Exclusive tumor necrosis factor (TNF) signaling by the p75TNF receptor triggers inflammatory ischemia in the CNS of transgenic mice

Tumor necrosis factor (TNF) is up-regulated in a variety of central nervous system (CNS) diseases with diverse etiology and pathologic manifestation. TNF mediates multiple biological activities through two membrane receptors, the p55 and p75 TNF receptors (TNFRs). We have shown previously that human transmembrane TNF (tmTNF)/p55TNFR signaling in transgenic mice triggers oligodendrocyte apoptosis, endothelial cell activation, parenchymal inflammation, and primary demyelinating lesions similar to those of acute multiple sclerosis. To address the role of the p75TNFR in the CNS, we have generated "humanized" mice that express human tmTNF in astrocytes and a physiologically regulated human p75TNFR transgene, in the absence of the endogenous (murine) p55TNFR. Human tmTNF/p75TNFR transgenic mice develop CNS vascular pathology, characterized by endothelial cell activation, meningeal inflammation, and vessel fibrosis. There is no evidence of oligodendrocyte apoptosis or primary demyelination in these mice. Late in disease, vasculitis can result in vessel occlusion and secondary, multifocal CNS ischemic injury. These results identify a proinflammatory role for the p75TNFR at the level of the CNS vascular endothelium, which correlates with the expression pattern of this receptor in the CNS, and indicate that the differential expression patterns of the two TNFRs within the CNS play a significant role in shaping the outcome of TNF signaling during neuroimmune interactions.