Objective: Characterizing the Bcl-2 Associated Athanogene 5 (BAG5) interactome will uncover the molecular pathways with which BAG5 associates and further elucidate its role in dopaminergic neurodegeneration.  

Background: Monogenic PD is caused by heritable mutations to the genes encoding proteins such as α-synuclein, LRRK2, PINK1 and Parkin. BAG5 has been shown to interact with several of these proteins and to enhance protein aggregation and neurodegeneration in the substantia nigra. The pathological effect of BAG5 is thought to be due to its inhibitory effect on the chaperone proteins Hsp70 and CHIP, which normally antagonize protein aggregation. However, BAG5 may also contribute to neurodegeneration by modulating the cellular processes responsible for maintaining mitochondrial health: a function independent of its association with Hsp70. The precise role of BAG5 in the pathobiology of PD is still unclear. 

Methods: The BAG5 interactome was characterized by immunoprecipitating BAG5 from a tetracycline inducible SH-SY5Y stable cell line and identifying co-immunoprecipitated proteins via mass spectrometry. To minimize the effects of random genomic integration, the BAG5 transgene was inserted into the AAVS1 genomic safe harbor. To assess which BAG5 interactions are dependent on its association with Hsp70, the same procedure was performed with a mutated form of BAG5 [BAG5(mut)] incapable of binding Hsp70. The relative affinity of interacting proteins for either BAG5 or BAG5(mut) was gauged using isobaric tags. 

Results: The interactome analysis revealed 288 high confidence BAG5 interacting proteins, including α-synuclein, LRRK2 and several other proteins commonly mutated in familial PD. Both Hsp70 and CHIP were found to preferentially associate with BAG5 relative to BAG5(mut), which was expected based on previous reports. GO term enrichment and KEGG pathway analysis revealed that BAG5 is associated with a number of diverse cellular processes including mRNA processing in the nucleus, microtubule dynamics and response to misfolded proteins. 

Conclusions: This characterization of the BAG5 interactome validated previously known PD relevant BAG5-protein interactions and revealed novel interactions that may be important for further investigation into the molecular mechanisms of PD. 

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MDS Abstracts - https://www.mdsabstracts.org/abstract/characterizing-the-bcl-2-associated-athanogene-5-interactome/