Persistent Borna Disease Virus (BDV) infection activates microglia prior to a detectable loss of granule cells in the hippocampus

Neonatal Borna Disease Virus (BDV) infection in rats leads to a neuronal loss in the cortex, hippocampus and cerebellum. Since BDV is a non-lytic infection in vitro, it has been suggested that activated microglia could contribute to neuronal damage. It is also conceivable that BDV-induced cell death triggers activation of microglia to remove cell debris. Although an overall temporal association between neuronal loss and microgliosis has been demonstrated in BDV-infected rats, it remains unclear if microgliosis precedes or results from neuronal damage. We investigated the timing of microglia activation and neuronal elimination in the dentate gyrus (DG) of the hippocampus. We found a significant increase in the number of ED1+ microglia cells as early as 10 days post infection (dpi) while a detectable loss of granule cells of the DG was not seen until 30 dpi. The data demonstrate for the first time that a non-lytic persistent virus infection of neurons activates microglia long before any measurable neuronal loss

Astrocytes play a key role in activation of microglia by persistent Borna disease virus infection

Neonatal Borna disease virus (BDV) infection of the rat brain is associated with microglial activation and damage to certain neuronal populations. Since persistent BDV infection of neurons is nonlytic in vitro, activated microglia have been suggested to be responsible for neuronal cell death in vivo. However, the mechanisms of activation of microglia in neonatally BDV-infected rat brains remain unclear. Our previous studies have shown that activation of microglia by BDV in culture requires the presence of astrocytes as neither the virus nor BDV-infected neurons alone activate microglia. Here, we evaluated the mechanisms whereby astrocytes can contribute to activation of microglia in neuron-glia-microglia mixed cultures. We found that persistent infection of neuronal cells leads to activation of uninfected astrocytes as measured by elevated expression of RANTES. Activation of astrocytes then produces activation of microglia as evidenced by increased formation of round-shaped, MHCI-, MHCII- and IL-6-positive microglia cells. Our analysis of possible molecular mechanisms of activation of astrocytes and/or microglia in culture indicates that the mediators of activation may be soluble heat-resistant, low molecular weight factors. The findings indicate that astrocytes may mediate activation of microglia by BDV-infected neurons. The data are consistent with the hypothesis that microglia activation in the absence of neuronal damage may represent initial steps in the gradual neurodegeneration observed in brains of neonatally BDV-infected rats

Comparative Thrombin Generation in Animal Plasma: Sensitivity to Human Factor XIa and Tissue Factor

Preclinical evaluation of drugs in animals helps researchers to select potentially informative clinical laboratory markers for human trials. To assess the utility of animal thrombin generation (TG) assay, we studied the sensitivity of animal plasmas to triggers of TG, human Tissue Factor (TF), and Activated Factor XI (FXIa). Pooled human, mouse, rat, guinea pig, rabbit, bovine, sheep, and goat plasmas were used in this study. TF- or FXIa-triggered TG and clotting were measured via fluorescence and optical density, respectively. Thrombin peak height (TPH) and time (TPT), clot time (CT), and fibrin clot density (FCD) were all analyzed. The trigger low and high sensitivity borders (LSB and HSB) for each assay parameter were defined as TF and FXIa concentrations, providing 20 and 80% of the maximal parameter value, unless the baseline (no trigger) value exceeded 20% of the maximal, in which case, LSB was derived from 120% of baseline value. Normal human samples demonstrated lower TPH HSB than most of the animal samples for both TF and FXIa. Animal samples, except mice, demonstrated lower TPT LSB for FXIa versus humans. Most rodent and rabbit samples produced baseline TG in the absence of TG triggers that were consistent with the pre-activation of blood coagulation. FCD was not sensitive to both TF and FXIa in either of the plasmas. Animal plasmas have widely variable sensitivities to human TF and FXIa, which suggests that optimization of trigger concentration is required prior to test use, and this complicates the extrapolation of animal model results to humans

