The D2 dopamine receptor (D2R) is important in the pathogenesis of human essential hypertension. D2R, rs6276 is associated with salt-sensitive hypertension in Caucasians. Depending on the genetic background, deletion of Drd2 (D2-/-) in mice causes salt-sensitive hypertension. In addition, as with the D5-/-mice, D2-/- mice are in a state of oxidative stress caused by increased expression and activity of NADPH oxidase and decreased expression and activity of HO-2 rather than HO-1, as is the case in D5-/- mice. Although the D2R and DSR can co-regulate certain enzymes (e.g., phospholipase C), there is no evidence for such a direct interaction in renal tubules. We hypothesize that NADPH oxidase isoforms are targets of both DSR and D2R but are regulated differentially by these two dopamine receptor genes. One such D2R target may be paraoxonase (PON). The PON family comprises three members: P0N1, P0N2, and PONS. P0N1 and PONS are circulating in serum associated with the high-density lipoprotein fraction. In contrast, P0N2 is cell- associated and protects against cellular oxidative stress. Renal P0N2 expression is decreased in D2-/- mice. Silencing P0N2 in RPT cells increases the production of ROS that is not affected by D2R/D3R agonist, indicating a response downstream to D2R. Other genes involved in the negative regulation of oxidative stress and regulated by D2R include sestrin-2 and DJ1. Sestrins accumulate in cells in response to oxidative stress and DJ1 may function as an atypical peroxiredoxin-like peroxidase. The deletion or silencing of Drd2 in mice decreases the renal expression of DJ1 and silencing DJ1 in RPT cells increases ROS production, reminiscent of P0N2. We will test the overall hypothesis that the inhibition of ROS production by D2R is caused by a positive regulation of P0N2, interacting with sestrin-2 and DJ1.
Specific aim 1 will test the hypothesis that P0N2 mediates the inhibitory effect of D2R on the production of ROS.
Specific Aim 2 will test the hypothesis that D2R directly regulates P0N2 and other interacting proteins that negatively regulate ROS production, e.g., sestrin-2 and DJ1. Abnormal D2R expression or function may result in salt-dependent hypertension in humans, caused by abnormal regulation of PON, sestrin 2, and DJ1 function.
Recent large association studies identified genes that cause 12% of blood pressure variability. A D2R gene variant, rs6276, is associated with salt-sensitive hypertension in a Caucasian population and DJ1 locus is linked to hypertension. Abnormal D2R expression or function may result in salt-dependent hypertension iri humans, caused by abnormal regulation of PON, sestrin 2, and DJ1 function.
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