ABSTRACT
Multiple system atrophy (MSA) is a progressive, neurodegenerative disease characterized by parkinsonism, ataxia, autonomic dysfunction, and accumulation of alpha-synuclein (alpha-syn) in oligodendrocytes. To better understand the mechanisms of neurodegeneration and the role of alpha-syn accumulation in oligodendrocytes in the pathogenesis of MSA, we generated transgenic mouse lines expressing human (h) alpha-syn under the control of the murine myelin basic protein promoter. Transgenic mice expressing high levels of halpha-syn displayed severe neurological alterations and died prematurely at 6 months of age. Furthermore, mice developed progressive accumulation of halpha-syn-immunoreactive inclusions in oligodendrocytes along the axonal tracts in the brainstem, basal ganglia, cerebellum, corpus callosum, and neocortex. The inclusions also reacted with antibodies against phospho-serine (129) halpha-syn and ubiquitin, and halpha-syn was found in the detergent-insoluble fraction. In high-expresser lines, the white matter tracts displayed intense astrogliosis, myelin pallor, and decreased neurofilament immunostaining. Accumulation of halpha-syn in oligodendrocytes also leads to prominent neurodegenerative changes in the neocortex with decreased dendritic density and to loss of dopaminergic fibers in the basal ganglia. The oligodendrocytic inclusions were composed of fibrils and accompanied by mitochondrial alterations and disruption of the myelin lamina in the axons. Together, these studies support the contention that accumulation of alpha-syn in oligodendrocytes promotes neurodegeneration and recapitulates several of the key functional and neuropathological features of MSA.
Subject(s)
Multiple System Atrophy/genetics , Multiple System Atrophy/metabolism , Nerve Degeneration/genetics , Nerve Degeneration/metabolism , Oligodendroglia/metabolism , Promoter Regions, Genetic/physiology , alpha-Synuclein/biosynthesis , Animals , Disease Models, Animal , Humans , Male , Mice , Mice, Inbred C57BL , Mice, Inbred DBA , Mice, Transgenic , Middle Aged , Multiple System Atrophy/pathology , Nerve Degeneration/pathology , Oligodendroglia/pathology , alpha-Synuclein/geneticsABSTRACT
The cardinal pathological features of multiple system atrophy (MSA) are the presence of glial cytoplasmic inclusions (GCIs) in oligodendrocytes and loss of oligodendrocytes. To understand the mechanisms underlying MSA, we examined the effects of overexpression of human alpha-synuclein (halpha-syn) in CG-4 oligodendrocytic progenitor cells. CG-4 cells overexpressing halpha-syn (halpha-syn CG-4) demonstrated severely impaired adhesion and increased cell death when plated on fibronectin compared to laminin. The expression of the alphav integrin subunit in whole cell lysates was also significantly downregulated in halpha-syn CG-4. These results demonstrate a cytotoxic consequence of halpha-syn overexpression in CG-4. This cytotoxicity appears to be the result of alterations in cell-extracellular matrix interactions, where impaired adhesion to fibronectin is associated with downregulation of the alphav integrin subunit and increased cell death. It may, therefore, be one of the mechanisms underlying the loss of oligodendrocytes in MSA.
Subject(s)
Cell Adhesion/physiology , Fibronectins/metabolism , Multiple System Atrophy/metabolism , Nerve Tissue Proteins/metabolism , Oligodendroglia/metabolism , Animals , Animals, Newborn , Cell Death/physiology , Cell Line , Cells, Cultured , Down-Regulation/physiology , Extracellular Matrix/metabolism , Genetic Vectors , Humans , Inclusion Bodies/genetics , Inclusion Bodies/metabolism , Inclusion Bodies/pathology , Integrin alphaV/metabolism , Multiple System Atrophy/pathology , Multiple System Atrophy/physiopathology , Myelin Sheath/genetics , Myelin Sheath/metabolism , Myelin Sheath/pathology , Nerve Tissue Proteins/genetics , Oligodendroglia/pathology , Rats , Synucleins , Transfection , alpha-SynucleinABSTRACT
Sonic hedgehog (Shh), a member of hedgehog (hh) family of signaling molecules, is necessary for normal axial patterning and cellular differentiation in the developing central nervous system. Shh also promotes the survival of fetal dopaminergic neurons and protects cultures of fetal midbrain dopaminergic neurons from the toxic effects of N-methyl-4-phenylpyridinium (MPP(+)), a neurotoxin that selectively injures nigral dopaminergic neurons. The mRNA expression of Shh and its putative receptor in the adult brain indicates an important role of Shh in the mature nervous system in addition to its roles during embryogenesis. In this study we examined the behavioral and anatomical effects of intrastriatal injection of singly myristoylated wild-type human Sonic hedgehog N-terminal fragment (Shh-M) in a rat model of Parkinson's disease (PD). Five groups of rats received a series of four intrastriatal injections of Shh-M (180 ng, 540 ng, or 4.275 microg per injection), glial cell line-derived neurotrophic factor (GDNF) (1 microg/injection), or vehicle on days 1, 3, 5, and 8. On day 4, the animals received an intrastriatal injection of 15 microg 6-hydroxydopamine (6-OHDA) free base. Intrastriatal administration of Shh (180 ng/injection) twice before and after a single intrastriatal injection of 6-OHDA reduced apomorphine- and amphetamine-induced rotation and forelimb akinesia and partially preserved dopaminergic axons in the striatum. This is the first demonstration in vivo that Shh reduces behavioral deficits induced by intrastriatal 6-OHDA lesion and suggests that Shh may be useful in the treatment of disorders that affect the nigrostriatal system, such as PD.
