Heme oxygenase-1 derived carbon monoxide suppresses Aβ1-42 toxicity in astrocytes

Putative Molecular Mechanisms Underpinning the Inverse Roles of Mitochondrial Respiration and Heme Function in Lung Cancer and Alzheimer's Disease

Mitochondria are the powerhouse of the cell. Mitochondria serve as the major source of oxidative stress. Impaired mitochondria produce less adenosine triphosphate (ATP) but generate more reactive oxygen species (ROS), which could be a major factor in the oxidative imbalance observed in Alzheimer's disease (AD). Well-balanced mitochondrial respiration is important for the proper functioning of cells and human health. Indeed, recent research has shown that elevated mitochondrial respiration underlies the development and therapy resistance of many types of cancer, whereas diminished mitochondrial respiration is linked to the pathogenesis of AD. Mitochondria govern several activities that are known to be changed in lung cancer, the largest cause of cancer-related mortality worldwide. Because of the significant dependence of lung cancer cells on mitochondrial respiration, numerous studies demonstrated that blocking mitochondrial activity is a potent strategy to treat lung cancer. Heme is a central factor in mitochondrial respiration/oxidative phosphorylation (OXPHOS), and its association with cancer is the subject of increased research in recent years. In neural cells, heme is a key component in mitochondrial respiration and the production of ATP. Here, we review the role of impaired heme metabolism in the etiology of AD. We discuss the numerous mitochondrial effects that may contribute to AD and cancer. In addition to emphasizing the significance of heme in the development of both AD and cancer, this review also identifies some possible biological connections between the development of the two diseases. This review explores shared biological mechanisms (Pin1, Wnt, and p53 signaling) in cancer and AD. In cancer, these mechanisms drive cell proliferation and tumorigenic functions, while in AD, they lead to cell death. Understanding these mechanisms may help advance treatments for both conditions. This review discusses precise information regarding common risk factors, such as aging, obesity, diabetes, and tobacco usage.

The Role of Gasotransmitter-Dependent Signaling Mechanisms in Apoptotic Cell Death in Cardiovascular, Rheumatic, Kidney, and Neurodegenerative Diseases and Mental Disorders

Cardiovascular, rheumatic, kidney, and neurodegenerative diseases and mental disorders are a common cause of deterioration in the quality of life up to severe disability and death worldwide. Many pathological conditions, including this group of diseases, are based on increased cell death through apoptosis. It is known that this process is associated with signaling pathways controlled by a group of gaseous signaling molecules called gasotransmitters. They are unique messengers that can control the process of apoptosis at different stages of its implementation. However, their role in the regulation of apoptotic signaling in these pathological conditions is often controversial and not completely clear. This review analyzes the role of nitric oxide (NO), carbon monoxide (CO), hydrogen sulfide (H₂S), and sulfur dioxide (SO₂) in apoptotic cell death in cardiovascular, rheumatic, kidney, and neurodegenerative diseases. The signaling processes involved in apoptosis in schizophrenia, bipolar, depressive, and anxiety disorders are also considered. The role of gasotransmitters in apoptosis in these diseases is largely determined by cell specificity and concentration. NO has the greatest dualism; scales are more prone to apoptosis. At the same time, CO, H₂S, and SO₂ are more involved in cytoprotective processes.

Arc Regulates Transcription of Genes for Plasticity, Excitability and Alzheimer’s Disease

The immediate early gene Arc is a master regulator of synaptic function and a critical determinant of memory consolidation. Here, we show that Arc interacts with dynamic chromatin and closely associates with histone markers for active enhancers and transcription in cultured rat hippocampal neurons. Both these histone modifications, H3K27Ac and H3K9Ac, have recently been shown to be upregulated in late-onset Alzheimer’s disease (AD). When Arc induction by pharmacological network activation was prevented using a short hairpin RNA, the expression profile was altered for over 1900 genes, which included genes associated with synaptic function, neuronal plasticity, intrinsic excitability, and signalling pathways. Interestingly, about 100 Arc-dependent genes are associated with the pathophysiology of AD. When endogenous Arc expression was induced in HEK293T cells, the transcription of many neuronal genes was increased, suggesting that Arc can control expression in the absence of activated signalling pathways. Taken together, these data establish Arc as a master regulator of neuronal activity-dependent gene expression and suggest that it plays a significant role in the pathophysiology of AD.

