The locus control region of the MHC class II promoter acts as a repressor element, the activity of which is inhibited by CIITA

Association of CIITA (rs8048002) and CLEC2D (rs2114870) gene variants and type 1 diabetes mellitus

Background

Type I diabetes mellitus (T1DM) is a significant health challenge, especially for children, owing to its chronic autoimmune nature. Although the exact etiology of T1DM remains elusive, the interplay of genetic predisposition, immune responses, and environmental factors are postulated. Genetic factors control immune reactivity against β-cells. Given the pivotal roles of CIITA and CLEC2D genes in modulating a variety of immune pathologies, we hypothesized that genetic variations in CIITA and CLEC2D genes may impact T1DM disease predisposition. This study was designed to explore the association between gene polymorphisms in CIITA (rs8048002) and CLEC2D (rs2114870) and type 1 diabetes (T1DM), with a focus on analyzing the functional consequence of those gene variants.

Methods

The study enlisted 178 healthy controls and 148 individuals with type 1 diabetes (T1DM) from Suez Canal University Hospital. Genotyping for CIITA and CLEC2D was done using allelic-discrimination polymerase chain reaction (PCR). Levels of glycated hemoglobin (HbA1c) and lipid profiles were determined through automated analyzer, while fasting blood glucose and insulin serum levels were measured using the enzyme-linked immunosorbent assay (ELISA) technique. RegulomeDB was used to examine the regulatory functions of CIITA (rs8048002) and CLEC2D (rs2114870) gene variants.

Results

Analysis of the genotype distribution of the CIITA rs8048002 polymorphism revealed a significantly higher prevalence of the rare C allele in T1DM patients compared to the control group (OR = 1.77; P = 0.001). Both the CIITA rs8048002 heterozygote TC genotype (OR = 1.93; P = 0.005) and the rare homozygote CC genotype (OR = 3.62; P = 0.006) were significantly more frequent in children with T1DM when compared to the control group. Conversely, the rare A allele of CLEC2D rs2114870 was found to be significantly less frequent in T1DM children relative to the control group (OR = 0.58; P = 0.002). The heterozygote GA genotype (OR = 0.61; P = 0.033) and the rare homozygote AA genotype (OR = 0.25; P = 0.004) were also significantly less frequent in T1DM patients compared to the control group. Both CIITA (rs8048002) and CLEC2D (rs2114870) gene variants were predicted to have regulatory functions, indicated by a RegulomeDB score of (1f) for each.

Conclusion

The rare C allele of CIITA rs8048002 genetic variant was associated with an increased risk of developing T1DM, while the less common A allele of CLEC2D rs2114870 was associated with a reduced risk of T1DM.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40200-024-01402-w.

Induction of CIITA by IFN-γ in macrophages involves STAT1 activation by JAK and JNK

The induction of major histocompatibility complex (MHC) class II proteins by interferon gamma (IFN-γ) in macrophages play an important role during immune responses. Here we explore the signaling pathways involved in the induction by IFN-γ of the MHC II transactivator (CIIta) required for MHC II transcriptional activation. Cyclophilin A (CypA) is required for IFN-γ-dependent induction of MHC II in macrophages, but not when it is mediated by GM-CSF. The effect of CypA appears to be specific because it does not affect the expression of other molecules or genes triggered by IFN-γ, such as FcγR, NOS2, Lmp2, and Tap1. We found that CypA inhibition blocked the IFN-γ-induced expression of CIIta at the transcriptional level in two phases. In an early phase, during the first 2 h of IFN-γ treatment, STAT1 is phosphorylated at Tyrosine 701 and Serine 727, residues required for the induction of the transcription factor IRF1. In a later phase, STAT1 phosphorylation and JNK activation are required to trigger CIIta expression. CypA is needed for STAT1 phosphorylation in this last phase and to bind the CIIta promoter. Our findings demonstrate that STAT1 is required in a two-step induction of CIIta, once again highlighting the significance of cross talk between signaling pathways in macrophages.

HLA-DRB1 genes and the expression dynamics of HLA CIITA determine the susceptibility to T2DM

Type 2 diabetes mellitus (T2DM) is a disease with polygenic inheritance. The expression of major histocompatibility complex class II genes are regulated by several trans-activators. We have studied the expression of HLA-DRB1, RFX, CIITA-P1, PIV transactivators, immunophenotyping of cells, SNPs in CIITA-168 (A/G) and IFN-γ + 874 (T/A) in T2DM patients and controls (n = 201 each). We observed increased frequencies of DRB1*03, DRB1*04 and DRB1*07 and decreased frequencies of DRB1*10, DRB1*14, and DRB1*15 alleles among patients. Significant up-regulations of HLA-DRB1 genes were observed in patients (p < 0.0001). Down-regulated expressions were documented in DRB1*03-homo (p < 0.002) and DRB1*04-homo (p < 0.009) patients. No significant differences were observed for CIITA-P1 expression except DRB1*04-pooled (p < 0.0113). The CIITA-PIV was up-regulated in overall (p < 0.0001), DRB1*03-pooled (p < 0.0006), DRB1*03-hetero (p < 0.0006) and DRB1*03-homo (p < 0.001) T2DM patients. However, significant down-regulations were documented for DRB1*04-pooled (p < 0.040), DRB1*04-hetero (p < 0.060), and DRB1*04-homo (p < 0.027) combinations. Further, significant down-regulations of RFX5 were observed in overall (p < 0.0006), DRB1*04-pooled (p < 0.0022), and DRB1*04-hetero (p < 0.0004) combinations. Immunophenotyping studies revealed significant increase of CD45⁺ CD14^-, CD19⁺, CD14^- and CD8 cells and elevated level of expression of IFN-γ (p < 0.0001) in patients. A significant increase of TT (p < 3.35 × 10^-6) and decrease of TA (p < 4.57 × 10^-4) genotypes of IFN-γ + 874 (T/A) and an increase of GG (p < 0.001) and decrease of AG (p < 8.24 × 10^-5) genotypes of CIITA-168 A/G SNPs were observed. The combinatorial analysis revealed susceptible associations for DRB1*03 + AA, *03 + AG, *03 + GG and *04 + GG and protective associations for DRB1*10 + AG, *10 + GG, *15 + AG, and *14 + GG combinations. Thus, the present study corroborated the effect of differential expressions of promoters of risk alleles in the pathogenesis of T2DM.