In the current study, we analyzed the association between SNPs in the promoter of MALAT1 gene and IS risk. Significant differences were observed in the distribution of the rs1194338 AC/AA genotype and A allele between controls and cases. Further analysis shows that MALAT1 rs1194338 A allele, AA, AC genotype and the dominant model were associated with decreasing IS risk. Regression analysis revealed that rs1194338AC/AA was impact factors of IS together with lipid index such as TC, TG, HDL - C, etc. In addition, results from Haplotype analysis showed that rs600231-rs1194338-rs4102217- rs591291 (A-C-G-C) haplotype had a 1.3-fold increase of IS risk. These findings implicate that analysis of rs1194338 may reveal the roles of MALAT1 in the etiology of IS in the future.
MALAT1, an 8.1 kb lncRNA, located on human chromosome 11q13. In 2003, Ji et al discovered firstly and named from lung cancer cells[25]. Subsequently, MALAT1 was reported to be associated with tumors cell proliferation, metastasis, survival, and recurrence[26]. New evidences show that MALAT1 was abundantly expressed in vascular endothelial cells and participated in processes of neuroprotection of IS by improvement of cognitive function, promotion of angiogenesis, inhibition of apoptosis and inflammation, regulation of autophagy, and protection of blood-brain barrier function[15–17, 27, 28]. The PI3K/AKT pathway have recently been implicated in cell proliferation, apoptosis, and survival in physiological and pathological conditions[29]. Study showed a neuroprotective role of early activation of PI3K in ischemic stroke[30]. The result from Yuan et al. invested that overexpression of MALAT1 decreased cell apoptosis by activating of PI3K/AKT pathway, eventually protect human cerebrovascular endothelial cells in OGD and reoxygenation condition[31]. The above indicates that the MALAT1 plays a critical role in ischemic stroke, and its high expression may contribute to the protection against brain injury.
The ischemic stroke is one of diseases threatening human health, which underlying mechanism are less well understood. Actually, increasing studies focused on SNPs of lncRNA involved in process of IS. For example, the rs2240183 C allele of lncRNA TUG1 was associated with a higher risk of IS possibly by binding to GATA-1 and elevating TUG1 levels [20], the ANRIL rs2383207 increased the risk of IS by 1.52-fold under the recessive mode [21], the rs217727 TT and rs4929984 AA in the H19 increase the risk of IS, with adjusted OR 4.288, 3.020, respectively [22]. Those provide a new perspective on the genetic mechanism of IS. Given above, we hypothesized that the MALAT1 gene polymorphisms are associated with IS risk. Our results supported the above assumption. As shown in Table 3, case-control studies indicated the rs1194338 A allele, AC and AA genotype of MALAT1 contributed to the decrease of IS susceptibility, and A-C-A-G haplotype increased IS risk (Table 4). logistic regression also validated effect of the rs1194338 AC/AA for IS risk (Table 5).
The rs1194338, a functional site, located in the promoter region of the MALAT1. Recently, several studies indicated the relationship between rs1194338 variant and human diseases. In hepatocellular carcinoma (HCC), female patients and patients with a smoking habit who carried the CA + AA genotype of rs1194338 had a lower risk of developing vascular invasion and a high Child-Pugh grade, respectively[32]. This suggested there was an interactive function between rs1194338 and the environment, whether it interacts with the environment in IS remains to be further explored. In colorectal cancer, previous study found carriers with AA and AC genotype of the rs1194338 were lower risk than CC genotype, and the conclusion from Li’s study showed no statistically significant difference in expression levels of MALAT1 between CC and AA genotype at rs1194338[33, 34]. However, data from the GTEx database showed rs1194338 SNP had a difference in expression of MALAT1. Particularly, the rs1194338 SNP AA indicated a significant increase of expression compared to the CC genotype in brain brain-hippocampus and cerebellar hemisphere tissues (P < 0.001) (Fig. 1). Based on the above background, we hypothesized that the rs1194338 AC/AA genotype may increase the expression levels of MALAT1, which activating related pathways such as PI3K/AKT, thereby reducing the risk of IS. Further studies are needed to investigate the correlation between the rs1194338 SNP and MALAT1 expression and the precise mechanism of rs1194338 SNP in IS.
At present, studies on rs600231 A > G variant with disease have not been reported, but rs4102217 and rs591291 SNPs were evaluated in rheumatoid arthritis (RA) and HCC. Zhang et al. indicated rs4102217 and rs591291 SNPs were not associated with RA susceptibility[35]. Studies of association with HCC have shown rs4102217 had a 1.32-fold risk in the dominant model, and rs591291 highlighted better prognosis in female and HBV negative subgroups, but association between MALAT1 haplotype (rs4102217-rs591291-rs11227209- rs619586) and HCC risk were not found[22]. In our study, we found that A-C-A-G (rs600231-rs1194338- rs4102217-rs591291) haplotype had a 1.3-fold IS risk (Table 4) although SNPs (rs600231, rs4102217, rs591291) did not correlate with IS susceptibility. It is well known that alteration in blood lipid level is one of the relevant risk factor in atherosclerotic plaques formation, which cause easily hypoxia and possibly lead to injury in downstream tissues such as ischemic stroke[36]. According to the report, MALAT1 involved in lipid metabolism[37]. Thus, we further analyzed the relationship between the SNPs of MALAT1 and blood lipids. Unfortunately, we did not observe a relationship between the four SNPs of the MALAT1 and lipid levels. These founding would help improve our understanding of the roles of MALAT1 genetic variants in the pathogenesis of IS.
Our study is not without limitations. Firstly, a relatively small sample may limit the statistical analysis of our research. Secondly, there are distribution differences in polymorphisms of the same locus among different races according to the 1000 Genomes Project Data. The population we studied came from the southwest of China. It was a hospital-based case-control study, which may have a choice bias. Therefore, larger sample sizes from other medical centers among different races and ethnic groups are needed to further confirm the role of MALAT1 SNPs in IS susceptibility. Finally, the functional correlation of MALAT1 SNPs in IS is very interesting, but it is not clear, both RNA and DNA should be collected simultaneously from the same samples to further verify the effect of SNPs on MALAT1 expression.