Beneficial and Detrimental Roles of Heme Oxygenase-1 in the Neurovascular System

Heme oxygenase (HO) has both beneficial and detrimental effects via its metabolites, including carbon monoxide (CO), biliverdin or bilirubin, and ferrous iron. HO-1 is an inducible form of HO that is upregulated by oxidative stress, nitric oxide, CO, and hypoxia, whereas HO-2 is a constitutive form that regulates vascular tone and homeostasis. In brains injured by trauma, ischemia-reperfusion, or Alzheimer’s disease (AD), the long-term expression of HO-1 can be detected, which can lead to cytotoxic ferroptosis via iron accumulation. In contrast, the transient induction of HO-1 in the peri-injured region may have regenerative potential (e.g., angiogenesis, neurogenesis, and mitochondrial biogenesis) and neurovascular protective effects through the CO-mediated signaling pathway, the antioxidant properties of bilirubin, and the iron-mediated ferritin synthesis. In this review, we discuss the dual roles of HO-1 and its metabolites in various neurovascular diseases, including age-related macular degeneration, ischemia-reperfusion injury, traumatic brain injury, Gilbert’s syndrome, and AD.

NO, CO and H2S: A Trinacrium of Bioactive Gases in the Brain

Oxygen and carbon dioxide are time honored gases that have direct bearing on almost all life forms, but over the past thirty years, and in large part due to the Nobel Prize Award in Medicine for the elucidation of nitric oxide (NO) as a bioactive gas, the research and medical communities now recognize other gases as critical for survival. In addition to NO, hydrogen sulfide (H₂S) and carbon monoxide (CO) have emerged as a triumvirate or Trinacrium of gases with analogous importance and that serve important homeostatic functions. Perhaps, one of the most intriguing aspects of these gases is the functional interaction between them, which is intimately linked by the enzyme systems that produce them. Despite the need to better understand NO, H₂S and CO biology, the notion that these are environmental pollutants remains ever present. For this reason, incorporating the concept of hormesis becomes imperative and must be included in discussions when considering developing new therapeutics that involve these gases. While there is now an enormous literature base for each of these gasotransmitters, we provide here an overview of their respective physiologic roles in the brain.

Repair Mechanisms of the Neurovascular Unit after Ischemic Stroke with a Focus on VEGF

The functional neural circuits are partially repaired after an ischemic stroke in the central nervous system (CNS). In the CNS, neurovascular units, including neurons, endothelial cells, astrocytes, pericytes, microglia, and oligodendrocytes maintain homeostasis; however, these cellular networks are damaged after an ischemic stroke. The present review discusses the repair potential of stem cells (i.e., mesenchymal stem cells, endothelial precursor cells, and neural stem cells) and gaseous molecules (i.e., nitric oxide and carbon monoxide) with respect to neuroprotection in the acute phase and regeneration in the late phase after an ischemic stroke. Commonly shared molecular mechanisms in the neurovascular unit are associated with the vascular endothelial growth factor (VEGF) and its related factors. Stem cells and gaseous molecules may exert therapeutic effects by diminishing VEGF-mediated vascular leakage and facilitating VEGF-mediated regenerative capacity. This review presents an in-depth discussion of the regeneration ability by which endogenous neural stem cells and endothelial cells produce neurons and vessels capable of replacing injured neurons and vessels in the CNS.

Prophylactic role of Korean red ginseng in astrocytic mitochondrial biogenesis through HIF-1α

Background

Methods

Results

Conclusion

Intersection between Redox Homeostasis and Autophagy: Valuable Insights into Neurodegeneration

Autophagy, a main degradation pathway for maintaining cellular homeostasis, and redox homeostasis have recently been considered to play protective roles in neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis. Increased levels of reactive oxygen species (ROS) in neurons can induce mitochondrial damage and protein aggregation, thereby resulting in neurodegeneration. Oxidative stress is one of the major activation signals for the induction of autophagy. Upon activation, autophagy can remove ROS, damaged mitochondria, and aggregated proteins from the cells. Thus, autophagy can be an effective strategy to maintain redox homeostasis in the brain. However, the interaction between redox homeostasis and autophagy is not clearly elucidated. In this review, we discuss recent studies on the relationship between redox homeostasis and autophagy associated with neurodegenerative diseases and propose that autophagy induction through pharmacological intervention or genetic activation might be a promising strategy to treat these disorders.

