Relationship Between Matrix Metalloproteinase-9 1562C/T Polymorphism and Liver Diseases: A Meta-Analysis

Liver diseases have an adverse impact on human’s body and life, and many factors, such as genes, etc., are closely related to the occurrence and development of liver diseases. This study tries to explore the relationship between liver diseases and one of the genetic polymorphisms (MMP-9-1562 C/T polymorphism) by meta-analysis, to provide basis for the prevention and treatment of liver diseases and to promote the study of the mechanism of liver diseases by the exploration of etiology.


Conclusions
Our meta-analysis suggested that the TT genotype of MMP-9-1562 C/T polymorphism might be associated with the risk of nonalcoholic fatty liver disease, hepatocellular carcinoma, and primary liver cancer. If these diseases are present, screening genotype of MMP-9 and aggressive treatment of the primary disease is necessary.
Background Liver disease is a common and extremely harmful global disease [1]. In recent years, the incidence and mortality of liver disease have been increasing, which has become a challenging and urgent clinical problem to be solved. Drug toxicity, virus infection, alcohol and other factors will lead to the occurrence of liver disease, and often due to the delay of the treatment time or early neglected, prompting the activation of hepatic stellate cells and liver damage of the structure, and then liver brosis, the pathological basis of cirrhosis or cancer occurred. If not timely intervention and treatment, early liver disease may develop irreversible damage namely liver cirrhosis ,even liver cancer. [2].
Matrix Metalloproteinases (MMPs), a family of zinc-dependent proteolytic enzymes, which plays a key role in the degradation of ECM and the injury and repair of liver structure, and is also closely related to the progress and repair of liver brosis [3]. Matrix Metalloproteinase-9 (MMP-9), also known as gelatinase B [4], is one of the important components of ECM degradation and has a bearing on the dynamic changes of liver brosis.
The activity of MMP-9 is signi cantly affected by gene polymorphism. Current studies have identi ed MMP-9-1562 C/T (rs3918242) polymorphism within the promoter of the MMP-9 gene [5], which can vitally affect its function, and thus may be close to various liver diseases.
In order to clarify the relationship between MMP-9-1562C/T (rs3918242) polymorphism and liver diseases, this study conducted a comprehensive meta-analysis (META) on published studies to obtain more reliable conclusions, providing scienti c basis for the prevention and treatment of liver diseases and the exploration of etiology to help for the study of the mechanism of liver diseases.

Literature retrieval
We searched related articles published in PubMed, EMBASE, Web of Science, CNKI and China Biomedical Literature Database with the retrieval date of Dec. 1, 2020. Retrieval words: "MMP-9, matrix metalloproteinase-9 or gelatinase B", "polymorphism, single nucleotide polymorphism or SNP" and "liver or hepatic".

Inclusion and exclusion criteria
The relationship between MMP-9 polymorphism and liver diseases was analyzed and determine the inclusion criteria: a) case-control study; B) polymorphism of MMP-9 1562; C) liver disease; D) there were odds ratios (ORs) and 95% con dence intervals (CIs) for polymorphism in the case group and control group. Exclusion criteria: a) case reports, reviews, excerpts, or unpublished data; B) overlapping data; C) research on family members.

Data extraction
Yang Tianling, a student, extracted data independently from all the selected studies, and the differences in the included literature were handled by instructor Ji Yangtao. The following information was extracted: rst author, year of publication, race, source of control group, liver disease type, genotyping method, number of case and control group, distribution frequency of MMP-9-1562 polymorphisms CC, CT, TT, and literature quality score.

Literature quality evaluation
For the included case-control studies, the Newcastle-Ottawa Scale (NOS) literature quality evaluation Scale (full score is 9, including object selection, comparability and exposure) was used to conduct methodological quality evaluation. Literature quality was considered to be good if the score was above 5.

