Regulation of glomerular mesangial cell proliferation in culture by adrenomedullin

Adrenomedullin is a recently discovered vasodilatory peptide that has been shown to be a potent activator of adenylate cyclase in a variety of cell sy stems, including rat mesangial cells. The major aim of the present study wa s to determine the regulation of rat mesangial cell proliferation (using [H -3]thymidine incorporation as an index), apoptosis (using nucleosome-associ ated cytoplasmic DNA fragmentation as an index) and mitogen-activated prote in kinase (MAPK) cascade, specifically extracellular signal-regulated kinas e (ERK), jun-amino terminal kinase (JNK) and P38 mitogen-activated protein kinase (P38 MAPK) activities, by adrenomedullin-stimulated cyclicAMP-protei n kinase-A pathway. Adrenomedullin increased cAMP levels significantly abov e basal and the response was inhibited by the adrenomedullin receptor antag onist, adrenomedullin-(22-52). Adrenomedullin also decreased [H-3]thymidine incorporation and increased nucleosome-associated cytoplasmic DNA fragment ation, in a concentration-dependent fashion. Both these responses were rece ptor mediated as, adrenomedullin-(22-52) inhibited these effects, The decre ase in proliferation and increase in apoptosis were both mimicked by forsko lin, a direct adenylate cyclase activator. Adrenomedullin-mediated decrease in proliferation and increase in apoptosis were inhibited by H89 [{N-[2-(( p-bromocinnamyl)amino)ethyl]-5-isoquinolinesulfonamide, hydrochloride}], a potent protein kinase-A inhibitor. Associated with the changes in prolifera tion and apoptosis, adrenomedullin decreased ERK2 activity, and increased J NK1 and P38 MAPK activities. An these kinase activities, except the increas e in JNK1 activity could be simulated using forskolin. In addition, only ad renomedullin-mediated changes in ERK2 and P38 MAPK activities were inhibite d by H89 while, adrenomedullin-stimulated JNK1 was not consistently inhibit ed by the protein kinase-A inhibitor. These results suggest that adrenomedu llin might play an important role in mesangial cell turnover and that altho ugh adrenomedullin-mediated responses are primarily cAMP-dependent, it does not preclude the involvement of cAMP-independent pathways. (C) 1999 Elsevi er Science B.V. All rights reserved.