POSSIBLE IMPLICATIONS OF TOLL-LIKE RECEPTOR 4 (TLR4) MUTATIONS IN PATIENTS WITH NON-ALCOHOLIC FATTY LIVER DISEASE (NAFLD)

Abstract

Title: Possible Implications of Toll-like receptor 4 mutations in patients with NonAlcoholic Fatty Liver Disease Non-Alcoholic Fatty Liver Disease (NAFLD) is defined as the accumulation of fats, mainly triglycerides, in the liver exceeding 5% of its weight in the absence of any significant alcohol consumption. It comprises a wide spectrum of diseases that include non-alcoholic fatty liver (NAFL) characterized by simple steatosis and non-alcoholic steatohepatitis (NASH) characterized by steatosis with inflammation and fibrosis. The prevalence of NAFLD has increased in the recent years reaching 37.3% in 2019 due to the rise in metabolic disorder. NAFLD is a multifactorial disease that is associated with several factors of the metabolic syndrome including obesity, type-2 diabetes, and insulin resistance. Several genes also affect the development and pathogenesis of NAFLD such as Patatin-like phospholipase domain-containing protein 3 (PNPLA3), monocyte differentiation antigen CD14 (CD14), tumor necrosis factor (TNF), and tolllike receptor 4 (TLR4). In the current study, we examined the role of TLR4 polymorphisms in the progression of NAFLD in a sample of Lebanese individuals, and we attempted to identify a genotype-phenotype correlation between TLR4 gene mutations and the fibrosis stage of the patients. NAFLD patients (30) and healthy controls (19) underwent a number of clinical tests and examinations including liver function tests, hematological tests and lipid profiling. Moreover, blood samples were collected form all individuals for nucleotide base changes in the TLR4 gene. DNA extraction was performed followed by PCR amplification of the 3 exons, followed by agarose gel electrophoresis and sequencing of the amplicons to identify mutations and polymorphisms in patients and healthy individuals. The sequencing of TLR4 gene revealed the presence of many heterozygous missense mutations and frameshifts in exon-1 and 3. No frame shifts were detected in exon-2. The majority of mutations were located in exon-3 encoding the extracellular domain involved in ligand recognition and binding. Our findings were not conclusive when attempts to correlate NAFLD with obesity, diabetes or age were examined. Furthermore, we have detected in our sample: a) the two mutations Thr399Ile and Asp299Gly reported to exhibit a protective role in line with literature; b) A new homozygous mutation Gly249Val, in exon -3 present in patients with F0 fibrosis stage, may have a protective role in NAFLD progression; and c) frameshift mutations localized 3 between positions 241-251 identified in most patients with F0 stage and controls suggesting a possible protective role, that may be attributed to the disruption of ligand binding or recognition. To sum up, TLR4 gene is highly polymorphic making it difficult to correlate the genotype with the NAFLD progression and fibrosis stage. The role of other genes may not be excluded and should be investigated to delineate the role of these genes in disease progression and fibrosis.