RGS4, a GTPase activator, improves renal function in ischemia-reperfusion injury

Single-cell transcriptomic profiling reveals decreased ER protein Reticulon3 drives the progression of renal fibrosis

Chronic kidney disease (CKD) poses a significant global health dilemma, emerging from complex causes. Although our prior research has indicated that a deficiency in Reticulon-3 (RTN3) accelerates renal disease progression, a thorough examination of RTN3 on kidney function and pathology remains underexplored. To address this critical need, we generated Rtn3-null mice to study the consequences of RTN3 protein deficiency on CKD. Single-cell transcriptomic analyses were performed on 47,885 cells from the renal cortex of both healthy and Rtn3-null mice, enabling us to compare spatial architectures and expression profiles across 14 distinct cell types. Our analysis revealed that RTN3 deficiency leads to significant alterations in the spatial organization and gene expression profiles of renal cells, reflecting CKD pathology. Specifically, RTN3 deficiency was associated with Lars2 overexpression, which in turn caused mitochondrial dysfunction and increased reactive oxygen species levels. This shift induced a transition in renal epithelial cells from a functional state to a fibrogenic state, thus promoting renal fibrosis. Additionally, RTN3 deficiency was found to drive the endothelial-to-mesenchymal transition process and disrupt cell-cell communication, further exacerbating renal fibrosis. Immunohistochemistry and Western-Blot techniques were used to validate these observations, reinforcing the critical role of RTN3 in CKD pathogenesis. The deficiency of RTN3 protein in CKD leads to profound changes in cellular architecture and molecular profiles. Our work seeks to elevate the understanding of RTN3's role in CKD's narrative and position it as a promising therapeutic contender.

Regulator of G-protein signaling 14 protects the liver from ischemia-reperfusion injury by suppressing TGF-β-activated kinase 1 activation

BACKGROUND AND AIMS

Hepatic ischemia-reperfusion injury (IRI) is a common complication of hepatectomy and liver transplantation. However, the mechanisms underlying hepatic IRI have not been fully elucidated. Regulator of G-protein signaling 14 (RGS14) is a multifunctional scaffolding protein that integrates the G-protein and mitogen-activated protein kinase (MAPK) signaling pathways. However, the role of RGS14 in hepatic IRI remains unclear.

APPROACH AND RESULTS

We found that RGS14 expression increased in mice subjected to hepatic ischemia-reperfusion (IR) surgery and during hypoxia reoxygenation in hepatocytes. We constructed global RGS14 knockout (RGS14-KO) and hepatocyte-specific RGS14 transgenic (RGS14-TG) mice to establish 70% hepatic IRI models. Histological hematoxylin and eosin staining, levels of alanine aminotransferase and aspartate aminotransferase, expression of inflammatory factors, and apoptosis were used to assess liver damage and function in these models. We found that RGS14 deficiency significantly aggravated IR-induced liver injury and activated hepatic inflammatory responses and apoptosis in vivo and in vitro. Conversely, RGS14 overexpression exerted the opposite effect of the RGS14-deficient models. Phosphorylation of TGF-β-activated kinase 1 (TAK1) and its downstream effectors c-Jun N-terminal kinase (JNK) and p38 increased in the liver tissues of RGS14-KO mice but was repressed in those of RGS14-TG mice. Furthermore, inhibition of TAK1 phosphorylation rescued the effect of RGS14 deficiency on JNK and p38 activation, thus blocking the inflammatory responses and apoptosis.

CONCLUSIONS

RGS14 plays a protective role in hepatic IR by inhibiting activation of the TAK1-JNK/p38 signaling pathway. This may be a potential therapeutic strategy for reducing incidences of hepatic IRI in the future.

