Age-dependent oxidation of extracellular cysteine/cystine redox state (Eh(Cys/CySS)) in mouse lung fibroblasts is mediated by a decline in Slc7a11 expression

Impact of homocysteine on acute ischemic stroke severity: possible role of aminothiols redox status

BACKGROUND

Acute ischemic stroke (AIS) is one of the most common cerebrovascular diseases which accompanied by a disruption of aminothiols homeostasis. To explore the relationship of aminothiols with neurologic impairment severity, we investigated four aminothiols, homocysteine (Hcy), cysteine (Cys), cysteinylglycine (CG) and glutathione (GSH) in plasma and its influence on ischemic stroke severity in AIS patients.

METHODS

A total of 150 clinical samples from AIS patients were selected for our study. The concentrations of free reduced Hcy (Hcy), own oxidized Hcy (HHcy), free reduced Cys (Cys), own oxidized Cys (cysteine, Cyss), free reduced CG (CG) and free reduced GSH (GSH) were measured by our previously developed hollow fiber centrifugal ultrafiltration (HFCF-UF) method coupled with high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). The concentration ratio of Hcy to HHcy (Hcy/HHcy), Cys to Cyss (Cys/Cyss) were also calculated. The neurologic impairment severity of AIS was evaluated using National Institutes of Health Stroke Scale (NIHSS). The Spearman correlation coefficient and logistic regression analysis was used to estimate and perform the correlation between Hcy, HHcy, Cys, Cyss, CG, GSH, Hcy/HHcy, Cys/Cyss and total Hcy with NIHSS score.

RESULTS

The reduced Hcy and Hcy/HHcy was both negatively correlated with NIHSS score in AIS patients with P = 0.008, r=-0.215 and P = 0.002, r=-0.249, respectively. There was no significant correlation of Cys, CG, GSH, HHcy, Cyss, Cys/Cyss and total Hcy with NIHSS score in AIS patients with P value > 0.05.

CONCLUSIONS

The reduced Hcy and Hcy/HHcy, not total Hcy concentration should be used to evaluate neurologic impairment severity of AIS patient.

Osteocyte ferroptosis induced by ATF3/TFR1 contributes to cortical bone loss during ageing

Cortical bone loss is intricately associated with ageing and coincides with iron accumulation. The precise role of ferroptosis, characterized by iron overload and lipid peroxidation, in senescent osteocytes remains elusive. We found that ferroptosis was a crucial mode of osteocyte death in cortical bone during ageing. Using a single-cell transcriptome analysis, we identified activating transcription factor 3 (ATF3) as a critical driver of osteocyte ferroptosis. Elevated ATF3 expression in senescent osteocytes promotes iron uptake by upregulating transferrin receptor 1 while simultaneously inhibiting solute carrier family 7-member 11-mediated cystine import. This process leads to an iron overload and lipid peroxidation, culminating in ferroptosis. Importantly, ATF3 inhibition in aged mice effectively alleviated ferroptosis in the cortical bone and mitigated cortical bone mass loss. Taken together, our findings establish a pivotal role of ferroptosis in cortical bone loss in older adults, providing promising prevention and treatment strategies for osteoporosis and fractures.

Fibroblasts-Warriors at the Intersection of Wound Healing and Disrepair

Wound healing is triggered by inflammation elicited after tissue injury. Mesenchymal cells, specifically fibroblasts, accumulate in the injured tissues, where they engage in tissue repair through the expression and assembly of extracellular matrices that provide a scaffold for cell adhesion, the re-epithelialization of tissues, the production of soluble bioactive mediators that promote cellular recruitment and differentiation, and the regulation of immune responses. If appropriately deployed, these processes promote adaptive repair, resulting in the preservation of the tissue structure and function. Conversely, the dysregulation of these processes leads to maladaptive repair or disrepair, which causes tissue destruction and a loss of organ function. Thus, fibroblasts not only serve as structural cells that maintain tissue integrity, but are key effector cells in the process of wound healing. The review will discuss the general concepts about the origins and heterogeneity of this cell population and highlight the specific fibroblast functions disrupted in human disease. Finally, the review will explore the role of fibroblasts in tissue disrepair, with special attention to the lung, the role of aging, and how alterations in the fibroblast phenotype underpin disorders characterized by pulmonary fibrosis.

