Hypoxia-inducible factor-1 α regulates prion protein expression to protect against neuron cell damage

Hypoxia-Targeted Responsive Delivery of Doxorubicin and Digoxin for Synergistic Treatment of Triple-Negative Breast Cancer

To enhance the therapeutic efficacy and safety of triple-negative breast cancer (TNBC) treatment, we developed a hypoxia-responsive drug delivery system utilizing digoxin (DIG) to inhibit HIF-1α and sensitize TNBC to doxorubicin (DOX). DIG, a cardiac steroid with a well-characterized pharmacological mechanism, was encapsulated in micelles composed of methoxy-polyethylene glycol (mPEG) and poly(lactic acid) (PLA) copolymers, incorporating an azobenzene (AZO) trigger for hypoxia-sensitive drug release. The loading ratio of DOX to DIG was optimized based on DIG's minimum effective dose. In vitro and in vivo studies demonstrated that the micelles efficiently delivered their payload to hypoxic tumor regions, enabling rapid drug release. DIG-mediated HIF-1α inhibition enhanced TNBC sensitivity to DOX, leading to significant suppression of both primary tumor growth and pulmonary metastasis. This study presents a promising and clinically feasible strategy for TNBC and other hypoxia-driven malignancies.

HIF-1α stabilization inhibits Japanese encephalitis virus propagation and neurotoxicity via autophagy pathways

Japanese encephalitis (JE) is a widespread flavivirus that induces brain inflammation and affects the central nervous system (CNS). Deferoxamine, an iron chelator, has shown promising results in stabilizing HIF-1α, a protein that improves hypoxic conditions, offers protective effects against neurological, and neurodegenerative diseases. This study aimed to assess the impact of HIF-1α stabilization during JEV infection using SH-SY5Y neuroblastoma cell lines as a model. Our findings demonstrated that deferoxamine treatment increased HIF-1α protein levels, leading to a reduction in JEV propagation. Moreover, RT-PCR analysis revealed that deferoxamine ameliorated JEV-induced neuroinflammation and neurotoxicity. We proved that inducing HIF-1α is essential for having an impact of deferoxamine against JEV-mediated neurotoxicity. Thus, our findings offer a potential therapeutic approach to mitigate the detrimental effects of JEV infection on neuronal cells. Further investigations also demonstrated that deferoxamine could reverse JEV-induced autophagy inhibition by stabilizing HIF-1α, which plays a crucial role in mitigating neuronal cell damage and neuroinflammation. Based on our data, HIF-1α stabilization emerges as a vital factor against JEV infection in the neurons, highlighting deferoxamine as a promising and innovative target for developing anti-JEV agents.

Persistent ER stress causes GPI anchor deficit to convert a GPI-anchored prion protein into pro-PrP via the ATF6-miR449c-5p-PIGV axis

Endoplasmic reticulum (ER) stress and unfolded protein response are cells' survival strategies to thwart disruption of proteostasis. Tumor cells are continuously being challenged by ER stress. The prion protein, PrP, normally a glycosylphosphatidylinositol (GPI)-anchored protein exists as a pro-PrP retaining its GPI-peptide signal sequence in human pancreatic ductal cell adenocarcinoma (PDAC). Higher abundance of pro-PrP indicates poorer prognosis in PDAC patients. The reason why PDAC cells express pro-PrP is unknown. Here, we report that persistent ER stress causes conversion of GPI-anchored PrP to pro-PrP via a conserved ATF6-miRNA449c-5p-PIGV axis. Mouse neurons and AsPC-1, a PDAC cell line, express GPI-anchored PrP. However, continuous culture of these cells with the ER stress inducers thapsigargin or brefeldin A results in the conversion of a GPI-anchored PrP to pro-PrP. Such a conversion is reversible; removal of the inducers allows the cells to re-express a GPI-anchored PrP. Mechanistically, persistent ER stress increases the abundance of an active ATF6, which increases the level of miRNA449c-5p (miR449c-5p). By binding the mRNA of PIGV at its 3'-UTRs, miR449c-5p suppresses the level of PIGV, a mannosyltransferase pivotal in the synthesis of the GPI anchor. Reduction of PIGV leads to disruption of the GPI anchor assembly, causing pro-PrP accumulation and enhancing cancer cell migration and invasion. The importance of ATF6-miR449c-5p-PIGV axis is recapitulated in PDAC biopsies as the higher levels of ATF6 and miR449c-5p and lower levels of PIGV are markers of poorer outcome for patients with PDAC. Drugs targeting this axis may prevent PDAC progression.

Prion therapeutics: Lessons from the past

Prion diseases are a group of incurable zoonotic neurodegenerative diseases (NDDs) in humans and other animals caused by the prion proteins. The abnormal folding and aggregation of the soluble cellular prion proteins (PrPC) into scrapie isoform (PrPSc) in the Central nervous system (CNS) resulted in brain damage and other neurological symptoms. Different therapeutic approaches, including stalling PrPC to PrPSc conversion, increasing PrPSc removal, and PrPC stabilization, for which a spectrum of compounds, ranging from organic compounds to antibodies, have been explored. Additionally, a non-PrP targeted drug strategy using serpin inhibitors has been discussed. Despite numerous scaffolds being screened for anti-prion activity in vitro, only a few were effective in vivo and unfortunately, almost none of them proved effective in the clinical studies, most likely due to toxicity and lack of permeability. Recently, encouraging results from a prion-protein monoclonal antibody, PRN100, were presented in the first human trial on CJD patients, which gives a hope for better future for the discovery of other new molecules to treat prion diseases. In this comprehensive review, we have re-visited the history and discussed various classes of anti-prion agents, their structure, mode of action, and toxicity. Understanding pathogenesis would be vital for developing future treatments for prion diseases. Based on the outcomes of existing therapies, new anti-prion agents could be identified/synthesized/designed with reduced toxicity and increased bioavailability, which could probably be effective in treating prion diseases.

