The Pro12Ala polymorphism in the PPAR­γ2 gene is not associated with an increased risk of NAFLD in Iranian patients with type 2 diabetes mellitus

Saremi et al. Cellular & Molecular Biology Letters https://doi.org/10.1186/s11658-019-0138-0 SHORT REPORT (2019) 24:12 Cellular & Molecular Biology Letters Open Access The Pro12Ala polymorphism in the PPARγ2 gene is not associated with an increased risk of NAFLD in Iranian patients with type 2 diabetes mellitus Leila Saremi1, Shirin Lotfipanah2, Masumeh Mohammadi1, Hassan Hosseinzadeh3, Mina Fathi-Kazerooni4, Behrooz Johari5 and Zohreh Saltanatpour6* * Correspondence: z-saltanatpour@ razi.tums.ac.ir; zohre_saltanatpour@ yahoo.com 6 Medical Genetic Center, Endocrinology and Metabolism Research Institute (EMRI), Tehran University of Medical Sciences (TUMS), Tehran, Iran Full list of author information is available at the end of the article Abstract Background: The peroxisome proliferator-activated receptors (PPARs) are ligandactivated transcription factors that belong to the nuclear hormone receptor superfamily. Several studies have demonstrated a significant association between Pro12Ala polymorphism of the PPARγ2 gene and metabolic disorders. Therefore, this study aimed to evaluate the association of Pro12Ala polymorphism with increased risk of NAFLD in Iranian patients with type 2 diabetes mellitus. Methods: This cross-sectional study was performed on 145 healthy control subjects and 145 NAFLD patients with a history of type 2 diabetes. Pro12Ala polymorphism genotyping was performed using PCR–restriction fragment length polymorphism (RFLP) technique with the Bs1I restriction enzyme. Results: Our results demonstrated that CC and GG genotypes of Pro12Ala were found in the participants, but there was no statistically significant difference between NAFLD patients and healthy controls (P = 0.64 and χ2 = 0.21). Conclusion: This study suggests that Pro12Ala polymorphism of the PPARγ2 gene cannot be considered as a risk factor for NAFLD in the Iranian population. Keywords: Pro12Ala polymorphism, PPARγ2 gene, NAFLD, Type 2 diabetes mellitus Introduction Nonalcoholic fatty liver disease (NAFLD) is one of the most prevalent forms of progressive liver disease, which is characterized by obesity, dyslipidemia, type 2 diabetes mellitus (T2DM), hypercholesterolemia, hypertension, insulin resistance, cirrhosis, liver failure and hepatocellular carcinoma [1–3]. NAFLD is highly prevalent in T2DM and the prevalence of NAFLD in obese adults with T2DM has been estimated to be greater than 70%. The most important treatment method of NAFLD is to increase insulin sensitivity by lifestyle changes [2–10]. Epidemiological, familial, and twin studies have suggested that genetic background and environmental factors play important roles in the pathogenesis of NAFLD as multifactorial diseases [8–16]. The peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors which belong to the nuclear hormone receptor superfamily and © The Author(s). 2019 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/ publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Saremi et al. Cellular & Molecular Biology Letters (2019) 24:12 Page 2 of 8 consist of three subtypes, each of them encoded by different genes: PPARα (NR1C1), PPARγ (NR1C3) and PPARδ (NP1C2) [3, 16–18]. The PPARγ receptor plays a key role in the regulation of adipocyte-specific genes, lipid metabolism, glucose homeostasis, insulin sensitivity and blood pressure [2, 16, 19, 20]. The human PPARγ gene, located on chromosome 3p25, has nine exons (A1, A2, B, exons 1–6 from 5′ to 3′ direction), and its protein product has three isoforms, PPARγ1, PPAR-γ2 and PPARγ3, which are produced by mRNA alternative splicing of PPARγ [4, 20, 21]. Among them, the PPAR-γ2 isoform is expressed predominantly in the adipose tissue, where it plays an important role in regulating adipogenic differentiation and as a mediator of insulin sensitivity [20, 22–25]. The single nucleotide polymorphisms (SNPs) of the PPAR-γ2 gene have been shown to be associated with susceptibility to several metabolic disorders and many studies have shown a strong relationship between this gene and the occurrence of T2DM in many populations [9, 10, 26, 27]. The polymorphism rs1801282 (c.34C > G) on codon 12 of exon B of the PPAR-γ2 gene, which leads to the substitution of proline with alanine (Pro12Ala), was found to be associated with higher insulin sensitivity, lower body mass index (BMI), decreased risk of T2DM and diabetic nephropathy [28–32]. Several investigations have shown that there is an association between this polymorphism and increased risk of metabolic disorders in various populations. However, published results on the genetic associations of this SNP with NAFLD are controversial and inconclusive [33–36]. This study aimed to elucidate the association of Pro12Ala with increased risk of NAFLD in Iranian patients with type 2 diabetes mellitus as a common metabolic disorder. Material and methods Subjects This case–control study was based on 290 individuals of Iranian ancestry. The patient group included 145 patients with biopsy-proven NAFLD with a history of type 2 diabetes attending the Shahid Rajaei Cardiovascular Medical and Research Center in Tehran, Iran. All patients were recruited by use of liver biopsy. Only patients with a negative history of alcohol consumption and other known causes of chronic liver disease (e.g. autoimmune hepatitis, viral hepatitis, use of hepatotoxic medications such as antibiotics, glucocorticoids, tamoxifen or other anti-neoplastic drugs) were analyzed [5, 37]. Patients with unavailable liver ultrasound examination were excluded from the study. The controls were 145 individuals representing a general population sample from the same geographical region who had normal abdominal ultrasonography. Participants were matched for sex and age and numbers of men and women were equal in both groups. All participants gave written informed consent, and this study conforms to the principles of the Declaration of Helsinki. Both patient and control subjects’ characteristics including gender and age are shown in Table 1. Table 1 Characteristics of study population Characteristics Total Patients Controls P value 145 145 – 1.0 Men 73 73 Women 72 72 Mean age 53.9±9 51.3±10 0.98 Saremi et al. Cellular & Molecular Biology Letters (2019) 24:12 Clinical and laboratory findings were collected for each NAFLD patient from the clinical charts, including fasting blood sugar (FBS), BMI, creatine (Cr), total serum cholesterol (TC), triglyceride (TG), lo (...truncated)