Abstract
Injury to the kidney triggers a cell proliferation response that can be adaptive, leading to repair of the tubular epithelium, or maladaptive, leading to fibrosis and chronic kidney disease. The Wnt pathway is activated in response to kidney injury and contributes to the fibrotic response. Although transient activation of the pathway is needed for repair of injured tissue and increase in cell proliferation, the sustained activation may promote fibrosis. The mechanisms regulating the expression of a key Wnt ligand, Wnt3a, or the modulation of its activity are unknown. We tested the hypothesis that dopamine D 2 receptor (D2R) signaling modulates β-catenin and T-cell factor (TCF)/lymphoid enhancer factor (LEF)-mediated transcriptional activity by effects on Wnt3a expression. In mice and human renal proximal tubule cells (RPTCs) D2R downregulation (siRNA, 20 nM, 72h) or antagonism (sulpiride, 1 μM, 6h), decreased β-catenin phosphorylation and increased TCF/LEF reporter activity (50-70%, P<0.05) and Wnt3a expression. Conversely D2R agonism (quinpirole, 1 μM, 24h) increased β-catenin phosphorylation (20%, P<0.05), and decreased TCF/LEF reporter activity (35%; P<0.05) and Wnt3a expression (45%, P<0.05). Human RPTCs carrying D2R variants (SNPs) resulting in decreased D2R expression have increased expressions of Wnt3a (50%, p<0.05) and Ki-67, a cell proliferation marker, that are decreased by transient overexpression of the D2R. Furthermore, selective renal D2R silencing or renal ischemia/reperfusion in mice increases renal expression of Wnt3a and Ki-67, which are both are reversed by selective D2R overexpression in the kidney. Wnt3a and Ki-67 colocalize in the nucleus of proximal tubules cells of mice subjected to ischemia/reperfusion indicating the involvement of the Wnt/β-catenin pathway in injury-induced cell proliferation. Conversely, Wnt3a downregulation in RPTCs carrying D2R variants not only decreased Ki-67 but also decreased cell apoptosis (Tunel reaction). Our results suggest that D2R is a transcriptional modulator of canonical Wnt signal transduction with broad implications for health and development of new therapeutics.
Published Version
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