LRP1 Protein Deficiency Exacerbates Palmitate-induced Steatosis and Toxicity in Hepatocytes

Allyson N Hamlin,Joshua E Basford,Anja Jaeschke,David Y Hui

doi:10.1074/jbc.m116.717744

Allyson N Hamlin, Joshua E Basford + Show 2 more

Open Access

https://doi.org/10.1074/jbc.m116.717744

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Abstract

LRP1 (LDL receptor-related protein-1) is a ubiquitous receptor with both cell signaling and ligand endocytosis properties. In the liver, LRP1 serves as a chylomicron remnant receptor and also participates in the transport of extracellular cathepsin D to the lysosome for prosaposin activation. The current study showed that in comparison with wild type mice, hepatocyte-specific LRP1 knock-out (hLrp1(-/-)) mice were more susceptible to fasting-induced lipid accumulation in the liver. Primary hepatocytes isolated from hLrp1(-/-) mice also accumulated more intracellular lipids and experienced higher levels of endoplasmic reticulum (ER) stress after palmitate treatment compared with similarly treated hLrp1(+/+) hepatocytes. Palmitate-treated hLrp1(-/-) hepatocytes displayed similar LC3-II levels, but the levels of p62 were elevated in comparison with palmitate-treated hLrp1(+/+) hepatocytes, suggesting that the elevated lipid accumulation in LRP1-defective hepatocytes was not due to defects in autophagosome formation but was due to impairment of lipophagic lipid hydrolysis in the lysosome. Additional studies showed increased palmitate-induced oxidative stress, mitochondrial and lysosomal permeability, and cell death in hLrp1(-/-) hepatocytes. Importantly, the elevated cell death and ER stress observed in hLrp1(-/-) hepatocytes were abrogated by E64D treatment, whereas inhibiting ER stress diminished cell death but not lysosomal permeabilization. Taken together, these results documented that LRP1 deficiency in hepatocytes promotes lipid accumulation and lipotoxicity through lysosomal-mitochondrial permeabilization and ER stress that ultimately result in cell death. Hence, LRP1 dysfunction may be a major risk factor in fatty liver disease progression.

Highlights

LRP1 (LDL receptor-related protein-1) is a ubiquitously expressed 600-kDa receptor that was originally identified as an endocytic receptor responsible for cellular uptake and plasma clearance of macromolecules such as apolipoprotein E-containing lipoproteins and protease-protease inhibitor complexes
When primary hepatocytes isolated from hLrp1ϩ/ϩ and hLrp1Ϫ/Ϫ mice were incubated with or without VLDL, significantly less lipid accumulation was observed in hepatocytes without LRP1 expression (Fig. 2A)
The condition is generally asymptomatic and considered benign, ϳ10 –20% of nonalcoholic fatty liver disease cases progress to nonalcoholic steatohepatitis, a chronic liver disease characterized by fatty liver degeneration, fibrosis, and inflammation

Summary

Introduction

LRP1 (LDL receptor-related protein-1) is a ubiquitously expressed 600-kDa receptor that was originally identified as an endocytic receptor responsible for cellular uptake and plasma clearance of macromolecules such as apolipoprotein E-containing lipoproteins and protease-protease inhibitor complexes. Impaired Lipophagy with Defective LRP1 Expression in Hepatocytes—The set of experiments was undertaken to explore the mechanism underlying the increased lipid accumulation observed in palmitate-treated hLrp1Ϫ/Ϫ hepatocytes.

Results

Conclusion