Regulation of Endothelial and Vascular Functions by Carbon Monoxide via Crosstalk With Nitric Oxide

Carbon monoxide (CO), generated by heme oxygenase (HO), has been considered a signaling molecule in both the cardiovascular and central nervous systems. The biological function of the HO/CO axis is mostly related to other gaseous molecules, including nitric oxide (NO), which is synthesized by nitric oxide synthase (NOS). Healthy blood vessels are essential for the maintenance of tissue homeostasis and whole-body metabolism; however, decreased or impaired vascular function is a high-risk factor of cardiovascular and neuronal diseases. Accumulating evidence supports that the interplay between CO and NO plays a crucial role in vascular homeostasis and regeneration by improving endothelial function. Moreover, endothelial cells communicate with neighboring cells, such as, smooth muscle cells, immune cells, pericytes, and astrocytes in the periphery and neuronal vascular systems. Endogenous CO could mediate the cell-cell communication and improve the physiological functions of the cardiovascular and neurovascular systems via crosstalk with NO. Thus, a forward, positive feedback circuit between HO/CO and NOS/NO pathways can maintain cardiovascular and neurovascular homeostasis and prevent various human diseases. We discussed the crucial role of CO-NO crosstalk in the cardiovascular and neurovascular systems.

Chemical Reactivities of Two Widely Used Ruthenium-Based CO-Releasing Molecules with a Range of Biologically Important Reagents and Molecules

Ruthenium-based CO-releasing molecules (CO-RMs), CORM-2 and CORM-3, have been widely used as surrogates of CO for studying its biological effects in vitro and in vivo with much success. However, several previous solution-phase and in vitro studies have revealed the ability of such CO-RMs to chemically modify proteins and reduce aromatic nitro groups due to their intrinsic chemical reactivity under certain conditions. In our own work of studying the cytoprotective effects of CO donors, we were in need of assessing chemical factors that could impact the interpretation of results from CO donors including CORM-2,3 in various in vitro assays. For this, we examined the effects of CORM-2,3 toward representative reagents commonly used in various bioassays including resazurin, tetrazolium salts, nitrites, and azide-based H₂S probes. We have also examined the effect of CORM-2,3 on glutathione disulfide (GSSG), which is a very important redox regulator. Our studies show the ability of these CO-RMs to induce a number of chemical and/or spectroscopic changes for several commonly used biological reagents under near-physiological conditions. These reactions/spectroscopic changes cannot be duplicated with CO-deleted CO-RMs (iCORMs), which are often used as negative controls. Furthermore, both CORM-2 and -3 are capable of consuming and reducing GSSG in solution. We hope that the results described will help in the future design of control experiments using Ru-based CO-RMs.

Gasotransmitter signaling in energy homeostasis and metabolic disorders

Gasotransmitters are small molecules of gases, including nitric oxide (NO), hydrogen sulfide (H₂S), and carbon monoxide (CO). These three gasotransmitters can be endogenously produced and regulate a wide range of pathophysiological processes by interacting with specific targets upon diffusion in the biological media. By redox and epigenetic regulation of various physiological functions, NO, H₂S, and CO are critical for the maintenance of intracellular energy homeostasis. Accumulated evidence has shown that these three gasotransmitters control ATP generation, mitochondrial biogenesis, glucose metabolism, insulin sensitivity, lipid metabolism, and thermogenesis, etc. Abnormal generation and metabolism of NO, H₂S, and/or CO are involved in various abnormal metabolic diseases, including obesity, diabetes, and dyslipidemia. In this review, we summarized the roles of NO, H₂S, and CO in the regulation of energy homeostasis as well as their involvements in the metabolism of dysfunction-related diseases. Understanding the interaction among these gasotransmitters and their specific molecular targets are very important for therapeutic applications.

Pterostilbene Alleviates Aβ1-42 -Induced Cognitive Dysfunction via Inhibition of Oxidative Stress by Activating Nrf2 Signaling Pathway

SCOPE

In the present study, effect of pterostilbene on β-amyloid 1-42 (Aβ_1-42 ) induced cognitive impairment in mice is investigated and explored its possible mechanism of action.

