Familial amyotrophic lateral sclerosis with an I104F mutation in the SOD1 gene: Multisystem degeneration with neurofilamentous aggregates and SOD1 inclusions

Blood-brain barrier dysfunction in multiple system atrophy: A human postmortem study

Multiple system atrophy (MSA) is a rare neurodegenerative disease characterized by an accumulation of phosphorylated α-synuclein (p-αsyn) in oligodendrocytes in the form of glial cytoplasmic inclusions (GCIs). In MSA, not only mature oligodendrocytes but also oligodendrocyte precursor cells (OPCs) are affected. The latter play an important role in remyelination by differentiating into mature oligodendrocytes, as well as maintaining the blood-brain barrier (BBB) by promoting the expression of tight junction proteins. We have hypothesized that in MSA, the BBB is impaired as a result of aberrant interactions between affected OPCs and the cerebral vasculature. To verify this hypothesis, we conducted a neuropathological examination of postmortem brains from MSA patients and control subjects, focusing on the primary motor area, one of the main regions affected in MSA. Using double immunofluorescence, we quantified the expression of tight junction protein claudin-5 in capillary endothelial cells and found that it was significantly lower in MSA than in controls in both the gray matter and white matter. Furthermore, a significantly higher amount of fibrinogen was extravasated into the brain parenchyma in MSA patients than in controls. In addition, leakage of IgG was detected almost specifically in MSA brain parenchyma, as visualized in three dimensions by combining techniques of chemical tissue clearing and light sheet microscopy. Finally, we confirmed accumulation of p-αsyn-positive GCIs along the cerebral vasculature within OPCs. These results suggest that BBB dysfunction and associated fibrinogen extravasation are constant findings in MSA, presumably triggered by the deposition of p-αsyn in perivascular OPCs.

Cell type-specific abnormalities of central nervous system in myotonic dystrophy type 1

Myotonic dystrophy type 1 is a multisystem genetic disorder involving the muscle, heart and CNS. It is caused by toxic RNA transcription from expanded CTG repeats in the 3′-untranslated region of DMPK, leading to dysregulated splicing of various genes and multisystemic symptoms. Although aberrant splicing of several genes has been identified as the cause of some muscular symptoms, the pathogenesis of CNS symptoms prevalent in patients with myotonic dystrophy type 1 remains unelucidated, possibly due to a limitation in studying a diverse mixture of different cell types, including neuronal cells and glial cells. Previous studies revealed neuronal loss in the cortex, myelin loss in the white matter and the presence of axonal neuropathy in patients with myotonic dystrophy type 1. To elucidate the CNS pathogenesis, we investigated cell type-specific abnormalities in cortical neurons, white matter glial cells and spinal motor neurons via laser-capture microdissection. We observed that the CTG repeat instability and cytosine–phosphate–guanine (CpG) methylation status varied among the CNS cell lineages; cortical neurons had more unstable and longer repeats with higher CpG methylation than white matter glial cells, and spinal motor neurons had more stable repeats with lower methylation status. We also identified splicing abnormalities in each CNS cell lineage, such as DLGAP1 in white matter glial cells and CAMKK2 in spinal motor neurons. Furthermore, we demonstrated that aberrant splicing of CAMKK2 is associated with abnormal neurite morphology in myotonic dystrophy type 1 motor neurons. Our laser-capture microdissection-based study revealed cell type-dependent genetic, epigenetic and splicing abnormalities in myotonic dystrophy type 1 CNS, indicating the significant potential of cell type-specific analysis in elucidating the CNS pathogenesis.

Current and future applications of induced pluripotent stem cell-based models to study pathological proteins in neurodegenerative disorders

Neurodegenerative disorders emerge from the failure of intricate cellular mechanisms, which ultimately lead to the loss of vulnerable neuronal populations. Research conducted across several laboratories has now provided compelling evidence that pathogenic proteins can also contribute to non-cell autonomous toxicity in several neurodegenerative contexts, including Alzheimer's, Parkinson's, and Huntington's diseases as well as Amyotrophic Lateral Sclerosis. Given the nearly ubiquitous nature of abnormal protein accumulation in such disorders, elucidating the mechanisms and routes underlying these processes is essential to the development of effective treatments. To this end, physiologically relevant human in vitro models are critical to understand the processes surrounding uptake, release and nucleation under physiological or pathological conditions. This review explores the use of human-induced pluripotent stem cells (iPSCs) to study prion-like protein propagation in neurodegenerative diseases, discusses advantages and limitations of this model, and presents emerging technologies that, combined with the use of iPSC-based models, will provide powerful model systems to propel fundamental research forward.

A clinicopathological study of ALS with L126S mutation in the SOD1 gene presenting with isolated inferior olivary hypertrophy

We report an autopsy case of amyotrophic lateral sclerosis with L126S mutation in the superoxide dismutase 1 (SOD1) gene (SOD1). The patient was a 69-year-old Japanese man without relevant family history, who initially presented with slow progressive muscle weakness of the lower extremities without upper motor neuron signs, and died of respiratory failure 6 years after the onset. Neuropathological examination revealed a loss of lower motor neurons and degeneration of Clarke's column commensurate with that of the posterior spinocerebellar tract and the middle root zone of the posterior column. The primary motor area was minimally affected. Characteristic SOD1-immunopositive neuronal intracytoplasmic inclusions, mixed with neurofilament accumulation, were present in the affected areas. Isolated inferior olivary hypertrophy was observed, but did not involve the contralateral dentate nucleus, or the ipsilateral red nucleus and central tegmental tract, where no neuronal inclusions were found. In combination with data from a previous autopsy case, this study suggests that the L126S mutation may cause focal neuronal degeneration in the brainstem.