GIMAP GTPase family genes: potential modifiers in autoimmune diabetes, asthma, and allergy

Abstract

GTPase of the immunity-associated protein (GIMAP) family members are differentially regulated during human Th cell differentiation and have been previously connected to immune-mediated disorders in animal studies. GIMAP4 is believed to contribute to the Th cell subtype-driven immunological balance via its role in T cell survival. GIMAP5 has a key role in BB-DR rat and NOD mouse lymphopenia. To elucidate GIMAP4 and GIMAP5 function and role in human immunity, we conducted a study combining genetic association in different immunological diseases and complementing functional analyses. Single nucleotide polymorphisms tagging the GIMAP haplotype variation were genotyped in Finnish type 1 diabetes (T1D) families and in a prospective Swedish asthma and allergic sensitization birth cohort. Initially, GIMAP5 rs6965571 was associated with risk for asthma and allergic sensitization (odds ratio [OR] 3.74, p = 0.00072, and OR 2.70, p = 0.0063, respectively) and protection from T1D (OR 0.64, p = 0.0058); GIMAP4 rs13222905 was associated with asthma (OR 1.28, p = 0.035) and allergic sensitization (OR 1.27, p = 0.0068). However, after false discovery rate correction for multiple testing, only the associations of GIMAP4 with allergic sensitization and GIMAP5 with asthma remained significant. In addition, transcription factor binding sites surrounding the associated loci were predicted. A gene-gene interaction in the T1D data were observed between the IL2RA rs2104286 and GIMAP4 rs9640279 (OR 1.52, p = 0.0064) and indicated between INS rs689 and GIMAP5 rs2286899. The follow-up functional analyses revealed lower IL-2RA expression upon GIMAP4 knockdown and an effect of GIMAP5 rs2286899 genotype on protein expression. Thus, the potential role of GIMAP4 and GIMAP5 as modifiers of immune-mediated diseases cannot be discarded.

FIGURE 1.

A map of Finland indicating the geographical division of the FPDRNF family data into SW and NE datasets. The SW population shows a GIMAP5 association with T1D.

FIGURE 2.

Genotyped SNP locations in GIMAP4 and GIMAP5. SNPs genotyped in GIMAP4 (A); IL2RA interacting rs9640279 is indicated by IL-2RA and rs13222905, which associates with asthma and allergic sensitization by asterisk (*). SNPs genotyped in GIMAP5 (B); INS interacting rs2286899 is indicated by INS and SNP rs6965571, which associates with T1D and asthma and allergic sensitization by asterisk (*). Representation of LD structure (r²): (CI) GIMAP4 in BAMSE, (CII) GIMAP5 in BAMSE, and (CIII) GIMAP5 in FDPRNF. The associated SNPs are indicated with boxes.

FIGURE 3.

GIMAP4 downregulation affects IL-2RA expression during early human Th cell differentiation. The siGimap4 and nontargeting siScramble-treated cells were cultures 72 h after anti-CD3/anti-CD28 activation with or without IL-12 and with IL-2 added at 48 h or without IL-2. The intracellular GIMAP4, to verify the knockdown (p = 0.03) and the extracellular IL-2RA expressions, were measured at 72 h after the activation (A). The average GeoMean of IL-2RA expression under GIMAP4 downregulation in comparison with the matching control in six biological replicates (act. p = 0.01, act. + IL-12 p = 0.02, act. + IL-2 p = 0.02, act. + IL-12+IL-2 p = 0.01, *p < 0.05) (B). A representative figure of the IL-2RA downregulation under GIMAP4 depletion, gated according to the living cell population in unstained sample (C).

FIGURE 4.

GIMAP5 3′-UTR rs2286899 genotype effect on protein expression. A schematic model of the constructs R1(TT), R2(CC), and pGL3-control with luc as a reporter gene (A). The average Luc protein activity of pGL3-GIMAP5 3′-UTR R2(CC) vector in comparison with the pGL3-GIMAP5 3′-UTR R1(TT) vector (p = 0.044) and with the control pGL3 reporter vector (p = 0.035). Results are based on three biological and technical replicates (*p < 0.05) (B). Statistical significance was calculated by using the two-tailed Student t test.