Publications by authors named "Francesca-Fang Liao"

42 Publications

Discovery of a Highly Selective and Potent TRPC3 Inhibitor with High Metabolic Stability and Low Toxicity.

ACS Med Chem Lett 2021 Apr 5;12(4):572-578. Epub 2021 Mar 5.

Department of Pharmaceutical Sciences, College of Pharmacy, the University of Tennessee Health Science Center, Memphis, Tennessee 38163, United States.

The overactivation of transient receptor potential canonical 3 (TRPC3) is associated with neurodegenerative diseases and hypertension. Pyrazole 3 (Pyr3) is reported as the most selective TRPC3 inhibitor, but it has two inherent structural limitations: (1) the labile ester moiety leads to its rapid hydrolysis to the inactive Pyr8 , and (2) the alkylating trichloroacrylic amide moiety is known to be toxic. To circumvent these limitations, we designed a series of conformationally restricted Pyr3 analogues and reported that compound maintains high potency and selectivity for human TRPC3 over its closely related TRP channels. It has significantly improved metabolic stability compared with Pyr3 and has a good safety profile. Preliminary evaluation of demonstrated its ability to rescue Aβ-induced neuron damage with similar potency to that of Pyr3 . Collectively, these results suggest that represents a promising scaffold to potentially ameliorate the symptoms associated with TRPC3-mediated neurological and cardiovascular disorders.
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http://dx.doi.org/10.1021/acsmedchemlett.0c00571DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8040052PMC
April 2021

Endothelial Nitric Oxide Synthase-Deficient Mice.

Am J Pathol 2021 Mar 10. Epub 2021 Mar 10.

Department of Pharmacology, Addiction Science, Toxicology, University of Tennessee Health Science Center, College of Medicine, Memphis, Tennessee; Department of Neurology, Nanhai Hospital of Southern Medical University, Foshan, China.

Aging-associated cerebral small-vessel disease (CSVD) is a major cause of stroke and dementia. Despite a widespread acceptance of small-vessel arteriopathy, lacunar infarction, diffuse white matter injury, and cognitive impairment as four cardinal features of CSVD, a unifying pathologic mechanism of CSVD remains elusive. Herein, we introduce partial endothelial nitric oxide synthase (eNOS)-deficient mice as a model of age-dependent, spontaneous CSVD. These mice develop cerebral hypoperfusion and blood-brain barrier leakage at a young age, which progressively worsens with advanced age. Their brains exhibit elevated oxidative stress, astrogliosis, cerebral amyloid angiopathy, microbleeds, microinfarction, and white matter pathology. Partial eNOS-deficient mice develop gait disturbances at middle age, and hippocampus-dependent memory deficits at older ages. These mice also show enhanced expression of bone morphogenetic protein 4 (BMP4) in brain pericytes before myelin loss and white matter pathology. Because BMP4 signaling not only promotes astrogliogenesis but also blocks oligodendrocyte differentiation, we posit that paracrine actions of BMP4, localized within the neurovascular unit, promote white matter disorganization and neurodegeneration. These observations point to BMP4 signaling pathway in the aging brain vasculature as a potential therapeutic target. Finally, because partial eNOS-deficient mice corroborate recent clinical evidence that blood-brain barrier disruption is a primary cause of white matter pathology, the mechanism of impaired nitric oxide signaling-mediated CSVD warrants further investigation.
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http://dx.doi.org/10.1016/j.ajpath.2021.02.022DOI Listing
March 2021

Temporal unsnarling of brain's acute neuroinflammatory transcriptional profiles reveals panendothelitis as the earliest event preceding microgliosis.

Mol Psychiatry 2020 Dec 8. Epub 2020 Dec 8.

Department of Pharmacology, Addiction Science and Toxicology, College of Medicine, University of Tennessee Health Science Center, Memphis, TN, 38103, USA.

Sepsis-associated encephalopathy (SAE) is an acutely progressing brain dysfunction induced by systemic inflammation. The mechanism of initiation of neuroinflammation during SAE, which ultimately leads to delirium and cognitive dysfunction, remains elusive. We aimed to study the molecular events of SAE to capture its onset and progression into the central nervous system (CNS), and further identify the cellular players involved in mediating acute inflammatory signaling. Gene expression profiling on the cerebral vessels isolated from the brains of the mice treated with peripheral lipopolysaccharide (LPS) revealed that the cerebral vasculature responds within minutes to acute systemic inflammation by upregulating the expression of immediate early response genes, followed by activation of the nuclear factor-κB pathway. To identify the earliest responding cell type, we used fluorescence-activated cell sorting (FACS) to sort the glial and vascular cells from the brains of the mice treated with LPS at different time points, and RNA-seq was performed on microglia and cerebral endothelial cells (CECs). Bioinformatic analysis followed by further validation in all the cell types revealed that panendothelitis. i.e., the activation of CECs is the earliest event in the CNS during the inception of acute neuroinflammation. Microglial activation occurs later than that of CECs, suggesting that CECs are the most likely initial source of proinflammatory mediators, which could further initiate glial cell activation. This is then followed by the activation of apoptotic signaling in the CECs, which is known to lead to the blood-brain barrier disruption and allow peripheral cytokines to leak into the CNS, exacerbate the gliosis, and result in the vicious neuroinflammatory cascade. Together, our results model the earliest sequential events during the advancement of systemic inflammation into the CNS and facilitate to understand the interplay between the vascular and glial cells in initiating and driving acute neuroinflammation during SAE.
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http://dx.doi.org/10.1038/s41380-020-00955-5DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7722246PMC
December 2020

Regulation of BACE1 expression after injury is linked to the p75 neurotrophin receptor.

Mol Cell Neurosci 2019 09 15;99:103395. Epub 2019 Aug 15.

Departments of Cell Biology, Physiology & Neuroscience, and Psychiatry, Skirball Institute of Biomolecular Medicine, New York University Langone Medical Center, New York, New York 10016, USA. Electronic address:

BACE1 is a transmembrane aspartic protease that cleaves various substrates and it is required for normal brain function. BACE1 expression is high during early development, but it is reduced in adulthood. Under conditions of stress and injury, BACE1 levels are increased; however, the underlying mechanisms that drive BACE1 elevation are not well understood. One mechanism associated with brain injury is the activation of injurious p75 neurotrophin receptor (p75), which can trigger pathological signals. Here we report that within 72 h after controlled cortical impact (CCI) or laser injury, BACE1 and p75 are increased and tightly co-expressed in cortical neurons of mouse brain. Additionally, BACE1 is not up-regulated in p75 null mice in response to focal cortical injury, while p75 over-expression results in BACE1 augmentation in HEK-293 and SY5Y cell lines. A luciferase assay conducted in SY5Y cell line revealed that BACE1 expression is regulated at the transcriptional level in response to p75 transfection. Interestingly, this effect does not appear to be dependent upon p75 ligands including mature and pro-neurotrophins. In addition, BACE1 activity on amyloid precursor protein (APP) is enhanced in SY5Y-APP cells transfected with a p75 construct. Lastly, we found that the activation of c-jun n-terminal kinase (JNK) by p75 contributes to BACE1 up-regulation. This study explores how two injury-induced molecules are intimately connected and suggests a potential link between p75 signaling and the expression of BACE1 after brain injury.
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http://dx.doi.org/10.1016/j.mcn.2019.103395DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6993608PMC
September 2019

Thioredoxin-Interacting Protein (TXNIP) Associated NLRP3 Inflammasome Activation in Human Alzheimer's Disease Brain.

