Downregulation of Cytoskeletal Protein Kazrin in Lung Endothelial Cells of Preclinical Sickle Cell Disease Mouse Model - Essential Role of Endothelial Barrier Function

Background: Lung capillary barrier dysfunction is common to all causes of acute chest syndrome (ACS), a leading cause of morbidity and mortality in individuals with sickle cell disease (SCD). Our published data (Haematologica 2017, 102, e26-e29) demonstrated, for the first time, an impaired barrier function in freshly isolated endothelial cells (EC) from the lungs of Townes transgenic sickle cell anemia (SS) mice, compared to heterozygote (AS) or control (AA) mice. In addition, we showed a sub-stimulatory dose (0.05 mg/kg) of bacterial toxin lipopolysaccharide, which did not cause prominent acute lung injury in control AS/AA mice, was fatal to SS mice suggesting an enhanced hypersensitivity of sickle EC to infection. Hemolysis is a fundamental feature of SCD that contributes to its pathophysiology. Hemolysis results in the leakage of vast amounts of hemoglobin, and subsequently, heme into the plasma. Although, previous studies have demonstrated the detrimental effect of heme in SCD, the mechanisms of heme-mediated lung EC barrier dysfunction have not been studied. Recently, Kazrin was identified as a widely expressed protein influencing intercellular adhesion and co-localizes with the cortical actin ring to stabilize cell-cell junctions. In this study, we investigated the mechanisms of heme-induced EC barrier dysfunction related to Kazrin function, using primary EC isolated from the lungs of SCD mice and controls. Methods: Primary EC from the lungs of SS, AS, and AA mice (6-8 weeks old) were isolated according to methods described in our recent publication. The EC barrier function was measured using electrical cell-substrate impedance sensing (ECIS) and Evans blue dye transendothelial permeability was done using a transwell filter assay system. Western blot was performed to measure total and phosphorylated expression levels of protein involved in the regulation of EC barrier function. Immunocytochemistry was performed using specific antibodies and actin cytoskeleton was identified using a known F-actin binding fluorescent marker Phalloidin. Results: Our data demonstrated a significantly reduced basal expression of the Kazrin mRNA and protein in freshly isolated SS-EC compared to AS-EC or AA-EC. To determine the effects of Kazrin downregulation on the EC barrier function, we depleted the Kazrin protein in AS-EC using Kazrin specific siRNA and scrambled control siRNA. Kazrin depleted cells demonstrate an attenuated EC barrier function as evidenced by reduced trans-endothelial electrical resistance by ECIS and increased Evans blue dye leak by transwell filter assay (p<0.05). By contrast, control siRNA treated AS-EC displayed normal barrier function. Therefore, our data, for the first time, suggest that Kazrin is essential for the EC barrier function. Given the crucial role of hemolysis in SCD, we detected that clinically relevant dose of heme (5 µM; 60 min) significantly decreases the AS-EC barrier function (p<0.05) and the heme-mediated decrease of barrier function is dose-dependent. Moreover prolonged treatment of AS-EC with heme (5 µM; 24-48 hrs) downregulated the Kazrin protein levels. These results are intriguing since the SS-EC inherently show downregulated Kazrin when compared with AS-EC. Therefore, it is possible that impaired barrier function in SS-EC that we recently published could be an effect of Kazrin downregulation since hemolysis is a constant process in SCD. We also found that incubation of AS-EC with heme upregulated the efficacy of barrier disruption agent RhoA. Previous studies have indicated that activated RhoA promotes the actin stress fibers by stimulating actin-myosin contractility and increased endothelial permeability. Our immunocytochemistry data reveal that heme incubated AS-EC develop severe actin stress fibers. Studies in progress to determine the mechanistic link between Kazrin downregulation, RhoA activation and impaired EC barrier function in SS-EC. Conclusions and Future Direction: Our findings support the notion that Kazrin participates in the EC barrier function and its downregulation cause an impaired EC barrier function. Our future studies will focus on to identify protective mechanisms of lung EC barrier function in SCD. Disclosures Kutlar: Bluebird Bio: Other: DSMB Member; Novo Nordisk: Research Funding; Novartis: Consultancy; Micelle Biopharma: Other: DSMB Chair; Global Blood Therapeutics, Inc. (GBT): Research Funding.

The utility of the AC/TC ratio for watershed management: a case study

A human-impacted watershed was monitored during the dry summer seasons in 2002 and 2003 to investigate the impact of providing access to sewer mains to local village residences. Faecal coliform concentrations were monitored at select sites along the 30-mile stretch of creek, together with faecal streptococci, enterococci and total coliforms. Analysis of the results found that levels of faecal coliforms were inadequate at identifying significant known influxes of human and animal sewage established by sanitary survey. However, the bacterial ratio of atypical colonies to total coliform colonies (AC/TC), obtained from the total coliform membrane filter assay on m-Endo media, correctly indexed human faecal impact of inadequately sewered villages located along the creek. In addition, the AC/TC ratio correctly classified the predominant source of faecal runoff in the creek headwaters as agricultural, and indicated when aged agricultural faecal material was introduced by tributaries. An approach for watershed management that uses the AC/TC ratio in addition to levels of bacteria is proposed.

Evaluation of a Membrane Filter Assay System, Ortho HCV Ab Quik Pack, for Detection of Anti-Hepatitis C Virus Antibody

A simple membrane immunoassay assay system, Quik Pack, for the detection of hepatitis C virus antibody was compared with two enzyme-linked immunosorbent assays (ELISAs) in a study of 600 serum samples. Quik Pack exhibited excellent sensitivity and specificity: 96.0 and 99.7%, respectively, versus the ELISA-2 and 99.7 and 99.4%, respectively, versus the ELISA-3.

Glycohemoglobin filter assay for doctors’ offices based on boronic acid affinity principle

We present a new filter assay for the determination of glycohemoglobin as a unique application of the boronic acid affinity principle. With the use of a water-soluble blue-colored boronic acid derivative and a specific precipitation method for hemoglobin, total hemoglobin including bound boronic acid is precipitated and collected on a filter strip before quantification. Hemoglobin and boronic acid are quantified by a dual-wavelength reflectometric measurement, and the result is reported directly as percent glycohemoglobin. The test is simple, quick, and designed as a doctors’ office test for the monitoring and management of diabetes. The imprecision of the assay is &lt;4% over the range 3–18% Hb A1c, and the method is linear up to at least 20% Hb A1c. Comparisons with four well-established glycohemoglobin methods yielded correlation coefficients ranging from 0.94 to 0.99, with slopes from 0.94 to 1.01.