Biomedical subjects

Huang Guo

Publications and source records attributed to Huang Guo.

9 recordsLinked to original sources

PubMed2006

The promise of protein C.

Protein C, a vitamin K-dependent serine protease zymogen that circulates in plasma, is converted by limited proteolysis to activated protein C (APC) by the thrombin-thrombomodulin complex. APC exerts anticoagulant, antiinflammatory, cytoprotective, and antiapoptotic activities. Recombinant APC therapy reduces mortality in severe sepsis patients. This review summarizes data from clinical observations, from in vitro studies, and from animal models of focal ischemic injury that provide a compelling rationale for clinical trials of APC for ischemic stroke.

Animals↗

PubMed2005

IgG-assisted age-dependent clearance of Alzheimer's amyloid beta peptide by the blood-brain barrier neonatal Fc receptor.

The role of blood-brain barrier (BBB) transport in clearance of amyloid beta-peptide (Abeta) by Abeta immunotherapy is not fully understood. To address this issue, we studied the effects of peripherally and centrally administered Abeta-specific IgG on BBB influx of circulating Abeta and efflux of brain-derived Abeta in APPsw(+/-) mice, a model that develops Alzheimer's disease-like amyloid pathology, and wild-type mice. Our data show that anti-Abeta IgG blocks the BBB influx of circulating Abeta in APPsw(+/-) mice and penetrates into the brain to sequester brain Abeta. In young mice, Abeta-anti-Abeta complexes were cleared from brain to blood by transcytosis across the BBB via the neonatal Fc receptor (FcRn) and the low-density lipoprotein receptor-related protein (LRP), whereas in older mice, there was an age-dependent increase in FcRn-mediated IgG-assisted Abeta BBB efflux and a decrease in LRP-mediated clearance of Abeta-anti-Abeta complexes. Inhibition of the FcRn pathway in older APPsw(+/-) mice blocked clearance of endogenous Abeta40/42 by centrally administered Abeta immunotherapy. Moreover, deletion of the FcRn gene in wild-type mice inhibited clearance of endogenous mouse Abeta40/42 by systemically administered anti-Abeta. Our data suggest that the FcRn pathway at the BBB plays a crucial role in IgG-assisted Abeta removal from the aging brain.

Aging↗

PubMed2005

Role of the MEOX2 homeobox gene in neurovascular dysfunction in Alzheimer disease.

Neurovascular dysfunction substantially contributes to Alzheimer disease. Here, we show that transcriptional profiling of human brain endothelial cells (BECs) defines a subset of genes whose expression is age-independent but is considerably altered in Alzheimer disease, including the homeobox gene MEOX2 (also known as GAX), a regulator of vascular differentiation, whose expression is low in Alzheimer disease. By using viral-mediated MEOX2 gene silencing and transfer, we show that restoring expression of the protein it encodes, GAX, in BECs from individuals with Alzheimer disease stimulates angiogenesis, transcriptionally suppresses AFX1 forkhead transcription factor-mediated apoptosis and increases the levels of a major amyloid-beta peptide (Abeta) clearance receptor, the low-density lipoprotein receptor-related protein 1 (LRP), at the blood-brain barrier. In mice, deletion of Meox2 (also known as Gax) results in reductions in brain capillary density and resting cerebral blood flow, loss of the angiogenic response to hypoxia in the brain and an impaired Abeta efflux from brain caused by reduced LRP levels. The link of MEOX2 to neurovascular dysfunction in Alzheimer disease provides new mechanistic and therapeutic insights into this illness.

Alzheimer Disease↗

PubMed2004

Tissue plasminogen activator neurovascular toxicity is controlled by activated protein C.

Although thrombolytic effects of tissue plasminogen activator (tPA) are beneficial, its neurotoxicity is problematic. Here, we report that tPA potentiates apoptosis in ischemic human brain endothelium and in mouse cortical neurons treated with N-methyl-D-aspartate (NMDA) by shifting the apoptotic pathways from caspase-9 to caspase-8, which directly activates caspase-3 without amplification through the Bid-mediated mitochondrial pathway. In vivo, tPA-induced cerebral ischemic injury in mice was reduced by intracerebroventricular administration of caspase-8 inhibitor, but not by caspase-9 inhibitor, in contrast to controls in which caspase-9 inhibitor, but not caspase-8 inhibitor, was protective. Activated protein C (APC), a serine protease with anticoagulant, anti-inflammatory and antiapoptotic activities, which is neuroprotective during transient ischemia and promotes activation of antiapoptotic mechanisms in brain cells by acting directly on endothelium and neurons, blocked tPA vascular and neuronal toxicities in vitro and in vivo. APC inhibited tPA-induced caspase-8 activation of caspase-3 in endothelium and caspase-3-dependent nuclear translocation of apoptosis-inducing factor in NMDA-treated neurons and reduced tPA-mediated cerebral ischemic injury in mice. Data suggest that tPA shifts the apoptotic signal in stressed brain cells from the intrinsic to the extrinsic pathway which requires caspase-8. APC blocks tPA's neurovascular toxicity and may add substantially to the effectiveness of tPA therapy for stroke.