J Alzheimers Dis 2019 ;68(1):255-265

Department of Anatomy and Neurobiology, College of Medicine, The University of Tennessee Health Science Center, Memphis, TN, USA.

Alzheimer's disease (AD) is the most common form of age-associated dementia characterized by amyloid-β plaques and neurofibrillary tangles. Recent studies have demonstrated that thioredoxin-interacting protein (TXNIP), an endogenous regulator of redox/glucose induced stress and inflammation, is now known to be upregulated in stroke, traumatic brain injury, diabetes and AD. We hypothesized that TXNIP overexpression sustains neurodegeneration through activation of the nucleotide binding and oligomerization domain-like receptor protein 3 in human AD brains. We analyzed TXNIP and the components of the NLRP3 inflammasome in the cortex of postmortem human brain samples by western blotting, real-time PCR, and immunohistochemical techniques in comparison with age-matched non-demented controls. Our results demonstrate that TXNIP protein as well as its mRNA levels in the cortex was significantly upregulated in AD compared to control brains. Moreover, using double immunofluorescence staining, TXNIP and interlukin-1β (IL-1β) were co-localized near Aβ plaques and p-tau. These results suggest an association between TXNIP overexpression levels and AD pathogenesis. Further, a significant increased expression of cleaved caspase-1 and IL-1β, the products of inflammasome activation, was detected in the cortex of AD brains. Together, these findings suggest that TXNIP, an upstream promising new therapeutic target, is a molecular link between inflammation and AD. The significant contribution of TXNIP to AD pathology suggests that strategies focusing on specific targeting of the TXNIP-NLRP3 inflammasome may lead to novel therapies for the management of AD and other age-related dementias.
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http://dx.doi.org/10.3233/JAD-180814DOI Listing
June 2020

Brain Cytosolic Phospholipase A2α Mediates Angiotensin II-Induced Hypertension and Reactive Oxygen Species Production in Male Mice.

Am J Hypertens 2018 04;31(5):622-629

Department of Pharmacology, College of Medicine, University of Tennessee HSC, Memphis, Tennessee, USA.

Background: Recently, we reported that angiotensin II (Ang II)-induced hypertension is mediated by group IV cytosolic phospholipase A2α (cPLA2α) via production of prohypertensive eicosanoids. Since Ang II increases blood pressure (BP) via its action in the subfornical organ (SFO), it led us to investigate the expression and possible contribution of cPLA2α to oxidative stress and development of hypertension in this brain area.

Methods: Adenovirus (Ad)-green fluorescence protein (GFP) cPLA2α short hairpin (sh) RNA (Ad-cPLA2α shRNA) and its control Ad-scrambled shRNA (Ad-Scr shRNA) or Ad-enhanced cyan fluorescence protein cPLA2α DNA (Ad-cPLA2α DNA) and its control Ad-GFP DNA were transduced into SFO of cPLA2α+/+ and cPLA2α-/- male mice, respectively. Ang II (700 ng/kg/min) was infused for 14 days in these mice, and BP was measured by tail-cuff and radio telemetry. cPLA2 activity, reactive oxygen species production, and endoplasmic reticulum stress were measured in the SFO.

Results: Transduction of SFO with Ad-cPLA2α shRNA, but not Ad-Scr shRNA in cPLA2α+/+ mice, minimized expression of cPLA2α, Ang II-induced cPLA2α activity and oxidative stress in the SFO, BP, and cardiac and renal fibrosis. In contrast, Ad-cPLA2α DNA, but not its control Ad-GFP DNA in cPLA2α-/- mice, restored the expression of cPLA2α, and Ang II-induced increase in cPLA2 activity and oxidative stress in the SFO, BP, cardiac, and renal fibrosis.

Conclusions: These data suggest that cPLA2α in the SFO is crucial in mediating Ang II-induced hypertension and associated pathogenesis. Therefore, development of selective cPLA2α inhibitors could be useful in treating hypertension and its pathogenesis.
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http://dx.doi.org/10.1093/ajh/hpy009DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5905655PMC
April 2018

In vivo evidence for the contribution of peripheral circulating inflammatory exosomes to neuroinflammation.

J Neuroinflammation 2018 Jan 8;15(1). Epub 2018 Jan 8.

Department of Pharmacology, University of Tennessee Health Science Center, 71 South Manassas Street, Memphis, TN, 38103, USA.

Background: Neuroinflammation is implicated in the development and progression of many neurodegenerative diseases. Conditions that lead to a peripheral immune response are often associated with inflammation in the central nervous system (CNS), suggesting a communication between the peripheral immune system and the neuroimmune system. The underlying mechanism of this relationship remains largely unknown; however, experimental studies have demonstrated that exposure to infectious stimuli, such as lipopolysaccharide (LPS) or high-fat diet (HFD) feeding, result in profound peripheral- and neuro-inflammation.

Methods: Using the model of endotoxemia with LPS, we studied the role of serum-derived exosomes in mediating neuroinflammation. We purified circulating exosomes from the sera of LPS-challenged mice, which were then intravenously injected into normal adult mice.

Results: We found that the recipient mice that received serum-derived exosomes from LPS-challenged mice exhibited elevated microglial activation. Moreover, we observed astrogliosis, increased systemic pro-inflammatory cytokine production, and elevated CNS expression of pro-inflammatory cytokine mRNA and the inflammation-associated microRNA (miR-155) in these recipient mice. Gene expression analysis confirmed that many inflammatory microRNAs were significantly upregulated in the purified exosomes under LPS-challenged conditions. We observed accumulated signaling within the microglia of mice that received tail-vein injections of fluorescently labeled exosomes though the percentage of those microglial cells was found low. Finally, purified LPS-stimulated exosomes from blood when infused directly into the cerebral ventricles provoked significant microgliosis and, to a lesser extent, astrogliosis.

Conclusions: The experimental results suggest that circulating exosomes may act as a neuroinflammatory mediator in systemic inflammation.
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http://dx.doi.org/10.1186/s12974-017-1038-8DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5759808PMC
January 2018

Does pathology of small venules contribute to cerebral microinfarcts and dementia?

