Kazuhiro Imamura

Distribution of major histocompatibility complex class II-positive microglia and cytokine profile of Parkinson's disease brains

There are numerous observations confirming that microglia expressing major histocompatibility complex (MHC) class II molecules are associated with the central nervous system (CNS) in aging and pathological conditions. In this study, we investigated the distribution of MHC class II-positive microglia in Parkinsons disease (PD) brains. The number of MHC class II-positive microglia in the substantia nigra (SN) and putamen increased as the neuronal degeneration of the SN proceeded. These cells were also ICAM-1 (CD54) and LFA-1 (CD11a) positive. The number of activated microglia not only in the SN and putamen but also in the hippocampus, transentorhinal cortex, cingulate cortex and temporal cortex in PD was significantly higher than that in the normal control. Most activated microglia persisted regardless of the presence or absence of Lewy bodies. They were frequently associated not only with α-synuclein-positive Lewy neurites, but also with TH-16-positive dopaminergic and WH-3-positive serotonergic neurites, as well as MAP-2- and SMI-32-positive neurites. These activated microglia were also positive for TNF-α and interleukin-6, which are known to have a neuroprotective function. We conclude that MHC class II-positive microglia are a sensitive index of neuropathological change and are actively associated with damaged neurons and neurites.

Role of cytokines in inflammatory process in Parkinson's disease.

We investigated whether the cytokines produced in activated microglia in the substantia nigra (SN) and putamen in sporadic Parkinsons disease (PD) are neuroprotective or neurotoxic. In autopsy brains of PD, the number of MHC class II (CR3/43)-positive activated microglia, which were also ICAM-1 (CD 54)-, LFA-1 (CD 11a)-, TNF-alpha-, and IL-6-positive, increased in the SN and putamen during progress of PD. At the early stage activated microglia were mainly associated with tyrosine hydroxylase (TH)-positive neurites in the putamen, and at the advanced stage with damaged TH-positive neurons in the SN. The activated microglia in PD were observed not only in the nigro-striatal region, but also in various brain regions such as the hippocampus and cerebral cortex. We examined the distribution of activated microglia and the expression of cytokines and neurotrophins in the hippocampus of PD and Lewy body disease (LBD). The levels of IL-6 and TNF-alpha mRNAs increased both in PD and LBD, but those of BDNF mRNA and protein drastically decreased specifically in LBD, in which neuronal loss was observed not only in the nigro-striatum but also in the hippocampus. The results suggest activated microglia in the hippocampus to be probably neuroprotective in PD, but those to be neurotoxic in LBD. As an evidence supporting this hypothesis, two subsets of microglia were isolated from mouse brain by cell sorting: one subset with high production of reactive oxygen species (ROS) and the other with no production of ROS. When co-cultured with neuronal cells, one microglia clone with high ROS production was neurotoxic, but another clone with no ROS production neuroprotective. On the other hand, Sawada with coworkers found that a neuroprotective microglial clone in a culture experiment converted to a toxic microglial clone by transduction of the HIV-1 Nef protein with increasing NADPH oxidase activity. Taken together, all these results suggest that activated microglia may change in vivo from neuroprotective to neurotoxic subtsets as degeneration of dopamine neurons in the SN progresses in PD. We conclude that the cytokines from activated microglia in the SN and putamen may be initially neuroprotective, but may later become neurotoxic during the progress of PD. Toxic change of activated microglia may also occur in Alzheimers disease and other neurodegenerative diseases in which inflammatory process is found.

