Unveiling the Antiviral Properties of Panduratin A through SARS-CoV-2 Infection Modeling in Cardiomyocytes

Establishing a drug-screening platform is critical for the discovery of potential antiviral agents against SARS-CoV-2. In this study, we developed a platform based on human induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) to investigate SARS-CoV-2 infectivity, with the aim of evaluating potential antiviral agents for anti-SARS-CoV-2 activity and cardiotoxicity. Cultured myocytes of iPSC-CMs and immortalized human cardiomyocyte cell line (AC-16) were primarily characterized for the expression of cardiac markers and host receptors of SARS-CoV-2. An infectivity model for the wild-type SARS-CoV-2 strain was then established. Infection modeling involved inoculating cells with SARS-CoV-2 at varying multiplicities of infection (MOIs) and then quantifying infection using immunofluorescence and plaque assays. Only iPSC-CMs, not AC16 cells, expressed angiotensin-converting enzyme 2 (ACE-2), and quantitative assays confirmed the dose-dependent infection of iPSC-CMs by SARS-CoV-2, unlike the uninfectable AC16 cells lacking the expression of ACE2. Cytotoxicity was evaluated using MTT assays across a concentration range. An assessment of the plant-derived compound panduratin A (panA) showed cytotoxicity at higher doses (50% cytotoxic concentration (CC50) 10.09 μM) but promising antiviral activity against SARS-CoV-2 (50% inhibition concentration (IC50) 0.8-1.6 μM), suppressing infection at concentrations 10 times lower than its CC50. Plaque assays also showed decreased viral production following panA treatment. Overall, by modeling cardiac-specific infectivity, this iPSC-cardiomyocyte platform enables the reliable quantitative screening of compound cytotoxicity alongside antiviral efficacy. By combining disease pathogenesis and pharmacology, this system can facilitate the evaluation of potential novel therapeutics, such as panA, for drug discovery applications.

Establishment and Characterization of MUi027-A: A Novel Patient-Derived Cell Line of Polycystic Kidney Disease with PKD1 Mutation

Autosomal dominant polycystic kidney disease (ADPKD) is one of the most prevalent genetic diseases affecting the kidneys. A genetically specific mutation model is required to comprehend its pathophysiology and to develop a drug treatment. In this study, we successfully developed human induced pluripotent stem cells (hiPSCs) named MUi027-A from skin fibroblasts of a patient diagnosed with ADPKD and carrying the PKD1 frameshift mutation (c.7946_7947delCT). MUi027-A cells showed the same genetic fingerprints as the parental cells, including the presence of the PKD1 mutation. MUi027-A hiPSCs displayed embryonic stem cell-like characteristics with the capability of differentiating into the three germ layers. Upon directed differentiation, MUi027-A hiPSCs could be differentiated into tubular organoids with the expression of renal cell markers. Furthermore, we compared the efficiency of cyst formation in two human iPSC lines with different PKD1 mutations. When cyst formation was induced by either forskolin or blebbistatin, MUi027-A hiPSC-derived kidney organoids displayed higher frequencies of cyst formation when compared to organoids generated from an iPSC cell line with non-truncating PKD1 mutation genotype (c.5878C > T), suggesting the presence of physiological differences in the mechanism of cyst formation between different PKD1 mutants. Overall, we generated and characterized a novel human iPSC line with a specific PKD mutation and demonstrated its potential as a disease model to study the pathophysiology of genetic determinants in the development of ADPKD disease.

N-Terminally Added Tag Selectively Enhances Heterologous Expression of VacA Cytotoxin Variants from Helicobacter pylori

BACKGROUND

Gastric pathogen Helicobacter pylori secretes VacA cytotoxin displaying a high degree of polymorphic variations of which the highest VacA pathogenicity correlates with m1-type variant followed by VacA-m2.

OBJECTIVE

To comparatively evaluate expression in Escherichia coli of the mature VacA variants (m1- and m2-types) and their 33- and 55/59-kDa domains fused with His₍₆₎ tag at N- or C-terminus.