Macrophage secretion of miR-106b-5p causes renin-dependent hypertension

Myeloid cells are known mediators of hypertension, but their role in initiating renin-induced hypertension has not been studied. Vitamin D deficiency causes pro-inflammatory macrophage infiltration in metabolic tissues and is linked to renin-mediated hypertension. We tested the hypothesis that impaired vitamin D signaling in macrophages causes hypertension using conditional knockout of the myeloid vitamin D receptor in mice (KODMAC). These mice develop renin-dependent hypertension due to macrophage infiltration of the vasculature and direct activation of renal juxtaglomerular (JG) cell renin production. Induction of endoplasmic reticulum stress in knockout macrophages increases miR-106b-5p secretion, which stimulates JG cell renin production via repression of transcription factors E2f1 and Pde3b. Moreover, in wild-type recipient mice of KODMAC/miR106b^−/− bone marrow, knockout of miR-106b-5p prevents the hypertension and JG cell renin production induced by KODMAC macrophages, suggesting myeloid-specific, miR-106b-5p-dependent effects. These findings confirm macrophage miR-106b-5p secretion from impaired vitamin D receptor signaling causes inflammation-induced hypertension.

Myeloid cells are involved in hypertension, but their exact role in renin-induced hypertension remains unclear. Here the authors show that impaired vitamin D signaling in myeloid cells causes hypertension via macrophage-specific miR-106b-5p secretion, which activates renin production in the kidney.

miR-218 Expressed in Endothelial Progenitor Cells Contributes to the Development and Repair of the Kidney Microvasculature

Ischemia due to hypoperfusion is one of the most common forms of acute kidney injury. We hypothesized that kidney hypoxia initiates the up-regulation of miR-218 expression in endothelial progenitor cells (EPCs) to guide endocapillary repair. Murine renal artery-derived EPCs (CD34+/CD105-) showed down-regulation of mmu-Mir218-5p/U6 RNA ratio after ischemic injury, while in human renal arteries, MIR218-5p expression was up-regulated after ischemic injury. MIR218 expression was clarified in cell culture experiments in which increases in both SLIT3 and MIR218-2-5p expressions were observed after 5 minutes of hypoxia. ROBO1 transcript, a downstream target of MIR218-2-5p, showed inverse expression to MIR218-2-5p. EPCs transfected with a MIR218-5p inhibitor in three-dimensional normoxic culture showed premature capillary formation. Organized progenitor cell movement was reconstituted when cells were co-transfected with Dicer siRNA and low-dose Mir218-5p mimic. A Mir218-2 knockout was generated to assess the significance of miR-218-2 in a mammalian model. Mir218-2-5p expression was decreased in Mir218-2-/- embryos at E16.5. Mir218-2-/- decreased CD34+ angioblasts in the ureteric bud at E16.5 and were nonviable. Mir218-2+/- decreased peritubular capillary density at postnatal day 14 and increased serum creatinine after ischemia in adult mice. Systemic injection of miR-218-5p decreased serum creatinine after injury. These experiments demonstrate that miR-218 expression can be triggered by hypoxia and modulates EPC migration in the kidney.

MiR-21-3p modulates lipopolysaccharide-induced inflammation and apoptosis via targeting TGS4 in retinal pigment epithelial cells

Age-related macular degeneration (AMD) is a major reason of blindness in the elderly. MicroRNAs are implicated in various pathological processes, including inflammation and apoptosis. In this study, we aim to investigate the biological functions of miR-21-3p in inflammation and apoptosis caused by lipopolysaccharide (LPS) in human retinal pigment epithelial (ARPE-19) cells. The miR-21-3p inhibitor and mimic were transfected into ARPE-19 cells for 48 hours, followed by exposed to LPS (10 μg/mL) for 24 hours. The mRNA and protein expression of IL-6 and MCP-1 were measured using real-time PCR (RT-PCR) and enzyme-linked immunosorbent assays. Cell viability, apoptosis, caspase 3 activity, cleaved caspase-3 and cleaved-PARP protein levels were detected to evaluate the effects of miR-21-3p on apoptosis. Additionally, the target relationship between miR-21-3p and regulator of G-protein signalling 4 (RGS4) was verified by dual luciferase reporter assay. RT-PCR analysis demonstrated that LPS induced miR-21-3p expression. Inhibition of miR-21-3p reduced the mRNA and protein levels of IL-6 and MCP-1. Apoptosis, caspase-3 activity, and cleaved-caspase 3 and cleaved PARP protein levels were repressed by the miR-21-3p inhibitor. However, overexpression of miR-21-3p showed the opposite results. Furthermore, we identified that miR-21-3p directly targeted the 3' untranslated region of RGS4. MiR-21-3p negatively regulated the expression of RGS4 both in mRNA and protein levels. Silencing RGS4 reduced the anti-inflammatory and anti-apoptotic effects of miR-21-3p inhibitor. Our results revealed that miR-21-3p inhibition targeted RGS4 to attenuate inflammatory responses and apoptosis caused by LPS in ARPE-19 cells.

