Cystathionine β-synthase is required for body iron homeostasis

Transferrin receptors

The transferrin receptor (TfR) is one of the key proteins involved in cellular iron uptake. TfR-mediated endocytosis of transferrin-bound iron is the major pathway for iron acquisition by most cells in the body. Over the past three decades, the studies on TfR have made significant progress, and also, our knowledge on cell iron uptake has greatly been improved. Here we focus on recent advances in the studies on TfR and a brief discussion of the structures and functions of four different types of TfR, namely TfR1 (transferrin receptor 1), TfR2 (transferrin receptor 2), TfR3 (glyceraldehyde-3-phosphate dehydrogenase) and TfR4 (cubilin). These proteins work in different cells or organs and at different times, ensuring that cells and tissues get the iron they need. Their normal expression and function are fundamental to the body's iron homeostasis.

Bio-nanocomplexes impair iron homeostasis to induce non-canonical ferroptosis in cancer cells

The targeted elevation of the labile iron pool (LIP) represents the most direct and effective strategy to induce ferroptosis in cancer cells. However, the efficiency of increasing LIP to induce ferroptosis via iron supplementation is controversial due to the iron homeostasis between LIP and storage iron pool, leading to poor effects and serious safety concerns. In this study, a bio-nanocomplex named AbDA-Lim, composed of albumin, polydopamine, and limonene, is prepared to promote LIP and induce non-canonical ferroptosis in cancer cells by destroying the iron balance. Albumin avidity drives AbDA-Lim entering cancer cells. Subsequently, the released polydopamine enhances the expression of HMOX1 to degrade haem and facilitate the transformation of Fe (III) to Fe (II). Meanwhile, limonene reduces glutathione (GSH) levels via inhibiting CBS, thereby, triggering the release of Fe (II) into LIP from its GSH-bound storage state. The augmentation of LIP ultimately triggers non-canonical ferroptosis in cancer cells. Furthermore, the photothermal property of polydopamine augments the synergistic anti-tumor efficiency of AbDA-Lim by incorporating photothermal therapy. This study presents a distinctive, cascading, and biotic strategy for promoting LIP non-canonically to induce ferroptosis.

Rubiadin Mediates the Upregulation of Hepatic Hepcidin and Alleviates Iron Overload via BMP6/SMAD1/5/9-Signaling Pathway

Iron overload disease is characterized by the excessive accumulation of iron in the body. To better alleviate iron overload, there is an urgent need for safe and effective small molecule compounds. Rubiadin, the active ingredient derived from the Chinese herb Prismatomeris tetrandra, possesses notable anti-inflammatory and hepatoprotective properties. Nevertheless, its impact on iron metabolism remains largely unexplored. To determine the role of rubiadin on iron metabolism, Western blot analysis, real-time PCR analysis, and the measurement of serum iron were performed. Herein, we discovered that rubiadin significantly downregulated the expression of transferrin receptor 1, ferroportin 1, and ferritin light chain in ferric-ammonium-citrate-treated or -untreated HepG2 cells. Moreover, intraperitoneal administration of rubiadin remarkably decreased serum iron and duodenal iron content and upregulated expression of hepcidin mRNA in the livers of high-iron-fed mice. Mechanistically, bone morphogenetic protein 6 (BMP6) inhibitor LDN-193189 completely reversed the hepcidin upregulation and suppressor of mother against decapentaplegic 1/5/9 (SMAD1/5/9) phosphorylation induced by rubiadin. These results suggested that rubiadin increased hepcidin expression through the BMP6/SMAD1/5/9-signaling pathway. Collectively, our findings uncover a crucial mechanism through which rubiadin modulates iron metabolism and highlight it as a potential natural compound for alleviating iron-overload-related diseases.

Genetic Markers of Postmortem Brain Iron

Brain iron (Fe) dyshomeostasis is implicated in neurodegenerative diseases. Genome-wide association studies (GWAS) have identified plausible loci correlated with peripheral levels of Fe. Systemic organs and the brain share several Fe regulatory proteins but there likely exist different homeostatic pathways. We performed the first GWAS of inductively coupled plasma mass spectrometry measures of postmortem brain Fe from 635 Rush Memory and Aging Project (MAP) participants. Sixteen single nucleotide polymorphisms (SNPs) associated with Fe in at least one of four brain regions were measured (p < 5 × 10-8). Promising SNPs (p < 5 × 10-6) were followed up for replication in published GWAS of blood, spleen, and brain imaging Fe traits and mapped to candidate genes for targeted cortical transcriptomic and epigenetic analysis of postmortem Fe in MAP. Results for SNPs previously associated with other Fe traits were also examined. Ninety-eight SNPs associated with postmortem brain Fe were at least nominally (p < 0.05) associated with one or more related Fe traits. Most novel loci identified had no direct links to Fe regulatory pathways but rather endoplasmic reticulum-Golgi trafficking (SORL1, SORCS2, MARCH1, CLTC), heparan sulfate (HS3ST4, HS3ST1), and coenzyme A (SLC5A6, PANK3); supported by nearest gene function and omic analyses. We replicated (p < 0.05) several previously published Fe loci mapping to candidate genes in cellular and systemic Fe regulation. Finally, novel loci (BMAL, COQ5, SLC25A11) and replication of prior loci (PINK1, PPIF, LONP1) lend support to the role of circadian rhythms and mitochondria function in Fe regulation more generally. In summary, we provide support for novel loci linked to pathways that may have greater relevance to brain Fe accumulation; some of which are implicated in neurodegeneration. However, replication of a subset of prior loci for blood Fe suggests that genetic determinants or biological pathways underlying Fe accumulation in the brain are not completely distinct from those of Fe circulating in the periphery.

