Cystathionine beta-synthase, a key enzyme for homocysteine metabolism, is preferentially expressed in the radial glia/astrocyte lineage of developing mouse CNS

Modes of physiologic H2S signaling in the brain and peripheral tissues

SIGNIFICANCE

Hydrogen sulfide (H2S), once associated with rotten eggs and sewers, is now recognized as a gasotransmitter that is synthesized in vivo in a regulated fashion. This ancient gaseous molecule has been retained throughout evolution to perform various roles in different life forms. H2S modulates important signaling functions in diverse cellular processes ranging from regulation of blood pressure to redox homeostasis.

RECENT ADVANCES

One of the modes by which H2S signals is by post-translational modification of reactive cysteine residues in a process designated as sulfhydration, resulting in conversion of the -SH groups of target cysteine residues to -SSH. Using the modified biotin-switch assay and a fluorescent maleimide-based analysis, sulfhydration of several proteins has been detected in various cell types. Aberrant sulfhydration patterns occur in neurodegenerative conditions such as Parkinson's disease.

CRITICAL ISSUES

The exact concentration, source of H2S, and conditions under which various stores of H2S are utilized have not been fully elucidated. Currently, available inhibitors of the biosynthetic enzymes of H2S lack sufficient specificity to shed light on detailed mechanisms of H2S action. Probes with a higher sensitivity that can reliably detect cellular and tissue H2S levels are yet to be developed.

FUTURE DIRECTIONS

Availability of advanced probes and biosynthesis inhibitors would help in the measurement of real-time changes of endogenous H2S levels in an in vivo context. The study of the dynamics of sulfhydration and nitrosylation of critical cysteine residues of regulatory proteins involved in physiology and pathophysiology is an area of interest for the future.

Role of hydrogen sulfide in brain synaptic remodeling

Synapses are the functional connection between neurons which are necessary for the transfer of electric activity or chemical activity from one cell to another. Synapses are formed by the pre- and postsynaptic membrane which communicates between pre- and postneurons while a neurochemical modulator is operated in this process. H2S has been known as a toxic gas with rotten eggs smell. However, increasing number of researches show that it regulate a variety of physiological and pathological processes in mammals. Hence, H2S is a physiologically important molecule and has been referred to as the third gaseous molecule alongside carbon monoxide and nitric oxide. The previous era has made an exponential development in the physiological and pathological significance of H2S. Specifically, in the central nervous system, H2S facilitates long-term potentiation and regulates intracellular calcium concentration in brain cells. We as well as others have also shown that H2S has antioxidant, antiapoptotic, and anti-inflammatory properties against various neurodegenerative disorders such as stroke, Alzheimer's disease, and vascular dementia. In this chapter, we highlight the current knowledge of H2S and its neuroprotective effects with a special emphasis on synaptic remodeling.

Neuroprotective effects of hydrogen sulfide in Parkinson's disease animal models: methods and protocols

Hydrogen sulfide (H2S) was first proposed to be a neuromodulator in 1996. After that, multiple biological functions of H2S have been revealed. In brain, it regulates intracellular calcium, intracellular pH, and cAMP level in different brain cells via regulation of the functions of different proteins. In pathological situations, H2S produces anti-inflammatory, -oxidant, and -apoptotic effects, and therefore is potentially used to treat neurodegenerative diseases, especially Parkinson's disease (PD). In this chapter, we summarized the methods commonly used to create PD animal models followed by description of evaluations of PD pathology. The PD models described in this chapter included those caused by various neurotoxins like 6-hydroxydopamine, rotenone, and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine. Methods for examination of dopaminergic neuron loss and microglial activation in both substantia nigra and striatum are also described. The role of H2S and its therapeutic potentials are discussed in the last section of this chapter.

Brain, Learning, and Memory: Role of H2S in Neurodegenerative Diseases

For more than 300 years, the toxicity of hydrogen sulfide (H2S) has been known to mankind. However, this point of view is changing as an increased interest was observed in H2S biology in the last two decades. The scientific community has succeeded to unravel many important physiological and pathological effects of H2S on mammalian body systems. Thus, H2S is now referred to as a third endogenous gaseous mediator along with nitric oxide and carbon monoxide. Acting as a neuromodulator, H2S facilitates long-term potentiation and regulates intracellular calcium levels, which are important processes in learning and memory. Aberrant endogenous production and metabolism of H2S are implicated in pathogenesis of neurodegenerative diseases including Alzheimer's disease (AD) and Parkinson's disease (PD). Various H2S donors have shown beneficial therapeutic effects in neurodegenerative disease models by targeting hallmark pathological events (e.g., amyloid-β production in AD and neuroinflammation in PD). The results obtained from many in vivo studies clearly show that H2S not only prevents neuronal and synaptic deterioration but also improves deficits in memory, cognition, and learning. The anti-inflammatory, antioxidant, and anti-apoptotic effects of H2S underlie its neuroprotective properties. In this chapter, we will overview the current understanding of H2S in context of neurodegenerative diseases, with special emphasis on its corrective effects on impaired learning, memory, and cognition.

Neuroprotective effects of hydrogen sulfide and the underlying signaling pathways

Hydrogen sulfide (H

Hydrogen sulfide and polysulfides as signaling molecules

Hydrogen sulfide (H2S) is a familiar toxic gas that smells of rotten eggs. After the identification of endogenous H2S in the mammalian brain two decades ago, studies of this molecule uncovered physiological roles in processes such as neuromodulation, vascular tone regulation, cytoprotection against oxidative stress, angiogenesis, anti-inflammation, and oxygen sensing. Enzymes that produce H2S, such as cystathionine β-synthase, cystathionine γ-lyase, and 3-mercaptopyruvate sulfurtransferase have been studied intensively and well characterized. Polysulfides, which have a higher number of inner sulfur atoms than that in H2S, were recently identified as potential signaling molecules that can activate ion channels, transcription factors, and tumor suppressors with greater potency than that of H2S. This article focuses on our contribution to the discovery of these molecules and their metabolic pathways and mechanisms of action.

