Hydrogen sulfide down-regulates BACE1 and PS1 via activating PI3K/Akt pathway in the brain of APP/PS1 transgenic mouse

A novel NIR fluorescent probe for visualizing hydrogen sulfide in Alzheimer's disease

Alzheimer's disease (AD) represents a devastating form of neurodegeneration, hallmarked by a relentless erosion of memory and cognitive faculties. One key player in this complex pathology is hydrogen sulfide (H2S), a gaseous neurotransmitter that is highly concentrated in the brain. Its fluctuating levels have been compellingly linked to the onset and progression of AD. Despite the availability of numerous fluorescent probes for detecting H2S, targeted imaging of this neurotransmitter within AD models remains underexplored. To bridge this gap, we have engineered an innovative near-infrared (NIR) "turn-on" fluorescent probe, designated as probe 1. Crafted around a dicyanoisophorone scaffold, the probe incorporates a strategic methoxy modification to facilitate a bathochromic spectral shift. Impressively, upon binding with H2S, probe 1 exhibited a robust 46-fold enhancement in fluorescence at a wavelength of 680 nm. We successfully deployed this probe to visualize both exogenous and endogenous H2S in living cells and zebrafish. Further, our pathogenic investigations have corroborated that diminished H2S levels are intricately linked to an escalation in amyloid plaque formation. Most crucially, we employed probe 1 to capture real-time images of H2S concentrations within the hippocampal tissue of AD mouse models. This revealed a significant depletion in H2S levels, thereby underscoring the probe's immense potential as an effective tool for the diagnosis and prevention of Alzheimer's disease.

What Threshold of Amyloid Reduction Is Necessary to Meaningfully Improve Cognitive Function in Transgenic Alzheimer's Disease Mice?

Background

Amyloid-β plaques (Aβ) are associated with Alzheimer's disease (AD). Pooled assessment of amyloid reduction in transgenic AD mice is critical for expediting anti-amyloid AD therapeutic research.

Objective

The mean threshold of Aβ reduction necessary to achieve cognitive improvement was measured via pooled assessment (n = 594 mice) of Morris water maze (MWM) escape latency of transgenic AD mice treated with substances intended to reduce Aβ via reduction of beta-secretase cleaving enzyme (BACE).

Methods

Machine learning and statistical methods identified necessary amyloid reduction levels using mouse data (e.g., APP/PS1, LPS, Tg2576, 3xTg-AD, control, wild type, treated, untreated) curated from 22 published studies.

Results

K-means clustering identified 4 clusters that primarily corresponded with level of Aβ: untreated transgenic AD control mice, wild type mice, and two clusters of transgenic AD mice treated with BACE inhibitors that had either an average 25% "medium reduction" of Aβ or 50% "high reduction" of Aβ compared to untreated control. A 25% Aβ reduction achieved a 28% cognitive improvement, and a 50% Aβ reduction resulted in a significant 32% improvement compared to untreated transgenic mice (p < 0.05). Comparatively, wild type mice had a mean 41% MWM latency improvement over untreated transgenic mice (p < 0.05). BACE reduction had a lesser impact on the ratio of Aβ42 to Aβ40. Supervised learning with an 80% -20% train-test split confirmed Aβ reduction was a key feature for predicting MWM escape latency (R2 = 0.8 to 0.95).

Conclusions

Results suggest a 25% reduction in Aβ as a meaningful treatment threshold for improving transgenic AD mouse cognition.

Tetrahydroalstonine possesses protective potentials on palmitic acid stimulated SK-N-MC cells by suppression of Aβ1-42 and tau through regulation of PI3K/Akt signaling pathway

Alzheimer's disease (AD) is the most common neurodegenerative disease. The morbidity of Alzheimer's disease is currently on the rise worldwide, but no effective treatment is available. Cornus officinalis is an herb and edible plant used in traditional Chinese medicine, whose extract has neuroprotective properties. In this investigation, we endeavored to refine a systems pharmacology strategy combining bioinformatics analysis, drug prediction, network pharmacology, and molecular docking to screen tetrahydroalstonine (THA) from Cornus officinalis as a therapeutic component for AD. Subsequent in vitro experiments were validated using MTT assay, Annexin V-PI flow cytometry, Western blotting, and immunofluorescence analysis. In Palmitate acid-induced SK-N-MC cells, THA restored the impaired PI3K/AKT signaling pathway, regulated insulin resistance, and attenuated BACE1 and GSK3β activity. In addition, THA significantly reduced cell apoptosis rate, down-regulated relative levels of p-JNK/JNK, Bax/Bcl-2, cytochrome C, active caspase-3 and caspase-3, and attenuated Palmitate acid-induced Aβ1-42 and Tau generation. THA may regulate the phenotype of AD and reduce cell apoptosis by modulating the PI3K/AKT signaling pathway. This systematic analysis provides new ramifications concerning the therapeutic utility of tetrahydroalstonine for AD.

Mechanisms Underlying the Hydrogen Sulfide Actions: Target Molecules and Downstream Signaling Pathways

Significance: As a new important gas signaling molecule like nitric oxide (NO) and carbon dioxide (CO), hydrogen sulfide (H2S), which can be produced by endogenous H2S-producing enzymes through l-cysteine metabolism in mammalian cells, has attracted wide attention for long. H2S has been proved to play an important regulatory role in numerous physiological and pathophysiological processes. However, the deep mechanisms of those different functions of H2S still remain uncertain. A better understanding of the mechanisms can help us develop novel therapeutic strategies. Recent Advances: H2S can play a regulating role through various mechanisms, such as regulating epigenetic modification, protein expression levels, protein activity, protein localization, redox microenvironment, and interaction with other gas signaling molecules such as NO and CO. In addition to discussing the molecular mechanisms of H2S from the above perspectives, this article will review the regulation of H2S on common signaling pathways in the cells, including the phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt), mitogen-activated protein kinase (MAPK), Janus kinase (JAK)/signal transducer, and activator of transcription (STAT) signaling pathway. Critical Issues: Although there are many studies on the mechanism of H2S, little is known about its direct target molecules. This article will also review the existing reports about them. Furthermore, the interaction between direct target molecules of H2S and the downstream signaling pathways involved also needs to be clarified. Future Directions: An in-depth discussion of the mechanism of H2S and the direct target molecules will help us achieving a deeper understanding of the physiological and pathophysiological processes regulated by H2S, and lay a foundation for developing new clinical therapeutic drugs in the future. Innovation: This review focuses on the regulation of H2S on signaling pathways and the direct target molecules of H2S. We also provide details on the underlying mechanisms of H2S functions from the following aspects: epigenetic modification, regulation of protein expression levels, protein activity, protein localization, redox microenvironment, and interaction with other gas signaling molecules such as NO and CO. Further study of the mechanisms underlying H2S will help us better understand the physiological and pathophysiological processes it regulates, and help develop new clinical therapeutic drugs in the future. Antioxid. Redox Signal. 40, 86-109.

