Ablation of the microglial protein DOCK2 reduces amyloid burden in a mouse model of Alzheimer's disease

Alzheimer's disease (AD) neuropathology is characterized by innate immune activation primarily through prostaglandin E2 (PGE₂) signaling. Dedicator of cytokinesis 2 (DOCK2) is a guanyl nucleotide exchange factor expressed exclusively in microglia in the brain and is regulated by PGE₂ receptor EP2. DOCK2 modulates microglia cytokine secretion, phagocytosis, and paracrine neurotoxicity. EP2 ablation in experimental AD results in reduced oxidative damage and amyloid beta (Aβ) burden. This discovery led us to hypothesize that genetic ablation of DOCK2 would replicate the anti-Aβ effects of loss of EP2 in experimental AD. To test this hypothesis, we crossed mice that lacked DOCK2 (DOCK2 −/−), were hemizygous for DOCK2 (DOCK2 +/−), or that expressed two DOCK2 genes (DOCK2 +/+) with APPswe-PS1Δe9 mice (a model of AD). While we found no DOCK2-dependent differences in cortex or in hippocampal microglia density or morphology in APPswe-PS1Δe9 mice, cerebral cortical and hippocampal Aβ plaque area and size were significantly reduced in 10-month-old APPswe-PS1Δe9/DOCK2 −/− mice compared with APPswe-PS1Δe9/DOCK2 +/+ controls. DOCK2 hemizygous APPswe-PS1Δe9 mice had intermediate Aβ plaque levels. Interestingly, soluble Aβ₄₂ was not significantly different among the three genotypes, suggesting the effects were mediated specifically in fibrillar Aβ. In combination with earlier cell culture results, our in vivo results presented here suggest DOCK2 contributes to Aβ plaque burden via regulation of microglial innate immune function and may represent a novel therapeutic target for AD.     

Interference with Ca2+ release activated Ca2+ (CRAC) channel function delays T‐cell arrest in vivo

Entry of lymphocytes into secondary lymphoid organs (SLOs) involves intravascular arrest and intracellular calcium ion ([Ca²⁺]_i) elevation. TCR activation triggers increased [Ca²⁺]_i and can arrest T‐cell motility in vitro. However, the requirement for [Ca²⁺]_i elevation in arresting T cells in vivo has not been tested. Here, we have manipulated the Ca²⁺ release‐activated Ca²⁺ (CRAC) channel pathway required for [Ca²⁺]_i elevation in T cells through genetic deletion of stromal interaction molecule (STIM) 1 or by expression of a dominant‐negative ORAI1 channel subunit (ORAI1‐DN). Interestingly, the absence of CRAC did not interfere with homing of naïve CD4⁺ T cells to SLOs and only moderately reduced crawling speeds in vivo. T cells expressing ORAI1‐DN lacked TCR activation induced [Ca²⁺]_i elevation, yet arrested motility similar to control T cells in vitro. In contrast, antigen‐specific ORAI1‐DN T cells had a twofold delayed onset of arrest following injection of OVA peptide in vivo. CRAC channel function is not required for homing to SLOs, but enhances spatiotemporal coordination of TCR signaling and motility arrest.     

Tumor‐induced myeloid‐derived suppressor cell subsets exert either inhibitory or stimulatory effects on distinct CD8+ T‐cell activation events

Tumor growth coincides with an accumulation of myeloid‐derived suppressor cells (MDSCs), which exert immune suppression and which consist of two main subpopulations, known as monocytic (MO) CD11b⁺CD115⁺Ly6G^?Ly6C^high MDSCs and granulocytic CD11b⁺CD115^?Ly6G⁺Ly6C^int polymorphonuclear (PMN)‐MDSCs. However, whether these distinct MDSC subsets hamper all aspects of early CD8⁺ T‐cell activation — including cytokine production, surface marker expression, survival, and cytotoxicity — is currently unclear. Here, employing an in vitro coculture system, we demonstrate that splenic MDSC subsets suppress antigen‐driven CD8⁺ T‐cell proliferation, but differ in their dependency on IFN‐γ, STAT‐1, IRF‐1, and NO to do so. Moreover, MO‐MDSC and PMN‐MDSCs diminish IL‐2 levels, but only MO‐MDSCs affect IL‐2Rα (CD25) expression and STAT‐5 signaling. Unexpectedly, however, both MDSC populations stimulate IFN‐γ production by CD8⁺ T cells on a per cell basis, illustrating that some T‐cell activation characteristics are actually stimulated by MDSCs. Conversely, MO‐MDSCs counteract the activation‐induced change in CD44, CD62L, CD162, and granzyme B expression, while promoting CD69 and Fas upregulation. Together, these effects result in an altered CD8⁺ T‐cell adhesiveness to the extracellular matrix and selectins, sensitivity to FasL‐mediated apoptosis, and cytotoxicity. Hence, MDSCs intricately influence different CD8⁺ T‐cell activation events in vitro, whereby some parameters are suppressed while others are stimulated.     