Central hydrogen sulphide mediates ventilatory responses to hypercapnia in adult conscious rats

AIM

Hydrogen sulphide (H2S) is endogenously produced and plays an important role as a modulator of neuronal functions; however, its modulatory role in the central CO2 chemoreception is unknown. The aim of the present study was to assess the role of endogenously produced H2S in the ventilatory response to hypercapnia in adult conscious rats.

METHODS

Cystathionine β-synthase (CBS) and cystathionine γ-lyase (CSE) inhibitors (aminooxyacetate: AOA and propargylglycine: PAG respectively) and a H2S donor (sodium sulphide: Na2S) were microinjected into the fourth ventricle (4V). Ventilation (V̇(E)), oxygen consumption (V̇O2) and body temperature were recorded before (room air) and during a 30-min CO2 exposure (hypercapnia, 7% CO2). Endogenous H2S levels were measured in the nucleus tractus solitarius (NTS).

RESULTS

Microinjection of Na2S (H2S donor), AOA (CBS inhibitor) or PAG (CSE inhibitor) did not affect baseline of the measured variables compared to control group (vehicle). In all experimental groups, hypercapnia elicited an increase in V̇(E). However, AOA microinjection, but not PAG, attenuated the ventilatory response to hypercapnia (P < 0.05), whereas Na2S elicited a slight, not significant, enhancement. Moreover, endogenous H2S levels were found higher in the NTS after hypercapnia (P < 0.05) compared to room air (normoxia) condition.

CONCLUSION

There are a few reports on the role of gaseous transmitters in the control of breathing. Importantly, the present data suggest that endogenous H2S via the CBS-H2S pathway mediates the ventilatory response to hypercapnia playing an excitatory role.

Hydrogen sulfide in signaling pathways

For a long time hydrogen sulfide (H₂S) was considered a toxic compound, but recently H₂S (at low concentrations) has been found to play an important function in physiological processes. Hydrogen sulfide, like other well-known compounds - nitric oxide (NO) and carbon monoxide (CO) is a gaseous intracellular signal transducer. It regulates the cell cycle, apoptosis and the oxidative stress. Moreover, its functions include neuromodulation, regulation of cardiovascular system and inflammation. In this review, I focus on the metabolism of hydrogen sulfide (including enzymatic pathways of H₂S synthesis from l- and d-cysteine) and its signaling pathways in the cardiovascular system and the nervous system. I also describe how hydrogen sulfide may be used as therapeutic agent, i.e. in the cardiovascular diseases.

Hydrogen sulfide inhibits opioid withdrawal-induced pain sensitization in rats by down-regulation of spinal calcitonin gene-related peptide expression in the spine

Hyperalgesia often occurs in opioid-induced withdrawal syndrome. In the present study, we found that three hourly injections of DAMGO (a μ-opioid receptor agonist) followed by naloxone administration at the fourth hour significantly decreased rat paw nociceptive threshold, indicating the induction of withdrawal hyperalgesia. Application of NaHS (a hydrogen sulfide donor) together with each injection of DAMGO attenuated naloxone-precipitated withdrawal hyperalgesia. RT-PCR and Western blot analysis showed that NaHS significantly reversed the gene and protein expression of up-regulated spinal calcitonin gene-related peptide (CGRP) in naloxone-treated animals. NaHS also inhibited naloxone-induced cAMP rebound and cAMP response element-binding protein (CREB) phosphorylation in rat spinal cord. In SH-SY5Y neuronal cells, NaHS inhibited forskolin-stimulated cAMP production and adenylate cyclase (AC) activity. Moreover, NaHS pre-treatment suppressed naloxone-stimulated activation of protein kinase C (PKC) α, Raf-1, and extracellular signal-regulated kinase (ERK) 1/2 in rat spinal cord. Our data suggest that H2S prevents the development of opioid withdrawal-induced hyperalgesia via suppression of synthesis of CGRP in spine through inhibition of AC/cAMP and PKC/Raf-1/ERK pathways.

Inhibition of hydrogen sulfide production by gene silencing attenuates inflammatory activity by downregulation of NF-κB and MAP kinase activity in LPS-activated RAW 264.7 cells

Hydrogen sulfide is an endogenous inflammatory mediator produced by the activity of cystathionine γ-lyase (CSE) in macrophages. The objective of this study was to explore the mechanism by which hydrogen sulfide acts as an inflammatory mediator in lipopolysaccharide- (LPS-) induced macrophages. In this study, we used small interfering RNA (siRNA) to inhibit CSE expression in macrophages. We found that CSE silencing siRNA could reduce the LPS-induced activation of transcription factor nuclear factor-κB (NF-κB) significantly. Phosphorylation and activation of extra cellular signal-regulated kinase 1/2 (ERK1/2) increased in LPS-induced macrophages. We showed that phosphorylation of ERK in LPS-induced RAW 264.7 cells reached a peak 30 min after activation. Our findings show that silencing CSE gene by siRNA reduces phosphorylation and activation of ERK1/2 in LPS-induced RAW 264.7 cells. These findings suggest that siRNA reduces the inflammatory effects of hydrogen sulfide through the ERK-NF-κB signalling pathway and hydrogen sulfide plays its inflammatory role through ERK-NF-κB pathway in these cells.

