Growth factors and apoptosis in acute renal injury

Steamed Panax notoginseng attenuates renal anemia in an adenine-induced mouse model of chronic kidney disease

ETHNOPHARMACOLOGICAL RELEVANCE

Panax notoginseng (PN) (Burk.) F. H. Chen is a medicinal herb used to treat blood disorders since ancient times, of which the steamed form exhibits the anti-anemia effect and acts with a "blood-tonifying" function according to the traditional use. However, its pharmacological effect and mechanism on alleviating renal anemia (RA) are still unclear.

AIMS OF THE STUDY

The study aims to investigate the effect of steamed Panax notoginseng (SPN) to attenuate RA and its underlying mechanism based on the model of adenine-induced RA mice.

MATERIALS AND METHODS

Seventy mice were randomly divided into seven groups of ten: the control group, model group, the erythropoietin (EPO) group, the Fufang E'jiao Jiang (FEJ) group, the high-dose steamed PN (H-SPN) group, the middle-dose steamed PN (M-SPN) group, and the low-dose steamed PN (L-SPN) group. The adenine induction RA model was applied to assess the "blood enriching" function of SPN. The blood routine indexes, erythrocyte fragility, pathologic morphology of kidney tissue and the expression levels of related cytokines and proteins in the mice were detected after 3-week administration with SPN and positive drugs.

RESULTS

Our study provided evidences that SPN could ameliorate RA. Compared with the control group, SPN could attenuate RA by significantly increasing the numbers of peripheral blood cells (p < 0.01), improving the erythrocyte fragility (p < 0.01), and restoring the expression of EPO mRNA in the kidneys and EPO receptor mRNA in bone marrow nucleated cells. The expression of TGF-β₁ mRNA was declined and the expression of HGF mRNA was significantly increased in a dose-dependent way after the treatment of SPN. Additionally, the expression of Bcl-2 and Bcl-2/Bax ratio in the kidneys were significantly increased. In contrast, there was a highly significant decrease in the expression of Bax (p < 0.01), following SPN treatment.

CONCLUSION

SPN could alleviate RA by promoting the overall hematopoiesis and inhibiting the progress of renal injury in mice.

The epidermal growth factor receptor pathway in chronic kidney diseases

The epidermal growth factor receptor (EGFR) pathway has a critical role in renal development, tissue repair and electrolyte handling. Numerous studies have reported an association between dysregulation of this pathway and the initiation and progression of various chronic kidney diseases such as diabetic nephropathy, chronic allograft nephropathy and polycystic kidney disease through the promotion of renal cell proliferation, fibrosis and inflammation. In the oncological setting, compounds that target the EGFR pathway are already in clinical use or have been evaluated in clinical trials; in the renal setting, therapeutic interventions targeting this pathway by decreasing ligand availability with disintegrin and metalloproteinase inhibitors or with ligand-neutralizing antibodies, or by inhibiting receptor activation with tyrosine kinase inhibitors or monoclonal antibodies are only just starting to be explored in animal models of chronic kidney disease and in patients with autosomal dominant polycystic kidney disease. In this Review we focus on the role of the EGFR signalling pathway in the kidney under physiological conditions and during the pathophysiology of chronic kidney diseases and explore the clinical potential of interventions in this pathway to treat chronic renal diseases.

A role for the age-dependent loss of α(E)-catenin in regulation of N-cadherin expression and cell migration

The aging kidney has a decreased ability to repair following acute kidney injury. Previous studies from our laboratory have demonstrated a loss in α‐catenin expression in the aging rat kidney. We hypothesize that loss of α‐catenin expression in tubular epithelial cells may induce changes that result in a decreased repair capacity. In these studies, we demonstrate that decreased α‐catenin protein expression is detectable as early as 20 months of age in male Fischer 344 rats. Protein loss is also observed in aged nonhuman primate kidneys, suggesting that this is not a species‐specific response. In an effort to elucidate alterations due to the loss of α‐catenin, we generated NRK‐52E cell lines with stable knockdown of α(E)‐catenin (C2 cells). Interestingly, C2 cells had decreased expression of N‐cadherin, decreased cell–cell adhesion, and increased monolayer permeability. C2 had deficits in wound repair, due to alterations in cell migration. Analysis of gene expression in the migrating control cells indicated that expression of N‐cadherin and N‐CAM was increased during repair. In migrating C2 cells, expression of N‐CAM was also increased, but the expression of N‐cadherin was not upregulated. Importantly, a blocking antibody against N‐cadherin inhibited repair in NRK‐52E cells, suggesting an important role in repair. Taken together, these data suggest that loss of α‐catenin, and the subsequent downregulation of N‐cadherin expression, is a mechanism underlying the decreased migration of tubular epithelial cells that contributes to the inability of the aging kidney to repair following injury.