A more accurate indicator to evaluate oxidative stress in rat plasma with osteoporosis

Background: oxidative stress is linked to various human diseases which developed into the idea of "disrupted redox signaling". Osteoporosis (OP) is a chronic skeletal disorder characterized by low bone mineral density and deterioration of bone microarchitecture among which estrogen deficiency is the main cause. Lack of estrogen leads to the imbalance between oxidation and anti-oxidation in patients, and oxidative stress is an important link in the pathogenesis of OP. The ratio of the reduced to the oxidized thiols can characterize the redox status. However, few methods have been reported for the simultaneous determination of reduced forms and their oxidized forms of thiols in plasma. Methods: we developed a hollow fiber centrifugal ultrafiltration (HFCF-UF) method for sample preparation and validated a high-performance liquid chromatography tandem mass spectrometry (HPLC-MS/MS) method to determine two reduced forms of thiols-homocysteine (Hcy), cysteine (Cys) levels and their respective oxidized compounds, homocystine (HHcy) and cystine (Cyss) in rat plasma simultaneously for the first time. Thirty-six female rats were randomly divided into three groups: normal control (NC), oxidative stress (ovariectomy, OVX) and ovariectomy with hydrogen-rich saline administration (OVX + HRS). Results: the validation parameters for the methodological results were within the acceptance criteria. There were both significant differences of Hcy/HHcy (Hcy reduced/oxidized) and Cys/Cyss (Cys reduced/oxidized) in rat plasma between three groups with both p < 0.05 and meanwhile, the p values of malondialdehyde, superoxide dismutase and glutathione peroxidase were all less than 0.01. The value of both Hcy/HHcy and Cys/Cyss were significantly decreased with the change of Micro-CT scan result of femoral neck in OVX group (both the trabecular thickness and trabecular number significantly decreased with a significant increase of trabecular separation) which demonstrate OP occurs. The change of Hcy/HHcy is more obvious and prominent than Cys/Cyss. Conclusions: the Hcy/HHcy and Cys/Cyss could be suitable biomarkers for oxidative stress and especially Hcy/HHcy is more sensitive. The developed method is simple and accurate. It can be easily applied in clinical research to further evaluate the oxidative stress indicator for disease risk factors.

The solute carrier family 7 member 11 (SLC7A11) is regulated by LH/androgen and required for cystine/glutathione homeostasis in mouse Sertoli cells

Luteinizing hormone (LH) stimulates testosterone production from Leydig cells. Both LH and testosterone play important roles in spermatogenesis and male fertility. To identify LH - and testosterone - responsive transporter genes that play key roles in spermatogenesis, we performed large-scale gene expression analyses on testes obtained from adult control and Lhb knockout mice. We found a significant reduction in cystine/glutamate transporter encoding Slc7a11 mRNA in testes of Lhb null mice. We observed that Slc7a11/SLC7A11 expression was initiated pre-pubertally and developmentally regulated in mouse testis. Immunolocalization studies confirmed that SLC7A11 was mostly expressed in Sertoli cells in testes of control and germ cell-deficient mice. Western blot analyses indicated that SLC7A11 was significantly reduced in testes of mutant mice lacking either LH or androgen receptor selectively in Sertoli cells. Genetic and pharmacological rescue of Lhb knockout mice restored the testicular expression of Slc7a11 comparable to that observed in controls. Additionally, Slc7a11 mRNA was significantly suppressed upon Sertoli cell/testicular damage induced in mice by cadmium treatment. Knockdown of Slc7a11 in vitro in TM4 Sertoli cells or treatment of mice with sulfasalazine, a SLC7A11 inhibitor caused a significant reduction in intracellular cysteine and glutathione levels but glutamate content remained unchanged as determined by metabolomic analysis. Knockdown of Slc7a11 resulted in compensatory upregulation of other glutamate transporters belonging to the Slc1a family presumably to maintain intracellular glutamate levels. Collectively, our studies identified that SLC7A11 is an LH/testosterone-regulated transporter that is required for cysteine/glutathione but not glutamate homeostasis in mouse Sertoli cells.

