Yan-Jiang Wang

Peroxisome Proliferator-Activated Receptor δ Regulation of miR-15a in Ischemia-Induced Cerebral Vascular Endothelial Injury

Cerebral vascular endothelial cell (CEC) degeneration significantly contributes to blood–brain barrier (BBB) breakdown and neuronal loss after cerebral ischemia. Recently, emerging data suggest that peroxisome proliferator-activated receptor δ (PPARδ) activation has a potential neuroprotective role in ischemic stroke. Here we report for the first time that PPARδ is significantly reduced in oxygen-glucose deprivation (OGD)-induced mouse CEC death. Interestingly, PPARδ overexpression can suppress OGD-induced caspase-3 activity, Golgi fragmentation, and CEC death through an increase of bcl-2 protein levels without change of bcl-2 mRNA levels. To explore the molecular mechanisms, we have identified that upregulation of PPARδ can alleviate ODG-activated microRNA-15a (miR-15a) expression in CECs. Moreover, we have demonstrated that bcl-2 is a translationally repressed target of miR-15a. Intriguingly, gain- or loss-of-miR-15a function can significantly reduce or increase OGD-induced CEC death, respectively. Furthermore, we have identified that miR-15a is a transcriptional target of PPARδ. Consistent with the in vitro findings, we found that intracerebroventricular infusion of a specific PPARδ agonist, GW 501516 (2-[2-methyl-4-[[4-methyl-2-[4-(trifluoromethyl)phenyl]-1,3-thiazol-5-yl]methylsulfanyl]phenoxy]acetic acid), significantly reduced ischemia-induced miR-15a expression, increased bcl-2 protein levels, and attenuated caspase-3 activity and subsequent DNA fragmentation in isolated cerebral microvessels, leading to decreased BBB disruption and reduced cerebral infarction in mice after transient focal cerebral ischemia. Together, these results suggest that PPARδ plays a vascular-protective role in ischemia-like insults via transcriptional repression of miR-15a, resulting in subsequent release of its posttranscriptional inhibition of bcl-2. Thus, regulation of PPARδ-mediated miR-15a inhibition of bcl-2 could provide a novel therapeutic strategy for the treatment of stroke-related vascular dysfunction.

Immunotherapy for Alzheimer disease—the challenge of adverse effects

Amyloid-β (Aβ) plays a crucial part in the pathogenesis of Alzheimer disease (AD), making this peptide an attractive therapeutic target. However, clearance of brain Aβ in clinical trials of Aβ-specific antibodies did not improve cognition in patients with AD, leading to reassessment of the current therapeutic strategies. Moreover, current immunotherapies are associated with autoimmunity-related adverse effects, and mobilization of neurotoxic insoluble Aβ-oligomers. Despite the fact that antibodies to the N-terminal domain of Aβ can promote Aβ production, immunotherapies in ongoing clinical trials predominantly target this peptide region. Here, we address the challenges of adverse effects of immunotherapy for AD. We discuss available evidence regarding the mechanisms of both endogenous and exogenous Aβ-specific antibodies, with a view to developing optimal immunotherapy based on peripheral Aβ clearance, targeting of the toxic domain of Aβ, and improvement of antibody specificity. Such strategies should help to make immunotherapy a safe and efficacious disease-modifying treatment option for AD.

Grape seed polyphenols and curcumin reduce genomic instability events in a transgenic mouse model for Alzheimer's disease

