Daiju Tsuchiya

Microglial transplantation increases amyloid-β clearance in Alzheimer model rats

Immunization with amyloid‐β (Aβ) peptides, a therapeutic approach in Alzheimers disease (AD), reduces brain Aβ, and microglial Aβ phagocytosis has been proposed as an Aβ‐lowering mechanism. We transplanted rat microglia into the rat lateral ventricle just after intra‐hippocampal Aβ injection, and then investigated the contribution of exogenous microglia to Aβ clearance. Migration of exogenous microglia from the lateral ventricle to Aβ plaque was detected by magnetic resonance imaging and histochemical analysis, and the clearance of Aβ was increased by transplantation. These results suggest the possible usefulness of exogenous microglia to the therapeutic approach in AD.

Role of high mobility group protein-1 (HMG1) in amyloid-β homeostasis☆

Abstract In Alzheimer’s disease (AD), fibrillar amyloid-β (Aβ) peptides form senile plaques associated with activated microglia. Recent studies have indicated that microglial Aβ clearance is facilitated by several activators such as transforming growth factor-β1 (TGF-β1). The relationship between microglia and Aβ formation and deposition is still unclear. In the present study, high mobility group protein-1 (HMG1) inhibited the microglial uptake of Aβ (1–42) in the presence and absence of TGF-β1. In addition, HMG1 bound to Aβ (1–42) and stabilized the oligomerization. In AD brains, protein levels of HMG1 were significantly increased in both the cytosolic and particulate fractions, and HMG1 and Aβ were colocalized in senile plaques associated with microglia. These results suggest that HMG1 may regulate the homeostasis of extracellular Aβ (1–42) and Aβ oligomerization.

High mobility group box protein-1 inhibits microglial Aβ clearance and enhances Aβ neurotoxicity

One pathogenic characteristic of Alzheimers disease (AD) is the formation of extracellular senile plaques with accumulated microglia. According to the amyloid hypothesis, the increase or accumulation of amyloid‐β (Aβ) peptides in the brain parenchyma is the primary event that influences AD pathology. Although the role of microglia in AD pathology has not been clarified, their involvement in Aβ clearance has been noted. High mobility group box protein‐1 (HMGB1) is an abundant nonhistone chromosomal protein. We reported recently that HMGB1 was associated with senile plaques and the total protein level significantly increased in AD brain. In this study, diffuse HMGB1 immunoreactivity was observed around dying neurons in the kainic acid‐ and Aβ1–42 (Aβ42)‐injected rat hippocampi. HMGB1 also colocalized with Aβ in the Aβ42‐injected rats but not in transgenic mice, which show massive Aβ production without neuronal loss in their brains. Furthermore, coinjection of HMGB1 delayed the clearance of Aβ42 and accelerated neurodegeneration in Aβ42‐injected rats. These results suggest that HMGB1 released from dying neurons may inhibit microglial Aβ42 clearance and enhance the neurotoxicity of Aβ42. HMGB1 may thus be another target in the investigation of a therapeutic strategy for AD.

Improvement of focal ischemia-induced rat dopaminergic dysfunction by striatal transplantation of mouse embryonic stem cells.

Middle cerebral artery occlusion (MCAO) caused behavioral dysfunction with massive neuronal loss. Cell transplantation may recover this deficit by replacing damaged brain cells. In this study, we examined the effects of transplantation of mouse embryonic stem (ES) cells or ES cell-derived neuron-like (ES-N) cells on behavioral function in ischemic rats. Seven days after MCAO, ES or ES-N cells were transplanted into ipsilateral striata (but not the substantia nigra) of ischemic rats. Transplanted rats exhibited a gradual reduction in the number of rotations induced by methamphetamine compared to vehicle-injected rats. These rats also showed a significant improvement in rota-rod performance. At 15 weeks after transplantation, immunoreactivities for tyrosine hydroxylase (TH) and dopamine transporter (DAT) in the striatum were significantly recovered in rats grafted with ES or ES-N cells compared to vehicle-injected rats. These results suggest that intrastriatal-transplantation of ES or ES-N cells improved the dopaminergic function and subsequently recover behavioral dysfunction in focal ischemic rats.

Heat shock protein-90-induced microglial clearance of exogenous amyloid-β1–42 in rat hippocampus in vivo

Alzheimers disease is characterized by the accumulation of extracellular amyloid-beta (A beta) fibrils with microglia. In an in vitro microglial culture, we recently found that heat-shock protein-90 (Hsp90) enhanced the microglial phagocytosis and clearance of A beta (1-42) (A beta 42). In this study, we examined the microinjection of A beta 42 in the presence or absence of Hsp90 into the rat hippocampus in vivo. Intrahippocampal injection of A beta 42 alone induced microglial accumulation, and the amount of A beta 42 then gradually decreased. In addition, simultaneous injection with Hsp90 significantly reduced the amount of A beta 42 and increased the production of cytokines. These results suggest that Hsp90 may facilitate microglial A beta 42 clearance in rat brain in vivo.

Serofendic acid prevents 6-hydroxydopamine-induced nigral neurodegeneration and drug-induced rotational asymmetry in hemi-parkinsonian rats.