The multiple functions of PrPC in physiological, cancer, and neurodegenerative contexts

Cellular prion protein (PrP^C) is a highly conserved glycoprotein, present both anchored in the cell membrane and soluble in the extracellular medium. It has a diversity of ligands and is variably expressed in numerous tissues and cell subtypes, most notably in the central nervous system (CNS). Its importance has been brought to light over the years both under physiological conditions, such as embryogenesis and immune system homeostasis, and in pathologies, such as cancer and neurodegenerative diseases. During development, PrP^C plays an important role in CNS, participating in axonal growth and guidance and differentiation of glial cells, but also in other organs such as the heart, lung, and digestive system. In diseases, PrP^C has been related to several types of tumors, modulating cancer stem cells, enhancing malignant properties, and inducing drug resistance. Also, in non-neoplastic diseases, such as Alzheimer's and Parkinson's diseases, PrP^C seems to alter the dynamics of neurotoxic aggregate formation and, consequently, the progression of the disease. In this review, we explore in detail the multiple functions of this protein, which proved to be relevant for understanding the dynamics of organism homeostasis, as well as a promising target in the treatment of both neoplastic and degenerative diseases.

Hypoxia and the Kynurenine Pathway: Implications and Therapeutic Prospects in Alzheimer's Disease

Neurodegenerative diseases (NDs) like Alzheimer's disease, multiple sclerosis, amyotrophic lateral sclerosis, Parkinson's disease, and Huntington's disease predominantly pose a significant socioeconomic burden. Characterized by progressive neural dysfunction coupled with motor or intellectual impairment, the pathogenesis of ND may result from contributions of certain environmental and molecular factors. One such condition is hypoxia, characterized by reduced organ/tissue exposure to oxygen. Reduced oxygen supply often occurs during the pathogenesis of ND and the aging process. Despite the well-established relationship between these two conditions (i.e., hypoxia and ND), the underlying molecular events or mechanisms connecting hypoxia to ND remain ill-defined. However, the relatedness may stem from the protective or deleterious effects of the transcription factor, hypoxia-inducible factor 1-alpha (HIF-1α). The upregulation of HIF-1α occurs in the pathogenesis of most NDs. The dual function of HIF-1α in acting as a "killer factor" or a "protective factor" depends on the prevailing local cellular condition. The kynurenine pathway is a metabolic pathway involved in the oxidative breakdown of tryptophan. It is essential in neurotransmission and immune function and, like hypoxia, associated with ND. Thus, a good understanding of factors, including hypoxia (i.e., the biochemical implication of HIF-1α) and kynurenine pathway activation in NDs, focusing on Alzheimer's disease could prove beneficial to new therapeutic approaches for this disease, thus the aim of this review.

Temporal Transcript Profiling Identifies a Role for Unfolded Protein Stress in Human Gut Ischemia-Reperfusion Injury

BACKGROUND & AIMS

Intestinal ischemia-reperfusion injury is a serious and life-threatening condition. A better understanding of molecular mechanisms related to intestinal ischemia-reperfusion injury in human beings is imperative to find therapeutic targets and improve patient outcome.

METHODS

First, the in vivo dynamic modulation of mucosal gene expression of the ischemia-reperfusion-injured human small intestine was studied. Based on functional enrichment analysis of the changing transcriptome, one of the predominantly regulated pathways was selected for further investigation in an in vitro human intestinal organoid model.

RESULTS

Ischemia-reperfusion massively changed the transcriptional landscape of the human small intestine. Functional enrichment analysis based on gene ontology and pathways pointed to the response to unfolded protein as a predominantly regulated process. In addition, regulatory network analysis identified hypoxia-inducing factor 1A as one of the key mediators of ischemia-reperfusion-induced changes, including the unfolded protein response (UPR). Differential expression of genes involved in the UPR was confirmed using quantitative polymerase chain reaction analysis. Electron microscopy showed signs of endoplasmic reticulum stress. Collectively, these findings point to a critical role for unfolded protein stress in intestinal ischemia-reperfusion injury in human beings. In a human intestinal organoid model exposed to hypoxia-reoxygenation, attenuation of UPR activation with integrated stress response inhibitor strongly reduced pro-apoptotic activating transcription factor 4 (ATF4)-CCAAT/enhancer-binding protein homologous protein (CHOP) signaling.

CONCLUSIONS

Transcriptome analysis showed a crucial role for unfolded protein stress in the response to ischemia-reperfusion in human small intestine. UPR inhibition during hypoxia-reoxygenation in an intestinal organoid model suggests that downstream protein kinase R-like ER kinase (PERK) signaling may be a promising target to reduce intestinal ischemia-reperfusion injury. Microarray data are available in GEO (https://www.ncbi.nlm.nih.gov/gds, accession number GSE37013).

