Sterol regulatory element–binding protein 1c (SREBP-1c) is a central regulator of lipogenesis whose activity is controlled by proteolytic cleavage. The metabolic factors that affect its processing are incompletely understood. Here, we show that dynamic changes in the acyl chain composition of ER phospholipids affect SREBP-1c maturation in physiology and disease. The abundance of polyunsaturated phosphatidylcholine in liver ER is selectively increased in response to feeding and in the setting of obesity-linked insulin resistance. Exogenous delivery of polyunsaturated phosphatidylcholine to ER accelerated SREBP-1c processing through a mechanism that required an intact SREBP cleavage–activating protein (SCAP) pathway. Furthermore, induction of the phospholipid-remodeling enzyme LPCAT3 in response to liver X receptor (LXR) activation promoted SREBP-1c processing by driving the incorporation of polyunsaturated fatty acids into ER. Conversely, LPCAT3 deficiency increased membrane saturation, reduced nuclear SREBP-1c abundance, and blunted the lipogenic response to feeding, LXR agonist treatment, or obesity-linked insulin resistance. Desaturation of the ER membrane may serve as an auxiliary signal of the fed state that promotes lipid synthesis in response to nutrient availability.
Xin Rong, Bo Wang, Elisa N.D. Palladino, Thomas Q. de Aguiar Vallim, David A. Ford, Peter Tontonoz
Usage data is cumulative from November 2018 through November 2019.
Usage information is collected from two different sources: this site (JCI) and Pubmed Central (PMC). JCI information (compiled daily) shows human readership based on methods we employ to screen out robotic usage. PMC information (aggregated monthly) is also similarly screened of robotic usage.
Various methods are used to distinguish robotic usage. For example, Google automatically scans articles to add to its search index and identifies itself as robotic; other services might not clearly identify themselves as robotic, or they are new or unknown as robotic. Because this activity can be misinterpreted as human readership, data may be re-processed periodically to reflect an improved understanding of robotic activity. Because of these factors, readers should consider usage information illustrative but subject to change.