Inhibition of Autophagy by Captopril Attenuates Prion Peptide-Mediated Neuronal Apoptosis via AMPK Activation

Melatonin-mediated calcineurin inactivation attenuates amyloid beta-induced apoptosis

Alzheimer's disease (AD) is the most common age-related progressive neurodegenerative disorder. The accumulation of amyloid beta-peptide is a neuropathological marker of AD. While melatonin is recognized to have protective effects on aging and neurodegenerative disorders, the therapeutic effect of melatonin on calcineurin in AD is poorly understood. In this study, we examined the effect and underlying molecular mechanisms of melatonin treatment on amyloid beta-mediated neurotoxicity in neuroblastoma cells. Melatonin treatment decreased calcineurin and autophagy in neuroblastoma cells. Electron microscopy images showed that melatonin inhibited amyloid beta-induced autophagic vacuoles. The increase in the amyloid beta-induced apoptosis rate was observed more in PrPC-expressing ZW cells than in PrPC-silencing Zpl cells. Taken together, the results suggest that by mitigating the effect of calcineurin and autophagy flux activation, melatonin could also rescue amyloid beta-induced neurotoxic effects. These findings may be relevant to therapy for neurodegenerative diseases, including AD.

Roles of Apigenin and Nepetin in the Assembly Behavior and Cytotoxicity of Prion Neuropeptide PrP106-126

Development of potential inhibitors to prevent prion protein (PrP) fibrillation is a therapeutic strategy for prion diseases. The prion neuropeptide PrP106-126, a research model of abnormal PrP (PrPSc), presents similar physicochemical and biochemical characters to PrPSc, which is also a target of potential inhibitors against prion deposition. Many flavones have antioxidant, anti-inflammatory, and antibacterial properties, and they are applied in treating prion disorder and other amyloidosis as well. However, the inhibition mechanism of flavones on PrP106-126 fibrillation is still unclear. In the current work, apigenin and nepetin were used to suppress the aggregation of PrP106-126 and to alleviate the peptide-induced cytotoxicity. The results showed that apigenin and nepetin impeded the fibril formation of PrP106-126 and depolymerized the preformed fibrils. They were bound to PrP106-126 predominantly by hydrophobic and hydrogen bonding interactions. In addition, both flavones upregulated cell viability and decreased membrane leakage through reducing peptide oligomerization. The differences in inhibition and cell protection between the two small molecules were presumably attributed to the substitution of hydroxyl and methoxy groups in nepetin, which demonstrated the significant structure-function relationship of flavones with prion neuropeptide and the prospect of flavonoids as drug candidates against prion diseases.

Bradykinin produced during Plasmodium falciparum erythrocytic cycle drives monocyte adhesion to human brain microvascular endothelial cells

Cerebral malaria (CM) pathogenesis is described as a multistep mechanism. In this context, monocytes have been implicated in CM pathogenesis by increasing the sequestration of infected red blood cells to the brain microvasculature. In disease, endothelial activation is followed by reduced monocyte rolling and increased adhesion. Nowadays, an important challenge is to identify potential pro-inflammatory stimuli that can modulate monocytes behavior. Our group have demonstrated that bradykinin (BK), a pro-inflammatory peptide involved in CM, is generated during the erythrocytic cycle of P. falciparum and is detected in culture supernatant (conditioned medium). Herein we investigated the role of BK in the adhesion of monocytes to endothelial cells of blood brain barrier (BBB). To address this issue human monocytic cell line (THP-1) and human brain microvascular endothelial cells (hBMECs) were used. It was observed that 20% conditioned medium from P. falciparum infected erythrocytes (Pf-iRBC sup) increased the adhesion of THP-1 cells to hBMECs. This effect was mediated by BK through the activation of B2 and B1 receptors and involves the increase in ICAM-1 expression in THP-1 cells. Additionally, it was observed that angiotensin-converting enzyme (ACE) inhibitor, captopril, enhanced the effect of both BK and Pf-iRBC sup on THP-1 adhesion. Together these data show that BK, generated during the erythrocytic cycle of P. falciparum, could play an important role in adhesion of monocytes in endothelial cells lining the BBB.

