Intracellular Proprotein convertase subtilisin/kexin type 9: Recruitment and regulatory role in mitochondrial architecture and bioenergetic

Objective

Circulating Proprotein convertase subtilisin/kexin type 9 (PCSK9) captured the scientific community's attention as powerful target to fight against high serum cholesterol and its associated adverse consequences. Despite the well-described role of PCSK9 in impairing the recycling of low-density lipoprotein receptor (LDLR) on hepatocytes, its intracellular importance in metabolism modulations remain largely unexplored. Here, we describe a novel intracellular function of PCSK9 in hepatocyte metabolism and in liver regeneration.

Methods

A surgical model of partial hepatectomy (PH) was used to induce liver cell proliferation and serological and histological lipo- and glyco-metabolic perturbations were investigated in PCSK9 knockout and wild-type mice before and after PH. Mitochondrial bioenergetic level, compartmental architecture as well as intracellular localization and function of PCSK9 were further analyzed in vitro on murine primary isolated hepatocytes and PCSK9 lentiviral knockdown human liver cancer cell lines.

Results

Loss of PCSK9 expression led to a basal higher mitochondrial bioenergetic status in hepatocytes, characterized by a profound remodeling of mitochondrial architecture. Livers from PCSK9 knockout mice displayed a diffuse oxidative stress and a significant upregulation of cellular detoxification and superoxide radicals removal genes induced by the activation of c-Jun N-terminal kinase (JNK) pathway before PH. PCSK9 deficient mice showed a primed compensatory hepatic hyperplasia after PH, accompanied by an earlier transient regeneration-associated steatosis due to a higher LDLR expression and cholesterol uptake, with an increased β-oxidation, gluconeogenesis and glycolysis rate. Tetramethylrhodamine ethyl ester staining of isolated hepatocytes and liver cancer PCSK9 knockdown clones revealed a significantly reduced mitochondrial membrane potential when compared to controls. Confocal live-cell imaging and proteins immunoprecipitation showed respectively a mitochondrial recruitment of PCSK9 in proliferating cells and its interaction with mitochondrial membrane carriers and chaperons.

Conclusion

Despite the role played by circulating PCSK9 in regulating systemic cholesterol levels, our data shed light on its intracellular impact on mitochondrial architecture, membrane polarization and related metabolic perturbations in compartmental bioenergetics.

Ultrasensitive Label-Free Detection of Protein-Membrane Interaction Exemplified by Toxin-Liposome Insertion

Measuring the high-affinity binding of proteins to liposome membranes remains a challenge. Here, we show an ultrasensitive and direct detection of protein binding to liposome membranes using high throughput second harmonic scattering (SHS). Perfringolysin O (PFO), a pore-forming toxin, with a highly membrane selective insertion into cholesterol-rich membranes is used. PFO inserts only into liposomes with a cholesterol concentration >30%. Twenty mole-percent cholesterol results in neither SHS-signal deviation nor pore formation as seen by cryo-electron microscopy of PFO and liposomes. PFO inserts into cholesterol-rich membranes of large unilamellar vesicles in an aqueous solution with K_d = (1.5 ± 0.2) × 10^-12 M. Our results demonstrate a promising approach to probe protein-membrane interactions below sub-picomolar concentrations in a label-free and noninvasive manner on 3D systems. More importantly, the volume of protein sample is ultrasmall (<10 μL). These findings enable the detection of low-abundance proteins and their interaction with membranes.

Optimal liver metabolism and proliferation require the tight junction protein claudin-3

Objective

The expression of hepatic tight junction proteins and their contribution to homeostasis and regeneration remained largely unexplored. Here, we determine the cell type specific expression of tight junction genes in murine livers. We further explore the regulation and functional importance of the transmembrane protein CLDN3 in normal and regenerating livers.

Methods

Murine livers were used for tissue- and single cell RNA-seq. CLDN3 localization was determined by immunofluorescence. CLDN3+/+ or CLDN3-/- livers were analysed by electron microscopy, fluorescence-activated cell sorting and liquid chromatography mass spectrometry. Lipid content was quantified with oil-red. Mice were subjected to 2/3 partial hepatectomy. Proliferation was quantified with Ki67 and pHH3 stainings. Cell cycle gene expression was determined by RT-qPCR. Barrier impairments were assessed with total bile acid measurements. Differential gene expression was analysed by tissue RNAseq with DESeq2.

Results

We determined the profile of tight junction gene expression the main liver cell types, showing that tight junction transcripts can be found in hepatocytes and cholangiocytes but also on non-parenchymal cell populations. CLDN3 was among the highly expressed- and regulated genes in native and regenerating livers. CLDN3 had a zonated expression pattern. CLDN3-/- mice had microscopically intact tight junctions, but showed significantly downregulated hepatic energy metabolism and suboptimal cell proliferation in the regeneration model.