METHODS AND RESULTS

The behavior results show that pterostilbene alleviated Aβ_1-42 -induces cognitive dysfunction assessed using the Y-maze test, novel object recognition task, Morris water maze test, and passive avoidance test. Pterostilbene alleviates neuron loss and accumulation of reactive oxygen species in Aβ_1-42 treated mouse brain. Additionally, pterostilbene promotes nuclear factor-E2 p45-related factor 2 (Nrf2) nuclear translocation and enhance the transcription and expression of antioxidant genes such as heme oxygenase-1 and superoxide dismutase both in vivo and in vitro. Nrf2 inhibitor ML385 reverses the antioxidant function of pterostilbene in SH-SY5Y cells. Nrf2 is the master regulator of oxidative homeostasis and can be activated by substrate adaptor sequestosome-1 (also named p62). Pterostilbene promotes the binding of Kelch-like ECH-associated protein 1 and p62, which enhanced activation of Nrf2.

CONCLUSION

The present study reports that pterostilbene alleviated Aβ_1-42 -induces cognitive dysfunction in mice. The mechanism of pterostilbene can be associated to the inhibition of oxidative stress through the Nrf2 signaling pathway.

Celecoxib Exerts Neuroprotective Effects in β-Amyloid-Treated SH-SY5Y Cells Through the Regulation of Heme Oxygenase-1: Novel Insights for an Old Drug

The formation and aggregation of amyloid-β-peptide (Aβ) into soluble and insoluble species represent the pathological hallmarks of Alzheimer’s disease (AD). Over the last few years, however, soluble Aβ (sAβ) prevailed over fibrillar Aβ (fAβ) as determinant of neurotoxicity. One of the main therapeutic strategies for challenging neurodegeneration is to fight against neuroinflammation and prevent free radical-induced damage: in this light, the heme oxygenase/biliverdin reductase (HO/BVR) system is considered a promising drug target. The aim of this work was to investigate whether or not celecoxib (CXB), a selective inhibitor of the pro-inflammatory cyclooxygenase-2, modulates the HO/BVR system and prevents lipid peroxidation in SH-SY5Y neuroblastoma cells. Both sAβ (6.25–50 nM) and fAβ (1.25–50 nM) dose-dependently over-expressed inducible HO (HO-1) after 24 h of incubation, reaching statistical significance at 25 and 6.25 nM, respectively. Interestingly, CXB (1–10 μM, for 1 h) further enhanced Aβ-induced HO-1 expression through the nuclear translocation of the transcriptional factor Nrf2. Furthermore, 10 μM CXB counteracted the Aβ-induced ROS production with a mechanism fully dependent on HO-1 up-regulation; nevertheless, 10 μM CXB significantly counteracted only 25 nM sAβ-induced lipid peroxidation damage in SH-SY5Y neurons by modulating HO-1. Both carbon monoxide (CORM-2, 50 nM) and bilirubin (50 nM) significantly prevented ROS production in Aβ-treated neurons and favored both the slowdown of the growth rate of Aβ oligomers and the decrease in oligomer/fibril final size. In conclusion, these results suggest a novel mechanism through which CXB is neuroprotective in subjects with early AD or mild cognitive impairment.

The Role of Bilirubin and the Other "Yellow Players" in Neurodegenerative Diseases

Bilirubin is a yellow endogenous derivate of the heme catabolism. Since the 1980s, it has been recognized as one of the most potent antioxidants in nature, able to counteract 10,000× higher intracellular concentrations of H2O2. In the recent years, not only bilirubin, but also its precursor biliverdin, and the enzymes involved in their productions (namely heme oxygenase and biliverdin reductase; altogether the "yellow players"-YPs) have been recognized playing a protective role in diseases characterized by a chronic prooxidant status. Based on that, there is an ongoing effort in inducing their activity as a therapeutic option. Nevertheless, the understanding of their specific contributions to pathological conditions of the central nervous system (CNS) and their role in these diseases are limited. In this review, we will focus on the most recent evidence linking the role of the YPs specifically to neurodegenerative and neurological conditions. Both the protective, as well as potentially worsening effects of the YP's activity will be discussed.

