Elucidating mechanisms of cellular metabolic dysfunction and lipotoxicity

Abstract

The accumulation of lipids is a hallmark of metabolic disease due to disruption of normal functions of cells and tissues, a condition referred to as lipotoxicity. For example, in lipodystrophy, excess lipids build up ectopically in non-adipose tissue, and in obesity, fat deposits in adipocytes are overwhelmed by lipid accumulation. Saturated fatty acids (SFA), such as palmitate, are particularly toxic lipids in skeletal muscle, heart, liver, and pancreatic β-cells and can contribute to obesity-associated diseases. Although canonical adaptive metabolic processes like lipid storage or desaturation are known cellular responses to saturated fat exposure, the link between SFA metabolism and organellar biology remains an area of active inquiry. We performed a genome-wide CRISPR knockout screen in human epithelial cells to identify modulators of SFA toxicity. We combined unbiased screening methods to identify changes to the cellular lipidome and cellular pathways that were dependent on SFA exposure. This analysis identified Fas-associated factor family member 2 (FAF2) as a mediator of the stress response to SFA exposure. We further reveal that organellar compartmentalization of metabolism, specifically peroxisomal proteins involved in ether lipid synthesis, are important regulators of lipotoxicity. We found that in addition to lipid regulatory effects, FAF2 is a critical bifunctional coregulator of peroxisomal and fatty acid biology. We further demonstrated the requirement of the ubiquitin-regulatory X (UBX) and UAS thioredoxin-like domains of FAF2 for peroxisomal protein abundance and SFA-induced cellular stress. Our work highlights the role of FAF2 in regulating peroxisomal abundance and function, and the peroxisome as a key organelle in the cellular response to SFAs.