Conclusion

Our data suggests a functional role of CLDN3 for maintenance of energy homeostasis and optimal regeneration, proving that the function of hepatic tight junction proteins extends beyond basic membrane sealing.

Primordial GATA6 macrophages function as extravascular platelets in sterile injury

Most multicellular organisms have a major body cavity that harbors immune cells. In primordial species such as purple sea urchins, these cells perform phagocytic functions but are also crucial in repairing injuries. In mammals, the peritoneal cavity contains large numbers of resident GATA6⁺ macrophages, which may function similarly. However, it is unclear how cavity macrophages suspended in the fluid phase (peritoneal fluid) identify and migrate toward injuries. In this study, we used intravital microscopy to show that cavity macrophages in fluid rapidly form thrombus-like structures in response to injury by means of primordial scavenger receptor cysteine-rich domains. Aggregates of cavity macrophages physically sealed injuries and promoted rapid repair of focal lesions. In iatrogenic surgical situations, these cavity macrophages formed extensive aggregates that promoted the growth of intra-abdominal scar tissue known as peritoneal adhesions.

Impact of intensive care unit relocation and role of tap water on an outbreak of Pseudomonas aeruginosa expressing OprD-mediated resistance to imipenem

BACKGROUND

To assess the impact of the incidental relocation of an intensive care unit (ICU) on the risk of colonizations/infections with Pseudomonas aeruginosa exhibiting OprD-mediated resistance to imipenem (PA-OprD).

AIM

The primary aim was to compare the proportion of PA-OprD among P. aeruginosa samples before and after an incidental relocation of the ICU. The role of tap water as a route of contamination for colonization/infection of patients with PA-OprD was assessed as a secondary aim.

METHODS

A single-centre, observational, before/after comparison study was conducted from October 2013 to October 2015. The ICU was relocated at the end of October 2014. All P. aeruginosa-positive samples isolated from patients hospitalized ≥48 h in the ICU were included. Tap water specimens were collected every three months in the ICU. PA-OprD strains isolated from patients and tap water were genotyped using pulse-field gel electrophoresis.

FINDINGS

A total of 139 clinical specimens of P. aeruginosa and 19 tap water samples were analysed. The proportion of PA-OprD strains decreased significantly from 31% to 7.7% after the relocation of the ICU (P = 0.004). All PA-OprD clinical specimens had a distinct genotype. Surprisingly, tap water was colonized with a single PA-OprD strain during both periods, but this single clone has never been isolated from clinical specimens.

CONCLUSION

Relocation of the ICU was associated with a marked decrease in P. aeruginosa strains resistant to imipenem. The polyclonal character of PA-OprD strains isolated from patients and the absence of tap-water-to-patient contamination highlight the complexity of the environmental impact on the endogenous colonization/infection with P. aeruginosa.

Compression and crevasses in vitreous sections under different cutting conditions

Compression and crevasses are common cutting artefacts in cryo-ultramicrotomy of vitreous sections. They can be reduced or suppressed under optimal cutting conditions. In the present study, compression and thickness were measured for different cutting speeds and knife angles. It was found that compression decreased with feed and that crevasses appeared only above a certain thickness. The optimal feed for vitreous sections was between 50 and 80 nm. The thickness, calculated by two independent methods, was quantitatively related to feed and compression.

The lipophilic hapten parthenolide induces interferon-gamma and interleukin-13 production by peripheral blood-derived CD8+ T cells from contact allergic subjects in vitro

BACKGROUND

Peripheral blood mononuclear cells (PBMC) from persons with contact allergy to nickel react in vitro predominantly with nickel-induced CD4+ T cell-mediated production of both T-cell type 1 and 2 cytokines.

OBJECTIVES

The aim of the present study was to investigate if the contact allergen parthenolide, a sesquiterpene lactone of lipophilic character, elicits an immune response which differs from that induced by water-soluble nickel ions.

PATIENTS AND METHODS

Ten allergic subjects with strong (n = 6), moderate (n = 2), or weak (n = 2) patch-test reactivity to parthenolide and five patch test-negative control subjects participated in the study. PBMC from the subjects were analysed for in vitro reactivity with parthenolide by an enzyme-linked immunospot (ELISpot) assay, measuring cytokine production at the single-cell level.