Antioxidant and neuroprotective effects of mGlu3 receptor activation on astrocytes aged in vitro

Astrocytes play a key role by providing antioxidant support to nearby neurons under oxidative stress. We have previously demonstrated that in vitro astroglial subtype 3 metabotropic glutamate receptor (mGlu3R) is neuroprotective. However, its role during aging has been poorly explored. Our study aimed to determine whether LY379268, an mGlu3R agonist, exerts an antioxidant effect on aged cultured rat astrocytes. Aged cultured astrocytes obtained after 9-weeks (9w) in vitro were positive for β-galactosidase stain, showed decreased mGlu3R and glutathione (GSH) levels and superoxide dismutase (SOD) activity, while nuclear erythroid factor 2 (Nrf2) protein levels, reactive oxygen species (ROS) production and apoptosis were increased. Treatment of 9w astrocytes with LY379268 resulted in an increase in mGlu3R and Nrf2 protein levels and SOD activity, and decreased mitochondrial ROS levels and apoptosis. mGlu3R activation in aged astrocytes also prevented hippocampal neuronal death induced by Aβ_1-42 in co-culture assays. We conclude that activation of mGlu3R in aged astrocytes had an anti-oxidant effect and protected hippocampal neurons against Aβ-induced neurotoxicity. The present study suggests mGlu3R activation in aging astrocytes as a therapeutic strategy to slow down age-associated neurodegeneration.

Modulation of Amyloidogenic Peptide Aggregation by Photoactivatable CO-Releasing Ruthenium(II) Complexes

Three Ru(II)-based CO-releasing molecules featuring bidentate benzimidazole and terpyridine derivatives as ligands were investigated for their ability to modulate the aggregation process of the second helix of the C-terminal domain of nucleophosmin 1, namely nucleophosmin 1 (NPM1)_264-277, a model amyloidogenic system, before and after irradiation at 365 nm. Thioflavin T (ThT) binding assays and UV/Vis absorption spectra indicate that binding of the compounds to the peptide inhibits its aggregation and that the inhibitory effect increases upon irradiation (half maximal effective concentration (EC₅₀) values in the high micromolar range). Electrospray ionization mass spectrometry data of the peptide in the presence of one of these compounds confirm that the modulation of amyloid aggregation relies on the formation of adducts obtained when the Ru compounds react with the peptide upon releasing of labile ligands, like chloride and carbon monoxide. This mechanism of action explains the subtle different behavior of the three compounds observed in ThT experiments. Overall, data support the hypothesis that metal-based CO releasing molecules can be used to develop metal-based drugs with potential application as anti-amyloidogenic agents.

Aging and Progression of Beta-Amyloid Pathology in Alzheimer's Disease Correlates with Microglial Heme-Oxygenase-1 Overexpression

Neuroinflammation and oxidative stress are being recognized as characteristic hallmarks in many neurodegenerative diseases, especially those that portray proteinopathy, such as Alzheimer’s disease (AD). Heme-oxygenase 1 (HO-1) is an inducible enzyme with antioxidant and anti-inflammatory properties, while microglia are the immune cells in the central nervous system. To elucidate the brain expression profile of microglial HO-1 in aging and AD-progression, we have used the 5xFAD (five familial AD mutations) mouse model of AD and their littermates at different ages (four, eight, 12, and 18 months). Total brain expression of HO-1 was increased with aging and such increase was even higher in 5xFAD animals. In co-localization studies, HO-1 expression was mainly found in microglia vs. other brain cells. The percentage of microglial cells expressing HO-1 and the amount of HO-1 expressed within microglia increased progressively with aging. Furthermore, this upregulation was increased by 2–3-fold in the elder 5xFAD mice. In addition, microglia overexpressing HO-1 was predominately found surrounding beta-amyloid plaques. These results were corroborated using postmortem brain samples from AD patients, where microglial HO-1 was found up-regulated in comparison to brain samples from aged matched non-demented patients. This study demonstrates that microglial HO-1 expression increases with aging and especially with AD progression, highlighting HO-1 as a potential biomarker or therapeutic target for AD.

Regenerative Potential of Carbon Monoxide in Adult Neural Circuits of the Central Nervous System

Regeneration of adult neural circuits after an injury is limited in the central nervous system (CNS). Heme oxygenase (HO) is an enzyme that produces HO metabolites, such as carbon monoxide (CO), biliverdin and iron by heme degradation. CO may act as a biological signal transduction effector in CNS regeneration by stimulating neuronal intrinsic and extrinsic mechanisms as well as mitochondrial biogenesis. CO may give directions by which the injured neurovascular system switches into regeneration mode by stimulating endogenous neural stem cells and endothelial cells to produce neurons and vessels capable of replacing injured neurons and vessels in the CNS. The present review discusses the regenerative potential of CO in acute and chronic neuroinflammatory diseases of the CNS, such as stroke, traumatic brain injury, multiple sclerosis and Alzheimer’s disease and the role of signaling pathways and neurotrophic factors. CO-mediated facilitation of cellular communications may boost regeneration, consequently forming functional adult neural circuits in CNS injury.