Prion protein is associated with a worse prognosis of head and neck squamous cell carcinoma

BACKGROUND

Head and neck squamous cell carcinoma (HNSC) etiopathogenesis remains unclear, and the biological changes with the activation of heat shock proteins (HSPs) and prion protein (PRNP) promoted by hypoxia in HNSC are undetermined. This study investigates hypoxia's effect in lymph node metastasis by PRNP expression changes and its main partners.

METHODS

The study combined a theoretical/cell culture study with a case-control study. First, bioinformatics and cell culture were performed. A case-control study was performed in a second step by comparing HNSC patients with and without lymph node metastasis.

ANALYSES

The Cancer Genome Atlas (TCGA) data source validates the theory in the global population study.

RESULTS

Bioinformatics analysis suggests that hypoxia-inducible factor-1α (HIF1A) is associated with HSPA4, HSP90AA1 and PRNP expression. TCGA data validate the hypothesis that higher HSP90AA1, HSPA4 and PRNP are related to metastases and low survival. Herein, the cell study demonstrated that muted PRNP did not respond to hypoxia.

DISCUSSION

Our results collectively provide the first evidence that PRNP promotes HNSC lymph node metastasis progression through the upregulation of HSPA4, HSP90AA1 and HIF1A. Our findings may provide a molecular basis for the promoting Role of PRNP in HNSC progression.

Stress Response Is the Main Trigger of Sporadic Amyloidoses

Amyloidoses are a group of diseases associated with the formation of pathological protein fibrils with cross-β structures. Approximately 5-10% of the cases of these diseases are determined by amyloidogenic mutations, as well as by transmission of infectious amyloids (prions) between organisms. The most common group of so-called sporadic amyloidoses is associated with abnormal aggregation of wild-type proteins. Some sporadic amyloidoses are known to be induced only against the background of certain pathologies, but in some cases the cause of amyloidosis is unclear. It is assumed that these diseases often occur by accident. Here we present facts and hypotheses about the association of sporadic amyloidoses with vascular pathologies, trauma, oxidative stress, cancer, metabolic diseases, chronic infections and COVID-19. Generalization of current data shows that all sporadic amyloidoses can be regarded as a secondary event occurring against the background of diseases provoking a cellular stress response. Various factors causing the stress response provoke protein overproduction, a local increase in the concentration or modifications, which contributes to amyloidogenesis. Progress in the treatment of vascular, metabolic and infectious diseases, as well as cancers, should lead to a significant reduction in the risk of sporadic amyloidoses.

Physiological role of Prion Protein in Copper homeostasis and angiogenic mechanisms of endothelial cells

The Prion Protein (PrP) is mostly known for its role in prion diseases, where its misfolding and aggregation can cause fatal neurodegenerative conditions such as the bovine spongiform encephalopathy and human Creutzfeldt–Jakob disease. Physiologically, PrP is involved in several processes including adhesion, proliferation, differentiation and angiogenesis, but the molecular mechanisms behind its role remain unclear. PrP, due to its well-described structure, is known to be able to regulate copper homeostasis; however, copper dyshomeostasis can lead to developmental defects. We investigated PrP-dependent regulation of copper homeostasis in human endothelial cells (HUVEC) using an RNA-interference protocol. PrP knockdown did not influence cell viability in silenced HUVEC (PrPKD) compared to control cells, but significantly increased PrPKD HUVEC cells sensitivity to cytotoxic copper concentrations. A reduction of PrPKD cells reductase activity and copper ions transport capacity was observed. Furthermore, PrPKD-derived spheroids exhibited altered morphogenesis and their derived cells showed a decreased vitality 24 and 48 hours after seeding. PrPKD spheroid-derived cells also showed disrupted tubulogenesis in terms of decreased coverage area, tubule length and total nodes number on matrigel, preserving unaltered VEGF receptors expression levels. Our results highlight PrP physiological role in cellular copper homeostasis and in the angiogenesis of endothelial cells.

Autophagic flux induced by graphene oxide has a neuroprotective effect against human prion protein fragments

Graphene oxide (GO) is a nanomaterial with newly developing biological applications. Autophagy is an intracellular degradation system that has been associated with the progression of neurodegenerative disorders. Although induction of autophagic flux by GO has been reported, the underlying signaling pathway in neurodegenerative disorders and how this is involved in neuroprotection remain obscure. We show that GO itself activates autophagic flux in neuronal cells and confers a neuroprotective effect against prion protein (PrP) (106–126)-mediated neurotoxicity. GO can be detected in SK-N-SH neuronal cells, where it triggers autophagic flux signaling. GO-induced autophagic flux prevented PrP (106–126)-induced neurotoxicity in SK-N-SH cells. Moreover, inactivation of autophagic flux blocked GO-induced neuroprotection against prion-mediated mitochondrial neurotoxicity. This is the first study to demonstrate that GO regulates autophagic flux in neuronal cells, and that activation of autophagic flux signals, induced by GO, plays a neuroprotective role against prion-mediated mitochondrial neurotoxicity. These results suggest that the nanomaterial GO may be used to activate autophagic flux and could be used in neuroprotective strategies for treatment of neurodegenerative disorders, including prion diseases.