J Neurochem 2018 03 7;144(5):517-526. Epub 2017 Nov 7.

Department of Neurosciences, Medical University of South Carolina, Charleston, South Carolina, USA.

Microinfarcts are small, but strikingly common, ischemic brain lesions in the aging human brain. There is mounting evidence that microinfarcts contribute to vascular cognitive impairment and dementia, but the origins of microinfarcts are unclear. Understanding the vascular pathologies that cause microinfarcts may yield strategies to prevent their occurrence and reduce their deleterious effects on brain function. Current thinking suggests that cortical microinfarcts arise from the occlusion of penetrating arterioles, which are responsible for delivering oxygenated blood to small volumes of tissue. Unexpectedly, pre-clinical studies have shown that the occlusion of penetrating venules, which drain deoxygenated blood from cortex, lead to microinfarcts that appear identical to those resulting from arteriole occlusion. Here we discuss the idea that cerebral venule pathology could be an overlooked source for brain microinfarcts in humans. This article is part of the Special Issue "Vascular Dementia". Cover Image for this Issue: doi: 10.1111/jnc.14167.
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http://dx.doi.org/10.1111/jnc.14228DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5869083PMC
March 2018

Bidirectional interplay of HSF1 degradation and UPR activation promotes tau hyperphosphorylation.

PLoS Genet 2017 Jul 5;13(7):e1006849. Epub 2017 Jul 5.

Departments of Pharmacology and Department of Anatomy and Neurobiology, TSRB 218A, University of Tennessee Health Science Center, Memphis, Tennessee, United States of America.

The unfolded protein response (UPR) in the endoplasmic reticulum (ER) and the cytoplasmic heat stress response are two major stress response systems necessary for maintaining proteostasis for cellular health. Failure of either of these systems, such as in sustained UPR activation or in insufficient heat shock response activation, can lead to the development of neurodegeneration. Alleviation of ER stress and enhancement of heat shock response through heat shock factor 1 (HSF1) activation have previously been considered as attractive potential therapeutic targets for Alzheimer's disease (AD)-a prevalent and devastating tauopathy. Understanding the interplay of the two aforementioned systems and their cooperative role in AD remain elusive. Here we report studies in human brain and tau pathogenic mouse models (rTg4510, PS19, and rTg21221), identifying HSF1 degradation and UPR activation as precursors of aberrant tau pathogenesis. We demonstrate that chemical ER stress inducers caused autophagy-lysosomal HSF1 degradation, resulting in tau hyperphosphorylation in rat primary neurons. In addition, permanent HSF1 loss reversely causes chronic UPR activation, leading to aberrant tau phosphorylation and aggregation in the hippocampus of aged HSF1 heterozygous knock-out mice. The deleterious interplay of UPR activation and HSF1 loss is exacerbated in N2a cells stably overexpressing a pro-aggregation mutant TauRD ΔK280 (N2a-TauRD ΔK280). We provide evidence of how these two stress response systems are intrinsically interweaved by showing that the gene encoding C/EBP-homologous protein (CHOP) activation in the UPR apoptotic pathway facilitates HSF1 degradation, which likely further contributes to prolonged UPR via ER chaperone HSP70 a5 (BiP/GRP78) suppression. Upregulating HSF1 relieves the tau toxicity in N2a-TauRD ΔK280 by reducing CHOP and increasing HSP70 a5 (BiP/GRP78). Our work reveals how the bidirectional crosstalk between the two stress response systems promotes early tau pathology and identifies HSF1 being one likely key player in both systems.
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http://dx.doi.org/10.1371/journal.pgen.1006849DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5517072PMC
July 2017

Ubiquitin Ligase NEDD4 Regulates PPARγ Stability and Adipocyte Differentiation in 3T3-L1 Cells.

Sci Rep 2016 12 5;6:38550. Epub 2016 Dec 5.

Department of Pharmacology, University of Tennessee Health Science Center, Memphis, Tennessee 38103, USA.

Peroxisome proliferator-activated receptor-γ (PPARγ) is a ligand-activated nuclear receptor which controls lipid and glucose metabolism. It is also the master regulator of adipogenesis. In adipocytes, ligand-dependent PPARγ activation is associated with proteasomal degradation; therefore, regulation of PPARγ degradation may modulate its transcriptional activity. Here, we show that neural precursor cell expressed developmentally down-regulated protein 4 (NEDD4), an E3 ubiquitin ligase, interacts with the hinge and ligand binding domains of PPARγ and is a bona fide E3 ligase for PPARγ. NEDD4 increases PPARγ stability through the inhibition of its proteasomal degradation. Knockdown of NEDD4 in 3T3-L1 adipocytes reduces PPARγ protein levels and suppresses adipocyte conversion. PPARγ correlates positively with NEDD4 in obese adipose tissue. Together, these findings support NEDD4 as a novel regulator of adipogenesis by modulating the stability of PPARγ.
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http://dx.doi.org/10.1038/srep38550DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5137149PMC
December 2016

NEDD4-mediated HSF1 degradation underlies α-synucleinopathy.

Hum Mol Genet 2016 Jan 26;25(2):211-22. Epub 2015 Oct 26.

Department of Pharmacology and Department of Anatomy and Neurobiology, University of Tennessee Health Science Center, 874 Union Avenue/Crowe 401, Memphis, TN 38163, USA,

Cellular protein homeostasis is achieved by a delicate network of molecular chaperones and various proteolytic processes such as ubiquitin-proteasome system (UPS) to avoid a build-up of misfolded protein aggregates. The latter is a common denominator of neurodegeneration. Neurons are found to be particularly vulnerable to toxic stress from aggregation-prone proteins such as α-synuclein. Induction of heat-shock proteins (HSPs), such as through activated heat shock transcription factor 1 (HSF1) via Hsp90 inhibition, is being investigated as a therapeutic option for proteinopathic diseases. HSF1 is a master stress-protective transcription factor which activates genes encoding protein chaperones (e.g. iHsp70) and anti-apoptotic proteins. However, whether and how HSF1 is dysregulated during neurodegeneration has not been studied. Here, we discover aberrant HSF1 degradation by aggregated α-synuclein (or α-synuclein-induced proteotoxic stress) in transfected neuroblastoma cells. HSF1 dysregulation via α-synuclein was confirmed by in vivo assessment of mouse and in situ studies of human specimens with α-synucleinopathy. We demonstrate that elevated NEDD4 is implicated as the responsible ubiquitin E3 ligase for HSF1 degradation through UPS. Furthermore, pharmacologically induced SIRT1-mediated deacetylation can attenuate aberrant NEDD4-mediated HSF1 degradation. Indeed, we define the acetylation status of the Lys 80 residue located in the DNA-binding domain of HSF1 as a critical factor in modulating HSF1 protein stability in addition to its previously identified role in the transcriptional activity. Together with the finding that preserving HSF1 can alleviate α-synuclein toxicity, this study strongly suggests that aberrant HSF1 degradation is a key neurodegenerative mechanism underlying α-synucleinopathy.
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http://dx.doi.org/10.1093/hmg/ddv445DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4706110PMC
January 2016

All-trans-retinoic acid reduces BACE1 expression under inflammatory conditions via modulation of nuclear factor κB (NFκB) signaling.

