Intercellular Propagation and Aggregate Seeding of Mutant Ataxin-1

Abstract

Intercellular propagation of aggregated protein inclusions along actin-based tunneling nanotubes (TNTs) has been reported as a means of pathogenic spread in Alzheimer’s, Parkinson’s and Huntington’s Disease. Propagation of oligomeric-structured polyglutamine-expanded ataxin-1 (Atxn1[154Q]) has been reported in the cerebellum of a Spinocerebellar ataxia type 1 (SCA1) knock-in mouse to correlate with disease propagation. In this study, we investigated whether a physiologically-relevant polyglutamine-expanded ATXN1 protein (ATXN1[82Q]) could propagate intercellularly. Using a cerebellar-derived live cell model, we observed ATXN1 aggregates form in the nucleus, export out of the nucleus into the cytoplasm, and finally, propagate to neighboring cells along actin-based intercellular connections. Additionally, we observed the facilitation of aggregate-resistant proteins into aggregates given the presence of aggregation-prone proteins within a cell. Taken together, our results support a pathogenic role of intercellular propagation of polyglutamine-expanded ATXN1 inclusions.

Mechanisms of tunneling nanotube-based propagation of neurodegenerative disease proteins

“…Attempts to manipulate tau aggregation clearance by application of bafilomycin A1, an inhibitor of late-stage autophagy via inhibition of autophagosome-lysosome fusion, and application of Bortezomide, a proteasome enzyme complex inhibitor, had little effect. Similarly, our study (Huang et al, 2022) found that induction of autophagy with 500 nM rapamycin or arrest of autophagy by 60 µM chloroquine redistributed diffuse RFP-ATXN1[82Q] into aggregates but did not clear the aggregates. Notably, induction of autophagy clears aggregation-resistant and diffuse RFP-ATXN1[30Q] protein, while arrest of autophagy induced the formation of RFP-ATXN1[30Q] into large aggregates.…”

“…Taken together, their work as well as the other studies illustrated here suggest a model by which amplification of TNT formation as a protective mechanism allows diseased or vulnerable cells to export their inclusions and in exchange import healthy mitochondria and lysosomes. However, Chastagner et al (2020) and Huang et al (2022) demonstrate seeding of non-aggregation prone proteins by aggregation-prone proteins following transfer. How do we reconcile the two seemingly disparate functions of TNTs?…”

“…Our lab demonstrated that stable over-expression of the RFP-fused aggregation-prone ataxin-1 protein [RFP-ATXN1(82Q)] in human medulloblastoma-derived Daoy cells as well as transient over-expression of GFP-fused aggregation-prone ataxin-1 protein [GFP-ATXN1(85Q)] in mouse neuroblastoma neuro2A cells led to TNT formation and subsequent aggregate transfer across TNTs within 72 h (Figure 1; Huang et al, 2022). We did not find extensive TNT formation in cells expressing aggregation-resistant forms of ataxin-1 [RFP-ATN1(82Q-A776), RFP-ATXN1(30Q), GFP-ATXN1(32Q)], nor did we see the extracellular presence of these proteins.…”

“…RD-YFP aggregates from K18 tau-challenged cells propagated over several generations. In addition, Huang et al (2022)…”

Striatal Induction and Spread of the Huntington’s Disease Protein: A Novel Rhes Route

“…TNTs also spread alpha synuclein and amyloid proteins between cells [76][77][78][79]. Similarly, the polyglutamine-expanded ATXN1 protein (ATXN1[82Q]), DNA-binding protein of 43 kDa (TDP-43), and Tau could transmit intercellularly via TNTs [80][81][82][83][84]. Although cellular models played a key role in discovering pathogenic protein transfer via TNTs, recent advancements in imaging technologies have identified TNT-like transfer of disease protein in vivo [73].…”