Serofendic acid was recently identified as a neuroprotective factor from fetal calf serum. This study was designed to evaluate the neuroprotective effects of an intranigral microinjection of serofendic acid based on behavioral, neurochemical and histochemical studies in hemi‐parkinsonian rats using 6‐hydroxydopamine (6‐OHDA). Rats were injected with 6‐OHDA in the presence or absence of serofendic acid, or were treated with serofendic acid on the same lateral side, at 12, 24 or 72 h after 6‐OHDA lesion. Intranigral injection of 6‐OHDA alone induced a massive loss of tyrosine hydroxylase (TH)‐immunopositive neurons in the substantia nigra pars compacta (SNpc). Either simultaneous or 12 h post‐administration of serofendic acid significantly prevented both dopaminergic neurodegeneration and drug‐induced rotational asymmetry. Immunoreactivities for oxidative stress markers, such as 3‐nitrotyrosine (3‐NT) and 4‐hydroxy‐2‐nonenal (4‐HNE), were markedly detected in the SNpc of rats injected with 6‐OHDA alone. These immunoreactivities were markedly suppressed by the co‐administration of serofendic acid, similar to the results in vehicle‐treated control rats. In addition, serofendic acid inhibited 6‐OHDA‐induced α‐synuclein expression and glial activation in the SNpc. These results suggest that serofendic acid protects against 6‐OHDA‐induced SNpc dopaminergic neurodegeneration in a rat model of Parkinsons disease.

Possible involvement of Wiskott–Aldrich syndrome protein family in aberrant neuronal sprouting in Alzheimer's disease

One of the pathological characteristics of Alzheimers disease (AD) is the formation of dystrophic neurites accompanied by aberrant neuronal sprouting. Although a number of studies have focussed on the formation of amyloid plaques and neurofibrillary tangles, the mechanism of neuronal sprouting in AD is not fully understood. The protein levels of neural Wiskott-Aldrich syndrome protein (N-WASP), WASP interacting SH3 protein (WISH) and WASP family verprolin-homologous protein (WAVE) were significantly increased in AD brains. In addition, N-WASP, WISH and WAVE were co-localized with filamentous actin in abnormal dendrite-like processes sprouting from staurosporine-treated human SH-SY5Y cells. These results suggest that N-WASP, WISH and WAVE may participate in the neurodegenerative aberrant sprouting in AD neurons.

Transplantation of mouse embryonic stem cell-derived neurons into the striatum, subthalamic nucleus and substantia nigra, and behavioral recovery in hemiparkinsonian rats.

Usefulness of the in vitro and in vivo generation of neural precursors from embryonic stem (ES) cells has been widely discussed, but functional recovery in animal models of Parkinsons disease (PD) is not fully understood. The aim of this study was to investigate a transplantation strategy for PD by assessing whether double-transplants in the striatum (ST) and substantia nigra (SN), or ST and subthalamic nucleus (STN) induce functional recovery in 6-hydroxydopamine-lesioned rats. Methamphetamine-induced rotation was significantly reduced by transplantation of mouse ES cell-derived neurons into the ST, but not the STN or SN alone. Double-transplantation was also effective at recovering rotational behavior. Although immunoreactivity for tyrosine hydroxylase (TH) was almost completely lost in the ipsilateral striatum in hemiparkinsonian rats, TH immunoreactivity was detected in transplanted cells and sprouting fibers in the ST, STN and SN. These results suggest that both the involvement of ST as a place of transplantation and the number of ES cell-derived neurons are essential factors for efficacy on hemiparkinsonian behaviors.

Developmental expression of neural Wiskott–Aldrich syndrome protein (N-WASP) and WASP family verprolin-homologous protein (WAVE)-related proteins in postnatal rat cerebral cortex and hippocampus

The actin cytoskeleton plays a critical role in the cellular morphological changes. Its organization is essential for neurite extension and synaptogenesis under the processes of neuronal development. Recently, neural Wiskott-Aldrich syndrome protein (N-WASP) and WASP family verprolin-homologous protein (WAVE) have been identified as key molecules, which specifically participate in regulation of actin cytoskeleton through small GTPases. The functions of these factors have been investigated using cultured cells; however, in vivo developmental changes in these factors are not fully understood. In this study, we examined the expression levels and distributions of N-WASP, WAVE and their related proteins in the rat cerebral cortex and hippocampus during postnatal development. Protein levels of these factors were progressively increased during development, and actin was accumulated in membranous fractions. Immunoreactivities for these factors were widely but differentially observed in entire brain. In the developing brain, N-WASP and WAVE seemed to exist in the synapse-rich areas, such as stratum radiatum of hippocampal CA1 subfield. A similar tendency in the distributions of these factors was observed in the mature brain. Taken together, N-WASP, WAVE and their related proteins may participate in normal brain development and synaptic plasticity by regulating the actin cytoskeleton.

Microglial activation around amyloid-β deposits in mouse and rat models

Abstract One of the principal pathological features of Alzheimers disease (AD) is the extracellular deposition of fibrillar amyloid-β (Aβ) associated with reactive microglia. However, microglial pathogenesis in AD is still unclear. In this study, we examined the relationship between microglial activation and Aβ deposition on trasgenic mice and Aβ1–42 (Aβ42)-injected rats. In the brain of a double-transgenic mouse carrying mutations in both the presenilin-1 and Aβ precursor protein (APP) transgenes, there was a marked production of Aβ peptides and reactive microglia were accumulated around Aβ deposits, but global neuronal loss was not detected. Intrahippocampal injection of Aβ42 induced microglial accumulation and then Aβ42 gradually decreased. Recent studies suggest that several cytokines produced by reactive microglia have neuroprotective effects. In addition, anti-Aβ antibodies, produced by Aβ-vaccine therapy, induce microglial phagocytosis. Taken together, microglial activation may essentially contribute to compensatory neuroprotection by Aβ phagocytosis and production of cytokines.