B cell triggering by bacterial lipopeptide involves both translocation and activation of the membrane-bound form of protein kinase C

B cell activation by the lipopeptide trispalmitoyl-cysteinyl-alanyl-glycine (TPP), the biologically active moiety of bacterial lipoprotein, results in protein kinase C (PKC) translocation from the cytosol to the plasma membrane, as well as a significant increase in the activity of membrane-associated PKC that can be observed by in vitro incubation with TPP of partially purified PKC at calcium concentrations in the range of those prevailing in unstimulated B cells. TPP does not affect either the phosphoinositide turnover or the cytosolic-free calcium concentration, but promotes an increase in the intracellular pH that can be blocked by the PKC-inhibitors staurosporine or H-7. Moreover, incubation of B cells with staurosporine suppressed the proliferative response promoted by TPP at a half-maximum effective dose of 16 nM. Activation by TPP of PKC isoenzymes resolved after hydroxylapatite chromatography revealed that the resulting beta I/beta II isoenzyme was more sensitive than the alpha isoenzyme. These results suggest that TPP might mediate B cell activation via interaction with the membrane-associated fraction of PKC.

Protein kinase C mobilization in B lymphocytes. Differential isoenzyme translocation upon activation

The subcellular distribution of protein kinase C has been analyzed in murine B lymphocytes exposed to LPS, anti-IgM antibodies and phorbol dibutyrate. An accurate determination of the enzyme mobilized from the soluble to the particulate fractions by these activators, has been made possible by the use of B cells in which the major part of the activity was present in the cytosol. Upon stimulation, we have analyzed the isoenzymatic forms translocated to the B cell membrane, showing a differential pattern of isoenzyme mobilization between LPS and anti-IgM antibodies. These data, together with the different Ca2+ requirements for the activation of the translocated protein kinase C isoenzymes, might help to unravel the mechanism responsible for the clonal expansion and differentiation of B lymphocytes, induced by the two ligands.

Interferon (IFN)-gamma and Herpes simplex virus/tumor necrosis factor-alpha synergistically induce nitric oxide synthase 2 in macrophages through cooperative action of nuclear factor-kappa B and IFN regulatory factor-1

The radical nitric oxide (NO) constitutes an important part of the innate immune response to many viruses, and among these notably Herpes simplex virus (HSV). We have previously shown that HSV/tumor necrosis factor-alpha (TNF-alpha) and IFN-gamma synergistically induce NO production in macrophages, and here we have investigated the molecular mechanism underlying this phenomenon. The enhancement of NO production was regulated at the level of NO synthase 2 (NOS2, iNOS) transcription. The ISRE element of the NOS2 promoter, which binds IFN regulatory factor (IRF)-1, was essential both for full responsiveness to IFN-gamma and the synergistic response. The GAS motif, binding signal transducer and activator of transcription 1 (STAT1), did not contribute to the cross-talk with virus/TNF-induced signals, but was necessary for full responsiveness to IFN-gamma. The distal binding site for nuclear factor (NF)-kappa B was important for the cooperative response, while the proximal kappa B site was not involved in the cooperative promoter activation but played a role in full promoter inducibility. By ectopic expression of IRF-1 and NF-kappa B (p65), we found that these factors synergistically induce NO accumulation. Together, our results show that binding of IRF-1 and NF-kappa B to their respective sites in the distal domain of the NOS2 promoter, creates a potent trans-activating complex with the ability to induce NOS2 transcription synergistically in response to simultaneous HSV-2/TNF-alpha and IFN-gamma treatment.

