Interferon-gamma increases inositol phosphate formation and cellular calcium ion concentration independent of ICAM-1 antigen enhancement in renal tubular cells

Fibronectin promotes calcium signaling by interferon-gamma in human neutrophils via G-protein and sphingosine kinase-dependent mechanisms

A common intracellular signal activating polymorphonuclear leukocytes (PMN) in inflammation is a change in cytosolic calcium concentration. Previously, we have shown that interferon-gamma (IFN-gamma) induces transient calcium signals in PMN, but only after intracellular calcium store depletion. Using a digital imaging system, we show that adhesion of PMN is critical for IFN-gamma-induced calcium signals, and with PMN attached to the optimal coating, the calcium signals are evoked even in presence of extracellular calcium, that is, non-depleted calcium stores. Adhesion to fibronectin, pure or extracted from plasma by gelatin, improved the IFN-gamma responses compared with serum, plasma, or vitronectin coats. In accordance with previous observations, IFN-gamma-induced calcium signals in fibronectin adherent cells were totally abolished by the G-protein inhibitor pertussis toxin and were also inhibited by the sphingosine kinase inhibitors dimethylsphingosine (DMS) and N-acetylsphingosine (N-Ac-Sp). PMN contact with fibronectin alone, measured in cells sedimenting onto a fibronectin-coated surface or by addition of fibronectin to glass-adherent cells, evoked transient calcium signals. However, PMN in suspension did not respond to the addition of fibronectin or arginine-glycine-aspartate (RGD). The fibronectin-induced calcium signals were also clearly depressed by pertussis toxin and by the sphingosine kinase inhibitors DMS, dihydrosphingosine (DHS), and N-Ac-Sp. When the product of sphingosine kinase activity, sphingosine 1-phosphate (S1-P), was added to the cells, similar calcium signals were induced, which were dependent on a pertussis toxin-sensitive G-protein activity. Finally, addition of S1-P to the cells prior to stimulation with IFN-gamma partly mimicked the priming effect of fibronectin. In conclusion, fibronectin contact evokes by itself a calcium signal in PMN and further promotes calcium signaling by IFN-gamma. We suggest that fibronectin might activate sphingosine kinase, and that the sphingosine 1-phosphate thereby generated induces a calcium signal via a G-protein-dependent mechanism. Apparently, sphingosine kinase activity is also involved in IFN-gamma induced calcium signals.

Interferon-gamma-induced changes in synaptic activity and AMPA receptor clustering in hippocampal cultures

Extended release of interferon-gamma (IFN-gamma) in the nervous system during immunological and infectious conditions may trigger demyelinating disorders and cause disturbances in brain function. The aim of this study was to examine the effects of IFN-gamma on neuronal function in rat hippocampal cell cultures by using whole cell patch clamp analysis together with quantitative immunocytochemistry. Acute application of IFN-gamma to differentiated neurons in culture caused no immediate neurophysiological responses, but recordings after 48 h of incubation displayed an increase in frequency of AMPA receptor (AMPAR)-mediated spontaneous excitatory postsynaptic currents (EPSCs). Quantitative immunocytochemistry for the AMPAR subunit GluR1 showed no alteration in receptor clustering at this time point. However, prolonged treatment with IFN-gamma for 2 weeks resulted in a significant reduction in AMPAR clustering on dendrites but no marked differences in EPSC frequency between treated neurons and controls could be observed. On the other hand, treatment of hippocampal neurons for 4 weeks, instituted at an immature stage (1 day in culture), caused a significant reduction in spontaneous EPSC frequency. These neurons developed with no overt alterations in dendritic arborization or in the appearance of dendritic spines as visualized by alpha-actinin immunocytochemistry. Nonetheless, there was a marked reduction in AMPAR clustering on dendrites. These observations show that a key immunomodulatory molecule, IFN-gamma, can cause long-term modifications of synaptic activity and perturb glutamate receptor clustering.