Targeted overexpression of human alpha-synuclein in oligodendroglia induces lesions linked to MSA-like progressive autonomic failure

Abstract

Multiple system atrophy (MSA) is a rare neurodegenerative disease of undetermined cause manifesting with progressive autonomic failure (AF), cerebellar ataxia and parkinsonism due to neuronal loss in multiple brain areas associated with (oligodendro)glial cytoplasmic alpha-synuclein (alpha SYN) inclusions (GCIs). Using proteolipid protein (PLP)-alpha-synuclein (alpha SYN) transgenic mice we have previously reported parkinsonian motor deficits triggered by MSA-like alpha SYN inclusions. We now extend these observations by demonstrating degeneration of brain areas that are closely linked to progressive AF and other non-motor symptoms in MSA, in (PLP)-alpha SYN transgenic mice as compared to age-matched non-transgenic controls. We show delayed loss of cholinergic neurons in nucleus ambiguus at 12 months of age as well as early neuronal loss in laterodorsal tegmental nucleus, pedunculopontine tegmental nucleus and Onuf's nucleus at 2 months of age associated with alpha SYN oligodendroglial overexpression. We also report that neuronal loss triggered by MSA-like alpha SYN inclusions is absent up to 12 months of age in the thoracic intermediolateral cell column suggesting a differential dynamic modulation of alpha SYN toxicity within the murine autonomic nervous system. Although the spatial and temporal evolution of central autonomic pathology in MSA is unknown our findings corroborate the utility of the (PLP)-alpha SYN transgenic mouse model as a testbed for the study of oligodendroglial alpha SYN mediated neurodegeneration replicating both motor and non-motor aspects of MSA.

Fig. 1

(A) Tail clip PCR was applied to genotype (PLP)-α-SYN transgenic mice used in this study (i.e. six mice at 2 months of age and 6 mice at 12 months of age) by applying primers which amplified a 450 bp fragment of the human α-synuclein (AD, distilled water; −, non-transgenic negative control; +, positive control of the reaction for human αSYN). (B) Immunohistochemistry with 15G7 antibody against human α-synuclein demonstrated strong expression of the transgenic protein in the spinal cord of (PLP)-α-SYN transgenic mice. Inset: The colocalisation of 15G7 (red) and CNP (green) confirmed the expression of human α-synuclein in oligodendrocytes of (PLP)-α-SYN transgenic mice (bar, 10 µm).

Fig. 2

Immunolabelling for ChAT of the nucleus ambiguus (A), laterodorsal tegmental nucleus (C) and pedunculopontine tegmental nucleus (E) of non-transgenic (non-tg) and transgenic (tg) mice with oligodendroglial expression of human αSYN was performed. Morphometric analysis of ChAT-immunoreactive (ChAT-IR) neurons indicated age- and genotype-related loss of neurons in nucleus ambiguus (B), laterodorsal tegmental nucleus (D) and pedunculopontine tegmental nucleus (F). (*p < 0.05, **p < 0.01, ***p < 0.001).

Fig. 3

(A) Thoracic spinal cord was processed for acetylcholinesterase (AChE) and cresyl violet (CV) histochemistry to localise the intermediolateral column (IML, encircled). (B) Morphometric analysis indicated age-related loss of preganglionic sympathetic neurons in IML with no significant difference between non-transgenic (non-tg) and transgenic (tg) mice with oligodendroglial expression of human αSYN both at 2 and 12 months of age. (C) The mouse analogue of the human Onuf's nucleus (ExA9 and ExU9) in lamina 9 at the level of L6 (Jacob et al., 2005) was visualised in cresyl violet staining. (D) Significant loss of neurons in the Onuf's nucleus analogue was detected in transgenic versus non-transgenic mice both at 2 and 12 months of age. Age-related increase in the number of motoneurons was found in Onuf's nucleus of non-tg animals but not detected in tg mice with αSYN pathology (**p < 0.01; *** p < 0.001).