Potential Beneficial Role of Nitric Oxide in SARS-CoV-2 Infection: Beyond Spike-Binding Inhibition

SARS-CoV-2, the causative virus for the COVID-19 disease, uses its spike glycoprotein to bind to human ACE2 as a first step for viral entry into the cell. For this reason, great efforts have been made to find mechanisms that disrupt this interaction, avoiding the infection. Nitric oxide (NO) is a soluble endogenous gas with known antiviral and immunomodulatory properties. In this study, we aimed to test whether NO could inhibit the binding of the viral spike to ACE2 in human cells and its effects on ACE2 enzymatic activity. Our results show that ACE2 activity was decreased by the NO donors DETA-NONOate and GSNO and by the NO byproduct peroxynitrite. Furthermore, we found that DETA-NONOate could break the spike-ACE2 interaction using the spike from two different variants (Alpha and Gamma) and in two different human cell types. Moreover, the same result was obtained when using NO-producing murine macrophages, while no significant changes were observed in ACE2 expression or distribution within the cell. These results support that it is worth considering NO as a therapeutic agent for COVID-19, as previous reports have suggested.

Nitric oxide synthesis in rat peritoneal macrophages is induced by IgE/DNP complexes and cyclic AMP analogues. Evidence in favor of a common signaling mechanism

The production of nitric oxide was studied in rat adherent peritoneal cells stimulated with preformed IgE/DNP-BSA complexes made of IgE obtained from a secreting hybridoma. Stimulation with complexes at equivalence induced both the production of NO and an increased expression of the mRNA of the inducible isoform of NO synthase (iNOS). Production of NO was also elicited by a rabbit polyclonal F(ab')2 anti-CD23 cross-reacting with rat CD23. Because IgE/DNP-BSA complexes did not elicit Ca2+ mobilization and genistein did not influence the production of NO, cyclic AMP was considered as an alternative signaling molecule. Combination of a suboptimal concentration of dibutyryl cyclic AMP and IgE/DNP-BSA complexes showed an additive effect on NO production, whereas this was not observed when the agonists were used at supraoptimal doses. The inhibitor of cyclic AMP-specific phosphodiesterase IV, rolipram, which acts on the enzyme isoform predominantly expressed in inflammatory cells, also induced the production of NO. Furthermore, IgE/DNP-BSA complexes increased intracellular levels of cyclic AMP. Taken together, these data indicate that stimulation of mononuclear phagocytes via the low-affinity receptor Fc epsilon RII or rising intracellular concentrations of cyclic AMP leads to an enhanced expression of iNOS. Evidence in favor of the involvement of cyclic AMP in the signaling pathway linked to Fc epsilon RII is provided by the effect of IgE/DNP-BSA complexes on intracellular cyclic AMP levels and by the additive effect produced by dibutyryl cyclic AMP on NO production elicited by IgE/DNP-BSA complexes.

Reprogramming of the LXRα Transcriptome Sustains Macrophage Secondary Inflammatory Responses

Macrophages regulate essential aspects of innate immunity against pathogens. In response to microbial components, macrophages activate primary and secondary inflammatory gene programs crucial for host defense. The liver X receptors (LXRα, LXRβ) are ligand-dependent nuclear receptors that direct gene expression important for cholesterol metabolism and inflammation, but little is known about the individual roles of LXRα and LXRβ in antimicrobial responses. Here, the results demonstrate that induction of LXRα transcription by prolonged exposure to lipopolysaccharide (LPS) supports inflammatory gene expression in macrophages. LXRα transcription is induced by NF-κB and type-I interferon downstream of TLR4 activation. Moreover, LPS triggers a reprogramming of the LXRα cistrome that promotes cytokine and chemokine gene expression through direct LXRα binding to DNA consensus sequences within cis-regulatory regions including enhancers. LXRα-deficient macrophages present fewer binding of p65 NF-κB and reduced histone H3K27 acetylation at enhancers of secondary inflammatory response genes. Mice lacking LXRα in the hematopoietic compartment show impaired responses to bacterial endotoxin in peritonitis models, exhibiting reduced neutrophil infiltration and decreased expansion and inflammatory activation of recruited F4/80lo-MHC-IIhi peritoneal macrophages. Together, these results uncover a previously unrecognized function for LXRα-dependent transcriptional cis-activation of secondary inflammatory gene expression in macrophages and the host response to microbial ligands.

