Mice carrying a targeted disruption of the Npr1 gene (coding for guanylyl cyclase/natriuretic peptide receptor A (NPRA)) exhibit increased blood pressure, cardiac hypertrophy, and congestive heart failure, similar to untreated human hypertensive patients. The objective of this study was to determine whether permanent ablation of NPRA signaling in mice alters the expression of matrix metalloproteinase (MMP)-2 and MMP-9 and pro-inflammatory mediators such as tumor necrosis factor-α (TNF-α), leading to myocardial collagen remodeling. Here, we report that expression levels of the MMP-2 and MMP-9 genes were increased by 3-5-fold and that the expression of the TNF-α gene was enhanced by 8-fold in Npr1 homozygous null mutant (Npr1^-/-) mouse hearts compared with wild-type (Npr1^+/+) control mouse hearts. Myocardial fibrosis, total collagen, and the collagen type I/III ratio (p < 0.01) were dramatically increased in adult Npr1^-/- mice compared with age-matched wild-type counterparts. Hypertrophic marker genes, including the β-myosin heavy chain and transforming growth factor-β1, were significantly up-regulated (3-5-fold) in both young and adult Npr1^-/- mouse hearts. NF-κB binding activity in ventricular tissues was enhanced by 4-fold with increased translocation of the p65 subunit from the cytoplasmic to nuclear fraction in Npr1^-/- mice. Our results show that reduced NPRA signaling activates MMP, transforming growth factor-β1, and TNF-α expression in Npr1^-/- mouse hearts. The findings of this study demonstrate that disruption of NPRA/cGMP signaling promotes hypertrophic growth and extracellular matrix remodeling, leading to the development of cardiac hypertrophy, myocardial fibrosis, and congestive heart failure.

Guanylyl cyclase/natriuretic peptide receptor-A (GC-A/NPRA) plays a critical role in the regulation of blood pressure and fluid volume homeostasis. Mice lacking functional Npr1 (coding for GC-A/NPRA) exhibit hypertension and congestive heart failure. However, the underlying mechanisms remain largely less clear. The objective of the present study was to determine the physiological efficacy and impact of all- trans-retinoic acid (ATRA) and sodium butyrate (NaBu) in ameliorating the renal fibrosis, inflammation, and hypertension in Npr1 gene-disrupted haplotype (1-copy; +/−) mice (50% expression levels of NPRA). Both ATRA and NaBu, either alone or in combination, decreased the elevated levels of renal proinflammatory and profibrotic cytokines and lowered blood pressure in Npr1^+/−mice compared with untreated controls. The treatment with ATRA-NaBu facilitated the dissociation of histone deacetylase (HDAC) 1 and 2 from signal transducer and activator of transcription 1 (STAT1) and enhanced its acetylation in the kidneys of Npr1^+/−mice. The acetylated STAT1 formed a complex with nuclear factor-κB (NF-κB) p65, thereby inhibiting its DNA-binding activity and downstream proinflammatory and profibrotic signaling cascades. The present results demonstrate that the treatment of the haplotype Npr1^+/−mice with ATRA-NaBu significantly lowered blood pressure and reduced the renal inflammation and fibrosis involving the interactive roles of HDAC, NF-κB (p65), and STAT1. The current findings will help in developing the molecular therapeutic targets and new treatment strategies for hypertension and renal dysfunction in humans.

Internalization and trafficking of cell-surface membrane receptors and proteins into subcellular compartments is mediated by specific short-sequence signal motifs, which are usually located within the cytoplasmic domains of these receptor and protein molecules. The signals usually consist of short linear amino acid sequences, which are recognized by adaptor coat proteins along the endocytic and sorting pathways. The complex arrays of signals and recognition proteins ensure the dynamic movement, accurate trafficking, and designated distribution of transmembrane receptors and ligands into intracellular compartments, particularly to the endosomal-lysosomal system. This review summarizes the new information and concepts, integrating them with the current and established views of endocytosis, intracellular trafficking, and sorting of membrane receptors and proteins. Particular emphasis has been given to the functional roles of short-sequence signal motifs responsible for the itinerary and destination of membrane receptors and proteins moving into the subcellular compartments. The specific characteristics and functions of short-sequence motifs, including various tyrosine-based, dileucine-type, and other short-sequence signals in the trafficking and sorting of membrane receptors and membrane proteins are presented and discussed.

The deficiency of Npr1 [genetic determinant of natriuretic peptide receptor A (NPRA)] increases arterial pressures and causes hypertensive heart disease in mice similar to those seen in untreated human hypertensive patients. However, the quantitative role of NPRA in mediating the renal responses to blood volume expansion remains uncertain. To determine the specific contribution of NPRA in mediating the signaling mechanisms responsible for natriuretic and diuretic responses to nondilutional intravascular expansion, we administered whole blood to anesthetized Npr1 homozygous null mutant (0-copy), wild-type (2-copy), and gene-duplicated (4-copy) mice. In wild-type (2-copy) animals, urinary flow (μl · min^–1· g kidney wt^–1) increased from 4.9 ± 1.0 to 14.4 ± 1.8 and sodium excretion (μeq · min^–1· g kidney wt^–1) from 1.15 ± 0.22 to 3.11 ± 0.60, associated with a rise in glomerular filtration rate (GFR; ml · min^–1· g kidney wt^–1) from 0.63 ± 0.03 to 0.82 ± 0.09 and renal plasma flow (RPF; ml · min^–1· g kidney wt^–1) from 2.96 ± 0.17 to 4.36 ± 0.41, whereas arterial pressure did not significantly increase. After volume expansion, 0-copy mice showed significantly lesser increases in urinary flow ( P < 0.001) and sodium excretory ( P < 0.001) responses even though the increases in arterial pressures were greater ( P < 0.001) compared with 2-copy mice. The 4-copy mice showed augmented responses in urinary flow ( P < 0.01) and sodium excretion ( P < 0.001) along with rises in both GFR ( P < 0.01) and RPF ( P < 0.01) compared with 2-copy wild-type mice. These results establish that NPRA activation is the predominant mechanism mediating the natriuretic, diuretic, and renal hemodynamic responses to acute blood volume expansion.