Tanshinone IIA, the key compound in Salvia miltiorrhiza, improves cognitive impairment by upregulating Aβ-degrading enzymes in APP/PS1 mice

In Alzheimer's disease (AD), amyloid-beta (Aβ) plays a crucial role in pathogenesis. Clearing Aβ from the brain is considered as a key therapeutic strategy. Previous studies indicated that Salvia miltiorrhiza (Danshen) could protect against AD. However, the main anti-AD components in Danshen and their specific mechanisms are not clear. In this study, pharmacological network analysis indicated that Tanshinone IIA (Tan IIA) was identified as the key active compound in Danshen contributing to protect against AD. Then, APP/PS1 double transgenic mice were employed to examine the neuroprotective effect of Tan IIA. APP/PS1 mice (age, 6 months) were administered (10 and 20 mg/kg) for 8 weeks. Tan IIA improved learning and anxiety behaviors in APP/PS1 mice. Furthermore, Tan IIA reduced oxidative stress, inhibited neuronal apoptosis, improved cholinergic nervous system and decreased endoplasmic reticulum stress in the brain of APP/PS1 mice. Moreover, Tan IIA treatment reduced the level of Aβ. Molecular docking result showed that Tan IIA might block AD by upregulating Aβ-degrading enzymes. Western blot results confirmed that the expressions of insulin degrading enzymes (IDE) and neprilysin (NEP) were significantly increased after Tan IIA treatment, which demonstrated that Tan IIA improved AD by increasing Aβ-degrading enzymes.

Preliminary In Vitro and In Vivo Insights of In Silico Candidate Repurposed Drugs for Alzheimer's Disease

Alzheimer's disease (AD) is a progressive neurodegenerative disease and is the most common type of dementia. Although a considerably large amount of money has been invested in drug development for AD, no disease modifying treatment has been detected so far. In our previous work, we developed a computational method to highlight stage-specific candidate repurposed drugs against AD. In this study, we tested the effect of the top 13 candidate repurposed drugs that we proposed in our previous work in a severity stage-specific manner using an in vitro BACE1 assay and the effect of a top-ranked drug from the list of our previous work, tetrabenazine (TBZ), in the 5XFAD as an AD mouse model. From our in vitro screening, we detected 2 compounds (clomiphene citrate and Pik-90) that showed statistically significant inhibition against the activity of the BACE1 enzyme. The administration of TBZ at the selected dose and therapeutic regimen in 5XFAD in male and female mice showed no significant effect in behavioral tests using the Y-maze and the ELISA immunoassay of Aβ40. To our knowledge, this is the first time the drug tetrabenazine has been tested in the 5XFAD mouse model of AD in a sex-stratified manner. Our results highlight 2 drugs (clomiphene citrate and Pik-90) from our previous computational work for further investigation.

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.

Activation of TNF Receptor 2 Improves Synaptic Plasticity and Enhances Amyloid-β Clearance in an Alzheimer's Disease Mouse Model with Humanized TNF Receptor 2

BACKGROUND

Tumor necrosis factor-alpha (TNF-α) is a master cytokine involved in a variety of inflammatory and neurological diseases, including Alzheimer's disease (AD). Therapies that block TNF-α proved ineffective as therapeutic for neurodegenerative diseases, which might be explained by the opposing functions of the two receptors of TNF (TNFRs): while TNFR1 stimulation mediates inflammatory and apoptotic pathways, activation of TNFR2 is related to neuroprotection. Despite the success of targeting TNFR2 in a transgenic AD mouse model, research that better mimics the human context is lacking.

OBJECTIVE

The aim of this study is to investigate whether stimulation of TNFR2 with a TNFR2 agonist is effective in activating human TNFR2 and attenuating AD neuropathology in the J20xhuTNFR2-k/i mouse model.

METHODS

Transgenic amyloid-β (Aβ)-overexpressing mice containing a human extracellular TNFR2 domain (J20xhuTNFR2-k/i) were treated with a TNFR2 agonist (NewStar2). After treatment, different behavioral tests and immunohistochemical analysis were performed to assess different parameters, such as cognitive functions, plaque deposition, synaptic plasticity, or microglial phagocytosis.

RESULTS

Treatment with NewStar2 in J20xhuTNFR2-k/i mice resulted in a drastic decrease in plaque load and beta-secretase 1 (BACE-1) compared to controls. Moreover, TNFR2 stimulation increased microglial phagocytic activity, leading to enhanced Aβ clearance. Finally, activation of TNFR2 rescued cognitive impairments and improved synaptic plasticity.

CONCLUSION

Our findings demonstrate that activation of human TNFR2 ameliorates neuropathology and improves cognitive functions in an AD mouse model. Moreover, our study confirms that the J20xhuTNFR2-k/i mouse model is suitable for testing human TNFR2-specific compounds.