J Biol Chem 2015 Sep 3;290(37):22532-42. Epub 2015 Aug 3.

From the Department of Pharmacology, University of Tennessee Health Science Center, Memphis, Tennessee 38163,

Insulin resistance and neuroinflammation have emerged as two likely key contributors in the pathogenesis of Alzheimer disease (AD), especially in those sporadic AD cases compromised by diabetes or cardiovascular disease. Amyloid-β (Aβ) deposition and its associated inflammatory response are hallmarks in sporadic AD brains. Elevated expression and activity of β-secretase 1 (BACE1), the rate-limiting enzyme responsible for the β-cleavage of amyloid precursor proteins to Aβ peptides, are also observed in sporadic AD brains. Previous studies have suggested that there is therapeutic potential for retinoic acid in treating neurodegeneration based on decreased Aβ. Here we discovered that BACE1 expression is elevated in the brains of both Tg2576 transgenic mice and mice on high fat diets. These conditions are associated with a neuroinflammatory response. We found that administration of all-trans-retinoic acid (atRA) down-regulated the expression of BACE1 in the brains of Tg2576 mice and in mice fed a high fat diet. Moreover, in LPS-treated mice and cultured neurons, BACE1 expression was repressed by the addition of atRA, correlating with the anti-inflammatory efficacy of atRA. Mutations of the NFκB binding site in BACE1 promoter abolished the suppressive effect of atRA. Furthermore, atRA disrupted LPS-induced nuclear translocation of NFκB and its binding to BACE1 promoter as well as promoting the recruitment of the corepressor NCoR. Our findings indicate that atRA represses BACE1 gene expression under inflammatory conditions via the modulation of NFκB signaling.
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http://dx.doi.org/10.1074/jbc.M115.662908DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4566228PMC
September 2015

Partial eNOS deficiency causes spontaneous thrombotic cerebral infarction, amyloid angiopathy and cognitive impairment.

Mol Neurodegener 2015 Jun 24;10:24. Epub 2015 Jun 24.

Departments of Pharmacology, University of Tennessee Health Science Center, 874 Union Avenue/Crowe 401, Memphis, TN, 38163, USA.

Background: Cerebral infarction due to thrombosis leads to the most common type of stroke and a likely cause of age-related cognitive decline and dementia. Endothelial nitric oxide synthase (eNOS) generates NO, which plays a crucial role in maintaining vascular function and exerting an antithrombotic action. Reduced eNOS expression and eNOS polymorphisms have been associated with stroke and Alzheimer's disease (AD), the most common type of dementia associated with neurovascular dysfunction. However, direct proof of such association is lacking. Since there are no reports of complete eNOS deficiency in humans, we used heterozygous eNOS(+/-) mice to mimic partial deficiency of eNOS, and determine its impact on cerebrovascular pathology and perfusion of cerebral vessels.

Results: Combining cerebral angiography with immunohistochemistry, we found thrombotic cerebral infarctions in eNOS(+/-) mice as early as 3-6 months of age but not in eNOS(+/+) mice at any age. Remarkably, vascular occlusions in eNOS(+/-) mice were found almost exclusively in three areas: temporoparietal and retrosplenial granular cortexes, and hippocampus this distribution precisely matching the hypoperfused areas identified in preclinical AD patients. Moreover, progressive cerebral amyloid angiopaphy (CAA), blood brain barrier (BBB) breakdown, and cognitive impairment were also detected in aged eNOS(+/-) mice.

Conclusions: These data provide for the first time the evidence that partial eNOS deficiency results in spontaneous thrombotic cerebral infarctions that increase with age, leading to progressive CAA and cognitive impairments. We thus conclude that eNOS(+/-) mouse may represent an ideal model of ischemic stroke to address early and progressive damage in spontaneously-evolving chronic cerebral ischemia and thus, study vascular mechanisms contributing to vascular dementia and AD.
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http://dx.doi.org/10.1186/s13024-015-0020-0DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4479241PMC
June 2015

Genetic variability to diet-induced hippocampal dysfunction in BXD recombinant inbred (RI) mouse strains.

Behav Brain Res 2015 Oct 16;292:83-94. Epub 2015 Jun 16.

Department of Pharmacology, USA. Electronic address:

Evidence has emerged suggesting that diet-induced obesity can have a negative effect on cognitive function. Here, we exploited a mouse genetic reference population to look for the linkage between these two processes on a genome-wide scale. The focus of this report is to determine whether the various BXD RI strains exhibited different behavioral performance and hippocampal function under high fat dietary (HFD) condition. We quantified genetic variation in body weight gain and consequent influences on behavioral tests in a cohort of 14 BXD strains of mice (8-12 mice/strain, n = 153), for which we have matched data on gene expression and neuroanatomical changes in the hippocampus. It showed that BXD66 was the most susceptible, whereas BXD77 was the least susceptible strain to dietary influences. The performance of spatial reference memory tasks was strongly correlated with body weight gain (P < 0.05). The obesity-prone strains displayed more pronounced spatial memory defects compared to the obesity-resistant strains. These abnormalities were associated with neuroinflammation, synaptic dysfunction, and neuronal loss in the hippocampus. The biological relevance of DSCAM gene polymorphism was assessed using the trait correlation analysis tool in Genenetwork. Furthermore, a significant strain-dependent gene expression difference of DSCAM was detected in the hippocampus of obese BXD strains by real-time quantitative PCR. In conclusion, a variety of across-strain hippocampal alterations and genetic predispositions to diet-induced obesity were found in a set of BXD strains. The obesity-prone and obesity-resistant lines we have identified should be highly useful to study the molecular genetics of diet-induced cognitive decline.
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http://dx.doi.org/10.1016/j.bbr.2015.06.023DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5226443PMC
October 2015

Anti-oxidant polydatin (piceid) protects against substantia nigral motor degeneration in multiple rodent models of Parkinson's disease.

Mol Neurodegener 2015 Mar 2;10. Epub 2015 Mar 2.

Department of Pharmacology, School of Pharmaceutical Sciences, Southern Medical University, Guangzhou, 510515, China.

Background: Compelling evidence suggests that inhibition of the complex I of the electron transport chain and elevated oxidative stress are the earliest events during the pathogenesis of Parkinson's disease (PD). Therefore, anti-oxidants, especially those from natural sources, hold good promise in treating PD as demonstrated mostly by the studies in rodent models.

