H2S counteracts proinflammatory effects of LPS through modulation of multiple pathways in human cells

BACKGROUND

Hydrogen sulfide donors reduce inflammatory signaling in vitro and in vivo. The biological effect mediated by H₂S donors depends on the kinetics of the gas release from the donor molecule. However, the molecular mechanisms of H₂S-induced immunomodulation were poorly addressed. Here, we studied the effect of two different hydrogen sulfide (H₂S)-producing agents on the generation of the LPS-induced inflammatory mediators. Importantly, we investigated the transcriptomic changes that take place in human cells after the LPS challenge, combined with the pretreatment with a slow-releasing H₂S donor-GYY4137.

METHODS

We investigated the effects of GYY4137 and sodium hydrosulfide on the release of proinflammatory molecules such as ROS, NO and TNF-α from LPS-treated human SH-SY5Y neuroblastoma and the THP-1 promonocytic cell lines. Transcriptomic and RT-qPCR studies using THP-1 cells were performed to monitor the effects of the GYY4137 on multiple signaling pathways, including various immune-related and proinflammatory genes after combined action of LPS and GYY4137.

RESULTS

The GYY4137 and sodium hydrosulfide differed in the ability to reduce the production of the LPS-evoked proinflammatory mediators. The pre-treatment with GYY4137 resulted in a drastic down-regulation of many TNF-α effectors that are induced by LPS treatment in THP-1 cells. Furthermore, GYY4137 pretreatment of LPS-exposed cells ameliorates the LPS-mediated induction of multiple pro-inflammatory genes and decreases expression of immunoproteasome genes. Besides, in these experiments we detected the up-regulation of several important pathways that are inhibited by LPS.

CONCLUSION

Based on the obtained results we believe that our transcriptomic analysis significantly contributes to the understanding of the molecular mechanisms of anti-inflammatory and cytoprotective activity of hydrogen sulfide donors, and highlights their potential against LPS challenges and other forms of inflammation.

[Heat-shock protein HSP70 protects neuroblastoma cells SK-N-SH from the neurotoxic effects hydrogen peroxide and the β-amyloid peptide]

Neuronal cell death in Alzheimer's disease is associated with the development of oxidative stress caused by the reactive oxygen species (ROS), which can be generated as a result of the effect of beta-amyloid peptides. One of the sources of ROS is hydrogen peroxide, inducing the apoptosis and necrosis of neural tissue cells. The mechanism of hydrogen peroxide apoptotic action includes launching signaling pathways that involve protein kinases PI3K, p38MAPK, JNK and ERK. Oxidative stress leads to increased synthesis of heat-shock proteins in the cells including HSP70. It was shown that the exogenous HSP70 could reduce generation of ROS in cells. In this study, we determined how HSP70 affected apoptosis and necrosis in human neuroblastoma cells SK-N-SH, induced by hydrogen peroxide and β-amyloid peptide Aβ(1-42). It was shown that HSP70 reduces the cytotoxic effects of hydrogen peroxide and beta-amyloid, and protein kinases PI3K and JNK play an important role in the mechanism of HSP70 protective effect on the peroxide induced apoptosis in SK-N-SH cells.

Encapsulated Hsp70 decreases endotoxin-induced production of ROS and TNFα in human phagocytes

Human heat shock protein Hsp70 was experimentally inserted into polyelectrolyte microcapsules. Encapsulated recombinant Hsp70 was studied in terms of its effects on neutrophil apoptosis, the production of reactive oxygen species, and the secretion of tumor necrosis factor alpha by promonocytic THP-1 cells. It was found that encapsulated Hsp70 effectively inhibits neutrophil apoptosis, unlike free exogenous protein used in solution. In THP-1 cells, encapsulated and free Hsp70 reduced LPS-induced tumor necrosis factor alpha production with a similar efficiency. Encapsulated Hsp70 reduces LPS-induced reactive oxygen species production by neutrophils in the course of its release from the microcapsules but not as much as free Hsp70. Thus, the polyelectrolyte microcapsules can be used as containers for the effective delivery of Hsp70 to neutrophils and monocytes to significantly improve the functioning of the innate immune system.

