ASN's Mission

ASN leads the fight to prevent, treat, and cure kidney diseases throughout the world by educating health professionals and scientists, advancing research and innovation, communicating new knowledge, and advocating for the highest quality care for patients.

learn more

Contact ASN

1401 H St, NW, Ste 900, Washington, DC 20005

email@asn-online.org

202-640-4660

The Latest on Twitter

Kidney Week

Abstract: TH-OR072

Cholesterol, a Repressor of Natriuretic Genes

Session Information

Category: Hypertension and CVD

  • 1403 Hypertension and CVD: Mechanisms

Authors

  • Rohatgi, Rajeev, Northport VAMC, Northport, New York, United States
  • Repetti, Robert Lawrence, Northport VAMC, Northport, New York, United States
  • Meth, Jennifer, Northport VAMC, Northport, New York, United States
  • Flores, Daniel, Icahn School of Medicine at Mount Sinai, New York, New York, United States
  • Satlin, Lisa M., Icahn School of Medicine at Mount Sinai, New York, New York, United States
Background

Salt-sensitivity in Dahl rats is due, in part, to the reduction of hemoxygenase-1 (HO1), cyclooxygenase 2 (COX2), and nitric oxide synthase-2 (NOS2) in the renal medulla. Renal overexpression of HIF1-α, a regulator of HO1, COX2, and NOS2, enhances salt and water excretion and reduces blood pressure. Cholesterol (chol) incorporation into collecting duct (CD) cells, in vivo or in vitro, represses COX2 activity in response to tubular flow or fluid shear stress (FSS). We hypothesized that dietary chol ingestion represses flow responsive genes necessary to effectuate salt and water excretion.

Methods

To this end, mice were fed either a 0% or 1% chol diet for up to 12 weeks, injected with SQ isotonic saline at 5% of body weight, and urine collected at 2, 4, and 6 hrs. Kidneys were extracted to measure medullary expression of HO1, COX1, and NOS2. Mice were divided into three dietary time points: (1) 3-5 (2) 6-8 and (3) >9 weeks of diet.

Results

Urine volume was less in the chol group at the 6 hr urine collection for 6-8 wks of diet group (n=8 control and chol; p<0.05) . Urinary [Na], [K] and osmolality were higher while Na excretion was lower at the 6 hr urine collection time point in the chol (p<0.05) vs. control fed mice. Renal medullary HO1 (0.76±0.09; p<0.05), and NOS2 (0.76±0.1; p<0.05) mRNA levels were reduced compared to controls (HO1, 1.00±0.02; NOS2, 1.00±0.03) while COX2 and HIF1-α were unaffected. ATP-binding cassette transporter (ABCA1), a tissue chol efflux transporter, was increased in the medulla (2.0±0.3 fold; p<0.05) of chol vs. control fed mice. To test the flow responsiveness of HO1, COX2, NOS2 and HIf1-α, IMCD3 cells were exposed to 0.4 dynes/cm2 of FSS for up to 6 hours. HO1 mRNA increased by 350X fold, COX2 by 25X fold, and NOS2 by 8X fold at 6 hrs in sheared (n=4-6; p<0.01) vs.static (n=3-6) cells. HIF1-α mRNA increased by ~50% (p<0.05) at 4 and 6 hrs. Western blotting of FSS exposed cells demonstrated an increase in HIF1-α and HO1 protein compared to static cells (p<0.05).Similar to mouse, chol incorporation into cells raised ABCA1 mRNA levels 3.7±0.2 fold vs. untreated cells.

Conclusion

Dietary chol is associated reduced urine volume and Na excretion at 6 hrs after saline injection and suppressed flow induced HO1 and NOS2 gene expression. Studies will test whether chol incorporation into the tubule represses of natriuretic factors to reduce Na excretion.


.

Funding

  • Veterans Affairs Support