Spontaneous activation of the NF- B signaling pathway in isolated normal glomeruli

Hayakawa, Kunihiro, Yiman Meng, Nobuhiko Hiramatsu, Ayumi Kasai, Jian Yao, and Masanori Kitamura. Spontaneous activation of the NFB signaling pathway in isolated normal glomeruli. Am J Physiol Renal Physiol 291: F1169–F1176, 2006. First published May 16, 2006; doi:10.1152/ajprenal.00513.2005.—In this report, we describe that NFB is spontaneously activated in isolated, normal glomeruli. Ex vivo incubation of isolated rat glomeruli triggered expression of a NFB-dependent gene, monocyte chemoattractant protein-1 (MCP-1), in parallel with downregulation of I B and I B proteins and activation of the p65 NFB subunit. The induction of MCP-1 was also observed in mesangial cells coincubated with isolated glomeruli or exposed to media conditioned by isolated glomeruli (GCM), which was abrogated by inhibition of NFB. The activation of NFB by glomerulus-derived factors was confirmed using reporter mesangial cells that produce secreted alkaline phosphatase (SEAP) under the control of the B enhancer element. When the reporter cells were adoptively transferred into normal glomeruli, expression of SEAP mRNA and activity of SEAP were also upregulated in the explanted glomeruli. The molecular weight of factors responsible for activation of NFB was 50 kDa, and TNFwas identified as one of glomerulus-derived activators. To examine upstream events involved, we focused on MAP kinases that are spontaneously activated in explanted glomeruli. Selective suppression of ERK or p38 MAP kinase significantly attenuated activation of NFB in mesangial cells triggered by coculture with isolated glomeruli. Interestingly, the suppressive effects by MAP kinase inhibitors were not observed in mesangial cells treated with GCM. These data suggested that NFB was spontaneously activated in explanted glomeruli via autocrine/paracrine factors including TNFand that the production of NFB activators by glomeruli was, at least in part, through MAP kinase pathways.