Cytokine production of activated microglia and decrease in neurotrophic factors of neurons in the hippocampus of Lewy body disease brains

Dementia is a frequent complication of Parkinson’s disease (PD) and usually occurs late in the protracted course of the illness. We have already reported numerous MHC class II-positive microglia in the hippocampus in PD patients, and that this phenomenon may be responsible for functional changes in the neurons and the cognitive decline in PD patients. In this study, we have investigated the distribution of activated microglia and the immunohistochemical and the mRNA expression of several cytokines and neurotrophic factors of the hippocampus in PD and dementia with Lewy bodies (DLB). The brains from five cases of PD and five cases of DLB that were clinically and neuropathologically diagnosed, and those from four normal controls (NC) were evaluated by immunohistochemistry using anti-HLA-DP, -DQ, -DR (CR3/43), anti-α-synuclein, anti-brain-derived neurotrophic factor (BDNF), and anti-glial fibrillary acidic protein antibodies. In addition, the mRNA expressions of cytokines (IL-1α, IL-1β, TNF-α, IL-6, TGF-β) and neurotrophic factors (BDNF, GDNF, NGF, NT-3) of these brains were evaluated by the reverse transcription-PCR method. MHC class II-positive microglia were distributed diffusely in the hippocampus of PD and DLB brains. Although the cytoplasm of pyramidal and granular cells of the hippocampus in NC brains was strongly stained by anti-BDNF antibodies, it was only weakly stained in PD and DLB brains. The mRNA expression of IL-6 was significantly increased in the hippocampus of PD and DLB brains, and that of BDNF was significantly decreased in the hippocampus of DLB brains. The increased number of activated microglia and the production of neurotrophic cytokines such as IL-6, together with the decreased expression of the neurotrophic factors of neurons in the hippocampus of PD and DLB brains, may be related to functional cellular changes associated with dementia.

Induction of MHC class II antigen expression on murine microglia by interleukin-3

The effects of various cytokines on MHC class II antigen expression were examined in murine microglia. Interleukin-3 (IL-3), as well as interferon-gamma (IFN-gamma), induced MHC class II antigen expression on these cells. IL-3 additionally enhanced MHC class II antigen expression induced by IFN-gamma. The induction of MHC class II antigen expression by IL-3 was not mediated via IFN-gamma production, because the effect was not blocked by antibodies to IFN-gamma. In contrast, granulocyte-macrophage colony-stimulating factor (GM-CSF) did not affect the expression of MHC class II antigen on naive cells and down-regulated IFN-gamma-mediated induction of MHC class II antigen expression on microglia. Because IL-3 and GM-CSF are apparently produced in the central nervous system, MHC class II antigen expression on microglia may be regulated by these cytokines synthesized in the central nervous system.

Brainstem-type Lewy body disease presenting with progressive autonomic failure and lethargy.

The authors report an autopsy case characterized by progressive lethargy and autonomic failure with a distinctive pattern of occurrence of Lewy bodies. Autonomic dysfunction such as sleep apnea, orthostatic hypotension, dysuria, and hypohidrosis predominated with lethargy, whereas parkinsonism was not apparent. Numerous Lewy bodies were widely evident microscopically in brainstem nuclei and the intermediolateral cell columns of the spinal cord, as well as in the sympathetic ganglia, but were rare or absent in the cerebral cortex and other supratentorial structures. Marked neuronal loss was seen in the locus ceruleus, raphe nuclei, dorsal vagal nuclei, and intermediolateral cell columns, but neurons in the substantia nigra, other brain regions, and sympathetic ganglia appeared undiminished. This case represents a specific clinicopathologic from of Lewy body disease occurring predominantly in the brainstem, spinal cord, and sympathetic ganglia.

Activation mechanism of brain microglia in patients with diffuse neurofibrillary tangles with calcification: a comparison with Alzheimer disease.

Diffuse neurofibrillary tangles with calcification (DNTC) is an atypical dementia and is characterized pathologically by diffuse neurofibrillary tangles (NFTs) without senile plaques (SPs). In this study, we investigated the distribution of human leukocyte antigen (HLA)-DR–positive activated microglia in postmortem brain tissue of six patients with DNTC and six patients with Alzheimer disease (AD). HLA-DR–positive activated microglia were observed to associate with SPs in AD. In the DNTC brain, which lacks SPs, HLA-DR–positive microglia were mainly accumulated around weakly tau-positive NFTs, which were also positive for anti–amyloid-P and anti-C3d antibodies. The results of this study suggest that the complement pathway is also activated in the DNTC brain and that immune and inflammatory responses, including microglia activation, may occur around extracellular NFTs in DNTC patients.

