Abstract MP11: Striatin Heterozygous Knockout Mice Have Increased Aldosterone Sensitivity

Background: We recently demonstrated that mice lacking one copy of the striatin gene (Strn+/-) have salt sensitivity of blood pressure (BP) as compared with WT mice. To determine whether Strn+/- mice have increased sensitivity to aldosterone (ALDO), we assessed the effect on blood pressure of an ALDO infusion in WT and Strn+/- mice fed a liberal sodium diet. Methods: In this study we used 12 week old WT and Strn+/- littermate male mice. For each genotype, mice were placed on HS diet and randomized to either: 1) placebo 2) ALDO (200 μg/Kg/day) or 3) ALDO plus 100 mg/kg/day eplerenone. BP was measured by tail cuff plethysmography at baseline and after treatment. After 21 days of treatment, animals were placed in metabolic cages for 24 hours. Finally, animals were sacrificed and organs excised. Primary endpoints were BP, renal immunohistochemistry, protein analysis by western blot and mRNA expression by RT-PCR. Results: BP increased significantly in Strn+/- mice treated with ALDO (ΔBP: 12 ± 4 mmHg, p=0.03) but not placebo (ΔBP 6± 6 mmHg); the BP effect of ALDO was blunted by eplerenone (Δ 6 ± 3 mmHg). In contrast, none of the treatments had a significant effect on BP in WT mice. Kidney weight was significantly increased after 3 weeks of ALDO treatment in both WT and Strn+/- mice and this increase in kidney weight was prevented by treatment with eplerenone, with no difference between genotypes. WT mice had an increase in glomerular volume (GV) in HS/ALDO treated that was blunted by eplerenone. Interestingly, Strn+/- mice had increased GV across all 3 treatment groups compared with WT mice. pAkt/Akt ratios were reduced in Strn+/- mice versus WT mice across all treatments. Classic genomic MR targets (ENaC and SGK1) and non-genomic targets (pAkt/Akt) were significantly modulated in kidney tissue of Strn+/- mice compared to WT mice with chronic ALDO. Conclusion: Strn+/- mice have an increased sensitivity to infused ALDO (increased BP response and increased rise in renal ENaC and SGK1 protein) as compared to WT mice. Since loss of striatin directly reduces nongenomic not genomic action of ALDO, this study demonstrates for the first time that modifying the nongenomic pathway may under chronic, in vivo conditions led to increased sensitivity to the genomic actions of ALDO.

In a Nongenomic Action, Steroid Hormone 20-Hydroxyecdysone Induces Phosphorylation of Cyclin-Dependent Kinase 10 to Promote Gene Transcription

The insect steroid hormone 20-hydroxyecdysone (20E) regulates gene transcription via a genomic pathway by forming a transcription complex that binds to DNA with the help of the chaperone proteins, heat shock proteins (Hsps) Hsc70 and Hsp90. However, the nongenomic mechanisms by which 20E regulates gene expression remain unclear. In this study, we found that 20E regulated the phosphorylation of serine/threonine protein kinase cyclin-dependent kinase 10 (CDK10) through a nongenomic pathway to mediate gene transcription in the lepidopteran Helicoverpa armigera. The down-regulation of CDK10 by RNA interference in larvae and the epidermal cell line delayed development and suppressed 20E-induced gene transcription. CDK10 was localized to the nucleus via its KKRR motif, and this nuclear localization and the ATPase motif were necessary for the efficient expression of the 20E-inducible gene. The rapid phosphorylation of CDK10 was induced by 20E, whereas it was repressed by the inhibitors of G-protein–coupled receptors, phospholipase C, and Ca2+ channels. Phosphorylated CDK10 exhibited increased interactions with Hsps Hsc70 and Hsp90 and then promoted the interactions between Hsps and ecdysone receptor EcRB1 and the binding of the Hsps-EcRB1 complex to the 20E response element for the regulation of gene transcription. CDK10 depletion suppressed the formation of the Hsps-EcRB1 complex at the hormone receptor 3 promoter. These results suggest that 20E induces CDK10 phosphorylation via a nongenomic pathway to regulate gene transcription in the nucleus.