Results: Herein, we determined if polydatin (piceid), a natural polyphenol, could exert anti-oxidative activity and attenuate dopaminergic neurodegeneration in three commonly used rodent models of PD. Male Sprague Dawley rats given rotenone subcutaneously for 5 weeks developed all the essential features of PD, including a strong increase in catalepsy score and a decrease in motor coordination activity, starting at 4 weeks. Selective increase in oxidative damage was found in the striatal region as compared to the hippocampus and cortex, accompanied by massive degeneration of dopaminergic neurons in the substantia nigra (SNc). Co-administration of piceid orally was able to attenuate rotenone-induced motor defects in a dose dependent manner, with 80 mg/kg dosage showing even better effect than L-levodopa (L-dopa). Piceid treatment significantly prevented the rotenone-induced changes in the levels of glutathione, thioredoxin, ATP, malondialdehyde (MDA) and the manganese superoxide dismutases (SOD) in striatum. Furthermore, piceid treatment rescued rotenone-induced dopaminergic neurodegeneration in the SNc region. Similar protective effect of piceid was also observed in two additional models of PD, MPTP in mice and 6-OHDA in rats, showing corrected motor functions, SOD and MDA activities as well as p-Akt and activated caspase-3 levels.

Conclusion: In three rodent models of PD, piceid preserves and corrects several major anti-oxidant pathways/parameters selectively in the affected SNc region. This implies its potent anti-oxidant activity as one major underscoring mechanism for protecting the vulnerable SNc neurodegeneration in these models. Taken together, these findings strongly suggest a therapeutic potential of piceid in treating PD.
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http://dx.doi.org/10.1186/1750-1326-10-4DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4506434PMC
March 2015

Nedd4 haploinsufficient mice display moderate insulin resistance, enhanced lipolysis, and protection against high-fat diet-induced obesity.

Endocrinology 2015 Apr 21;156(4):1283-91. Epub 2015 Jan 21.

Departments of Pharmacology (J.J.L., S.D., S.W.B., F.-F.L.) and Pediatrics (R.J.F.), University of Tennessee Health Science Center, Memphis, Tennessee 38163; Department of Psychology (R.J.F), University of Memphis, Memphis, Tennessee 38152; and Department of Biology (B.X.), Georgia State University, Atlanta, Georgia 30302.

Neural precursor cell expressed developmentally down-regulated protein 4 (Nedd4) is the prototypical protein in the Nedd4 ubiquitin ligase (E3) family, which governs ubiquitin-dependent endocytosis and/or degradation of plasma membrane proteins. Loss of Nedd4 results in embryonic or neonatal lethality in mice and reduced insulin/IGF-1 signaling in embryonic fibroblasts. To delineate the roles of Nedd4 in vivo, we examined the phenotypes of heterozygous knockout mice using a high-fat diet-induced obesity (HFDIO) model. We observed that Nedd4+/- mice are moderately insulin resistant but paradoxically protected against HFDIO. After high-fat diet feeding, Nedd4+/- mice showed less body weight gain, less fat mass, and smaller adipocytes vs the wild type. Despite ameliorated HFDIO, Nedd4+/- mice did not manifest improvement in glucose tolerance vs the wild type in both genders. Nedd4+/- male, but not female, mice displayed significantly lower fasting blood glucose levels and serum insulin levels. Under obesogenic conditions, Nedd4+/- mice displayed elevated stimulated lipolytic activity, primarily through a β2-adrenergic receptor. Combined, these data support novel complex roles for Nedd4 in metabolic regulation involving altered insulin and β-adrenergic signaling pathways.
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http://dx.doi.org/10.1210/en.2014-1909DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4399314PMC
April 2015

Homocysteine disrupts outgrowth of microvascular endothelium by an iNOS-dependent mechanism.

Microcirculation 2014 Aug;21(6):541-50

Department of Biological Sciences, Idaho State University, Pocatello, Idaho, USA.

Objective: To test the hypothesis that Hcy impairs angiogenic outgrowth through an iNOS-dependent mechanism.

Methods: Adult C57Bl/6 mouse choroid explants were used in angiogenic outgrowth assays. Mouse microvascular endothelial cells were studied in culture during scrape-induced migration and dispersed cell locomotion experiments. Activity of iNOS was manipulated with pharmacology (1400 W), siRNA, and by use of choroid explants from iNOS knockout mice (iNOS(-/-)).

Results: Hcy (20 μM) significantly decreased the area of endothelial outgrowth without altering the number of cells in the choroid explant angiogenic assay, resulting in more densely packed outgrowth. Hcy prevented the outward orientation of actin filaments and decreased the number of actin projections along the leading edge of outgrowth. Hcy also slowed outgrowth from the edge of a scraped endothelial monolayer and in cultures of dispersed cells, Hcy impaired cell locomotion without affecting proliferation. Inhibition of iNOS activity rescued the effect of Hcy on area of explant outgrowth, cell density, number of projections, cell locomotion, and rate of outgrowth following scraping.

Conclusions: Hcy impairs microvascular endothelial outgrowth, but not proliferation, by disrupting cell locomotion through an iNOS-dependent mechanism.
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http://dx.doi.org/10.1111/micc.12133DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4126873PMC
August 2014

Soluble beta-amyloid peptides, but not insoluble fibrils, have specific effect on neuronal microRNA expression.

PLoS One 2014 4;9(3):e90770. Epub 2014 Mar 4.

Department of Pharmacology, University of Tennessee Health Science Center, Memphis, Tennessee, United States of America.

Recent studies indicate that soluble β-amyloid (sAβ) oligomers, rather than their fibrillar aggregates, contribute to the pathogenesis of Alzheimer's disease (AD), though the mechanisms of their neurotoxicity are still elusive. Here, we demonstrate that sAβ derived from 7PA2 cells exert a much stronger effect on the regulation of a set of functionally validated microRNAs (miRNAs) in primary cultured neurons than the synthetic insoluble Aβ fibrils (fAβ). Synthetic sAβ peptides at a higher concentration present comparable effect on these miRNAs in our neuronal model. Further, the sAβ-induced miR-134, miR-145 and miR-210 expressions are fully reversed by two selective N-methyl-d-aspartate (NMDA) receptor inhibitors, but are neither reversed by insulin nor by forskolin, suggesting an NMDA receptor-dependent, rather than PI3K/AKT or PKA/CREB signaling dependent regulatory mechanism. In addition, the repression of miR-107 expression by the sAβ containing 7PA2 CM is likely involved multiple mechanisms and multiple players including NMDA receptor, N-terminally truncated Aβ and reactive oxygen species (ROS).
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0090770PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3942478PMC
November 2014

Hsp90 chaperone inhibitor 17-AAG attenuates Aβ-induced synaptic toxicity and memory impairment.