Aging is associated with loss of α‐catenin and N‐cadherin expression in the kidney. In these studies, we demonstrate that α‐catenin regulates, in part, N‐cadherin expression and migration in tubular epithelial cells.

Genetic mechanisms and signaling pathways in autosomal dominant polycystic kidney disease

Recent advances in defining the genetic mechanisms of disease causation and modification in autosomal dominant polycystic kidney disease (ADPKD) have helped to explain some extreme disease manifestations and other phenotypic variability. Studies of the ADPKD proteins, polycystin-1 and -2, and the development and characterization of animal models that better mimic the human disease, have also helped us to understand pathogenesis and facilitated treatment evaluation. In addition, an improved understanding of aberrant downstream pathways in ADPKD, such as proliferation/secretion-related signaling, energy metabolism, and activated macrophages, in which cAMP and calcium changes may play a role, is leading to the identification of therapeutic targets. Finally, results from recent and ongoing preclinical and clinical trials are greatly improving the prospects for available, effective ADPKD treatments.

Parathyroid hormone-related protein protects renal tubuloepithelial cells from apoptosis by activating transcription factor Runx2

Runx2 is a key transcription factor in bone development regulating several processes, including osteoblast apoptosis. The antiapoptotic effects of parathyroid hormone (PTH) in osteoblasts depend on Runx2-mediated transcription of prosurvival genes. In the kidney, PTH-related protein (PTHrP) promotes tubulointerstitial cell survival by activating the PTH/PTHrP type 1 receptor. We found that Runx2 is expressed in renal tubuloepithelial MCT and HK2 cell lines in vitro and in the mouse kidney tubuloepithelium in vivo. The 1-36 amino-acid fragment of PTHrP was found to increase the expression and nuclear translocation of Runx2 in both cell lines in a dose- and time-dependent manner. PTHrP(1-36) protected renal tubuloepithelial cells from folic acid toxicity and serum deprivation, an effect inhibited by a dominant-negative Runx2 construct or a Runx2 siRNA. Furthermore, PTHrP(1-36) upregulated the antiapoptotic proteins Bcl-2 and osteopontin, and these effects were abolished by Runx2 siRNA. Runx2, osteopontin, and Bcl-2 were increased in tubuloepithelial cells from transgenic mice with PTHrP overexpression and in wild-type mice with acute or chronic renal failure. Thus, PTHrP regulates renal tubuloepithelial cell survival via Runx2 in the mammalian kidney.

Expression of Bcl-2 and Bax in mouse renal tubules during kidney development

Bcl-2 and Bax play an important role in apoptosis regulation, as well as in cell adhesion and migration during kidney morphogenesis, which is structurally and functionally related to mitochondria. In order to elucidate the role of Bcl-2 and Bax during kidney development, it is essential to establish the exact location of their expression in the kidney. The present study localized their expression during kidney development. Kidneys from embryonic (E) 16-, 17-, 18-day-old mouse fetuses, and postnatal (P) 1-, 3-, 5-, 7-, 14-, 21-day-old pups were embedded in Epon. Semi-thin serial sections from two E17 kidneys underwent computer assisted 3D tubule tracing. The tracing was combined with a newly developed immunohistochemical technique, which enables immunohistochemistry on glutaraldehyde fixated plastic embedded sections. Thereby, the microstructure could be described in detail, and the immunochemistry can be performed using exactly the same sections. The study showed that Bcl-2 and Bax were strongly expressed in mature proximal convoluted tubules at all time points, less strongly expressed in proximal straight tubules, and only weakly in immature proximal tubules and distal tubules. No expression was detected in ureteric bud and other earlier developing structures, such as comma bodies, S shaped bodies, glomeruli, etc. Tubules expressing Bcl-2 only were occasionally observed. The present study showed that, during kidney development, Bcl-2 and Bax are expressed differently in the proximal and distal tubules, although these two tubule segments are almost equally equipped with mitochondria. The functional significance of the different expression of Bcl-2 and Bax in proximal and distal tubules is unknown. However, the findings of the present study suggest that the mitochondrial function differs between mature proximal tubules and in the rest of the tubules. The function of Bcl-2 and Bax during tubulogenesis still needs to be investigated.