Role of hypoxia‑mediated cellular prion protein functional change in stem cells and potential application in angiogenesis (Review)

Cellular prion protein (PrP^C) can replace other pivotal molecules due to its interaction with several partners in performing a variety of important biological functions that may differ between embryonic and mature stem cells. Recent studies have revealed major advances in elucidating the putative role of PrP^C in the regulation of stem cells and its application in stem cell therapy. What is special about PrP^C is that its expression may be regulated by hypoxia-inducible factor (HIF)-1α, which is the transcriptional factor of cellular response to hypoxia. Hypoxic conditions have been known to drive cellular responses that can enhance cell survival, differentiation and angiogenesis through adaptive processes. Our group recently reported hypoxia-enhanced vascular repair of endothelial colony-forming cells on ischemic injury. Hypoxia-induced AKT/signal transducer and activator of transcription 3 phosphorylation eventually increases neovasculogenesis. In stem cell biology, hypoxia promotes the expression of growth factors. According to other studies, aspects of tissue regeneration and cell function are influenced by hypoxia, which serves an essential role in stem cell HIF-1α signaling. All these data suggest the possibility that hypoxia-mediated PrP^C serves an important role in angiogenesis. Therefore, the present review summarizes the characteristics of PrP^C, which is produced by HIF-1α in hypoxia, as it relates to angiogenesis.

Chronic Oxidative Stress, Mitochondrial Dysfunction, Nrf2 Activation and Inflammation in the Hippocampus Accompany Heightened Systemic Inflammation and Oxidative Stress in an Animal Model of Gulf War Illness

Memory and mood dysfunction are the key symptoms of Gulf war illness (GWI), a lingering multi-symptom ailment afflicting >200,000 veterans who served in the Persian Gulf War-1. Research probing the source of the disease has demonstrated that concomitant exposures to anti-nerve gas agent pyridostigmine bromide (PB), pesticides, and war-related stress are among the chief causes of GWI. Indeed, exposures to GWI-related chemicals (GWIR-Cs) and mild stress in animal models cause memory and mood impairments alongside reduced neurogenesis and chronic low-level inflammation in the hippocampus. In the current study, we examined whether exposure to GWIR-Cs and stress causes chronic changes in the expression of genes related to increased oxidative stress, mitochondrial dysfunction, and inflammation in the hippocampus. We also investigated whether GWI is linked with chronically increased activation of Nrf2 (a master regulator of antioxidant response) in the hippocampus, and inflammation and enhanced oxidative stress at the systemic level. Adult male rats were exposed daily to low-doses of PB and pesticides (DEET and permethrin), in combination with 5 min of restraint stress for 4 weeks. Analysis of the hippocampus performed 6 months after the exposure revealed increased expression of many genes related to oxidative stress response and/or antioxidant activity (Hmox1, Sepp1, and Srxn1), reactive oxygen species metabolism (Fmo2, Sod2, and Ucp2) and oxygen transport (Ift172 and Slc38a1). Furthermore, multiple genes relevant to mitochondrial respiration (Atp6a1, Cox6a1, Cox7a2L, Ndufs7, Ndufv1, Lhpp, Slc25a10, and Ucp1) and neuroinflammation (Nfkb1, Bcl6, Csf2, IL6, Mapk1, Mapk3, Ngf, N-pac, and Prkaca) were up-regulated, alongside 73–88% reduction in the expression of anti-inflammatory genes IL4 and IL10, and nuclear translocation and increased expression of Nrf2 protein. These hippocampal changes were associated with elevated levels of pro-inflammatory cytokines and chemokines (Tnfa, IL1b, IL1a, Tgfb, and Fgf2) and lipid peroxidation byproduct malondialdehyde in the serum, suggesting the presence of an incessant systemic inflammation and elevated oxidative stress. These results imply that chronic oxidative stress, inflammation, and mitochondrial dysfunction in the hippocampus, and heightened systemic inflammation and oxidative stress likely underlie the persistent memory and mood dysfunction observed in GWI.

Hinokitiol protects primary neuron cells against prion peptide-induced toxicity via autophagy flux regulated by hypoxia inducing factor-1

Prion diseases are fatal neurodegenerative disorders that are derived from structural changes of the native PrPc. Recent studies indicated that hinokitiol induced autophagy known to major function that keeps cells alive under stressful conditions. We investigated whether hinokitiol induces autophagy and attenuates PrP (106-126)-induced neurotoxicity. We observed increase of LC3-II protein level, GFP-LC3 puncta by hinokitiol in neuronal cells. Addition to, electron microscopy showed that hinokitiol enhanced autophagic vacuoles in neuronal cells. We demonstrated that hinokitiol protects against PrP (106-126)-induced neurotoxicity via autophagy by using autophagy inhibitor, wortmannin and 3MA, and ATG5 small interfering RNA (siRNA). We checked hinokitiol activated the hypoxia-inducible factor-1α (HIF-1α) and identified that hinokitiol-induced HIF-1α regulated autophagy. Taken together, this study is the first report demonstrating that hinokitiol protected against prion protein-induced neurotoxicity via autophagy regulated by HIF-1α. We suggest that hinokitiol is a possible therapeutic strategy in neuronal disorders including prion disease.

