Abstract
Persons with Down syndrome (DS, trisomy 21) have widespread cellular protein trafficking defects. There is a paucity of data describing the intracellular transport of IgG in the context of endosomal-lysosomal alterations linked to trisomy 21. In this study, we analyzed the intracellular traffic of IgG mediated by the human neonatal Fc receptor (FcRn) in fibroblast cell lines with trisomy 21. Intracellular IgG trafficking studies in live cells showed that fibroblasts with trisomy 21 exhibit higher proportion of IgG in lysosomes (~10% increase), decreased IgG content in intracellular vesicles (~9% decrease), and a trend towards decreased IgG recycling (~55% decrease) in comparison to diploid cells. Amyloid-beta precursor protein (APP) overexpression in diploid fibroblasts replicated the increase in IgG sorting to the degradative pathway observed in cells with trisomy 21. The impact of APP on the expression of FCGRT (alpha chain component of FcRn) was investigated by APP knock down and overexpression of the APP protein. APP knock down increased the expression of FCGRT mRNA by ~60% in both diploid and trisomic cells. Overexpression of APP in diploid fibroblasts and HepG2 cells resulted in a decrease in FCGRT and FcRn expression. Our results indicate that the intracellular traffic of IgG is altered in cells with trisomy 21. This study lays the foundation for future investigations into the role of FcRn in the context of DS.
Competing Interest Statement
The authors have declared no competing interest.
Nonstandard abbreviations
- ACTB
- Actin beta
- AD
- Alzheimer’s disease
- AICD
- APP intracellular domain
- APP
- Amyloid-beta precursor protein
- APP-βCTF
- APP β-carboxyl-terminal fragment
- BACE1
- Beta-site APP cleaving enzyme 1
- BSA
- Bovine serum albumin
- DIC
- Differential interference contrast
- DS
- Down syndrome
- EEA1
- Early endosome antigen 1
- ELISA
- Enzyme-linked immunosorbent assay
- EV
- Empty vector
- FCGRT
- Fc fragment of IgG receptor and transporter
- FcRn
- Neonatal Fc receptor
- GFP
- Green fluorescent protein
- hIgG1
- Human IgG type 1
- IgG
- Immunoglobulin G
- LAMP1
- Lysosome-associated membrane glycoprotein 1
- mAbs
- Monoclonal Antibody drugs
- MEM
- Minimal essential medium
- mRNA
- Messenger RNA
- NDS
- No-DS
- NS-siRNA
- Non-Targeting siRNA
- PBS
- Phosphate-buffered saline
- PCC
- Pearson’s correlation coefficient
- PCR
- Polymerase chain reaction
- Rab11
- Ras-related protein Rab-11A
- RSV
- respiratory syncytial virus infections
- RNA
- Ribonucleic acid
- ROI
- Region of interest
- SD
- Standard deviation
- siRNA
- Silencing RNA