Ischemic kidney injury and mechanisms of tissue repair

Acute kidney injury (AKI) may result from ischemia or by the use of nephrotoxic agents. The incidence of AKI is variable, depends on comorbidities, and ranges from 5 to 35% in all hospitalized patients. The mechanisms of kidney injury exist within a large network of signaling pathways driven by interplay of inflammatory cytokines/chemokines, reactive oxygen species (ROS), and apoptotic factors. The effects and progression of injury overlap extensively with the remarkable ability of the kidney to repair itself both by intrinsic and extrinsic mechanisms that involve specific cell receptors/ligands as well as possible paracrine influences. The fact that kidney injury is usually part of a generalized comorbid condition makes it all the more challenging in terms of assessment of severity. In this review, we attempt to analyze the mechanisms of ischemic injury and repair in acute and chronic kidney disease from the perspectives of both preclinical and human studies.

VEGF-121 preserves renal microvessel structure and ameliorates secondary renal disease following acute kidney injury

Acute kidney injury induced by renal ischemia-reperfusion (I/R) compromises microvascular density and predisposes to chronic kidney disease (CKD) and sodium-dependent hypertension. VEGF-121 was administered to rats fed a standard (0.4%) sodium diet at various times following recovery from I/R injury for up to 35 days. VEGF-121 had no effect on the initial loss of renal function, as indicated by serum creatinine levels measured 24 h after injury. Serum creatinine levels declined thereafter, indicative of renal repair. Rats were then switched to an elevated (4.0%) sodium diet for an additional 28 days to induce CKD. The 4.0% sodium diet enhanced renal hypertrophy, interstitial volume, albuminuria, and cardiac hypertrophy relative to postischemic animals maintained on the 0.4% sodium diet. Administration of VEGF-121 from day 0 to 14, day 0 to 35, or day 3 to 35 after I/R suppressed the effects of sodium diet on CKD development, while delayed administration of VEGF-121 from day 21 to 35 had no effect. Endothelial nitric oxide synthase protein levels were upregulated in postischemic animals, and this effect was significantly increased by the 4.0% sodium diet but was not influenced by prior treatment with VEGF. Conversely, microvascular density was preserved in postischemic animals treated with VEGF-121 relative to vehicle-treated postischemic animals. These data suggest that early, but not delayed, treatment with VEGF-121 can preserve vascular structure after ischemia and influence chronic renal function in response to elevated sodium intake.

Opposing roles of EGF in IFN-α-induced epithelial barrier destabilization and tissue repair

Balance between damaging influences and repair mechanisms determines the degree of tissue deterioration by inflammatory and other injury processes. Destabilization of the proximal tubular barrier has been previously shown to be induced by IFN-α, a cytokine crucial for linking innate and adaptive immune responses. EGF was implicated in rescue mechanisms from renal injury. To study the interplay between the two processes, we determined if EGF can prevent IFN-α-induced barrier permeabilization. EGF did not counteract but even exacerbated the IFN-α-induced decrease of transepithelial electrical resistance in LLC-PK1 monolayers. For this effect Erk1/2 activation was necessary, linking barrier regulation to EGF-induced cell cycle progression. In contrast to its damage-intensifying effect, EGF also facilitated the regeneration of epithelial barrier function after the termination of IFN-α treatment. This effect was not mediated by Erk1/2 activation or cell proliferation since U0126, an Erk1/2 inhibitor, did not prevent but ameliorated recovery. However, EGF accelerated the downregulation of caspase-3 in recovering cells. Similarly, a pan-caspase inhibitor was able to block caspase activity and, concomitantly, promote restoration of barrier function. Thus, barrier repair might be linked to an EGF-mediated antiapoptotic mechanism. EGF appears to sensitize epithelial cells to the detrimental effects of IFN-α but also helps to restore barrier function in the healing phase. The observed dual effect of EGF might be explained by the different impact of proproliferative and antiapoptotic signaling pathways during and after cytokine treatment. The timing of epithelial exposure to damaging agents and repair factors was identified as a crucial parameter determining tissue fate.