Animals↗

PubMed2004

LRP/amyloid beta-peptide interaction mediates differential brain efflux of Abeta isoforms.

LRP (low-density lipoprotein receptor-related protein) is linked to Alzheimer's disease (AD). Here, we report amyloid beta-peptide Abeta40 binds to immobilized LRP clusters II and IV with high affinity (Kd = 0.6-1.2 nM) compared to Abeta42 and mutant Abeta, and LRP-mediated Abeta brain capillary binding, endocytosis, and transcytosis across the mouse blood-brain barrier are substantially reduced by the high beta sheet content in Abeta and deletion of the receptor-associated protein gene. Despite low Abeta production in the brain, transgenic mice expressing low LRP-clearance mutant Abeta develop robust Abeta cerebral accumulations much earlier than Tg-2576 Abeta-overproducing mice. While Abeta does not affect LRP internalization and synthesis, it promotes proteasome-dependent LRP degradation in endothelium at concentrations > 1 microM, consistent with reduced brain capillary LRP levels in Abeta-accumulating transgenic mice, AD, and patients with cerebrovascular beta-amyloidosis. Thus, low-affinity LRP/Abeta interaction and/or Abeta-induced LRP loss at the BBB mediate brain accumulation of neurotoxic Abeta.

Amyloid beta-Peptides↗

PubMed2004

Activated protein C prevents neuronal apoptosis via protease activated receptors 1 and 3.

Activated protein C (APC), a serine protease with anticoagulant and anti-inflammatory activities, exerts direct cytoprotective effects on endothelium via endothelial protein C receptor-dependent activation of protease activated receptor 1 (PAR1). Here, we report that APC protects mouse cortical neurons from two divergent inducers of apoptosis, N-methyl-D-aspartate (NMDA) and staurosporine. APC blocked several steps in NMDA-induced apoptosis downstream to nitric oxide, i.e., caspase-3 activation, nuclear translocation of apoptosis-inducing factor (AIF), and induction of p53, and prevented staurosporine-induced apoptosis by blocking caspase-8 activation upstream of caspase-3 activation and AIF nuclear translocation. Intracerebral APC infusion dose dependently reduced NMDA excitotoxicity in mice. By using different anti-PARs antibodies and mice with single PAR1, PAR3, or PAR4 deletion, we demonstrated that direct neuronal protective effects of APC in vitro and in vivo require PAR1 and PAR3. Thus, PAR1 and PAR3 mediate anti-apoptotic signaling by APC in neurons, which may suggest novel treatments for neurodegenerative disorders.

Animals↗

PubMed2004

Activated protein C and ischemic stroke.

OBJECTIVE: To summarize clinical observations, animal model experimentation, and in vitro studies that advance knowledge of the protein C system, including activated protein C (APC), in the setting of ischemic stroke. DATA SOURCE: Narrative review of selected published primary basic and clinical literature from MEDLINE for 2000-2003. DATA SYNTHESIS: Low levels of plasma APC and a poor response to APC in clotting assays may be markers or risk factors for ischemic stroke. Ischemia during routine endarterectomy causes APC generation in the affected region of the human brain. The prospective epidemiologic Atherosclerosis Risk in Communities (ARIC) study reported that plasma protein C may be protective for ischemic stroke. In murine models of focal cerebral ischemia, APC provided remarkable anti-inflammatory and neuroprotective effects in vivo and increased survival at 24 hrs. Recent in vitro and in vivo studies provide remarkable insights into mechanisms of the neuroprotective activities of APC. Independent of its well-known anticoagulant activity, APC acts directly on cells and alters gene expression profiles, inhibits apoptosis, and down-regulates inflammation. These effects require protease-activated receptor-1 and the endothelial protein C receptor. In an in vitro model involving hypoxia-induced apoptosis of human brain endothelial cells, protease-activated receptor-1 and endothelial protein C receptor were required for APC to exert its anti-apoptotic effects. In these cells, APC blunts hypoxia-induced increases in p53 messenger RNA and protein, reduces pro-apoptotic Bax, and increases anti-apoptotic Bcl-2, thereby inhibiting mitochondrial-dependent apoptosis. Murine ischemic stroke model studies have provided in vivo evidence for the physiologic roles of protease-activated receptor-1 and endothelial protein C receptor in the neuroprotective activities of APC. Because the low doses required for recombinant murine APC to provide neuroprotection do not cause observable anticoagulant effects, the in vivo neuroprotective action of APC seems, at least in part, to be independent of its anticoagulant activity and is likely to involve its anti-apoptotic activity. CONCLUSIONS: There is compelling evidence that ischemic stroke is an attractive target for therapy with APC.

