Background: Gastric cancer (GC) is one of the most common causes of cancer-related mortality worldwide with its development largely being attributed to persistent Helicobacter pylori infection. Only 1-3% of H. pylori cases progress to GC, suggesting the influence of host-related factors such as single nucleotide polymorphisms (SNPs) in genes responsible for modulating the host inflammatory response. Prime candidates include Toll-like receptors (TLRs), which recognise H. pylori with downstream influence on inflammation, autophagy, cellular survival and migration. The intronic SNP, TLR4 rs11536889, is believed to prevent mRNA transcript degradation, contributing to exacerbated TLR4-activated chronic inflammation.
Aims: To evaluate the impact of TLR4 rs11536889 (G>C) on the risk of GC in ethnically diverse populations.
Methods: DNA was extracted from whole blood samples from Australian Caucasians (N=100 GC, N=232 controls), Han Chinese (N=83 GC, N=264 functional dyspepsia (FD) controls) and Colombian Mestizos (N=91 GC, N=376 FD controls). Genotyping TLR4 rs11536889 involved matrix-assisted laser-desorption ionisation time-of-flight (MALDI-TOF) mass spectrometry. Bivariate, multivariate, and joint effect analyses evaluated the relationship between this SNP, H. pylori infection and GC aetiology. Systemic inflammation was assessed in H. pylori-infected FD patients using a multiplex ELISA. Microbiota analysis was conducted using gastric biopsies and 16s rRNA gene sequencing, to correlate the relative abundance of bacterial taxa of interest with TLR4 rs11536889 carriage.
Results: The CC genotype was found to increase the risk of GC in the combined populations (adjusted odds ratio (OR) of 2.299; p-value=0.037). Analysis of the total population demonstrated that the C allele decreased the risk against H. pylori infection (adjusted OR=0.538; p-value=<0.0001). The synergistic effect of TLR4 rs11536889 and H. pylori infection contributed to elevated risk of GC in Han Chinese (OR=8.907; p-value=<0.0001) and Australian Caucasians (OR=2.540; p-value=0.0099). In Colombian Mestizos (N=54), the C allele was associated with decreased expression of IL-1RA (p-value=0.0066), an important IL-1 antagonist. Interestingly, in the absence of H. pylori infection, it was found that the C allele was correlated with an increased relative abundance of Leptotrichia in FD patients from the same population (p-value=0.0123).
Conclusions: TLR4 rs11536889 may lead to increased inflammatory responses via IL-1, leading to better bacterial clearance. Given that inflammation is a hallmark of cancer, however, this enhanced inflammatory responses increase the risk of GC in the long-term. TLR4 rs11536889 may also act to support the growth of non-H. pylori taxa linked to GC, and further transduce these signalling pathways to sustain inflammation.