The oleic/palmitic acid imbalance in exosomes isolated from NAFLD patients induces necroptosis of liver cells via the elongase-6/RIP-1 pathway

Abstract

Excessive toxic lipid accumulation in hepatocytes underlies the development of non-alcoholic fatty liver disease (NAFLD), phenotypically characterized by necrosis and steato-fibrosis, whose molecular mechanism is not yet fully understood. Patients with NAFLD display an imbalanced palmitic (PA) to oleic acid (OA) ratio. Moreover, increasing experimental evidence points out a relevant involvement of the exosomal content in disease progression. Aim of the study was to highlight the PA/OA imbalance within circulating exosomes, the subsequent intracellular alterations, and the impact on NALFD. Liver cells were challenged with exosomes isolated from both healthy subjects and NAFLD patients. The exosomal PA/OA ratio was artificially modified, and biological effects were evaluated. A NAFLD-derived exosomal PA/OA imbalance impacts liver cell cycle and cell viability. OA-modified NAFLD-derived exosomes restored cellular viability and proliferation, whereas the inclusion of PA into healthy subjects-derived exosomes negatively affected cell viability. Moreover, while OA reduced the phosphorylation and activation of the necroptosis marker, Receptor-interacting protein 1 (phospho-RIP-1), PA induced the opposite outcome, alongside increased levels of stress fibers, such as vimentin and fibronectin. Administration of NAFLD-derived exosomes led to increased expression of Elongase 6 (ELOVL6), Stearoyl-CoA desaturase 1 (SCD1), Tumor necrosis factor α (TNF-α), Mixed-lineage-kinase-domain-like-protein (MLKL) and RIP-1 in the hepatocytes, comparable to mRNA levels in the hepatocytes of NAFLD patients reported in the Gene Expression Omnibus (GEO) database. Genetic and pharmacological abrogation of ELOVL6 elicited a reduced expression of downstream molecules TNF-α, phospho-RIP-1, and phospho-MLKL upon administration of NAFLD-derived exosomes. Lastly, mice fed with high-fat diet exhibited higher phospho-RIP-1 than mice fed with control diet. Targeting the Elongase 6–RIP-1 signaling pathway offers a novel therapeutic approach for the treatment of the NALFD-induced exosomal PA/OA imbalance.

Unveiling the Potential of Extracellular Vesicles as Biomarkers and Therapeutic Nanotools for Gastrointestinal Diseases

“…When the exosomes carry a higher concentration of palmitic acid compared to oleic acid, the hepatic cells that endocytose these vesicles activate the necroptosis pathway, leading to cell death. Conversely, restoring the balance of these two acids in exosomes from MASLD patients prevents cell death [ 44 ]. Therefore, the use of a lipidomic analysis of plasma-derived exosomes could be a good diagnostic and prognostic approach in patients with MASLD.…”

“…These modifications in exosomal membranes influence the membranes of stellate cells (LX2) stimulated by the exosomes from these patients. This suggests a potential role in the early detection of disease progression, which could be discerned through the lipidomic analysis of exosomal membranes [ 44 , 45 ]. In the realm of liver pathologies, the analysis of circulating EVs has proven effective in distinguishing patients with metabolic dysfunction-associated steatohepatitis (MASH) from those with chronic hepatitis compared to healthy controls.…”

“…Scavo et al demonstrated that rebalancing the fatty acid composition in liver cells, using exosomes derived from MASLD patients loaded with oleic acid, can reverse MASLD degeneration. This approach inhibits the enzymatic cascade involved in disease progression and reduces the fibrotic state [ 44 ].…”

Significant Increase in Oxidative Stress Indices in Erythrocyte Membranes of Obese Patients with Metabolically-Associated Fatty Liver Disease

“…The erythrocyte membrane might be a valid biomarker for the fatty acid composition present in other body cells. Several studies have shown that changes in the fatty acid composition of red blood cell (RBC) membranes have been observed in different metabolic diseases, including Nonalcoholic Fatty Liver Disease (NAFLD) and colorectal cancer (CRC) [ 7 , 8 , 9 , 10 ]. In this regard, we have previously found low levels of Saturation Index, given by the relationship of stearic acid to oleic acid in RBC membranes of patients with severe Nonalcoholic Fatty Liver Disease (NAFLD) compared to controls [ 11 ].…”