The profibrotic and senescence phenotype of old lung fibroblasts is reversed or ameliorated by genetic and pharmacological manipulation of Slc7a11 expression

Increased senescence and expression of profibrotic genes in old lung fibroblasts contribute to disrepair responses. We reported that primary lung fibroblasts from old mice have lower expression and activity of the cystine transporter Slc7a11/xCT than cells from young mice, resulting in changes in both the intracellular and extracellular redox environments. This study examines the hypothesis that low Slc7a11 expression in old lung fibroblasts promotes senescence and profibrotic gene expression. The levels of mRNA and protein of Slc7a11, senescence markers, and profibrotic genes were measured in primary fibroblasts from the lungs of old (24 mo) and young (3 mo) mice. In addition, the effects of genetic and pharmacological manipulation of Slc7a11 were investigated. We found that decreased expression of Slc7a11 in old cells was associated with elevated markers of senescence (p21, p16, p53, and β-galactosidase) and increased expression of profibrotic genes (Tgfb1, Smad3, Acta2, Fn1, Col1a1, and Col5a1). Silencing of Slc7a11 in young cells replicated the aging phenotype, whereas overexpression of Slc7a11 in old cells decreased expression of senescence and profibrotic genes. Young cells were induced to express the senescence and profibrotic phenotype by sulfasalazine, a Slc7a11 inhibitor, whereas treatment of old cells with sulforaphane, a Slc7a11 inducer, decreased senescence without affecting profibrotic genes. Like aging cells, idiopathic pulmonary fibrosis fibroblasts show decreased Slc7a11 expression and increased profibrotic markers. In short, old lung fibroblasts manifest a profibrotic and senescence phenotype that is modulated by genetic or pharmacological manipulation of Slc7a11.

Donor factors and risk of primary graft dysfunction and mortality post lung transplantation: A proposed conceptual framework

Lung transplantation remains a therapeutic option in end-stage lung disease. However, despite advances in the field, early allograft function can be compromised by the development of primary graft dysfunction (PGD); this being the leading cause of morbidity and mortality immediately following the lung transplant procedure. Several recipient factors have been associated with increased risk of PGD, but less is known about donor factors. Aging, tobacco, and chronic alcohol use are donor factors implicated, but how these factors promote PGD remains unclear. Herein, we discuss the available clinical data that link these donor factors with outcomes after lung transplantation, and how they might render the recipient susceptible to PGD through a two-hit process.

S-Sulfocysteine - Investigation of cellular uptake in CHO cells

For the generation of therapeutic proteins in cell culture, high producing clones are used. These clones have a high demand in amino acids to support cell growth and productivity. l-cysteine (Cys) is critical in highly concentrated feeds due to low stability of Cys and low solubility of the oxidation product cystine at neutral pH. S-sulfocysteine (SSC) was developed to substitute the Cys source and fed-batch experiments using SSC showed good cellular performance regarding viable cell density and titer, indicating uptake and metabolization of SSC by Chinese hamster ovary cells. However, the responsible transporter allowing cellular uptake remains unclear and was studied in this work. Due to the structure similarity of SSC with cystine and glutamate, it was proposed that the cystine/glutamate antiporter (x_c^-) allows cellular uptake of SSC. The uptake was assessed via transporter inhibition using sulfasalazine and transporter overexpression using either sulforaphane or sulforaphane-N-acetylcysteine during fed-batch experiments. Following daily addition of 50 μM and 100 μM sulfasalazine, the extracellular SSC concentration was increased by 65 % and 177 % respectively, suggesting a reduced uptake due to x_c^- inhibition. In contrast, enhanced transporter activity through 15 μM sulforaphane and sulforaphane-N-acetylcysteine treatment, induced a 60 % and 52 % reduced extracellular SSC concentration, respectively. These inverse uptake results strongly suggest that x_c^- is facilitating the transport of SSC.

