ELOVL6 in the C16/C18 Ratio Control: An Emerging Regulator of Lipid and Glucose Metabolism

Background/Objectives: Elongation of very long chain fatty acids protein 6 (ELOVL6) is a key enzyme that catalyzes the conversion of palmitoyl-CoA (C16:0-CoA) to stearoyl-CoA (C18:0-CoA). Its product C18:0-CoA is further desaturated by stearoyl-CoA desaturase 1 (SCD1) to generate C18:1n-9-CoA. In this review, C18:0/C16:0 refers to the molar ratio of C18:0 to C16:0 within a specified lipid pool, such as acyl coenzyme A (acyl-CoA), total fatty acids, or phospholipids. It serves as a surrogate marker for ELOVL6 elongation flux under specific conditions. C18:1n-9/C18:0 refers to the oleic acid to stearic acid molar ratio. It serves as a surrogate marker for SCD1-related flux. C16:0/C18:1n-9 refers to the palmitic acid to oleic acid molar ratio. It is a composite readout influenced by both ELOVL6 and SCD1-related reactions. The “C16/C18 ratio” is used only as an umbrella term for C16/C18-related ratios. This review aims to explore how ELOVL6 modulates the balance of the C16/C18 ratio through molecular mechanisms. It also examines how this regulation contributes to glucose and lipid metabolism and to tissue-specific functions, and evaluates the potential of ELOVL6 as a therapeutic target for metabolic diseases. Methods: A structured literature search was conducted on recent advances regarding the enzymatic properties, transcriptional regulation, and animal model phenotypes of ELOVL6. A comprehensive synthesis was performed from molecular mechanisms to clinical translation. Results: In the liver, ELOVL6 mainly influences the direction of fatty acid storage and ceramide signaling. In adipose tissue, it influences insulin signal transduction by remodeling membrane phospholipid composition. In pancreatic β-cells, it affects insulin secretory function by contributing to the C16/C18 ratio. When the C16/C18 ratio becomes imbalanced, cells progress toward insulin resistance (IR), inflammation, and hepatic steatosis. Conclusions: Restoring the balance of the C16/C18 ratio is a potential therapeutic strategy for metabolic diseases. However, targeting ELOVL6 faces challenges such as structural biology bottlenecks and tissue-specific side effects. Future research should focus on the fine regulation of ELOVL6, combined with dietary interventions, to advance the translation of ELOVL6 from basic research to clinical intervention for metabolic diseases.