Apolipoprotein E deficiency leads to the polarization of splenic macrophages towards M1 phenotype by increasing iron content

Apolipoprotein E (ApoE) plays a crucial role in iron homeostasis in the body, while macrophages are the principal cells responsible for handling iron in mammals. However, it is unknown whether ApoE can affect the functional subtypes and the iron handling capacity of splenic macrophages (SM). Here, we investigated the effects of ApoE deficiency (ApoE-/-) on the polarization and iron content of SM and its potential mechanisms. ApoE-/- was found to induce a significant increase in the expressions of M1 marker genes CD86, IL-1β, IL-6, IL-12, TNF-α and iNOS and a reduction in M2 marker genes CD206, Arg-1, IL-10 and Ym-1 in SM of mice aged 28 weeks, Meanwhile, ApoE-/- caused a significant increase in iron content and expression of ferritin, transferrin receptor 1 (TfR1), iron regulatory protein 1 (IRP1) and heme oxygenase-1 (HO-1) and a reduction in ferroportin1 (Fpn1) in spleen and/or SM of mice aged 28 weeks. It was concluded that ApoE-/- can increase iron content through increased iron uptake mediated by TfR/ IRPs and decreased iron release mediated by Fpn1, leading to polarization of the SM to M1 phenotype.

Rocaglamide regulates iron homeostasis by suppressing hepcidin expression

The anemia of inflammation (AI) is characterized by the presence of inflammation and abnormal elevation of hepcidin. Accumulating evidence has proved that Rocaglamide (RocA) was involved in inflammation regulation. Nevertheless, the role of RocA in AI, especially in iron metabolism, has not been investigated, and its underlying mechanism remains elusive. Here, we demonstrated that RocA dramatically suppressed the elevation of hepcidin and ferritin in LPS-treated mice cell line RAW264.7 and peritoneal macrophages. In vivo study showed that RocA can restrain the depletion of serum iron (SI) and transferrin (Tf) saturation caused by LPS. Further investigation showed that RocA suppressed the upregulation of hepcidin mRNA and downregulation of Fpn1 protein expression in the spleen and liver of LPS-treated mice. Mechanistically, this effect was attributed to RocA's ability to inhibit the IL-6/STAT3 pathway, resulting in the suppression of hepcidin mRNA and subsequent increase in Fpn1 and TfR1 expression in LPS-treated macrophages. Moreover, RocA inhibited the elevation of the cellular labile iron pool (LIP) and reactive oxygen species (ROS) induced by LPS in RAW264.7 cells. These findings reveal a pivotal mechanism underlying the roles of RocA in modulating iron homeostasis and also provide a candidate natural product on alleviating AI.

Hydrogen Sulfide and Liver Health: Insights into Liver Diseases

Significance: Hydrogen sulfide (H2S) is a recently recognized gasotransmitter involved in physiological and pathological conditions in mammals. It protects organs from oxidative stress, inflammation, hypertension, and cell death. With abundant expression of H2S-production enzymes, the liver is closely linked to H2S signaling. Recent Advances: Hepatic H2S comes from various sources, including gut microbiota, exogenous sulfur salts, and endogenous production. Recent studies highlight the importance of hepatic H2S in liver diseases such as nonalcoholic fatty liver disease (NAFLD), liver injury, and cancer, particularly at advanced stages. Endogenous H2S production deficiency is associated with severe liver disease, while exogenous H2S donors protect against liver dysfunction. Critical Issues: However, the roles of H2S in NAFLD, liver injury, and liver cancer are still debated, and its effects depend on donor type, dosage, treatment duration, and cell type, suggesting a multifaceted role. This review aimed to critically evaluate H2S production, metabolism, mode of action, and roles in liver function and disease. Future Direction: Understanding H2S's precise roles and mechanisms in liver health will advance potential therapeutic applications in preclinical and clinical research. Targeting H2S-producing enzymes and exogenous H2S sources, alone or in combination with other drugs, could be explored. Quantifying endogenous H2S levels may aid in diagnosing and managing liver diseases. Antioxid. Redox Signal. 40, 122-144.

Targeting one-carbon metabolism for cancer immunotherapy

BACKGROUND

One-carbon (1C) metabolism is a metabolic network that plays essential roles in biological reactions. In 1C metabolism, a series of nutrients are used to fuel metabolic pathways, including nucleotide metabolism, amino acid metabolism, cellular redox defence and epigenetic maintenance. At present, 1C metabolism is considered the hallmark of cancer. The 1C units obtained from the metabolic pathways increase the proliferation rate of cancer cells. In addition, anticancer drugs, such as methotrexate, which target 1C metabolism, have long been used in the clinic. In terms of immunotherapy, 1C metabolism has been used to explore biomarkers connected with immunotherapy response and immune-related adverse events in patients.

METHODS

We collected numerous literatures to explain the roles of one-carbon metabolism in cancer immunotherapy.

