Effect Of D₅Dopamine Receptor On Renalase In Renal Proximal Tubule Cells From WKY Rats And SHR And Its Role In The Pathogenesis Of Essential Hypertension

Background:Essential hypertension and its complications emerge to be one of the major cause tothreat human health. Sympathetic overactivity plays a key role in the pathogenesis ofessential hypertension. Redundant norepinephrine （NE） and epinephrine （EP） can increasevascular resistance by contracting vessels, and influence blood pressure by inducingoxidative stress and apoptosis. On the contrary, dopamine, which also belongs to the familyof catecholamine, lowers the blood pressure through activating the dopamine receptors. As aG protein-coupled receptors, dopamine receptors include two families, D₁-like （D₁and D₅）and D₂-like （D₂, D₃, and D₄） dopamine receptors. Regulation of dopamines receptors caninduce natriuresis and diuresis, relaxation of resistance arteries, and can also effect onsympathtic activity. Pervious studies demonstrated that activation of sympatheticpreganglionic fibers of D₁-like or D₂-like receptors results in a reduction of NE release fromthe teleneuron. In addition, mice lacking D4or D5dopamine receptor have increasedsympathetic activity and develope hypertension. These suggest that dopamine receptors cannegatively regulate the sympathetic activity.Recently, it is recognized that many cardiovascular diseases are associated withincreased sympathetic activity. As a novel soluble monoamine oxidase, renalase has beenreported to degrade catecholamine of the circulatory system. Synthesized and secreted bykidney, renalase play important roles in the genesis of hypertension for Chronic KindeyDisease （CKD） and End-stage Renal Disease （ESRD）. Renalase deficiency increases bloodpressure and elevates circulating catecholamines. Catecholamines regulate renalase secreteand activity. Dopamine increases renalase gene transcription in H9C2cells. However, thereis still no direct evidence of regulation of renalase synthesized by renal proximal tubules bydopamine receptors. Whether the dopamine receptors influence sympathetic activity through a renalase dependent pathway is yet to be confirmed. Further, the roles of dopaminereceptor subtypes in the regulation of renalase need to be determined. Studies have shownthe co-expression of dopamine D1-like receptor and renalase in the renal proximaltubules（RPTs）. We thus hypothesize that the dopamine D1-like receptor inflences renalseexpression and function, further regulates sympathetic activity and blood pressure.Objective1, Investigate the expression and activity of renalase in the kindey of the Wistar-Kyoto（WKY） rats and Spontaneously hypertensive rats （SHR）.2, Identify the effect of dopamine D₁-like receptor on renalase gene transcription,protein expression and activity.3, Determine the mechanisms of the effect of dopamine D1-like receptor on renalase.4, Determine the difference of the regulation of renalase in renal proximal tubule （RPT）cells by dopamine D1receptor between WKY rats and SHR.Methods1, Culture of renal proximal tubule from WKY rats and SHR.2, Detect mRNA of renalase of WKY RPTs and SHR RPTs under treatment of D1receptor activator fenoldopam.3, With western blots, detect renalase protein expression in kidney of WKY rats andSHR, and detect renalase protein expression of WKY RPTs and SHR RPTs under treatmentof fenoldopam.4, With NADH oxidation method, detect the renalase activity in kidney of WKY ratsand SHR, and oxidation activity changes of of WKY RPTs and SHR RPTs under treatmentof fenoldopam.Result:1, Renalase protein expression and activity were decreased in kidney of SHR,compared with WKY rats.2, Activition of dopamine D1-like receptor by fenoldopam increased renalase mRNAand protein expression, and increased oxidative activity of renalase secreted from RPT cellsof WKY rats.3, Fenoldopam decreased renalase protein expression and activity in aconcentration-dependent manner in RPT cells of SHR. 4, Fenoldopam upregulation of renalase in WKY-RPT cells was mainly through adopamine D5receptor mediated PKC pathway.Conclusion:Activition of dopamine D1receptor increases renalase synthesis, secretion and activityin WKY-RPT cells, mainly through a dopamine D₅receptor mediated PKC pathway.Activition of dopamine D₁receptor does not affect renalase in SHR-RPT cells, but canaccelerate the degradation of renalase protein. In the physiological state, dopamine D₁-likereceptor downregulation of blood pressure and sympathetic acitivity may be partly throughrenalase dependent pathway. The regulation of renalase by dopamine D₁-like receptors inSHR may contribute to the genesis and progress of hypertension.