Endocytosis and Transcytosis of Amyloid-β Peptides by Astrocytes: A Possible Mechanism for Amyloid-β Clearance in Alzheimer's Disease

Amyloid-β (Aβ) peptides, Aβ40, Aβ42, and recently Aβ25 - 35, have been directly implicated in the pathogenesis of Alzheimer's disease (AD). We have previously shown that all three peptides decrease neuronal viability, but Aβ40 also promotes synaptic disassembling. In this work, we have studied the effects of these peptides on astrocytes in primary culture and found that the three Aβ peptides were internalized by astrocytes and significantly decreased astrocyte viability, while increasing ROS production. Aβ peptide internalization is temperature-dependent, a fact that supports the idea that Aβ peptides are actively endocytosed by astrocytes. However, inhibiting caveolae formation by methyl-beta-cyclodextrin or by silencing caveolin-1 with RNA interference did not prevent Aβ endocytosis, which suggests that Aβ peptides do not use caveolae to enter astrocytes. Conversely, inhibition of clathrin-coated vesicle formation by chlorpromazine or by silencing clathrin with RNA interference significantly decreased Aβ internalization and partially reverted the decrease of astrocyte viability caused by the presence of Aβ. These results suggest that Aβ is endocytosed by clathrin-coated vesicles in astrocytes. Aβ-loaded astrocytes, when co-incubated with non-treated astrocytes in separate wells but with the same incubation medium, promoted cell death in non-treated astrocytes; a fact that was associated with the presence of Aβ inside previously unloaded astrocytes. This phenomenon was inhibited by the presence of chlorpromazine in the co-incubation medium. These results suggest that astrocyte may perform Aβ transcytosis, a process that could play a role in the clearance of Aβ peptides from the brain to cerebrospinal fluid.

Investigating in Vitro Amyloid Peptide 1-42 Aggregation: Impact of Higher Molecular Weight Stable Adducts

The self-assembly of amyloid peptides (Aβ), in particular Aβ_1-42, into oligomers and fibrils is one of the main pathological events related to Alzheimer's disease. Recent studies have demonstrated the ability of carbon monoxide-releasing molecules (CORMs) to protect neurons and astrocytes from Aβ_1-42 toxicity. In fact, CORMs are able to carry and release controlled levels of CO and are known to exert a wide range of anti-inflammatory and anti-apoptotic activities at physiologically relevant concentrations. In order to investigate the direct effects of CORMs on Aβ_1-42, we studied the reactivity of CORM-2 and CORM-3 with Aβ_1-42 in vitro and the potential inhibition of its aggregation by mass spectrometry (MS), as well as fluorescence and circular dichroism spectroscopies. The application of an electrospray ionization-MS (ESI-MS) method allowed the detection of stable Aβ_1-42/CORMs adducts, involving the addition of the Ru(CO)₂ portion of CORMs at histidine residues on the Aβ_1-42 skeleton. Moreover, CORMs showed anti-aggregating properties through formation of stable adducts with Aβ_1-42 as demonstrated by a thioflavin T fluorescence assay and MS analysis. As further proof, comparison of the CD spectra of Aβ_1-42 recorded in the absence and in the presence of CORM-3 at a 1:1 molar ratio showed the ability of CORM-3 to stabilize the peptide in its soluble, unordered conformation, thereby preventing its misfolding and aggregation. This multi-methodological investigation revealed novel interactions between Aβ_1-42 and CORMs, contributing new insights into the proposed neuroprotective mechanisms mediated by CORMs and disclosing a new strategy to divert amyloid aggregation and toxicity.

