Mesangial cells (MC) of renal glomeruli respond to immune-inflammatory injury by accelerated proliferation and generation of reactive
oxygen metabolites (ROM). We studied in vivo and in vitro roles of
cAMP-protein kinase A (PKA) signaling in modulation of these pathobiologic processes with focus on PDE
isozymes. Mitogenic synthesis of
DNA in mesangial cells grown in primary culture was blocked by
forskolin and dibutyryl cyAMP. Incubation of MC with
PDE-3 inhibitors,
cilostamide and
lixazinone, inhibited (> 50%) mitogenesis, whereas inhibitors of PDE-4,
rolipram and
denbufylline, caused little or no inhibition. Conversely, inhibitors of PDE-4 suppressed generation of ROM in MC, whereas inhibitors of PDE-3 had no effect. Incubation of mesangial cells with
cilostamide or with
rolipram increased in situ activity of PKA, and effects of the two inhibitors were additive. PDE inhibitors also decreased activity of
mitogen-activated protein kinase. The efficacy of PDE
isozyme inhibitors (IC50) to suppress mitogenesis or ROM generation paralleled IC50 for inhibition of cAMP hydrolysis by extracts from mesangial cells. Administration of
lixazinone or
lixazinone in combination with
rolipram to rats with mesangial proliferative
glomerulonephritis induced by antithymic serum suppressed proliferation of mesangial cells and also reduced other histopathologic manifestations of the disease. Based on these observations, we propose that in MC, a cAMP pool that is hydrolyzed by PDE-3 inhibits by negative crosstalk via activation of PKA,
mitogen-activated protein kinase (MAPK) pathway, and mitogenesis; whereas cAMP pool linked to PDE-4 inhibits, also via activation of PKA, ROM generation in mesangial cells. Results also suggest that PDE
isozyme inhibitors, in particular inhibitors of PDE-3, should be investigated for potential use for "signal transduction
pharmacotherapy" of
glomerulonephritis.