Increasing evidence suggests that Alzheimer's disease pathogenesis is not restricted to the neuronal compartment but strongly interacts with immunological mechanisms in the brain. Misfolded and aggregated proteins bind to pattern recognition receptors on micro- and astroglia and trigger an innate immune response, characterized by the release of inflammatory mediators, which contribute to disease progression and severity. Genome wide analysis suggests that several genes, which increase the risk for sporadic Alzheimer's disease en-code for factors that regulate glial clearance of misfolded proteins and the inflammatory reaction. External factors, including systemic inflammation and obesity are likely to interfere with the immunological processes of the brain and further promote disease progression. This re-view provides an overview on the current knowledge and focuses on the most recent and exciting findings. Modulation of risk factors and intervention with the described immune mechanisms are likely to lead to future preventive or therapeutic strategies for Alzheimer's disease.

The only treatment of patients with acute ischemic stroke is thrombolytic therapy, which benefits only a fraction of stroke patients. Both human and experimental studies indicate that ischemic stroke involves secondary inflammation that significantly contributes to the outcome after ischemic insult. Minocycline is a semisynthetic second-generation tetracycline that exerts antiinflammatory effects that are completely separate from its antimicrobial action. Because tetracycline treatment is clinically well tolerated, we investigated whether minocycline protects against focal brain ischemia with a wide therapeutic window. Using a rat model of transient middle cerebral artery occlusion, we show that daily treatment with minocycline reduces cortical infarction volume by 76 ؎ 22% when the treatment is started 12 h before ischemia and by 63 ؎ 35% when started even 4 h after the onset of ischemia. The treatment inhibits morphological activation of microglia in the area adjacent to the infarction, inhibits induction of IL-1␤-converting enzyme, and reduces cyclooxygenase-2 expression and prostaglandin E2 production. Minocycline had no effect on astrogliosis or spreading depression, a wave of ionic transients thought to contribute to enlargement of cortical infarction. Treatment with minocycline may act directly on brain cells, because cultured primary neurons were also salvaged from glutamate toxicity. Minocycline may represent a prototype of an antiinflammatory compound that provides protection against ischemic stroke and has a clinically relevant therapeutic window.

Ischemic stroke is the most common lifethreatening neurological disease and has limited therapeutic options. One component of ischemic neuronal death is inf lammation. Here we show that doxycycline and minocycline, which are broad-spectrum antibiotics and have antiinf lammatory effects independent of their antimicrobial activity, protect hippocampal neurons against global ischemia in gerbils. Minocycline increased the survival of CA1 pyramidal neurons from 10.5% to 77% when the treatment was started 12 h before ischemia and to 71% when the treatment was started 30 min after ischemia. The survival with corresponding pre-and posttreatment with doxycycline was 57% and 47%, respectively. Minocycline prevented completely the ischemiainduced activation of microglia and the appearance of NADPH-diaphorase reactive cells, but did not affect induction of glial acidic fibrillary protein, a marker of astrogliosis. Minocycline treatment for 4 days resulted in a 70% reduction in mRNA induction of interleukin-1␤-converting enzyme, a caspase that is induced in microglia after ischemia. Likewise, expression of inducible nitric oxide synthase mRNA was attenuated by 30% in minocycline-treated animals. Our results suggest that lipid-soluble tetracyclines, doxycycline and minocycline, inhibit inf lammation and are neuroprotective against ischemic stroke, even when administered after the insult. Tetracycline derivatives may have a potential use also as antiischemic compounds in humans.

Minocycline, a semisynthetic tetracycline derivative, protects brain against global and focal ischemia in rodents. We examined whether minocycline reduces excitotoxicity in primary neuronal cultures. Minocycline (0.02 M) significantly increased neuronal survival in mixed spinal cord (SC) cultures treated with 500 M glutamate or 100 M kainate for 24 hr. Treatment with these excitotoxins induced a dose-dependent proliferation of microglia that was associated with increased release of interleukin-1␤ (IL-1␤) and was followed by increased lactate dehydrogenase (LDH) release. The excitotoxicity was enhanced when microglial cells were cultured on top of SC cultures. Minocycline prevented excitotoxin-induced microglial proliferation and the increased release of nitric oxide (NO) metabolites and IL-1␤. Excitotoxins induced microglial proliferation and increased the release of NO metabolites and IL-1␤ also in pure microglia cultures, and these responses were inhibited by minocycline. In both SC and pure microglia cultures, excitotoxins activated p38 mitogen-activated protein kinase (p38 MAPK) exclusively in microglia. Minocycline inhibited p38 MAPK activation in SC cultures, and treatment with SB203580, a p38 MAPK inhibitor, but not with PD98059, a p44/42 MAPK inhibitor, increased neuronal survival. In pure microglia cultures, glutamate induced transient activation of p38 MAPK, and this was inhibited by minocycline. These findings indicate that the proliferation and activation of microglia contributes to excitotoxicity, which is inhibited by minocycline, an antibiotic used in severe human infections.

