Modulation of K+ channel N-type inactivation by sulfhydration through hydrogen sulfide and polysulfides

Hydrogen sulfide mitigates ox‑LDL‑induced NLRP3/caspase‑1/GSDMD dependent macrophage pyroptosis by S‑sulfhydrating caspase‑1

Macrophage pyroptosis mediates vascular inflammation and atherosclerosis (AS). Hydrogen sulfide (H2S) exerts a protective role in preventing inflammation and AS. However, its molecular mechanisms of regulating the pyroptosis signaling pathway and inhibiting macrophage pyroptosis remain unexplored. The present study aimed to determine whether H2S mitigates macrophage pyroptosis by downregulating the pyroptosis signaling pathway and S‑sulfhydrating caspase‑1 under the stimulation of oxidized low‑density lipoprotein (ox‑LDL), a pro‑atherosclerotic factor. Macrophages derived from THP‑1 monocytes were pre‑treated using exogenous H2S donors sodium hydrosulfide (NaHS) and D,L‑propargylglycine (PAG), a pharmacological inhibitor of endogenous H2S‑producing enzymes, alone or in combination. Subsequently, cells were stimulated with ox‑LDL or the desulfhydration reagent dithiothreitol (DTT) in the presence or absence of NaHS and/or PAG. Following treatment, the levels of H2S in THP‑1 derived macrophages were measured by a methylene blue colorimetric assay. The pyroptotic phenotype of THP‑1 cells was observed and evaluated by light microscopy, Hoechst 33342/propidium iodide fluorescent staining and lactate dehydrogenase (LDH) release assay. Caspase‑1 activity in THP‑1 cells was assayed by caspase‑1 activity assay kit. Immunofluorescence staining was used to assess the accumulation of active caspase‑1. Western blotting and ELISA were performed to determine the expression of pyroptosis‑specific markers (NLRP3, pro‑caspase‑1, caspase‑1, GSDMD and GSDMD‑N) in cells and the secretion of pyroptosis‑related cytokines [interleukin (IL)‑1β and IL‑18] in the cell‑free media, respectively. The S‑sulfhydration of pro‑caspase‑1 in cells was assessed using a biotin switch assay. ox‑LDL significantly induced macrophage pyroptosis by activating the pyroptosis signaling pathway. Inhibition of endogenous H2S synthesis by PAG augmented the pro‑pyroptotic effects of ox‑LDL. Conversely, exogenous H2S (NaHS) ameliorated ox‑LDL‑and ox‑LDL + PAG‑induced macrophage pyroptosis by suppressing the activation of the pyroptosis signaling pathway. Mechanistically, ox‑LDL and the DTT increased caspase‑1 activity and downstream events (IL‑1β and IL‑18 secretion) of the caspase‑1‑dependent pyroptosis pathway by reducing S‑sulfhydration of pro‑caspase‑1. Conversely, NaHS increased S‑sulfhydration of pro‑caspase‑1, reducing caspase‑1 activity and caspase‑1‑dependent macrophage pyroptosis. The present study demonstrated the molecular mechanism by which H2S ameliorates macrophage pyroptosis by suppressing the pyroptosis signaling pathway and S‑sulfhydration of pro‑caspase‑1, thereby suppressing the generation of active caspase-1 and activity of caspase-1.

Protein Persulfidation: Recent Progress and Future Directions

Significance: Hydrogen sulfide (H2S) is considered to be a gasotransmitter along with carbon monoxide (CO) and nitric oxide (NO), and is known as a key regulator of physiological and pathological activities. S-sulfhydration (also known as persulfidation), a mechanism involving the formation of protein persulfides by modification of cysteine residues, is proposed here to explain the multiple biological functions of H2S. Investigating the properties of protein persulfides can provide a foundation for further understanding of the potential functions of H2S. Recent Advances: Multiple methods have been developed to determine the level of protein persulfides. It has been demonstrated that protein persulfidation is involved in many biological processes through various mechanisms including the regulation of ion channels, enzymes, and transcription factors, as well as influencing protein-protein interactions. Critical Issues: Some technical and theoretical questions remain to be solved. These include how to improve the specificity of the detection methods for protein persulfidation, why persulfidation typically occurs on one or a few thiols within a protein, how this modification alters protein functions, and whether protein persulfidation has organ-specific patterns. Future Directions: Optimizing the detection methods and elucidating the properties and molecular functions of protein persulfidation would be beneficial for current therapeutics. In this review, we introduce the detailed mechanism of the persulfidation process and discuss persulfidation detection methods. In addition, this review summarizes recent discoveries of the selectivity of protein persulfidation and the regulation of protein functions and cell signaling pathways by persulfidation. Antioxid. Redox Signal. 39, 829-852.