Autopsied case of non-plaque-type dura mater graft-associated Creutzfeldt-Jakob disease presenting with extensive amyloid-β deposition: Dura mater graft-associated CJD

We present an autopsied case of non‐plaque‐type dura mater graft‐associated Creutzfeldt‐Jakob disease (dCJD) with extensive amyloid‐β (Aβ) deposition in the brain. A 39‐year‐old Japanese woman presented with memory disturbance and abnormal behavior. The patient had a history of craniotomy with dura matter‐graft transplant for a head injury which occurred when she was 19 years old. Magnetic resonance imaging (MRI) showed hyperintensities in the cerebral cortex and striatum on diffusion‐weighted images, particularly on the dura mater‐grafted right side. Her clinical symptoms, including rapidly progressing cognitive impairment, myoclonus, and periodic sharp wave complexes on electroencephalogram, could not be distinguished from typical sporadic CJD cases. The patient died 11 months after symptom onset, and pathological investigations showed extensive spongiform degeneration with prion protein (PrP) deposition without Kuru plaques; these observations were essentially the same as those of typical sporadic CJD cases. Furthermore, Aβ immunohistochemistry showed extensive diffuse staining in the cerebral neocortex, plaque‐type deposition, positive staining in the pia mater, and cerebral amyloid angiopathy. Although the MRI findings suggested that the pathological involvement originated from the dura mater‐grafted right side, the PrP and Aβ depositions showed no apparent regionalization and laterality. Tau‐pathology including neurofibrillary tangles was hardly identified. The proteins phosphorylated α‐synuclein and phosphorylated transactivation response DNA‐binding protein 43 kDa were not detected on immunostaining. Although this report describes only one case, various speculations were made based on detailed clinical and pathological observations in conjunction with previous reports of dCJD. In particular, this report provides significant insight into the characteristics and progression of dCJD pathology and its relationship with Aβ pathology.

Role of Microglia in Inflammatory Process in Parkinson’s Disease

1.1 What is Parkinson’s disease Parkinson’s disease (PD) is the second most common neurodegenerative disease after Alzheimer’s disease (AD). PD is characterized by degeneration and cell death in dopaminergic neurons in the substantia nigra pars compacta (SNpc) and loss of their nerve terminals in the striatum (putamen and caudate nucleus), accompanied by the depletion of the neurotransmitter dopamine (DA) in the striatum. This depletion causes motor symptoms, i.e., resting tremor, muscle rigidity, and akinesia. The level of tyrosine hydroxylase (TH), the rate-limiting enzyme of catecholamine (DA, noradrenaline, and adrenaline) synthase in the nigro-striatal region of PD patients is decreased (Nagatsu and Sawada M., 2007). A small percentage of PD is familial with a hereditary history. However, most cases of PD (approximately 90-95 %) are sporadic without any hereditary history. In 2009, 16 causative genes of familial PD have been identified (Satake et al., 2009), including PARK1 (αsynuclein), PARK2 (parkin), PARK4 (α-synuclein), PARK5 (UCHL-1), PARK6 (PINK1), PARK7 (DJ-1), PARK8 (LRRK2), and PARK9 (ATP13A2). Sporadic PD and some cases of familial PD are characterized by the presence of cytoplasmic inclusions named Lewy bodies, which consist mainly of α-synuclein protein, the product of the PARK1 gene. α-Synuclein is observed not only in PD but also in various neurodegenerative diseases, such as dementia with Lewy bodies (DLB). Based on their investigation of the distribution of α-synuclein-positive Lewy bodies and Lewy neurites in PD patients, Braak et al. (2003) proposed a hypothesis that the pathological process of PD starts first from the lower brain stem and then spreads to the midbrain, limbic system, and cerebral cortex. α-Synuclein-positive inclusions are observed in the anterior olfactory nucleus, dorsal motor nucleus of vagus nerves, and also in peripheral autonomic neurons including those of the sympathetic ganglia, adrenal medulla, and intestinal Auerbach’s plexus. Braak et al. (2003) proposed that symptoms of PD appears when Lewy bodies are formed in dopaminergic neurons in the substantia nigra (SN) .