene co-expression network analysis (WGCNA), which identifies genes active at the same time.
The results showed that in all B-cells subtypes found in the pSS patients, genes that stimulate a pathway called the interferon (IFN) pathway were highly expressed (upregulated), compared with controls. Of note, interferons are signaling proteins released by immune cells in response to infections or foreign substances.
Genes that encode proteins essential to immune responses, called human leukocyte antigens (HLA), also were upregulated in those with pSS.
The team then identified a molecule named LINC00487, known as a long non-coding RNA (lncRNA), that was significantly upregulated in B-cells from pSS patients compared with controls. The levels in those with pSS were about 10 times higher than those in the control group. lncRNAs are a type of RNA, different from mRNA, that is essential for the regulation of mRNAs and protein production.
The levels of LINC00487 significantly correlated with genes that control the production of interferon, the investigators found. In addition, the levels significantly correlated with the clinical disease activity score of the patients studied, as measured by the Primary Sjögren’s Syndrome Disease Activity Index.
A separate validation experiment, conducted on B-cells isolated from an additional 14 pSS patients and 12 controls, confirmed these results and identified a type of interferon, called interferon-alpha, as a stimulator of LINC00487 expression.
Finally, WGCNA analysis revealed six abnormal gene networks in pSS B-cells compared with controls.
The most significant network, which was associated with clinical disease severity and is enriched in the early stage of B-cell development in pSS patients, was related to the T-cell acute lymphocytic leukemia protein 1 (TAL1), necessary for the regulation of B-cell growth and development. Another vital gene central to many other genes was SOX4, which also is required for B-cell development.
“Our focus on B-cell subpopulation using a multi-level approach employing the analysis of DEGs and WGCNA identified significant genes and networks as novel players in the pathogenesis of pSS,” the researchers wrote.
Nonetheless, “to confirm our results, further study is needed,” the team concluded.
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