Carboxy‐terminal truncations of mouse α‐synuclein alter aggregation and prion‐like seeding

Abstract

Edited by Sandro Sonnino a-synuclein (asyn) forms pathologic inclusions in several neurodegenerative diseases termed synucleinopathies. The inclusions are comprised of asyn fibrils harboring prion-like properties. Prion-like activity of asyn has been studied by intracerebral injection of fibrils into mice, where the presence of a species barrier requires the use of mouse asyn. Post-translational modifications to asyn such as carboxy (C)-terminal truncation occur in synucleinopathies, and their implications for prion-like aggregation and seeding are under investigation. Herein, C-truncated forms of asyn found in human disease are recapitulated in mouse asyn to study their seeding activity in vitro, in HEK293T cells, in neuronal-glial culture, and in nontransgenic mice. The results show that C-truncation of mouse asyn accelerates aggregation of asyn but alters prion-like seeding of inclusion formation.

The emerging role of α-synuclein truncation in aggregation and disease

“…Extending the study of prion-like seeding capacity of truncated αsyn fibrils to cellular and animal models is complicated due to additional extrinsic factors now involved such as modulation of cellular uptake and spread of fibrils due to truncation (194,195), trafficking to subcellular compartments (196), and structural changes to the truncated fibril due to additional PTMs; most of these variables have not been studied in relation to truncated αsyn fibrils or even typical αsyn seeding experiments. Nonetheless, cellular (22, 38, 91-93, 103, 120, 159, 189, 197, 198) and animal (133,159,189,199) experiments using fibrils containing truncated αsyn have shown some similar findings to in vitro studies.…”

“…C-truncation of αsyn increases aggregation in vivo as well; in addition to the structural aspects, removal of the C-terminus may further enhance aggregation in a cellular milieu through impaired αsyn degradation due to loss of consensus motifs for ubiquitin ligases and chaperone mediators of autophagy (169)(170)(171), and through loss of normally protective C-terminal interactions such as binding of oxidized dopamine (172,173). Although not as numerous as the in vitro studies, experiments have been conducted demonstrating that C-truncation of αsyn promotes aggregation into pathologic inclusions in cultured cells and animal models (22,130,159,(174)(175)(176)(177)(178)(179)(180)(181)(182)(183). These same studies often demonstrated toxic consequences from Ctruncation of αsyn that will be discussed further.…”

“…Likewise, over-expression of 1-120, 1-108, and 1-103 αsyn have been demonstrated to form more and/or larger inclusions than FL αsyn in cultured cells, including with unique inclusion morphology as 1-120 αsyn formed larger volume inclusions than FL αsyn in primary neurons (130,175,183). In a prion-like induction cell model, our group studied 8 C-truncated forms of both human and mouse αsyn overexpressed in HEK293T cells and demonstrated that with increasing extent of C-truncation there is more aggregation compared to FL αsyn when exposed to the same PFFs as measured by amount of insoluble αsyn formed and number of inclusions observed (22,159).…”

“…Indeed, although 1-108 αsyn fibrils seeded FL αsyn poorly, they promptly templated 1-108 αsyn monomers to elongate the seed fibril (33). This may be a simplistic explanation as it has also been observed that FL αsyn fibrils may seed Ctruncated αsyn monomers equally or superiorly to FL αsyn monomers (22,33,159,163), as the increased aggregation propensity of C-truncated αsyn must also be taken into account, but the general idea of compatibility between seeding fibril and templated monomer is likely occurring to a degree.…”

“…In cellular and animal models, there are again heterogeneous results depending on the exact truncation where most studies observe decreased seeding of FL αsyn when fibrils are comprised entirely of truncated αsyn (22,103,120,159,189), some see increased seeding of FL αsyn (38,160,189), and others observe equal seeding capacity (91-93, 97, 159, 189, 197-199) compared with FL αsyn fibrils. In most of these studies, analyzing the seeding behavior of truncated αsyn fibrils was not the focus and likewise mostly qualitative results are available.…”