Statistical analysis
Review Manager 5.3 was used for statistical analysis. The association between MMP-9-1562 C/T gene polymorphism and liver disease was examined by odds ratio (OR) and 95% con dence interval (CI). Four genetic models were analyzed: homozygous contrast model (TT vs CC), heterozygous contrast model (CT vs

CC), dominant model (TT+CT vs CC) and recessive model (TT vs CT+CC).
For the included studies, X 2 test was used to evaluate the heterogeneity among the studies, and I 2 was used to quantitatively analyze the heterogeneity. I 2 ≦50% was considered to be small heterogeneity, and xed effect model was used; I 2 > 50% is expected to exist large heterogeneity among the studies, and random effect model was used. Find the sources of heterogeneity, when I 2 = 0, no heterogeneity. Funnel plot was used for publication bias analysis. P value<0.05 was considered statistically signi cant.

Basic features of the included study
The literature retrieval process is shown in Fig. 1. A total of 162 studies were identi ed through key words retrieval. According to strict inclusion and exclusion criteria, 7 related studies were nally included for metaanalysis. The included literatures were evaluated with the NOS Literature Quality Evaluation Scale, and their scores all ≧ 5, suggesting that they belonged to literatures with better quality. The sample characteristics of the 7 case-control studies are shown in Table 1 and Table 2, including a total of 1415 cases and 1592 controls. Of these, 3 studies were related to hepatocellular carcinoma [6][7][8], 2 studies were related to liver cirrhosis [9,10], and 2 studies involved primary liver cancer [11], and non-alcoholic fatty liver disease respectively [12]. Six studies focused on Asian population, one on African.    Table 3. (As TT genotype samples did not appear in the studies of Yun Zhai, we assume that the number of TT genotypes in this study is 1.)

Analysis of publication bias
In a meta-analysis, when there are less than 10 studies, the power of tests for funnel plot asymmetry is too low to distinguish chance from real asymmetry. Even so, we examined publication bias by a funnel plot with the effect size. The evaluation of publication bias of the four groups of models is shown in Fig. 4. The funnel plot data points of each model were not symmetric, hint that there may be publication bias, but also might cause from small sample size, methodological quality, and the presence of random error etc.

Sensitivity analysis
The results of homozygous models before literature exclusion showed that I 2 = 37%, and that of recessive models before literature exclusion was 41%. The source of heterogeneity was analyzed by sensitivity analysis. Results after each study was excluded in turn were shown in Table 4 and Table 5. It was found that I 2 was reduced to 0% after Wu Shisheng's study was excluded from the two models, suggesting that the heterogeneity of the study results may be caused by this study, while the heterogeneity after the exclusion of the rest of the studies showed little change, indicating that these studies were relatively stable. Due to Wu Shisheng's small sample size, low literature quality and unknown sample source, it can be inferred that the heterogeneity between studies may be caused by sample size, quality of included literature and sample source.