Induction of cellular prion protein (PrPc) under hypoxia inhibits apoptosis caused by TRAIL treatment

Hypoxia decreases cytotoxic responses to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) protein. Cellular prion protein (PrPc) is regulated by HIF-1α in neurons. We hypothesized that PrPc is involved in hypoxia-mediated resistance to TRAIL-induced apoptosis. We found that hypoxia induced PrPc protein and inhibited TRAIL-induced apoptosis. Thus silencing of PrPc increased TRAIL-induced apoptosis under hypoxia. Overexpression of PrPc protein using an adenoviral vector inhibited TRAIL-induced apoptosis. In xenograft model in vivo, shPrPc transfected cells were more sensitive to TRAIL-induced apoptosis than in shMock transfected cells. Molecular chemo-therapy approaches based on the regulation of PrPc expression need to address anti-tumor function of TRAIL under hypoxia. Molecular chemo-therapy approaches based on the regulation of PrPc expression need to address anti-tumor function of TRAIL under hypoxia.

Behind the Link between Copper and Angiogenesis: Established Mechanisms and an Overview on the Role of Vascular Copper Transport Systems

Angiogenesis critically sustains the progression of both physiological and pathological processes. Copper behaves as an obligatory co-factor throughout the angiogenic signalling cascades, so much so that a deficiency causes neovascularization to abate. Moreover, the progress of several angiogenic pathologies (e.g. diabetes, cardiac hypertrophy and ischaemia) can be tracked by measuring serum copper levels, which are being increasingly investigated as a useful prognostic marker. Accordingly, the therapeutic modulation of body copper has been proven effective in rescuing the pathological angiogenic dysfunctions underlying several disease states. Vascular copper transport systems profoundly influence the activation and execution of angiogenesis, acting as multi-functional regulators of apparently discrete pro-angiogenic pathways. This review concerns the complex relationship among copper-dependent angiogenic factors, copper transporters and common pathological conditions, with an unusual accent on the multi-faceted involvement of the proteins handling vascular copper. Functions regulated by the major copper transport proteins (CTR1 importer, ATP7A efflux pump and metallo-chaperones) include the modulation of endothelial migration and vascular superoxide, known to activate angiogenesis within a narrow concentration range. The potential contribution of prion protein, a controversial regulator of copper homeostasis, is discussed, even though its angiogenic involvement seems to be mainly associated with the modulation of endothelial motility and permeability.

Neuroprotective effect of cellular prion protein (PrPC) is related with activation of alpha7 nicotinic acetylcholine receptor (α7nAchR)-mediated autophagy flux

Activation of the alpha7 nicotinic acetylcholine receptor (α7nAchR) is regulated by prion protein (PrPC) expression and has a neuroprotective effect by modulating autophagic flux. In this study, we hypothesized that PrPC may regulate α7nAchR activation and that may prevent prion-related neurodegenerative diseases by regulating autophagic flux. PrP(106-126) treatment decreased α7nAchR expression and activation of autophagic flux. In addition, the α7nAchR activator PNU-282987 enhanced autophagic flux and protected neuron cells against PrP(106-126)-induced apoptosis. However, activation of autophagy and the protective effects of PNU-282987 were inhibited in PrPC knockout hippocampal neuron cells. In addition, PrPC knockout hippocampal neuron cells showed decreased α7nAchR expression levels. Adenoviral overexpression of PrPC in PrPC knockout hippocampal neuron cells resulted in activation of autophagic flux and inhibition of prion peptide-mediated cell death via α7nAchR activation. This is the first report demonstrating that activation of α7nAchR-mediated autophagic flux is regulated by PrPC, and that activation of α7nAchR regulated by PrPC expression may play a pivotal role in protection of neuron cells against prion peptide-induced neuron cell death by autophagy. These results suggest that α7nAchR-mediated autophagic flux may be involved in the pathogenesis of prion-related diseases and may be a therapeutic target for prion-related neurodegenerative diseases.

Melatonin regulates the autophagic flux via activation of alpha-7 nicotinic acetylcholine receptors

Our previous study suggested that melatonin-mediated neuroprotective effects are related with the activation of autophagy. However, the mechanism of melatonin-mediated autophagic activation in prion-mediated mitochondrial damage is not reported. Alpha-7 nicotinic acetylcholine receptors (α7nAchR) is a member of nicotinic acetylcholine receptors, and α7nAchR activation regulates via melatonin. Thus, we hypothesized that melatonin-mediated neuroprotective effect related with to autophagy pathway as a result of α7nAchR regulation. Inactivation of α7nAchR inhibited melatonin-mediated autophagic activation and protective effect against prion-mediated mitochondrial neurotoxicity. Also, knockdown of ATG5 blocked the melatonin-mediated neuroprotection and did not influence to the activation of α7nAchR caused by melatonin. This report is the first study demonstrating that melatonin-mediated autophagic activation regulates via modulation of α7nAchR signals, and upregulation of α7nAchR signals induced by melatonin plays a pivotal role in neuroprotection of prion-mediated mitochondrial neurotoxicity. Our results suggested that regulator of α7 nAChR signals including melatonin may have used for neuroprotective strategies for the neurodegenerative disorders including prion diseases.

Deferoxamine, Cerebrovascular Hemodynamics, and Vascular Aging: Potential Role for Hypoxia-Inducible Transcription Factor-1-Regulated Pathways

BACKGROUND AND PURPOSE

Iron chelation therapy is emerging as a novel neuroprotective strategy. The mechanisms of neuroprotection are diverse and include both neuronal and vascular pathways. We sought to examine the effect of iron chelation on cerebrovascular function in healthy aging and to explore whether hypoxia-inducible transcription factor-1 activation may be temporally correlated with vascular changes.