Effects of methionine intake on cognitive function in mild cognitive impairment patients and APP/PS1 Alzheimer's Disease model mice: Role of the cystathionine-β-synthase/H2S pathway

As a dietary intervention, methionine restriction (MR) has been reported to increase longevity and improve metabolism disorders. However, the effects of MR on alleviating neurodegenerative diseases such as Alzheimer's disease (AD) are largely unexplored. Here we sought to investigate the neuroprotective effects of low methionine intake in mild cognitive impairment (MCI) patients and APP/PS1 AD model mice, and to uncover the underlying mechanisms. In a cohort composed of 45 individuals diagnosed with MCI and 61 healthy controls without cognitive impairment, methionine intake was found to be positively associated with the increased risk of MCI, where no sex differences were observed. We further conducted a 16-week MR intervention (0.17% methionine, w/w) on APP/PS1 AD model mice. Although MR reduced Aβ accumulation in the brain of both male and female APP/PS1 mice, MR improved cognitive function only in male mice, as assessed by the Morris water maze test. Consistently, MR restored synapse ultrastructure and alleviated mitochondrial dysfunction by enhancing mitochondrial biogenesis in the brain of male APP/PS1 mice. Importantly, MR effectively balanced the redox status and activated cystathionine-β-synthase (CBS)/H₂S pathway in the brain of male APP/PS1 mice. Together, our study indicated that lower dietary methionine intake is associated with improved cognitive function, in which CBS/H₂S pathway plays an essential role. MR could be a promising nutritional intervention for preventing AD development.

Treadmill exercise promotes E3 ubiquitin ligase to remove amyloid β and P-tau and improve cognitive ability in APP/PS1 transgenic mice

Background

Moderate physical exercise is conducive to the brains of healthy humans and AD patients. Previous reports have suggested that treadmill exercise plays an anti-AD role and improves cognitive ability by promoting amyloid clearance, inhibiting neuronal apoptosis, reducing oxidative stress level, alleviating brain inflammation, and promoting autophagy–lysosome pathway in AD mice. However, few studies have explored the relationships between the ubiquitin–proteasome system and proper exercise in AD. The current study was intended to investigate the mechanism by which the exercise-regulated E3 ubiquitin ligase improves AD.

Methods

Both wild type and APP/PS1 transgenic mice were divided into sedentary (WTC and ADC) and exercise (WTE and ADE) groups (n = 12 for each group). WTE and ADE mice were subjected to treadmill exercise of 12 weeks in order to assess the effect of treadmill running on learning and memory ability, Aβ plaque burden, hyperphosphorylated Tau protein and E3 ubiquitin ligase.

Results

The results indicated that exercise restored learning and memory ability, reduced Aβ plaque areas, inhibited the hyperphosphorylation of Tau protein activated PI3K/Akt/Hsp70 signaling pathway, and improved the function of the ubiquitin–proteasome system (increased UCHL-1 and CHIP levels, decreased BACE1 levels) in APP/PS1 transgenic mice.

Conclusions

These findings suggest that exercise may promote the E3 ubiquitin ligase to clear β-amyloid and hyperphosphorylated Tau by activating the PI3K/Akt signaling pathway in the hippocampus of AD mice, which is efficient in ameliorating pathological phenotypes and improving learning and memory ability.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-022-02607-7.

A TNF receptor 2 agonist ameliorates neuropathology and improves cognition in an Alzheimer's disease mouse model

Tumor necrosis factor-α (TNF-α) is a pleiotropic, proinflammatory cytokine related to different neurodegenerative diseases, including Alzheimer's disease (AD). Although the linkage between increased TNF-α levels and AD is widely recognized, TNF-α-neutralizing therapies have failed to treat AD. Previous research has associated this with the antithetic functions of the two TNF receptors, TNF receptor 1, associated with inflammation and apoptosis, and TNF receptor 2 (TNFR2), associated with neuroprotection. In our study, we investigated the effects of specifically stimulating TNFR2 with a TNFR2 agonist (NewStar2) in a transgenic Aβ-overexpressing mouse model of AD by administering NewStar2 in two different ways: centrally, via implantation of osmotic pumps, or systemically by intraperitoneal injections. We found that both centrally and systemically administered NewStar2 resulted in a drastic reduction in amyloid β deposition and β-secretase 1 expression levels. Moreover, activation of TNFR2 increased microglial and astrocytic activation and promoted the uptake and degradation of Aβ. Finally, cognitive functions were also improved after NewStar2 treatment. Our results demonstrate that activation of TNFR2 mitigates Aβ-induced cognitive deficits and neuropathology in an AD mouse model and indicates that TNFR2 stimulation might be a potential treatment for AD.

Hydrogen Sulfide (H2S) Signaling as a Protective Mechanism against Endogenous and Exogenous Neurotoxicants

In view of the significant role of H₂S in brain functioning, it is proposed that H₂S may also possess protective effects against adverse effects of neurotoxicants. Therefore, the objective of the present review is to discuss the neuroprotective effects of H₂S against toxicity of a wide spectrum of endogenous and exogenous agents involved in the pathogenesis of neurological diseases as etiological factors or key players in disease pathogenesis. Generally, the existing data demonstrate that H₂S possesses neuroprotective effects upon exposure to endogenous (amyloid β, glucose, and advanced-glycation end-products, homocysteine, lipopolysaccharide, and ammonia) and exogenous (alcohol, formaldehyde, acrylonitrile, metals, 6-hydroxydopamine, as well as 1-methyl-4-phenyl- 1,2,3,6- tetrahydropyridine (MPTP) and its metabolite 1-methyl-4-phenyl pyridine ion (MPP)) neurotoxicants. On the one hand, neuroprotective effects are mediated by S-sulfhydration of key regulators of antioxidant (Sirt1, Nrf2) and inflammatory response (NF-κB), resulting in the modulation of the downstream signaling, such as SIRT1/TORC1/CREB/BDNF-TrkB, Nrf2/ARE/HO-1, or other pathways. On the other hand, H₂S appears to possess a direct detoxicative effect by binding endogenous (ROS, AGEs, Aβ) and exogenous (MeHg) neurotoxicants, thus reducing their toxicity. Moreover, the alteration of H₂S metabolism through the inhibition of H₂S-synthetizing enzymes in the brain (CBS, 3-MST) may be considered a significant mechanism of neurotoxicity. Taken together, the existing data indicate that the modulation of cerebral H₂S metabolism may be used as a neuroprotective strategy to counteract neurotoxicity of a wide spectrum of endogenous and exogenous neurotoxicants associated with neurodegeneration (Alzheimer's and Parkinson's disease), fetal alcohol syndrome, hepatic encephalopathy, environmental neurotoxicant exposure, etc. In this particular case, modulation of H₂S-synthetizing enzymes or the use of H₂S-releasing drugs should be considered as the potential tools, although the particular efficiency and safety of such interventions are to be addressed in further studies.

