Abstract P230: Depletion Of Cyclic-gmp Levels And The Inhibition Of Cgks Activate P21 ^Cip1 /p27 ^Kip1 Pathways And Trigger High Blood Pressure With Renal Fibrosis And Dysfunction

Abstract

Targeted-deletion of Npr1 gene (coding for guanylyl cyclase/natriuretic peptide receptor-A, GC-A/NPRA) exhibits hypertrophic and proliferative effects in target organs of Npr 1 gene-knockout mice. Fibrosis and hypertrophy are regulated by p21 Cip1 and p27 Kip1 , cell-cycle regulatory proteins that inhibit target cyclin and cyclin-dependent kinase (cyclin-CDK) complex. We examined the activation of CDK blocker (p21 Cip1 /p27 Kip1 ) in Npr1 gene-knockout (0-copy; Npr 1 -/- ) mice and guanylyl cyclase (GC) inhibitor, A71915-treated and cGMP-dependent protein kinase (cGK) inhibitor, Rp-8-Br-cGMPS (Rp)-treated wild-type 2-copy ( Npr 1 +/+ ) and gene-duplicated 4-copy ( Npr 1 ++/++ ) mice. Blood pressure (BP) was significantly higher in 0-copy mice (138.6 ± 3.1 mmHg) and lower in 4-copy mice (86.0 ± 2.8 mmHg) than 2-copy mice (102.2 ± 1.7 mmHg). Treatment with A71915 and Rp showed significant changes in BP in 2-copy mice but caused only small increase in 4-copy mice. We found a significant decrease in renal cGMP levels with diminished cGK activity in 0-copy mice (p<0.0001) as well as A71915-treated (p<0.001) and Rp-treated (p<0.05) 2-copy and 4-copy mice as compared with controls animals. While significant activation of p-Erk1/2 (3-fold), p-p38MAPK (4-fold), p21 Cip1 (6-fold), and p27 Kip1 (5-fold) occurred in 0-copy, A71915-treated 2-copy, and A71915-treated 4-copy mice but Rp treatment caused minimal changes compared to control mice. There were significant increases in the proinflammatory cytokines, including TNF-α (6-fold), and IL-6 (3-fold) and profibrotic cytokine TGF-β1 (4-fold) in plasma and kidneys of 0-copy and A791915-treated 2-copy mice, but less in A71915-treated 4-copy mice than controls. Progressive renal pathology, including fibrosis, mesangial matrix expansion, tubular hypertrophy, and perivascular infiltration were significantly scored in 0-copy and A71915-treated 2-copy mice, but did so minimally in 4-copy mice compared with controls. The present results suggest that Npr1 has a pivotal role in inhibiting the renal fibrosis and pathology and exerts renal protective effects through the cGMP/cGK axis by repressing the CDK inhibitors, p21 Cip1 and p27 Kip1 . This work was supported by NIH grant (HL062147).