Intramuscular injection of α-synuclein induces CNS α-synuclein pathology and a rapid-onset motor phenotype in transgenic mice

Abstract

It has been hypothesized that α-synuclein (αS) misfolding may begin in peripheral nerves and spread to the central nervous system (CNS), leading to Parkinson disease and related disorders. Although recent data suggest that αS pathology can spread within the mouse brain, there is no direct evidence for spread of disease from a peripheral site. In the present study, we show that hind limb intramuscular (IM) injection of αS can induce pathology in the CNS in the human Ala53Thr (M83) and wild-type (M20) αS transgenic (Tg) mouse models. Within 2-3 mo after IM injection in αS homozygous M83 Tg mice and 3-4 mo for hemizygous M83 Tg mice, these animals developed a rapid, synchronized, and predictable induction of widespread CNS αS inclusion pathology, accompanied by astrogliosis, microgliosis, and debilitating motor impairments. In M20 Tg mice, starting at 4 mo after IM injection, we observed αS inclusion pathology in the spinal cord, but motor function remained intact. Transection of the sciatic nerve in the M83 Tg mice significantly delayed the appearance of CNS pathology and motor symptoms, demonstrating the involvement of retrograde transport in inducing αS CNS inclusion pathology. Outside of scrapie-mediated prion disease, to our knowledge, this findiing is the first evidence that an entire neurodegenerative proteinopathy associated with a robust, lethal motor phenotype can be initiated by peripheral inoculation with a pathogenic protein. Furthermore, this facile, synchronized rapid-onset model of α-synucleinopathy will be highly valuable in testing disease-modifying therapies and dissecting the mechanism(s) that drive αS-induced neurodegeneration.amyloid | Parkinson disease S ynucleinopathies are a group of diseases defined by the presence of amyloidogenic α-synuclein (αS) inclusions that can occur in neurons and glia of the central nervous system (CNS) (1-4). In Parkinson disease (PD), a causative role for αS has been established via the discovery of mutations in the αS gene SNCA resulting in autosomal-dominant PD (4-11). Although αS inclusions (e.g., Lewy bodies) are the hallmark pathology of PD, how they contribute to disease pathogenesis remains controversial (1,3,4,12).Postmortem studies have suggested that αS pathology may spread following neuroanatomical tracts (13-15) and between cells (16-18). αS pathology has also been found in the peripheral nervous system (PNS): for example, in the enteric and pelvic plexus (19,20). And it has been suggested that αS pathology might originate in the nerves of the PNS and spread to the CNS (14). Experimentally, it has been reported that intracerebral injections of preformed amyloidogenic αS fibrils in nontransgenic (nTg) and αS transgenic (Tg) mice induce the formation of intracellular αS inclusions that appear to progress from the site of injection (21-26). Collectively, these studies support the notion that αS inclusion pathology may propagate via a prion-like conformational self-templating mechanism (27, 28). A caveat of the direct intracerebral injection of αS is tha...

Robust Central Nervous System Pathology in Transgenic Mice following Peripheral Injection of α-Synuclein Fibrils

“…Retrograde transport of ␣S aggregates followed by seeding and further transmission was suggested as the major mechanism involved, as transection of the sciatic nerve prior to i.m. injection of ␣S fibs significantly delayed, but did not completely block, disease induction in this model (40). Herein, we expand these studies of CNS induction of ␣S pathology from peripheral challenges of ␣S fibs and control proteins by comparing the outcomes of tail vein, intraperitoneal (i.p.)…”

“…We previously reported that, consistent with a prion-like mechanism, peripheral hind limb intramuscular (i.m.) injection of ␣S fibs leads to the progressive formation of CNS ␣S pathology in both M20 and M83 ␣S Tg mice and to motor impairment in the latter line of mice (40). Retrograde transport of ␣S aggregates followed by seeding and further transmission was suggested as the major mechanism involved, as transection of the sciatic nerve prior to i.m.…”

Transmission of Tau Pathology from Human to Rodent Brain: How to Humanise Animal Models for Alzheimer’s Disease Research

“…Moreover, HEK293 cells expressing human mutant P301L tau develop intracellular tau aggregates and co-culture of these cells with hippocampal neurons induced tau pathology in these neurons [93], indicating a possibility transmission of tau pathology from nonneuronal donor to neuronal cell. Interestingly, the infectivity of prions and α-synuclein between distal non-neuronal cells and the brain has also been reported [98][99][100]. It would be interesting to study whether similar infectivity of tau is observed in vivo in transgenic models or AD.…”

New ¿- and ¿-synuclein immunopathological lesions in human brain

“…The role of neuron-glia interaction in the etiology of NDDs is an important area of current investigations due to the involvement of naturally unfolded proteins in prion-like transmission of pathology [16][17][18]24]. The results presented here are in agreement with previous observations of aberrant γ-syn accumulation in the optic nerve astrocytes and spheroids which is not accompanied by the formation of inclusion bodies or deposits [10,11] We identified several types of oxi-γ-syn positive astrocytes with different morphology and examined their immunohistochemical phenotypes.…”

“…Our recent results indicate that γ-syn is easily oxidized at Methionine-38 (Met-38) forming oxidized-γ-syn (oxi-γ-syn) and after oxidation it can induce aggregation of α-syn [15]. Moreover, γ-syn can be transmitted between cells [15] and presumably to spread pathology as was shown for α-syn [16][17][18]. These findings raise a possibility that oxidation and/or aggregation of this protein might be involved in the pathogenesis of some NDDs.…”