Is DEXI a Multiple Sclerosis Susceptibility Gene?

Abstract

The genetic landscape of multiple sclerosis (MS) has been extensively mapped, yielding significant insights into the molecular mechanisms of the disorder. Early studies highlighted key genes associated with the immune system, particularly T cells, as critical for MS susceptibility. Subsequent large-scale genome-wide association studies (GWASs) identified over 200 genetic variants linked to MS, revealing a complex interplay between MS risk and genes involved in various processes within adaptive and innate immune cells, as well as brain-resident microglia. Recently, a groundbreaking GWAS pinpointed the first gene variant associated with MS disease progression, distinguishing the mechanisms driving disease onset from those influencing progression. The C-type lectin domain family 16, member A (CLEC16A) gene within the 16p13 region has consistently been shown to be associated with increased risk of developing both MS and other autoimmune disorders. Notably, several autoimmune-associated genetic variants in CLEC16A introns act as expression quantitative trait loci for the dexamethasone-induced protein (DEXI gene, adding DEXI to the growing list of MS susceptibility genes. This review explores the molecular and functional characterization of DEXI with a particular focus on recent advances in understanding its role in autoimmunity, specifically in the context of multiple sclerosis. We underscore the importance of continued molecular investigation of susceptibility loci for MS identified in genetic studies, with the goal of translating this knowledge into clinical applications.

Keywords: CLEC16A; DEXI; autoimmunity; multiple sclerosis; susceptibility genes.

Figure 1

The 16p13 genomic region with the CIITA, DEXI, CLEC16A and SOCS1. The map depicts the genes in the 16p13 chromosomal region (in blue), a histone H3 histone epigenetic mark common near regulatory elements [16] (peaks in different colours), and selected MS-associated CLEC16A single nucleotide polymorphisms (SNPs; yellow lines). CIITA—major histocompatibility complex (MHC) class II transactivator, DEXI—dexamethasone-induced protein, CLEC16A—The C-type lectin domain family 16, member A, SOCS1—suppressor of cytokine signalling 1.

Figure 2

DEXI expression is downmodulated upon T cell activation. (A) CD8⁺ T cells were purified from whole blood by positive selection, followed by isolation of CD4⁺ T cells (A,C) by negative selection as described [46] and stored live on liquid nitrogen (C). (A) Freshly purified peripheral T cells were activated with anti-CD3/CD28 antibody-coated magnetic beads and (B) Jurkat Tag cells were stimulated with phorbol 12-myristate 13-acetate (PMA) and ionomycin (IO), for indicated time points as previously described [25], or (C) CD4⁺ T cells from healthy controls (HC) and MS patients [46] were stored on liquid nitrogen, thawed, and were left unstimulated or stimulated with plate-bound anti-CD3 (5 µg/mL was used for over-night coating of the wells; CD3+ Mouse-anti-human clone: OKT3, eBioscience by Thermo Fisher Scientific, San Diego, CA, USA) and soluble anti-CD28 (4 µg/mL; CD28 Purified NA/LE Mouse anti-human clone CD28.2, eBioscience by Thermo Fisher Scientific, San Diego, CA, USA) antibodies. After activation, cells were harvested, and quantitative PCR analyses performed to analyze DEXI expression as described in [46]. (A,B) The graphs display the mean (with standard error of the mean (SEM)) of DEXI expression relative to TATA-box binding protein (TBP) and importin-8 (IPO8) in CD4⁺ and CD8⁺ T cells from four healthy donors (A), and relative to 18S rRNA in Jurkat cells from three independent experiments (B). The relative DEXI expression is normalized to time point 0. One-sample t-tests were used for comparisons. (C) The graph displays DEXI expression relative to TBP, normalized to the unstimulated control at four and 24 h, respectively, in samples from 16 healthy controls (HC) and 16 MS patients; the horizontal line represents the mean. Mann–Whitney tests were performed to compare DEXI expression between samples from HC and MS patients. * p <0.05; ** p <0.01.

Figure 3

Schematic representation of the DEXI protein and sequence alignment. (A) The two α-helixes, predicted with high confidence, are depicted as grey and black boxes; TM = trans-membrane domain; the sequences with a potential nuclear export signal (NES) are shown as boxes with graded colour. (B) Protein sequence alignment of DEXI from zebrafish, chicken, human and mouse, where “*” indicates identical amino acids in all four species, “:” indicates conserved substitution of amino acids, “.” Indicates semi-conserved substitution of amino acids, and open space indicates no conservation of amino acids between the four species.

Figure 4

DEXI accumulates in the T cell nucleus upon activation. (A) Confocal images of Jurkat T cells left unstimulated (dimethyl sulfoxide, DMSO) or activated for 24 h with anti-CD3/CD28 antibodies or PMA and IO, fixed, permeabilized, and stained with antibodies against DEXI (green; Thermo Fisher Scientific, Madison, WI, USA) and the nuclear marker Hoechst (blue), as described in [25]. The images show representative cells in one out of two independent experiments. In each experiment, 500 cells were visualized. (B,C) Cytosolic and nuclear fractions were harvested according to the NE-PER Nuclear and Cytoplasmic Extraction Kit (Thermo Fisher Scientific, Madison, WI, USA) and the presence of DEXI in unstimulated and stimulated Jurkat T cells overexpressing Myc-DDK-DEXI (RC207463; Origene Technologies, Rockville, MD, USA) were analyzed by Western blotting (rabbit anti-DEXI (Thermo Fisher Scientific, Madison, WI, USA.), using antibodies against Lamin B1 (ab16048, Abcam, Cambridge, UK) and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) (Santa Cruz Biotechnology, Dallas, TX, USA) as markers for the nuclear and cytosolic fractions, respectively. The signals were quantified by Image Studio Lite version 5.2.5 (Li-Cor, Lincoln, USA), and the signals from DEXI were normalized against the expression of cytosolic and nuclear markers, respectively. The graph displays the mean of the normalized signals relative to the unstimulated control (DMSO) in each fraction with SEM; * p-value < 0.05 and *** p-value < 0.001, using one-sample t-tests.