Juxtacrine activation of epidermal growth factor (EGF) receptor by membrane-anchored heparin-binding EGF-like growth factor protects epithelial cells from anoikis while maintaining an epithelial phenotype

Loss of cell-matrix adhesion is often associated with acute epithelial injury, suggesting that "anoikis" may be an important contributor to cell death. Resistance against anoikis is a key characteristic of transformed cells. When nontransformed epithelia are injured, activation of the epidermal growth factor (EGF) receptor (EGFR) by paracrine/autocrine release of soluble ligands can induce a prosurvival program, but there is generally evidence for concomitant dedifferentiation. The EGFR ligand, heparin-binding EGF-like growth factor (HB-EGF), is synthesized as a membrane-anchored precursor that can activate the EGFR via juxtacrine signaling or can be released and act as a soluble growth factor. In Madin-Darby canine kidney cells, expression of membrane-anchored HB-EGF increases cell-cell and cell-matrix adhesion. Therefore, these studies were designed to test the effects of juxtacrine HB-EGF signaling upon cell survival and epithelial integrity when cells are denied proper cell-matrix interactions. Cells expressing a noncleavable mutated form of membrane-anchored HB-EGF demonstrated increased survival from anoikis, formed larger cell aggregates, and maintained epithelial characteristics even following prolonged detachment from the substratum. Physical association between membrane-anchored HB-EGF and EGFR was observed. Signaling studies indicated synergistic effects of EGFR activation and phosphatidylinositol 3-kinase signaling to regulate apoptotic and survival pathways. In contrast, although administration of exogenous EGF partially suppressed anoikis in wild type cells, it also led to an increased expression of mesenchymal markers, suggesting dedifferentiation. Taken together, we propose a novel role for membrane-anchored HB-EGF in the cytoprotection of epithelial cells.

Regulation of proliferation and apoptosis during development of the preimplantation embryo and the placenta

The preimplantation embryo starts as a single cell, the zygote. The first cell divisions do not lead to volume expansion, but rather to an increasing number of small cells. At the morula stage the first two cell lineages differentiate into the trophoblast and the inner cells mass/embryoblast. During development of the preimplantation embryo, apoptosis occurs only after the onset of the embryonic genome. It has become clear that the development of a healthy child requires not only very high rates of proliferation and differentiation, but also apoptosis, which is a crucial mechanism for morphogenesis and the development of the inner organs. Furthermore, the generation of specific cell types, such as lens cells, erythrocytes, and thrombocytes, depends on the apoptosis pathways. This is also true later in gestation, when the trophoblasts form the placenta and provide the epithelial cover of the villous trees of the placenta. This layer is in direct contact with maternal blood and, as do all epithelia, displays a continuous turnover of cells. Thus, apoptosis is a normal constituent of survival in this layer as well, and changes in the regulation and rate of apoptosis have deleterious effects on the trophoblast and consequently the developing embryo or fetus. Here we present a very brief overview of the importance of apoptosis for the development of the preimplantation embryo and the maintenance of placental trophoblasts. Furthermore, we highlight what happens when regulation of proliferation or apoptosis fails in these systems, and attempt to show that apoptosis is only the consequence of poor embryo or trophoblast development -- not its cause.

Expression of apoptosis-related proteins bcl-2 and bax along with transforming growth factor (TGF-beta1) in the kidney of patients with glomerulonephritides

BACKGROUND

Apoptosis, a gene-directed form of cell death, has been involved in the resolution of renal injury but also in the development of scarring. Bcl-2 and bax are proteins related to apoptotic process that either provides a survival advantage to rapidly proliferating cells (bcl-2) or promote cell death by apoptosis (bax). Various cytokines and growth factors are involved in this process. This study investigates the expression of bcl-2 and bax and the presence of apoptotic bodies in relation to the TGF-beta1 expression at the time of diagnosis in the renal biopsies of patients with glomerulonephritis (GN).

METHODS

Fifty patients with various types of GN and ten controls were included in the study. Bcl-2, bax and Transforming Growth Factor (TGF-beta1) positive cells were detected in kidney biopsies by immunohistochemistry, while apoptotic cells were detected by in situ end labeling of fragmented DNA (ISEL). Morphometric analysis was used for quantitation of immunostaining.