RESULTS

In this review, we focus on the important pathways in 1C metabolism and the function of 1C metabolism enzymes in cancer immunotherapy. Then, we summarise the inhibitors acting on 1C metabolism and their potential application on cancer immunotherapy. Finally, we provide a viewpoint and conclusion regarding the opportunities and challenges of targeting 1C metabolism for cancer immunotherapy in clinical practicability in the future.

CONCLUSION

Targeting one-carbon metabolism is useful for cancer immunotherapy.

Ferroportin1 in the brain

Despite years of research, it remains unclear why certain brain regions of patients with neurodegenerative diseases (NDs) have abnormally high levels of iron, although it has long been suggested that disrupted expression of iron-metabolizing proteins due to genetic or non-genetic factors is responsible for the enhancement in brain iron contents. In addition to the increased expression of cell-iron importers lactoferrin (lactotransferrin) receptor (LfR) in Parkinson's disease (PD) and melanotransferrin (p97) in Alzheimer's disease (AD), some investigations have suggested that cell-iron exporter ferroportin 1 (Fpn1) may be also associated with the elevated iron observed in the brain. The decreased expression of Fpn1 and the resulting decrease in the amount of iron excreted from brain cells has been thought to be able to enhance iron levels in the brain in AD, PD and other NDs. Cumulative results also suggest that the reduction of Fpn1 can be induced by hepcidin-dependent and -independent pathways. In this article, we discuss the current understanding of Fpn1 expression in the brain and cell lines of rats, mice and humans, with emphasis on the potential involvement of reduced Fpn1 in brain iron enhancement in patients with AD, PD and other NDs.

Apolipoprotein E is required for brain iron homeostasis in mice

BACKGROUND

Apolipoprotein E deficiency (ApoE^-/-) increases progressively iron in the liver, spleen and aortic tissues with age in mice. However, it is unknown whether ApoE affects brain iron.

METHODS

We investigated iron contents, expression of transferrin receptor 1 (TfR1), ferroportin 1 (Fpn1), iron regulatory proteins (IRPs), aconitase, hepcidin, Aβ42, MAP2, reactive oxygen species (ROS), cytokines and glutathione peroxidase 4 (Gpx4) in the brain of ApoE^-/- mice.

RESULTS

We demonstrated that ApoE^-/- induced a significant increase in iron, TfR1 and IRPs and a reduction in Fpn1, aconitase and hepcidin in the hippocampus and basal ganglia. We also showed that replenishment of ApoE absent partly reversed the iron-related phenotype in ApoE^-/- mice at 24-months old. In addition, ApoE^-/- induced a significant increase in Aβ42, MDA, 8-isoprostane, IL-1β, IL-6, and TNFα and a reduction in MAP2 and Gpx4 in hippocampus, basal ganglia and/or cortex of mice at 24-months old.

CONCLUSIONS

Our findings implied that ApoE is required for brain iron homeostasis and ApoE^-/--induced increase in brain iron is due to the increased IRP/TfR1-mediated cell-iron uptake as well as the reduced IRP/Fpn1 associated cell-iron export and suggested that ApoE^-/- induced neuronal injury resulted mainly from the increased iron and subsequently ROS, inflammation and ferroptosis.

Hydrogen Sulfide Biomedical Research in China-20 Years of Hindsight

Hydrogen sulfide (H2S) is an important gasotransmitter that is produced by mammalian cells and performs profound physiological and pathophysiological functions. Biomedical research on H2S metabolism and function in China began 20 years ago, which pioneered the examination of the correlation of abnormal H2S metabolism and cardiovascular diseases. Over the last two decades, research teams in China have made numerous breakthrough discoveries on the effects of H2S metabolism on hypertension, atherosclerosis, pulmonary hypertension, shock, angiogenesis, chronic obstructive pulmonary disease, pain, iron homeostasis, and testicle function, to name a few. These research developments, carried by numerous research teams all over China, build nationwide research network and advance both laboratory study and clinical applications. An integrated and collaborative research strategy would further promote and sustain H2S biomedical research in China and in the world.

Hydrogen Sulfide Attenuates High-Fat Diet-Induced Obesity: Involvement of mTOR/IKK/NF-κB Signaling Pathway

Obesity has become a public health epidemic worldwide and is associated with many diseases with high mortality including hypertension, diabetes, and heart disease. High-fat diet (HFD)-induced energy imbalance is one of the primary causes of obesity, but the underlying mechanisms are not fully elucidated. Our study showed that HFD reduced the level of hydrogen sulfide (H₂S) and its catalytic enzyme cystathionine β-synthase (CBS) in mouse hypothalamus and plasma. We found that HFD activated mTOR, IKK/NF-κB, the main pathway regulating inflammation. Activation of inflammatory pathway promoted the production of pro-inflammatory cytokines including IL-6, IL-1β, and TNF-α, which caused cell damage and loss in the hypothalamus. The disturbance of the hypothalamic neuron circuits resulted in body weight gain in HFD-induced mice. Importantly, we also showed that restoration of H₂S level with NaHS or activation of CBS with SAMe attenuated HFD-induced activation of mTOR, IKK/NF-κB signaling, which reduced the inflammation and the neuronal cell loss in the hypothalamus, and also inhibited body weight gain in mice. The same effects were obtained by inhibiting mTOR or NF-κB, which suggested that mTOR and NF-κB were the critical molecular factors involved in hypothalamic inflammation. Taken together, this study identified that HFD-induced hypothalamus inflammation plays a critical role in the development of obesity. Moreover, the inhibition of hypothalamic inflammation by regaining H₂S level could be a potential therapeutic to prevent the development of obesity.

