The adaptor protein PID1 regulates receptor-dependent endocytosis of postprandial triglyceride-rich lipoproteins

Abstract

ObjectiveInsulin resistance is associated with impaired receptor dependent hepatic uptake of triglyceride-rich lipoproteins (TRL), promoting hypertriglyceridemia and atherosclerosis. Next to low-density lipoprotein (LDL) receptor (LDLR) and syndecan-1, the LDLR-related protein 1 (LRP1) stimulated by insulin action contributes to the rapid clearance of TRL in the postprandial state. Here, we investigated the hypothesis that the adaptor protein phosphotyrosine interacting domain-containing protein 1 (PID1) regulates LRP1 function, thereby controlling hepatic endocytosis of postprandial lipoproteins.MethodsLocalization and interaction of PID1 and LRP1 in cultured hepatocytes was studied by confocal microscopy of fluorescent tagged proteins, by indirect immunohistochemistry of endogenous proteins, by GST-based pull down and by immunoprecipitation experiments. The in vivo relevance of PID1 was assessed using whole body as well as liver-specific Pid1-deficient mice on a wild type or Ldlr-deficient (Ldlr−/−) background. Intravital microscopy was used to study LRP1 translocation in the liver. Lipoprotein metabolism was investigated by lipoprotein profiling, gene and protein expression as well as organ-specific uptake of radiolabelled TRL.ResultsPID1 co-localized in perinuclear endosomes and was found associated with LRP1 under fasting conditions. We identified the distal NPxY motif of the intracellular C-terminal domain (ICD) of LRP1 as the site critical for the interaction with PID1. Insulin-mediated NPxY-phosphorylation caused the dissociation of PID1 from the ICD, causing LRP1 translocation to the plasma membrane. PID1 deletion resulted in higher LRP1 abundance at the cell surface, higher LDLR protein levels and, paradoxically, reduced total LRP1. The latter can be explained by higher receptor shedding, which we observed in cultured Pid1-deficient hepatocytes. Consistently, PID1 deficiency alone led to increased LDLR-dependent endocytosis of postprandial lipoproteins and lower plasma triglycerides. In contrast, hepatic PID1 deletion on an Ldlr−/− background reduced lipoprotein uptake into liver and caused plasma TRL accumulation.ConclusionsBy acting as an insulin-dependent retention adaptor, PID1 serves as a regulator of LRP1 function controlling the disposal of postprandial lipoproteins. PID1 inhibition provides a novel approach to lower plasma levels of pro-atherogenic TRL remnants by stimulating endocytic function of both LRP1 and LDLR in the liver.

Heritability and Genome-Wide Association Study of Plasma Cholesterol in Chinese Adult Twins

“…Substantive SNPs introduced by imputation reached the suggestive level associated with cholesterol. SNPs rs17578959 and rs28845526 were located in the PID1 gene, which served as the regulator of the LDLR-related protein 1 ( LRP1 ) function and controlled the processing of postprandial lipoproteins ( 68 ). Solute Carrier Family 13 Member 1 ( SLC13A1 ) gene can regulate the cholesterol level by participating in transport of glucose and other sugars, bile salts and organic acids, metal ions and amine compounds pathways.…”

Metabolic regulation through the endosomal system

“…It will be interesting to see how cargo specificity in the retrieving pathway is achieved and how this is physiologically regulated. Recently, an elegant study has suggested that the adaptor protein PID1, which regulates whole body glucose homeostasis, is an insulin‐dependent molecular switch that regulates the cellular distribution of another cholesterol transporter, LRP1 (low density lipoprotein particle related protein 1), and functions in the postprandial state by controlling SNX17 binding to LRP1 . Interestingly, the CCC complex is also required for LRP1 trafficking to the plasma membrane, suggesting that this complex could mediate the insulin‐dependent regulation of LRP1 trafficking via PID1 .…”

Overexpression of PID1 reduces high density lipoprotein level and functionality in swine

“…LRP1 belongs to the LDL receptor (LDLR) family and involves in various biological processes, such as lipid metabolism, degradation of proteases, tissue invasion, and cell growth or differentiation . Recent study has found that PID1 lowers plasma levels of pro‐atherogenic triglyceride‐rich lipoproteins (TRL) remnants by stimulating endocytic function of both LRP1 and LDLR in the liver . Thus we hypothesized that PID1 might play a role in lipid metabolism.…”