RESULTS

The intensity of bcl-2, bax and TGF-beta1 immunostaining in the renal tissue of patients with GN was significantly more to the observed in the control biopsies. Bcl-2 and bax were expressed within the epithelial cells of proximal, distal and collecting tubules and in the renal interstitium. Bax and bcl-2 proteins were also identified within the glomeruli in a few patients but their distribution was not related to the type of GN. TGF-beta1 was expressed in the cytoplasm of tubular epithelial cells and to a lesser extent in the renal interstitium and glomeruli. A positive correlation of TGF-beta1 with the extent of bax immunostaining (r=0.498, p<0.05) and an inverse correlation with that of bcl-2 (r= -0.490, p<0.05) were identified. Apoptotic bodies were identified only in the renal tissue of patients with GN and were mainly localized among tubular epithelial and interstitial cells.

CONCLUSION

The intensity of bcl-2 and bax proteins expression and the presence of apoptotic bodies in the renal tissue of patients with GN suggest that apoptotic process is ongoing during the evolution of renal disease. The correlation of TGF-beta1 expression with that of apoptosis-related proteins might represent an implication of this growth factor with apoptotic process in the human diseased kidney.

Molecular mechanisms of acute renal failure following ischemia/reperfusion

Acute renal failure (ARF) necessitating renal replacement therapy is a common problem associated with high morbidity and mortality in the critically ill. Hypotension, followed by resuscitation, is the most common etiologic factor, mimicked by ischemia/reperfusion (I/R) in animal models. Although knowledge of the pathophysiology of ARF in the course of this condition is increasingly detailed, the intracellular and molecular mechanisms leading to ARF are still incompletely understood. This review aims at describing the role of cellular events and signals, including collapse of the cytoskeleton, mitochondrial and nuclear changes, in mediating cell dysfunction, programmed cell death (apoptosis), necrosis and others. Insight into the molecular pathways in the various elements of the kidney, such as vascular endothelium and smooth muscle and tubular epithelium leading to cell damage upon I/R will, hopefully, open new therapeutic modalities, to mitigate the development of ARF after hypotensive episodes and to promote repair and resumption of renal function once ARF has developed.

Effect of colchicine on cyclosporine nephrotoxicity, reduction of TGF-beta overexpression, apoptosis, and oxidative damage: an experimental animal study

BACKGROUND

Proinflamatory and profibrotic cytokines may be responsible for the cyclosporine A nephrotoxicity. Increased levels of apoptosis, free oxygen redicals, and transforming growth factor beta (TGF-beta), may play an important roles in the pathogenesis of nephrotoxicity. In this experimental animal study, we sought to investigate the effects of colchicine on the cyclosporine nephrotoxicity.

METHOD

Twenty-four Wistar albino rats were divided into three groups: cyclosporine 15 mg/kg subcutaneously (SC); cyclosporine 15 mg/kg SC plus colchicine 30 mcg/kg orally; and a control group; equal doses of olive oil orally were administered to groups 1, 2, and 3. Renal function, cyclosporine levels, and serum malonyldialdehyde (MDA) levels were measured at the end of 4 weeks. Apoptosis, TGF-beta, and other findings were detected in renal tissue with the TUNEL method, with a immunohistochemical method, and with routine staining procedures, respectively.

RESULTS

There were significant differences in the values of mean creatinine clearance between group 1 and group 3 and between group 2 and group 3 (P < .05 for each comparison), but not between group 1 and group 2 (P > .05). MDA levels in group 1 were high compared with the control group (P < .05) with a trend toward elevation relative to group 2 but the results were not statistically significant (P > .05). Renal tubular vacuolization in group 1 and group 2 animal were greater than in the control group, but no significant difference were observed between any of the groups (P > .05). Mononuclear cell infiltration in group 1 and group 2 hosts were higher than the control group, but there was no significant differences between the groups (P > .05). Afferent arteriolar hyalinization was observed group 1 and 2 but not group 3. There was a statistically significant difference between group 1 and group 3 and between group 2 and group 3 (P < .05 for each comparison). The expression level of TGF-beta was higher in group 1 than group 2 or group 3 (P <.05 for each comparison) but group 2 and group 3 were similar (P > .05). Apoptotic cell death count of group 1 was higher than that in group 2 or group 3 (P < .05, for each comparison); moreover, group 2 also showed greater numbers of apoptotic cells than group 3 (P < .001). At the end of the 4 weeks, there was no intersititial fibrosis in any of the hosts.

CONCLUSION

While cyclosporine caused increased TGF-beta expression and apoptotic cell death in the renal tissue of rats colchicine prevented the increase in MDA serum levels, TGF-beta expression, and apoptosis in renal tissue. Our study suggests that colchicine may diminish the cyclosporine nephrotoxicity by its suppressing the expression of TGF-beta, apoptotic cell death, and MDA production.