Network Biology Approaches to Uncover Therapeutic Targets Associated with Molecular Signaling Pathways from circRNA in Postoperative Cognitive Dysfunction Pathogenesis

Postoperative cognitive dysfunction (POCD) is a cognitive deterioration and dementia that arise after a surgical procedure, affecting up to 40% of surgery patients over the age of 60. The precise etiology and molecular mechanisms underlying POCD remain uncovered. These reasons led us to employ integrative bioinformatics and machine learning methodologies to identify several biological signaling pathways involved and molecular signatures to better understand the pathophysiology of POCD. A total of 223 differentially expressed genes (DEGs) comprising 156 upregulated and 67 downregulated genes were identified from the circRNA microarray dataset by comparing POCD and non-POCD samples. Gene ontology (GO) analyses of DEGs were significantly involved in neurogenesis, autophagy regulation, translation in the postsynapse, modulating synaptic transmission, regulation of the cellular catabolic process, macromolecule modification, and chromatin remodeling. Pathway enrichment analysis indicated some key molecular pathways, including mTOR signaling pathway, AKT phosphorylation of cytosolic targets, MAPK and NF-κB signaling pathway, PI3K/AKT signaling pathway, nitric oxide signaling pathway, chaperones that modulate interferon signaling pathway, apoptosis signaling pathway, VEGF signaling pathway, cellular senescence, RANKL/RARK signaling pathway, and AGE/RAGE pathway. Furthermore, seven hub genes were identified from the PPI network and also determined transcription factors and protein kinases. Finally, we identified a new predictive drug for the treatment of SCZ using the LINCS L1000, GCP, and P100 databases. Together, our results bring a new era of the pathogenesis of a deeper understanding of POCD, identified novel therapeutic targets, and predicted drug inhibitors in POCD.

Emerging roles of cystathionine β-synthase in various forms of cancer

The expression of the reverse transsulfuration enzyme cystathionine-β-synthase (CBS) is markedly increased in many forms of cancer, including colorectal, ovarian, lung, breast and kidney, while in other cancers (liver cancer and glioma) it becomes downregulated. According to the clinical database data in high-CBS-expressor cancers (e.g. colon or ovarian cancer), high CBS expression typically predicts lower survival, while in the low-CBS-expressor cancers (e.g. liver cancer), low CBS expression is associated with lower survival. In the high-CBS expressing tumor cells, CBS, and its product hydrogen sulfide (H₂S) serves as a bioenergetic, proliferative, cytoprotective and stemness factor; it also supports angiogenesis and epithelial-to-mesenchymal transition in the cancer microenvironment. The current article reviews the various tumor-cell-supporting roles of the CBS/H₂S axis in high-CBS expressor cancers and overviews the anticancer effects of CBS silencing and pharmacological CBS inhibition in various cancer models in vitro and in vivo; it also outlines potential approaches for biomarker identification, to support future targeted cancer therapies based on pharmacological CBS inhibition.

Comorbidity of osteoporosis and Alzheimer's disease: Is `AKT `-ing on cellular glucose uptake the missing link?

Osteoporosis and Alzheimer's disease (AD) are both degenerative diseases. Osteoporosis often proceeds cognitive deficits, and multiple studies have revealed common triggers that lead to energy deficits in brain and bone. Risk factors for osteoporosis and AD, such as obesity, type 2 diabetes, aging, chemotherapy, vitamin deficiency, alcohol abuse, and apolipoprotein Eε4 and/or Il-6 gene variants, reduce cellular glucose uptake, and protective factors, such as estrogen, insulin, exercise, mammalian target of rapamycin inhibitors, hydrogen sulfide, and most phytochemicals, increase uptake. Glucose uptake is a fine-tuned process that depends on an abundance of glucose transporters (Gluts) on the cell surface. Gluts are stored in vesicles under the plasma membrane, and protective factors cause these vesicles to fuse with the membrane, resulting in presentation of Gluts on the cell surface. This translocation depends mainly on AKT kinase signaling and can be affected by a range of factors. Reduced AKT kinase signaling results in intracellular glucose deprivation, which causes endoplasmic reticulum stress and iron depletion, leading to activation of HIF-1α, the transcription factor necessary for higher Glut expression. The link between diseases and aging is a topic of growing interest. Here, we show that diseases that affect the same biochemical pathways tend to co-occur, which may explain why osteoporosis and/or diabetes are often associated with AD.

Transfer of Tumor-Bearing Mice Intestinal Flora Can Ameliorate Cognition in Alzheimer's Disease Mice

BACKGROUND

Fecal microbiota transplant (FMT) is a potential treatment approach for many diseases. Alzheimer's disease (AD) and cancer have been proven to have a specific antagonistic relationship to FMT.

OBJECTIVE

This article aims to explore whether intestinal flora transplantation from cancer individuals can ameliorate cognitive impairment.

METHODS

Morris water maze and object recognition tests were performed to assess cognitive function after the fecal flora from tumor-bearing and WT mice were transplanted into AD mice by gavage. The effect of flora transplantation on AD was analyzed by thioflavin T staining, western blot, and 16S RNA sequencing.

