Acute Blood Loss Stimulates Fibroblast Growth factor 23 Production

Fibroblast growth factor 23 (FGF23) production is upregulated by iron deficiency and hypoxia. However, the influence of acute blood loss, and the resulting increases in circulating erythropoietin, on FGF23 production is unknown. Using wild-type C57BL/6 mice, we show that acute loss of 10% total blood volume leads to an increase in plasma C-terminal FGF23 (cFGF23) levels within 6 h, while plasma levels of intact FGF23, phosphate, calcium, parathyroid hormone, iron, and ferritin remain similar to control mice without acute blood loss. Volume resuscitation with PBS did not significantly alter these findings. The increase in plasma cFGF23 levels in bled animals was accompanied by increased plasma erythropoietin levels at 6 h. Administration of erythropoietin led to an acute increase in plasma cFGF23 levels similar to that observed in acute blood loss. Fgf23 mRNA expression was increased 20-fold in bone marrow, but not in bone, of bled vs. control mice, suggesting bone marrow as a key source of elevated plasma FGF23 levels following acute blood loss. To extend these findings to humans, we measured plasma cFGF23 levels in 131 critically ill patients admitted to the intensive care unit. In univariate and multivariate models, we found a positive association between number of red blood cell transfusions, an indirect indicator of acute blood loss, and plasma cFGF23 levels. We conclude that FGF23 production is rapidly increased after acute blood loss and that erythropoietin may be the mediator of this increase. Thus erythropoietin may represent a novel physiological regulator of FGF23 production

Role of Peroxiredoxin of the AhpC/TSA Family in Antioxidant Defense Mechanisms of Francisella tularensis

Francisella tularensis is a Gram-negative, facultative intracellular pathogen and the causative agent of a lethal human disease known as tularemia. Due to its extremely high virulence and potential to be used as a bioterror agent, F. tularensis is classified by the CDC as a Category A Select Agent. As an intracellular pathogen, F. tularensis during its intracellular residence encounters a number of oxidative and nitrosative stresses. The roles of the primary antioxidant enzymes SodB, SodC and KatG in oxidative stress resistance and virulence of F. tularensis live vaccine strain (LVS) have been characterized in previous studies. However, very fragmentary information is available regarding the role of peroxiredoxin of the AhpC/TSA family (annotated as AhpC) of F. tularensis SchuS4; whereas the role of AhpC of F. tularensis LVS in tularemia pathogenesis is not known. This study was undertaken to exhaustively investigate the role of AhpC in oxidative stress resistance of F. tularensis LVS and SchuS4. We report that AhpC of F. tularensis LVS confers resistance against a wide range of reactive oxygen and nitrogen species, and serves as a virulence factor. In highly virulent F. tularensis SchuS4 strain, AhpC serves as a key antioxidant enzyme and contributes to its robust oxidative and nitrosative stress resistance, and intramacrophage survival. We also demonstrate that there is functional redundancy among primary antioxidant enzymes AhpC, SodC, and KatG of F. tularensis SchuS4. Collectively, this study highlights the differences in antioxidant defense mechanisms of F. tularensis LVS and SchuS4

Identification of a live attenuated vaccine candidate for tularemia prophylaxis.

