RTP801 Mediates Transneuronal Toxicity via Extracellular Vesicles by Affecting Their Protein Cargo and Abrogating Their Trophic Effect

Abstract

Background Extracellular vesicles (EVs) play a crucial role in intercellular communication, participating in the paracrine trophic support or in the propagation of toxic molecules, including proteins. RTP801 is a stress-regulated protein, whose levels are elevated during neurodegeneration and induce neuron death. However, whether RTP801 toxicity is transferred trans-neuronally via EVs remains unknown. Methods We overexpressed or silenced RTP801 protein in cultured cortical neurons and isolated the neural-derived EVs (RTP801-EVs, or shRTP801-EVs respectively). We characterized their protein content by mass spectrometry (MS) and western blotting (WB). RTP801-EVs toxicity was assessed by treating cultured neurons with these EVs and quantifying apoptotic neuron death and branching. We also tested shRTP801-EVs functionality in the pathologic in vitro model of 6-Hydroxydopamine (6-OHDA) by biochemical analyses. Results Expression of RTP801 increased the number of EVs released by neurons. Moreover, RTP801 led to a distinct proteomic signature of neural-derived EVs, containing more pro-apoptotic markers. Hence, we observed that RTP801 toxicity was transferred to neurons via EVs, activating apoptosis and impairing neuron morphology complexity. In contrast, EVs derived from neurons where RTP801 was silenced were able to increase the arborization of recipient neurons. We also showed that 6-OHDA neurotoxin elevated protein levels of RTP801 in both cell lysates and EVs. Furthermore, neural-derived EVs induced phosphorylation of Ser473-Akt and Ser235/236-RPS6 in recipient neurons, and this effect was lost when EVs were derived from neurons treated with 6-OHDA. Interestingly, EVs derived from neurons where RTP801 was silenced prior to exposing them to 6-OHDA maintained Akt and RPS6 transactivation in recipient neurons. Conclusion Taken together, these results suggest that RTP801 toxicity can be spread via EVs and therefore, it could contribute to the progression of neurodegenerative diseases in which RTP801 is involved.