Melatonin inhibits Japanese encephalitis virus replication and neurotoxicity via calcineurin-autophagy pathways

BACKGROUND

Japanese encephalitis virus (JEV) is a mosquito-borne flavivirus that has no specific treatment except for supportive medical care. JEV is a neurotropic virus that affects the nervous system and triggers inflammation in the brain.

METHODS

Melatonin is used as a sleep-inducing agent in neurophysiology and may serve as a protective agent against neurological and neurodegenerative diseases. Herein, we investigated the effects of melatonin and the critical roles of the serine/threonine protein phosphatase calcineurin during JEV infection in SK-N-SH neuroblastoma cells.

RESULTS

Melatonin treatment decreased JEV replication and JEV-mediated neurotoxicity. Calcineurin activity was increased by JEV infection and inhibited by melatonin treatment. Through calcineurin regulation, melatonin decreased the JEV-mediated neuroinflammatory response and attenuated JEV-induced autophagy.

CONCLUSIONS

Calcineurin inactivation has a protective effect in JEV-infected neuronal cells, and melatonin is a novel resource for the development of anti-JEV agents.

Endothelial Sp1/Sp3 are essential to the effect of captopril on blood pressure in male mice

Endothelial dysfunction represents a major cardiovascular risk factor for hypertension. Sp1 and Sp3 belong to the specificity protein and Krüppel-like transcription factor families. They are ubiquitously expressed and closely associated with cardiovascular development. We investigate the role of Sp1 and Sp3 in endothelial cells in vivo and evaluate whether captopril, an angiotensin-converting enzyme inhibitor (ACEI), targets Sp1/Sp3 to exert its effects. Inducible endothelial-specific Sp1/Sp3 knockout mice are generated to elucidate their role in endothelial cells. Tamoxifen-induced deletion of endothelial Sp1 and Sp3 in male mice decreases the serum nitrite/nitrate level, impairs endothelium-dependent vasodilation, and causes hypertension and cardiac remodeling. The beneficial actions of captopril are abolished by endothelial-specific deletion of Sp1/Sp3, indicating that they may be targets for ACEIs. Captopril increases Sp1/Sp3 protein levels by recruiting histone deacetylase 1, which elevates deacetylation and suppressed degradation of Sp1/Sp3. Sp1/Sp3 represents innovative therapeutic target for captopril to prevent cardiovascular diseases.

Thymosin Beta 4 Protects Hippocampal Neuronal Cells against PrP (106-126) via Neurotrophic Factor Signaling

Prion protein peptide (PrP) has demonstrated neurotoxicity in brain cells, resulting in the progression of prion diseases with spongiform degenerative, amyloidogenic, and aggregative properties. Thymosin beta 4 (Tβ₄) plays a role in the nervous system and may be related to motility, axonal enlargement, differentiation, neurite outgrowth, and proliferation. However, no studies about the effects of Tβ₄ on prion disease have been performed yet. In the present study, we investigated the protective effect of Tβ₄ against synthetic PrP (106-126) and considered possible mechanisms. Hippocampal neuronal HT22 cells were treated with Tβ₄ and PrP (106-126) for 24 h. Tβ₄ significantly reversed cell viability and reactive oxidative species (ROS) affected by PrP (106-126). Apoptotic proteins induced by PrP (106-126) were reduced by Tβ₄. Interestingly, a balance of neurotrophic factors (nerve growth factor and brain-derived neurotrophic factor) and receptors (nerve growth factor receptor p75, tropomyosin related kinase A and B) were competitively maintained by Tβ₄ through receptors reacting to PrP (106-126). Our results demonstrate that Tβ₄ protects neuronal cells against PrP (106-126) neurotoxicity via the interaction of neurotrophic factors/receptors.

