Citations

AbstractIn this study, we tested the hypothesis that reduced bioavailability of tetrahydrobiopterin (BH4) is a major mechanism responsible for pathogenesis of endothelial dysfunction in cerebral microvessels of transgenic mice expressing the Swedish double mutation of human amyloid precursor protein (APP) (Tg2576 mice). Endothelial nitric oxide synthase (eNOS) protein expression was significantly increased in cerebral vasculature of Tg2576 mice. In contrast, bioavailability of BH4 was significantly reduced (p < 0.05). Moreover, superoxide anion production was increased in cerebral microvessels of Tg2576 mice (p < 0.05). Incubation with NOS inhibitor, Nω‐nitro‐L‐arginine methyl ester, decreased superoxide anion indicating that uncoupled eNOS is most likely the source of superoxide anion. Increasing BH4 bioavailability either exogenously by BH4 supplementation or endogenously by treatment with the selective peroxisome proliferator‐activated receptor – delta activator GW501516 (2 mg/kg/day, 14 days) attenuated eNOS uncoupling and decreased superoxide anion production in cerebral microvessels of Tg2576 mice (p < 0.05). Treatment with GW501516 restored the biological activity of endothelial nitric oxide in cerebral microvessels of Tg2576 mice, as indicated by the increased nitrite/nitrate content and 3,5‐cyclic guanosine monophosphate levels (p < 0.05). Our studies indicate that sub‐optimal BH4 bioavailability in cerebral vasculature is an important contributor to oxidant stress and endothelial dysfunction in Tg2576 mouse model of Alzheimer's disease. imageExisting evidence suggests that Aβ peptides‐induced up‐regulation of expression and activity of NADPH oxidase causes increased production of superoxide anion (.O2−). .O2− can also be converted to hydrogen peroxide (H2O2) by enzymatic activity of superoxide dismutase (SOD) or spontaneous dismutation. Elevation of .O2− and H2O2 might cause oxidation of tetrahydrobiopterin (BH4) to dihydrobiopterin (BH2) and subsequent uncoupling of endothelial nitric oxide synthase (eNOS) (a) thus reducing levels of nitric oxide (NO) and 3′,5′‐cyclic guanosine monophosphate (cGMP). Supplementation of BH4 or activation of PPARδ prevents detrimental effects of eNOS uncoupling by restoring bioavailability of BH4 and scavenging of .O2−, respectively (b). Activation of PPARδ also increases expression of catalase thereby inactivating H2O2. Generation of H2O2 by uncoupled eNOS in cerebral microvessels of Tg2576 mice is hypothetical.

Blood-brain barrier (BBB) dysfunction in acute liver failure (ALF) results in increased BBB permeability that often precludes the patients from obtaining a life-saving liver transplantation. It remains controversial whether matrix metalloproteinase-9 (MMP-9) from the injured liver contributes to the deregulation of BBB function in ALF. We selectively upregulated a physiologic inhibitor of MMP-9 (TIMP-1) with a single intracerebroventricular injection of TIMP-1 cDNA plasmids at 48 and 72 hours, or with pegylated-TIMP-1 protein. Acute liver failure was induced with tumor necrosis factor-α and D-(+)-galactosamine in mice. Permeability of BBB was assessed with sodium fluorescein (NaF) extravasation. We found a significant increase in TIMP-1 within the central nervous system (CNS) after the administration of TIMP-1 cDNA plasmids and that increased TIMP-1 within the CNS resulted in an attenuation of BBB permeability, a reduction in activation of epidermal growth factor receptor and p38 mitogen-activated protein kinase signals, and a restoration of the tight junction protein occludin in mice with experimental ALF. Pegylated TIMP-1 provided similar protection against BBB permeability in mice with ALF. Our results provided a proof of principle that MMP-9 contributes to the BBB dysfunction in ALF and suggests a potential therapeutic role of TIMP-1 in ALF.

Abstract Reactive gliosis surrounding amyloid β (Aβ) plaques is an early feature of Alzheimer’s disease pathogenesis and has been postulated to represent activation of the innate immune system in an apparently ineffective attempt to clear or neutralize Aβ aggregates. To evaluate the role of IFN-γ–mediated neuroinflammation on the evolution of Aβ pathology in transgenic (Tg) mice, we have expressed murine IFN-γ (mIFN-γ) in the brains of Aβ precursor protein (APP) Tg mice using recombinant adeno-associated virus serotype 1. Expression of mIFN-γ in brains of APP TgCRND8 mice results in robust noncell autonomous activation of microglia and astrocytes, and a concomitant significant suppression of Aβ deposition. In these mice, mIFN-γ expression upregulated multiple glial activation markers, early components of the complement cascade as well as led to infiltration of Ly-6c positive peripheral monocytes but no significant effects on APP levels, APP processing or steady-state Aβ levels were noticed in vivo. Taken together, these results suggest that mIFN-γ expression in the brain suppresses Aβ accumulation through synergistic effects of activated glia and components of the innate immune system that enhance Aβ aggregate phagocytosis.

Proinflammatory stimuli, after amyloid β (Aβ) deposition, have been hypothesized to create a self‐reinforcing positive feedback loop that increases amyloidogenic processing of the Aβ precursor protein (APP), promoting further Aβ accumulation and neuroinflammation in Alzheimer's disease (AD). Interleukin‐6 (IL‐6), a proinflammatory cytokine, has been shown to be increased in AD patients implying a pathological interaction. To assess the effects of IL‐6 on Aβ deposition and APP processing in vivo ,we overexpressed murine IL‐6 (mIL‐6) in the brains of APP transgenic TgCRND8 and TG2576 mice. mIL‐6 expression resulted in extensive gliosis and concurrently attenuated Aβ deposition in TgCRND8 mouse brains. This was accompanied by up‐regulation of glial phagocytic markers in vivo and resulted in enhanced microglia‐mediated phagocytosis of Aβ aggregates in vitro . Further, mIL‐6‐induced neuroinflammation had no effect on APP processing in TgCRND8 and had no effect on APP processing or steady‐state levels of Aβ in young Tg2576 mice. These results indicate that mIL‐6‐mediated reactive gliosis may be beneficial early in the disease process by potentially enhancing Aβ plaque clearance rather than mediating a neurotoxic feedback loop that exacerbates amyloid pathology. This is the first study that methodically dissects the contribution of mIL‐6 with regard to its potential role in modulating Aβ deposition in vivo .—Chakrabarty, P., Jansen‐West, K., Beccard, A., Ceballos‐Diaz, C., Levites, Y., Verbeeck, C., Zubair, A. C., Dickson, D., Golde, T. E., Das, P. Massive gliosis induced by interleukin‐6 suppresses Aβ deposition in vivo: evidence against inflammation as a driving force for amyloid deposition. FASEB J . 24, 548–559 (2010). www.fasebj.org