J Neurosci 2014 Feb;34(7):2464-70

Neurodegenerative Disease Research Program, Sanford-Burnham Medical Research Institute, La Jolla, California 92037, Department of Pharmacology and Anatomy & Neurobiology, University of Tennessee Health Science Center, College of Medicine, Memphis, Tennessee 38163, and Department of Pathophysiology, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei 430030, China.

The excessive accumulation of soluble amyloid peptides (Aβ) plays a crucial role in the pathogenesis of Alzheimer's disease (AD), particularly in synaptic dysfunction. The role of the two major chaperone proteins, Hsp70 and Hsp90, in clearing misfolded protein aggregates has been established. Despite their abundant presence in synapses, the role of these chaperones in synapses remains elusive. Here, we report that Hsp90 inhibition by 17-AAG elicited not only a heat shock-like response but also upregulated presynaptic and postsynaptic proteins, such as synapsin I, synaptophysin, and PSD95 in neurons. 17-AAG treatment enhanced high-frequency stimulation-evoked LTP and protected neurons from synaptic damage induced by soluble Aβ. In AD transgenic mice, the daily administration of 17-AAG over 7 d resulted in a marked increase in PSD95 expression in hippocampi. 17-AAG treatments in wild-type C57BL/6 mice challenged by soluble Aβ significantly improved contextual fear memory. Further, we demonstrate that 17-AAG activated synaptic protein expression via transcriptional mechanisms through the heat shock transcription factor HSF1. Together, our findings identify a novel function of Hsp90 inhibition in regulating synaptic plasticity, in addition to the known neuroprotective effects of the chaperones against Aβ and tau toxicity, thus further supporting the potential of Hsp90 inhibitors in treating neurodegenerative diseases.
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http://dx.doi.org/10.1523/JNEUROSCI.0151-13.2014DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3921421PMC
February 2014

APP regulates NGF receptor trafficking and NGF-mediated neuronal differentiation and survival.

PLoS One 2013 1;8(11):e80571. Epub 2013 Nov 1.

Fujian Provincial Key Laboratory of Neurodegenerative Disease and Aging Research and Institute of Neuroscience, College of Medicine, Xiamen University, Xiamen, China ; Neurodegenerative Disease Research Program, Sanford-Burnham Medical Research Institute, La Jolla, California, United States of America.

β-Amyloid precursor protein (APP) is a key factor in Alzheimer's disease (AD) but its physiological function is largely undetermined. APP has been found to regulate retrograde transport of nerve growth factor (NGF), which plays a crucial role in mediating neuronal survival and differentiation. Herein, we reveal the mechanism underlying APP-mediated NGF trafficking, by demonstrating a direct interaction between APP and the two NGF receptors, TrkA and p75NTR. Downregulation of APP leads to reduced cell surface levels of TrkA/p75NTR and increased endocytosis of TrkA/p75NTR and NGF. In addition, APP-deficient cells manifest defects in neurite outgrowth and are more susceptible to Aβ-induced neuronal death at physiological levels of NGF. However, APP-deficient cells show better responses to NGF-stimulated differentiation and survival than control cells. This may be attributed to increased receptor endocytosis and enhanced activation of Akt and MAPK upon NGF stimulation in APP-deficient cells. Together, our results suggest that APP mediates endocytosis of NGF receptors through direct interaction, thereby regulating endocytosis of NGF and NGF-induced downstream signaling pathways for neuronal survival and differentiation.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0080571PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3815101PMC
June 2014

Repression of Alzheimer's beta-secretase.

Aging (Albany NY) 2013 Nov;5(11):789-90

Department of Pharmacology, University of Tennessee Health Science Center, College of Medicine, Memphis TN, 38163, USA.

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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3868720PMC
http://dx.doi.org/10.18632/aging.100612DOI Listing
November 2013

Synaptic protein α1-takusan mitigates amyloid-β-induced synaptic loss via interaction with tau and postsynaptic density-95 at postsynaptic sites.

J Neurosci 2013 Aug;33(35):14170-83

Del E. Web Center for Neuroscience, Aging, and Stem Cell Research, and Bioinformatics Shared Resource, Sanford-Burnham Medical Research Institute, La Jolla, California 92037, USA.

The synaptic toxicity of soluble amyloid-β (Aβ) oligomers plays a critical role in the pathophysiology of Alzheimer's disease (AD). Here we report that overexpressed α1-takusan, which we previously identified as a protein that enhances synaptic activity via interaction with PSD-95, mitigates oligomeric Aβ-induced synaptic loss. In contrast, takusan knockdown results in enhanced synaptic damage. α1-Takusan interacts with tau either directly or indirectly, and prevents Aβ-induced tau hyperphosphorylation and mitochondrial fragmentation. Deletion analysis identified the second domain (D2) within the takusan protein that is required for PSD-95 clustering and synaptic protection from Aβ. A 51 aa sequence linking D2 to the PDZ-binding C terminus was found to be as effective as full-length takusan in protecting synapses from Aβ-induced damage. Moreover, a sequence containing the D2 from the human protein discs large homolog 5, when linked to a C-terminal PDZ-binding motif, can also increase the clustering of PSD-95 in cortical dendrites. In summary, α1-takusan protects synapses from Aβ-induced insult via interaction with PSD-95 and tau. Thus, takusan-based protein sequences from either mouse or human may be of potential therapeutic benefit in AD.
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http://dx.doi.org/10.1523/JNEUROSCI.4646-10.2013DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3756761PMC
August 2013

Metabolic stress modulates Alzheimer's β-secretase gene transcription via SIRT1-PPARγ-PGC-1 in neurons.

Cell Metab 2013 May;17(5):685-94

Department of Pharmacology, University of Tennessee Health Science Center, College of Medicine, 874 Union Avenue, Memphis, TN 38163, USA.

Classic cardio-metabolic risk factors such as hypertension, stroke, diabetes, and hypercholesterolemia all increase the risk of Alzheimer's disease. We found increased transcription of β-secretase/BACE1, the rate-limiting enzyme for Aβ generation, in eNOS-deficient mouse brains and after feeding mice a high-fat, high-cholesterol diet. Up- or downregulation of PGC-1α reciprocally regulated BACE1 in vitro and in vivo. Modest fasting in mice reduced BACE1 transcription in the brains, which was accompanied by elevated PGC-1 expression and activity. Moreover, the suppressive effect of PGC-1 was dependent on activated PPARγ, likely via SIRT1-mediated deacetylation in a ligand-independent manner. The BACE1 promoter contains multiple PPAR-RXR sites, and direct interactions among SIRT1-PPARγ-PGC-1 at these sites were enhanced with fasting. The interference on the BACE1 gene identified here represents a unique noncanonical mechanism of PPARγ-PGC-1 in transcriptional repression in neurons in response to metabolic signals that may involve recruitment of corepressor NCoR.
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http://dx.doi.org/10.1016/j.cmet.2013.03.016DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5396538PMC
May 2013

Appoptosin is a novel pro-apoptotic protein and mediates cell death in neurodegeneration.