RESULTS

The allergic group, but not the control group, responded to parthenolide with increased numbers of cells producing interferon (IFN)-gamma, interleukin (IL)-2, IL-4, IL-5 (P < 0.05 for all) and IL-13 (P < 0.01). The responses manifested by T-cell type 1 (IFN-gamma and IL-2) and type 2 (IL-4, IL-5 and IL-13) cytokines were positively correlated between cytokines. Subjects with a strong or moderate, but not weak or negative, patch-test reaction displayed detectable in vitro responses. In contrast to the CD4+ T cell-mediated peripheral reactivity induced by nickel, cell depletion experiments identified the parthenolide-reactive IFN-gamma- and IL-13-producing cells as CD8+ T cells.

CONCLUSIONS

The finding that the PBMC reactivity to parthenolide in humans involves a CD8+ T cell-mediated type 1 and 2 cytokine response warrants further studies on the relationship between the chemical nature of a hapten and the resulting immune response.

Nickel-induced IL-10 down-regulates Th1- but not Th2-type cytokine responses to the contact allergen nickel

Whereas the involvement of Th1- and Th2-type cytokines in contact allergy to nickel (Ni) is well documented, the role of the regulatory cytokine IL-10 is less clear. We therefore investigated the impact of IL-10 on Ni-induced Th1- (IFN-gamma) and Th2-type (IL-4 and IL-13) cytokine responses in human peripheral blood mononuclear cells (PBMC). PBMC from 15 blood donors with reactivity to Ni (Ni-PBMC) and 8 control donors devoid of reactivity (control PBMC) were stimulated with Ni and the frequency of cytokine-producing cells and the levels of secreted cytokines were analysed by ELISpot (IL-4, IL-13 and IFN-gamma) and ELISA (IL-10, IL-13 and IFN-gamma), respectively. The Ni-induced response was further assessed in the presence of recombinant IL-10 (rIL-10) or neutralizing antibody to IL-10 and the phenotype of the Ni-specific cytokine-producing cells regulated by IL-10 was determined by cell depletion experiments. Ni induced IL-10 production in Ni-PBMC (mean, (range); 33.1 pg/ml (0-93.4 pg/ml)) but not control PBMC (2.2 pg/ml (0-14.9 pg/ml)) (P = 0.002). Ni also induced significant production of IL-4, IL-13 and IFN-gamma that correlated with the IL-10 response. Addition of rIL-10 down-regulated the Ni-induced production of all cytokines but with a more pronounced effect on IFN-gamma. However, neutralization of Ni-induced IL-10 enhanced the levels of IFN-gamma induced by Ni (P = 0.004) but did not affect the number of IFN-gamma-producing cells or the production of other cytokines. Cell depletion experiments suggested that the Ni-specific IFN-gamma (and Th2-type cytokine) producing cells were CD4(+) T cells. The impact of IL-10 on Ni-induced IFN-gamma responses by CD4(+) T cells suggests that an important role of IL-10 in vivo is to counteract the allergic reactions mediated by Th1-type cytokines.

Multi-subtype gp160 DNA immunization induces broadly neutralizing anti-HIV antibodies

A highly desirable feature for an human immunodeficiency virus type 1 (HIV-1) vaccine is the ability to induce broadly reactive anti-envelope antibodies that can neutralize primary HIV-1 isolates. Two immunizations with an HIV-1 envelope-encoding plasmid together with recombinant granulocyte-macrophage colony-stimulating factor (rGM-CSF) resulted in high antibody titers in mice. The antibody induction was further enhanced after immunization with genes encoding HIV-1 envelopes originating from subtypes A, B and C. The sera from these animals were able to neutralize A, B and C viral isolates, whereas the sera from animals immunized solely with subtype B DNA neutralized only subtype B virus. The combined DNA vaccine gave serum antibodies with broad recognition of HIV-1 envelope epitopes as determined by peptide mapping. Cell-mediated immunity was not compromised by the increased humoral immunity. This demonstrates the ability of multiple envelope genes to induce the desired antibody response against several subtypes. Moreover, it documents the ability of rGM-CSF to enhance the potency of such a vaccine when given simultaneously. The strategy may be useful for making an HIV vaccine more potent and broadly effective against strains of different clades.

Genetic immunization is augmented by murine polyomavirus VP1 pseudocapsids

To improve immune responses induced by DNA immunization, murine polyomavirus major capsid protein (VP1) pseudocapsids were complexed with a DNA plasmid encoding the p37 (p24 and p17) nucleocapsid proteins of the human immunodeficiency virus type 1 (HIV-1). A 10-fold increase in antibody titer was noted in mice given DNA plasmid together with VP1 pseudocapsids in comparison to animals that received DNA plasmid alone. Cell mediated responses to HIV-1 p24 occurred, but were not significantly augmented by delivering the DNA as a VP1 complex. We have consequently for the first time shown a carrier/adjuvant effect of polyomavirus pseudocapsids that strongly increased the humoral immune response in DNA immunization.

