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Yao Q, Mascarenhas dos Santos AC, Zhang H, Mañas A, Hussaini A, Kim U, Xu C, Basheer S, Tasaki S, Xiang J. Unconventional Source of Neurotoxic Protein Aggregation from Organelle Off-Target Bax∆2 in Alzheimer's Disease. Biomolecules 2023; 13:970. [PMID: 37371550 PMCID: PMC10296721 DOI: 10.3390/biom13060970] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2023] [Revised: 05/30/2023] [Accepted: 06/06/2023] [Indexed: 06/29/2023] Open
Abstract
Protein aggregates are a hallmark of Alzheimer's disease (AD). Extensive studies have focused on β-amyloid plaques and Tau tangles. Here, we illustrate a novel source of protein aggregates in AD neurons from organelle off-target proteins. Bax is a mitochondrial pore-forming pro-death protein. What happens to Bax if it fails to target mitochondria? We previously showed that a mitochondrial target-deficient alternatively spliced variant, Bax∆2, formed large cytosolic protein aggregates and triggered caspase 8-mediated cell death. Bax∆2 protein levels were low in most normal organs and the proteins were quickly degraded in cancer. Here, we found that 85% of AD patients had Bax∆2 required alternative splicing. Increased Bax∆2 proteins were mostly accumulated in neurons of AD-susceptible brain regions. Intracellularly, Bax∆2 aggregates distributed independently of Tau tangles. Interestingly, Bax∆2 aggregates triggered the formation of stress granules (SGs), a large protein-RNA complex involved in AD pathogenesis. Although the functional domains required for aggregation and cell death are the same as in cancer cells, Bax∆2 relied on SGs, not caspase 8, for neuronal cell death. These results imply that the aggregation of organelle off-target proteins, such as Bax∆2, broadens the scope of traditional AD pathogenic proteins that contribute to the neuronal stress responses and AD pathogenesis.
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Affiliation(s)
- Qi Yao
- Department of Biology, Illinois Institute of Technology, Chicago, IL 60616, USA (C.X.)
| | | | - Huaiyuan Zhang
- Department of Biology, Illinois Institute of Technology, Chicago, IL 60616, USA (C.X.)
| | - Adriana Mañas
- Department of Laboratory Medicine, Lund University, 22381 Lund, Sweden
| | - Ammarah Hussaini
- Department of Biology, Illinois Institute of Technology, Chicago, IL 60616, USA (C.X.)
| | - Ujin Kim
- Department of Biology, Illinois Institute of Technology, Chicago, IL 60616, USA (C.X.)
| | - Congtai Xu
- Department of Biology, Illinois Institute of Technology, Chicago, IL 60616, USA (C.X.)
| | - Sana Basheer
- Department of Biology, Illinois Institute of Technology, Chicago, IL 60616, USA (C.X.)
| | - Shinya Tasaki
- Rush Alzheimer’s Disease Center, Rush University Medical Center, Chicago, IL 60612, USA
| | - Jialing Xiang
- Department of Biology, Illinois Institute of Technology, Chicago, IL 60616, USA (C.X.)
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Yao Q, Zhang H, Standish C, Grube J, Mañas A, Xiang J. Expression profile of the proapoptotic protein Bax in the human brain. Histochem Cell Biol 2023; 159:209-220. [PMID: 35951115 DOI: 10.1007/s00418-022-02146-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/27/2022] [Indexed: 11/27/2022]
Abstract
Bax is a well-known universal proapoptotic protein. Bax protein is detected in almost all human organs, and its expression levels can be correlated with disease progression and therapeutic efficacy in certain settings. Interestingly, increasing evidence has shown that mature neuronal cell death is often not typical apoptosis. Most results on the expression of Bax proteins (predominantly Baxα) in the human brain come from disease-oriented studies, and the data on Bax protein expression in the normal brain are limited and lack consistency due to many variable factors. Here, we analyzed Bax RNA and protein expression data from multiple databases and performed immunostaining of over 80 samples from 25 healthy subjects across 7 different brain regions. We found that Bax protein expression was heterogeneous across brain regions and individual subjects. Both neurons and glial cells, such as astrocytes, could be Bax positive, but Bax positivity appeared to be highly selective, even within the same cell type in the same region. Furthermore, Bax proteins could be localized in the cytosol (evenly spread or concentrated to one region), nucleus or nucleolus depending on the cell type. Such variation and distribution in Bax expression suggest that Bax may function differently in the human brain than in other organs.
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Affiliation(s)
- Qi Yao
- Department of Biology, Lewis College of Science and Letters, Illinois Institute of Technology, 3101 South Dearborn Street, Chicago, IL, 60616, USA
| | - Huaiyuan Zhang
- Department of Biology, Lewis College of Science and Letters, Illinois Institute of Technology, 3101 South Dearborn Street, Chicago, IL, 60616, USA
| | - Collin Standish
- Department of Biology, Lewis College of Science and Letters, Illinois Institute of Technology, 3101 South Dearborn Street, Chicago, IL, 60616, USA
| | - Joshua Grube
- Department of Biology, Lewis College of Science and Letters, Illinois Institute of Technology, 3101 South Dearborn Street, Chicago, IL, 60616, USA
| | - Adriana Mañas
- Department of Biology, Lewis College of Science and Letters, Illinois Institute of Technology, 3101 South Dearborn Street, Chicago, IL, 60616, USA
| | - Jialing Xiang
- Department of Biology, Lewis College of Science and Letters, Illinois Institute of Technology, 3101 South Dearborn Street, Chicago, IL, 60616, USA.
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