RESULTS

AD mice with FMT significantly improved short-term memory level and cognitive ability compared with Tg + NaCl group. Inflammatory factors in the plasma were regulated, and Aβ plaques burden in the hippocampus and cortex were decreased. FMT in the tumor-bearing group showed a higher significant amelioration in symptoms compared to the healthy group. 16S RNA sequencing revealed that FMT treatments could reverse the increased Firmicutes and Prevotella and the decreased Bacteroidetes, Bacteroides, and Sutterella in AD mice. AD mice transplanted with tumor-bearing mice feces additionally increased the density of Oscillospira, Odoribacter, and AF12. Furthermore, the predicted functional analyses showed that the metabolism of inorganic and organic salts in the intestinal flora of AD mice was also reversed by FMT.

CONCLUSION

Intestinal flora transplantation from tumor-bearing mice can ameliorate the cognitive impairment of AD mice.

Composition of intestinal flora affects the risk relationship between Alzheimer's disease/Parkinson's disease and cancer

An increasing number of epidemiological studies have shown that there is a significant inverse relationship between the onset of Alzheimer's disease/Parkinson's disease (AD/PD) and cancer, but the mechanism is still unclear. Considering that intestinal flora can connect them, we tried to explain this phenomenon from the intestinal flora. This review briefly introduced the relationship among AD/PD, cancer, and intestinal flora, studied metabolites or components of the intestinal flora and the role of intestinal barriers and intestinal hormones in AD/PD and cancer. After screening, a part of the flora capable of participating in the occurrence processes of the three diseases at the same time was obtained, the abundance changes of the special flora in AD/PD and various types of cancers were summarized, and they were classified according to the flora function and abundance, which in turn innovatively and reasonably explained the fact that AD/PD and cancer showed certain antagonism in epidemiological statistics from the perspective of intestinal flora. This review also proposed that viewing the risk relationship between diseases from the perspective of intestinal flora may provide new research ideas for the treatment of fecal microbiota transplantation (FMT) and related diseases.

Hydrogen sulfide is neuroprotective in Alzheimer's disease by sulfhydrating GSK3β and inhibiting Tau hyperphosphorylation

Alzheimer's disease (AD), the most common cause of dementia and neurodegeneration in the elderly, is characterized by deterioration of memory and executive and motor functions. Neuropathologic hallmarks of AD include neurofibrillary tangles (NFTs), paired helical filaments, and amyloid plaques. Mutations in the microtubule-associated protein Tau, a major component of the NFTs, cause its hyperphosphorylation in AD. We have shown that signaling by the gaseous molecule hydrogen sulfide (H₂S) is dysregulated during aging. H₂S signals via a posttranslational modification termed sulfhydration/persulfidation, which participates in diverse cellular processes. Here we show that cystathionine γ-lyase (CSE), the biosynthetic enzyme for H₂S, binds wild type Tau, which enhances its catalytic activity. By contrast, CSE fails to bind Tau P301L, a mutant that is present in the 3xTg-AD mouse model of AD. We further show that CSE is depleted in 3xTg-AD mice as well as in human AD brains, and that H₂S prevents hyperphosphorylation of Tau by sulfhydrating its kinase, glycogen synthase kinase 3β (GSK3β). Finally, we demonstrate that sulfhydration is diminished in AD, while administering the H₂S donor sodium GYY4137 (NaGYY) to 3xTg-AD mice ameliorates motor and cognitive deficits in AD.

Hydrogen sulfide in longevity and pathologies: Inconsistency is malodorous

Hydrogen sulfide (H₂S) is one of the biologically active gases (gasotransmitters), which plays an important role in various physiological processes and aging. Its production in the course of methionine and cysteine catabolism and its degradation are finely balanced, and impairment of H₂S homeostasis is associated with various pathologies. Despite the strong geroprotective action of exogenous H₂S in C. elegans, there are controversial effects of hydrogen sulfide and its donors on longevity in other models, as well as on stress resistance, age-related pathologies and aging processes, including regulation of senescence-associated secretory phenotype (SASP) and senescent cell anti-apoptotic pathways (SCAPs). Here we discuss that the translation potential of H₂S as a geroprotective compound is influenced by a multiplicity of its molecular targets, pleiotropic biological effects, and the overlapping ranges of toxic and beneficial doses. We also consider the challenges of the targeted delivery of H₂S at the required dose. Along with this, the complexity of determining the natural levels of H₂S in animal and human organs and their ambiguous correlations with longevity are reviewed.

A Fundamental Role for Oxidants and Intracellular Calcium Signals in Alzheimer's Pathogenesis-And How a Comprehensive Antioxidant Strategy May Aid Prevention of This Disorder

Oxidative stress and increased cytoplasmic calcium are key mediators of the detrimental effects on neuronal function and survival in Alzheimer's disease (AD). Pathways whereby these perturbations arise, and then prevent dendritic spine formation, promote tau hyperphosphorylation, further amplify amyloid β generation, and induce neuronal apoptosis, are described. A comprehensive program of nutraceutical supplementation, comprised of the NADPH oxidase inhibitor phycocyanobilin, phase two inducers, the mitochondrial antioxidant astaxanthin, and the glutathione precursor N-acetylcysteine, may have important potential for antagonizing the toxic effects of amyloid β on neurons and thereby aiding prevention of AD. Moreover, nutraceutical antioxidant strategies may oppose the adverse impact of amyloid β oligomers on astrocyte clearance of glutamate, and on the ability of brain capillaries to export amyloid β monomers/oligomers from the brain. Antioxidants, docosahexaenoic acid (DHA), and vitamin D, have potential for suppressing microglial production of interleukin-1β, which potentiates the neurotoxicity of amyloid β. Epidemiology suggests that a health-promoting lifestyle, incorporating a prudent diet, regular vigorous exercise, and other feasible measures, can cut the high risk for AD among the elderly by up to 60%. Conceivably, complementing such lifestyle measures with long-term adherence to the sort of nutraceutical regimen outlined here may drive down risk for AD even further.