HIV subtypes and recombination strains--strategies for induction of immune responses in man

Clinical and experimental studies of HIV-1 subcomponents were made in order to increase their immunogenicity. HIV subtype envelopes A, B and C have been compared and a detailed analysis made by peptides of the coreceptor-ligand interactions. We identified a direct interaction between HIV-1 envelope and a cellular receptor at the amino acid level. Both the viral subtype and its tropism appeared to influence inhibition of infection. Genetic immunization induced new cytotoxic responses while proteins appeared to efficiently boost previous responses. One HIV-1 subtype B antigen was strongly immunogenic in a human immunotherapeutic trial and permitted better survival at 2 years of the study in patients with poor prognosis.

DNA-encoding enzymatically active HIV-1 reverse transcriptase, but not the inactive mutant, confers resistance to experimental HIV-1 challenge

The present study was undertaken to examine the immunogenicity of a single plasmid DNA representing the reverse transcriptase (RT) of HIV-1. Plasmids containing the enzymatically active RT as well as a mutated nonenzymatically active RT with nucleotide (nt)-binding motifs of YMDD and YMLL, respectively, were used to immunize mice. Both constructs induced similar good antibody and T cell responses, with a tendency towards antibody directed to peptides representing the active and mutated sites. Immunized mice were challenged with a murine pseudotype HIV-1/MuLV infected spleen cells. Seven out of 10 mice immunized with RT had no recoverable HIV-1, while 10 individuals immunized with the RT mutant and all the 18 controls had high levels of recoverable HIV-1. This indicates that mutation of RT reduces the desired immunogenicity.

An in vivo model for HIV resistance development

Treatment of human immunodeficiency virus (HIV-1) with drugs targeted to the reverse transcriptase (RT) rapidly selects for drug-resistant virus. It is essential to develop a suitable animal model that allows the study of the emergence and reversal of drug resistance. A monkey model was previously developed on the basis of a hybrid virus (RT-SHIV) of simian immunodeficiency virus (SIV) with its RT exchanged for HIV-1 RT. In the present study cynomolgus monkeys infected with RT-SHIV were treated with varying doses of the non-nucleoside RT inhibitor nevirapine. The drug was administered for 2-3 weeks, in agreement with clinical experience of resistance development during nevirapine monotherapy. This resulted in the selection of mutants with Y181C and K103N changes in RT, which correspond to the HIV-1 mutations in nevirapine-resistant HIV-1 patients. The mutants coexisted at varying levels with wild-type virus and fluctuations in the proportion of mutants could be closely monitored. Low-dose treatment was not more efficient in induction of mutations than a virus-inhibiting dose. Structured therapy interruptions could be performed. The monkey RT-SHIV infection offers an in vivo model to determine effects of therapies on resistance development.

Induction of immune responses and break of tolerance by DNA against the HIV-1 coreceptor CCR5 but no protection from SIVsm challenge

An inactivating mutation in the human CCR5 gene reduces the risk of HIV-1 infection in individuals with homozygous alleles. We explored whether genetic immunization would induce an immune response directed to CCR5 structures and if immunological tolerance toward endogenous CCR5 could be broken. We also studied whether this immunization approach could protect cynomolgus monkeys from an infection, with SIVsm, which primarily uses CCR5 as a coreceptor. Epidermal but not intramuscular delivery of the CCR5 gene to mice elicited strong IgG antibody binding responses to CCR5. Intramucosal immunization of cynomolgus macaques with CCR5 DNA followed by boosts with CCR5 peptides induced prominent IgG and IgA antibody responses in serum and vaginal washings. The CCR5-specific antibodies neutralized the infectivity of primary human R5 HIV-1 strains, and the macaque SIVsm but not that of a tissue culture-adapted X4 HIV-1 strain. The consecutive CCR5 gene and CCR5 peptide immunizations induced B- and T-cell responses to peptides representing both human and macaque amino acid sequences of the respective CCR5 proteins. This indicates that tolerance was broken against endogenous macaque CCR5, which has a 98% homology to the human CCR5 gene. After the final boost, the vaccinated monkeys together with two control monkeys were challenged with SIVsm. Neither protection against nor enhancement of SIVsm infection was achieved.

[Esophagus carcinoid--a rare differential diagnosis in malignant esophageal neoplasia]

Two of patients with a carcinoid tumor of the esophagus are reported, an extremely rare localisation. Eight months after esophagectomy the 50-year-old male is entirely well and without any sign of recurrence; the 56-year-old female has died in this time. Our two cases are discussed in comparison with seven cases found in the literature.