TitleAutophagy Is Required for Sortilin-Mediated Degradation of Apolipoprotein B100.
Publication TypeJournal Article
Year of Publication2018
AuthorsAmengual J, Guo L, Strong A, Madrigal-Matute J, Wang H, Kaushik S, Brodsky JL, Rader DJ, Cuervo AMaria, Fisher EA
JournalCirc Res
Date Published2018 Feb 16

RATIONALE: Genome-wide association studies identified single-nucleotide polymorphisms near the locus strongly associated with decreased plasma LDL-C (low-density lipoprotein cholesterol) levels and protection from atherosclerotic cardiovascular disease and myocardial infarction. The minor allele of the causal single-nucleotide polymorphism locus creates a putative C/EBPα (CCAAT/enhancer-binding protein α)-binding site in the promoter, thereby increasing in homozygotes sortilin expression by 12-fold in liver, which is rich in this transcription factor. Our previous studies in mice have showed reductions in plasma LDL-C and its principal protein component, apoB (apolipoprotein B) with increased expression, and in vitro studies suggested that sortilin promoted the presecretory lysosomal degradation of apoB associated with the LDL precursor, VLDL (very-low-density lipoprotein).

OBJECTIVE: To determine directly that overexpression results in apoB degradation and to identify the mechanisms by which this reduces apoB and VLDL secretion by the liver, thereby contributing to understanding the clinical phenotype of lower LDL-C levels.

METHODS AND RESULTS: Pulse-chase studies directly established that overexpression results in apoB degradation. As noted above, previous work implicated a role for lysosomes in this degradation. Through in vitro and in vivo studies, we now demonstrate that the sortilin-mediated route of apoB to lysosomes is unconventional and intersects with autophagy. Increased expression of sortilin diverts more apoB away from secretion, with both proteins trafficking to the endosomal compartment in vesicles that fuse with autophagosomes to form amphisomes. The amphisomes then merge with lysosomes. Furthermore, we show that sortilin itself is a regulator of autophagy and that its activity is scaled to the level of apoB synthesis.

CONCLUSIONS: These results strongly suggest that an unconventional lysosomal targeting process dependent on autophagy degrades apoB that was diverted from the secretory pathway by sortilin and provides a mechanism contributing to the reduced LDL-C found in individuals with overexpression.

Alternate JournalCirc. Res.
PubMed ID29301854
PubMed Central IDPMC5815905
Grant ListP30 DK079307 / DK / NIDDK NIH HHS / United States
P30 DK041296 / DK / NIDDK NIH HHS / United States
R01 HL058541 / HL / NHLBI NIH HHS / United States
R01 HL127930 / HL / NHLBI NIH HHS / United States
P30 AG038072 / AG / NIA NIH HHS / United States
R01 DK098408 / DK / NIDDK NIH HHS / United States
R01 HL084312 / HL / NHLBI NIH HHS / United States
P01 HL059407 / HL / NHLBI NIH HHS / United States
P01 AG031782 / AG / NIA NIH HHS / United States