Exogenous heat shock protein HSP70 reduces response of human neuroblastoma cells to lipopolysaccharide

The effect of exogenous heat shock protein HSP70 and lipopolysaccharide (LPS) on the production of reactive oxygen species (ROS), TNFα secretion, and mRNA expression by human neuroblastoma SK-N-SH cells. It was shown that exogenous HSP70 protects neuroblastoma cells from the action of LPS. The protection mechanism of HSP70 includes a reduction in the production of ROS and TNFα and a decrease in the expression of TLR4 and IL-1β mRNA in SK-N-SH cells induced by LPS.

Effect of various E. coli LPS chemotypes on apoptosis and activation of human neutrophils

We studied the effects of various Escherichia coli LPS chemotypes on the production of reactive oxygen species and regulation of apoptosis in human neutrophils. A correlation was found between the increase in chemiluminescence (Re-LPS<Ra-LPS<S-LPS) and lengthening of the polysaccharide chain in endotoxins. Shortening of the polysaccharide chain was associated with more pronounced inhibition of neutrophil apoptosis under the influence of endotoxins, which correlated with the increase in hydrophobicity of these chemotypes.

Effects of pH, Ca2+ and lanthanides on conformation of the sarcoplasmic reticulum Ca(2+)-ATPase catalytic site

The conformational changes at the ATP-catalytic site of the sarcoplasmic reticulum (SR) Ca(2+)-ATPase have been studied by the fluorescence of the fluorescein 5-isothiocyanate (FITC) bound to the adenine subsite. The FITC-SR fluorescence parameters have been examined in the pH range 5.7-8.0 in the presence of EGTA, Ca2+ or Ln3+ (La3+, Pr3+, Nd3+, Tb3+, etc.). A quantitative method to calculate the equilibrium between the protein conformers is proposed on the basis of the fluorometric titration curve analysis. The distance Nd(3+)-FITC was estimated to be about 1 nm at pH 6-7 and 1.7 nm at pH 8 which can be interpreted as an increase of the distance between the nucleotide and phosphorylation domains of Ca(2+)-ATPase in alkaline media. These studies suggest that the ligand-stabilized E1-form of Ca(2+)-ATPase can exist in two conformational states with the closed and opened interdomain cleft in the pH range 5.7-8.0. The pH-dependence of the ratio of these states correlates with that of the E1----E2 equilibrium without ligands. These dependences were approximated by simple Henderson-Hasselbach equations with pK 7.0 +/- 0.1, i.e. the transition between two protein conformations is probably governed by one proton dissociation.

[Enalaprilat Inhibits Zinc-Dependent Oligomerization of Metal-Binding Domain of Amyloid-beta Isoforms and Protects Human Neuroblastoma Cells from Toxic Action of these Isoforms]

Intact amyloid-β peptides (Aβ) may undergo prion-like aggregation when they interact with chemically or structurally modified variants of Aβ present in extracellular pathohistological inclusions (amyloid plaques). This aggregation is regarded as one of the key molecular mechanisms of Alzheimer's disease (AD) pathogenesis. Zinc ions are involved in the pathological dimerization and oligomerization of natural Aβ isoforms, and zinc-induced oligomers can also initiate the pathological aggregation of Aβ. Based on the earlier found molecular mechanism of zinc-dependent oligomerization of Aβ, it has been suggested that the targeted inhibition of the 11EVHH14 site in one Aβ molecule from zinc-mediated interactions with the same site of another Aβ molecule can effectively inhibit the oligomerization and aggregation of Aβ. Taking into account the similarity in the structural organization of zinc-binding sites within Aβ and angiotensin-converting enzyme (ACE), we hypothesized that inhibitors of the ACE active sites could specifically interact with the 11EVHH14 site of Aβ. Using a surface plasmon resonance biosensor and nuclear magnetic resonance spectroscopy, we have found that the ACE inhibitor enalaprilat effectively inhibits zinc-dependent dimerization of the metal-binding domains of intact Aβ and Aβ with isomerized Asp7 (isoAβ). We have also found that enalaprilat protects SH-SY5Y human neuroblastoma cells from the toxic effects of Aβ(1-42) and isoAβ(1-42), which are among the most common components of amyloid plaques. The results confirm the role of zincdependent oligomerization of Aβ in AD pathogenesis and make it possible one to consider enalaprilat as a prototype of antiaggregation agents for treating AD.