Activation of Microglia by Borna Disease Virus Infection: In Vitro Study

Neonatal Borna disease virus (BDV) infection of the rat brain is associated with microglial activation and damage to the certain neuronal populations. Since persistent BDV infection of neurons in vitro is noncytolytic and noncytopathic, activated microglia have been suggested to be responsible for neuronal cell death in vivo. However, the mechanisms of activation of microglia in neonatally BDV-infected rat brain have not been investigated. To address these issues, activation of primary rat microglial cells was studied following exposure to purified BDV or to persistently BDV-infected primary cortical neurons or after BDV infection of primary mixed neuron-glial cultures. Neither purified virus nor BDV-infected neurons alone activated primary microglia as assessed by the changes in cell shape or production of the proinflammatory cytokines. In contrast, in the BDV-infected primary mixed cultures, we observed proliferation of microglia cells that acquired the round morphology and expressed major histocompatibility complex molecules of classes I and II. These manifestations of microglia activation were observed in the absence of direct BDV infection of microglia or overt neuronal toxicity. In addition, compared to uninfected mixed cultures, activation of microglia in BDV-infected mixed cultures was associated with a significantly greater lipopolysaccharide-induced release of tumor necrosis factor alpha, interleukin 1β, and interleukin 10. Taken together, the present data are the first in vitro evidence that persistent BDV infection of neurons and astrocytes rather than direct exposure to the virus or dying neurons is critical for activating microglia

Isolated Variable Domains of an Antibody Can Assemble on Blood Coagulation Factor VIII into a Functional Fv-like Complex

Single-chain variable fragments (scFv) are antigen-recognizing variable fragments of antibodies (FV) where both subunits (VL and VH) are connected via an artificial linker. One particular scFv, iKM33, directed against blood coagulation factor VIII (FVIII) was shown to inhibit major FVIII functions and is useful in FVIII research. We aimed to investigate the properties of iKM33 enabled with protease-dependent disintegration. Three variants of iKM33 bearing thrombin cleavage sites within the linker were expressed using a baculovirus system and purified by two-step chromatography. All proteins retained strong binding to FVIII by surface plasmon resonance, and upon thrombin cleavage, dissociated into VL and VH as shown by size-exclusion chromatography. However, in FVIII activity and low-density lipoprotein receptor-related protein 1 binding assays, the thrombin-cleaved iKM33 variants were still inhibitory. In a pull-down assay using an FVIII-affinity sorbent, the isolated VH, a mixture of VL and VH, and intact iKM33 were carried over via FVIII analyzed by electrophoresis. We concluded that the isolated VL and VH assembled into scFv-like heterodimer on FVIII, and the isolated VH alone also bound FVIII. We discuss the potential use of both protease-cleavable scFvs and isolated Fv subunits retaining high affinity to the antigens in various practical applications such as therapeutics, diagnostics, and research

Engineering and evaluation of FXa bypassing agents that restore hemostasis following Apixaban associated bleeding

Abstract Direct oral anticoagulants (DOACs) targeting activated factor Xa (FXa) are used to prevent or treat thromboembolic disorders. DOACs reversibly bind to FXa and inhibit its enzymatic activity. However, DOAC treatment carries the risk of anticoagulant-associated bleeding. Currently, only one specific agent, andexanet alfa, is approved to reverse the anticoagulant effects of FXa-targeting DOACs (FXaDOACs) and control life-threatening bleeding. However, because of its mechanism of action, andexanet alfa requires a cumbersome dosing schedule, and its use is associated with the risk of thrombosis. Here, we present the computational design, engineering, and evaluation of FXa-variants that exhibit anticoagulation reversal activity in the presence of FXaDOACs. Our designs demonstrate low DOAC binding affinity, retain FXa-enzymatic activity and reduce the DOAC-associated bleeding by restoring hemostasis in mice treated with apixaban. Importantly, the FXaDOACs reversal agents we designed, unlike andexanet alfa, do not inhibit TFPI, and consequently, may have a safer thrombogenic profile