Adult renal stem cells and renal repair

PURPOSE OF REVIEW

Recent studies that might help in the search for stem cells in adult kidney and clarify the origin of proliferating cells during kidney repair are reviewed.

RECENT FINDINGS

Some of the most notable recent findings are as follows: (1) the 'stemness' profile may be determined by approximately 250 genes; (2) organ-specific stem-cell growth and differentiation are stimulated during the reparative phase following transient injury; (3) two bone marrow stem-cell types show a remarkable degree of differentiation potential; (4) some organs contain resident marrow-derived stem cells, and their differentiation potential may only be expressed during repair; (5) the metanephric mesenchyme contains pluripotent and self-renewing stem cells; (6) marrow-derived cells invade the kidney and differentiate into mesangial and tubular epithelial cells, and these processes are increased following renal injury; and (7) epithelial-to-mesenchymal transition generates renal fibroblasts.

SUMMARY

While it remains unknown whether there is a stem cell in the adult kidney, characterization of the cell populations involved in renal repair and misrepair is allowing a new understanding of the mechanisms that are responsible for renal homeostasis. The most surprising results suggest a very prominent role for cells exogenous to the kidney. Two recently published transcription profiles of 'stemness' and the phenotype of pluripotent metanephric mesenchymal cells may help in the search for adult renal stem cells.

Regulation of the voltage gated K+ channel Kv1.3 by the ubiquitin ligase Nedd4-2 and the serum and glucocorticoid inducible kinase SGK1

The stimulation of cell proliferation by insulin like growth factor IGF-1 has previously been shown to depend on activation of voltage gated K(+) channels. The signaling involved in activation of voltage gated K(+) channel Kv1.3 includes the phosphatidylinositol-3 (PI3) protein kinase, 3-phosphoinositide dependent protein kinase PDK1 and the serum and glucocorticoid inducible kinase SGK1. However, nothing is known about mechanisms mediating the stimulation of Kv1.3 by SGK1. Most recently, SGK1 has been shown to phosphorylate and thus inactivate the ubiquitin ligase Nedd4-2. The present study has been performed to explore whether the regulation of Kv1.3 involves Nedd4-2. To this end Kv1.3 has been expressed in Xenopus oocytes with or without coexpression of Nedd4-2 and/or constitutively active (S422D)SGK1. In oocytes expressing Kv1.3 but not in water injected oocytes, depolarization from a holding potential of -80 mV to +20 mV triggers rapidly inactivating currents typical for Kv1.3. Coexpression of Nedd4-2 decreases, coexpression of (S422D)SGK1 enhances the currents significantly. The effects of either Nedd4-2 or of SGK1 are abrogated by destruction of the respective catalytic subunits ((C938S)Nedd4-2 or (K127N)SGK1). Further experiments revealed that wild type SGK1 and SGK3 and to a lesser extent SGK2 are similarly effective in stimulating Kv1.3 in both, presence and absence of Nedd4-2. It is concluded that Kv1.3 is downregulated by Nedd4-2 and stimulates by SGK1, SGK2, and SGK3. The data thus disclose a novel mechanism of Kv1.3 channel regulation.

Identification of putative gene based markers of renal toxicity

This study, designed and conducted as part of the International Life Sciences Institute working group on the Application of Genomics and Proteomics, examined the changes in the expression profile of genes associated with the administration of three different nephrotoxicants--cisplatin, gentamicin, and puromycin--to assess the usefulness of microarrays in the understanding of mechanism(s) of nephrotoxicity. Male Sprague-Dawley rats were treated with daily doses of puromycin (5-20 mg/kg/day for 21 days), gentamicin (2-240 mg/kg/day for 7 days), or a single dose of cisplatin (0.1-5 mg/kg). Groups of rats were sacrificed at various times after administration of these compounds for standard clinical chemistry, urine analysis, and histological evaluation of the kidney. RNA was extracted from the kidney for microarray analysis. Principal component analysis and gene expression-based clustering of compound effects confirmed sample separation based on dose, time, and degree of renal toxicity. In addition, analysis of the profile components revealed some novel changes in the expression of genes that appeared to be associated with injury in specific portions of the nephron and reflected the mechanism of action of these various nephrotoxicants. For example, although puromycin is thought to specifically promote injury of the podocytes in the glomerulus, the changes in gene expression after chronic exposure of this compound suggested a pattern similar to the known proximal tubular nephrotoxicants cisplatin and gentamicin; this prediction was confirmed histologically. We conclude that renal gene expression profiling coupled with analysis of classical end points affords promising opportunities to reveal potential new mechanistic markers of renal toxicity.

