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

Abstract

Upregulation of cAMP-dependent and cAMP-independent PKA signaling is thought to promote cystogenesis in polycystic kidney disease (PKD). PKA-I regulatory subunit RI<i>α</i> is increased in kidneys of orthologous mouse models. Kidney-specific knockout of RI<i>α</i> upregulates PKA activity, induces cystic disease in wild-type mice, and aggravates it in <i>Pkd1</i>^RC/RC mice. PKA-I activation or inhibition was compared with EPAC activation or PKA-II inhibition using <i>Pkd1</i>^RC/RC metanephric organ cultures. The effect of constitutive PKA (preferentially PKA-I) downregulation <i>in vivo</i> was ascertained by kidney-specific expression of a dominant negative <i>RIαB</i> allele in <i>Pkd1</i>^RC/RC mice obtained by crossing <i>Prkar1α</i>^R1αB/WT, <i>Pkd1^RC/RC</i> , and <i>Pkhd1-</i>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 <i>Pkd1^RC/RC</i> mice on a C57BL/6 × 129S6/Sv F1 background. Mice were sacrificed at 16 weeks of age. PKA-I activation promoted and inhibition prevented <i>ex vivo</i> P-Ser133 CREB expression and cystogenesis. EPAC activation or PKA-II inhibition had no or only minor effects. BLU2864 inhibited <i>in vitro</i> mIMCD3 cystogenesis and <i>ex vivo</i> 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 <i>in vivo</i>. BLU2864 had no detectable on- or off-target adverse effects. 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.