Francisella tularensis is the causative agent of a fatal human disease, tularemia. F. tularensis was used in bioweapon programs in the past and is now classified as a category A select agent owing to its possible use in bioterror attacks. Despite over a century since its discovery, an effective vaccine is yet to be developed. In this study four transposon insertion mutants of F. tularensis live vaccine strain (LVS) in Na/H antiporter (FTL_0304), aromatic amino acid transporter (FTL_0291), outer membrane protein A (OmpA)-like family protein (FTL_0325) and a conserved hypothetical membrane protein gene (FTL_0057) were evaluated for their attenuation and protective efficacy against F. tularensis SchuS4 strain. All four mutants were 100-1000 fold attenuated for virulence in mice than parental F. tularensis. Except for the FTL_0304, single intranasal immunization with the other three mutants provided 100% protection in BALB/c mice against intranasal challenge with virulent F. tularensis SchuS4. Differences in the protective ability of the FTL_0325 and FTL_0304 mutant which failed to provide protection against SchuS4 were investigated further. The results indicated that an early pro-inflammatory response and persistence in host tissues established a protective immunity against F. tularensis SchuS4 in the FTL_0325 immunized mice. No differences were observed in the levels of serum IgG antibodies amongst the two vaccinated groups. Recall response studies demonstrated that splenocytes from the FTL_0325 mutant immunized mice induced significantly higher levels of IFN-γ and IL-17 cytokines than the FTL_0304 immunized counterparts indicating development of an effective memory response. Collectively, this study demonstrates that persistence of the vaccine strain together with its ability to induce an early pro-inflammatory innate immune response and strong memory responses can discriminate between successful and failed vaccinations against tularemia. This study describes a live attenuated vaccine which may prove to be an ideal vaccine candidate for prevention of respiratory tularemia

Immunization with the <i>FTL_0325</i> mutant results in a potent memory recall response.

<p>Cell culture supernatants collected from BMDMs infected with either the <i>F. tularensis</i> LVS (A–D) or <i>F. tularensis</i> SchuS4 (E and F) and co-cultured with the splenocytes prepared from immunized mice at day 45 post-immunization (A and C) or at day 60 (B–F) were analyzed for IFN-γ (A, B and E) and IL-17a (C,D and F) cytokines by Cytometric Bead Flex sets. The data are representative of two independent experiments and were analyzed using ANOVA with Tukey-Kramer Multiple Comparison post-test and <i>P</i> values recorded. *<i>P<</i>0.05<i>; **P</i><0.01; ***<i>P<</i>0.001.</p

Correlation analysis of bacterial burden and pro-inflammatory cytokine levels in mice infected with <i>F. tularensis</i> LVS, the <i>FTL_0325</i> and <i>FTL_0304</i> mutants.

*<p>r² value of 0.6 and above was considered as a strong correlation. Values in bold are strongly correlated.</p>**<p>P-value.</p

Immunization with the <i>FTL_0325</i> mutant induces an early pro-inflammatory cytokine response in lungs.

<p>BALB/c mice (n = 4) were infected with 1×10⁷ CFU of the indicated mutants and wild type <i>F. tularensis</i> LVS. At the indicated times, the levels of pro-inflammatory cytokines were measured in lung homogenates using a Cytometric Bead Array assay. The data are representative of two independent experiments conducted and were analyzed using ANOVA with Tukey-Kramer Multiple Comparison post-test and <i>P</i> values were recorded. <i>**P</i><0.01; ***<i>P<</i>0.001. Ψ = Mice infected with 1×10⁷ CFU of <i>F. tularensis</i> LVS succumbed to infection by day 7 PI and hence were unavailable for comparison.</p

<i>FTL_0304</i>, <i>FTL_0291</i>, <i>FTL_0325</i> and <i>FTL_0057</i> mutants are highly attenuated for virulence in BALB/c and C57BL/6 mice.

a<p>6–8 weeks old mice were infected i.n. with either <i>F. tularensis</i> LVS or the indicated mutants and monitored for mortality for 28 days. Data are shown as number of mice survived/total number of mice infected.</p

Recall memory response results in an enhanced killing of <i>F. tularensis</i> SchuS4.

<p>The BMDMs were infected with <i>F. tularensis</i> SchuS4 and co-incubated with the splenocytes from naïve, <i>FTL_0325</i> or <i>FTL_0304</i> immunized mice. The BMDMs were lysed 72 hrs PI, diluted 10-fold and plated on MH-chocolate agar plates to determine the intracellular bacterial replication. The results were expressed as log₁₀ CFU/ml and are representative of two independent experiments. The data were analyzed using ANOVA with Tukey-Kramer Multiple Comparison post-test and <i>P</i> values were recorded. ***<i>P<</i>0.001.</p