METHODS

We assessed cerebrovascular function (autoregulation, vasoreactivity, and neurovascular coupling) and serum concentrations of vascular endothelial growth factor and erythropoietin, as representative measures of hypoxia-inducible transcription factor-1 activation, during 6 hours of deferoxamine infusion in 24 young and 24 older healthy volunteers in a randomized, blinded, placebo-controlled cross-over study design. Cerebrovascular function was assessed using the transcranial Doppler ultrasound. Vascular endothelial growth factor and erythropoietin serum protein assays were conducted using the Meso Scale Discovery platform.

RESULTS

Deferoxamine elicited a strong age- and time-dependent increase in the plasma concentrations of erythropoietin and vascular endothelial growth factor, which persisted ≤3 hours post infusion (age effect P=0.04; treatment×time P<0.01). Deferoxamine infusion also resulted in a significant time- and age-dependent improvement in cerebral vasoreactivity (treatment×time P<0.01; age P<0.01) and cerebral autoregulation (gain: age×time×treatment P=0.04).

CONCLUSIONS

Deferoxamine infusion improved cerebrovascular function, particularly in older individuals. The temporal association between improved cerebrovascular function and increased serum vascular endothelial growth factor and erythropoietin concentrations is supportive of shared hypoxia-inducible transcription factor-1-regulated pathways. Therefore, pharmacological activation of hypoxia-inducible transcription factor-1 to enhance cerebrovascular function may be a promising neuroprotective strategy in acute and chronic ischemic syndromes, especially in elderly patients.

CLINICAL TRIAL REGISTRATION

URL: http://www.clinicaltrials.gov. Unique identifier: NCT013655104.

Cellular prion protein directly interacts with and enhances lactate dehydrogenase expression under hypoxic conditions

Although a physiological function of the cellular prion protein (PrP(c)) is still not fully clarified, a PrP(c)-mediated neuroprotection against hypoxic/ischemic insult is intriguing. After ischemic stroke prion protein knockout mice (Prnp(0/0)) display significantly greater lesions as compared to wild-type (WT) mice. Earlier reports suggested an interaction between the glycolytic enzyme lactate dehydrogenase (LDH) and PrP(c). Since hypoxic environment enhances LDH expression levels and compels neurons to rely on lactate as an additional oxidative substrate for energy metabolism, we examined possible differences in LDH protein expression in WT and Prnp(0/0) knockout models under normoxic/hypoxic conditions in vitro and in vivo, as well as in a HEK293 cell line. While no differences are observed under normoxic conditions, LDH expression is markedly increased after 60-min and 90-min of hypoxia in WT vs. Prnp(0/0) primary cortical neurons with concurrent less hypoxia-induced damage in the former group. Likewise, cerebral ischemia significantly increases LDH levels in WT vs. Prnp(0/0) mice with accompanying smaller lesions in the WT group. HEK293 cells overexpressing PrP(c) show significantly higher LDH expression/activity following 90-min of hypoxia as compared to control cells. Moreover, a cytoplasmic co-localization of LDH and PrP(c) was recorded under both normoxic and hypoxic conditions. Interestingly, an expression of monocarboxylate transporter 1, responsible for cellular lactate uptake, increases with PrP(c)-overexpression under normoxic conditions. Our data suggest LDH as a direct PrP(c) interactor with possible physiological relevance under low oxygen conditions.

HIF-1α regulated tongue squamous cell carcinoma cell growth via regulating VEGF expression in a xenograft model

OBJECTIVE

We aimed to study the mechanism of hypoxia-inducible factor 1 alpha (HIF-1α) regulating the cell proliferation of tongue squamous cell carcinoma (TSCC) via vascular endothelial growth factor (VEGF).

METHODS

We used RNA interference (RNAi) technique, transfected chemically synthesized siRNA against HIF-1α into CAL-27 cells, and detected the expression of HIF-1α and VEGF by real time-PCR and Western blotting in order to find out if HIF-1α regulated the expression of VEGF. A xenograft experiment was carried out to observe the role of HIF-1α on the tumor growth of tongue squamous cell carcinoma.

RESULTS

HIF-1α and VEGF mRNA expression was significantly downregulated 36 and 48 h after transfection (P<0.05); the protein expression of HIF-1α and VEGF was also significantly suppressed by siRNA against HIF-1α. Furthermore, intratumoraly injection of HIF-1α targeting siRNA suppressed tumor growth in nude mice.

CONCLUSIONS

HIF-1α regulated VEGF expression, and they may contribute to TSCC cell tumor growth.