Chronic treatment with acetaminophen protects against liver aging by targeting inflammation and oxidative stress

The liver exhibits a variety of functions that are well-preserved during aging. However, the cellular hallmarks of aging increase the risk of hepatic alterations and development of chronic liver diseases. Acetaminophen (APAP) is a first choice for relieving mild-to-moderate pain. Most of the knowledge about APAP-mediated hepatotoxicity arises from acute overdose studies due to massive oxidative stress and inflammation, but little is known about its effect in age-related liver inflammation after chronic exposure. Our results show that chronic treatment of wild-type mice on the B6D2JRcc/Hsd genetic background with APAP at an infratherapeutic dose reduces liver alterations during aging without affecting body weight. This intervention attenuates age-induced mild oxidative stress by increasing HO-1, MnSOD and NQO1 protein levels and reducing ERK1/2 and p38 MAPK phosphorylation. More importantly, APAP treatment counteracts the increase in Cd8+ and the reduction in Cd4+ T lymphocytes observed in the liver with age. This response was also found in peripheral blood mononuclear cells. In conclusion, chronic infratherapeutic APAP treatment protects mice from age-related liver alterations by attenuating oxidative stress and inflammation.

Experience with the ACURATE neo and neo2 transcatheter aortic valves in Spain. The PRECISA (PRospective Evaluation Complementing Investigation with ACURATE devices) registry

BACKGROUND

Previous studies have documented a high rate of implantation success with the ACURATE neo2 valve, as well as a reduction in paravalvular leak (PVL) compared to its predecessor, the ACURATE neo. However, there are no studies that have reviewed and compared the long-term clinical and hemodynamic outcomes of these patients.

AIMS

This study aimed to evaluate the results of the ACURATE neo transcatheter aortic valve in a real-world context, and to compare the results of the outcomes of both generations of this device (ACURATE neo and ACURATE neo2), with a specific focus on procedural success, safety, and long-term effectiveness.

METHODS

A prospective study including all consecutive patients treated with the ACURATE neo device in seven hospitals was conducted (Clinical Trials Identification Number: NCT03846557). The primary endpoint consisted of a composite of adverse events, including mortality, aortic insufficiency, and other procedural complications. As the second-generation device (ACURATE neo2) replaced the ACURATE neo during the study period, hemodynamic and clinical results before admission, at 30 days, and at 1 year of follow-up were compared between the two generations.

RESULTS

A total of 296 patients underwent transcatheter aortic valve implantation with the ACURATE device, with 178 patients receiving the ACURATE neo and 118 patients receiving the ACURATE neo2. In the overall population, the absence of device success occurred in 14.5%. The primary reason for the absence of device success was the presence of para-valvular regurgitation ≥ 2. There were no instances of coronary occlusions, valve embolization, annulus rupture, or procedural deaths. ACURATE neo2 was associated with a significantly higher device success rate (91.7% vs. 82%, p = 0.04), primarily due to a significantly lower rate of para-valvular regurgitation, which remained significant at 1 year.

CONCLUSION

The use of ACURATE neo and neo2 transcatheter aortic valves is associated with satisfactory clinical results and an extremely low rate of complications. The ACURATE neo2 enables a significantly higher device success rate, primarily attributed to a significant reduction in the rate of PVL.

Nitric oxide, vascular function and exercise

NO (nitric oxide) is a diffusible gas molecule produced intracellularly by three distinct nitric oxide synthase (NOS) enzymes that are highly conserved in mammalian species. The NOS enzymes are haemcontaining proteins that catalyse a fiveelectron oxidation process of the guanidino nitrogen of arginine and in the presence of O2. NOS activity is, in fact, a tandem of two consecutive reactions: a reductase step catalysed by a moiety of NOS homologous with the cytochrome P450 reductase, including the NADPH and flavin nucleotide cofactorbinding domains, and an oxygenase step coupling the reduction of Fe3+ to Fe2+ in the haem to the release of NO and citrulline from arginine and molecular oxygen. The reaction requires several cofactors, including tetrahydrobiopterin and calcium/calmodulin.