Discussion
MMP-9 is a signi cant member of the family of MMPs, which belong to collagenase IV, widely expresses in the tissues and cells of our body, and mainly from monocytes, macrophages, neutrophils, broblasts, endothelial cells ,and tumor cells [13]. MMP-9's gene locates on chromosome 20 q11.2-13.1, which is a vital component in degrading ECM and basement membrane [14]. Under normal physiological conditions, MMP-9 and TIMP work together to maintain the dynamic balance of the degradation and synthesis of ECM, and the stability of the tissue structure [15]. On the other hand, MMP-9 plays an important role in many physiological or pathological changes, such as in ammatory cells invasion and metastasis, vascular remodeling, organ brosis and cancer cell invasion and metastasis [16]. Under pathological conditions, the imbalance of ECM degradation and remodeling by MMP-9 affects the structure and function of various organs and cells, and changes the vascular microenvironment, thus promote the occurrence and development of various diseases [17,18]. Researches showed that MMP-9 is related to the susceptibility and development of some cardiovascular diseases such as coronary heart diseases (CHC), atherosclerosis, digestive system diseases such as gastric cancer, colorectal cancer, some liver diseases like NAFLD, HCC etc. [19][20][21]. Study [22] have found that MMP-9 has multiple gene polymorphism sites, among which the − 1562 C/T (rs3918242) SNP is located at the promoter polymorphism site, and is the most widely and deeply studied SNP site. In MMP-9-1562 T allele carriers, its level and activity of MMP-9 in plasma protein are higher than C allele carriers, and which is closely related to the susceptibility of various diseases, invasion and metastasis of tumor cells, etc. [23]. Therefore, MMP-9-1562 C/T polymorphism can be used as a potential biological detection index to evaluate the e cacy and prognosis of clinical individualized treatment and monitor the treatment process.
This study conducted a meta-analysis of 7 relevant literatures to explore the relationship between MMP-9-1562 C/T gene polymorphism and liver diseases. The results showed that the TT genotype may be a risk factor for primary hepatic cancer, hepatocellular carcinoma and nonalcoholic fatty liver disease. Research [24] showed that, compared with CC genotype carriers, the mRNA level, protein level and MMP-9 activity of -1562 T allele carriers were signi cantly increased, not only can promote the proliferation, activation, and migration of hepatic stellate cells (HSC), but also stimulate the development of liver in ammation and brosis [25], leading to vascular remodeling of organs and changes of microenvironment. So we can infer that, compared with non-carriers, the MMP-9 transcription and translation level in MMP-9-1562 T allele carriers was increased signi cantly, which promote the activation of HSC, and make HSC excessive secrete in ammatory factors and brosis factors such as IL-1, transforming growth factor (TGF-β), and platelet-derived growth factor (PDGF), which accelerate the imbalance of ECM degradation and synthesis, leading to excessive deposition of ECM in the liver, nally resulting in NAFLD from simple fatty liver to fatty liver brosis pathological change. At the same time, the overexpression of MMP-9 activates TGF-β /SMAD, PI3K/AKT and other signal transduction pathways, which stimulate the proliferation of HSC and inhibit its apoptosis, accelerating the invasion and metastasis of in ammatory cells or cancer cells, enhancing vascular remodeling and changes, and thus lead to the occurrence and development of primary liver cancer, hepatocellular carcinoma and other liver cancers.
There are still some limitations in this study: (1) the number of references included in this study is small, and the number of research samples is small, which limits the demonstration intensity of the results of the systematic evaluation; (2) The liver diseases included in this study refer to primary liver cancer, non-alcoholic fatty liver, liver cirrhosis, and hepatocellular carcinoma; However, there was only one reference for each of the rst two diseases, so there may be some bias and cannot represent the general situation.
With the development of society, liver disease has become a clinically urgent problem to be solved. This study suggests that in MMP-9-1562 C/T gene polymorphism, the TT genotype may be one of the risk factors for PHC, HCC and NAFLD. This means that patients with NAFLD with MMP-9-1562 TT genotype may have a higher risk of developing liver cancer, so early intervention should be carried out to prevent the occurrence of liver cancer in clinical practice; active diagnosis and treatment should be carried out for patients with HCC or PLC with TT genotype, and corresponding gene therapy should be explored to improve the quality of life and prognosis of cancer patients. Therefore, in the future clinical treatment of chronic liver diseases, more indepth researches are needed to explore the important role and mechanism of MMP-9-1562 gene polymorphism in the occurrence and development of liver diseases, so as to provide basis for individualized disease monitoring, curative effect evaluation and prognosis of liver diseases, and also provide help and new ideas for the study of liver diseases mechanism.

Conclusions
Our meta-analysis suggested that the TT genotype of MMP-9-1562 C/T polymorphism might be associated with the risk of nonalcoholic fatty liver disease, hepatocellular carcinoma, and primary liver cancer. If these diseases are present, screening genotype of MMP-9 and aggressive treatment of the primary disease is necessary. Availability of data and material

List Of Abbreviations
All data generated or analyzed in this study are included in this published article.