Hydrogen sulfide signalling in the CNS - Comparison with NO

Hydrogen sulfide (H₂ S) together with polysulfides (H₂ S_n , n > 2) are signalling molecules like NO with various physiological roles including regulation of neuronal transmission, vascular tone, inflammation and oxygen sensing. H₂ S and H₂ S_n diffuse to the target proteins for S-sulfurating their cysteine residues that induces the conformational changes to alter the activity. On the other hand, 3-mercaptopyruvate sulfurtransferase transfers sulfur from a substrate 3-mercaptopyruvate to the cysteine residues of acceptor proteins. A similar mechanism has also been identified in S-nitrosylation. S-sulfuration and S-nitrosylation by enzymes proceed only inside the cell, while reactions induced by H₂ S, H₂ S_n and NO even extend to the surrounding cells. Disturbance of signalling by these molecules as well as S-sulfuration and S-nitrosylation causes many nervous system diseases. This review focuses on the signalling by H₂ S and H₂ S_n with S-sulfuration comparing to that of NO with S-nitrosylation and discusses on their roles in physiology and pathophysiology.

Orexin-A aggravates cytotoxicity and mitochondrial impairment in SH-SY5Y cells transfected with APPswe via p38 MAPK pathway

Background

Alzheimer's disease (AD) is one of the common neurodegenerative diseases and is characterized by the accumulation of amyloid-β (Aβ). Orexin-A is a neuropeptide produced in the hypothalamus and thought to be involved in the pathogenesis of AD. However, its underlying mechanism and signaling pathway remains unclear. The aim of this work was to investigate the effect of Orexin-A on AD, and to explore its potential mechanism and signaling pathway.

Methods

SH-SY5Y cells that were stably transfected with the Swedish mutant amyloid precursor protein (APPswe), a cell model of AD with excessive Aβ production, were used in this study. Cells were treated with Orexin-A, and with or without SB203580, an inhibitor of the p38 mitogen-activated protein kinase (MAPK) pathway, one of the key MAPK pathways associated with cell death. Following treatment, cells were collected and analyzed by western blotting, ELISA, electron microscopy, real-time PCR, fluorescence microscopy, and other biochemical assays.

Results

Orexin-A increased the level of Aβ_1-40 and Aβ_1-42 in the cell medium, and activated the p38 MAPK pathway. As evidenced by the CCK-8 and ELISA BrdU assays, Orexin-A decreased cell viability and cell proliferation. Electron microscopic analysis used to observe the morphology of mitochondria, showed that Orexin-A increased the percentage of abnormal mitochondria. Further, decreased activity of cytochrome c oxidase (CCO), level of ATP, and mitochondrial DNA (mtDNA) copy number following Orexin-A treatment showed that Orexin-A exacerbated mitochondrial dysfunction. The level of intracellular reactive oxygen species (ROS), which is mainly generated in mitochondria and reflects mitochondrial dysfunction, was also increased by Orexin-A. SB203580 blocked the cytotoxicity and mitochondrial impairment aggravated by Orexin-A.

Conclusions

These findings demonstrate that Orexin-A aggravates cytotoxicity and mitochondrial impairment in SH-SY5Y cells transfected with APPswe through the p38 MAPK pathway, and suggest that Orexin-A participates in the pathogenesis of AD, which may provide a new treatment target in the future.

Hydrogen sulfide signaling in mitochondria and disease

Hydrogen sulfide can signal through 3 distinct mechanisms: 1) reduction and/or direct binding of metalloprotein heme centers, 2) serving as a potent antioxidant through reactive oxygen species/reactive nitrogen species scavenging, or 3) post-translational modification of proteins by addition of a thiol (-SH) group onto reactive cysteine residues: a process known as persulfidation. Below toxic levels, hydrogen sulfide promotes mitochondrial biogenesis and function, thereby conferring protection against cellular stress. For these reasons, increases in hydrogen sulfide and hydrogen sulfide-producing enzymes have been implicated in several human disease states. This review will first summarize our current understanding of hydrogen sulfide production and metabolism, as well as its signaling mechanisms; second, this work will detail the known mechanisms of hydrogen sulfide in the mitochondria and the implications of its mitochondrial-specific impacts in several pathologic conditions.-Murphy, B., Bhattacharya, R., Mukherjee, P. Hydrogen sulfide signaling in mitochondria and disease.

A diet rich in taurine, cysteine, folate, B12 and betaine may lessen risk for Alzheimer's disease by boosting brain synthesis of hydrogen sulfide

The gaseous physiological modulator hydrogen sulfide (H₂S) has recently been shown to exert a variety of neuroprotective effects. In particular, the treatment of transgenic mouse models of Alzheimer's disease (AD) with agents that release H₂S aids preservation of cognitive function, suppresses brain production of amyloid beta, and decreases tau phosphorylation. The possible physiological relevance of these findings is suggested by the finding that brain and plasma levels of H₂S are markedly lower in AD patients than matched controls. Hence, nutraceutical strategies which boost brain synthesis or levels of H₂S may have potential for prevention of AD. The chief enzyme which synthesizes H₂S in brain parenchyma, cystathionine beta-synthase (CBS), employs cysteine as its rate-limiting substrate, and is allosterically activated by S-adenosylmethionine (SAM). Supplemental taurine has been shown to boost expression of this enzyme, as well as that of another H₂S source, cystathionine gamma-lyase, in vascular tissue, and to enhance plasma H₂S levels; in rats subjected to hemorrhagic stroke, co-administration of taurine has been shown to blunt a marked reduction in brain CBS expression. Brain levels of SAM are about half as high in AD patients as in controls, and this is thought to explain the reduction of brain H₂S in these patients. These considerations suggest that supplementation with cysteine, taurine, and agents which promote methyl group availability - such as SAM, folate, vitamin B₁₂, and betaine - may have potential for boosting brain synthesis of H₂S and thereby aiding AD prevention. Indeed, most of these agents have already demonstrated utility in mouse AD models - albeit the extent to which increased H₂S synthesis contributes to this protection remains unclear. Moreover, prospective epidemiology has associated low dietary or plasma levels of folate, B12, and taurine with increased dementia risk. Rodent studies suggest that effective nutraceutical strategies for boosting brain H₂S synthesis may in fact have broad neuroprotective utility, possibly aiding prevention and/or control not only of AD but also Parkinson's disease and glaucoma, while diminishing the neuronal damage associated with brain trauma or stroke.