Animals↗

PubMed2003

Protein S confers neuronal protection during ischemic/hypoxic injury in mice.

BACKGROUND: Protein S is an antithrombotic factor that also exhibits mitogenic activity. Thus, we hypothesized that protein S may control cerebrovascular thrombosis in stroke and protect brain tissue from ischemic injury. METHODS AND RESULTS: We studied protein S in a murine in vivo model of stroke and an in vitro model of neuronal hypoxia/reoxygenation injury. Animals received purified human plasma-derived protein S or vehicle intravenously 10 minutes after initiation of middle cerebral artery occlusion followed by reperfusion. Protein S at 0.2 to 2 mg/kg significantly improved the motor neurological deficit by 3.8- to 3.2-fold and reduced infarction and edema volumes by 45% to 54% and 45% to 62%, respectively. Protein S at 2 mg/kg improved postischemic cerebral blood flow by 21% to 26% and reduced brain fibrin deposition and infiltration with neutrophils by 40% and 53%, respectively. Intracerebral bleeding was not observed with protein S. Protein S protected ischemic neurons in vivo and cultured neurons from hypoxia/reoxygenation-induced apoptosis in a time- and dose-dependent manner. Recombinant human protein S exerted protective effects from hypoxia-induced damage similar to the plasma-derived protein S both in vivo and in vitro. CONCLUSIONS: Protein S is a significant neuroprotectant during ischemic brain injury with direct effects on neurons and antithrombotic effects. Thus, protein S could be a prototype of a new class of agents for clinical stroke with combined direct neuronal protective effects and systemic antithrombotic and antiinflammatory activities.

Animals↗

PubMed2002

Neurotrophin-3 transduction attenuates cisplatin spiral ganglion neuron ototoxicity in the cochlea.

Ototoxicity is a major dose-limiting side effect of cisplatin chemotherapy for cancer patients. We previously demonstrated in vitro that herpes simplex type 1 (HSV-1) amplicon-mediated delivery of a neurotrophin-3 (NT-3)/myc chimera protects spiral ganglion neurons (SGNs) in murine cochlear cultures from cisplatin-induced ototoxicity. To extend these findings, a newly constructed amplicon vector (HSVnt-3myc/SV40lac) that expresses the NT-3myc chimera and the Escherichia coli beta-galactosidase (lacZ) reporter gene under separate transcriptional control was initially tested in vitro and then was delivered to the cochlea of aged mice that were subsequently treated with cisplatin. Successful transduction with the new amplicon was observed in vitro as determined by its capacity to infect SGNs and to express NT-3myc mRNA and protein. To determine whether amplicon-directed NT-3myc overexpression could abrogate the ototoxicity in vivo, two groups of aged mice (CBA) were inoculated with HSVnt-3myc/SV40lac or control vector, HSVSV40lac, preceding administration of cisplatin. Cochleas inoculated with HSVnt-3myc/SV40lac harbored significantly greater numbers of surviving SGNs and showed lower incidence of cisplatin-induced apoptosis or necrosis than those injected with the control virus. These data demonstrate that HSV amplicon-mediated NT-3 delivery can attenuate the ototoxic actions of cisplatin in the peripheral auditory system of the aged mouse. The potency of NT-3 in SGN neuroprotection suggests that in vivo neurotrophin-based gene therapy is a promising preventative treatment for chemical-induced hearing disorders, and potentially for hearing degeneration due to normal aging.

Animals↗