Astrocytic BAG3 regulates protein clearance systems linked to Alzheimer disease
Loss of the chaperone mediator in human astrocytes disrupts autophagy, proteasomes, and retromer traffic while impairing amyloid-beta proteostasis in neuron cocultures.
In human cell models and postmortem human brain tissue, researchers investigated how Bcl-2-associated athanogene 3 (BAG3) influences astrocyte biology and Alzheimer's disease. Using CRISPR/Cas9-edited human induced pluripotent stem cells, the team found that BAG3 loss disrupted astrocytes more severely than neurons. The deficient astrocytes showed reduced autophagy, diminished lysosomal abundance and activity, and compromised proteasome function. Coimmunoprecipitation revealed that BAG3 binds proteasome regulators, HSPB8, and the retromer complex component VPS35. BAG3 deficiency altered retromer function, affecting amyloid precursor protein localization in endosomes, and deregulated disease-relevant proteins including GFAP and BIN1. Coculturing BAG3-knockout astrocytes with mutant neurons impaired amyloid-beta proteostasis. In postmortem human brains, BAG3 marked a stress-responsive astrocyte subtype in aged individuals.
Why it matters
Proteostasis decline is a primary feature of brain aging and neurodegeneration. Identifying BAG3 as a coordinator of multiple clearance pathways in astrocytes highlights how non-neuronal cells maintain protein quality control in the aging brain.
Caveats
The functional experiments were conducted in cultured stem-cell-derived cells rather than in living model organisms. In addition, the findings in aged humans rely on observational analyses of postmortem brain tissue.
- BAG3 knockout
- Disabled macroautophagy
- Loss of proteostasis
- Autophagy
- Ubiquitin–proteasome system
- APP
- BAG3
- BIN1
- GFAP
- HSPB8
- PSEN1
- VPS35
The paper
BAG3 coordinates astrocytic proteostasis of Alzheimer's disease-linked proteins via proteasome, autophagy, and retromer interactions
Augur ZM, Fogo GM, Benoit CR et al.
Proceedings of the National Academy of Sciences of the United States of America · 28 Sep 2026