Glutamate excitotoxicity to a large extent is mediated through activation of the N-methyl-d-aspartate (NMDA)-gated ion channels in several neurodegenerative diseases and ischemic stroke. Minocycline, a tetracycline derivative with antiinflammatory effects, inhibits IL-1β-converting enzyme and inducible nitric oxide synthase up-regulation in animal models of ischemic stroke and Huntington’s disease and is therapeutic in these disease animal models. Here we report that nanomolar concentrations of minocycline protect neurons in mixed spinal cord cultures against NMDA excitotoxicity. NMDA treatment alone induced microglial proliferation, which preceded neuronal death, and administration of extra microglial cells on top of these cultures enhanced the NMDA neurotoxicity. Minocycline inhibited all these responses to NMDA. Minocycline also prevented the NMDA-induced proliferation of microglial cells and the increased release of IL-1β and nitric oxide in pure microglia cultures. Finally, minocycline inhibited the NMDA-induced activation of p38 mitogen-activated protein kinase (MAPK) in microglial cells, and a specific p38 MAPK inhibitor, but not a p44/42 MAPK inhibitor, reduced the NMDA toxicity. Together, these results suggest that microglial activation contributes to NMDA excitotoxicity and that minocycline, a tetracycline derivative, represents a potential therapeutic agent for brain diseases.

SummaryAlzheimer's disease (AD) is a common neurodegenerative disorder and the leading cause of cognitive impairment. Due to insufficient understanding of the disease mechanisms, there are no efficient therapies for AD. Most studies have focused on neuronal cells, but astrocytes have also been suggested to contribute to AD pathology. We describe here the generation of functional astrocytes from induced pluripotent stem cells (iPSCs) derived from AD patients with PSEN1 ΔE9 mutation, as well as healthy and gene-corrected isogenic controls. AD astrocytes manifest hallmarks of disease pathology, including increased β-amyloid production, altered cytokine release, and dysregulated Ca2+ homeostasis. Furthermore, due to altered metabolism, AD astrocytes show increased oxidative stress and reduced lactate secretion, as well as compromised neuronal supportive function, as evidenced by altering Ca2+ transients in healthy neurons. Our results reveal an important role for astrocytes in AD pathology and highlight the strength of iPSC-derived models for brain diseases.

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Background and Purpose-Activation of transcription factor nuclear factor-B (NF-B) may induce expression of either proinflammatory/apoptotic genes or antiapoptotic genes. Because a considerable number of middle cerebral artery occlusions (MCAOs) in humans are not associated with reperfusion during the first 24 hours, the role of NF-B after permanent MCAO (pMCAO) was investigated. Methods-Mice transgenic for a NF-B-driven ␤-globin reporter were exposed to pMCAO, and the expression of the reporter gene was quantified with real-time polymerase chain reaction. Mice lacking the p50 subunit of NF-B and wild-type controls were exposed to pMCAO with or without treatment with pyrrolidinedithiocarbamate (PDTC), an NF-B inhibitor. Brain sections of human stroke patients were immunostained for the activated NF-B. Results-pMCAO increased NF-B transcriptional activity to 260% (36.9Ϯ4.5 compared with 14.4Ϯ2.6; nϭ10; PϽ0.01) in the brain; this NF-B activation was completely blocked by PDTC (17.2Ϯ2.6; nϭ9; PϽ0.05). In p50 Ϫ/Ϫ mice, pMCAO resulted in 41% (18Ϯ3.2 mm 3 ; nϭ12) smaller infarcts compared with wild-type controls (32.9Ϯ3.8 mm 3 ; nϭ9; PϽ0.05), which was comparable to the protection achieved with PDTC in wild-type mice (19.6Ϯ4.2 mm 3 ; nϭ8). Pro-DTC, a PDTC analogue that does not cross the blood-brain barrier, had no effect, even though Pro-DTC and PDTC were equally protective in vitro. During the first 2 days of human stroke, NF-B was activated in neurons in the penumbral areas. Conclusions-NF-B is induced in neurons during