Molecular insights into onset of autoimmunity in SARS-CoV-2 infected patients.

Some of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infected patients are facing long-term devastating effects like induction of autoimmune diseases. Here, I discuss molecular mechanisms and risk factors involved in the induction of autoimmune diseases after SARS-CoV-2 infections. Transcript editing genes were upregulated during SARS-CoV-2 infections, which might have edited host gene transcripts and paved the way for autoantigens generation and presented as nonself to generate autoantibodies followed by auto immunogenicity after SARS-CoV-2 infections. Therefore, some SARS-CoV-2 patients acquire autoimmunity. The transient and/or innocuous autoimmune response in some SARS-CoV-2 infected patients may be due to a lack of repeated production of autoantibodies to host autoantigens and/or viral antigens, which are needed to boost autoimmune response. In the future, SARS-CoV-2 mediated autoimmune disease onset will be a challenging task. Therefore, possible preventive measures and strategies to minimize and/or preclude such SARS-CoV-2 mediated autoimmune diseases have been presented in this commentary.

Is Tolerance Broken in Autoimmunity?

Autoimmune diseases are classified into about 80 different types based on their specificity related to system, organ and/or tissue. About 5% of the western population is affected by this anomaly, but its worldwide incidence is unknown. Autoimmune diseases are heterogeneous in nature and clinical manifestations range from benign disorders to life-threatening conditions. Autoimmunity strikes at any stage of life, but age and/or gender also play role in onset of some of these anomalies. The autoimmune pathogenesis is initiated by the origination of autoantigens, which leads to the development of autoantibodies followed by auto-immunogenicity and the ultimate onset of autoimmunity. There is a lack of suitable therapies to treat autoimmune diseases, because mechanisms involved in the onset of these anomalies were poorly understood. Present therapies are limited to symptomatic treatment and come with severe side effects. Here, I described the molecular mechanisms and cellular events involved in the initiation of autoimmunity and proposed better strategies to modulate such molecular and cellular anomalies, which will help in preventing and/or controlling autoimmune pathogenesis and ultimately aid in enhancing the quality of life.

Altered editing in cyclic nucleotide phosphodiesterase 8A1 gene transcripts of systemic lupus erythematosus T lymphocytes.

The aetiopathogenesis of the abnormal immune response in systemic lupus erythematosus (SLE) remains incompletely understood. We and other investigators demonstrated altered expression of adenosine deaminase that act on RNA (ADAR) genes in SLE patients. Based on this information, we hypothesize that the altered expression and function of ADAR enzymes is a mechanism for the immunopathogenesis of SLE. ADARs edit gene transcripts through site-specific conversion of adenosine to inosine by hydrolytic deamination at C6 of the adenosine. Thirteen SLE subjects and eight healthy controls were studied. We assessed the role of ADAR enzymes in editing of PDE8A1 gene transcripts of normal and SLE T cells. These studies demonstrated the occurrence of ADAR-catalysed altered and site-selective editing profile of specific sites in the PDE8A1 gene transcripts of normal and SLE T cells. Two hot spots for A to I editing were observed in the PDE8A1 transcripts of normal and SLE T cells. A fundamental finding of this study is A to I hypo-editing followed by up-regulation of PDE8A1 transcripts in SLE T cells. These results are confirmed by analysing PDE8A1 transcripts of normal T cells activated with type I interferon-alpha. It is proposed that, the altered expression of ADAR enzymes tilt the balance of editing machinery and alter editing in SLE transcriptome. Such altered editing may contribute to the modulation of gene regulation and ultimately, immune functions in SLE and play an important role in the initiation and propagation of SLE pathogenesis.

Induction of 150-kDa adenosine deaminase that acts on RNA (ADAR)-1 gene expression in normal T lymphocytes by anti-CD3-epsilon and anti-CD28.

We and other investigators have demonstrated up-regulation of the expression of the RNA-editing gene 150-kDa adenosine deaminase that acts on RNA (ADAR1) in systemic lupus erythematosus (SLE) T cells and B cells, peripheral blood mononuclear cells (PBMC), natural killer (NK) cells. The presence of a small proportion of activated T cells is the hallmark of SLE. Therefore, it was hypothesized that 150-kDa ADAR1 gene expression is induced by the physiological activation of T cells. To examine this hypothesis, normal T cells were activated by anti-CD3-epsilon plus anti-CD28 for various time periods from 0 to 48 hr. The expression of 110-kDa and 150-kDa ADAR1, and interleukin (IL)-2 and beta-actin gene transcripts was analysed. An approximately fourfold increase in 150-kDa ADAR1 gene expression was observed in activated T cells. ADAR2 gene transcripts are substrates for ADAR1 and ADAR2 enzymes. Therefore, we assessed the role of the 150-kDa ADAR enzyme in editing of ADAR2 gene transcripts. In activated T cells, site-selective editing of the -2 site was observed. Previous studies indicate that this site is predominantly edited by ADAR1. In addition to this, novel editing sites at base positions -56, -48, -45, -28, -19, -15, +46 and +69 were identified in activated T cells. On the basis of these results, it is proposed that 150-kDa ADAR1 gene expression is selectively induced in T cells by anti-CD3-epsilon and anti-CD28 stimulation and that it may play a role in site-selective editing of gene transcripts and in altering the functions of several gene products of T cells during activation and proliferation.

