Masaaki Waragai

Interaction between Mutant Ataxin-1 and PQBP-1 Affects Transcription and Cell Death

PQBP-1 was isolated on the basis of its interaction with polyglutamine tracts. In this study, using in vitro and in vivo assays, we show that the association between ataxin-1 and PQBP-1 is positively influenced by expanded polyglutamine sequences. In cell lines, interaction between the two molecules induces apoptotic cell death. As a possible mechanism underlying this phenomenon, we found that mutant ataxin-1 enhances binding of PQBP-1 to the C-terminal domain of RNA polymerase II large subunit (Pol II). This reduces the level of phosphorylated Pol II and transcription. Our results suggest the involvement of PQBP-1 in the pathology of spinocerebellar ataxia type 1 (SCA1) and support the idea that modified transcription underlies polyglutamine-mediated pathology.

JNK activation is associated with intracellular β-amyloid accumulation

Abstract c-Jun has been implicated in the pathogenesis of Alzheimer’s disease (AD), but the upstream cascade leading to c-Jun activation in AD is not known. Activation of c-Jun N-terminal kinase (JNK) is obviously a candidate for the upstream event. We tested this possibility focusing on PS1-linked AD. First, we observed that JNK is actually activated in cerebral neurons of PS1-linked AD patients, using immunohistochemistry and Western blot analyses with anti-activated JNK antibodies. We analyzed the relationship between β-amyloid (βA) and JNK activation by using aged transgenic mice overexpressing mutant (M146L) PS1 and human AD brains. The mice showed no neuronal loss but a very few diffuse βA deposits, corresponding to the early stage of PS1-linked AD brain. Some neurons were reactive for anti-βA antibodies in the cerebral cortex. Interestingly, JNK activation was observed in neurons showing intracellular βA immunoreactivity in transgenic mice. Association between intracellular βA and JNK activation was confirmed in cortical neurons of sporadic and PS1-linked AD patients. Furthermore, introduction of βA peptides into the primary culture cortical neurons induced JNK activation and cell death. Collectively, these results suggested that intracellular βA accumulation might trigger JNK activation leading to neuronal death.

AP-2β represses D1A dopamine receptor gene transcription in Neuro2a cells

Abstract Expression of the D 1A dopamine receptor in brain is restricted to specific neuronal populations. To investigate the mechanism of this selective expression, we localized a silencer upstream of the human D 1A gene and identified its binding transcription factor in the D 1A -negative neural cell line Neuro2a. Using deletion CAT analysis, we narrowed this silencer to the region between nucleotides −561 and −532 relative to the CAP site. This 30-bp region, designated D1AS1, contains a sequence homologous to the AP-2 binding site and binds to a factor that also interacts with the AP-2 consensus sequence. In gel supershift assays, this factor is recognized by anti-AP-2β antibody. Co-transfection of Neuro2a cells with an AP-2β expression vector repressed the basal CAT activity of D 1A promoter–reporter plasmids in a D1AS1-dependent manner. RT-PCR analysis indicated that, among AP-2 family members, Neuro2a cells express only AP-2β. Furthermore, co-transfection of these cells with decoy oligonucleotides corresponding to the D1AS1 sequence de-repressed the D 1A gene promoter. Unlike in Neuro2a cells, AP-2β could not repress the D 1A promoter in the D 1A -positive neural cell line, NS20Y. In addition, the expression of AP-2β in different brain regions does not inversely correlate with that of D 1A dopamine receptor. These observations taken together indicate that AP-2β is a repressive transcription factor that acts on the D1AS1 silencer of the D 1A dopamine receptor gene via some cell-specific mechanism(s) in Neuro2a.

Serial MRI and SPECT in amyotrophic lateral sclerosis: A case report

We report the case of a 42 year-old woman with amyotrophic lateral sclerosis (ALS). Neurological examination showed spastic paraparesis and muscular atrophy of the upper extremities. Increased signal intensity areas were present in the lateral corticospinal tract of the brain and cervical spinal cord on a T2-weighted image. Decreased signal intensity of the motor cortex on the T2-weighted image appeared during the course of the illness. SPECT showed hypoperfusion confined to the motor cortex. The area of increased signal intensity in the cervical spinal cord on the T2-weighted MR images extended to the anterolateral columns of the spinal cord. The area of hypoperfusion in SPECT extended to the fronto-parietal area with the progression of the disease. These changes in the MRI and SPECT findings may reflect progressive degeneration of the upper motor neurons in ALS.

Serial MR findings of chronic idiopathic ataxic neuropathy

We report the case of a 70-year-old woman with chronic idiopathic ataxic neuropathy. Neurological examination, electrophysiological studies and a sural nerve biopsy suggested involvement of the axon and the dorsal root ganglia. Laboratory examination showed polyclonal elevation of serum IgA. MRI showed high signal intensity in the posterior column of the lumbar spinal cord on T2-weighted images. High signal intensity in the posterior column of the cervical spinal cord on T2-weighted images appeared during the course of the illness. MR abnormalities in this case may reflect the degeneration of the posterior column of the spinal cord subsequent to sensory ganglionic neuropathy.