Hydrogen sulfide offers neuroprotection on traumatic brain injury in parallel with reduced apoptosis and autophagy in mice

Hydrogen sulfide (H₂S), a novel gaseous mediator, has been recognized as an important neuromodulator and neuroprotective agent in the central nervous system. The present study was undertaken to study the effects of exogenous H₂S on traumatic brain injury (TBI) and the underlying mechanisms. The effects of exogenous H₂S on TBI were examined by using measurement of brain edema, behavior assessment, propidium iodide (PI) staining, and Western blotting, respectively. Compared to TBI groups, H₂S pretreatment had reduced brain edema, improved motor performance and ameliorated performance in Morris water maze test after TBI. Immunoblotting results showed that H₂S pretreatment reversed TBI-induced cleavage of caspase-3 and decline of Bcl-2, suppressed LC3-II, Beclin-1 and Vps34 activation and maintained p62 level in injured cortex and hippocampus post TBI. The results suggest a protective effect and therapeutic potential of H₂S in the treatment of brain injury and the protective effect against TBI may be associated with regulating apoptosis and autophagy.

Genetic variants of homocysteine metabolism and multiple sclerosis: a case-control study

Methylenetetrahydrofolate reductase (MTHFR) is necessary for the synthesis of methionine and S-adenosylmethionine, which is necessary for CNS (re-)myelination. The MTHFR variant c.1298A>C was associated with the development of relapsing remitting multiple sclerosis (RRMS) in a German population. This study aimed at analyzing whether further genetic variants of methionine metabolism are associated with the development or the clinical course of RRMS. Therefore, genomic DNA of 147 serial German RRMS patients and 147 matched healthy controls was genotyped for five polymorphic variants of methionine metabolism. Statistical analyses were performed using multivariate binary and linear regression analyses. We show that the insertion allele of cystathionine beta-synthase (CBS) c.844_855ins68bp and the G-allele of reduced folate carrier 1 (RFC1) c.80G>A were associated with an earlier age of onset of MS, suggesting gene-dose effects (median age of onset in years: 25-26-32; standardized regression coefficient beta: 0.216; p=0.030, and 29-31-35 years; beta: 0.282; p=0.005, respectively). Conclusively, mutant variants of CBS and RFC1 may be associated with the age of RRMS onset. Since methionine metabolism can be manipulated by supplementation of vitamins and amino acids, our data provide a rationale for novel ideas of preventive and therapeutic strategies in RRMS.

Endogenous Production of Hydrogen Sulfide in Human Sinus Mucosa and its Expression Levels are Altered in Patients with Chronic Rhinosinusitis with and without Nasal Polyps

Background

Chronic rhinosinusitis with nasal polyps (CRSwNPs) or CRS without nasal polyps (CRSsNPs) is characterized by persistent inflammation of sinonasal mucosa. No one causative factor fully explains for the pathological manifestations of CRS. Endogenous hydrogen sulfide (H2S) has been shown to participate in inflammatory diseases, functioning as an inflammatory mediator in various organs. We analyzed the contents and synthesis activity of H2S, the expression and distribution pattern of H2S-generating enzymes, cystathione β-synthase (CBS), and cystathione γ-lyase (CSE) in CRSwNPs and CRSsNPs. The effects of H2S on the expression of CRS-relevant cytokines and the effects of cytokines on the expression of CBS and CSE were assessed in an in vitro experiment.

Methods

The contents and synthesis activity of H2S and the expression and distribution pattern of CBS and CSE in sinus mucosa were evaluated using spectrophotometry, real-time polymerase chain reaction, Western blot, and immunohistochemistry. Cultured epithelial cells were used to elucidate the effects of H2S donor, sodium hydrosulfide (NaHS), on the expression of CRS-relevant cytokines and the effects of cytokines on H2S-generating enzymes expression.

Results

The contents and synthesis activity of H2S were increased in CRSwNPs and CRSsNPs. CBS and CSE were localized to the superficial epithelium and submucosal glands, but CSE was also found in vascular endothelium. N S induced increased expression of IL-4, IL-5, interferon γ, and TNF-α. CBS and CSE expression in cultured cells was up-regulated by CRS-relevant cytokines.

Conclusion

H2S levels are increased in CRS, contributing to increased production of cytokines. These results suggest that H2S may function as inflammatory mediator in CRS.

Hydrogen sulfide attenuates opioid dependence by suppression of adenylate cyclase/cAMP pathway

AIMS

The best-established mechanism of opioid dependence is the up-regulation of adenylate cyclase (AC)/cAMP pathway, which was reported to be negatively regulated by hydrogen sulfide (H2S), a novel endogenous neuromodulator. The present study was, therefore, designed to determine whether H2S is able to attenuate the development of opioid dependence via down-regulating AC/cAMP pathway.

RESULTS

We demonstrated that application of sodium hydrosulphide (NaHS) and GYY4137, two donors of H2S, significantly alleviated naloxone-induced robust withdrawal jumping (the most sensitive and reliable index of opioid physical dependence) in morphine-treated mice. Repeated treatment with NaHS inhibited the up-regulated protein expression of AC in the striatum of morphine-dependent mice. Furthermore, NaHS also attenuated morphine/naloxone-elevated mRNA levels of AC isoform 1 and 8, production of cAMP, and phosphorylation of cAMP response element-binding protein (CREB) in mice striatum. These effects were mimicked by the application of exogenous H2S or over-expression of cystathione-β-synthase, an H2S -producing enzyme, in SH-SY5Y neuronal cells on treatment with [D-Ala(2),N-Me-Phe(4),Gly(5)-ol]-Enkephalin, a selective μ-opioid receptor agonist. Blockade of extracellular-regulated protein kinase 1/2 (ERK1/2) with its specific inhibitor attenuated naloxone-induced CREB phosphorylation. Pretreatment with NaHS or stimulation of endogenous H2S production also significantly suppressed opioid withdrawal-induced ERK1/2 activation in mice striatum or SH-SY5Y cells.