Inhibitory effects of sesquiterpene lactones on the aggregation and cytotoxicity of prion neuropeptide

The misfolding and conformational transformation of prion protein (PrP) are crucial to the progression of prion diseases. Screening for available natural inhibitors against prion proteins can contribute to the rational design and development of new anti-prion drugs and therapeutic strategies. The prion neuropeptide, PrP106-126 is commonly used as a model peptide of the abnormal PrP^Sc, and a number of potential inhibitors were explored against the amyloid fibril formation of PrP106-126. The well-known sesquiterpene lactone, artemisinin, shows diverse biological functions in anti-malarial, anti-cancer and lowering glucose. However, its inhibitory effect on PrP106-126 fibrillation is unclear. In this work, we selected two sesquiterpene lactones, artemisinin (1) and artesunate (2), to explore their roles in PrP106-126 aggregation by a series of physicochemical and biochemical methods. The results demonstrated that 1 and 2 could effectively impede the formation of amyloid fibrils and remodel the preformed fibrils. The binding of the small molecules to PrP106-126 was dominated by electrostatic, hydrophobic and hydrogen bonding interactions. In addition, both compounds exhibited neuroprotective effects by reducing peptide oligomerization. 2 showed better inhibition and regulation on peptide aggregation and cellular viability than 1 due to its specific succinate modification. Our study provides the information of sesquiterpene lactones to prevent PrP fibril formation and other related amyloidosis.

Captopril exhibits protective effects through anti-inflammatory and anti-apoptotic pathways against hydrogen peroxide-induced oxidative stress in C6 glioma cells

Recent studies have shown that angiotensin-converting enzyme (ACE) inhibitors have reduced oxidative damage in the central nervous system (CNS). Accumulating evidence have also demonstrated that captopril, an ACE inhibitor, has protective effects on the CNS. However, its effects on hydrogen peroxide (H2O2)-induced oxidative damage in glial cells and interaction with the inflammatory system are still uncertain. Therefore, this study was aimed to investigate the protective effect of captopril on glial cell damage after H2O2-induced oxidative stress involved in the inflammatory and apoptotic pathways. The control group was without any treatment, and the H2O2 group was treated with 0.5 mM H2O2 for 24 h. The captopril group was treated with various concentrations of captopril for 24 h. The captopril + H2O2 group was pre-treated with captopril for 1 h and then exposed to 0.5 mM H2O2 for 24 h. In the captopril + H2O2 group, captopril at all concentrations significantly increased the cell viability in C6 cells. It also significantly increased the TAS and decreased the TOS levels which are an indicator of oxidative stress. Moreover, captopril significantly reduced the inflammation markers including NF-kB, IL-1 β, COX-1, and COX-2 levels. Flow cytometry results also exhibited that captopril pretreatment significantly decreased the apoptosis rate. Besides, captopril significantly reduced apoptotic Bax and raised anti-apoptotic Bcl-2 protein levels. In conclusion, captopril has protective effects on C6 cells after H2O2-induced oxidative damage by inhibiting oxidative stress, inflammation, and apoptosis. However, further studies need to be conducted to evaluate the potential of captopril as a neuroprotective agent.

EZH2 targeting to improve the sensitivity of acquired radio-resistance bladder cancer cells

Among the many treatments for Bladder cancer (BCa) patients, radiotherapy is an effective way to preserve the bladder. However, as the frequency of irradiation increases, the tumor cells appear "acquired radio-resistance" (ARR) and loss the sensitivity to radiotherapy. To explore the molecular mechanism of ARR, two BCa cell lines, 5637 and T24, were enrolled here and their ARR counterparts, 5637R and T24R, were obtained by exposure to γ-ray of 2 Gy for 30 times. Compared to parental cells, ARR cells have significantly enhanced stem cell-like phenotype, robust DNA damage repair capabilities and elevated expression of zeste homolog 2 (EZH2). Decreasing EZH2 expression, both parental and ARR cells exhibited reduced abilities of forming microsphere and repairing DNA damage, but enhanced cells radio-sensitivity and intracellular autophagy compared to untreated cells. Down-regulation the expression of EZH2 induced an increasing of both LC3 and P62 in parental cells, while in ARR cells, only LC3 increased upon EZH2 reduction. On the other hand, UNC1999 treatment caused the increasing of LC3B and P62 in all cells, suggested that siEZH2 and UNC1999 affect ARR cells autophagy through different mechanisms. In vivo study showed that pre-treated with UNC1999 greatly enhanced T24R cells sensitivity to IR, and knocking down the expression of EZH2 significantly suppressed the tumor growth. Combined with bioinformatics data analysis, we speculate that EZH2 is an important biomolecule linking the diagnosis, radiotherapy and prognosis of BCa. EZH2 targeted therapy may be an effective way to overcome ARR of BCa, and is worthy of in-depth study.

