Fumihiro Imai

Neuroprotective effect of exogenous microglia in global brain ischemia

Exogenous microglia pass through the blood—brain barrier and migrate to ischemic hippocampal lesions when injected into the circulation. We investigated the effect of exogenous microglia on ischemic CA1 pyramidal neurons. Microglia were isolated from neonatal mixed brain cultures, labeled with the fluorescent dye PKH26, and injected into the subclavian artery of Mongolian gerbils subjected to ischemia reperfusion neuronal injury. PKH26-labeled microglia migrated to the ischemic hippocampal lesion, resulting in increased numbers of surviving neurons compared with control animals, even when injected 24 h after ischemia. Interferon-γ stimulation of isolated microglia enhanced the neuroprotective effect. Administration of exogenous microglia resulted in normal performance in a passive avoidance-learning task. Additionally, administration of exogenous microglia increased the expression of brain-derived neurotrophic factor and glial cell line-derived neurotrophic factor in the ischemic hippocampus, and thus might have induced neurotrophin-dependent protective activity in damaged neurons. Peripherally injected microglia exhibited a specific affinity for ischemic brain lesions, and protected against ischemic neuronal injury in vivo. It is possible that administration of exogenous microglia can be developed as a potential candidate therapy for central nervous system repair after transitory global ischemia.

Brain-specific gene expression by immortalized microglial cell-mediated gene transfer in the mammalian brain

The intra‐arterial injection of immortalized microglia transfected with the lacZ gene, resulted in the expression of β‐galactosidase in the rat brain at 48 h and the activity of β‐galactosidase was detected for up to 3 weeks post‐injection. More than 30‐fold higher activity of β‐galactosidase was detected in the brain than in the liver, lung or spleen at 48 h post‐injection. This method allows us to easily deliver the gene of interest to the brain without influencing other organs. Our brain‐targeting gene delivery system can facilitate gene therapy of several brain disorders, including brain tumor, metabolic disorders, and degenerative disorders, as well as investigation into the roles of particular genes in brain function and development.

Migration activity of microglia and macrophages into rat brain

We examined the entry of intra-arterially injected microglia and macrophages into the brain using a rat muscle graft model to compare their respective abilities to invade the brain parenchyma. Isolated microglia without any activation treatment entered into the brain with or without the muscle graft, while macrophages activated by phorbol 12-myristate-13-acetate (PMA) entered the brain only in the presence of the muscle graft. These results suggest that microglia have a higher affinity for the brain than macrophages.

Preservation of neurotrophin expression in microglia that migrate into the gerbil's brain across the blood–brain barrier

Microglia isolated from a mixed glial culture drawn from neonatal Mongolian gerbils were demonstrated to produce high amounts of brain-derived neurotrophic factor (BDNF) and glial cell line-derived neurotrophic factor (GDNF). The gerbil microglia retained the capability to migrate into the brain parenchyma after intra-arterial injection. We found that exogenously migrated microglia retained their BDNF and GDNF productive ability and expressed large amounts of BDNF and GDNF in damaged brain areas which suggests microglias role as a protectant of damaged neurons. Since peripherally injected microglia exhibit specific affinity for areas of neural damage within the brain, we suggest that microglia are possible tools for cell therapy of brain damage.

Exogenous microglia enter the brain and migrate into ischaemic hippocampal lesions.

We compared migration of systemically injected microglia into normal brain vs. ischaemic brain using a model of ischaemic hippocampal lesion. Microglia were labeled by a fluorescent dye using our standard phagocytosis procedure of microscopic particles and then injected intra-arterially into Mongolian gerbils subjected to ischaemia reperfusion neuronal injury. Delayed death of pyramidal neurons was confirmed by conventional histological analysis and dUTP nick end labeling (TUNEL) method. Clusters of dye-tagged cells migrating into the hippocampal ischaemic lesions were confirmed histochemically to be microglia. Since peripherally injected microglia exhibit specific affinity for ischaemic brain lesions and does not exacerbate ischaemic neuronal injury in the present model, we suggest that microglia may have a potential to be used as a piggy-back ride to deliver therapeutic genes and/or drugs for CNS repair following transitory global ischaemic insult.

Synthesized surface anatomy scanning (SSAS) for surgical planning of brain metastasis at the sensorimotor region: initial experience with 5 patients.

SummarySurface anatomy scanning (SAS) is a powerful technique that uses T2-weighted magnetic resonance images (MRI) to visualize brain surface structures, and to precisely localize subcortical lesions. To overcome technical limitations of this method, synthesized SAS (SSAS) superimposes MR angiography (MRA) data on the SAS images. We describe our initial experience with surgical planning for the resection of metastases at the sensorimotor region in 5 patients using SSAS. Neurological deficits were assessed before and after surgical resection. Although 4 of 5 patients had mild to severe neurological deficits before surgery, three became symptom-free and no patient had an increased deficit after surgery. Our results undoubtedly provide palliative surgery for sensorimotor metastases. As SSAS is non-invasive and requires a short scanning time, this method could become a useful technique for the routine pre-operative simulation for surgery on brain surface lesions such as sensorimotor metastases.

Brain-Specific Migration and Protective Roles in Brain Damage of Microglia

The ability to manipulate the expression of genes within the mammalian brain provide unique opportunities to study and to potentially treat neurological disorders. The introduction of certain genes specifically in brain has been done with viral vectors or cells carrying DNA. However, these methods require surgery. Recently, we found that primary isolated microglia specifically entered the brain from blood flow when the cells were injected intra-arterially.1 Microglia, macrophage-like cells in the brain, are multi-functional cells; they play important roles in the development, differentiation and maintenance of neural cells via their phagocytic activity and production of enzymes, cytokines and trophic factors.2 Since intra-arterially-injected microglia were labeled with fluorescent dye microparticles by their phagocytic activity, this system could apply to a brain-specific delivery for medicines, or other bioactive materials, such as proteins or genes.3 To apply this brain-specific bio-targeting system for treatment of neurological disorders, vehicle microglia should migrate to the region of insult and not augment the insult. Therefore, we investigated migration of systemically injected microglia into the ischemic brain.

3002 Gene transfer specific for brain using microglial cell lines

Katsuya Yamada, Hideki Ohta, Haruka Ishii, Tetsuro Ogawa When 400 microns-thick adult neocortical slices were incubated in a commercially-available CO2 incubator with D-MEM/F-12, field potentials evoked by underlying white matter stimulation disappeared within 4 hours. On the other hand, a recording over long hours was possible by continuous culture medium perfusion. We found that several hours were needed until humidity and gas composition in the dish reached an equilibrium with the atmosphere inside the incubator by the previous method. By improving the incubating system so that adequate humidity and pH was obtained, field responses was obtained even in static medium.

Clinical utility of synthesised brain surface imaging: Surface anatomy scanning and MR angiography

An MRI technique permitting direct, noninvasive display of brain surface structures (surface anatomy scanning, SAS) was developed using T2-weighted images. In this study, synthesised SAS, which combines contrast-enhanced MR angiography and SAS, was used to 50 cases, and the detection rate of lesions and preoperative simulation was evaluated. Synthesised SAS enabled detection of more lesions (94%) than SAS alone (52%). Synthesised SAS has the following advantages: noninvasive visualisation of the brain surface structures (sulci, lesions and veins) and skin markers for surgical planning; practical data acquisition and postprocessing times; preoperative assessment of the suitability for a craniotomy; and minimisation of surgical damage to normal brain tissues and veins.