Gingerol prevents prion protein-mediated neuronal toxicity by regulating HIF prolyl hydroxylase 2 and prion protein

Prion diseases are a family of progressive neurodegenerative disorders, which are fatal in the majority of cases and affect both humans and domestic animals. Prion protein (PrP) (106–126) retains the neurotoxic properties of the entire pathological PrPsc and it is generally used as a reasonable model to study the mechanisms responsible for prion diseases. In our previous studies, we demonstrated that hypoxia-inducible factor (HIF)-1α is involved in the gingerol-mediated protection of neuronal cells. HIF mediates cellular adaptations to low oxygen. Prolyl hydroxylase domain-containing protein 2 (PHD2) is an oxygen sensor that hydroxylates the HIF-α-subunit, promoting its proteasomal degradation under normoxic conditions. Thus, in the present study we wished to determine whether gingerol inhibits the catalytic activity of PHD2 and prevents HIF-1α protein proteasomal degradation, thereby preventing the occurrence of PrP (106–126)-induced neuronal apoptosis. We used the pharmacological inhibition of PHD2 by dimethyloxalylglycine (DMOG) or deferoxamine (DFO) and the genetic inhibition of HIF-1α by HIF-1α small interfering RNA (siRNA) to block the effects of gingerol against PrP (106–126)-induced neurotoxicity. Our results demonstrated that gingerol prevented PrP (106–126)-induced neuronal apoptosis by upregulating HIF-1α and inhibiting the catalytic activity of PHD2 under normoxic conditions. Moreover, the protective effects of gingerol against PrP (106–126)-induced neuronal apoptosis were associated with the upregulation of the expression of cellular prion protein (PrPc). In conclusion, our results indicate that gingerol has therapeutic potential for use in the treatment or prevention of prion diseases, and its inhibitory effects on the catalytic activity of PHD2 may be of clinical benefit.

Translation of the prion protein mRNA is robust in astrocytes but does not amplify during reactive astrocytosis in the mouse brain

Prion diseases induce neurodegeneration in specific brain areas for undetermined reasons. A thorough understanding of the localization of the disease-causing molecule, the prion protein (PrP), could inform on this issue but previous studies have generated conflicting conclusions. One of the more intriguing disagreements is whether PrP is synthesized by astrocytes. We developed a knock-in reporter mouse line in which the coding sequence of the PrP expressing gene (Prnp), was replaced with that for green fluorescent protein (GFP). Native GFP fluorescence intensity varied between and within brain regions. GFP was present in astrocytes but did not increase during reactive gliosis induced by scrapie prion infection. Therefore, reactive gliosis associated with prion diseases does not cause an acceleration of local PrP production. In addition to aiding in Prnp gene activity studies, this reporter mouse line will likely prove useful for analysis of chimeric animals produced by stem cell and tissue transplantation experiments.

Prion (PrPC) expression in ovine uteroplacental tissues increases after estrogen treatment of ovariectomized ewes and during early pregnancy

Scrapie in sheep is spread laterally by placental transmission of an infectious misfolded form (PrPSc) of a normal prion protein (PrPC) used as a template in PrPSc formation. We hypothesized that PrPC would be expressed in uterine and placental tissues and estradiol-17β (E2) would affect uterine PrPC expression. PrPC expression was evaluated in the uterus of long-term ovariectomized (OVX) ewes treated with an E2 implant for 2-24 h and in uteroplacental tissues from day 20 to day 30 of pregnancy. Expression of PrPC mRNA and PrPC protein increased in the uterus after E2 treatment of OVX ewes. In the maternal placenta, expression of PrPC mRNA and PrPC protein were unchanged, but in the fetal membranes (FM) PrPC mRNA and PrPC protein expression increased from day 20 to day 28. In the nonpregnant uterus, PrPC protein was immunolocalized at apical borders of the surface epithelium, in outer smooth muscle layers of large blood vessels, and in scattered stromal cells of the deep intercaruncular areas of the uterus. In the maternal placenta, PrPC protein was immunolocalized in the cytoplasm of flattened luminal epithelial cells apposed to the FM, whereas in the FM PrPC protein was in trophoblast cells and was also in several tissues of the developing embryo during early pregnancy. These data linking estrogen stimulation to increases in PrPC expression in uteroplacental tissues suggest that PrPC has a specific function during the estrous cycle and early pregnancy. Future studies should determine whether or not estrogen influences PrPC expression in other tissues, such as the nervous system and brain.

FTY720 protects neuronal cells from damage induced by human prion protein by inactivating the JNK pathway

Prion diseases affect the central nervous system (CNS) in humans and animals, and are associated with the conversion of the cellular prion protein (PrPC) to the misfolded isoform (PrPSc). FTY720, an immune modulator and synthetic analogue of sphingosine-1-phosphate (S1P), activates S1P receptors and has been shown to be effective in experimental models of transplantation and autoimmunity, including multiple sclerosis. Whereas the immune modulatory functions of FTY720 have been extensively investigated, the other functions of FTY720 are not yet well understood. In this study, we investigated the effects of FTY720 phosphate (FTY720-p) on prion protein-mediated neuronal cell death, as well as its effects on intracellular apoptotic pathways. Treatment with FTY720-p protected neuronal cells from synthetic human prion protein peptide [PrP (106‑126)]-mediated damage and prevented mitochondrial dysfunction by inhibiting the activation of c-jun N-terminal kinase. Moreover, FTY720-p prevented the PrP (106‑126)-induced reduction in mitochondrial potential, the translocation of Bax to the mitochondria and the release of cytochrome c. To the best of our knowledge, this study is the first to demonstrate the effects of FTY720 on prion protein-mediated neurotoxicity and to suggest that FTY720 has therapeutic potential in prion diseases.