J Neurosci 2012 Oct;32(44):15565-76

Fujian Provincial Key Laboratory of Neurodegenerative Disease and Aging Research and Institute of Neuroscience, College of Medicine, Xiamen University, Xiamen, Fujian 361005, China.

Apoptosis is an essential cellular process in multiple diseases and a major pathway for neuronal death in neurodegeneration. The detailed signaling events/pathways leading to apoptosis, especially in neurons, require further elucidation. Here we identify a β-amyloid precursor protein (APP)-interacting protein, designated as appoptosin, whose levels are upregulated in brain samples from Alzheimer's disease and infarct patients, and in rodent stroke models, as well as in neurons treated with β-amyloid (Aβ) and glutamate. We further demonstrate that appoptosin induces reactive oxygen species release and intrinsic caspase-dependent apoptosis. The physiological function of appoptosin is to transport/exchange glycine/5-amino-levulinic acid across the mitochondrial membrane for heme synthesis. Downregulation of appoptosin prevents cell death and caspase activation caused by glutamate or Aβ insults. APP modulates appoptosin-mediated apoptosis through interaction with appoptosin. Our study identifies appoptosin as a crucial player in apoptosis and a novel pro-apoptotic protein involved in neuronal cell death, providing a possible new therapeutic target for neurodegenerative disorders.
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http://dx.doi.org/10.1523/JNEUROSCI.3668-12.2012DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3509748PMC
October 2012

Upregulation of the E3 ligase NEDD4-1 by oxidative stress degrades IGF-1 receptor protein in neurodegeneration.

J Neurosci 2012 Aug;32(32):10971-81

Department of Pharmacology, University of Tennessee Health Science Center, College of Medicine, Memphis, Tennessee 38163, USA.

The importance of ubiquitin E3 ligases in neurodegeneration is being increasingly recognized. The crucial role of NEDD4-1 in neural development is well appreciated; however, its role in neurodegeneration remains unexplored. Herein, we report increased NEDD4-1 expression in the degenerated tissues of several major neurodegenerative diseases. Moreover, its expression is upregulated in cultured neurons in response to various neurotoxins, including zinc and hydrogen superoxide, via transcriptional activation likely mediated by the reactive oxygen species (ROS)-responsive FOXM1B. Reduced protein levels of the insulin-like growth factor receptor (IGF-1Rβ) were observed as a consequence of upregulated NEDD4-1 via the ubiquitin-proteasome system. Overexpression of a familial mutant form of superoxide dismutase 1 (SOD1) (G93A) in neuroblastoma cells resulted in a similar reduction of IGF-1Rβ protein. This inverse correlation between NEDD4-1 and IGF-1Rβ was also observed in the cortex and spinal cords of mutant (G93A) SOD1 transgenic mice at a presymptomatic age, which was similarly induced by in vivo-administered zinc in wild-type C57BL/6 mice. Furthermore, histochemistry reveals markedly increased NEDD4-1 immunoreactivity in the degenerating/degenerated motor neurons in the lumbar anterior horn of the spinal cord, suggesting a direct causative role for NEDD4-1 in neurodegeneration. Indeed, downregulation of NEDD4-1 by shRNA or overexpression of a catalytically inactive form rescued neurons from zinc-induced cell death. Similarly, neurons with a NEDD4-1 haplotype are more resistant to apoptosis, largely due to expression of higher levels of IGF-1Rβ.Together, our work identifies a novel molecular mechanism for ROS-upregulated NEDD4-1 and the subsequently reduced IGF-1Rβ signaling in neurodegeneration.
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http://dx.doi.org/10.1523/JNEUROSCI.1836-12.2012DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3681290PMC
August 2012

Differential regulation of BACE1 expression by oxidative and nitrosative signals.

Mol Neurodegener 2011 Mar 3;6:17. Epub 2011 Mar 3.

Department of Pharmacology, University of Tennessee Health Science Center, College of Medicine, 874 Union Avenue, Memphis TN, 38163, USA.

Background: It is well established that both cerebral hypoperfusion/stroke and type 2 diabetes are risk factors for Alzheimer's disease (AD). Recently, the molecular link between ischemia/hypoxia and amyloid precursor protein (APP) processing has begun to be established. However, the role of the key common denominator, namely nitric oxide (NO), in AD is largely unknown. In this study, we investigated redox regulation of BACE1, the rate-limiting enzyme responsible for the β-cleavage of APP to Aβ peptides.

Results: Herein, we studied events such as S-nitrosylation, a covalent modification of cysteine residues by NO, and H2O2-mediated oxidation. We found that NO and H2O2 differentially modulate BACE1 expression and enzymatic activity: NO at low concentrations (<100 nM) suppresses BACE1 transcription as well as its enzymatic activity while at higher levels (0.1-100 μM) NO induces S-nitrosylation of BACE1 which inactivates the enzyme without altering its expression. Moreover, the suppressive effect on BACE1 transcription is mediated by the NO/cGMP-PKG signaling, likely through activated PGC-1α. H2O2 (1-10 μM) induces BACE1 expression via transcriptional activation, resulting in increased enzymatic activity. The differential effects of NO and H2O2 on BACE1 expression and activity are also reflected in their opposing effects on Aβ generation in cultured neurons in a dose-dependent manner. Furthermore, we found that BACE1 is highly S-nitrosylated in normal aging brains while S-nitrosylation is markedly reduced in AD brains.

Conclusion: This study demonstrates for the first time that BACE1 is highly modified by NO via multiple mechanisms: low and high levels of NO suppress BACE1 via transcriptional and post translational regulation, in contrast with the upregulation of BACE1 by H2O2-mediated oxidation. These novel NO-mediated regulatory mechanisms likely protect BACE1 from being further oxidized by excessive oxidative stress, as from H2O2 and peroxynitrite which are known to upregulate BACE1 and activate the enzyme, resulting in excessive cleavage of APP and Aβ generation; they likely represent the crucial house-keeping mechanism for BACE1 expression/activation under physiological conditions.
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http://dx.doi.org/10.1186/1750-1326-6-17DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3059281PMC
March 2011

NO signaling and S-nitrosylation regulate PTEN inhibition in neurodegeneration.

Mol Neurodegener 2010 Nov 10;5:49. Epub 2010 Nov 10.

Department of Pharmacology, University of Tennessee Health Science Center, College of Medicine, 874 Union Avenue, Memphis TN, 38163, USA.

Background: The phosphatase PTEN governs the phosphoinositide 3-kinase (PI3K)/Akt signaling pathway which is arguably the most important pro-survival pathway in neurons. Recently, PTEN has also been implicated in multiple important CNS functions such as neuronal differentiation, plasticity, injury and drug addiction. It has been reported that loss of PTEN protein, accompanied by Akt activation, occurs under excitotoxic conditions (stroke) as well as in Alzheimer's (AD) brains. However the molecular signals and mechanism underlying PTEN loss are unknown.

