Erythropoietin Protects the Kidney against the Injury and Dysfunction Caused by Ischemia-Reperfusion

Abstract

Abstract. Erythropoietin (EPO) is upregulated by hypoxia and causes proliferation and differentiation of erythroid progenitors in the bone marrow through inhibition of apoptosis. EPO receptors are expressed in many tissues, including the kidney. Here it is shown that a single systemic administration of EPO either preischemia or just before reperfusion prevents ischemia-reperfusion injury in the rat kidney. Specifically, EPO (300 U/kg) reduced glomerular dysfunction and tubular injury (biochemical and histologic assessment) and prevented caspase-3, -8, and -9 activation in vivo and reduced apoptotic cell death. In human (HK-2) proximal tubule epithelial cells, EPO attenuated cell death in response to oxidative stress and serum starvation. EPO reduced DNA fragmentation and prevented caspase-3 activation, with upregulation of Bcl-X L and XIAP. The antiapoptotic effects of EPO were dependent on JAK2 signaling and the phosphorylation of Akt by phosphatidylinositol 3-kinase. These findings may have major implications in the treatment of acute renal tubular damage.Erythropoietin (EPO) is the major regulator of proliferation and differentiation of erythroid progenitor cells through its antiapoptotic actions (1). EPO gene expression is under the control of the oxygen-sensitive transcription factor hypoxiainducible factor (HIF-1), which consists of the regulatory subunit HIF-1␣ and the constitutively expressed subunit HIF-1␤. Low oxygen tension adverts enzymatic prolyl-residue hydroxylation by prolyl-4-hydroxylase, which, in normoxia, serves as a signal for polyubiquitination and proteosomal degradation, thereby preventing von-Hippel-Lindau (VHL)-dependent HIF degradation, leading to nuclear accumulation of HIF-1 (2). HIF-1 controls the expression of several cytokines that mediate the adaptive response to ischemia, including vascular endothelial growth factor and glucose metabolism. The prolyl-4-hydroxylase requires iron as a co-factor, and cobalt mimics the effect of hypoxia on HIF-1␣ activation (3). Cobalt administration to rats caused upregulation of HIF-dependent proteins, including EPO, and diminished the degree of renal injury caused by ischemia-reperfusion (I/R), suggesting the HIF/EPO pathway may play an important role in ischemic preconditioning (4). EPO is upregulated in the brain and spinal cord after hypoxic stimuli and protects neurones against ischemic or oxidative injury in vivo and in vitro (5,6). The neuroprotective effects of EPO are dependent on EPO receptormediated JAK2 phosphorylation and NF-B-dependent transcription of antiapoptotic genes, including endogenous inhibitors of apoptosis XIAP and cIAP-2 (7). In the retina, EPO upregulation is essential for hypoxic preconditioning via HIF-1␣ stabilization. The systemic administration of recombinant EPO also reduces the degree of retinal apoptosis induced by high-intensity light insult (8). EPO receptor-mediated intracellular signaling may involve nuclear translocation of the transcription factor NF-B and phosphorylation of Akt (protein kinase B) by phosph...

Redox Control of Renal Function and Hypertension

“…For example, by virtue of close proximity to EPO expression, Nox4 might regulate EPO production in the kidney. The major site for EPO synthesis in adults is generally believed to be the peritubular fibroblast-like cells, although EPO receptors have been demonstrated in mesangial cells, PTCs, and the glomerulus (208,238,297). As mentioned before, EPO synthesis is ramped up in response to hypoxia (with proline hydroxylases as main sensors) and anemia.…”

Cyclooxygenase-2 and hypoxia-regulated proteins are modulated by basic fibroblast growth factor in acute renal failure

“…EPO has protective effects on retina and renal tubular cells; in the specifi c context of ARF (Sharples et al, 2005), EPO exerts its action through the activation of Janus kinase 2, Akt, and multiple targets with antiapoptotic effects (Sharples et al, 2004). In addition, FGF has been reported to inhibit EPO-induced erythropoiesis (Schmerer et al, 2006;Kreja et al, 1993).…”

Erythropoietin and Oxidative Stress

“…In addition, EPO may foster the preservation of microglial cells for neuronal and vascular restructuring by preventing apoptotic injury in microglia , Vairano, et al, 2002. In regards to the capacity of EPO to maintain microglial cellular integrity, EPO retains its capacity to prevent early apoptotic injury with membrane PS externalization as well as later stages of apoptotic injury involving DNA fragmentation in microglia ) similar to other cell systems of neurovascular origin , Chong, et al, 2002b, Chong, et al, 2005d, Parsa, et al, 2003, Sharples, et al, 2004.As a robust cytoprotectant, EPO can enhance the survival of cells during several types of injury models in the nervous system (Lykissas, et al, 2007. In cells that involve the brain or the retina, EPO can prevent injury from hypoxic ischemia , Chong, et al, 2002b, Liu, et al, 2006, Meloni, et al, 2006, Wei, et al, 2006, Yu, et al, 2005, excitotoxicity (Montero, et al, 2007, Yamasaki, et al, 2005, infection (Kaiser, et al, 2006), free radical exposure , Chong, et al., 2003e, Yamasaki, et al, 2005, staurosporine (Pregi, et al, 2006), and dopaminergic cell injury (Demers, et al, 2005, McLeod, et al, 2006.…”

“…The amino-terminal domain of Jak2 is responsible for the binding of Jak2 with the β-subunit of the EPOR at a region proximal to the membrane that contains the Box 1 sequence (Zhao, et al, 1995). EPO can prevent apoptotic injury through its reliance on Jak2 phosphorylation (Kawakami, et al, 2001, Sharples, et al, 2004, since loss of Jak2 activity reduces protection by EPO (Digicaylioglu, et al, 2004, Lipton, 2007.The signal transducer and activator of transcription (STAT) proteins are direct substrates of Janus kinases. Seven mammalian STAT genes encoding proteins exist and are considered to be latent DNA binding factors that can be activated by tyrosine phosphorylation (Reich, 2007).…”

“…Activation of Akt is usually cytoprotective, such as during free radical exposure , Matsuzaki, et al, 1999, hyperglycemia (Anitha, et al, 2006), endothelial cell hypoxia (Chong, et al, 2002b), β-amyloid toxicity , Chong, et al, 2005d, cardiomyopathy (Kim, et al, 2008), and oxidative stress . EPO uses the PI 3-K/Akt pathway in a variety of experimental models of injury (Bahlmann, et al, 2004, Chong, et al, 2002b, Chong, et al, 2003e, Chong and Maiese, 2007a, Miki, et al, 2006, Parsa, et al, 2003, Sharples, et al, 2004, Um, et al, 2007, Um and Lodish, 2006, Wu, et al, 2007b. These can involve transcription factor regulation (Chong and Maiese, 2007a), maintenance of ΔΨ m , prevention of cytochrome c release , and blockade of caspase activity , Chong, et al, 2002b.…”