Abstract Body (Do not enter title and authors here): Introduction: Atrial and brain natriuretic peptides (ANP and BNP) bind to natriuretic peptide receptor-A (NPRA), generate the second messenger cGMP, and lower blood pressure (BP). NPRA is expressed in various tissues and cells, including the vascular smooth muscle cells; however, the role of ANP/NPRA signaling in smooth muscle cells (SMCs) remains unclear. The objective of this study was to determine the effect of conditional deletion of SMC-specific Npr1 (encoding NPRA) in gene-deleted male mice.
Methods: The wild-type control (SMC-Npr1 f/f; WT), heterozygous (SMC-Cre-Npr1 f/+; HT), and knockout (SMC-Cre-Npr1 f/-; KO) male mice were intraperitoneally injected with tamoxifen (20 mg/day in Olive oil) on 5 consecutive days to inactivate Npr1 followed by a 10-day off period, after which all experiments were commenced. Systolic blood pressure (SBP) was determined by non-invasive computerized tail-cuff method (Visitech 2000), carotid-femoral pulse wave velocity (cfPWV) and intracarotid PWV (icPWV) were assessed with high resolution ultrasound. Endothelium denuded aortic rings reactivity was measured using wire myography in male SMC-specific Npr1 disrupted HT, KO, and WT mice. The toll-like receptors 2/4 (TLR2, TLR4) proteins and nuclear factor-kappa B 65 (NF-kB p65) in the endothelium-denuded aortic rings were measured by Western blot.
Results: SBP was significantly (P < 0.01; P < 0.001) elevated in SMC-Npr1 HT (114 ± 2 mmHg) and KO mice (131 ± 3 mmHg) compared to WT (101 ± 2 mmHg) mice. Mean arterial pressure (MAP) measured by radiotelemetry, was increased by 26+2 mmHg in SMC-Npr1 KO mice compared with SMC-Npr1 WT mice. cfPWV and icPWV were significantly (P < 0.05; P < 0.01) increased in SMC- Npr1 KO mice compared to WT mice. Treatment with increasing concentrations of ANP (IC50 = 6 × 10^-9M) relaxed aortic rings that had been contracted with PGF2α. However, the relaxation activity in the aortic rings of SMC-Npr1 KO mice was significantly lower than that of WT mice. The NF-kB p65, TLR2, and TLR4 protein expression were markedly increased in SMC- Npr1 HT and SMC-Npr1 KO mice compared to WT mice.
Conclusion: The present results suggest that ANP/NPRA signaling in SMCs may play a crucial role in regulating BP, vasorelaxation activity, and inflammation in vascular bed. Supported by NIH/NIDDK grant (DK133833).