Tsutomu Hashikawa

Bio: Tsutomu Hashikawa is an academic researcher from RIKEN Brain Science Institute. The author has contributed to research in topics: Parvalbumin & Neocortex. The author has an hindex of 54, co-authored 148 publications receiving 10758 citations.

The neuroinvasive potential of SARS-CoV2 may play a role in the respiratory failure of COVID-19 patients

Abstract: Following the severe acute respiratory syndrome coronavirus (SARS-CoV) and Middle East respiratory syndrome coronavirus (MERS-CoV), another highly pathogenic coronavirus named SARS-CoV-2 (previously known as 2019-nCoV) emerged in December 2019 in Wuhan, China, and rapidly spreads around the world. This virus shares highly homological sequence with SARS-CoV, and causes acute, highly lethal pneumonia coronavirus disease 2019 (COVID-19) with clinical symptoms similar to those reported for SARS-CoV and MERS-CoV. The most characteristic symptom of patients with COVID-19 is respiratory distress, and most of the patients admitted to the intensive care could not breathe spontaneously. Additionally, some patients with COVID-19 also showed neurologic signs, such as headache, nausea, and vomiting. Increasing evidence shows that coronaviruses are not always confined to the respiratory tract and that they may also invade the central nervous system inducing neurological diseases. The infection of SARS-CoV has been reported in the brains from both patients and experimental animals, where the brainstem was heavily infected. Furthermore, some coronaviruses have been demonstrated able to spread via a synapse-connected route to the medullary cardiorespiratory center from the mechanoreceptors and chemoreceptors in the lung and lower respiratory airways. Considering the high similarity between SARS-CoV and SARS-CoV2, it remains to make clear whether the potential invasion of SARS-CoV2 is partially responsible for the acute respiratory failure of patients with COVID-19. Awareness of this may have a guiding significance for the prevention and treatment of the SARS-CoV-2-induced respiratory failure.

Early and progressive accumulation of reactive microglia in the Huntington disease brain.

Abstract: Microglia may contribute to cell death in neurodegenerative diseases. We studied the activation of microglia in affected regions of Huntington disease (HD) brain by localizing thymosin β-4 (Tβ4), which is increased in reactive microglia. Activated microglia appeared in the neostriatum, cortex, and globus pallidus and the adjoining white matter of the HD brain, but not in control brain. In the striatum and cortex, reactive microglia occurred in all grades of pathology, accumulated with increasing grade, and grew in density in relation to degree of neuronal loss. The predominant morphology of activated microglia differed in the striatum and cortex. Processes of reactive microglia were conspicuous in low-grade HD, suggesting an early microglia response to changes in neuropil and axons and in the grade 2 and grade 3 cortex, were aligned with the apical dendrites of pyramidal neurons. Some reactive microglia contacted pyramidal neurons with huntingtin-positive nuclear inclusions. The early and proximate association of activated microglia with degenerating neurons in the HD brain implicates a role for activated microglia in HD pathogenesis.

Retrograde modulation of presynaptic release probability through signaling mediated by PSD-95-neuroligin.

Abstract: The structure and function of presynaptic and postsynaptic components of the synapse are highly coordinated. How such coordination is achieved and the molecules involved in this process have not been clarified. Several lines of evidence suggest that presynaptic functionalities are regulated by retrograde mechanisms from the postsynaptic side. We therefore sought postsynaptic mechanisms responsible for trans-synaptic regulation of presynaptic function at excitatory synapses in rat hippocampal CA1 pyramidal neurons. We show here that the postsynaptic complex of scaffolding protein PSD-95 and neuroligin can modulate the release probability of transmitter vesicles at synapse in a retrograde way, resulting in altered presynaptic short-term plasticity. Presynaptic beta-neurexin serves as a likely presynaptic mediator of this effect. Our results indicate that trans-synaptic protein-protein interactions can link postsynaptic and presynaptic function.

Tau filament formation and associative memory deficit in aged mice expressing mutant (R406W) human tau

Abstract: The R406W tau mutation found in frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP-17) causes a hereditary tauopathy clinically resembling Alzheimer's disease. Expression of modest levels of the longest human tau isoform with this mutation under the control of the α-calcium–calmodulin-dependent kinase-II promoter in transgenic (Tg) mice resulted in the development of congophilic hyperphosphorylated tau inclusions in forebrain neurons. These inclusions appeared as early as 18 months of age. As with human cases, tau inclusions were composed of both mutant and endogenous wild-type tau, and were associated with microtubule disruption and flame-shaped transformations of the affected neurons. Straight tau filaments were recovered from Sarkosyl-insoluble fractions from only the aged Tg brains. Behaviorally, aged Tg mice had associative memory impairment without obvious sensorimotor deficits. Therefore, these mice that exhibit a phenotype mimicking R406W FTDP-17 provide an animal model for investigating the adverse properties associated with this mutation, which might potentially recapitulate some etiological events in Alzheimer's disease.

The glutamate receptor ion channels

Abstract: The ionotropic glutamate receptors are ligand-gated ion channels that mediate the vast majority of excitatory neurotransmission in the brain. The cloning of cDNAs encoding glutamate receptor subunits, which occurred mainly between 1989 and 1992 ([Hollmann and Heinemann, 1994][1]), stimulated this

Astrocytes: biology and pathology

Abstract: Astrocytes are specialized glial cells that outnumber neurons by over fivefold. They contiguously tile the entire central nervous system (CNS) and exert many essential complex functions in the healthy CNS. Astrocytes respond to all forms of CNS insults through a process referred to as reactive astrogliosis, which has become a pathological hallmark of CNS structural lesions. Substantial progress has been made recently in determining functions and mechanisms of reactive astrogliosis and in identifying roles of astrocytes in CNS disorders and pathologies. A vast molecular arsenal at the disposal of reactive astrocytes is being defined. Transgenic mouse models are dissecting specific aspects of reactive astrocytosis and glial scar formation in vivo. Astrocyte involvement in specific clinicopathological entities is being defined. It is now clear that reactive astrogliosis is not a simple all-or-none phenomenon but is a finely gradated continuum of changes that occur in context-dependent manners regulated by specific signaling events. These changes range from reversible alterations in gene expression and cell hypertrophy with preservation of cellular domains and tissue structure, to long-lasting scar formation with rearrangement of tissue structure. Increasing evidence points towards the potential of reactive astrogliosis to play either primary or contributing roles in CNS disorders via loss of normal astrocyte functions or gain of abnormal effects. This article reviews (1) astrocyte functions in healthy CNS, (2) mechanisms and functions of reactive astrogliosis and glial scar formation, and (3) ways in which reactive astrocytes may cause or contribute to specific CNS disorders and lesions.

Microglia-mediated neurotoxicity: uncovering the molecular mechanisms

Abstract: Mounting evidence indicates that microglial activation contributes to neuronal damage in neurodegenerative diseases. Recent studies show that in response to certain environmental toxins and endogenous proteins, microglia can enter an overactivated state and release reactive oxygen species (ROS) that cause neurotoxicity. Pattern recognition receptors expressed on the microglial surface seem to be one of the primary, common pathways by which diverse toxin signals are transduced into ROS production. Overactivated microglia can be detected using imaging techniques and therefore this knowledge offers an opportunity not only for early diagnosis but, importantly, for the development of targeted anti-inflammatory therapies that might slow or halt the progression of neurodegenerative disease.