Yan Zhang

University of Chicago, Chicago, IL, United States

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Publications (7)52.85 Total impact

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    ABSTRACT: Analogs of vitamin D attenuate renal injury in several models of kidney disease, but the mechanism underlying this renoprotective effect is unknown. To address the role of the vitamin D receptor (VDR) in renal fibrogenesis, we subjected VDR-null mice to unilateral ureteral obstruction for 7 days. Compared with wild-type mice, VDR-null mice developed more severe renal damage in the obstructed kidney, with marked tubular atrophy and interstitial fibrosis. Significant induction of extracellular matrix proteins (fibronectin and collagen I), profibrogenic and proinflammatory factors (TGF-beta, connective tissue growth factor, and monocyte chemoattractant protein 1), and epithelial-to-mesenchymal transition accompanied this histologic damage. Because VDR ablation activates the renin-angiotensin system and leads to accumulation of angiotensin II (AngII) in the kidney, we assessed whether elevated AngII in the VDR-null kidney promotes injury. Treatment with the angiotensin type 1 antagonist losartan eliminated the difference in obstruction-induced interstitial fibrosis between wild-type and VDR-null mice, suggesting that AngII contributes to the enhanced renal fibrosis observed in obstructed VDR-null kidneys. Taken together, these results suggest that the VDR attenuates obstructive renal injury at least in part by suppressing the renin-angiotensin system.
    Journal of the American Society of Nephrology 04/2010; 21(6):966-73. · 8.99 Impact Factor
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    ABSTRACT: We recently showed that losartan and paricalcitol are synergistic in the treatment of diabetic nephropathy in a model of type 1 diabetes. To test this strategy in a model of type 2 diabetes, we treated 2-month-old diabetic Lprdb/db mice with losartan, paricalcitol, or a combination of losartan and paricalcitol for 3 months. Vehicle-treated diabetic mice developed progressive albuminuria and glomerular abnormalities with mesangial expansion and glomerulosclerosis compared to their non-diabetic littermate control mice. Accompanying damage of the glomerular filtration barrier was a marked reduction in podocyte number as well as reduced expression of slit diaphragm proteins. Further, there was increased glomerular expression of extracellular matrix proteins, monocyte chemoattractant protein-1 and transforming growth factor-beta. Losartan or paricalcitol each alone moderately ameliorated albuminuria and glomerular damage. However, their combined use showed a dramatic therapeutic synergism, manifested by prevention of progressive albuminuria, restoration of the glomerular filtration barrier, reversal of the decline in slit diaphragm proteins, reduced synthesis of extracellular matrix proteins, and reduction of glomerulosclerosis. These effects were accompanied by blockade of the compensatory increase of renin production and angiotensin I/II accumulation in the kidney. Thus, our study further shows that vitamin D analogs can increase the efficacy of AT1 receptor blockade, leading to a more effective prevention of kidney disease in type 2 diabetes.
    Kidney International 02/2010; 77(11):1000-9. · 8.52 Impact Factor
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    ABSTRACT: The intrarenal renin-angiotensin system (RAS) plays a key role in the development of diabetic nephropathy. Recently, we showed that combination therapy with an AT(1) receptor blocker (ARB) and an activated vitamin D analog produced excellent synergistic effects against diabetic nephropathy, as a result of blockade of the ARB-induced compensatory renin increase. Given the diversity of vitamin D analogs, here we used a pro-drug vitamin D analog, doxercalciferol (1alpha-hydroxyvitamin D(2)), to further test the efficacy of the combination strategy in long-term treatment. Streptozotocin-induced diabetic DBA/2J mice were treated with vehicle, losartan, doxercalciferol (0.4 and 0.6 microg/kg), or losartan and doxercalciferol combinations for 20 wk. Vehicle-treated diabetic mice developed progressive albuminuria and glomerulosclerosis. Losartan alone moderately ameliorated kidney injury, with renin being drastically upregulated. A similar therapeutic effect was seen with doxercalciferol alone, which markedly suppressed renin and angiotensinogen expression. The losartan and doxercalciferol combination most effectively prevented albuminuria, restored glomerular filtration barrier structure, and dramatically reduced glomerulosclerosis in a dose-dependent manner. These effects were accompanied by blockade of intrarenal renin upregulation and ANG II accumulation. These data demonstrate an excellent therapeutic potential for doxercalciferol in diabetic renal disease and confirm the concept that blockade of the compensatory renin increase enhances the efficacy of RAS inhibition and produces synergistic therapeutic effects in combination therapy.
    AJP Renal Physiology 07/2009; 297(3):F791-801. · 4.42 Impact Factor
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    ABSTRACT: The renin-angiotensin system (RAS) is a major mediator of renal injury in diabetic nephropathy. Our previous studies demonstrated that 1,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)] plays a renoprotective role by suppressing the RAS, with renin and angiotensinogen (AGT) as the main targets. The mechanism whereby 1,25(OH)(2)D(3) transcriptionally suppresses renin gene expression has been elucidated; however, how vitamin D regulates AGT remains unknown. Exposure of mesangial cells or podocytes to high glucose (HG; 30 mM) markedly stimulated AGT expression. In mesangial cells, the stimulation was inhibited by 1,25(OH)(2)D(3) (20 nM) or NF-kappaB inhibitor BAY 11-7082, suggesting the involvement of NF- kappaB in HG-induced AGT expression and the interaction between 1,25(OH)(2)D(3) and NF-kappaB in the regulation. Plasmid pNF-kappaB-Luc luciferase reporter assays showed that 1,25(OH)(2)D(3) blocked HG-induced NF-kappaB activity. EMSA and ChIP assays demonstrated increased p65/p50 binding to a NF-kappaB binding site at -1734 in the AGT gene promoter upon high glucose stimulation, and the binding was disrupted by 1,25(OH)(2)D(3) treatment. Overexpression of p65/p50 overcame 1,25(OH)(2)D(3) suppression, and mutation of this NF-kappaB binding site blunted 1,25(OH)(2)D(3) suppression of the promoter activity. In mice lacking the vitamin D receptor, AGT mRNA expression in the kidney was markedly increased compared with wild-type mice, and AGT induction in diabetic mice was suppressed by treatment with a vitamin D analog. These data indicate that 1,25(OH)(2)D(3) suppresses hyperglycemia-induced AGT expression by blocking NF-kappaB-mediated pathway.