Ca2+-dependent large conductance K+ currents in thalamocortical relay neurons of different rat strains

Mutations in genes coding for Ca²⁺ channels were found in patients with childhood absence epilepsy (CAE) indicating a contribution of Ca²⁺-dependent mechanisms to the generation of spike-wave discharges (SWD) in humans. Since the involvement of Ca²⁺ signals remains unclear, the aim of the present study was to elucidate the function of a Ca²⁺-dependent K⁺ channel (BK_Ca) under physiological conditions and in the pathophysiological state of CAE. The activation of BK_Ca channels is dependent on both voltage and intracellular Ca²⁺ concentrations. Moreover, these channels exhibit an outstandingly high level of regulatory heterogeneity that builds the basis for the influence of BK_Ca channels on different aspects of neuronal activity. Here, we analyse the contribution of BK_Ca channels to firing of thalamocortical relay neurons, and we test the hypothesis that BK_Ca channel activity affects the phenotype of a genetic rat model of CAE. We found that the activation of the β₂-adrenergic receptor/protein kinase A pathway resulted in BK_Ca channel inhibition. Furthermore, BK_Ca channels affect the number of action potentials fired in a burst and produced spike frequency adaptation during tonic activity. The latter result was confirmed by a computer modelling approach. We demonstrate that the β₂-adrenergic inhibition of BK_Ca channels prevents spike frequency adaptation and, thus, might significantly support the tonic firing mode of thalamocortical relay neurons. In addition, we show that BK_Ca channel functioning differs in epileptic WAG/Rij and thereby likely contributes to highly synchronised, epileptic network activity.     

Using Vocally Inspired Mechanical Conditioning to Enhance the Synthesis of a Cell-derived Biomaterial

The collection of cell-derived extracellular matrix (ECM) to form implantable biomaterials has therapeutic potential. However, a significant challenge to the creation of these biomaterials is the ability to produce an adequate quantity of ECM from cells in culture. Mechanical stimulation has long been viewed as a practical means to enhance cellular matrix production. In this study we explored the influence of vocally inspired mechanical stimulation, a unique combination of high frequency vibration and low frequency strain, on the production of ECM. Using a custom fabricated vocal bioreactor, tracheal fibroblast seeded sacrificial foams were treated for 3 weeks using either isolated cyclic strain, combined cyclic strain and vibration (dual mode), or static conditioning. When compared to static controls, ECM production was significantly increased for samples conditioned with either cyclic strain or dual mode stimulation. The quantity of ECM harvested from sacrificial foams increased from 25 ± 1 mg for statically conditioned control foams, to 34 ± 3 and 52 ± 10 mg for cyclic strain and dual mode conditioned samples respectively. Furthermore, mechanical conditioning significantly increased the elastic modulus of ECM biomaterials collected from sacrificial foams. Static control modulus increased from 40 ± 2 to 63 ± 7 kPa and 92 ± 7 kPa following isolated cyclic strain and dual mode conditioning, respectively. These results indicate that cyclic strain conditioning can be used to accelerate the production of ECM by human tracheal cells during growth in culture, and that the addition of high frequency vibration to the conditioning program further enhances ECM production.     

Virus Detection and Semiquantitation in Explanted Heart Tissues of Idiopathic Dilated Cardiomyopathy Adult Patients by Use of PCR Coupled with Mass Spectrometry Analysis

Viral detection in heart tissues has become a central issue for the diagnosis and exploration of the pathogenesis of idiopathic dilated cardiomyopathy (IDCM). In the present study, common cardiotropic viruses in 67 explanted heart samples of 31 IDCM adult patients were detected and semiquantified by using for the first time a new technology based on PCR assay coupled to electrospray ionization-time of flight mass spectrometry analysis (PCR-MS), with comparison to reference quantitative real-time PCR (RT-qPCR) assay. PCR-MS identified single or mixed enterovirus (EV) and parvovirus B19 (PVB19) infections in 27 (40.2%) of 67 samples, corresponding to 15 (48.3%) of the 31 patients, whereas RT-qPCR identified viral infections in 26 (38.8%) samples, corresponding to 16 (51.6%) of the patients. The PCR-MS results correlated well with EV and PVB19 detection by RT-qPCR (kappa = 0.85 [95% confidence interval {CI}, 0.72 to 1.00] and kappa = 0.82 [95% CI, 0.66 to 0.99], respectively). The levels of EV RNA (median, 550 [range, 178 to 3,200] copies/μg of total extracted nucleic acids) and of PVB19 DNA (median, 486 [range, 80 to 1,157] copies/μg of total extracted nucleic acids) were measured using PCR-MS and correlated with those obtained by RT-qPCR (r² = 0.57, P = 0.002 and r² = 0.64, P < 0.001 for EV and PVB19, respectively). No viruses other than EV and PVB19 strains were detected using the new PCR-MS technology, which is capable of simultaneously identifying 84 known human viruses in one assay. In conclusion, we identified single or mixed EV and PVB19 cardiac infections as potential causes of IDCM. The PCR-MS analysis appeared to be a valuable tool to rapidly detect and semiquantify common viruses in cardiac tissues and may be of major interest to better understand the role of viruses in unexplained cardiomyopathies.