The study set out to determine (a) whether DNA damage is elevated in mice that carry mutations in the amyloid precursor protein (APP695swe) and presenilin 1 (PSEN1-dE9) that predispose to Alzheimers disease (AD) relative to non-transgenic control mice, and (b) whether increasing the intake of dietary polyphenols from curcumin or grape seed extract could reduce genomic instability events in a transgenic mouse model for AD. DNA damage was measured using the micronucleus (MN) assay in both buccal mucosa and erythrocytes and an absolute telomere length assay for both buccal mucosa and olfactory bulb tissue. MN frequency tended to be higher in AD mice in both buccal mucosa (1.7-fold) and polychromatic erythrocytes (1.3-fold) relative to controls. Telomere length was significantly reduced by 91% (p=0.04) and non-significantly reduced by 50% in buccal mucosa and olfactory bulbs respectively in AD mice relative to controls. A significant 10-fold decrease in buccal MN frequency (p=0.01) was found for AD mice fed diets containing curcumin (CUR) or micro-encapsulated grape seed extract (MGSE) and a 7-fold decrease (p=0.02) for AD mice fed unencapsulated grape seed extract (GSE) compared to the AD group on control diet. Similarly, in polychromatic erythrocytes a significant reduction in MN frequency was found for the MGSE cohort (65.3%) (p<0.05), whereas the AD CUR and AD GSE groups were non-significantly reduced by 39.2 and 34.8% respectively compared to the AD Control. A non-significant 2-fold increase in buccal cell telomere length was evident for the CUR, GSE and MGSE groups compared to the AD control group. Olfactory bulb telomere length was found to be non-significantly 2-fold longer in mice fed on the CUR diet compared to controls. These results suggest potential protective effects of polyphenols against genomic instability events in different somatic tissues of a transgenic mouse model for AD.

p75NTR Regulates Aβ Deposition by Increasing Aβ Production But Inhibiting Aβ Aggregation with Its Extracellular Domain

Accumulation of toxic amyloid-β (Aβ) in the cerebral cortex and hippocampus is a major pathological feature of Alzheimers disease (AD). The neurotrophin receptor p75NTR has been proposed to mediate Aβ-induced neurotoxicity; however, its role in the development of AD remains to be clarified. The p75NTR/ExonIII−/− mice and APPSwe/PS1dE9 mice were crossed to generate transgenic AD mice with deletion of p75NTR gene. In APPSwe/PS1dE9 transgenic mice, p75NTR expression was localized in the basal forebrain neurons and degenerative neurites in neocortex, increased with aging, and further activated by Aβ accumulation. Deletion of the p75NTR gene in APPSwe/PS1dE9 mice reduced soluble Aβ levels in the brain and serum, but increased the accumulation of insoluble Aβ and Aβ plaque formation. There was no change in the levels of amyloid precursor protein (APP) and its proteolytic derivatives, or α-, β-, and γ-secretase activities, or in levels of BACE1, neprilysin (NEP), and insulin-degrading enzyme (IDE) proteins. Aβ production by cortical neurons of APPSwe/PS1dE9 mice was reduced by deletion of p75NTR gene in vitro. Recombinant extracellular domain of p75NTR attenuated the oligomerization and fibrillation of synthetic Aβ42 peptide in vitro, and reduced local Aβ plaques after hippocampus injection in vivo. In addition, deletion of p75NTR attenuated microgliosis but increased the microhemorrhage profiles in the brain. The deletion of p75NTR did not significantly change the cognitive function of the mice up to the age of 9 months. Our data suggest that p75NTR plays a critical role in regulating Aβ levels by both increasing Aβ production and attenuating its aggregation, and they caution that a therapeutic intervention simply reducing p75NTR may exacerbate AD pathology.

Intramuscular delivery of a single chain antibody gene reduces brain Aβ burden in a mouse model of Alzheimer's disease