METHODS

All VacA clones expressed in E. coli TOP10™ were analyzed by SDS-PAGE and Western blotting. VacA inclusions were solubilized under native conditions (~150-rpm shaking at 37°C for 2 h in 20 mM HEPES (pH7.4) and 150 mM NaCl). Membrane-perturbing and cytotoxic activities of solubilized VacA proteins were assessed via liposome-entrapped dye leakage and resazurin- based cell viability assays, respectively. VacA binding to human gastric adenocarcinoma cells was assessed by immunofluorescence microscopy. Side-chain hydrophobicity of VacA was analyzed through modeled structures constructed by homology- and ab initio-based modeling.

RESULTS

Both full-length VacA-m1 and 33-kDa domain were efficiently expressed only in the presence of N-terminal extension while its 55-kDa domain was capably expressed with either N- or Cterminal extension. Selectively enhanced expression was also observed for VacA-m2. Protein expression profiles revealed a critical period in IPTG-induced production of the 55-kDa domain with N-terminal extension unlike its C-terminal extension showing relatively stable expression. Both VacA- m1 isolated domains were able to independently bind to cultured gastric cells similar to the full- length toxin, albeit the 33-kDa domain exhibited significantly higher activity of membrane perturbation than others. Membrane-perturbing and cytotoxic activities observed for VacA-m1 appeared to be higher than those of VacA-m2. Homology-based modeling and sequence analysis suggested a potential structural impact of non-polar residues located at the N-terminus of the mature VacA toxin and its 33-kDa domain.

CONCLUSION

Our data provide molecular insights into selective influence of the N-terminally added tag on efficient expression of recombinant VacA variants, signifying biochemical and biological implications of the hydrophobic stretch within the N-terminal domain.

Molecular Insights into Zn2+ Inhibition of the Antibacterial Endopeptidase Lysostaphin from Staphylococcus simulans

BACKGROUND

Mature lysostaphin (~28-kDa Lss) from Staphylococcus simulans proves effective in killing methicillin-resistant Staphylococcus aureus (MRSA) which is endemic in hospitals worldwide. Lss is Zn²⁺-dependent endopeptidase, but its bacteriolytic activity could be affected by exogenously added Zn²⁺.

OBJECTIVE

To gain greater insights into structural and functional impacts of Zn²⁺and Ni²⁺on Lss-induced bioactivity.

METHODS

Lss purified via immobilized metal ion-affinity chromatography was assessed for bioactivity using turbidity reduction assays. Conformational change of metal ion-treated Lss was examined by circular dichroism and intrinsic fluorescence spectroscopy. Co-sedimentation assay was performed to study interactions between Zn²⁺-treated Lss and S. aureus peptidoglycans. Metal ionbinding prediction and intermolecular docking were used to locate an extraneous Zn²⁺-binding site.

RESULTS

A drastic decrease in Lss bioactivity against S. aureus and MRSA was revealed only when treated with Zn²⁺, but not Ni²⁺, albeit no negative effect of diethyldithiocarbamate-Zn²⁺-chelator on Lss-induced bioactivity. No severe conformational change was observed for Lss incubated with exogenous Zn²⁺ or Ni²⁺. Lss pre-treated with Zn²⁺ efficiently bound to S. aureus cell-wall peptidoglycans, suggesting non-interfering effect of exogenous metal ions on cell-wall targeting (CWT) activity. In silico analysis revealed that exogenous Zn²⁺, but not Ni²⁺, preferably interacted with a potential extraneous Zn²⁺-binding site (His253, Glu318 and His323) placed near the Zn²⁺-coordinating Lssactive site within the catalytic (CAT) domain.

CONCLUSION

Our present data signify the adverse influence of exogenous Zn²⁺ ions on Lss-induced staphylolytic activity through the exclusive presence within the CAT domain of an extraneous inhibitory Zn²⁺-binding site, without affecting the CWT activity.

Generation of human induced pluripotent stem cell line (MUi026-A) from a patient with autosomal dominant polycystic kidney disease carrying PKD1 point mutation

Autosomal dominant polycystic kidney disease (ADPKD) is one of the common genetic kidney disorders that are caused by mutations in PKD1 or PKD2 gene. In this report, the MUi026-A human induced pluripotent stem cell (hiPSC) line was established from the skin fibroblasts of a female ADPKD patient who had the PKD1 mutation with c.5878C > T. The iPSC line retained normal karyotype. The cells displayed embryonic stem cell-like characteristics with pluripotency marker expression and were able to differentiate into three germ layers.

