Differential cellular expression of tumor necrosis factor-α and Type I tumor necrosis factor receptor after transient global forebrain ischemia

Abstract

We examined the expression of tumor necrosis factor-α (TNF-α) and the Type I tumor necrosis factor receptor, (TNFR1), in relation to c- fos, a known regulator gene of immediate cellular responses, after an extended period of global ischemia. The number of TNF-α mRNA expressing cells peaked in most brain areas after 8 h of reperfusion. Significant increases in TNFR1 mRNA expression were evident in the cortex at 2 and 8 h of reperfusion and after 8 h of reperfusion in the CA3/CA4 region of the hippocampus. Transient neuronal c- fos mRNA expression preceded these responses. TNF-α immunoreactivity was seen in neurons⋙oligodendrocytes=perivascular cells=ependymal cells=vessel wall structures. After ischemia/reperfusion, increased TNF-α immunoreactivity was evident only in oligodendrocytes. TNFR1 immunoreactivity in sham brains manifested in bundles of cellular fibers of variable length and thickness. In post-ischemic brains, immunoreactivity in these cellular processes representing mainly astroglial extensions was suppressed at 2 h but recovered partially by 8 and 24 h of reperfusion. In contradiction, transient ischemia-induced TNFR1 immunoreactivity was observed in somas of large cortical neurons, in activated microglia/macrophages, perivascular and endothelial cells. Taken together, the increase in neuronal TNF-α mRNA appeared not to be followed by substantial translation to protein in the cerebral tissue after an extended period of global ischemia. However, there was increased neuronal TNFR1 immunostaining in conjunction with increased immunostaining for TNF-α in oligoglial elements, which suggests signaling to neurons by enhanced oligoglial TNF-α.