Spermine increases acetylation of tubulins and facilitates autophagic degradation of prion aggregates

Abstract

Autolysosomal dysfunction and unstable microtubules are hallmarks of chronic neurodegenerative diseases associated with misfolded proteins. Investigation of impaired protein quality control and clearance systems could therefore provide an important avenue for intervention. To investigate this we have used a highly controlled model for protein aggregation, an in vitro prion system. Here we report that prion aggregates traffic via autolysosomes in the cytoplasm. Treatment with the natural polyamine spermine clears aggregates by enhancing autolysosomal flux. We demonstrated this by blocking the formation of mature autophagosomes resulting in accumulation of prion aggregates in the cytoplasm. Further we investigated the mechanism of spermine’s mode of action and we demonstrate that spermine increases the acetylation of microtubules, which is known to facilitate retrograde transport of autophagosomes from the cellular periphery to lysosomes located near the nucleus. We further report that spermine facilitates selective autophagic degradation of prion aggregates by binding to microtubule protein Tubb6. This is the first report in which spermine and the pathways regulated by it are applied as a novel approach towards clearance of misfolded prion protein and we suggest that this may have important implication for the broader family of protein misfolding diseases.

Full restoration of specific infectivity and strain properties from pure mammalian prion protein

“…However, as discussed above, protein-only recPrP Sc would be expected to be structurally similar to cofactor recPrP Sc , and both of these recombinant conformers lack PTMs such as sialylation, which can influence protein clearance [67, 68]. Therefore, it difficult to envision how cellular prion clearance mechanisms, such as autophagy [69–72] or uptake by resident innate immune cells [73–75], could specifically distinguish between these two conformers. A more likely explanation is that PMCA experimental conditions allow BV PrP C to be more structurally accommodating in vitro than in vivo .…”

Altered brain arginine metabolism in a mouse model of tauopathy

“…Accumulation and aggregation of misfolded proteins are hallmarks of neurodegenerative diseases, such as AD, FTD, and prion diseases. Interestingly, spermine increases the acetylation of microtubules (enhancing microtubule stability) and facilitates autophagic degradation of prion aggregates (Phadwal et al 2018) . Our preliminary work has demonstrated that polyamines (spermine in particular) decrease tau aggregation and promote microtubule assembly (Hunt et al 2015b).…”

“…Using rTg4510 mice bearing the human tau P301L mutation, Hunt et al (2015a) demonstrated that sustained arginase I overexpres-sion over a 4-month period from the beginning of brain tau deposition markedly reduced tau pathology and several kinases capable of phosphorylating tau and mitigated hippocampal atrophy in this mouse model of forebrain tauopathy. It has been shown that polyamines are critically involved in microtubule assembly and stabilization (Savarin et al 2010 ; Hamon et al 2011; Song et al 2013), and the high-order polyamine spermine increases the acetylation of microtubules and facilitates autophagic degradation of prion aggregates (Phadwal et al 2018). Moreover, our recent preliminary work demonstrated that polyamines (spermine in particular) decreased tau aggregation and promoted micro-tubule assembly (Hunt et al 2015b ).…”

“…Remarkably, synapse loss and synaptic dysfunction in the hippocampus are evident in PS19 mice at 3 months of age, even prior to the formation of fibrillary tau tangles (Yoshiyama et al 2007). Given the role of polyamines in maintaining microtubule stability and degrading protein aggregates (Savarin et al 2010; Hamon et al 2011; Song et al 2013; Phadwal et al 2018), we hypothesized that this could be due, in part, to alterations in brain arginine metabolism (polyamines in particular) in PS19 mice. To test this hypothesis, the present study systematically determined the time course of the arginine metabolic profile changes in the frontal cortex, hippocampus, para-hippocampal region, striatum, thalamus, and cerebellum of PS19 mice at 4, 8, and 12–14 months of age.…”

Global profiles of a cetylated proteins in the brains of scrapie agents 139A- and ME7-infected mice collected at mid-early, mid-late and terminal stage

“…Recently, we have also con rmed the declined levels of Sirt3 in the brain tissues of several scrapie infected mice and in SMB-S15 cells, leading to increases of acetylating forms of SOD2 and ATP5β that subsequently induce increase of intracellular ROS and reduction of ATP [20]. Aberrant alterations of acetylation modi cations for other proteins have been also found in the brain tissues or the models in vitro of several neurodegenerative diseases, e.g., tau, microtubules, SOD1 [21][22][23]. However, the global change of protein acetylation in the brain tissues of prion diseases remains unsettled.…”