Impact of Pharmacological Inhibition of Hydrogen Sulphide Production in the SOD1G93A-ALS Mouse Model

A number of factors can trigger amyotrophic lateral sclerosis (ALS), although its precise pathogenesis is still uncertain. In a previous study done by us, poisonous liquoral levels of hydrogen sulphide (H₂S) in sporadic ALS patients were reported. In the same study very high concentrations of H₂S in the cerebral tissues of the familial ALS (fALS) model of the SOD1G93A mouse, were measured. The objective of this study was to test whether decreasing the levels of H₂S in the fALS mouse could be beneficial. Amino-oxyacetic acid (AOA)—a systemic dual inhibitor of cystathionine-β-synthase and cystathionine-γ lyase (two key enzymes in the production of H₂S)—was administered to fALS mice. AOA treatment decreased the content of H₂S in the cerebral tissues, and the lifespan of female mice increased by approximately ten days, while disease progression in male mice was not affected. The histological evaluation of the spinal cord of the females revealed a significant increase in GFAP positivity and a significant decrease in IBA1 positivity. In conclusion, the results of the study indicate that, in the animal model, the inhibition of H₂S production is more effective in females. The findings reinforce the need to adequately consider sex as a relevant factor in ALS.

Hydrogen sulfide inhibits ATP-induced neuroinflammation and Aβ1-42 synthesis by suppressing the activation of STAT3 and cathepsin S

Neuroinflammation and excessive β-amyloid_1-42 (Aβ_1-42) generation contribute to the pathogenesis of Alzheimer's disease (AD). Emerging evidence has demonstrated that hydrogen sulfide (H₂S), an endogenous gasotransmitter, produces therapeutic effects in AD; however, the underlying mechanisms remain largely elusive. In the present study, we investigated the effects of H₂S on exogenous ATP-induced inflammation and Aβ_1-42 production in both BV-2 and primary cultured microglial cells and analyzed the potential mechanism(s) mediating these effects. Our results showed that NaHS, an H₂S donor, inhibited exogenous ATP-stimulated inflammatory responses as manifested by the reduction of pro-inflammatory cytokines, ROS and activation of nuclear factor-κB (NF-κB) pathway. Furthermore, NaHS also suppressed the enhanced production of Aβ_1-42 induced by exogenous ATP, which is probably due to its inhibitory effect on exogenous ATP-boosted expression of amyloid precursor protein (APP) and activation of β- and γ-secretase enzymes. Thereafter, we found that exogenous ATP-induced inflammation and Aβ_1-42 production requires the activation of signal transducer and activator of transcription 3 (STAT3) and cathepsin S (Cat S) as inhibition of the activity of either proteins attenuated the effect of exogenous ATP. Intriguingly, NaHS suppressed exogenous ATP-induced phosphorylation of STAT3 and the activation of Cat S. In addition, we observed that NaHS led to the persulfidation of Cat S at cysteine-25. Importantly, mutation of cysteine-25 into serine attenuated the activity of Cat S stimulated by exogenous ATP and subsequent inflammation and Aβ_1-42 production, indicating its involvement in H₂S-mediated effect. Taken together, our data provide a novel understanding of H₂S-mediated effect on neuroinflammation and Aβ_1-42 production by suppressing the activation of STAT3 and Cat S.

BACE1 gene silencing alleviates isoflurane anesthesia‑induced postoperative cognitive dysfunction in immature rats by activating the PI3K/Akt signaling pathway

Postoperative cognitive dysfunction (POCD) is a severe complication characterized by cognitive dysfunction following anesthesia and surgery. The aim of the present study was to investigate the effects of β-site amyloid precursor protein cleavage enzyme 1 (BACE1) gene silencing on isoflurane anesthesia-induced POCD in immature rats via the phosphatidylinositol-3-kinase (PI3K)/protein kinase B (Akt) signaling pathway. Rat models were established and then transfected with BACE1 small interfering RNA and wortmannin (an inhibitor of PI3K). Blood gas analysis was performed, and a series of behavioral experiments were conducted to evaluate the cognitive function, learning ability and locomotor activity of rats. Reverse transcription quantitative polymerase chain reaction and western blot analysis were employed to determine the mRNA and protein expression of the associated genes. An ELISA was used to detect the inflammatory indicators and the content of amyloid precursor protein (APP) and amyloid-β (Aβ). Apoptosis of the hippocampal CA1 region was observed by terminal deoxynucleotidyl transferase dUTP nick-end labeling staining. Initially, it was revealed that the percentage of stagnation time in rats was increased by BACE1 gene silencing; the escape latency and swimming distance were markedly reduced from the 4th to the 6th day, the time the rats spent in first passing the target area was shortened, and the times of passing the target area were increased by BACE1 gene silencing, demonstrating that BACE1 gene silencing enhanced the spatial memory ability of rats. Additionally, it was determined that silencing BACE1 improved the pathological state induced by isoflurane anesthesia in immature rats, and attenuated the inflammatory response and the levels of APP and Aβ in hippocampal tissues. Furthermore, it was suggested that silencing BACE1 may have promoted the activation of the PI3K/Akt signaling pathway, thereby inhibiting the apoptosis of the hippocampal CA1 region. Taken together, these results indicated that BACE1 gene silencing may improve isoflurane anesthesia-induced POCD in immature rats by activating the PI3K/Akt signaling pathway and inhibiting the Aβ generated by APP.