INNOVATION

H2S treatment is important in prevention of the development of opioid dependence via suppression of cAMP pathway in both animal and cellular models.

CONCLUSION

Our data suggest a potential role of H2S in attenuating the development of opioid dependence, and the underlying mechanism is closely related to the inhibition of AC/cAMP pathway.

Role of hydrogen sulfide in secondary neuronal injury

In acute neuronal insult events, such as stroke, traumatic brain injury, and spinal cord injury, pathological processes of secondary neuronal injury play a key role in the severity of insult and clinical prognosis. Along with nitric oxide (NO) and carbon monoxide (CO), hydrogen sulfide (H2S) is regarded as the third gasotransmitter and endogenous neuromodulator and plays multiple roles in the central nervous system under physiological and pathological states, especially in secondary neuronal injury. The endogenous level of H2S in the brain is significantly higher than that in peripheral tissues, and is mainly formed by cystathionine β-synthase (CBS) in astrocytes and released in response to neuronal excitation. The mechanism of secondary neuronal injury exacerbating the damage caused by the initial insult includes microcirculation failure, glutamate-mediated excitotoxicity, oxidative stress, inflammatory responses, neuronal apoptosis and calcium overload. H2S dilates cerebral vessels by activating smooth muscle cell plasma membrane ATP-sensitive K channels (KATP channels). This modification occurs on specific cysteine residues of the KATP channel proteins which are S-sulfhydrated. H2S counteracts glutamate-mediated excitotoxicity by inducing astrocytes to intake more glutamate from the extracellular space and thus increasing glutathione in neurons. In addition, H2S protects neurons from secondary neuronal injury by functioning as an anti-oxidant, anti-inflammatory and anti-apoptotic mediator. However, there are still some reports suggest that H2S elevates neuronal Ca(2+) concentration and may contribute to the formation of calcium overload in secondary neuronal injury. H2S also elicits calcium waves in primary cultures of astrocytes and may mediate signals between neurons and glia. Consequently, further exploration of the molecular mechanisms of H2S in secondary neuronal injury will provide important insights into its potential therapeutic uses for the treatment of acute neuronal insult events.

Redox signaling pathways involved in neuronal ischemic preconditioning

There is extensive evidence that the restoration of blood flow following cerebral ischemia contributes greatly to the pathophysiology of ischemia mediated brain injury. The initiating stimulus of reperfusion injury is believed to be the excessive production of reactive oxygen (ROS) and nitrogen (RNS) species by the mitochondria. ROS and RNS generation leads to mitochondrial protein, lipid and DNA oxidation which impedes normal mitochondrial physiology and initiates cellular death pathways. However not all ROS and RNS production is detrimental. It has been demonstrated that low levels of ROS production are protective and may serve as a trigger for activation of ischemic preconditioning. Ischemic preconditioning is a neuroprotective mechanism which is activated upon a brief sublethal ischemic exposure and is sufficient to provide protection against a subsequent lethal ischemic insult. Numerous proteins and signaling pathways have been implicated in the ischemic preconditioning neuroprotective response. In this review we examine the origin and mechanisms of ROS and RNS production following ischemic/reperfusion and the role of free radicals in modulating proteins associated with ischemic preconditioning neuroprotection.

Nutritional essentiality of sulfur in health and disease

Sulfur is the seventh most abundant element measurable in the human body and is supplied mainly by the intake of methionine (Met), an indispensable amino acid found in plant and animal proteins. Met controls the initiation of protein synthesis, governs major metabolic and catalytic activities, and may undergo reversible redox processes safeguarding protein integrity. Withdrawal of Met from customary diets causes the greatest downsizing of lean body mass following either unachieved replenishment (malnutrition) or excessive losses (inflammation). These physiopathologically unrelated morbidities nevertheless stimulate comparable remethylation reactions from homocysteine, indicating that Met homeostasis benefits from high metabolic priority. Inhibition of cystathionine-β-synthase activity causes the upstream sequestration of homocysteine and the downstream drop in cysteine and glutathione. Consequently, the enzymatic production of hydrogen sulfide and the nonenzymatic reduction of elemental sulfur to hydrogen sulfide are impaired. Sulfur operates as cofactor of several enzymes critically involved in the regulation of oxidative processes. A combination of malnutrition and nutritional deprivation of sulfur maximizes the risk of cardiovascular disorders and stroke, constituting a novel clinical entity that threatens plant-eating population groups.

Depolarizing actions of hydrogen sulfide on hypothalamic paraventricular nucleus neurons

Hydrogen sulfide (H₂S) is a novel neurotransmitter that has been shown to influence cardiovascular functions as well and corticotrophin hormone (CRH) secretion. Since the paraventricular nucleus of the hypothalamus (PVN) is a central relay center for autonomic and endocrine functions, we sought to investigate the effects of H₂S on the neuronal population of the PVN. Whole cell current clamp recordings were acquired from the PVN neurons and sodium hydrosulfide hydrate (NaHS) was bath applied at various concentrations (0.1, 1, 10, and 50 mM). NaHS (1, 10, and 50 mM) elicited a concentration-response relationship from the majority of recorded neurons, with almost exclusively depolarizing effects following administration. Cells responded and recovered from NaHS administration quickly and the effects were repeatable. Input differences from baseline and during the NaHS-induced depolarization uncovered a biphasic response, implicating both a potassium and non-selective cation conductance. The results from the neuronal population of the PVN shed light on the possible physiological role that H₂S has in autonomic and endocrine function.

