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KCa3.1-Dependent Hyperpolarization Enhances Intracellular Ca2+ Signaling Induced by fMLF in Differentiated U937 Cells.

ABSTRACT: Formylated peptides are chemotactic agents generated by pathogens. The most relevant peptide is fMLF (formyl-Met-Leu-Phe) which participates in several immune functions, such as chemotaxis, phagocytosis, cytokine release and generation of reactive oxygen species. In macrophages fMLF-dependent responses are dependent on both, an increase in intracellular calcium concentration and on a hyperpolarization of the membrane potential. However, the molecular entity underlying this hyperpolarization remains unknown and it is not clear whether changes in membrane potential are linked to the increase in intracellular Ca2+. In this study, differentiated U937 cells, as a macrophage-like cell model, was used to characterize the fMLF response using electrophysiological and Ca2+ imaging techniques. We demonstrate by means of pharmacological and molecular biology tools that fMLF induces a Ca2+-dependent hyperpolarization via activation of the K+ channel KCa3.1 and thus, enhancing fMLF-induced intracellular Ca2+ increase through an amplification of the driving force for Ca2+ entry. Consequently, enhanced Ca2+ influx would in turn lengthen the hyperpolarization, operating as a positive feedback mechanism for fMLF-induced Ca2+ signaling.

SUBMITTER: Penna A

PROVIDER: S-EPMC4587941 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:BACKGROUND:The intermediate-conductance Ca2+-activated K+ channel KCa3.1 was recently shown to control the phenotype switch of reactive astrogliosis (RA) in Alzheimer's disease (AD). METHODS:KCa3.1 channels expression and cell localization in the brains of AD patients and APP/PS1 mice model were measured by immunoblotting and immunostaining. APP/PS1 mice and KCa3.1-/-/APP/PS1 mice were subjected to Morris water maze test to evaluate the spatial memory deficits. Glia activation and neuron loss was measured by immunostaining. Fluo-4AM was used to measure cytosolic Ca2+ level in ?-amyloid (A?) induced reactive astrocytes in vitro. RESULTS:KCa3.1 expression was markedly associated with endoplasmic reticulum (ER) stress and unfolded protein response (UPR) in both A?-stimulated primary astrocytes and brain lysates of AD patients and APP/PS1 AD mice. The KCa3.1 channel was shown to regulate store-operated Ca2+ entry (SOCE) through an interaction with the Ca2+ channel Orai1 in primary astrocytes. Gene deletion or pharmacological blockade of KCa3.1 protected against SOCE-induced Ca2+ overload and ER stress via the protein kinase B (AKT) signaling pathway in astrocytes. Importantly, gene deletion or blockade of KCa3.1 restored AKT/mechanistic target of rapamycin signaling both in vivo and in vitro. Consistent with these in vitro data, expression levels of the ER stress markers 78-kDa glucose-regulated protein and CCAAT/enhancer-binding protein homologous protein, as well as that of the RA marker glial fibrillary acidic protein were increased in APP/PS1 AD mouse model. Elimination of KCa3.1 in KCa3.1-/-/APP/PS1 mice corrected these abnormal responses. Moreover, glial activation and neuroinflammation were attenuated in the hippocampi of KCa3.1-/-/APP/PS1 mice, as compared with APP/PS1 mice. In addition, memory deficits and neuronal loss in APP/PS1 mice were reversed in KCa3.1-/-/APP/PS1 mice. CONCLUSIONS:Overall, these results suggest that KCa3.1 is involved in the regulation of Ca2+ homeostasis in astrocytes and attenuation of the UPR and ER stress, thus contributing to memory deficits and neuronal loss.

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KCa3.1-Dependent Hyperpolarization Enhances Intracellular Ca2+ Signaling Induced by fMLF in Differentiated U937 Cells.

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