Anti-beta-amyloid (Abeta) immunotherapy has been well documented to effectively elicit amyloid plaque clearance and slow cognitive decline in experimental and clinical studies. However, anti-Abeta immunotherapy was associated with detrimental effects of brain inflammation and microhemorrhage, presumably induced by T-cell-mediated and/or Fc-mediated inflammatory responses. In the present study, a single chain antibody (scFv) against Abeta could effectively inhibit the aggregation of Abeta and promote the disaggregation of preformed Abeta fibrils. The recombined adeno-associated virus vectors carrying the scFv gene were produced to delivery the scFv gene. Hippocampus delivery of the scFv gene was effective in reducing the amyloid plaque in the hippocampus of an Alzheimers disease (AD) mouse model. Further studies demonstrated that intramuscular delivery of the scFv gene was as effective as intracranial delivery in reducing the total Abeta level in the brain with a concomitant elevated Abeta level in serum. No enhanced microglial activation, discernable T lymphocyte infiltration, and increased microhemorrhage were found after intracranial and intramuscular delivery of the scFv gene. Our results suggest that intramuscular delivery of the scFv gene would be a novel peripheral noninflammatory immunological modality targeting Abeta clearance and be promising in future drug development for the prevention and treatment of AD.

Edaravone alleviates Alzheimer’s disease-type pathologies and cognitive deficits

Significance Alzheimer’s disease (AD) is a devastating disease that results in the progressive cognitive deficits of elderly and has become one of major social and economic burdens worldwide. There is no effective drug or therapy to prevent or halt the progressive cognitive dysfunctions due to the complex mechanisms such as accumulation of amyloid-β (Aβ), increase in oxidative stress, and formation of neurofibrillary tangle that drive the development of the disease. We found here that Edaravone, a drug that has been used for ischemic stroke, is able to prevent and treat AD by targeting multiple pathways of AD pathogenesis and rescuing the cognitive deficits of a mouse model of AD. Our study suggests Edaravone is a promising drug candidate for AD. Alzheimer’s disease (AD) is one of most devastating diseases affecting elderly people. Amyloid-β (Aβ) accumulation and the downstream pathological events such as oxidative stress play critical roles in pathogenesis of AD. Lessons from failures of current clinical trials suggest that targeting multiple key pathways of the AD pathogenesis is necessary to halt the disease progression. Here we show that Edaravone, a free radical scavenger that is marketed for acute ischemic stroke, has a potent capacity of inhibiting Aβ aggregation and attenuating Aβ-induced oxidation in vitro. When given before or after the onset of Aβ deposition via i.p. injection, Edaravone substantially reduces Aβ deposition, alleviates oxidative stress, attenuates the downstream pathologies including Tau hyperphosphorylation, glial activation, neuroinflammation, neuronal loss, synaptic dysfunction, and rescues the behavioral deficits of APPswe/PS1 mice. Oral administration of Edaravone also ameliorates the AD-like pathologies and memory deficits of the mice. These findings suggest that Edaravone holds a promise as a therapeutic agent for AD by targeting multiple key pathways of the disease pathogenesis.

Clearance of Amyloid-Beta in Alzheimer’s Disease: Shifting the Action Site from Center to Periphery

Amyloid-beta (Aβ) is suggested to play a causal role in the pathogenesis of Alzheimer’s disease (AD). Immunotherapies are among the most promising Aβ-targeting therapeutic strategies for AD. But, to date, all clinical trials of this modality have not been successful including Aβ vaccination (AN1792), anti-Aβ antibodies (bapineuzumab, solanezumab and ponezumab), and intravenous immunoglobulin (IVIG). We propose that one reason for the failures of these clinical trials may be the adverse effects of targeting the central clearance of amyloid plaques. The potential adverse effects include enhanced neurotoxicity related to Aβ oligomerization from plaques, neuroinflammation related to opsonized Aβ phagocytosis, autoimmunity related to cross-binding of antibodies to amyloid precursor protein (APP) on the neuron membrane, and antibody-mediated vascular and neuroskeletal damage. Overall, the majority of the adverse effects seen in clinical trials were associated with the entry of antibodies into the brain. Finally, we propose that peripheral Aβ clearance would be effective and safe for future Aβ-targeting therapies.