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.

Hydrogen sulfide alleviates particulate matter-induced emphysema and airway inflammation by suppressing ferroptosis

BACKGROUND

Redox imbalance is an vital mechanism for COPD. At present, insufficient researches have been conducted on the protective effect of hydrogen sulfide (H₂S) on PM-induced COPD. However, whether H₂S exerts the anti-injury role by blocking ferroptosis and restoring redox equilibrium remain to be investigated.

METHODS

Human lung tissue samples were collected for IHC staining, and the expressions of Nrf2, ferritinophagy- and ferroptosis-related proteins were observed. The WT C57BL/6 and Nrf2 knockout mice models were established with PM(200 μg per mouse). NaHS(Exogenous H₂S) was injected intraperitoneally 30 min in advance. Twenty-nine days later, mice lung tissues were evaluated by HE's and PERLS-DAB's staining. Meanwhile, inflammation and oxidative stress indicators and iron levels were assessed by corresponding ELISA kit. Related protein expressions were detected through Western blot. BEAS-2B cells with or without H₂S were exposed to PM2.5 for 36 h. Cell viability, mitochondrial morphology, inflammatory cytokines, antioxidant factors, iron levels, autophagic flux and the levels of ROS, LIP ROS, MitoROS, MMP, as well as related protein expressions were detected by specific methods, respectively. In addition, V5-Nrf2, Nrf2 siRNA, Nrf2 inhibitor ML385, PPAR-γ inhibitor GW9662, autophagy inhibitor CQ, iron chelator DFO and ferroptosis inhibitor Fer-1 were used to verify the target signaling pathways.

RESULTS

We found that the expressions of LIP ROS, ROS, COX2, MDA and other oxidative factors increased, while the antioxidant markers GPX4, GSH and GSH-Px significantly decreased, as well as active iron accumulation in COPD patients, PM-exposured WT and Nrf2-KO mice models and PM2.5-mediated cell models. NaHS pretreatment markedly inhibited PM-induced emphysema and airway inflammation by alleviating ferroptotic changes in vivo and vitro. With the use of V5-Nrf2 overexpression plasmid, Nrf2 siRNA and pathway inhibitors, we found NaHS activates the expressions of Nrf2 and PPAR-γ, and inhibites ferritinophagy makers LC3B, NCOA4 and FTH1 in BEAS-2B cells. Moreover, the anti-ferroptotic effect of NaHS was further verified to be related to the activation of Nrf2 signal in MEF cells.

CONCLUSION

This research suggested that H₂S alleviated PM-induced emphysema and airway inflammation via restoring redox balance and inhibiting ferroptosis through regulating Nrf2-PPAR-ferritinophagy signaling pathway.

Iron accumulation with age alters metabolic pattern and circadian clock gene expression through the reduction of AMP-modulated histone methylation

Iron accumulates with age in mammals, and its possible implications in altering metabolic responses are not fully understood. Here, we report that both high-iron diet and advanced age in mice consistently altered gene expression of many pathways, including those governing the oxidative stress response and the circadian clock. We used a metabolomic approach to reveal similarities between metabolic profiles and the daily oscillation of clock genes in old and iron-overloaded mouse livers. In addition, we show that phlebotomy decreased iron accumulation in old mice, partially restoring the metabolic patterns and amplitudes of the oscillatory expression of clock genes Per1 and Per2. We further identified that the transcriptional regulation of iron occurred through a reduction in AMP-modulated methylation of histone H3K9 in the Per1 and H3K4 in the Per2 promoters, respectively. Taken together, our results indicate that iron accumulation with age can affect metabolic patterns and the circadian clock.

Physiological roles of hydrogen sulfide in mammalian cells, tissues and organs

H2S belongs to the class of molecules known as gasotransmitters, which also includes nitric oxide (NO) and carbon monoxide (CO). Three enzymes are recognized as endogenous sources of H2S in various cells and tissues: cystathionine g-lyase (CSE), cystathionine β-synthase (CBS) and 3-mercaptopyruvate sulfurtransferase (3-MST). The current article reviews the regulation of these enzymes as well as the pathways of their enzymatic and non-enzymatic degradation and elimination. The multiple interactions of H2S with other labile endogenous molecules (e.g. NO) and reactive oxygen species are also outlined. The various biological targets and signaling pathways are discussed, with special reference to H2S and oxidative posttranscriptional modification of proteins, the effect of H2S on channels and intracellular second messenger pathways, the regulation of gene transcription and translation and the regulation of cellular bioenergetics and metabolism. The pharmacological and molecular tools currently available to study H2S physiology are also reviewed, including their utility and limitations. In subsequent sections, the role of H2S in the regulation of various physiological and cellular functions is reviewed. The physiological role of H2S in various cell types and organ systems are overviewed. Finally, the role of H2S in the regulation of various organ functions is discussed as well as the characteristic bell-shaped biphasic effects of H2S. In addition, key pathophysiological aspects, debated areas, and future research and translational areas are identified A wide array of significant roles of H2S in the physiological regulation of all organ functions emerges from this review.

