Our results also highlight the possibility that the Golgi apparatus harbors a check point for QC of efficient post-translational N-glycosylation, allowing glycoproteins that fail QC to be diverted to the lysosomal compartment.Īberrant AT-1 activity affects secretory pathway-related processes Collectively our results indicate that AT-1 is essential to maintain proper organization and engagement of the secretory pathway. The AT-1 sTg cellular phenotype was associated with significant alterations in Golgi-based N-glycan modification, highlighting changes in the overall quality of the secretome, together with marked expansion of the lysosomal network. We found that AT-1 sTg animals display enlarged cisternae within the rough ER, enlarged ER Golgi Intermediate Compartment (ERGIC), and a marked delay in protein trafficking to the cell surface, while AT-1 S113R/+ mice display contraction of the Golgi apparatus.

In this study, we investigated the outcomes of dysregulated cytosol-to-ER acetyl-CoA flux within AT-1 sTg and AT-1 S113R/+ mice on the engagement and functional organization of the secretory pathway, as well as the overall quality of secreted glycoproteins (referred to as the secretome).

Mice with neuronal-specific overexpression of AT-1 (AT-1 nTg) develop an autistic-like phenotype 5 while mice with systemic overexpression (AT-1 sTg) develop a progeria-like phenotype 6. AT-1 S113R/S113R mice, which lack AT-1 activity, die during embryogenesis, while AT-1 S113R/+ mice, a model of AT-1 haploinsufficiency, develop peripheral and central neuropathy as well as propensity to infections and cancer 4. These human disorders have been effectively recapitulated in mouse models. Loss-of-function mutations or gene duplication events in AT-1/SLC33A1 are associated with severe disease phenotypes spanning from spastic paraplegia (heterozygous mutation) to developmental delay and premature death (homozygous mutations) 9, 10, 11 and intellectual disability with autistic-like traits and progeria-like dysmorphic features (gene duplication) 12, 13. Supporting evidence comes from mouse models of increased or decreased ER acetylation 4, 5, 6. Studies performed with type I glycoproteins suggest that successful acetylation of the nascent polypeptide is necessary for successful engagement of the secretory pathway 2, 8. The acetylation of ER cargo nascent glycoproteins requires ATase1 and ATase2 to interact with the oligosaccharyl tranferase complex (OST) and acetylate correctly folded nascent glycoproteins that are transiting across the ER membrane 1, 2. ER acetylation requires an ER membrane transporter, AT-1/SLC33A1, which translocates acetyl-CoA from the cytosol to the ER lumen, and two ER membrane-bound acetyltransferases, ATase1/NAT8B and ATase2/NAT8, which acetylate ER cargo proteins within the lumen of the organelle 1, 3, 7. Nε-lysine acetylation in the Endoplasmic Reticulum (ER) has emerged as an essential component of the quality control (QC) machinery that maintains protein homeostasis (proteostasis) within the ER 1, 2, 3, 4, 5, 6. In particular, AT-1 sTg animals displayed a marked delay in Golgi-to-plasma membrane protein trafficking, significant alterations in Golgi-based N-glycan modification, and a marked expansion of the lysosomal network. The animals displayed reorganization of the ER, ERGIC, and Golgi apparatus.

Here, we used two models of AT-1 dysregulation to investigate dynamics of the secretory pathway: AT-1 sTg, a model of systemic AT-1 overexpression, and AT-1 S113R/+, a model of AT-1 haploinsufficiency. Dysfunctional AT-1, as caused by gene mutation or duplication events, results in severe disease phenotypes. ER acetylation is ensured by a membrane transporter, AT-1/SLC33A1, which translocates cytosolic acetyl-CoA into the ER lumen, and two acetyltransferases, ATase1 and ATase2, which acetylate nascent polypeptides within the ER lumen. Nε-lysine acetylation in the ER is an essential component of the quality control machinery.

Cytosol and er lumen