Autoinhibition by Iodide Ion in the Methionine-Iodine Reaction

The methionine–iodine reaction was reinvestigated spectrophotometrically in detail monitoring the absorbance belonging to the isosbestic point of iodine at 468 nm, at T = 25.0 ± 0.1 °C, and at 0.5 M ionic strength in buffered acidic medium. The stoichiometric ratio of the reactants was determined to be 1:1 producing methionine sulfoxide as the lone sulfur-containing product. The direct reaction between methionine and iodine was found to be relatively rapid in the absence of initially added iodide ion, and it can conveniently be followed by the stopped-flow technique. Reduction of iodine eventually leads to the formation of iodide ion that inhibits the reaction making the whole system autoinhibitory with respect to the halide ion. We have also shown that this inhibitory effect appears quite prominently, and addition of iodide ion in the millimole concentration range may result in a rate law where the formal kinetic order of this species becomes −2. In contrast to this, hydrogen ion has just a mildly inhibitory effect giving rise to the fact that iodine is the kinetically active species in the system but not hypoiodous acid. The surprisingly complex kinetics of this simple reaction may readily be interpreted via the initiating rapidly established iodonium-transfer process between the reactants followed by the subsequent hydrolytic decomposition of the short-lived iodinated methionine. A seven-step kinetic model to be able to describe the most important characteristics of the measured kinetic curves is established and discussed in detail.

Redox States of Protein Cysteines in Pathways of Protein Turnover and Cytoskeleton Dynamics Are Changed with Aging and Reversed by Slc7a11 Restoration in Mouse Lung Fibroblasts

Slc7a11 is the key component of system X_c⁻, an antiporter that imports cystine (CySS) and exports glutamate. It plays an important role in cellular defense against oxidative stress because cysteine (Cys), reduced from CySS, is used for and limits the synthesis of glutathione (GSH). We have shown that downregulation of Slc7a11 is responsible for oxidation of extracellular Cys/CySS redox potential in lung fibroblasts from old mice. However, how age-related change of Slc7a11 expression affects the intracellular redox environment of mouse lung fibroblasts remains unexplored. The purpose of this study is to evaluate the effects of aging on the redox states of intracellular proteins and to examine whether Slc7a11 contributes to the age-dependent effects. Iodoacetyl Tandem Mass Tags were used to differentially label reduced and oxidized forms of Cys residues in primary lung fibroblasts from young and old mice, as well as old fibroblasts transfected with Slc7a11. The ratio of oxidized/reduced forms (i.e., redox state) of a Cys residue was determined via multiplexed tandem mass spectrometry. Redox states of 151 proteins were different in old fibroblasts compared to young fibroblasts. Slc7a11 overexpression restored redox states of 104 (69%) of these proteins. Ingenuity Pathway Analysis (IPA) showed that age-dependent Slc7a11-responsive proteins were involved in pathways of protein translation initiation, ubiquitin-proteasome-mediated degradation, and integrin-cytoskeleton-associated signaling. Gene ontology analysis showed cell adhesion, protein translation, and organization of actin cytoskeleton were among the top enriched terms for biological process. Protein-protein interaction network demonstrated the interactions between components of the three enriched pathways predicted by IPA. Follow-up experiments confirmed that proteasome activity was lower in old cells than in young cells and that upregulation of Slc7a11 expression by sulforaphane restored this activity. This study finds that aging results in changes of redox states of proteins involved in protein turnover and cytoskeleton dynamics, and that upregulating Slc7a11 can partially restore the redox states of these proteins.

Impact of sex, age and diet on the cysteine/cystine and glutathione/glutathione disulfide plasma redox couples in mice

Age, sex and diet are well-established risk factors for several diseases. In humans, each of these variables has been linked to differences in plasma redox potentials (E_h) of the glutathione/glutathione disulfide (GSH/GSSG) and cysteine/cystine (Cys/CySS) redox couples. Mice have been very useful for modeling human disease processes, but it is unknown if age, sex and diet affect redox couples in mice as they do in humans. The purpose of the present study was to examine the effects of these factors on plasma redox potentials in C57BL/6J mice. We found that age had no effect on either redox couple in either sex. Plasma E_h Cys/CySS and E_h GSH/GSSG were both more oxidized (more positive) in females than in males. A 24-hour fast negated the sex differences in both redox potentials by oxidizing both redox couples in male mice, while having no effect on E_h Cys/CySS and a smaller effect on E_h GSH/GSSG in female mice. A diet with excess sulfur amino acids reduced the plasma E_h Cys/CySS in females to a level comparable to that seen in male mice. Thus, sex-specific differences in plasma E_h Cys/CySS could be normalized by two different dietary interventions. Some of these findings are consistent with reported human studies, while others are not. Most strikingly, mice do not exhibit age-dependent oxidation of plasma redox potentials. Care must be taken when designing and interpreting mouse studies to investigate redox regulation in humans.