Signaling Integration of Hydrogen Sulfide and Iron on Cellular Functions

Significance: Hydrogen sulfide (H₂S) is an endogenous signaling molecule, regulating numerous physiological functions from vasorelaxation to neuromodulation. Iron is a well-known bioactive metal ion, being the central component of hemoglobin for oxygen transportation and participating in biomolecule degradation, redox balance, and enzymatic actions. The interplay between H₂S and iron metabolisms and functions impacts significantly on the fate and wellness of different types of cells. Recent Advances: Iron level in vivo affects the production of H₂S via nonenzymatic reactions. On the contrary, H₂S quenches excessive iron inside the cells and regulates the redox status of iron. Critical Issues: Abnormal metabolisms of both iron and H₂S are associated with various conditions and diseases such as iron overload, anemia, oxidative stress, and cardiovascular and neurodegenerative diseases. The molecular mechanisms for the interactions between H₂S and iron are unsettled yet. Here we review signaling links of the production, metabolism, and their respective and integrative functions of H₂S and iron in normalcy and diseases. Future Directions: Physiological and pathophysiological importance of H₂S and iron as well as their therapeutic applications should be evaluated jointly, not separately. Future investigation should expand from iron-rich cells and tissues to the others, in which H₂S and iron interaction has not received due attention. Antioxid. Redox Signal. 36, 275-293.

Cystathionine β-synthase mediated PRRX2/IL-6/STAT3 inactivation suppresses Tregs infiltration and induces apoptosis to inhibit HCC carcinogenesis

Background

Hepatocellular carcinoma (HCC) is characterized by inflammation and immunopathogenesis. Accumulating evidence has shown that the cystathionine β-synthase/hydrogen sulfide (CBS/H₂S) axis is involved in the regulation of inflammation. However, roles of CBS in HCC development and immune evasion have not been systematically investigated, and their underlying mechanisms remain elusive. Here, we investigated the roles of CBS in tumor cells and tumor microenvironment of HCC.

Methods

236 HCC samples were collected to detect the expression of CBS, cleaved Caspase-3 and paired related homeobox 2 (PRRX2) and the number of immune cells. HCC cell lines were employed to examine the effects of CBS on cellular viability, apoptosis and signaling in vitro. Cbs heterozygous knockout mice, C57BL/6 mice, nude mice and non-obese diabetic severe combined immunodeficiency mice were used to investigate the in vivo functions of CBS.

Results

Downregulation of CBS was observed in HCC, and low expression of CBS predicted poor prognosis in HCC patients. CBS overexpression dramatically promoted cellular apoptosis in vitro and inhibited tumor growth in vivo. Activation of the Cbs/H₂S axis also reduced the abundance of tumor-infiltrating Tregs, while Cbs deficiency promoted Tregs-mediated immune evasion and boosted tumor growth in Cbs heterozygous knockout mice. Mechanistically, CBS facilitated the expression cleaved Caspase-3 in tumor cells, and on the other hand, suppressed Foxp3 expression in Tregs via inactivating IL-6/STAT3 pathway. As a transcription factor of IL-6, PRRX2 was reduced by CBS. Additionally, miR-24-3p was proven to be an upstream suppressor of CBS in HCC.

Conclusions

Our results indicate the antitumor function of CBS in HCC by inactivation of the PRRX2/IL-6/STAT3 pathway, which may serve as a potential target for HCC clinical immunotherapy.

An insulin-independent mechanism for transcriptional regulation of Foxo1 in type 2 diabetic mice

Hepatic gluconeogenesis is the major contributor to the hyperglycemia observed in both patients and animals with type 2 diabetes. The transcription factor FOXO1 plays a dominant role in stimulating hepatic gluconeogenesis. FOXO1 is mainly regulated by insulin under physiological conditions, but liver-specific disruption of Foxo1 transcription restores normal gluconeogenesis in mice in which insulin signaling has been blocked, suggesting that additional regulatory mechanisms exist. Understanding the transcriptional regulation of Foxo1 may be conducive to the development of insulin-independent strategies for the control of hepatic gluconeogenesis. Here, we found that elevated plasma levels of adenine nucleotide in type 2 diabetes are the major regulators of Foxo1 transcription. We treated lean mice with 5'-AMP and examined their transcriptional profiles using RNA-seq. KEGG analysis revealed that the 5'-AMP treatment led to shifted profiles that were similar to db/db mice. Many of the upregulated genes were in pathways associated with the pathology of type 2 diabetes including Foxo1 signaling. As observed in diabetic db/db mice, lean mice treated with 5'-AMP displayed enhanced Foxo1 transcription, involving an increase in cellular adenosine levels and a decrease in the S-adenosylmethionine to S-adenosylhomocysteine ratio. This reduced methylation potential resulted in declining histone H3K9 methylation in the promoters of Foxo1, G6Pc, and Pepck. In mouse livers and cultured cells, 5'-AMP induced expression of more FOXO1 protein, which was found to be localized in the nucleus, where it could promote gluconeogenesis. Our results revealed that adenine nucleotide-driven Foxo1 transcription is crucial for excessive glucose production in type 2 diabetic mice.

