# VPS35 Deficiency Markedly Reduces the Proliferation of HEK293 Cells

## TL;DR

This study shows that VPS35 deficiency significantly reduces cell growth and survival in HEK293 cells by affecting apoptosis, mitochondrial function, and the cell cycle.

## Contribution

The study reveals the critical role of VPS35 in retromer function and cell survival through a detailed analysis of KO HEK293 cells.

## Key findings

- VPS35 deficiency impairs retromer formation and reduces cell proliferation.
- VPS35 KO increases apoptosis markers and mitochondrial fragmentation.
- Restoring VPS35 recovers retromer components and normalizes cell death.

## Abstract

Background/Objectives: The retromer protein complex is involved in various physiological processes, especially endosomal trafficking, and its dysregulation has been linked to Alzheimer’s disease and Parkinson’s disease, as well as VPS35 knockout (KO), causing early embryonic lethality. We aimed to investigate the cellular consequences of VPS35 deficiency. Methods: To investigate the effects of VPS35 loss, we used CRISPR/Cas9 to generate VPS35 KO human embryonic kidney 293 (HEK293) cells. We analyzed changes in retromer component expression, cell proliferation, apoptosis, and mitochondrial dynamics using Western blotting, terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay, and confocal microscopy. Results: VPS35 KO led to a significant reduction in cell proliferation and decreased expression of VPS29 and VPS26, both essential for retromer complex assembly. Consequently, retromer formation was impaired. Compared to control cells, KO cells exhibited elevated levels of cleaved caspase-3, poly(ADP-ribose) polymerase, cytochrome C, and p21, while the expression of Ki-67, CDK4, and cyclin D was reduced. Additionally, VPS35 deletion also promoted mitochondrial fragmentation, associated with increased expression of mitochondrial fission-related proteins. Finally, the rescue experiment using the human VPS35 gene confirmed that the recovery of VPS35 not only led to the recovery of the essential elements constituting the retromer but also the recovery of molecules related to the cell cycle, restoring cell death to a normal level. Conclusions: These findings suggest that VPS35 plays a critical role in cell growth and survival by modulating apoptosis, mitochondrial dynamics, and cell cycle progression.