INTERLEUKIN-1-BETA AND TUMOR-NECROSIS-FACTOR-ALPHA SYNERGISTICALLY STIMULATE NERVE GROWTH-FACTOR SYNTHESIS IN RAT MESANGIAL CELLS

Recent evidence indicates that cytokines are potent inducers of nerve growth factor (NGF) expression both in peripheral tissues and the central nervous system and that NGF, in addition to its neurotrophic action, also acts as an immunoregulatory agent. It was of interest to investigate whether inflammatory cytokines affect NGF production in renal mesangial cells, which play a crucial role in the modulation of the local immune function in the glomerulus. Our results show that the simultaneous addition of interleukin-1-beta (IL-1-beta) and tumor necrosis factor-alpha (TNF-alpha) elicited a marked (13-fold) increase of NGF protein released by cultured rat glomerular mesangial cells within 24 h, whereas IL-1-alpha in combination with TNF-alpha, as well as the cytokines alone, did not promote the synthesis of NGF. The synergistic effect was dose dependent (maximal at 1 nM) and due to enhanced gene expression, since the cytokine treatment caused a fivefold increase in NGF mRNA after 8 h. Stimulation of NGF synthesis was abolished by mepacrine and dexamethasone, indicating that phospholipase A2 may be involved in NGF regulation. Moreover, pretreatment of the cells with the lipoxygenase inhibitor nordihydroguaiaretic acid (NDGA) abolished induction of NGF by cytokines; in contrast, the specific cyclooxygenase inhibitors indomethacin and diclofenac failed to modify NGF production. These data suggest that a lipoxygenase metabolite produced in response to IL-1-beta and TNF-alpha acts as a mediator in NGF gene expression. In conclusion, these findings support a model in which a cytokine cascade including NGF may play an important role in the pathophysiology of inflammatory renal diseases.