Molecular engineering of benzenesulfonyl analogs for visual hydrogen polysulfide fluorescent probes based on Nile red skeleton

Hydrogen polysulfide (H₂S_n, n > 1) has a valuable function in various aspects of biological regulation. Therefore, it is of great significance to realize the visual monitoring of H₂S_n levels in vivo. Herein, a series of fluorescent probes NR-BS were constructed by changing types and positions of substituents on the benzene ring of benzenesulfonyl. Among them, probe NR-BS4 was optimized due to its wide linear range (0 ∼ 350 μM) and little interference from biothiols. In addition, NR-BS4 has a broad pH tolerance range (pH = 4 ∼ 10) and high sensitivity (0.140 μM). In addition, the PET mechanism of probe NR-BS4 and H₂S_n was demonstrated by DFT calculations and LC-MS. The intracellular imaging studies indicate that NR-BS4 can be successfully devoted to monitor the levels of exogenous and endogenous H₂S_n in vivo.

N-Type Inactivation Variances in Honeybee and Asian Giant Hornet Kv Channels

Background

With the emergence of the Asian giant hornet as a threat to honeybee survival, knowledge of potential ion channel targets expressed in the nervous system can propel the development of new insecticides that are safe for pollinators. We therefore examined the biophysical properties of the Shaker-like voltage-gated potassium (Kv) channel of Apis mellifera (AmKv1; Western honeybee) and Vespa mandarinia (VmKv1; Asian giant hornet) and compared these data with isoforms that differ in N-terminal amino acid sequence.

Methods

We expressed AmKv1 and VmKv1 in Xenopus laevis oocytes and determined their gating characteristics using electrophysiological measurements. Resulting features were compared with those gleaned from N-terminal isoforms.

Results

AmKv1 generates large potassium currents, but lacks an extended N-terminal region and therefore rapid N-type inactivation, as originally described in Shaker channels. Of its seven isoforms, two have a long N-tail and subsequently display inactivation. Notably, the isoform with the lengthiest N-terminal region only partially inactivates. VmKv1 potassium currents display N-type inactivation, as expected with an extended N-tail. One isoform shows an enhanced inactivation rate, whereas currents from another isoform with a substantially different N-terminal sequence could not be measured.

Conclusion

AmKv1 and VmKv1 are functional Kv channels with strikingly different gating properties. Due to the presence of an extended N-terminal region, VmKv1 inactivates rapidly, whereas AmKv1 does not possess these residues and N-type inactivation is absent. Remarkably, virtually all isoforms of AmKv1 lack fast inactivation, whereas all studied VmKv1 isoforms inactivate, thereby suggesting a functional divergence that may be exploited for insecticide design.

Protein S-sulfhydration: Unraveling the prospective of hydrogen sulfide in the brain, vasculature and neurological manifestations

Hydrogen sulfide (H₂S) and hydrogen polysulfides (H₂S_n) are essential regulatory signaling molecules generated by the entire body, including the central nervous system. Researchers have focused on the classical H₂S signaling from the past several decades, whereas the last decade has shown the emergence of H₂S-induced protein S-sulfhydration signaling as a potential therapeutic approach. Cysteine S-persulfidation is a critical paradigm of post-translational modification in the process of H₂S signaling. Additionally, studies have shown the cross-relationship between S-sulfhydration and other cysteine-induced post-translational modifications, namely nitrosylation and carbonylation. In the central nervous system, S-sulfhydration is involved in the cytoprotection through various signaling pathways, viz. inflammatory response, oxidative stress, endoplasmic reticulum stress, atherosclerosis, thrombosis, and angiogenesis. Further, studies have demonstrated H₂S-induced S-sulfhydration in regulating different biological processes, such as mitochondrial integrity, calcium homeostasis, blood-brain permeability, cerebral blood flow, and long-term potentiation. Thus, protein S-sulfhydration becomes a crucial regulatory molecule in cerebrovascular and neurodegenerative diseases. Herein, we first described the generation of intracellular H₂S followed by the application of H₂S in the regulation of cerebral blood flow and blood-brain permeability. Further, we described the involvement of S-sulfhydration in different biological and cellular functions, such as inflammatory response, mitochondrial integrity, calcium imbalance, and oxidative stress. Moreover, we highlighted the importance of S-sulfhydration in cerebrovascular and neurodegenerative diseases.

Interplay between hydrogen sulfide and other signaling molecules in the regulation of guard cell signaling and abiotic/biotic stress response

Stomatal aperture controls the balance between transpirational water loss and photosynthetic carbon dioxide (CO2) uptake. Stomata are surrounded by pairs of guard cells that sense and transduce environmental or stress signals to induce diverse endogenous responses for adaptation to environmental changes. In a recent decade, hydrogen sulfide (H2S) has been recognized as a signaling molecule that regulates stomatal movement. In this review, we summarize recent progress in research on the regulatory role of H2S in stomatal movement, including the dynamic regulation of phytohormones, ion homeostasis, and cell structural components. We focus especially on the cross talk among H2S, nitric oxide (NO), and hydrogen peroxide (H2O2) in guard cells, as well as on H2S-mediated post-translational protein modification (cysteine thiol persulfidation). Finally, we summarize the mechanisms by which H2S interacts with other signaling molecules in plants under abiotic or biotic stress. Based on evidence and clues from existing research, we propose some issues that need to be addressed in the future.