H2S: a "double face" molecule in health and disease

H2S is a colorless, poisonous, and flammable gas with the characteristic foul odor of rotten eggs. H2S is present in effluent from hydrothermal vents and sulfur springs, which have been proposed to act as "pores" in the Earth surface, providing a source of energy in the form of reducing equivalents and of iron-sulfur centers. Remarkably, H2S-producing machineries or H2S-utilization capacity remain within a great diversity of microorganisms. In particular, two classes of bacteria have been identified, that is, sulfate- and sulfur-reducing and sulfur-oxidizing bacteria, both contributing to the balance of the H2S level. The human body produces H2S and uses it as a signaling molecule in several physiological processes. However, many diseases, including neurological diseases, cardiovascular diseases, inflammation, and metabolic disorders, have been linked to abnormal endogenous H2S functions and metabolism. Remarkably, in recent years, the therapeutic administration of H2S(-donors) appears relevant in the treatment of some diseases. Here, H2S metabolism, as well as its physiological and pathological roles in humans is reviewed. Furthermore, the therapeutic use of H2S is discussed.

The transcobalamin receptor knockout mouse: a model for vitamin B12 deficiency in the central nervous system

The membrane receptor (TCblR/CD320) for transcobalamin (TC)-bound cobalamin (Cbl) facilitates the cellular uptake of Cbl. A genetically modified mouse model involving ablation of the CD320 gene was generated to study the effects on cobalamin homeostasis. The nonlethal nature of this knockout and the lack of systemic cobalamin deficiency point to other mechanisms for cellular Cbl uptake in the mouse. However, severe cobalamin depletion in the central nervous system (CNS) after birth (P<0.01) indicates that TCblR is the only receptor responsible for Cbl uptake in the CNS. Metabolic Cbl deficiency in the brain was evident from the increased methylmalonic acid (P<0.01-0.04), homocysteine (P<0.01), cystathionine (P<0.01), and the decreased S-adenosylmethionine/S-adenosyl homocysteine ratio (P<0.01). The CNS pathology of Cbl deficiency seen in humans may not manifest in this mouse model; however, it does provide a model with which to evaluate metabolic pathways and genes affected.

Polysulfides are possible H2S-derived signaling molecules in rat brain

Accumulating evidence shows that hydrogen sulfide (H2S) has a variety of physiological functions. H2S is produced from cysteine by 3 sulfurtransferases. H2S, in turn, generates polysulfides, the functions of which are not well understood. H2S induces Ca(2+) influx in astrocytes, a type of glia. However, the receptor that mediates the response has not been identified. Here, we have shown that polysulfides induce Ca(2+) influx by activating transient receptor potential (TRP)A1 channels in rat astrocytes (EC50 91 nM, Hill coefficient value 1.77±0.26) and that the maximum response was induced at 0.5 μM, which is 1/320 of the concentration of H2S required to achieve a response of similar magnitude (160 μM, EC50 116 μM). TRPA1-selective agonists, allyl isothiocyanate and cinnamaldehyde, induced Ca(2+) influx, and responses to polysulfides were suppressed by TRPA1-selective inhibitors, HC-030031 and AP-18, as well as by siRNAs selective to TRPA1. The present study suggests that polysulfides are possible H2S-derived signaling molecules that stimulate TRP channels in the brain.

L-Cysteine promotes the proliferation and differentiation of neural stem cells via the CBS/H₂S pathway

Growing evidence has suggested that hydrogen sulfide (H₂S) acts as a novel neuro-modulator and neuroprotective agent; however, it remains to be investigated whether H2S has a direct effect on neural stem cells (NSCs). We report here that NSCs expressed cystathionine β synthase (CBS) and addition of exogenous H2S donor, L-cysteine, stimulated proliferation and increased the differentiation potential of NSCs to neurons and astroglia. Moreover, pre-treatment with aminooxyacetic acid, the inhibitor of CBS or knockdown of CBS in using siRNA, significantly attenuated the effects of L-cysteine on elevated H₂S levels and the cell proliferation; it also effectively suppressed L-cysteine-induced neurogenesis and astrocytogenesis. Further analysis revealed that L-cysteine-induced proliferation was associated with phosphorylation of extracellular signal-regulated kinases 1/2 and differentiation with altered expression of differentiation-related genes. Taken together, the present data suggest that L-cysteine can enhance proliferation and differentiation of NSCs via the CBS/H2S pathway, which may serve as a useful inference for elucidating its role in regulating the fate of NSCs in physiological and pathological settings.

A novel mechanism of formaldehyde neurotoxicity: inhibition of hydrogen sulfide generation by promoting overproduction of nitric oxide

Background

Formaldehyde (FA) induces neurotoxicity by overproduction of intracellular reactive oxygen species (ROS). Increasing studies have shown that hydrogen sulfide (H₂S), an endogenous gastransmitter, protects nerve cells against oxidative stress by its antioxidant effect. It has been shown that overproduction of nitric oxide (NO) inhibits the activity of cystathionine-beta-synthase (CBS), the predominant H₂S-generating enzyme in the central nervous system.

Objective

We hypothesize that FA-caused neurotoxicity involves the deficiency of this endogenous protective antioxidant gas, which results from excessive generation of NO. The aim of this study is to evaluate whether FA disturbs H₂S synthesis in PC12 cells, and whether this disturbance is associated with overproduction of NO.

Principal Findings

We showed that exposure of PC12 cells to FA causes reduction of viability, inhibition of CBS expression, decrease of endogenous H₂S production, and NO production. CBS silencing deteriorates FA-induced decreases in endogenous H₂S generation, neurotoxicity, and intracellular ROS accumulation in PC12 cells; while ADMA, a specific inhibitor of NOS significantly attenuates FA-induced decreases in endogenous H₂S generation, neurotoxicity, and intracellular ROS accumulation in PC12 cells.

Conclusion/Significance

Our data indicate that FA induces neurotoxicity by inhibiting the generation of H₂S through excess of NO and suggest that strategies to manipulate endogenous H₂S could open a suitable novel therapeutic avenue for FA-induced neurotoxicity.