The interplay between oxidative stress and autophagy: focus on the development of neurological diseases

Regarding the epidemiological studies, neurological dysfunctions caused by cerebral ischemia or neurodegenerative diseases (NDDs) have been considered a pointed matter. Mount-up shreds of evidence support that both autophagy and reactive oxygen species (ROS) are involved in the commencement and progression of neurological diseases. Remarkably, oxidative stress prompted by an increase of ROS threatens cerebral integrity and improves the severity of other pathogenic agents such as mitochondrial damage in neuronal disturbances. Autophagy is anticipated as a cellular defending mode to combat cytotoxic substances and damage. The recent document proposes that the interrelation of autophagy and ROS creates a crucial function in controlling neuronal homeostasis. This review aims to overview the cross-talk among autophagy and oxidative stress and its molecular mechanisms in various neurological diseases to prepare new perceptions into a new treatment for neurological disorders. Furthermore, natural/synthetic agents entailed in modulation/regulation of this ambitious cross-talk are described.

Calcineurin Activation by Prion Protein Induces Neurotoxicity via Mitochondrial Reactive Oxygen Species

Prion diseases are caused by PrPsc accumulation in the brain, which triggers dysfunctional mitochondrial injury and reactive oxygen species (ROS) generation in neurons. Recent studies on prion diseases suggest that endoplasmic reticulum (ER) stress induced by misfolding proteins such as misfolded prion protein results in activation of calcineurin. Calcineurin is a calcium-related protein phosphatase of type 2B that exists in copious quantities in the brain and acts as a critical nodal component in the control of cellular functions. To investigate the relationship between calcineurin and intracellular ROS, we assessed the alteration of CaN and ROS induced by prion peptide (PrP) 106-126. Human prion peptide increased mitochondrial ROS by activating calcineurin, and the inhibition of calcineurin activity protected mitochondrial function and neuronal apoptosis in neuronal cells. These results suggest that calcineurin plays a pivotal role in neuronal apoptosis by mediating mitochondrial injury and ROS in prion diseases.

Pyrroloquinoline quinone promotes mitochondrial biogenesis in rotenone-induced Parkinson's disease model via AMPK activation

Mitochondrial dysfunction is considered to be one of the important pathogenesis in Parkinson's disease (PD). We previously showed that pyrroloquinoline quinone (PQQ) could protect SH-SY5Y cells and dopaminergic neurons from cytotoxicity and prevent mitochondrial dysfunction in rotenone-induced PD models. In the present study we investigated the mechanisms underlying the protective effects of PQQ in a mouse PD model, which was established by intraperitoneal injection of rotenone (3 mg·kg-1·d-1, ip) for 3 weeks. Meanwhile the mice were treated with PQQ (0.8, 4, 20 mg·kg-1·d-1, ip) right after rotenone injection for 3 weeks. We showed that PQQ treatment dose-dependently alleviated the locomotor deficits and nigral dopaminergic neuron loss in PD mice. Furthermore, PQQ treatment significantly diminished the reduction of mitochondria number and their pathological change in the midbrain. PQQ dose-dependently blocked rotenone-caused reduction in the expression of PGC-1α and TFAM, two key activators of mitochondrial gene transcription, in the midbrain. In rotenone-injured human neuroblastoma SH-SY5Y cells, PTMScan Direct analysis revealed that treatment with PQQ (100 μM) differentially regulated protein phosphorylation; the differentially expressed phosphorylated proteins included the signaling pathways related with adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK) pathway. We conducted Western blot analysis and confirmed that AMPK was activated by PQQ both in PD mice and in rotenone-injured SH-SY5Y cells. Pretreatment with AMPK inhibitor dorsomorphin (4 μM) significantly attenuated the protective effect and mitochondrial biogenesis by PQQ treatment in rotenone-injured SH-SY5Y cells. Taken together, PQQ promotes mitochondrial biogenesis in rotenone-injured mice and SH-SY5Y cells via activation of AMPK signaling pathway.