Sodium and water regulation by the kidney plays a key role in hypertension and can be significantly compromised by pathways of oxidative stress. Two tubular elements are of major importance in establishing Na+ homeostasis and both are known to participate in salt-sensitive forms of hypertension, the medullary thick ascending limb of Henle (mTAL) and the aldosterone sensitive distal nephron (ASDN). The mTAL of SS rats produces excess ROS and the chronic intramedullary infusion of catalase, a scavenger of H2O2, reduces salt- induced hypertension nearly 50% in SS rats. Conversely, medullary infusion of H2O2 to normal rats reduces MBF and Na+ excretion resulting in a salt-sensitive form of hypertension. SS rats fed a high salt diet also exhibit greater expression and activity of ENaC in the ASDN segments leading to greater reabsorption of Na+ and enhancement of salt-induced hypertension. The major source of ROS and H2O2 in the kidney is NADPH oxidase but the roles of specific Nox isoforms such as Noxs 1, 2 and 4 and the mechanisms whereby they affect renal function have not been well elucidated. The most abundant isoform in the kidney is Nox4 which is unique in that it releases predominantly H2O2. Yet no studies have been carried out to determine the role of Nox4 in Na+ homeostasis and hypertension. We hypothesize that Nox4 plays a dominant role in determining blood pressure salt-sensitivity in the SS rat in two ways: 1) By excess production of H2O2 in the renal outer medullary thick ascending limbs of Henle (mTAL) which diffuses to surrounding vasa recta (VR) pericytes causing constriction and reduction of MBF; 2) Through H2O2-mediated increases of ENaC activity in the ASDN. To explore the role of Nox4, we have created a novel rat model with a null mutation of Nox4 in the SS rat. We will compare the responses of this mutant rat, SSNox4-/-, to those of the SS rat in four Specific Aims: 1- Determine physiological consequences of a null mutation of Nox4 in SS rats (SSNox4-/-) upon whole kidney function (MBF and GFR), renal oxidative stress, pressure-natriuresis, salt-induced hypertension and renal injury. 2-(New Aim) Determine the extent to which the reduced renal injury in SSNox4-/- rats is a consequence of a lower renal perfusion pressure versus an inherent intrarenal reduction of ROS production (servo-control of renal perfusion pressure studies). 3-Determine if Nox4 is importantly involved in H2O2 production in mTAL in response to increased luminal Na+ delivery and whether H2O2 can diffuse from mTAL to constrict surrounding VR. 4-Determine if production of H2O2 and ENaC expression/activity in ASDN of SS rats is Nox4-dependent. Studies are multiscale in design ranging from intracellular to those utilizing chronically instrumented rats which monitor changes in MBF and GFR over several weeks. The results are expected to greatly enhance our understanding of the role of Nox4 in renal function and lead to novel ways to target pathways of oxidative stress in the treatment of hypertension and renal disease.

Public Health Relevance

Oral antioxidant therapy has not been sufficient in scavenging free radicals and has failed to alleviate oxidative stress in patients with hypertension and kidney disease. The proposed studies will provide an understanding of the molecular and physiological mechanisms responsible for increased oxidative stress in the kidney and enable the targeting of enzymes responsible for its generation rather than scavenging of reactive molecules once they are formed, thus a more effective antioxidant therapeutic approach.

Agency
National Institute of Health (NIH)
Institute
National Heart, Lung, and Blood Institute (NHLBI)
Type
Research Project (R01)
Project #
1R01HL122662-01A1
Application #
8886255
Study Section
Hypertension and Microcirculation Study Section (HM)
Program Officer
OH, Youngsuk
Project Start
2015-04-01
Project End
2019-02-28
Budget Start
2015-04-01
Budget End
2016-02-29
Support Year
1
Fiscal Year
2015
Total Cost
$394,892
Indirect Cost
$132,752
Name
Medical College of Wisconsin
Department
Physiology
Type
Schools of Medicine
DUNS #
937639060
City
Milwaukee
State
WI
Country
United States
Zip Code
53226
Staruschenko, Alexander (2017) Hypertension and Diabetes Mellitus: The Chicken and Egg Problem. Hypertension 69:787-788
Palygin, O; Pochynyuk, O; Staruschenko, A (2017) Role and mechanisms of regulation of the basolateral Kir 4.1/Kir 5.1K+ channels in the distal tubules. Acta Physiol (Oxf) 219:260-273
Ilatovskaya, Daria V; Palygin, Oleg; Levchenko, Vladislav et al. (2017) The Role of Angiotensin II in Glomerular Volume Dynamics and Podocyte Calcium Handling. Sci Rep 7:299
Endres, Bradley T; Sandoval, Ruben M; Rhodes, George J et al. (2017) Intravital imaging of the kidney in a rat model of salt-sensitive hypertension. Am J Physiol Renal Physiol 313:F163-F173
Wright, Kevin David; Staruschenko, Alexander; Sorokin, Andrey (2017) IR- Role of adaptor protein p66Shc in renal pathologies. Am J Physiol Renal Physiol :ajprenal.00414.2017
Palygin, Oleg; Evans, Louise C; Cowley Jr, Allen W et al. (2017) Acute In Vivo Analysis of ATP Release in Rat Kidneys in Response to Changes of Renal Perfusion Pressure. J Am Heart Assoc 6:
Pavlov, Tengis S; Staruschenko, Alexander (2017) Involvement of ENaC in the development of salt-sensitive hypertension. Am J Physiol Renal Physiol 313:F135-F140
Palygin, Oleg; Levchenko, Vladislav; Ilatovskaya, Daria V et al. (2017) Essential role of Kir5.1 channels in renal salt handling and blood pressure control. JCI Insight 2:
Palygin, Oleg; Ilatovskaya, Daria V; Staruschenko, Alexander (2016) Protease-activated receptors in kidney disease progression. Am J Physiol Renal Physiol 311:F1140-F1144
Staruschenko, Alexander; Ilatovskaya, Daria V; Pavlov, Tengis S (2016) High salt diet and caffeine: food for thought. J Thorac Dis 8:E1410-E1412

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