Hydrogen sulfide is produced by cystathionine γ-lyase at the steady-state low intracellular Ca(2+) concentrations

Hydrogen sulfide (H(2)S) is recognized as a physiologic mediator produced in a variety of tissues. It is produced by three enzymes, cystathionine β-synthase (CBS), cystathionine γ-lyase (CSE) and 3-mercaptopyruvate sulfurtransferase (3MST). However, the regulation of H(2)S production by CSE has not well been understood. Here we show that H(2)S producing activity of CSE is regulated by intracellular Ca(2+) concentrations. In the presence of pyridoxal 5'-phosphate (PLP) CSE efficiently produces H(2)S at the steady-state low Ca(2+) concentrations but is suppressed at high Ca(2+) concentrations. In the absence of PLP H(2)S production maintains the suppressed levels at high Ca(2+) concentrations and decreased further at low Ca(2+) concentrations. These observations suggest that CSE produces H(2)S at the steady-state in cells and that the production is suppressed when the intracellular Ca(2+) concentrations are increased.

Hydrogen sulfide, the next potent preventive and therapeutic agent in aging and age-associated diseases

Hydrogen sulfide (H(2)S) is the third endogenous signaling gasotransmitter, following nitric oxide and carbon monoxide. It is physiologically generated by cystathionine-γ-lyase, cystathionine-β-synthase, and 3-mercaptopyruvate sulfurtransferase. H(2)S has been gaining increasing attention as an important endogenous signaling molecule because of its significant effects on the cardiovascular and nervous systems. Substantial evidence shows that H(2)S is involved in aging by inhibiting free-radical reactions, activating SIRT1, and probably interacting with the age-related gene Klotho. Moreover, H(2)S has been shown to have therapeutic potential in age-associated diseases. This article provides an overview of the physiological functions and effects of H(2)S in aging and age-associated diseases, and proposes the potential health and therapeutic benefits of H(2)S.

Site-specific hydrogen sulfide-mediated central regulation of respiratory rhythm in medullary slices of neonatal rats

Hydrogen sulfide (H₂S) is involved in central regulation of respiratory rhythm at the level of the medulla oblongata. The present study was carried out to test our hypothesis that H₂S exerts site-specific regulatory action on respiratory rhythm in the medulla oblongata of neonatal rats. The rhythmic discharge of hypoglossal rootlets in medullary slices of neonatal rats was recorded. 200 μM NaHS (an H₂S donor) increased burst frequency (BF) in 900-μm slices containing the pre-Bötzinger complex (preBötC), whereas it caused diphasic responses in 1200-, 1400- and 1800-μm slices containing both the preBötC and part or all of the parafacial respiratory group (pFRG): an initial decrease in BF followed by an increase. The initial decrease in BF was no longer observed after unilateral lesion of the pFRG region in the 1400-μm slices. In addition, BF was increased by a unilateral micro-injection of NaHS into the preBötC region, but was decreased by an injection into the pFRG region. These data support our hypothesis that the regulatory action of H₂S on respiratory rhythm in the medulla oblongata is site-specific. The excitatory effect is caused by the preBötC, while the inhibitory effect is from the pFRG.

Production of hydrogen sulfide from d-cysteine and its therapeutic potential

Accumulating evidence shows that H2S has physiological functions in various tissues and organs. It includes regulation of neuronal activity, vascular tension, a release of insulin, and protection of the heart, kidney, and brain from ischemic insult. H2S is produced by enzymes from l-cysteine; cystathionine β-synthase, cystathionine γ-lyase, and 3-mercaptopyruvate sulfurtransferase (3MST) along with cysteine aminotransferase. We recently discovered an additional pathway for the production of H2S from d-cysteine. d-Amino acid oxidase provides 3-mercaptopyruvate for 3MST to produce H2S. d-Cysteine protects cerebellar neurons from oxidative stress and attenuates ischemia-reperfusion injury caused in the kidney more effectively than l-cysteine. This review focuses on a novel pathway for the production of H2S and its therapeutic application especially to the renal diseases.

Altered sulfide (H(2)S) metabolism in ethylmalonic encephalopathy

Hydrogen sulfide (sulfide, H(2)S) is a colorless, water-soluble gas with a typical smell of rotten eggs. In the past, it has been investigated for its role as a potent toxic gas emanating from sewers and swamps or as a by-product of industrial processes. At high concentrations, H(2)S is a powerful inhibitor of cytochrome c oxidase; in trace amounts, it is an important signaling molecule, like nitric oxide (NO) and carbon monoxide (CO), together termed "gasotransmitters." This review will cover the physiological role and the pathogenic effects of H(2)S, focusing on ethylmalonic encephalopathy, a human mitochondrial disorder caused by genetic abnormalities of sulfide metabolism. We will also discuss the options that are now conceivable for preventing genetically driven chronic H(2)S toxicity, taking into account that a complete understanding of the physiopathology of H(2)S has still to be achieved.

Hydrogen sulfide as an endogenous modulator in mitochondria and mitochondria dysfunction

Hydrogen sulfide (H₂S) has historically been considered to be a toxic gas, an environmental and occupational hazard. However, with the discovery of its presence and enzymatic production through precursors of L-cysteine and homocysteine in mammalian tissues, H₂S has recently received much interest as a physiological signaling molecule. H₂S is a gaseous messenger molecule that has been implicated in various physiological and pathological processes in mammals, including vascular relaxation, angiogenesis, and the function of ion channels, ischemia/reperfusion (I/R), and heart injury. H₂S is an endogenous neuromodulator and present studies show that physiological concentrations of H₂S enhance NMDA receptor-mediated responses and aid in the induction of hippocampal long-term potentiation. Moreover, in the field of neuronal protection, physiological concentrations of H₂S in mitochondria have many favorable effects on cytoprotection.