Central Nervous System Inflammation Induced by Lipopolysaccharide Up-Regulates Hepatic Hepcidin Expression by Activating the IL-6/JAK2/STAT3 Pathway in Mice

It is known that lipopolysaccharide (LPS) triggers inflammatory response after intracerebroventricular (ICV) injection and elevates the expression of hepcidin through the interleukin 6/janus kinase 2/transducer and activator of the transcription 3 (IL-6/JAK2/STAT3) signaling pathway in the brain. This study was conducted to determine whether LPS ICV injection can regulate peripheral hepatic hepcidin expression and iron metabolism. Here, we studied the hepcidin expression in the liver, as well as serum iron and transferrin saturation, after LPS ICV injection. We also demonstrated the role of the IL-6/JAK2/STAT3 pathway in hepcidin expression in the livers of IL-6 knockout (IL-6–/– mice) and IL-6+/+ mice. AG490 was used to verify the effect of the IL-6/JAK2/STAT3 pathway on hepatic hepcidin expression. Our present study demonstrated that LPS ICV injection up-regulated hepatic hepcidin expression. This finding provides further evidence for highlighting the importance of the central inflammation on hepatic hepcidin expression and peripheral iron metabolism.

Apolipoprotein E deficiency induces a progressive increase in tissue iron contents with age in mice

Association of both iron/hepcidin and apolipoprotein E (ApoE) with development of Alzheimer disease (AD) and atherosclerosis led us to hypothesize that ApoE might be required for body iron homeostasis. Here, we demonstrated that ApoE knock-out (KO) induced a progressive accumulation of iron with age in the liver and spleen of mice. Subsequent investigations showed that the increased iron in the liver and spleen was due to phosphorylated extracellular regulated protein kinases (pERK) mediated up-regulation of transferrin receptor 1 (TfR1), and nuclear factor erythroid 2-related factor-2 (Nrf2)-dependent down-regulation of ferroportin 1. Furthermore, replenishment of ApoE could partially reverse the iron-related phenotype in ApoE KO mice. The findings imply that ApoE may be essential for body iron homeostasis and also suggest that clinical late-onset diseases with unexplained iron abnormality may partly be related to deficiency or reduced expression of ApoE.

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Apolipoprotein E deficiency induces a progressive increase in tissue iron contents with age in mice.

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ApoE−/− induced a progressive accumulation of iron with age in the liver and spleen of mice.

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The increased iron was due to upregulation of TfR1 and downregulation of Fpn1.

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Replenishment of ApoE could partially reverse the iron-related phenotype in ApoE KO mice.

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ApoE may be essential for body iron homeostasis.

Therapeutic effect of a histone demethylase inhibitor in Parkinson's disease

Iron accumulation in the substantia nigra is recognized as a hallmark of Parkinson's disease (PD). Therefore, reducing accumulated iron and associated oxidative stress is considered a promising therapeutic strategy for PD. However, current iron chelators have poor membrane permeability and lack cell-type specificity. Here we identified GSK-J4, a histone demethylase inhibitor with the ability to cross blood brain barrier, as a potent iron suppressor. Only a trace amount of GSK-J4 significantly and selectively reduced intracellular labile iron in dopaminergic neurons, and suppressed H2O2 and 6-OHDA-induced cell death in vitro. The iron-suppressive effect was mainly mediated by inducing an increase in the expression of the iron exporter ferroportin-1. In parallel, GSK-J4 rescued dopaminergic neuron loss and motor defects in 6-OHDA-induced PD rats, which was accompanied by reduction of oxidative stress. Importantly, GSK-J4 rescued the abnormal changes of histone methylation, H3K4me3 and H3K27me3 during 6-OHDA treatment although the iron-suppressive and neuroprotective effects were sensitive to H3K4me3 inhibition only. Also, upregulating H3K4me3 increased ferroportin-1 expression and neuroprotection. Taken together, we demonstrate a previously unappreciated action of GSK-J4 on cell-specific iron suppression and neuroprotection via epigenetic mechanism. Compared with conventional iron chelators, this compound has a stronger therapeutic potential for PD.

Cystathionine-β-Synthase: Molecular Regulation and Pharmacological Inhibition

Cystathionine-β-synthase (CBS), the first (and rate-limiting) enzyme in the transsulfuration pathway, is an important mammalian enzyme in health and disease. Its biochemical functions under physiological conditions include the metabolism of homocysteine (a cytotoxic molecule and cardiovascular risk factor) and the generation of hydrogen sulfide (H2S), a gaseous biological mediator with multiple regulatory roles in the vascular, nervous, and immune system. CBS is up-regulated in several diseases, including Down syndrome and many forms of cancer; in these conditions, the preclinical data indicate that inhibition or inactivation of CBS exerts beneficial effects. This article overviews the current information on the expression, tissue distribution, physiological roles, and biochemistry of CBS, followed by a comprehensive overview of direct and indirect approaches to inhibit the enzyme. Among the small-molecule CBS inhibitors, the review highlights the specificity and selectivity problems related to many of the commonly used "CBS inhibitors" (e.g., aminooxyacetic acid) and provides a comprehensive review of their pharmacological actions under physiological conditions and in various disease models.

Cyclophosphamide induces a significant increase in iron content in the liver and spleen of mice

Objective:

Oxidative stress is one of the major mechanisms of cyclophosphamide (CPX)-induced toxicities. However, it is unknown how CPX induces oxidative stress. Based on the available information, we speculated that CPX could increase iron content in the tissues and then induce oxidative stress.

Method:

We tested this hypothesis by investigating the effects of CPX on iron and ferritin contents, expression of transferrin receptor 1 (TfR1), ferroportin 1 (Fpn1), iron regulatory proteins (IRPs), hepcidin, and nuclear factor erythroid 2-related factor-2 (Nrf2) in the liver and spleen, and also on reticulocyte count, immature reticulocyte fraction, and hemoglobin (Hb) in the blood in c57/B6 mouse.