Altered editing in RNA editing adenosine deaminase ADAR2 gene transcripts of systemic lupus erythematosus T lymphocytes.

Adenosine Deaminases that act on RNA (ADARs) edit gene transcripts through site-specific conversion of adenosine to inosine by hydrolytic deamination at C6 of the adenosine. ADAR2 gene transcripts are substrates for the ADAR1 and ADAR2 enzymes and their expression is regulated by editing at the - 1 and - 2 sites. Our previous experiments demonstrated up-regulation of type I interferon (IFN) inducible 150 kDa ADAR1 in systemic lupus erythematosus (SLE) T cells. In this study we investigate the role of ADAR1 and ADAR2 in editing of ADAR2 gene transcripts of healthy controls and SLE patients. The ADAR2 gene transcripts were cloned into pCR2.1-TOPO vectors. A total of 150 clones from SLE and 150 clones from controls were sequenced. Sequence analysis demonstrated A to I editing at - 1, + 10, + 23 and + 24 in normal T cells. In SLE clones site-selective editing of the - 2 site was observed as a result of type I IFN-inducible 150 kDa ADAR1 expression. These results are confirmed by analysing ADAR2 transcripts of normal T cells activated with type I IFN-alpha. Editing of the + 23 and + 24 sites was decreased in SLE T cells compared to normal controls. In addition to A to G changes, U to C discrepancies were observed in normal and SLE T cells. In SLE cells, positions - 6 and + 30 were frequently edited from U to C compared to normal controls. Taken together, these results demonstrate altered and site-selective editing in ADAR2 transcripts of SLE patients. Based on these results, it is proposed that altered transcript editing contributes to the modulation of gene expression and immune functions in SLE patients.

Mechanisms of deficient type I protein kinase A activity in lupus T lymphocytes.

Systemic lupus erythematosus (SLE) is an autoimmune disease in which the immune response to antigen results in exaggerated CD4(+) T helper and diminished CD8(+) T cytotoxic responses. To determine the mechanisms underlying impaired T cell effector functions, we have investigated the cAMP/protein kinase A (cAMP/PKA) signaling pathway. The results demonstrate that diminished PKA-catalyzed protein phosphorylation is the result of deficient type I (PKA-I) and type II (PKA-II) isozyme-specific activities. The prevalence of deficient PKA-I and PKA-II activities in SLE T cells is approximately 80% and 40%, respectively. Diminished PKA-I activities are not associated with disease activity and appear to be stable over time. Two disparate mechanisms account for these low PKA-I and PKA-II isozyme activities. Moreover, novel transcript mutations of the RI alpha gene have been identified that are characterized by deletions, transitions, and transversions. Most mutations are clustered adjacent to GAGAG motifs and CT repeats. In conclusion, aberrant signaling via the cAMP/PKA pathway occurs in SLE T cells, and this is proposed to contribute to abnormal T cell effector functions.

Transcript mutations of the alpha regulatory subunit of protein kinase A and up-regulation of the RNA-editing gene transcript in lupus T lymphocytes.

BACKGROUND: Systemic lupus erythematosus (SLE) is an autoimmune disorder characterised by diverse dysfunctions of immune effector cells, including proliferation and cytotoxicity. In T cells from patients with SLE, activity of type 1 protein kinase A isozymes is greatly reduced because of decreased expression of the alpha and beta regulatory subunits (RI alpha and RI beta). We aimed to identify a molecular mechanism or mechanisms for this isozyme deficiency by assessing occurrence of mutations in transcripts of the RI alpha subunit in patients with SLE. METHODS: We cloned and sequenced cDNA of RI alpha and corresponding genomic DNA of the coding region to detect sequence changes from eight patients with SLE and six healthy controls. Because transcript editing is regulated by adenosine deaminases that act on RNA (ADAR), we quantified expression of ADAR1 transcripts in SLE and control T cells by competitive PCR. FINDINGS: Sequence analyses of cDNA showed heterogeneous transcript mutations, including deletions, transitions, and transversions. We identified 1.22 x 10(-3)/bp transcript mutations in SLE T cells-a frequency 7.5 times higher than that in control T cells. By contrast, we identified no genomic mutations. Two hotspots were identified in the RI alpha subunit transcripts from SLE T cells, one located adjacent to a pseudosubstrate site of the RI alpha subunit and the other a component of the cAMP binding A domain. ADAR1 mRNA content was 3.5 times higher in SLE cells than in control T cells (p=0.001). INTERPRETATION: An RNA-editing enzyme could be converting adenosine to inosine within double-stranded regions of RNA, resulting in transcript mutations. This process could be one mechanism resulting in mutations in the RI alpha subunit of type 1 protein kinase A.