Endogenous CSE/H2 S system mediates TNF-α-induced insulin resistance in 3T3-L1 adipocytes

Tumour necrosis factor-α (TNF- α)is a major contributor to the pathogenesis of insulin resistance associated with obesity and type 2 diabetes. It has been found that endogenous hydrogen sulfide (H2 S) contributes to the pathogenesis of diabetes. We have hypothesized that TNF-α-induced insulin resistance is involved in endogenous H2 S generation. The aim of the present study is to investigate the role of endogenous H2 S in TNF-α-induced insulin resistance by studying 3T3-L1 adipocytes. We found that treatment of 3T3-L1 adipocytes with TNF-α leads to deficiency in insulin-stimulated glucose consumption and uptake and increase in endogenous H2 S generation. We show that cystathionine γ-lyase (CSE) is catalysed in 3T3-L1 adipocytes to generate H2 S and that CSE expression and activity are upregulated by TNF-α treatment. Inhibited CSE by its potent inhibitors significantly attenuates TNF-α-induced insulin resistance in 3T3-L1 adipocytes, whereas H2 S treatment of 3T3-L1 adipocytes impairs insulin-stimulated glucose consumption and uptake. These data indicate that endogenous CSE/H2 S system contributes to TNF-α-caused insulin resistance in 3T3-L1 adipocytes. Our findings suggest that modulation of CSE/H2 S system is a potential therapeutic avenue for insulin resistance.

A mechanism of retinal protection from light-induced degeneration by hydrogen sulfide

Since our initial demonstrations that hydrogen sulfide (H(2)S) may function as a neuromodulator in the brain and a smooth muscle relaxant in the vascular system, accumulating evidence shows that H(2)S may function as a signaling molecule. We and others also found that H(2)S has a cytoprotective effect. Because H(2)S is well-known toxic gas, a cytoprotective role has been overlooked. H(2)S protects neurons from oxidative stress. It also protects cardiac muscle from ischemia-reperfusion injury. The finding led to the application of H(2)S to the bypass surgery patients in Phase II clinical trial. Cystathionine β-synthase (CBS) and cystathionine γ-lyase (CSE) are well known as H(2)S-producing enzymes. We recently demonstrated that the other H(2)S-producing enzyme, 3-mercaptopyruvate sulfurtransferase (3MST) along with cysteine aminotransferase (CAT) is localized to neurons in the brain and to the vascular endothelium. However, the regulation of H(2)S production by 3MST/CAT pathway had not been well understood. The present study shows that H(2)S production by 3MST/CAT pathway is regulated by Ca(2+) and that H(2)S protects retinal photoreceptor cells from light induced degeneration by suppressing excessive Ca(2+) influx caused by intense light.

Lanthionine synthetase C-like protein 1 interacts with and inhibits cystathionine β-synthase: a target for neuronal antioxidant defense

The finding that eukaryotic lanthionine synthetase C-like protein 1 (LanCL1) is a glutathione-binding protein prompted us to investigate the potential relationship between LanCL1 and cystathionine β-synthase (CBS). CBS is a trans-sulfuration enzyme critical for the reduced glutathione (GSH) synthesis and GSH-dependent defense against oxidative stress. In this study we found that LanCL1 bound to CBS in mouse cortex and HEK293 cells. Mapping studies revealed that the binding region in LanCL1 spans amino acids 158-169, and that in CBS contains N-terminal and C-terminal regulatory domains. Recombinant His-LanCL1 directly bound endogenous CBS from mouse cortical lysates and inhibited its activity. Overexpression of LanCL1 inhibited CBS activity in HEK293 cells. CBS activity is reported to be regulated by oxidative stress. Here we found that oxidative stress induced by H(2)O(2) or glutamate lowered the GSH/GSSG ratio, dissociated LanCL1 from CBS, and elevated CBS activity in primary rat cortical neurons. Decreasing the GSH/GSSG ratio by adding GSSG to cellular extracts also dissociated LanCL1 from CBS. Either lentiviral knockdown of LanCL1 or specific disruption of the LanCL1-CBS interaction using the peptide Tat-LanCL1(153-173) released CBS activity in neurons but occluded CBS activation in response to oxidative stress, indicating the major contribution of the LanCL1-CBS interaction to the regulation of CBS activity. Furthermore, LanCL1 knockdown or Tat-LanCL1(153-173) treatment reduced H(2)O(2) or glutamate-induced neuronal damage. This study implies potential therapeutic value in targeting the LanCL1-CBS interaction for neuronal oxidative stress-related diseases.

H₂S signalling through protein sulfhydration and beyond

Hydrogen sulfide (H(2)S) has recently emerged as a mammalian gaseous messenger molecule, akin to nitric oxide and carbon monoxide. H(2)S is predominantly formed from Cys or its derivatives by the enzymes cystathionine β-synthase and cystathionine γ-lyase. One of the mechanisms by which H(2)S signals is by sulfhydration of reactive Cys residues in target proteins. Although analogous to protein nitrosylation, sulfhydration is substantially more prevalent and usually increases the catalytic activity of targeted proteins. Physiological actions of sulfhydration include the regulation of inflammation and endoplasmic reticulum stress signalling as well as of vascular tension.