The Role of Astrocytes in the Central Nervous System Focused on BK Channel and Heme Oxygenase Metabolites: A Review

Astrocytes outnumber neurons in the human brain, and they play a key role in numerous functions within the central nervous system (CNS), including glutamate, ion (i.e., Ca²⁺, K⁺) and water homeostasis, defense against oxidative/nitrosative stress, energy storage, mitochondria biogenesis, scar formation, tissue repair via angiogenesis and neurogenesis, and synapse modulation. After CNS injury, astrocytes communicate with surrounding neuronal and vascular systems, leading to the clearance of disease-specific protein aggregates, such as β-amyloid, and α-synuclein. The astrocytic big conductance K⁺ (BK) channel plays a role in these processes. Recently, potential therapeutic agents that target astrocytes have been tested for their potential to repair the brain. In this review, we discuss the role of the BK channel and antioxidant agents such as heme oxygenase metabolites following CNS injury. A better understanding of the cellular and molecular mechanisms of astrocytes’ functions in the healthy and diseased brains will greatly contribute to the development of therapeutic approaches following CNS injury, such as Alzheimer’s disease, Parkinson’s disease, and stroke.

Astrocyte Biomarkers in Alzheimer's Disease

Astrocytic contributions to Alzheimer's disease (AD) progression were, until recently, largely overlooked. Astrocytes are integral to normal brain function and astrocyte reactivity is an early feature of AD, potentially providing a promising target for preclinical diagnosis and treatment. Several in vivo AD biomarkers already exist, but presently there is a paucity of specific and sensitive in vivo astrocyte biomarkers that can accurately measure preclinical AD. Measuring monoamine oxidase-B with neuroimaging and glial fibrillary acidic protein from bodily fluids are biomarkers that are currently available. Developing novel, more specific, and sensitive astrocyte biomarkers will make it possible to pharmaceutically target chemical pathways that preserve beneficial astrocytic functions in response to AD pathology. This review discusses astrocyte biomarkers in the context of AD.

Dexmedetomidine attenuates the toxicity of β‑amyloid on neurons and astrocytes by increasing BDNF production under the regulation of HDAC2 and HDAC5

Cytotoxicity of β-Amyloid (Aβ) is a major contributor to the pathogenesis of Alzheimer's disease. Dexmedetomidine (Dex) has been revealed to have multiple neuroprotective actions as a clinical anesthetic agent. The aim of the present study was to investigate the protection of Dex against Aβ in neurons and astrocytes, and the possible protective mechanisms. Primary neurons and astrocytes were isolated respectively from the hippocampus and cerebral cortex of neonatal Sprague Dawley rats. The neurons and astrocytes were incubated with Aβ in the presence or absence of Dex, which was followed by evaluation of the cell viability and apoptosis. Reverse transcription‑quantitative polymerase chain reaction, western blotting and ELISA assays were performed to assess the levels of specific genes or proteins. The results revealed that Aβ decreased the viabilities of neurons and astrocytes in a dose‑dependent manner, and elevated the rate of apoptosis. However, Dex attenuated the detrimental effects of Aβ. Aβ caused deacetylation of histone H3 by promoting the accumulation of histone deacetylase (HDAC)‑2 and HDAC5 in the cell nucleus, resulting in the reduced production of brain‑derived neurotrophic factor (BDNF). However, Dex reversed the Aβ‑induced deacetylation of histone H3 and thus, increased BDNF production. Using a HDAC inhibitor or recombinant BDNF protein also protected the neurons and astrocytes against Aβ cytotoxicity. These results suggested that the protective effect of Dex against Aβ is particularly relevant to BDNF. Thus, the present study provides a foundation for the further study of Dex protection against Aβ in animal models and pre‑clinical researches.

Heme Oxygenase 1 in the Nervous System: Does It Favor Neuronal Cell Survival or Induce Neurodegeneration?

Heme oxygenase 1 (HO-1) up-regulation is recognized as a pivotal mechanism of cell adaptation to stress. Under control of different transcription factors but with a prominent role played by Nrf2, HO-1 induction is crucial also in nervous system response to damage. However, several lines of evidence have highlighted that HO-1 expression is associated to neuronal damage and neurodegeneration especially in Alzheimer’s and Parkinson’s diseases. In this review, we summarize the current literature regarding the role of HO-1 in nervous system pointing out different molecular mechanisms possibly responsible for HO-1 up-regulation in nervous system homeostasis and neurodegeneration.