RGS4 Overexpression in Lung Attenuates Airway Hyperresponsiveness in Mice

A cardinal feature of asthma is airway hyperresponsiveness (AHR) to spasmogens, many of which activate G protein-coupled receptors (GPCRs) on airway smooth muscle (ASM) cells. Asthma subtypes associated with allergy are characterized by eosinophilic inflammation in the lung due to the type 2 immune response to allergens and proinflammatory mediators that promote AHR. The degree to which intrinsic abnormalities of ASM contribute to this phenotype remains unknown. The regulators of G protein signaling (RGS) proteins are a large group of intracellular proteins that inhibit GPCR signaling pathways. RGS2- and RGS5-deficient mice develop AHR spontaneously. Although RGS4 is upregulated in ASM from patients with severe asthma, the effects of increased RGS4 expression on AHR in vivo are unknown. Here, we examined the impact of forced RGS4 overexpression in lung on AHR using transgenic (Tg) mice. Tg RGS4 was expressed in bronchial epithelium and ASM in vivo, and protein expression in lung was increased at least 4-fold in Tg mice compared with wild-type (WT) mice. Lung slices from Tg mice contracted less in response to the m3 muscarinic receptor agonist methacholine compared with the WT, although airway resistance in live, unchallenged mice of both strains was similar. Tg mice were partially protected against AHR induced by fungal allergen challenge due to weakened contraction signaling in ASM and reduced type 2 cytokine (IL-5 and IL-13) levels in Tg mice compared with the WT. These results provide support for the hypothesis that increasing RGS4 expression and/or function could be a viable therapeutic strategy for asthma.

Regulating the regulators: Epigenetic, transcriptional, and post-translational regulation of RGS proteins

Regulators of G protein signaling (RGS) are a family of proteins classically known to accelerate the intrinsic GTPase activity of G proteins, which results in accelerated inactivation of heterotrimeric G proteins and inhibition of G protein coupled receptor signaling. RGS proteins play major roles in essential cellular processes, and dysregulation of RGS protein expression is implicated in multiple diseases, including cancer, cardiovascular and neurodegenerative diseases. The expression of RGS proteins is highly dynamic and is regulated by epigenetic, transcriptional and post-translational mechanisms. This review summarizes studies that report dysregulation of RGS protein expression in disease states, and presents examples of drugs that regulate RGS protein expression. Additionally, this review discusses, in detail, the transcriptional and post-transcriptional mechanisms regulating RGS protein expression, and further assesses the therapeutic potential of targeting these mechanisms. Understanding the molecular mechanisms controlling the expression of RGS proteins is essential for the development of therapeutics that indirectly modulate G protein signaling by regulating expression of RGS proteins.

Regulator of G protein signaling-1 modulates paraquat-induced oxidative stress and longevity via the insulin like signaling pathway in Caenorhabditis elegans

Insulin or insulin like signaling (IIS) pathway is a crucial pathway in Caenorhabditis elegans associated with mediating longevity, and stress resistance. Regulators of G protein signaling (RGS) also modulate stress resistance and longevity in multiple in vitro and in vivo models. However, the mechanism underlying RGS mediating stress resistance and longevity remains largely unclear. Here we report that rgs-1, an important member of rgs family, is a novel modulator of IIS pathway in C. elegans. We found that the loss of rgs-1 dramatically promoted paraquat resistance in C. elegans. Further genetic analyses demonstrated that rgs-1 acted downstream of daf-2 and upstream of age-1, pdk-1, daf-16. Instead of affecting those IIS-associated genes in transcriptional process, loss of rgs-1 promoted DAF-16's nucleus translocation and subset genes' expression in paraquat-induced oxidative status. By this way, rgs-1 mutant worms exhibited lower ROS damage and longer survival time than wild type worms when both exposed to paraquat. Other than paraquat exposure, rgs-1 mutant also promoted lifespan and cadmium resistance relying on daf-16. As rgs is evolutionarily conserved, our findings open a new insight into rgs family and its role in paraquat-induced oxidative stress and longevity in C. elegans or even mammals.