Results:

We demonstrated that CPX could induce a significant increase in iron contents and ferritin expression in the liver and spleen, notably inhibit erythropoiesis and Hb synthesis and lead to a reduction in iron usage. The reduced expression in TfR1 and Fpn1 is a secondary effect of CPX-induced iron accumulation in the liver and spleen and also partly associated with the suppressed IRP/iron-responsive element system, upregulation of hepcidin, and downregulation of Nrf2.

Conclusions:

The reduced iron usage is one of the causes for iron overload in the liver and spleen and the increased tissue iron might be one of the mechanisms for CPX to induce oxidative stress and toxicities.

Abdominal magnetic resonance imaging examination of Tibetan patients with abnormal iron metabolism and a preliminary study of correlations with blood cell analysis

OBJECTIVE

The objective was to investigate factors influencing the high incidence of abnormal iron metabolism in a Tibetan population.

METHODS

This was a retrospective observational study. Magnetic resonance imaging and blood analysis of 363 Tibetan patients were performed and patients divided into normal and abnormal groups based on the clinical diagnostic standard. The upper limit of normal liver iron content was 50 μmol/g. We analyzed the association between abnormal iron metabolism and blood cell indicators using the Spearman rank correlation test.

RESULTS

In male patients, differences in mean corpuscular hemoglobin (MCH) and MCH concentration in blood between the normal and abnormal groups were significant. Abnormal iron metabolism in male patients was positively correlated with MCH and MCH concentration. In female patients, differences in erythrocytes, hemoglobin, and hematocrit levels between the two groups were significant. Erythrocyte counts and hemoglobin and hematocrit levels of female patients were positively correlated.

CONCLUSION

Iron overload in male patients was correlated with an increase in MCH and MCH concentration, and that in female patients was correlated with levels of erythrocytes, hemoglobin, and hematocrit. The incidence rate of iron overload was higher in males than in females and was correlated with age in this Tibetan population.

A Novel Liposomal S-Propargyl-Cysteine: A Sustained Release of Hydrogen Sulfide Reducing Myocardial Fibrosis via TGF-β1/Smad Pathway

Purpose

S-propargyl-cysteine (SPRC; alternatively known as ZYZ-802) is a novel modulator of endogenous tissue H₂S concentrations with known cardioprotective and anti-inflammatory effects. However, its rapid metabolism and excretion have limited its clinical application. To overcome these issues, we have developed some novel liposomal carriers to deliver ZYZ-802 to cells and tissues and have characterized their physicochemical, morphological and pharmacological properties.

Methods

Two liposomal formulations of ZYZ-802 were prepared by thin-layer hydration and the morphological characteristics of each liposome system were assessed using a laser particle size analyzer and transmission electron microscopy. The entrapment efficiency and ZYZ-802 release profiles were determined following ultrafiltration centrifugation, dialysis tube and HPLC measurements. LC-MS/MS was used to evaluate the pharmacokinetic parameters and tissue distribution profiles of each formulation via the measurements of plasma and tissues ZYZ-802 and H₂S concentrations. Using an in vivo model of heart failure (HF), the cardio-protective effects of liposomal carrier were determined by echocardiography, histopathology, Western blot and the assessment of antioxidant and myocardial fibrosis markers.

Results

Both liposomal formulations improved ZYZ-802 pharmacokinetics and optimized H₂S concentrations in plasma and tissues. Liposomal ZYZ-802 showed enhanced cardioprotective effects in vivo. Importantly, liposomal ZYZ-802 could inhibit myocardial fibrosis via the inhibition of the TGF-β1/Smad signaling pathway.

Conclusion

The liposomal formulations of ZYZ-802 have enhanced pharmacokinetic and pharmacological properties in vivo. This work is the first report to describe the development of liposomal formulations to improve the sustained release of H₂S within tissues.

Cystathionine β-synthase (CBS) deficiency suppresses erythropoiesis by disrupting expression of heme biosynthetic enzymes and transporter

The reduced iron usage induced by the suppression of erythropoiesis is a major cause of the systemic iron overload in CBS knockout (CBS^−/−) mice. However, the relevant mechanisms are unknown. Here, we examined changes in granulocyte/erythroid cell ratios, iron content, and expression of iron-metabolism proteins, including; two key enzymes involved in the heme biosynthetic pathway, ALAS2 (delta-aminolevulinate synthase 2) and FECH (ferrochelatase), a heme exporter from the cytosol and mitochondria, FLVCR (feline leukemia virus subgroup C cellular receptor) as well as EPO (erythropoietin), EPOR (erythropoietin receptor) and HIF-2α (hypoxia inducible factor-2 subunit α), in the blood, bone marrow or liver of CBS^−/− (homozygous), CBS^+/− (heterozygous) and CBS^+/+ (Wild Type) mice. Our findings demonstrate that CBS deficiency can induce a significant reduction in the expression of ALAS2, FECH, FLVCR, HIF-2α, EPO, and EPOR as well as an increase in interleukin-6 (IL-6), hepcidin and iron content in the blood, bone marrow or liver of mice. We conclude that the suppression of erythropoiesis is mainly due to the CBS deficiency-induced disruption in the expression of heme biosynthetic enzymes and heme-transporter.