Ginsenoside Rg1 and Acori Graminei Rhizoma Attenuates Neuron Cell Apoptosis by Promoting the Expression of miR-873-5p in Alzheimer's Disease

Alzheimer's disease (AD) severely threatens human health in their old age, however the potential etiology underlying it is still unclear. Both Ginsenoside Rg1 (GRg1) and Acori graminei Rhizoma (AGR) are the traditional Chinese herbal drug, while their potential role in AD remains need further identification. Both SAMP1 and SAMP8 mice were employed as the control and AD mice. Morris water maze method was used to detect the cognitive function of the mice, TUNEL assay was performed to determine cell apoptosis. Real-time PCR and western blot were carried out to measure gene expression. The relationship between miR-873-5p and HMOX1 was determined using luciferase reporter assay. Comparing with SAMP1, the cognitive function was impaired and cell apoptosis was increased in SAMP8 mice. GRg1 + AGR treatment significantly attenuated the symptom of AD. The expression of miR-873-5p was decreased, while HMOX1 was increased in SAMP8 mice. GRg1 + AGR treatment significantly promoted the expression of miR-873-5p, but decreased HMOX1. MiR-873-5p targets HMOX1 to regulate its expression. Aβ1-42 stimulation decreased the expression of miR-873-5p, but increased HMOX1 in PC12 cells. GRg1 + AGR treatment reversed the effect of Aβ1-42, while miR-873-5p inhibitor abolished the effect of GRg1 + AGR. In vivo experiments confirmed the protect role of GRg1 + AGR in AD. GRg1 + AGR suppressed neuron cell apoptosis by regulating the expression of miR-873-5p in AD.

Could Heme Oxygenase-1 Be a New Target for Therapeutic Intervention in Malaria-Associated Acute Lung Injury/Acute Respiratory Distress Syndrome?

Malaria is a serious disease and was responsible for 429,000 deaths in 2015. Acute lung injury/acute respiratory distress syndrome (ALI/ARDS) is one of the main clinical complications of severe malaria; it is characterized by a high mortality rate and can even occur after antimalarial treatment when parasitemia is not detected. Rodent models of ALI/ARDS show similar clinical signs as in humans when the rodents are infected with murine Plasmodium. In these models, it was shown that the induction of the enzyme heme oxygenase 1 (HO-1) is protective against severe malaria complications, including cerebral malaria and ALI/ARDS. Increased lung endothelial permeability and upregulation of VEGF and other pro-inflammatory cytokines were found to be associated with malaria-associated ALI/ARDS (MA-ALI/ARDS), and both were reduced after HO-1 induction. Additionally, mice were protected against MA-ALI/ARDS after treatment with carbon monoxide- releasing molecules or with carbon monoxide, which is also released by the HO-1 activity. However, high HO-1 levels in inflammatory cells were associated with the respiratory burst of neutrophils and with an intensification of inflammation during episodes of severe malaria in humans. Here, we review the main aspects of HO-1 in malaria and ALI/ARDS, presenting the dual role of HO-1 and possibilities for therapeutic intervention by modulating this important enzyme.

Hmox1 promotes osteogenic differentiation at the expense of reduced adipogenic differentiation induced by BMP9 in C3H10T1/2 cells

Mesenchymal stem cells (MSCs) are multipotent progenitors that can differentiate into a variety of cell types under proper stimuli. Bone morphogenetic protein 9 (BMP9) is able to simultaneously induce both adipogenic and osteogenic differentiation of MSCs although the regulatory molecules involved remain to be fully identified and characterized. Heme oxygenase 1 (Hmox1) plays an essential role not only in fat metabolism, but also in bone development. In the present study, we investigated the functional role of Hmox1 in BMP9-induced osteogenic/adipogenic differentiation in MSCs line C3H10T1/2 and probed the possible mechanism involved. We found that BMP9 promoted the endogenous expression of Hmox1 in C3H10T1/2 cells. Overexpression of Hmox1 or cobalt protoporphyrin (CoPP), an inducer of Hmox1, increased BMP9-induced osteogenic differentiation in vitro. Subcutaneous stem cell implantation in nude mice further confirmed that Hmox1 potentiated BMP9-induced ectopic bone formation in vivo. In contrast, Hmox1 reduced BMP9-induced adipogenic differentiation in C3H10T1/2 cells. Although had no obvious effect on BMP9-induced Smad1/5/8 phosphorylation, Hmox1 enhanced phosphorylation of p38, and AKT, while decreased phosphorylation of ERK1/2. Furthermore, Hmox1 increased total β-catenin protein level, and promoted the nuclear translocation of β-catenin in C3H10T1/2 cells. Taken together, our study strongly suggests that Hmox1 is likely to potentiate osteogenic differentiation and yet decrease adipogenic differentiation induced by BMP9 possibly through regulation of multiple signaling pathways.