Human vascular progenitor cells derived from renal arteries are endothelial-like and assist in the repair of injured renal capillary networks

Vascular progenitor cells show promise for the treatment of microvasculature endothelial injury. We investigated the function of renal artery progenitor cells derived from radical nephrectomy patients, in animal models of acute ischemic and hyperperfusion injuries. Present in human adventitia, CD34positive/CD105negative cells were clonal and expressed transcription factors Sox2/Oct4 as well as surface markers CXCR4 (CD184)/KDR(CD309) consistent with endothelial progenitor cells. Termed renal artery-derived vascular progenitor cells (RAPC), injected cells were associated with decreased serum creatinine after ischemia/reperfusion, reduced albuminuria after hyperperfusion, and improved blood flow in both models. A small population of RAPC integrated with the renal microvasculature following either experimental injury. At a cellular level, RAPC promoted local endothelial migration in co-culture. Profiling of RAPC microRNA identified high levels of miRNA 218; also found at high levels in exosomes isolated from RAPC conditioned media after cell contact for 24 hours. After hydrogen peroxide-induced endothelial injury, RAPC exosomes harbored Robo-1 transcript; a gene known to be regulated by mir218. Such exosomes enhanced endothelial cell migration in culture in the absence of RAPC. Thus, our work shows the feasibility of pre-emptive pro-angiogenic progenitor cell procurement from a targeted patient population and potential therapeutic use in the form of autologous cell transplantation.

Accessory proteins for heterotrimeric G-proteins in the kidney

Heterotrimeric G-proteins play a fundamentally important role in regulating signal transduction pathways in the kidney. Accessory proteins are being identified as direct binding partners for heterotrimeric G-protein α or βγ subunits to promote more diverse mechanisms by which G-protein signaling is controlled. In some instances, accessory proteins can modulate the signaling magnitude, localization, and duration following the activation of cell membrane-associated receptors. Alternatively, accessory proteins complexed with their G-protein α or βγ subunits can promote non-canonical models of signaling activity within the cell. In this review, we will highlight the expression profile, localization and functional importance of these newly identified accessory proteins to control the function of select G-protein subunits under normal and various disease conditions observed in the kidney.

RGS4 inhibits angiotensin II signaling and macrophage localization during renal reperfusion injury independent of vasospasm

Vascular inflammation is a major contributor to the severity of acute kidney injury. In the context of vasospasm-independent reperfusion injury we studied the potential anti-inflammatory role of the Gα-related RGS protein, RGS4. Transgenic RGS4 mice were resistant to 25 minute injury, although post-ischemic renal arteriolar diameter was equal to the wild type early after injury. A 10 minute unilateral injury was performed to study reperfusion without vasospasm. Eighteen hours after injury blood flow was decreased in the inner cortex of wild type mice with preservation of tubular architecture. Angiotensin II levels in the kidneys of wild type and transgenic mice were elevated in a sub-vasoconstrictive range 12 and 18 hours after injury. Angiotensin II stimulated pre-glomerular vascular smooth muscle cells (VSMC) to secrete the macrophage chemoattractant, RANTES; a process decreased by angiotensin II R2 (AT2) inhibition. However, RANTES increased when RGS4 expression was suppressed implicating Gα protein activation in an AT2-RGS4-dependent pathway. RGS4 function, specific to VSMC, was tested in a conditional VSMC-specific RGS4 knockout showing high macrophage density by T2 MRI compared to transgenic and non-transgenic mice after the 10 minute injury. Arteriolar diameter of this knockout was unchanged at successive time points after injury. Thus, RGS4 expression, specific to renal VSMC, inhibits angiotensin II-mediated cytokine signaling and macrophage recruitment during reperfusion, distinct from vasomotor regulation.

