IRIP, a New Ischemia/Reperfusion-Inducible Protein That Participates in the Regulation of Transporter Activity

ABSTRACT We report the identification and characterization of a new ischemia/reperfusion-inducible protein (IRIP), which belongs to the SUA5/YrdC/YciO protein family. IRIP cDNA was isolated in a differential display analysis of an ischemia/reperfusion-treated kidney RNA sample. Mouse IRIP mRNA was expressed in all tissues tested, the highest level being in the testis, secretory, and endocrine organs. Besides ischemia/reperfusion, endotoxemia also activated the expression of IRIP in the liver, lung, and spleen. The transporter regulator RS1 was identified as an IRIP-interacting protein in yeast two-hybrid screening. The interaction between IRIP and RS1 was further confirmed in coimmunoprecipitation assays. A possible role of IRIP in regulating transporter activity was subsequently investigated. IRIP overexpression inhibited endogenous 1-methyl-4-phenylpyridinium (MPP+) uptake activity in HeLa cells. The activities of exogenous organic cation transporters (OCT2 and OCT3), organic anion transporter (OAT1), and monoamine transporters were also inhibited by IRIP. Conversely, inhibition of IRIP expression by small interfering RNA or antisense RNA increased MPP+ uptake. We measured transport kinetics of OCT2-mediated uptake and demonstrated that IRIP overexpression significantly decreased V max but did not affect Km . On the basis of these results, we propose that IRIP regulates the activity of a variety of transporters under normal and pathological conditions.

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Renal organic anion transporter 1 is maldistributed and diminishes in proximal tubule cells but increases in vasculature after ischemia and reperfusion

AJP Renal Physiology ◽

10.1152/ajprenal.90409.2008 ◽

2008 ◽

Vol 295 (6) ◽

pp. F1807-F1816 ◽

Cited By ~ 10

Author(s):

Osun Kwon ◽

Wei-Wei Wang ◽

Shane Miller

Keyword(s):

Proximal Tubule ◽

Ischemia Reperfusion ◽

Organic Anion ◽

Basolateral Membrane ◽

Kidney Injury ◽

Organic Anion Transporter ◽

Membrane Domain ◽

Proximal Tubule Cells ◽

Anion Transporter ◽

Tubule Cells

Renal solute clearances are reduced in ischemic acute kidney injury. However, the mechanisms explaining how solute clearance is impaired have not been clarified. Recently, we reported that cadaveric renal allografts exhibit maldistribution of organic anion transporter 1 (OAT1) in proximal tubule cells after ischemia and reperfusion, resulting in impairment of PAH clearance. In the present study, we characterized renal OAT1 in detail after ischemia-reperfusion using a rat model. We analyzed renal OAT1 using confocal microscopy with a three-dimensional reconstruction of serial optical images, Western blot, and quantitative real-time RT-PCR. OAT1 was distributed to basolateral membranes of proximal tubule cells in controls. With ischemia, OAT1 decreased in basolateral membrane, especially in the lateral membrane domain, and appeared diffusely in cytoplasm. After reperfusion following 60-min ischemia, OAT1 often formed cytoplasmic aggregates. The staining for OAT1 started reappearing in lateral membrane domain 1 h after reperfusion. The basolateral membrane staining was relatively well discernable at 240 h of reperfusion. Of note, a distinct increase in OAT1 expression was noted in vasculature early after ischemia and after reperfusion. The total amount of OAT1 protein expression in the kidney diminished after ischemia-reperfusion in a duration-dependent manner until 72 h, when they began to recover. However, even at 240 h, the amount of OAT1 did not reach control levels. The kidney tissues tended to show a remarkable but transient increase in mRNA expression for OAT1 at 5 min of ischemia. Our findings may provide insights of renal OAT1 in its cellular localization and response during ischemic acute kidney injury and recovery from it.

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Early Elimination of Uremic Toxin Ameliorates AKI to CKD Transition

Clinical Science ◽

10.1042/cs20210858 ◽

2021 ◽

Author(s):

Jia Huang Chen ◽

Chia-Ter Chao ◽

Jenq-Wen Huang ◽

Kuan-Yu Hung ◽

Shing-Hwa Liu ◽

...

Keyword(s):

Er Stress ◽

Renal Fibrosis ◽

Epithelial Mesenchymal Transition ◽

Early Stage ◽

Ischemia Reperfusion ◽

Organic Anion ◽

Organic Anion Transporter ◽

Uremic Toxin ◽

Mesenchymal Transition ◽

Anion Transporter

Acute kidney injury (AKI)-related fibrosis is a major driver of chronic kidney disease (CKD) development. Aberrant kidney recovery after AKI is multifactorial and still unclear. The accumulation of indoxyl sulfate (IS), a protein-bound uremic toxin, has been identified as a detrimental factor of renal fibrosis. However, the mechanisms underlying IS-related aberrant kidney recovery after AKI is still unknown. The study aims to elucidate the effects of IS in the pathogenesis of AKI to CKD transition. Our results showed that serum IS started to accumulate associated with the downregulation of tubular organic anion transporter, but not observed in the small-molecule uremic toxins of the unilateral ischemia-reperfusion injury without a contralateral nephrectomy model(UIRI). Serum IS is positively correlated with renal fibrosis and ER stress-related protein expression induction in the UIRI with a contralateral nephrectomy model (UIRI+Nx). To evaluate the effects of IS in the AKI to CKD transition, we administered indole, a precursor of IS, at the early stage of UIRI. Our results demonstrated IS potentiates renal fibrosis, senescence-associated secretory phenotype (SASP), and activation of ER, which is attenuated by synergistic AST-120 administration. Furthermore, we clearly demonstrated that IS exposure potentiated hypoxia-reperfusion (H/R) induced G2/M cell cycle arrest, epithelial-mesenchymal transition, and aggravated ER stress induction in vitro. Finally, the ER chemical chaperon, 4-PBA, successfully reversed the above-mentioned AKI to CKD transition. Taken together, early IS elimination in the early stage of AKI is likely to be a useful strategy in the prevention or treatment of the AKI to CKD transition.

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