Importance of the Cys124-Cys128 intermolecular disulfide bonding for oligomeric assembly and hemolytic activity of the Helicobacter pylori TlyA hemolysin

Although the TlyA hemolysin from Helicobacter pylori has been implicated as a potential virulence factor involved in mediating host cell colonization and hence disease progression, its structural determinants underlying the biological activity are still largely uncertain. In this study, an important role of the formation of a particular disulfide bond for functional oligomeric assembly of the H. pylori TlyA toxin was evidently elucidated. The 27-kDa TlyA recombinant protein was overexpressed in Escherichia coli, subsequently purified to near homogeneity by cation exchange chromatography, and proven to be hemolytically active against sheep erythrocytes. Additionally, TlyA-induced hemolytic activity was significantly diminished under conditions of disulfide bond reduction with a thiol-reducing agent, dithiothreitol. When the purified TlyA protein was subjected to modified SDS-PAGE under non-reducing conditions, the presence of an oligomeric state of this protein was clearly revealed by its apparent molecular mass of ∼48 kDa. Recombinant E. coli cells expressing TlyA also displayed contact-dependent hemolysis of erythrocytes, suggesting TlyA localization at the bacterial outer membrane and thus supporting the formation of disulfide-bonded TlyA. Homology-based modeling and in silico structural assembly analysis of TlyA signified potential intermolecular, rather than intramolecular, disulfide bonding through Cys¹²⁴ and Cys¹²⁸. Subsequently, single substitution of either of these Cys residues with Ser severely affected the oligomeric assembly of both TlyA mutants and hence abolished their hemolytic activity. Altogether, our present data provide pivotal evidence that the formation of intermolecular disulfide bonding between Cys¹²⁴ and Cys¹²⁸ plays a critical role in structural assembly of a biologically active-TlyA oligomer.

Vacuolating cytotoxin A (VacA) - A multi-talented pore-forming toxin from Helicobacter pylori

Helicobacter pylori is associated with severe and chronic diseases of the stomach and duodenum such as peptic ulcer, non-cardial adenocarcinoma and gastric lymphoma, making Helicobacter pylori the only bacterial pathogen which is known to cause cancer. The worldwide rate of incidence for these diseases is extremely high and it is estimated that about half of the world's population is infected with H. pylori. Among the bacterial virulence factors is the vacuolating cytotoxin A (VacA), which represents an important determinant of pathogenicity. Intensive characterization of VacA over the past years has provided insight into an ample variety of mechanisms contributing to host-pathogen interactions. The toxin is considered as an important target for ongoing research for several reasons: i) VacA displays unique features and structural properties and its mechanism of action is unrelated to any other known bacterial toxin; ii) the toxin is involved in disease progress and colonization by H. pylori of the stomach; iii) VacA is a potential and promising candidate for the inclusion as antigen in a vaccine directed against H. pylori and iv) the vacA gene is characterized by a high allelic diversity, and allelic variants contribute differently to the pathogenicity of H. pylori. Despite the accumulation of substantial data related to VacA over the past years, several aspects of VacA-related activity have been characterized only to a limited extent. The biologically most significant effect of VacA activity on host cells is the formation of membrane pores and the induction of vacuole formation. This review discusses recent findings and advances on structure-function relations of the H. pylori VacA toxin, in particular with a view to membrane channel formation, oligomerization, receptor binding and apoptosis.

Tuberculosis treatment outcomes among retreatment patients registered by private practitioners in Myanmar

The objectives of this retrospective cohort study were to report treatment outcomes and identify factors associated with treatment failure among all retreatment tuberculosis (TB) patients registered in the public-private mix DOTS programme of Populations Services International-Myanmar over 6 years. Among 3643 retreatment patients, 2657 (73%) were successfully treated and 309 (8.5%) failed. This study shows that retreatment patients who have failed treatment for their first TB episode are almost twice as likely to fail a second time (13.5%). We have identified some key programmatic challenges associated with retreatment TB in the private sector, and steps are being taken to address this issue.