CD47 blockade reduces ischemia-reperfusion injury and improves outcomes in a rat kidney transplant model

BACKGROUND

Ischemia-reperfusion injury (IRI) significantly contributes to delayed graft function and inflammation, leading to graft loss. Ischemia-reperfusion injury is exacerbated by the thrombospondin-1-CD47 system through inhibition of nitric oxide signaling. We postulate that CD47 blockade and prevention of nitric oxide inhibition reduce IRI in organ transplantation.

METHODS

We used a syngeneic rat renal transplantation model of IRI with bilaterally nephrectomized recipients to evaluate the effect of a CD47 monoclonal antibody (CD47mAb) on IRI. Donor kidneys were flushed with CD47mAb OX101 or an isotype-matched control immunoglobulin and stored at 4°C in University of Wisconsin solution for 6 hr before transplantation.

RESULTS

CD47mAb perfusion of donor kidneys resulted in marked improvement in posttransplant survival, lower levels of serum creatinine, blood urea nitrogen, phosphorus and magnesium, and less histological evidence of injury. In contrast, control groups did not survive more than 5 days, had increased biochemical indicators of renal injury, and exhibited severe pathological injury with tubular atrophy and necrosis. Recipients of CD47mAb-treated kidneys showed decreased levels of plasma biomarkers of renal injury including Cystatin C, Osteopontin, Tissue Inhibitor of Metalloproteinases-1 (TIMP1), β2-Microglobulin, Vascular Endothelial Growth Factor A (VEGF-A), and clusterin compared to the control group. Furthermore, laser Doppler assessment showed higher renal blood flow in the CD47mAb-treated kidneys.

CONCLUSION

These results provide strong evidence for the use of CD47 antibody-mediated blockade to reduce IRI and improve organ preservation for renal transplantation.

Suppression of renal TRPM7 may alleviate kidney injury in the renal transplantation

PURPOSE

The aim of this study was to investigate the effect of renal cortex transient receptor potential melastatin 7 (TRPM7) suppression on renal ischemia reperfusion injury induced by transplantation in mice.

METHODS

M7shRNA was used to decrease the expression of TRPM7 in NRK-52e cells. The mice were subjected to renal intra-parenchymal injection with lentivirus containing M7shRNA to produce hypo-expression of TRPM7 in renal cortex. Cell hypoxia mode and syngeneic renal transplantation in vivo were established. Then the effects of M7shRNA were measured by fluorescent probe for reactive oxygen species (ROS), intracellular calcium and magnesium; Western blot was applied for p38-MAPKs and Bax expression in cell studies. In vivo studies, mice were killed 24 h, 48 h, 72 h, 7 days and 21 days, respectively, after transplantation and the kidneys were dissected. Serum creatinine was measured, and the H&E, Masson's trichrome staining, TUNEL, Kim-1 and α-smooth muscle actin were used to evaluate pathological change.

RESULTS

In cell model of hypoxia, the level of ROS in NRK-52e-M7shRNA was significantly lower than that in both NRK-52e and NRK-52e control cells, while the activation of p38-MAPKs was limited. In renal transplanted mice, renal function of M7shRNA group was conspicuously better than PBS- and vector-control-treated group. The histological examination showed that renal tubule injury and interstitial fibrosis were lower in M7shRNA-treated group compared with PBS and vector-control group.

CONCLUSIONS

Suppression of renal cortex TRPM7 could alleviate kidney injury induced by transplantation in mice. The mechanism may involve reducing the early stage of ischemia reperfusion injury by inhibition of intracellular Ca(2+), Mg(2+) and ROS.

