The M235T polymorphism in the angiotensinogen gene is not a major risk factor for diabetic nephropathy; a meta-analysis

1Department of Zoology, Guru Ghasidas Vishwavidyalaya, Bilaspur 2Department of Biochemistry, Late Atal Bihari Vajpayee Memorial Medical College Rajnandgaon (C.G.), India 3Department of Immunopathology, Institute of lungs Biology and Disease, Comprehensive Pneumology Center, Helmholtz Zentrum, 85764 Neuherberg, Munich, Germany 4Centro Universitario de Ciencias de la Salud, Universidad de Guadalajara, Guadalajara, Jalisco, México 5Department of Biotechnology and Bioinformatics, Sambalpur University, Jyoti Vihar, Sambalpur, India


Introduction
Diabetic nephropathy (DN) is one of the common microvascular complications in patients with diabetes mellitus, and it is the leading cause of chronic kidney disease (CKD) and renal failure (1). In the past decade, the incidence of DN is increased and now accounting for approximately 50% of all end-stage renal diseases (ESRDs) (2). According to USA Renal Data System, DN was the most common primary diagnosis in 2018 (3). Both type 1 and type 2 diabetes induce changes in glomerulus, tubulointerstitium and vasculature in different kidney compartments (4). Besides, long-standing DM, poor glycemic control and genetic factors are the major risk factors for DN (5). However, despite the belief that genetic factors may have an impact on the DN risk, none of the genes have yet been clearly defined. The advancement of single-nucleotide polymorphism (SNP) technology has resulted in an increase in the number of studies being conducted to investigate the relationship between genetic polymorphism and DN risk (6). A number of candidate genes have been identified, including those involved in the regulation of reninangiotensin-aldosterone (RAAS) and lipid metabolism (7)(8)(9).
Previous evidence has shown that RAAS

Key point
Diabetic nephropathy in diabetes patients is positively correlated with end-stage renal disease (ESRD). Previous evidence has shown that RAAS plays an essential role in the development and progression of DN. The present meta-analysis analysed the association between AGT M235T polymorphism nephropathy in T2DM patients. This meta-analysis indicated that the AGT gene M235T polymorphism does not contribute to DN risk.
10.34172/jpe.2022.15 doi plays an essential role in the development and progression of DN (10). Recently, some genetic variants such as angiotensin-converting enzyme (ACE) I/D polymorphism, angiotensin II type 1 receptor (AT1R) A1166C (rs5186) gene polymorphism and AGT M235T (rs699) in the RAAS pathway have been significantly associated with the risk of DN (11,12). AGT is a vital component of level II angiotensin, which is a major component of the RAAS. Further, genetic polymorphism in the AGT gene may lead to DN progression in patients with DM.

Literature search
A meta-analysis was carried out to investigate the association between DN risk and AGT M235T. In this perspective, MEDLINE, PubMed, EMBASE, Scopus databases, Web of Science, used to conduct analysis using the search keywords of "Angiotensinogen", "AGT M235T", "rs699", "diabetic nephropathy" and "diabetic kidney disease. " All Information was collected upto July 2020.

Inclusion and exclusion criteria
The inclusion and exclusion criteria used in our study were as follows. Inclusion criteria; (a) case-control study design; (b) studies that addressed DN cases and diabetic controls; (c) Studies that assessed the link between AGT M235T and DN risk; (d) detailed genotype methods should be provided for the study. Exclusion criteria: (a) not case-control studies; (b) studies with AGT M235T with T1DM and (c) studies overlapped with any other articles. The names of the first author, year of publication, country, ethnicity, genotyping method and genotype data from the T2DM and T2DN groups were collected.

Statistical analysis
The association between AGT M235T and DN risk was measured in three genetic models (allelic, dominant and recessive) by estimating ORs and corresponding 95% CIs. The Cochran's Q test and I 2 values were applied to assess the degree of heterogeneity between studies (27). The results were pooled using a random-effects model. To test the robustness of this meta-analysis, sensitivity analysis was used, which involved removing one study at a time. Begg's funnel plot and Egger's test were used to investigate publication bias. Ethnicity based subgroup analysis was performed. All analysis were performed by MetaGenyo web tool (28).

Association of AGT M235T polymorphism with susceptibility to diabetic nephropathy
To explore the association between AGT M235T gene polymorphisms with the risk of DN, 14 studies were enrolled. Forest plot and overall pooled effect show the relationship between AGT M235T polymorphism and DN an independent studies in the dominant model ( Figure 2). The current meta-analysis shows that there was significant heterogeneity between studies (I 2 = 73% to 94%). The random-effect model was used to estimate the pooled ORs. The measures of the association between DN and AGT M235T polymorphism were documented in Table 2

Sensitivity analysis and publication bias
In sensitivity analysis, there was no significant difference in the OR when we excluded one study at a time. Sensitivity analysis pooled ORs were depicted in Figure 3. The results show that there was no difference in pooled ORs when we omit one study each time, indicating that our findings were statistically robust. There is no obvious asymmetry in the funnel plot's shape ( Figure 4)

Discussion
Diabetic nephropathy in diabetes patients is positively correlated with ESRD. DN has a multi-factorial etiology that includes both environmental and genetic factors. RAAS can be activated early in the course of diabetes, causing structural and intraglomerular hemodynamic changes in the diabetic kidney at both the glomerular  and tubulointerstitial levels (29,30). Microalbuminuria is considered a risk factor for early-stage DN progression and may occur due to endothelial dysfunction and hyperhomocysteinemia. Approximately one-third of diabetic patients are susceptible to nephrotic disease (31).
Poor glycemic control has been identified as one of the major causes of developing nephropathy. Despite the fact that a family history of DN is one of the most likely indicators of a hereditary genetic predisposition to DN, due to the involvement of multiple genetic and environmental risk factors in the pathogenesis of DN, determining an individual's risk of inheriting nephropathy is difficult. Despite extensive and thorough research efforts, the underlying causative genetic components remain elusive (32)(33)(34). The M235T variant has been shown to alter the plasma levels of AGT (35,36) with increased serum AGT levels for patients with T-allele (37). In addition, there is a positive correlation between AGT M235T genotype and AGT plasma levels in myocardial infarction (MI) (38,39). The present meta-analysis revealed that there was no significant association between AGT M235T and DN  risk. We also found that there is a potential heterogeneity between studies. The results of our meta-analysis are in consensus with a previous meta-analysis that provided no evidence of a significant association between AGT M235T polymorphism and DN risk (40). In contrast to this, two independent meta-analyses demonstrated the association between AGT M235T and DN risk in Caucasian (41) and Asian populations (42).

Conclusion
In conclusion, this meta-analysis found no evidence of a link between AGT M235T and DN risk. Since, the majority of the studies in this meta-analysis were Asian and Caucasian, the distribution of AGT M23T varies across ethnic groups and the results cannot be generalised. However, validation of this association will require multicenter and large population-based studies.