Protein kinase C isoenzymes display differential affinity for phorbol esters. Analysis of phorbol ester receptors in B cell differentiation

Protein kinase C (PKC) comprises a family of distinct isoenzymes that are involved in signal transduction pathways linking the cell to triggers perceived via membrane receptors. These isoenzymes differ in their tissue distribution, activation requirements, and substrate specificity. One common denominator among different PKC subspecies is their activation by phorbol esters. We have developed a sensitive method permitting the measurement of phorbol ester binding sites, their quantitation, as well as their dissociation kinetics, by performing cytofluorometric analyses on intact cells or on isolated PKC associated to phosphatidylserine vesicles incubated in the presence of fluorochrome-labeled phorbol ester. Both PKC isozymes beta I/beta II and alpha from brain and spleen after incorporation into phosphatidylserine vesicles, display affinities with apparent Kd of 120 and 50 nM, respectively; although PKC gamma from brain exhibits a Kd of 210 nM. In addition to these receptors, on PKC isozymes from spleen, an intermediate affinity phorbol ester receptor (Kd of 3 nM) and an additional high affinity phorbol ester binding site with a Kd of 0.1 to 0.5 nM were also detected. This latter receptor comigrates with high m.w. PKC isoforms. In different cell lines, the phorbol ester binding patterns, as well as the expression of individual PKC isoenzymes, could be positively correlated.

[Changes in distribution and isoenzymatic expression of protein kinase C in B lymphocytes induced by alloantigenic stimulation]

Protein kinase C comprises a family of distinct isoenzymes that are involved in signal transduction pathway triggered by activation of membrane receptor. These isoenzymes differ in their tissue distribution, activation requirements and substrate specificity. Recent reports have shown the regulation of PKC-isoenzymes expression in physiological and pathological models. Recently, we shown PKC participation in B cells allogeneic response to intact cells and solubilized alloantigen. Here, alloimmunization influence upon PKC isoforms expression on murine B cells was analyzed. Our data indicates that PKC beta is the main isoform expressed on B cells with a lesser amount of alpha, epsilon and zeta and a very small amount of delta isoform. When analyzing B cells from alloimmunized mice we observed an increment of isoforms a and e and a decrease of the beta isoforms while increasing the number of immunizations. An increase of membrane bound PKC enzyme was also observed. Furthermore with increasing number of immunizations a decrease in LPS induce proliferation was found. In contrary, while normal B cells showed non proliferation when stimulated with solubilized alloantigen, they displayed a strong proliferation when they were obtained from animals with 5-6 alloimmunizations. This results shown that alloimmunization induces changes in the distribution and expression of PKC isoenzymes that are correlated to changes in the biological response triggered by B cell stimulation.

3,4-dimethoxychalcone induces autophagy and reduces neointimal hyperplasia and aortic lesions in mouse models of atherosclerosis

Autophagy inducers can prevent cardiovascular aging and age-associated diseases including atherosclerosis. Therefore, we hypothesized that autophagy-inducing compounds that act on atherosclerosis-relevant cells might have a protective role in the development of atherosclerosis. Here we identified 3,4-dimethoxychalcone (3,4-DC) as an inducer of autophagy in several cell lines from endothelial, myocardial and myeloid/macrophagic origin, as demonstrated by the aggregation of the autophagosome marker GFP-LC3 in the cytoplasm of cells, as well as the downregulation of its nuclear pool indicative of autophagic flux. In this respect, 3,4-DC showed a broader autophagy-inducing activity than another chalcone (4,4- dimethoxychalcone), spermidine and triethylene tetramine. Thus, we characterized the potential antiatherogenic activity of 3,4-DC in two different mouse models, namely, (i) neointima formation with smooth muscle expansion of vein segments grafted to the carotid artery and (ii) genetically predisposed ApoE-/- mice fed an atherogenic diet. In the vein graft model, local application of 3,4-DC was able to maintain the lumen of vessels and to reduce neointima lesions. In the diet-induced model, intraperitoneal injections of 3,4-DC significantly reduced the number of atherosclerotic lesions in the aorta. In conclusion, 3,4-DC stands out as an autophagy inducer with potent antiatherogenic activity.