Patent Highlights

Snapshot of key developments in the patent literature of relevance to the advancement of pharmaceutical and medical R&D

Identification of a novel endoplasmic reticulum stress response element regulated by XBP1

Understanding the regulatory mechanisms mediating PRNP gene expression is highly relevant to elucidating normal cellular prion protein (PrP) function(s) and the transmissibility of prion protein neurodegenerative diseases. Here, luciferase reporter assays showed that an endoplasmic reticulum stress element (ERSE)-like element, CCAAT-N26-CCACG in the human PRNP promoter, is regulated by ER stress and X-box-binding protein 1 (XBP1) but not by activating transcription factor 6 α (ATF6α). Bioinformatics identified the ERSE-26 motif in 37 other human genes in the absence of canonical ERSE sites except for three genes. Several of these genes are associated with a synaptic function or are involved in oxidative stress. Brefeldin A, tunicamycin, and thapsigargin ER stressors induced gene expression of PRNP and four randomly chosen ERSE-26-containing genes, ERLEC1, GADD45B, SESN2, and SLC38A5, in primary human neuron cultures or in the breast carcinoma MCF-7 cell line, although the level of the response depends on the gene analyzed, the genetic background of the cells, the cell type, and the ER stressor. Overexpression of XBP1 increased, whereas siRNA knockdown of XBP1 considerably reduced, PRNP and ERLEC1 mRNA levels in MCF-7 cells. Taken together, these results identify a novel ER stress regulator, which implicates the ER stress response in previously unrecognized cellular functions.

Transcriptional regulation of specific protein 1 (SP1) by hypoxia-inducible factor 1 alpha (HIF-1α) leads to PRNP expression and neuroprotection from toxic prion peptide

Our previous study demonstrated that hypoxia-inducible factor-1 (HIF-1)-mediated neuroprotective effects are related to cellular prion protein (PrPc) gene (PRNP) regulation under hypoxic conditions. However, the mechanism of HIF-1α-mediated PRNP gene regulation in prion-mediated neurodegenerative disorders is not clear. Transcription factor specific protein 1 (SP1) is necessary for PRNP transcription initiation, and SP1 gene expression is regulated through HIF-1α activation under hypoxic conditions. Thus, we hypothesized that HIF-1α-mediated neuroprotection is related to the SP1 transcription pathway as a result of PRNP gene regulation. Inhibition of SP1 expression blocked the HIF-1α-mediated protective effect against prion-mediated neurotoxicity. Also, knockdown of HIF-1α induced downregulation of SP1 expression and sensitivity to prion-mediated neurotoxicity, whereas upregulation of SP1 transcriptional activity lead to protection against prion-mediated neuron cell death and PRNP gene expression even in HIF-1α depleted cells. This report is the first study demonstrating that HIF-1α-mediated SP1 expression regulates PrPc transcription, and upregulation of SP1 induced by HIF-1α plays a key role in protection from prion-mediated neurotoxicity. These studies suggest that transcription factor SP1 may be involved in the pathogenesis of prion diseases and also may be a potential therapeutic option for neurodegeneration caused by the pathological prion protein, PrPsc.

Atorvastatin stimulates neuroblastoma cells to induce neurite outgrowth by increasing cellular prion protein expression

Recently, 3-hydroxy-3-methyl glutaryl coenzyme A (HMG-CoA) reductase inhibitors were reported to induce neurite outgrowth in vitro. However, the mechanism underlying this effect remains unclear. Cellular prion protein (PrP(C)) is a ubiquitous glycoprotein present on the surfaces of various cells, including neurons, and is suggested to be involved in neurite outgrowth. Therefore, the present study aimed to determine whether PrP(C) mediates neurite outgrowth induced by HMG-CoA reductase inhibitors. Atorvastatin, a strong HMG-CoA reductase inhibitor, induced neurite outgrowth and increased PrP(C) levels in Neuro2a cells in a time- and dose-dependent manner. PrP(C) mRNA expression was also increased by atorvastatin. Farnesol, a non-sterol mevalonate derivative, attenuated the atorvastatin-induced neurite outgrowth and increase in PrP(C). Neuro2a cells overexpressing PrP(C) showed a remarkable enhancement of atorvastatin-induced neurite outgrowth compared with mock cells transfected with empty pCI-neo vector. These findings suggest that PrP(C) contributes, at least in part, to atorvastatin-induced neurite outgrowth. This phenomenon may be included among the mechanisms underlying decreased risk of Alzheimer's disease in patients treated with HMG-CoA reductase inhibitors.

Neuronal responses to physiological stress

Physiological stress can be defined as any external or internal condition that challenges the homeostasis of a cell or an organism. It can be divided into three different aspects: environmental stress, intrinsic developmental stress, and aging. Throughout life all living organisms are challenged by changes in the environment. Fluctuations in oxygen levels, temperature, and redox state for example, trigger molecular events that enable an organism to adapt, survive, and reproduce. In addition to external stressors, organisms experience stress associated with morphogenesis and changes in inner chemistry during normal development. For example, conditions such as intrinsic hypoxia and oxidative stress, due to an increase in tissue mass, have to be confronted by developing embryos in order to complete their development. Finally, organisms face the challenge of stochastic accumulation of molecular damage during aging that results in decline and eventual death. Studies have shown that the nervous system plays a pivotal role in responding to stress. Neurons not only receive and process information from the environment but also actively respond to various stresses to promote survival. These responses include changes in the expression of molecules such as transcription factors and microRNAs that regulate stress resistance and adaptation. Moreover, both intrinsic and extrinsic stresses have a tremendous impact on neuronal development and maintenance with implications in many diseases. Here, we review the responses of neurons to various physiological stressors at the molecular and cellular level.