Modification and functional inhibition of regulator of G-protein signaling 4 (RGS4) by 4-hydroxy-2-nonenal

Oxidative stress has been implicated as a component of various pathologies including ischemia/reperfusion injury (IRI) and neurodegenerative diseases such as Parkinson's disease (PD) and schizophrenia. Similarly, regulator of G-protein signaling 4 (RGS4) has been implicated as an important player in each of these pathologies. RGS4, like other RGS proteins, is responsible for temporally regulating G-protein coupled receptor signaling by increasing the intrinsic GTPase activity of Gα subunit of the heterotrimeric signaling complex. In this study we evaluated whether modification by 4-hydroxy-2-nonenal (4HNE), a common lipid peroxidation product, inhibits RGS4. Using immunoprecipitation, we first determined RGS4 modification was occurring in cells at concentrations of 4HNE within reported physiological conditions. Following this determination, we evaluated modification of RGS4 by 4HNE by both Western blot and mass spectrometry (MS). Once it was established that covalent modification occurred only on cysteine containing constructs, tryptic digest followed by mass spectrometry analysis revealed modification occurs at cysteine residues 71, 148, and 183. In order to determine the effect 4HNE had on RGS4 activity, a steady-state colorimetric assay was used to analyze the GAP activity of Δ51-RGS4 as well as the cysteine null mutant. From the data, we determined that RGS4 activity can be modulated by 4HNE through modification at cysteine residues similar to previously reported small molecule inhibition of RGS4.

Asymmetric dimethylarginine accumulates in the kidney during ischemia/reperfusion injury

Ischemia/reperfusion injury is the leading cause of acute tubular necrosis. Nitric oxide has a protective role against ischemia/reperfusion injury; however, the role of asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthase, in ischemia/reperfusion injury remains unclear. ADMA is produced by protein arginine methyltransferase (PRMT) and is mainly degraded by dimethylarginine dimethylaminohydrolase (DDAH). Here we examined the kinetics of ADMA and PRMT and DDAH expression in the kidneys of ischemia/reperfusion-injured mice. After the injury, DDAH-1 levels were decreased and renal and plasma ADMA values were increased in association with renal dysfunction. Renal ADMA was correlated with 8-hydroxy-2'-deoxyguanosine, a marker of oxidative stress. An antioxidant, N-acetylcysteine, or a proteasomal inhibitor, MG-132, restored these alterations. Infusion of subpressor dose of ADMA exacerbated renal dysfunction, capillary loss, and tubular necrosis in the kidneys of ischemia/reperfusion-injured wild mice, while damage was attenuated in DDAH transgenic mice. Thus, ischemia/reperfusion injury-induced oxidative stress may reduce DDAH expression and cause ADMA accumulation, which may contribute to capillary loss and tubular necrosis in the kidney.

miRNA profiling discriminates types of rejection and injury in human renal allografts

BACKGROUND

Increasing evidence accumulates on the central involvement of microRNAs (miRNAs) in disease pathophysiology. We identified distinctly deregulated miRNAs in human renal allograft biopsies from patients undergoing acute cellular rejection, antibody-mediated rejection (ABMR), and delayed graft function (DGF).

METHODS

Sixty-five posttransplantation kidney biopsy samples covering 41 cases with acute rejection (15 vascular rejection, 15 interstitial rejection, and 11 ABMR), 14 DGF cases, and 10 protocol biopsies serving as controls were analyzed using the Affymetrix GeneChip miRNA Array. Differentially regulated miRNAs were identified by Student's t test and Bonferroni correction. Target genes for the set of miRNAs were retrieved from miRTarBase (experimentally verified targets) as well as by applying the target prediction routines DIANAmT, miRanda, and Targetscan.

RESULTS

Patients with acute cellular rejection, ABMR, and DGF discriminate from the control group (protocol biopsies) in unsupervised clustering of miRNA profiles, clearly identifying deregulated miRNAs in rejection and DGF. Angiogenesis, apoptosis, and transforming growth factor-β signaling were identified as relevant pathways in ischemic response following an integrative analysis of miRNA targets and mRNA expression profiles. Inflammation by chemokine and cytokine signaling, T-cell activation, and B-cell activation were identified as relevant in acute rejection accordingly.

CONCLUSION

These data suggest that distinct miRNA signatures playing a role in specific biological pathways discriminate acute cellular and humoral rejection and DGF. This finding serves as valuable tool for a rational selection of diagnostic, prognostic, and potentially therapeutic molecular targets of posttransplantation events.