Results: In this study, we investigated redox regulation of PTEN, namely S-nitrosylation, a covalent modification of cysteine residues by nitric oxide (NO), and H2O2-mediated oxidation. We found that S-nitrosylation of PTEN was markedly elevated in brains in the early stages of AD (MCI). Surprisingly, there was no increase in the H2O2-mediated oxidation of PTEN, a modification common in cancer cell types, in the MCI/AD brains as compared to normal aged control. Using several cultured neuronal models, we further demonstrate that S-nitrosylation, in conjunction with NO-mediated enhanced ubiquitination, regulates both the lipid phosphatase activity and protein stability of PTEN. S-nitrosylation and oxidation occur on overlapping and distinct Cys residues of PTEN. The NO signal induces PTEN protein degradation via the ubiquitin-proteasome system (UPS) through NEDD4-1-mediated ubiquitination.

Conclusion: This study demonstrates for the first time that NO-mediated redox regulation is the mechanism of PTEN protein degradation, which is distinguished from the H2O2-mediated PTEN oxidation, known to only inactivate the enzyme. This novel regulatory mechanism likely accounts for the PTEN loss observed in neurodegeneration such as in AD, in which NO plays a critical pathophysiological role.
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http://dx.doi.org/10.1186/1750-1326-5-49DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2992530PMC
November 2010

The Rps23rg gene family originated through retroposition of the ribosomal protein s23 mRNA and encodes proteins that decrease Alzheimer's beta-amyloid level and tau phosphorylation.

Hum Mol Genet 2010 Oct 22;19(19):3835-43. Epub 2010 Jul 22.

Institute for Biomedical Research and Fujian Provincial Key Laboratory of Neurodegenerative Disease and Aging Research, Xiamen University, Xiamen 361005, China.

Retroposition is an important mechanism for gene origination. However, studies to elucidate the functions of new genes originated through retroposition, especially the functions related to diseases, are limited. We recently identified a mouse gene, Rps23 retroposed gene 1 (Rps23rg1), that regulates beta-amyloid (Abeta) level and tau phosphorylation, two major pathological hallmarks of Alzheimer's disease (AD), and found that Rps23rg1 originated through retroposition of the mouse ribosomal protein S23 (Rps23) mRNA. Here we show that retroposition of Rps23 mRNA occurred multiple times in different species but only generated another functionally expressed Rps23rg1-homologous gene, Rps23rg2, in mice, whereas humans may not possess functional Rps23rg homologs. Both Rps23rg1 and Rps23rg2 are reversely transcribed relative to the parental Rps23 gene, expressed in various tissues and encode proteins that interact with adenylate cyclases. Similar to the RPS23RG1 protein, RPS23RG2 can upregulate protein kinase A activity to reduce the activity of glycogen synthase kinase-3, Abeta level and tau phosphorylation. However, the effects of RPS23RG2 are weaker than those of RPS23RG1 and such a difference could be attributed to the extra carboxyl-terminal region of RPS23RG2, which may have an inhibitory effect. In addition, we show that the transmembrane domain of RPS23RG1 is important for its function. Together, our results present a new gene family, whose products and associated signaling pathways might prevent mice from developing AD-like pathologies.
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http://dx.doi.org/10.1093/hmg/ddq302DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2935860PMC
October 2010

Functional interaction of phosphatase and tensin homologue (PTEN) with the E3 ligase NEDD4-1 during neuronal response to zinc.

J Biol Chem 2010 Mar 25;285(13):9847-9857. Epub 2010 Jan 25.

Department of Pharmacology, College of Medicine, University of Tennessee Health Science Center, Memphis, Tennessee 38163. Electronic address:

The contribution of zinc-mediated neuronal death in the process of both acute and chronic neurodegeneration has been increasingly appreciated. Phosphatase and tensin homologue, deleted on chromosome 10 (PTEN), the major tumor suppressor and key regulator of the phosphatidylinositol 3-kinase (PI3K)/Akt pathway, plays a critical role in neuronal death in response to various insults. NEDD4-1-mediated PTEN ubiquitination and subsequent degradation via the ubiquitin proteosomal system have recently been demonstrated to be the important regulatory mechanism for PTEN in several cancer types. We now demonstrate that PTEN is also the key mediator of the PI3K/Akt pathway in the neuronal response to zinc insult. We used primary cortical neurons and neuroblastoma N2a cells to show that zinc treatment results in a reduction of the PTEN protein level in parallel with increased NEDD4-1 gene/protein expression. The reduced PTEN level is associated with an activated PI3K pathway as determined by elevated phosphorylation of both Akt and GSK-3 as well as by the attenuating effect of a specific PI3K inhibitor (wortmannin). The reduction of PTEN can be attributed to increased protein degradation via the ubiquitin proteosomal system, as we show NEDD4-1 to be the major E3 ligase responsible for PTEN ubiquitination in neurons. Moreover, PTEN and NEDD4-1 appear to be able to counter-regulate each other to mediate the neuronal response to zinc. This reciprocal regulation requires the PI3K signaling pathway, suggesting a feedback loop mechanism. This study demonstrates that NEDD4-1-mediated PTEN ubiquitination is crucial in the regulation of PI3K/Akt signaling by PTEN during the neuronal response to zinc, which may represent a common mechanism in neurodegeneration.
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http://dx.doi.org/10.1074/jbc.M109.091637DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2843233PMC
March 2010

A functional mouse retroposed gene Rps23r1 reduces Alzheimer's beta-amyloid levels and tau phosphorylation.

Neuron 2009 Nov;64(3):328-40

Institute for Biomedical Research, Xiamen University, Xiamen, China.

Senile plaques consisting of beta-amyloid (Abeta) and neurofibrillary tangles composed of hyperphosphorylated tau are major pathological hallmarks of Alzheimer's disease (AD). Elucidation of factors that modulate Abeta generation and tau hyperphosphorylation is crucial for AD intervention. Here, we identify a mouse gene Rps23r1 that originated through retroposition of ribosomal protein S23. We demonstrate that RPS23R1 protein reduces the levels of Abeta and tau phosphorylation by interacting with adenylate cyclases to activate cAMP/PKA and thus inhibit GSK-3 activity. The function of Rps23r1 is demonstrated in cells of various species including human, and in transgenic mice overexpressing RPS23R1. Furthermore, the AD-like pathologies of triple transgenic AD mice were improved and levels of synaptic maker proteins increased after crossing them with Rps23r1 transgenic mice. Our studies reveal a new target/pathway for regulating AD pathologies and uncover a retrogene and its role in regulating protein kinase pathways.
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http://dx.doi.org/10.1016/j.neuron.2009.08.036DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3846276PMC
November 2009