Abnormal salt retention by thick ascending limbs (THALs) causes salt-sensitive hypertension. Flow elevates both stretch and shear stress which stimulates THAL O2- synthesis by NADPH oxidase 4 (NOX4) and NO production by NO synthase 3 (NOS3), respectively. We reported that flow-stimulated THAL Na reabsorption depends on O2- and protein kinase C ? (PKC?) but that flow-induced NO buffers flow-stimulated NaCl reabsorption by directly inhibiting NaCl transport and blunting flow-induced O2-. A high-salt diet increases THAL flow and we reported it enhances THAL NO production by increasing NOS3 expression and activity via de- phosphorylation at threonine 495 (T495), an inhibitory site modified by PKC. Thus salt-induced increases in flow prevent salt-sensitive hypertension via NO. Mechano-transduction of flow-induced stretch and shear stress in epithelia may occur via TRPV4 channels and/or cilia and TRPV4-TRPP2 channels. We showed that flow-induced stretch stimulates TRPV4, increases intracellular Ca (Cai) and stimulates O2-. We also showed that TRPV4 mediates flow-induced increases in Cai and NO. Since cilia and TRPV4-TRPP2 channels sense shear stress, both may be involved in NO production. If so, stretch and shear stress may differentially activate TRPV4 channels and cilia/TRPV4-TRPP2 channels, respectively. This would allow cells to distinguish stretch- and shear stress-elevated Cai. In Dahl salt-sensitive rats (SS) an imbalance between O2- and NO favoring the former causes salt-induced increases in BP but the cause is unknown. Our data show that stretch-induced TRPV4-dependent increases in Cai and flow-induced O2- production are greater in SS than salt-resistant (SR) THALs; however flow-induced NO production is reduced. This decrease is NOT due to scavenging by O2- or differences in NOS3 expression. We also show that a high-salt diet augments the differences in flow-induced Cai and O2- between SS and SR THALs, and causes a difference in NOS3 expression. Thus, we hypothesize that SS THALs display increased TRPV4 channel activity in response to salt-enhanced luminal flow causing abnormally elevated Cai and O2- production by NOX4. Chronically elevated O2- blunts flow-induced NO synthesis due to diminished salt-stimulated NOS3 expression, enhanced NOS3 phosphorylation at T495 and reduced tetrahydrobiopterin (BH4) resulting in salt retention by THALs and salt-sensitivity of BP. We propose 3 aims.
Aim 1 : Elevating flow and stretch stimulates TRPV4 channel activity more in SS than SR THALs resulting in greater increases in Cai, O2- production by NOX4, PKC? activation and NaCl reabsorption.
Aim 2 : Chronically elevated O2- in SS THALs blunts the ability of flow-induced shear stress to stimulate NO synthesis as a result of enhanced phosphorylation of NOS3 at T495, reduced BH4, and diminished salt-stimulated NOS3 expression rather than by scavenging or affecting ciliary signaling.
Aim 3 : Elevated flow-induced O2- and consequent reduced NO production in SS THALs cause salt retention and salt-sensitive hypertension. This proposal may provide a fundamental explanation for disparate data concerning salt-sensitivity of BP in SS.

Public Health Relevance

High blood pressure is the leading cause of loss of health world-wide. Between 25 and 30% of all Americans will develop high blood pressure in their lifetimes. About half of the people that develop high blood pressure have so-called salt-sensitive hypertension in which blood pressure rises with an increase in dietary salt. This project will study the role of a specific part of the kidney in the development of salt-sensitive hypertension in a genetic animal model of the human disease. Successful completion of the project will lead to a better understanding of the causes of salt-sensitive hypertension and may lead to new targets for drug development to treat it.

Agency
National Institute of Health (NIH)
Institute
National Heart, Lung, and Blood Institute (NHLBI)
Type
Research Project (R01)
Project #
2R01HL070985-13A1
Application #
9171098
Study Section
Hypertension and Microcirculation Study Section (HM)
Program Officer
OH, Youngsuk
Project Start
2002-09-01
Project End
2020-04-30
Budget Start
2016-07-01
Budget End
2017-04-30
Support Year
13
Fiscal Year
2016
Total Cost
Indirect Cost
Name
Case Western Reserve University
Department
Physiology
Type
Schools of Medicine
DUNS #
077758407
City
Cleveland
State
OH
Country
United States
Zip Code
44106
Saez, Fara; Hong, Nancy J; Garvin, Jeffrey L (2018) NADPH oxidase 4-derived superoxide mediates flow-stimulated NKCC2 activity in thick ascending limbs. Am J Physiol Renal Physiol 314:F934-F941
Gonzalez-Vicente, Agustin; Garvin, Jeffrey L (2017) Effects of Reactive Oxygen Species on Tubular Transport along the Nephron. Antioxidants (Basel) 6:
Monzon, Casandra M; Occhipinti, Rossana; Pignataro, Omar P et al. (2017) Nitric oxide reduces paracellular resistance in rat thick ascending limbs by increasing Na+ and Cl- permeabilities. Am J Physiol Renal Physiol 312:F1035-F1043
Saez, Fara; Hong, Nancy J; Garvin, Jeffrey L (2016) Luminal flow induces NADPH oxidase 4 translocation to the nuclei of thick ascending limbs. Physiol Rep 4:
Gonzalez-Vicente, Agustin; Saikumar, Jagannath H; Massey, Katherine J et al. (2016) Angiotensin II stimulates superoxide production by nitric oxide synthase in thick ascending limbs. Physiol Rep 4:
Monzon, Casandra M; Garvin, Jeffrey L (2015) Nitric oxide decreases the permselectivity of the paracellular pathway in thick ascending limbs. Hypertension 65:1245-50
Cabral, P D; Capurro, C; Garvin, J L (2015) TRPV4 mediates flow-induced increases in intracellular Ca in medullary thick ascending limbs. Acta Physiol (Oxf) 214:319-28
Hong, Nancy J; Garvin, Jeffrey L (2015) Endogenous flow-induced nitric oxide reduces superoxide-stimulated Na/H exchange activity via PKG in thick ascending limbs. Am J Physiol Renal Physiol 308:F444-9
Cabral, Pablo D; Garvin, Jeffrey L (2014) TRPV4 activation mediates flow-induced nitric oxide production in the rat thick ascending limb. Am J Physiol Renal Physiol 307:F666-72
Hong, Nancy J; Garvin, Jeffrey L (2014) Endogenous flow-induced superoxide stimulates Na/H exchange activity via PKC in thick ascending limbs. Am J Physiol Renal Physiol 307:F800-5

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