Netrin-1 pretreatment protects rat kidney against ischemia/reperfusion injury via suppression of oxidative stress and neuropeptide Y expression

Netrin-1 has been found to protect kidneys from ischemia/reperfusion injury. In this study, we aimed to address whether the protective effects were mediated through suppression of oxidative stress and neuropeptide Y. Compared to sham-operated animals, animals after ischemia/reperfusion showed marked kidney damage and significantly increased levels of serum creatinine, blood urea nitrogen, malondialdehyde, and neuropeptide Y. Renal myeloperoxidase activity was elevated in animals with ischemia/reperfusion relative to sham-operated animals, whereas renal superoxide dismutase activity was reduced. Netrin-1 pretreatment attenuated ischemia/reperfusion-induced functional and pathological changes in the kidney. Moreover, the ischemia/reperfusion-induced changes in the oxidative stress biomarkers and neuropeptide Y were significantly counteracted by prior administration of netrin-1. Taken together, our data showed that netrin-1 pretreatment prevented renal ischemia/reperfusion injury, at least partially through reduction of oxidative stress and neuropeptide Y expression.

The nephroprotective properties of recombinant human erythropoietin in kidney transplantation: experimental facts and clinical proofs

Adaptive responses to hypoxia, including hypoxia-inducible factor signaling, allow the cell to satisfy its basal metabolic demand and avoid death, but these responses can also be deleterious by promoting inflammation, cell dedifferentiation and fibrogenesis. Therefore, targeting hypoxia constitutes a promising therapeutic avenue. Recombinant human erythropoietin (rhEPO) appeared as a good candidate therapy because its hematopoietic properties could reverse anemia, and its tissue-protective properties could reduce cell death and limit maladaptive cellular responses to hypoxia. Despite experimental evidence on the nephroprotecive properties of rhEPO, recent clinical trials provided evidence that rhEPO was ineffective in preventing delayed graft function after ischemic acute injury but that the normalization of hemoglobin values preserved kidney function deterioration and reduced graft loss. Our aim here is to provide a survey of the rationale for evaluating the administration of rhEPO in the setting of kidney transplantation. We will discuss the intriguing findings that emerged from the clinical trials and the discrepancies between promising experimental results and negative clinical studies, as well as the differences in terms of the benefits and safety profiles of the normalization of hemoglobin values in chronic kidney disease patients and kidney transplant patients.

Mouse model of ischemic acute kidney injury: technical notes and tricks

Renal ischemia-reperfusion leads to acute kidney injury (AKI), a major kidney disease associated with an increasing prevalence and high mortality rates. A variety of experimental models, both in vitro and in vivo, have been used to study the pathogenic mechanisms of ischemic AKI and to test renoprotective strategies. Among them, the mouse model of renal clamping is popular, mainly due to the availability of transgenic models and the relatively small animal size for drug testing. However, the mouse model is generally less stable, resulting in notable variations in results. Here, we describe a detailed protocol of the mouse model of bilateral renal ischemia-reperfusion. We share the lessons and experiences gained from our laboratory in the past decade. We further discuss the technical issues that account for the variability of this model and offer relevant solutions, which may help other investigators to establish a well-controlled, reliable animal model of ischemic AKI.

Delayed graft function in the kidney transplant

Acute kidney injury occurs with kidney transplantation and too frequently progresses to the clinical diagnosis of delayed graft function (DGF). Poor kidney function in the first week of graft life is detrimental to the longevity of the allograft. Challenges to understand the root cause of DGF include several pathologic contributors derived from the donor (ischemic injury, inflammatory signaling) and recipient (reperfusion injury, the innate immune response and the adaptive immune response). Progressive demand for renal allografts has generated new organ categories that continue to carry high risk for DGF for deceased donor organ transplantation. New therapies seek to subdue the inflammatory response in organs with high likelihood to benefit from intervention. Future success in suppressing the development of DGF will require a concerted effort to anticipate and treat tissue injury throughout the arc of the transplantation process.