Hydrogen sulfide regulates hippocampal neuron excitability via S-sulfhydration of Kv2.1

Hydrogen sulfide (H2S) is gaining interest as a mammalian signalling molecule with wide ranging effects. S-sulfhydration is one mechanism that is emerging as a key post translational modification through which H2S acts. Ion channels and neuronal receptors are key target proteins for S-sulfhydration and this can influence a range of neuronal functions. Voltage-gated K+ channels, including Kv2.1, are fundamental components of neuronal excitability. Here, we show that both recombinant and native rat Kv2.1 channels are inhibited by the H2S donors, NaHS and GYY4137. Biochemical investigations revealed that NaHS treatment leads to S-sulfhydration of the full length wild type Kv2.1 protein which was absent (as was functional regulation by H2S) in the C73A mutant form of the channel. Functional experiments utilising primary rat hippocampal neurons indicated that NaHS augments action potential firing and thereby increases neuronal excitability. These studies highlight an important role for H2S in shaping cellular excitability through S-sulfhydration of Kv2.1 at C73 within the central nervous system.

Hydrogen sulfide (H2S) signaling in plant development and stress responses

ABSTRACT

Hydrogen sulfide (H₂S) was initially recognized as a toxic gas and its biological functions in mammalian cells have been gradually discovered during the past decades. In the latest decade, numerous studies have revealed that H₂S has versatile functions in plants as well. In this review, we summarize H₂S-mediated sulfur metabolic pathways, as well as the progress in the recognition of its biological functions in plant growth and development, particularly its physiological functions in biotic and abiotic stress responses. Besides direct chemical reactions, nitric oxide (NO) and hydrogen peroxide (H₂O₂) have complex relationships with H₂S in plant signaling, both of which mediate protein post-translational modification (PTM) to attack the cysteine residues. We also discuss recent progress in the research on the three types of PTMs and their biological functions in plants. Finally, we propose the relevant issues that need to be addressed in the future research.

GRAPHIC ABSTRACT

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s42994-021-00035-4.

Impact of intracellular hemin on N-type inactivation of voltage-gated K+ channels

N-type inactivation of voltage-gated K⁺ channels is conferred by the N-terminal “ball” domains of select pore-forming α subunits or of auxiliary β subunits, and influences electrical cellular excitability. Here, we show that hemin impairs inactivation of K⁺ channels formed by Kv3.4 α subunits as well as that induced by the subunits Kvβ1.1, Kvβ1.2, and Kvβ3.1 when coexpressed with α subunits of the Kv1 subfamily. In Kvβ1.1, hemin interacts with cysteine and histidine residues in the N terminus (C7 and H10) with high affinity (EC₅₀ 100 nM). Similarly, rapid inactivation of Kv4.2 channels induced by the dipeptidyl peptidase-like protein DPP6a is also sensitive to hemin, and the DPP6a mutation C13S eliminates this dependence. The results suggest a common mechanism for a dynamic regulation of Kv channel inactivation by heme/hemin in N-terminal ball domains of Kv α and auxiliary β subunits. Free intracellular heme therefore has the potential to regulate cellular excitability via modulation of Kv channel inactivation.

Carotid body type I cells engage flavoprotein and Pin1 for oxygen sensing

Carotid body (CB) type I cells sense the blood Po₂ and generate a nervous signal for stimulating ventilation and circulation when blood oxygen levels decline. Three oxygen-sensing enzyme complexes may be used for this purpose: 1) mitochondrial electron transport chain metabolism, 2) heme oxygenase 2 (HO-2)-generating CO, and/or 3) an NAD(P)H oxidase (NOX). We hypothesize that intracellular redox changes are the link between the sensor and nervous signals. To test this hypothesis type I cell autofluorescence of flavoproteins (Fp) and NAD(P)H within the mouse CB ex vivo was recorded as Fp/(Fp+NAD(P)H) redox ratio. CB type I cell redox ratio transiently declined with the onset of hypoxia. Upon reoxygenation, CB type I cells showed a significantly increased redox ratio. As a control organ, the non-oxygen-sensing sympathetic superior cervical ganglion (SCG) showed a continuously reduced redox ratio upon hypoxia. CN^-, diphenyleneiodonium, or reactive oxygen species influenced chemoreceptor discharge (CND) with subsequent loss of O₂ sensitivity and inhibited hypoxic Fp reduction only in the CB but not in SCG Fp, indicating a specific role of Fp in the oxygen-sensing process. Hypoxia-induced changes in CB type I cell redox ratio affected peptidyl prolyl isomerase Pin1, which is believed to colocalize with the NADPH oxidase subunit p47_phox in the cell membrane to trigger the opening of potassium channels. We postulate that hypoxia-induced changes in the Fp-mediated redox ratio of the CB regulate the Pin1/p47_phox tandem to alter type I cell potassium channels and therewith CND.