Differential effects of pro-BDNF on sensory neurons after sciatic nerve transection in neonatal rats

Brain‐derived neurotrophic factor (BDNF) plays a critical role in the development of the central and peripheral nervous systems, and also in neuronal survival after injury. The actions of BDNF are mediated by its high‐affinity receptors TrkB and p75NTR. Recent studies have shown that proneurotrophins bind p75NTR and sortilin with high affinity, and trigger apoptosis of neurons in vitro. As proneurotrophins are a dominant form of gene products in developing and adult animals, it is imperative to understand their physiological functions in animals. Here, we showed differential roles of proBDNF in injured and uninjured sensory neurons. proBDNF, p75NTR and sortilin are highly expressed in dorsal root ganglia (DRG) neurons. Recombinant proBDNF induced a dose‐dependent death of PC12 cells and the death activity was completely abolished in the presence of antibodies against the prodomain of BDNF. The exogenous proBDNF enhanced the death of axotomized sensory neurons and the neutralizing antibodies to the prodomain or exogenous sortilin‐extracellular domain‐Fc fusion molecule reduced the death of axotomized sensory neurons. Interestingly, the treatment of neutralizing antibody in vivo increased the number of sensory neurons in the contralateral DRG. We conclude that proBDNF may induce the death of axotomized sensory neurons and suppress neuronal addition in the intact DRG in neonatal rats, and the suppression of endogenous proBDNF may protect neurons after neurotrauma.

A systemic view of Alzheimer disease — insights from amyloid-β metabolism beyond the brain

Alzheimer disease (AD) is the most common type of dementia, and is currently incurable; existing treatments for AD produce only a modest amelioration of symptoms. Research into this disease has conventionally focused on the CNS. However, several peripheral and systemic abnormalities are now understood to be linked to AD, and our understanding of how these alterations contribute to AD is becoming more clearly defined. This Review focuses on amyloid-β (Aβ), a major hallmark of AD. We review emerging findings of associations between systemic abnormalities and Aβ metabolism, and describe how these associations might interact with or reflect on the central pathways of Aβ production and clearance. On the basis of these findings, we propose that these abnormal systemic changes might not only develop secondary to brain dysfunction but might also affect AD progression, suggesting that the interactions between the brain and the periphery have a crucial role in the development and progression of AD. Such a systemic view of the molecular pathogenesis of AD could provide a novel perspective for understanding this disease and present new opportunities for its early diagnosis and treatment.

PPARγ attenuates intimal hyperplasia by inhibiting TLR4-mediated inflammation in vascular smooth muscle cells

AIMS Peroxisome proliferator-activated receptor γ (PPARγ) has been reported to attenuate intimal hyperplasia. This study aimed to test the hypothesis that PPARγ inhibits intimal hyperplasia through suppressing Toll-like receptor 4 (TLR4)-mediated inflammation in vascular smooth muscle cells. METHODS AND RESULTS TLR4(-/-) mice on a C57BL/6J background were used. Increased TLR4 and pro-inflammatory cytokines were observed in wire-injury-induced carotid neointima and in platelet-derived growth factor (PDGF)-activated vascular smooth muscle cells. The TLR4 deficiency protected the injured carotid from neointimal formation and impaired the cellular proliferation and migration in response to lipopolysaccharide and PDGF. Rosiglitazone attenuated intimal hyperplasia. Overexpression of PPARγ suppressed PDGF-induced proliferation and migration and inhibited TLR4-mediated inflammation in vascular smooth muscle cells, while PPARγ silencing exerted the opposite effect. Lipopolysaccharide counteracted the inhibitory effect of PPARγ on PDGF-induced proliferation and migration. Eritoran suppressed the proliferation and migration induced by PDGF and PPARγ silencing. Vascular smooth muscle cells derived from TLR4(-/-) mice showed impaired proliferation and migration upon PDGF activation and displayed no response to PPARγ manipulation. CONCLUSION PPARγ inhibits vascular smooth muscle cell proliferation and migration by suppressing TLR4-mediated inflammation and ultimately attenuates intimal hyperplasia after carotid injury.