MUC5AC Genetic Variation Is Associated With Tuberculous Meningitis Cerebral Spinal Fluid Cytokine Responses and Mortality

Abstract

Background: The purpose of this study was to assess if single nucleotide polymorphisms (SNPs) in lung mucins MUC5B and MUC5AC are associated with Mycobacterium tuberculosis outcomes.

Methods: Independent SNPs in MUC5B and MUC5AC (genotyped by Illumina HumanOmniExpress array) were assessed for associations with tumor necrosis factor (TNF) concentrations (measured by immunoassay) in cerebral spinal fluid (CSF) from tuberculous meningitis (TBM) patients. SNPs associated with CSF TNF concentrations were carried forward for analyses of pulmonary and meningeal tuberculosis susceptibility and TBM mortality.

Results: MUC5AC SNP rs28737416 T allele was associated with lower CSF concentrations of TNF (P = 1.8 × 10-8) and IFN-γ (P = 2.3 × 10-6). In an additive genetic model, rs28737416 T/T genotype was associated with higher susceptibility to TBM (odds ratio [OR], 1.24; 95% confidence interval [CI], 1.03-1.49; P = .02), but not pulmonary tuberculosis (OR, 1.11, 95% CI, .98-1.25; P = .10). TBM mortality was higher among participants with the rs28737416 T/T and T/C genotypes (35/119, 30.4%) versus the C/C genotype (11/89, 12.4%; log-rank P = .005) in a Vietnam discovery cohort (n = 210), an independent Vietnam validation cohort (n = 87; 9/87, 19.1% vs 1/20, 2.5%; log-rank P = .02), and an Indonesia validation cohort (n = 468, 127/287, 44.3% vs 65/181, 35.9%; log-rank P = .06).

Conclusions: MUC5AC variants may contribute to immune changes that influence TBM outcomes.

Keywords: MUC5AC; genetics; mucins; tuberculous meningitis.

Figure 1.

Chromosome map and linkage disequilibrium plots of independent single-nucleotide polymorphisms (SNPs) identified in MUC5B and MUC5AC gene regions. A, MUC5B and MUC5AC genes are located on band 1 of the p arm of chromosome 11; the locations of index SNPs are indicated. Vertical lines represent subband intervals of 0.004. B, Linkage disequilibrium (LD) plots showing R² (left) and D^′ (right) values for the index SNPs. The degree of shading is proportionate to the R² and D^′ values for paired SNPs. C, Minor allele frequency (MAF) for each SNP.

Figure 2.

Evaluation of CSF cytokine expression in TBM patients with MUC5AC SNP rs28737416 using additive and dominant genetic models. The associations between MUC5AC SNP rs28737416 and log₂ CSF cytokine concentrations (pg/mL) were evaluated using additive (A) and dominant genetic models (B). For the additive model, CSF cytokine concentrations were compared between participants with the T/T (shaded circles), T/C (open circles), or C/C (solid circles) genotypes using the Kruskal-Wallis test. In the dominant model, cytokine concentrations were compared between participants with a composite of the T/T and T/C genotypes (shaded circles) to participants with the C/C genotype (solid circles) using Wilcoxon rank-sum testing. For all graphs, the median is indicated by a thick, horizontal line, and the interquartile range is represented by thin, horizontal lines. To adjust for multiple comparisons, a Bonferroni correction was applied, and the significance threshold adjusted to the level of P < .005. P values for cytokines with statistically significant differences in expression after Bonferroni correction are shown. Abbreviations: CSF, cerebrospinal fluid; IFN-γ, interferon-γ; IL, interleukin; SNP, single-nucleotide polymorphism; TBM, tuberculous meningitis; TNF, tumor necrosis factor.

Figure 3.

Kaplan-Meier curves comparing survival in a dominant allelic model of MUC5AC SNP rs28737416 in the tuberculous meningitis (TBM) discovery and validation cohorts among participants who received dexamethasone. Kaplan-Meier curves displaying time to death using a dominant allelic model comparing participants with the T/T and T/C genotypes to those with the C/C genotype are shown for (A) Vietnam TBM discovery cohort, (B) Vietnam TBM validation cohort, and (C) Indonesia TBM validation cohort. Displayed P values represent comparison of the survival distributions by the log-rank test.

Figure 4.

Hypothesis to explain the underlying mechanism linking MUC5AC polymorphisms to TBM mortality. Based on mRNA expression findings from the Genotype-Tissue Expression Project (GTEx) portal, participants with the protective (C/C) rs28737416 MUC5AC genotype may have lower expression of MUC5AC in the lungs compared to those with the susceptible (T/T and T/C) genotypes. Altered MUC5AC expression may enhance mucosal barrier breakdown [37], potentially facilitating dissemination of M. tuberculosis and altering systemic adaptive immune signaling. In the presence of dexamethasone therapy, this results in lower concentrations of CSF TNF and IFN-γ and higher risk of death from TBM, a finding that is consistent with observations among participants with the susceptible LTA4H genotype [11, 27]. The figure was created with BioRender.com. Abbreviations: CSF, cerebrospinal fluid; IFN-γ, interferon-γ; TBM, tuberculous meningitis; TNF, tumor necrosis factor.