Physiological implications of hydrogen sulfide: a whiff exploration that blossomed

The important life-supporting role of hydrogen sulfide (H(2)S) has evolved from bacteria to plants, invertebrates, vertebrates, and finally to mammals. Over the centuries, however, H(2)S had only been known for its toxicity and environmental hazard. Physiological importance of H(2)S has been appreciated for about a decade. It started by the discovery of endogenous H(2)S production in mammalian cells and gained momentum by typifying this gasotransmitter with a variety of physiological functions. The H(2)S-catalyzing enzymes are differentially expressed in cardiovascular, neuronal, immune, renal, respiratory, gastrointestinal, reproductive, liver, and endocrine systems and affect the functions of these systems through the production of H(2)S. The physiological functions of H(2)S are mediated by different molecular targets, such as different ion channels and signaling proteins. Alternations of H(2)S metabolism lead to an array of pathological disturbances in the form of hypertension, atherosclerosis, heart failure, diabetes, cirrhosis, inflammation, sepsis, neurodegenerative disease, erectile dysfunction, and asthma, to name a few. Many new technologies have been developed to detect endogenous H(2)S production, and novel H(2)S-delivery compounds have been invented to aid therapeutic intervention of diseases related to abnormal H(2)S metabolism. While acknowledging the challenges ahead, research on H(2)S physiology and medicine is entering an exponential exploration era.

Hydrogen sulfide is a signaling molecule and a cytoprotectant

SIGNIFICANCE

Accumulating evidence shows that hydrogen sulfide may function as a signaling molecule in processes such as neuromodulation in the brain and smooth muscle relaxation in the vascular system. It also has a cytoprotective effect, since it can protect neurons and cardiac muscle from oxidative stress and ischemia-reperfusion injury, respectively. Hydrogen sulfide can also modulate inflammation, insulin release, and angiogenesis.

RECENT ADVANCES

The regulation of the activity of 3-mercaptopyruvate sulfur transferase (3MST) along with cysteine aminotransferase (CAT), one of the H(2)S producing pathways, has been demonstrated. The production of H(2)S by the pathway, which is regulated by Ca(2+) and facilitated by thioredoxin and dihydrolipoic acid, is also involved in H(2)S signaling as well as cytoprotection. Sulfur hydration of proteins by H(2)S has been proposed to modulate protein functions. H(2)S-sensitive fluorescent probes, which enable us to measure the localization of H(2)S in real time, have been developed.

CRITICAL ISSUES

The basal concentrations of H(2)S have recently been measured and found to be much lower than those initially reported. However, the concentration of H(2)S reached in stimulated cells, as well as the regulation of H(2)S producing enzymes is not well understood. It has been proposed that some of the effects of H(2)S on the regulation of enzymes and receptors might be explained through the properties of sulfane sulfur (S(0)), another form of active sulfur.

FUTURE DIRECTIONS

The determination of H(2)S concentrations in activated cells using new methods including H(2)S-sensitive fluorescent probes, as well as the investigation of the effects of H(2)S using specific inhibitors, may provide better understanding of the physiological function of this molecule. Clarifying mechanisms of H(2)S activity may also facilitate the development of new therapeutic compounds.

A systematic analysis of cell cycle regulators in yeast reveals that most factors act independently of cell size to control initiation of division

Upstream events that trigger initiation of cell division, at a point called START in yeast, determine the overall rates of cell proliferation. The identity and complete sequence of those events remain unknown. Previous studies relied mainly on cell size changes to identify systematically genes required for the timely completion of START. Here, we evaluated panels of non-essential single gene deletion strains for altered DNA content by flow cytometry. This analysis revealed that most gene deletions that altered cell cycle progression did not change cell size. Our results highlight a strong requirement for ribosomal biogenesis and protein synthesis for initiation of cell division. We also identified numerous factors that have not been previously implicated in cell cycle control mechanisms. We found that CBS, which catalyzes the synthesis of cystathionine from serine and homocysteine, advances START in two ways: by promoting cell growth, which requires CBS's catalytic activity, and by a separate function, which does not require CBS's catalytic activity. CBS defects cause disease in humans, and in animals CBS has vital, non-catalytic, unknown roles. Hence, our results may be relevant for human biology. Taken together, these findings significantly expand the range of factors required for the timely initiation of cell division. The systematic identification of non-essential regulators of cell division we describe will be a valuable resource for analysis of cell cycle progression in yeast and other organisms.

What determines when cells begin a new round of cell division also dictates how fast cells multiply. Knowing which cellular pathways and how these pathways affect the machinery of cell division will allow modulations of cell proliferation. Baker's yeast is suited for genetic and biochemical studies of eukaryotic cell division. Previous studies relied mainly on cell size changes to identify systematically factors that control initiation of cell division. Here, we measured the DNA content of each non-essential single gene deletion strain to identify genes required for the correct timing of cell cycle transitions. Our comprehensive strategy revealed new pathways that control cell division. We expect that this study will be a valuable resource for numerous future analyses of mechanisms that control cell division in yeast and other organisms, including humans.

Hydrogen sulfide: a gasotransmitter of clinical relevance

Though the existence of hydrogen sulfide (H2S) in biological tissues has been known for over 300 years, it is the most recently appreciated of the gasotransmitters as a physiologic messenger molecule. The enzymes cystathionine γ-lyase (CSE) and cystathionine β-synthase (CBS) had long been speculated to generate H2S, and inhibitors of these enzymes had been employed to characterize influences of H2S in various organs. Definitive evidence that H2S is a physiologic regulator came with the development of mice with targeted deletion of CSE and CBS. Best characterized is the role of H2S, formed by CSE, as an endothelial derived relaxing factor that normally regulates blood pressure by acting through ATP-sensitive potassium channels. H2S participates in various phases of the inflammatory process, predominantly exerting anti-inflammatory actions. Currently, the most advanced efforts to develop therapeutic agents involve the combination of H2S donors with non-steroidal anti-inflammatory drugs (NSAIDs). The H2S releasing moiety provides cytoprotection to gastric mucosa normally adversely affected by NSAIDs while the combination of H2S and inhibition of prostaglandin synthesis may afford synergistic anti-inflammatory influences.