The Meningococcal Cysteine Transport System Plays a Crucial Role in Neisseria meningitidis Survival in Human Brain Microvascular Endothelial Cells

Neisseria meningitidis colonizes at a nasopharynx of human as a unique host and has many strains that are auxotrophs for amino acids for their growth. To cause invasive meningococcal diseases (IMD) such as sepsis and meningitis, N. meningitidis passes through epithelial and endothelial barriers and infiltrates into blood and cerebrospinal fluid as well as epithelial and endothelial cells. However, meningococcal nutrients, including cysteine, become less abundant when it more deeply infiltrates the human body even during inflammation, such that N. meningitidis has to acquire nutrients in order to survive/persist, disseminate, and proliferate in humans. This was the first study to examine the relationship between meningococcal cysteine acquisition and the pathogenesis of meningococcal infections. The results of the present study provide insights into the mechanisms by which pathogens with auxotrophs acquire nutrients in hosts and may also contribute to the development of treatments and prevention strategies for IMD.

While Neisseria meningitidis typically exists in an asymptomatic nasopharyngeal carriage state, it may cause potentially lethal diseases in humans, such as septicemia or meningitis, by invading deeper sites in the body. Since the nutrient compositions of human cells are not always conducive to meningococci, N. meningitidis needs to exploit nutrients from host environments. In the present study, the utilization of cysteine by the meningococcal cysteine transport system (CTS) was analyzed for the pathogenesis of meningococcal infections. A N. meningitidis strain deficient in one of the three cts genes annotated as encoding cysteine-binding protein (cbp) exhibited approximately 100-fold less internalization into human brain microvascular endothelial cells (HBMEC) than the wild-type strain. This deficiency was restored by complementation with the three cts genes together, and the infectious phenotype of HBMEC internalization correlated with cysteine uptake activity. However, efficient accumulation of ezrin was observed beneath the cbp mutant. The intracellular survival of the cbp mutant in HBMEC was markedly reduced, whereas equivalent reductions of glutathione concentrations and of resistance to reactive oxygens species in the cbp mutant were not found. The cbp mutant grew well in complete medium but not in synthetic medium supplemented with less than 300 μM cysteine. Taking cysteine concentrations in human cells and other body fluids, including blood and cerebrospinal fluid, into consideration, the present results collectively suggest that the meningococcal CTS is crucial for the acquisition of cysteine from human cells and participates in meningococcal nutrient virulence.

Redox poise and metabolite changes in bread wheat seeds are advanced by priming with hot steam

Fast and uniform germination is key to agricultural production and can be achieved by seed 'priming' techniques. Here, we characterised the responses of bread wheat (Triticum aestivum L.) seeds to a hot steam treatment ('BioFlash'), which accelerated water uptake, resulting in faster germination and seedling growth, typical traits of primed seed. Before the completion of germination, metabolite profiling of seeds revealed advanced accumulation of several amino acids (especially cysteine and serine), sugars (ribose, glucose), and organic acids (glycerate, succinate) in hot steam-treated seeds, whereas sugar alcohols (e.g. arabitol, mannitol) and trehalose decreased in all seeds. Tocochromanols (the 'vitamin E family') rose independently of the hot steam treatment. We further assessed shifts in the half-cell reduction potentials of low-molecular-weight (LMW) thiol-disulfide redox couples [i.e. glutathione disulfide (GSSG)/glutathione (GSH) and cystine/cysteine], alongside the activities of the reactive oxygen species (ROS)-processing enzyme superoxide dismutase, catalase, ascorbate peroxidase, and glutathione reductase. Upon the first 4 h of imbibition, a rapid conversion of LMW disulfides to thiols occurred. Completion of germination was associated with a re-oxidation of the LMW thiol-disulfide cellular redox environment, before more reducing conditions were re-established during seedling growth, accompanied by an increase in all ROS-processing enzyme activities. Furthermore, changes in the thiol-disulfide cellular redox state were associated to specific stages of wheat seed germination. In conclusion, the priming effect of the hot steam treatment advanced the onset of seed metabolism, including redox shifts associated with germination and seedling growth.