Hepcidin and its therapeutic potential in neurodegenerative disorders

Abnormally high brain iron, resulting from the disrupted expression or function of proteins involved in iron metabolism in the brain, is an initial cause of neuronal death in neuroferritinopathy and aceruloplasminemia, and also plays a causative role in at least some of the other neurodegenerative diseases including Alzheimer's disease, Parkinson's disease, Huntington's disease, and Friedreich's ataxia. As such, iron is believed to be a novel target for pharmacological intervention in these disorders. Reducing iron toward normal levels or hampering the increases in iron associated with age in the brain is a promising therapeutic strategy for all iron-related neurodegenerative disorders. Hepcidin is a crucial regulator of iron homeostasis in the brain. Recent studies have suggested that upregulating brain hepcidin levels can significantly reduce brain iron content through the regulation of iron transport protein expression in the blood-brain barrier and in neurons and astrocytes. In this review, we focus on the discussion of the therapeutic potential of hepcidin in iron-associated neurodegenerative diseases and also provide a systematic overview of recent research progress on how misregulated brain iron metabolism is involved in the development of multiple neurodegenerative disorders.

Comparative localization of cystathionine beta synthases and cystathionine gamma lyase in canine, non-human primate and human retina

Chronic exposure of the retina to light and high concentrations of polyunsaturated fatty acid in photoreceptor cells make this tissue susceptible to oxidative damage. As retinal degenerative diseases are associated with photoreceptor degeneration, the antioxidant activity of both hydrogen sulfide (H2S) and glutathione (GSH) may play an important role in ameliorating disease progression. H2S production is driven by cystathionine-γ-lyase (CSE) and cystathionine-β-synthase (CBS), the key enzymes that also drive transsulfuration pathway (TSP) necessary for GSH production. As it is currently unclear whether localized production of either H2S or GSH contributes to retinal homeostasis, we undertook a comparative analysis of CBS and CSE expression in canine, non-human primate (NHP) and human retinas to determine if these antioxidants could play a regulatory role in age-related or disease-associated retinal degeneration. Retinas from normal dogs, NHPs and humans were used for the study. Laser capture microdissection (LCM) was performed to isolate individual layers of the canine retina and analyze CBS and CSE gene expression by qRT-PCR. Immunohistochemistry and western blotting were performed for CBS and CSE labeling and protein expression in dog, NHP, and human retina, respectively. Using qRT-PCR, western blot, and immunohistochemistry (IHC), we showed that CBS and CSE are expressed in the canine, NHP, and human retina. IHC results from canine retina demonstrated increased expression levels of CBS but not CSE with post-developmental aging. IHC results also showed non-overlapping localization of both proteins with CBS presenting in rods, amacrine, horizontal, and nerve fiber cell layers while CSE was expressed by RPE, cones and Mϋller cells. Finally, we demonstrated that these enzymes localized to all three layers of canine, NHP and human retina: photoreceptors, outer plexiform layer (OPL) and notably in the ganglion cells layer/nerve fiber layer (GCL/NFL). QRT-PCR performed using RNA extracted from tissues isolated from these cell layers using laser capture microdissection (LCM) confirmed that each of CBS and CSE are expressed equally in these three layers. Together, these findings reveal that CSE and CBS are expressed in the retina, thereby supporting further studies to determine the role of H2S and these proteins in oxidative stress and apoptosis in retinal degenerative diseases.

Tissue iron is negatively correlated with TERC or TERT mRNA expression: A heterochronic parabiosis study in mice

To test the hypothesis that iron accumulation in tissues with age is a key harmful factor for the development of aging, we established heterochronic parabiosis-pairings and investigated changes in serum iron, the expression of major iron transport proteins and iron contents, as well as telomerase reverse transcriptase (TERT), telomerase RNA component (TERC), and telomere length in the liver, kidney and heart of Y-O(O) (old pairing with young), Y-O(Y) (young pairing with old), O-O (pairings between two old) and Y-Y (pairings between two young) mice. We demonstrated that the reduced serum iron, increased iron and reduced expression of TERT and TERC in the tissues of aged mice are reversible by exposure to a younger mouse’s circulation. All of these measurements in young mice are reversible by exposure to an older mouse’s circulation. Correlation analysis showed that tissue iron is negatively correlated with TERT and TERC expression in the liver, kidney and heart of parabiotic mice. These findings provide new evidence for the key role of iron in aging and also imply the existence of rejuvenating factors in young serum with an anti-ageing role that act by reversing the impaired activity of iron metabolism in old mice.

A pharmacological probe identifies cystathionine β-synthase as a new negative regulator for ferroptosis

Cystathionine β-synthase (CBS) is responsible for the first enzymatic reaction in the transsulfuration pathway of sulfur amino acids. The molecular function and mechanism of CBS as well as that of transsulfuration pathway remain ill-defined in cell proliferation and death. In the present study, we designed, synthesized and obtained a bioactive inhibitor CH004 for human CBS, which functions in vitro and in vivo. CH004 inhibits CBS activity, elevated the cellular homocysteine and suppressed the production of hydrogen sulfide in a dose-dependent manner in cells or in vivo. Chemical or genetic inhibition of CBS demonstrates that endogenous CBS is closely coupled with cell proliferation and cell cycle. Moreover, CH004 substantially retarded in vivo tumor growth in a xenograft mice model of liver cancer. Importantly, inhibition of CBS triggers ferroptosis in hepatocellular carcinoma. Overall, the study provides several clues for studying the interplays amongst transsulfuration pathway, ferroptosis and liver cancer.