Hydrogen sulfide attenuates homocysteine-induced neurotoxicity by preventing mitochondrial dysfunctions and oxidative damage: In vitro and in vivo studies

Elevated homocysteine (Hcy) levels have been implicated in neurodevelopmental and neurodegenerative disorders. Induction of oxidative stress and apoptosis has been reported as major mechanism in Hcy-induced neurotoxicity. Hydrogen sulfide (H₂S), as an antioxidant molecule has been reported to exhibit novel protective effect against Hcy-induced cell damage. However, the mechanisms involved in protective effect of H₂S against Hcy-induced toxicity in neurons have not been fully elucidated. Herein, effect of sodium hydrogen sulfide (NaHS, a source of H₂S) on Hcy-induced neurotoxicity was studied on Neuro-2a (N2a) cells in vitro and in animals subjected to hyperhomocysteinemia. DCFH-DA staining revealed that NaHS effectively attenuated Hcy-induced oxidative damage by reducing intracellular reactive oxygen species (ROS) generation. JC-1 staining and western blot results showed that NaHS pre-treatment prevented Hcy-induced mitochondrial dysfunctions and mitochondria-mediated apoptosis. MTT assay, cell cycle analysis, ethidium bromide/acridine orange (EB/AO) and Hoechst staining results demonstrated that NaHS significantly alleviated Hcy-induced cytotoxicity in N2a cells by preventing oxidative damage. Importantly, the results from agarose gel electrophoresis, comet and TUNEL assay indicated that NaHS also prevented neurodegeneration by reducing DNA damage and apoptotic cell death in animals with hyperhomocysteinemia. Taken together, the results demonstrate that the protective potential of H₂S against Hcy-induced neurotoxicity is mediated by preventing oxidative DNA damage and mitochondrial dysfunctions. The findings validate that H₂S is a promising therapeutic molecule in neurodegenerative conditions associated with hyperhomocysteinemia.

Proteomics and Toxicity Analysis of Spinal-Cord Primary Cultures upon Hydrogen Sulfide Treatment

Hydrogen sulfide (H₂S) is an endogenous gasotransmitter recognized as an essential body product with a dual, biphasic action. It can function as an antioxidant and a cytoprotective, but also as a poison with a high probability of causing brain damage when present at noxious levels. In a previous study, we measured toxic liquoral levels of H₂S in sporadic amyotrophic lateral sclerosis (ALS) patients and in the familial ALS (fALS) mouse model, SOD1G93A. In addition, we experimentally demonstrated that H₂S is extremely and selectively toxic to motor neurons, and that it is released by glial cells and increases Ca²⁺ concentration in motor neurons due to a lack of ATP. The presented study further examines the effect of toxic concentrations of H₂S on embryonic mouse spinal-cord cultures. We performed a proteomic analysis that revealed a significant H₂S-mediated activation of pathways related to oxidative stress and cell death, particularly the Nrf-2-mediated oxidative stress response and peroxiredoxins. Furthermore, we report that Na₂S (a stable precursor of H₂S) toxicity is, at least in part, reverted by the Bax inhibitor V5 and by necrostatin, a potent necroptosis inhibitor.

Gasotransmitter hydrogen sulfide signaling in neuronal health and disease

Hydrogen sulfide is a gaseous signaling molecule or gasotransmitter which plays important roles in a wide spectrum of physiologic processes in the brain and peripheral tissues. Unlike nitric oxide and carbon monoxide, the other major gasotransmitters, research on hydrogen sulfide is still in its infancy. One of the modes by which hydrogen sulfide signals is via a posttranslational modification termed sulfhydration/persulfidation, which occurs on reactive cysteine residues on target proteins, where the reactive SH group is converted to an SSH group. Sulfhydration is a substantially prevalent modification, which modulates the structure or function of proteins being modified. Thus, precise control of endogenous hydrogen sulfide production and metabolism is critical for maintenance of optimal cellular function, with excess generation and paucity, both contributing to pathology. Dysregulation of the reverse transsulfuration pathway which generates hydrogen sulfide occurs in several neurodegenerative diseases such as Parkinson's disease, Huntington's disease and Alzheimer's disease. Accordingly, treatment with donors of hydrogen sulfide or stimulation of the reverse transsulfuration have proved beneficial in several neurodegenerative states. In this review we focus on hydrogen sulfide mediated neuronal signaling processes that contribute to neuroprotection.

Increased expression of Myc-interacting zinc finger protein 1 in APP/PS1 mice

Myc-interacting zinc-finger protein 1 (Miz1) is a member of the poxvirus and zinc-finger domain/zinc finger transcription factor family. Its transcription activation and repression functions in the nucleus are well elucidated; however its cytoplasmic inflammation function is poorly understood and may be associated with the pathogenesis of Alzheimer's disease (AD). The aim of the present study was to investigate the association between AD and Miz1 expression. In the present study, the expression and distribution of Miz1 in wild-type (WT) and amyloid precursor protein/presenelin-1 (AD) mice was studied using reverse transcription-quantitative polymerase chain reaction, western blot analysis, and immunohistochemical and immunofluorescence staining. The results indicated that Miz1 was significantly upregulated in the cortex of AD mice (P<0.05). Double immunofluorescence labeling revealed that Miz1 protein was predominantly expressed in neurons and astrocytes, as evidenced by co-localization with the dendritic markers microtubule associated protein 2 and glial fibrillary acidic protein, respectively. The results of the present study suggest that the expression of Miz1 in the brain tissue of AD mice may serve an important role in AD pathogenesis.

Hydrogen Sulfide: A Worthwhile Tool in the Design of New Multitarget Drugs

H₂S is a gaseous molecule able to trigger a plethora of central physiological and pharmacological effects as antioxidant, pro- and anti-inflammatory, pro- and anti-nociceptive, neuromodulator, and cytoprotective. The polypharmacology of H₂S depends on the wide variety of targets implicated, but, despite the efforts, the mechanisms of action that should clarify its activity are still not completely unrevealed. Nevertheless, many attempts to exploit the multifaceted profile of this molecule have already been accomplished and many chemical entities containing an H₂S-releasing pharmacophore have been synthetized. Here we discuss recent investigations on multitarget molecules able to release H₂S, with a particular focus on the combinations of "native drug" with moieties structurally able to release H₂S and their applications as therapeutic tools in bone disease, gastrointestinal system and neurodegenerative disorders.