    American journal of physiology. Renal physiology 03/2009; 296(5):F1212-8. · 3.61 Impact Factor
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    ABSTRACT: Vitamin D receptor (VDR)-null mice develop polyuria, but the underlying mechanism remains unknown. In this study, we investigated the relationship between vitamin D and homeostasis of water and electrolytes. VDR-null mice had polyuria, but the urine osmolarity was normal as a result of high salt excretion. The urinary responses to water restriction and to vasopressin were similar between wild-type and VDR-null mice, suggesting intact fluid-handling capacity in VDR-null mice. Compared with wild-type mice, however, renin and angiotensin II were dramatically upregulated in the kidney and brain of VDR-null mice, leading to a marked increase in water intake and salt appetite. Angiotensin II-mediated upregulation of intestinal NHE3 expression partially explained the increased salt absorption and excretion in VDR-null mice. In the brain of VDR-null mice, expression of c-Fos, which is known to associate with increased water intake, was increased in the hypothalamic paraventricular nucleus and the subfornical organ. Treatment with an angiotensin II type 1 receptor antagonist normalized water intake, urinary volume, and c-Fos expression in VDR-null mice. Furthermore, despite a salt-deficient diet to reduce intestinal salt absorption, VDR-null mice still maintained the increased water intake and urinary output. Together, these data indicate that the polyuria observed in VDR-null mice is not caused by impaired renal fluid handling or increased intestinal salt absorption but rather is the result of increased water intake induced by the increase in systemic and brain angiotensin II.
    Journal of the American Society of Nephrology 11/2008; 19(12):2396-405. · 8.99 Impact Factor
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    ABSTRACT: The renin-angiotensin system (RAS) plays a critical role in the development of diabetic nephropathy, and blockade of the RAS is currently used for treatment of diabetic nephropathy. One major problem for the current RAS inhibitors is the compensatory renin increase, which reduces the efficacy of RAS inhibition. We have shown that vitamin D exerts renoprotective actions by transcriptionally suppressing renin. Here we demonstrated that combination therapy with an AT1 receptor blocker and a vitamin D analog markedly ameliorated renal injury in the streptozotocin (STZ)-induced diabetes model due to the blockade of the compensatory renin rise by the vitamin D analog, leading to more effective RAS inhibition. STZ-treated diabetic DBA/2J mice developed progressive albuminuria and glomerulosclerosis within 13 weeks, accompanied by increased intrarenal production of angiotensin (Ang) II, fibronection, TGF-beta, and MCP-1 and decreased expression of slit diaphragm proteins. Treatment of the diabetic mice with losartan or paricalcitol (19-nor-1,25-dihydroxyvitamin D(2), an activated vitamin D analog) alone moderately ameliorated kidney injury; however, combined treatment with losartan and paricalcitol completely prevented albuminuria, restored glomerular filtration barrier structure, and markedly reduced glomerulosclerosis. The combined treatment suppressed the induction of fibronection, TGF-beta, and MCP-1 and reversed the decline of slit diaphragm proteins nephrin, Neph-1, ZO-1, and alpha-actinin-4. These were accompanied by blockade of intrarenal renin and Ang II accumulation induced by hyperglycemia and losartan. These data demonstrate that inhibition of the RAS with combination of vitamin D analogs and RAS inhibitors effectively prevents renal injury in diabetic nephropathy.
    Proceedings of the National Academy of Sciences 11/2008; 105(41):15896-901. · 9.81 Impact Factor
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    ABSTRACT: The renal renin-angiotensin system plays a major role in determining the rate of chronic renal disease progression. Treatment with activators of the vitamin D receptor retards the progression of experimental chronic renal disease, and vitamin D is known to suppress the renin-angiotensin system in other organs. Here we determined if the beneficial effects of paricalcitol (19-nor 1,25-dihydroxyvitamin D(2)) were associated with suppression of renin-angiotensin gene expression in the kidney. Rats with the remnant kidney model of chronic renal failure (5/6 nephrectomy) were given two different doses of paricalcitol thrice weekly for 8 weeks. Paricalcitol was found to decrease angiotensinogen, renin, renin receptor, and vascular endothelial growth factor mRNA levels in the remnant kidney by 30-50 percent compared to untreated animals. Similarly, the protein expression of renin, renin receptor, the angiotensin type 1 receptor, and vascular endothelial growth factor were all significantly decreased. Glomerular and tubulointerstitial damage, hypertension, proteinuria, and the deterioration of renal function resulting from renal ablation were all similarly and significantly improved with both treatment doses. These studies suggest that the beneficial effects of vitamin D receptor activators in experimental chronic renal failure are due, at least in part, to down-regulation of the renal renin-angiotensin system.
    Kidney International 09/2008; 74(11):1394-402. · 8.52 Impact Factor