Protein Kinase A Downregulation Delays the Development and Progression of Polycystic Kidney Disease

Significance Statement The only treatment approved for PKD inhibits production of cAMP, the main PKA activator. It is only partially effective, likely because side effects restrict dosing and because other sources of cAMP and mechanisms of cAMP-independent PKA activation exist. Which PKA isozyme(s) promotes PKD is uncertain and selective PKA inhibitors usable in vivo have not been available. Experiments in a mouse model show PKA-I is the main PKA isozyme promoting cystogenesis and that constitutive PKA-I downregulation and a novel, highly selective PKA inhibitor ameliorate PKD. The dose of PKA inhibitor used had no detectable adverse effects. This information provides a strong rationale for a strategy that may be more effective, or substantially increase the efficacy of the currently approved treatment. Background Upregulation of cAMP-dependent and cAMP-independent PKA signaling is thought to promote cystogenesis in polycystic kidney disease (PKD). PKA-I regulatory subunit RI α is increased in kidneys of orthologous mouse models. Kidney-specific knockout of RI α upregulates PKA activity, induces cystic disease in wild-type mice, and aggravates it in Pkd1 RC/RC mice. Methods PKA-I activation or inhibition was compared with EPAC activation or PKA-II inhibition using Pkd1 RC/RC metanephric organ cultures. The effect of constitutive PKA (preferentially PKA-I) downregulation in vivo was ascertained by kidney-specific expression of a dominant negative RIαB allele in Pkd1 RC/RC mice obtained by crossing Prkar1α R1αB/WT , Pkd1RC/RC , and Pkhd1- Cre mice (C57BL/6 background). The effect of pharmacologic PKA inhibition using a novel, selective PRKACA inhibitor (BLU2864) was tested in mIMCD3 3D cultures, metanephric organ cultures, and Pkd1RC/RC mice on a C57BL/6 × 129S6/Sv F1 background. Mice were sacrificed at 16 weeks of age. Results PKA-I activation promoted and inhibition prevented ex vivo P-Ser133 CREB expression and cystogenesis. EPAC activation or PKA-II inhibition had no or only minor effects. BLU2864 inhibited in vitro mIMCD3 cystogenesis and ex vivo P-Ser133 CREB expression and cystogenesis. Genetic downregulation of PKA activity and BLU2864 directly and/or indirectly inhibited many pro-proliferative pathways and were both protective in vivo . BLU2864 had no detectable on- or off-target adverse effects. Conclusions PKA-I is the main PKA isozyme promoting cystogenesis. Direct PKA inhibition may be an effective strategy to treat PKD and other conditions where PKA signaling is upregulated. By acting directly on PKA, the inhibition may be more effective than or substantially increase the efficacy of treatments that only affect PKA activity by lowering cAMP.