MBG promotes natriuresis, but causes vasoconstriction and induces fibrosis via PKC-dependent inhibition of Fli-1, a transcription factor and a negative regulator of collagen synthesis. We hypothesized that vascular smooth muscle cells (VSMC) from aged rats due to down-regulation of ANP/cGMP/PKG-dependent signaling would exhibit heightened sensitivity to the pro-fibrotic effect of MBG. In response to acute NaCl loading, aged (24-month old) Sprague-Dawley rats exhibited exaggerated MBG (5.40.4 vs. 1.90.2 pmol/hr;P<0.01) and pressor responses (29 vs. 15 mmHg;P<0.01), as well as greater inhibition of NKA in aorta as compared to young (3-month old) rats. Levels of vascular PKG1 and Fli-1 in aged rats were markedly reduced. In vitro, 1 nmol/L ANP prevented inhibition of vascular NKA by MBG in young, but not in the aged rats. In VSMC from young rats, 1 nmol/L MBG induced down-regulation of Fli-1 and a 1.5-fold increase in the levels of procollagen-1 and collagen-1, and 1 nmol/L ANP blocked this effect. In aged rats, levels of PKG-1 and Fli-1 in VSMC were markedly reduced vs. young rats, and 1 nmol/L MBG decreased Fli-1 (60%) and increased level of collagen-1 1.6-fold (P<0.01). In VSMC from aged rats, ANP failed to oppose the pro-fibrotic effect of MBG. Silencing of the PKG-1 gene in VSMC from young rats was associated with a marked increase in the sensitivity of VSMC to the pro-fibrotic effect of MBG;in this setting 1 nmol/L MBG increased levels of collagen-1 2.5-fold (P<0.01). These results demonstrate that the age-associated reduction in vascular PKG1 levels and resultant decline in cGMP signaling lead to the loss of ability of ANP to oppose MBG-induced inhibition of NKA and fibrosis. Silencing of PKG1 mimics effects of aging with respect to sensitivity of VSMC to pro-fibrotic action of cardiotonic steroids.

Agency
National Institute of Health (NIH)
Institute
National Institute on Aging (NIA)
Type
Investigator-Initiated Intramural Research Projects (ZIA)
Project #
1ZIAAG000868-03
Application #
8148334
Study Section
Project Start
Project End
Budget Start
Budget End
Support Year
3
Fiscal Year
2010
Total Cost
$163,224
Indirect Cost
Name
National Institute on Aging
Department
Type
DUNS #
City
State
Country
Zip Code
Fedorova, Olga V; Zernetkina, Valentina I; Shilova, Victoria Y et al. (2015) Synthesis of an Endogenous Steroidal Na Pump Inhibitor Marinobufagenin, Implicated in Human Cardiovascular Diseases, Is Initiated by CYP27A1 via Bile Acid Pathway. Circ Cardiovasc Genet 8:736-45
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Fedorova, Olga V; Kashkin, Vladimir A; Zakharova, Irina O et al. (2012) Age-associated increase in salt sensitivity is accompanied by a shift in the atrial natriuretic peptide modulation of the effect of marinobufagenin on renal and vascular sodium pump. J Hypertens 30:1817-26
Haller, Steven T; Kennedy, David J; Shidyak, Amjad et al. (2012) Monoclonal antibody against marinobufagenin reverses cardiac fibrosis in rats with chronic renal failure. Am J Hypertens 25:690-6
Nikitina, Elena R; Mikhailov, Anton V; Nikandrova, Ekaterina S et al. (2011) In preeclampsia endogenous cardiotonic steroids induce vascular fibrosis and impair relaxation of umbilical arteries. J Hypertens 29:769-76
Fedorova, Olga V; Shapiro, Joseph I; Bagrov, Alexei Y (2010) Endogenous cardiotonic steroids and salt-sensitive hypertension. Biochim Biophys Acta 1802:1230-6

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