Dermatan sulfate exerts an enhanced growth factor response on skeletal muscle satellite cell proliferation and migration

Skeletal muscle regeneration is a complex process in which many agents are involved. When skeletal muscle suffers an injury, quiescent resident myoblasts called satellite cells are activated to proliferate, migrate, and finally differentiate. This whole process occurs in the presence of growth factors, the extracellular matrix (ECM), and infiltrating macrophages. We have shown previously that different proteoglycans, either present at the plasma membrane or the ECM, are involved in the differentiation process by regulating growth factor activity. In this article, we evaluated the role of glycosaminoglycans (GAGs) in myoblast proliferation and migration, using C2C12, a satellite cell-derived cell line. A synergic stimulatory effect on myoblast proliferation was observed with hepatocyte growth factor (HGF) and fibroblast growth factor type 2 (FGF-2), which was dependent on cell sulfation. The GAG dermatan sulfate (DS) enhanced HGF/FGF-2-dependent proliferation at 1-10 ng/ml. However, decorin, a proteoglycan containing DS, was unable to reproduce this enhanced proliferative effect. On the other hand, HGF strongly increased myoblast migration. The HGF-dependent migratory process required the presence of sulfated proteoglycans/GAGs present on the myoblast surface, as inhibition of both cell sulfation, and heparitinase (Hase) and chondroitinase ABC (Ch(abc)) treatment of myoblasts, resulted in a very strong inhibition of cell migration. Among the GAGs analyzed, DS most increased HGF-dependent myoblast migration. Taken together, these findings showed that DS is an enhancer of growth factor-dependent proliferation and migration, two critical processes involved in skeletal muscle formation.

Prevention and nondialytic treatment of acute renal failure

Based on the progress made during the last few years in understanding the pathophysiology of acute renal failure, a plethora of therapeutic drug and nondrug interventions have been developed and tested in animal and human forms of this disease. The first part of this article focuses on the role of volume expansion and vasopressors in the prevention and treatment of acute renal failure in the critically ill. From all prophylactic measures that have been proposed, volume expansion, or at least correction of volume depletion, remains the most efficient and most evidence-based intervention in these patients. Norepinephrine is, out of all the vasopressors, probably the most appropriate to use in cases of hypotension, provided circulating volume is adequate. In hypotensive septic patients, vasopressin has been shown to be useful. Direct renal vasodilating substances, the most popular still being low-dose dopamine, have never been proved to be useful in carefully performed prospective trials. Moreover dopamine especially is associated with a number of side effects and complications. From the agents acting on tubular factors, the diuretic mannitol and loop diuretics are the most prescribed. Only in specific situations such as rhabdomyolysis and kidney transplant surgery has it been shown that mannitol was able to prevent acute renal failure. The loop diuretics are able, after establishing adequate circulating volume, to promote diuresis in some forms of oliguric acute renal failure; however, some recent papers have shown that the administration of loop diuretics may actually be associated with increased mortality and delayed recovery of renal function. The last few years have seen a number of trials with acetylcysteine in the prevention of mainly radiocontrast nephropathy. Although the results are still conflicting, the majority indicates that acetylcysteine, when applied together with adequate volume expansion, may be a useful drug to incorporate in the standard treatment procedures in patients at risk for acute renal failure. Interventions to stimulate the recovery process of the damaged kidney with growth factors, although theoretically sound, have thus far not led to successful results.

Peritubular capillary loss after mouse acute nephrotoxicity correlates with down-regulation of vascular endothelial growth factor-A and hypoxia-inducible factor-1 alpha

Although the response of kidneys acutely damaged by ischemia or toxins is dominated by epithelial destruction and regeneration, other studies have begun to define abnormalities in the cell biology of the renal microcirculation, especially with regard to peritubular capillaries. We explored the integrity of peritubular capillaries in relation to expression of vascular endothelial growth factor (VEGF)-A, hypoxia-inducible factor (HIF)-alpha proteins, and von Hippel-Lindau protein (pVHL) in mouse folic acid nephropathy, a model in which acute tubular damage is followed by partial regeneration and progression to patchy chronic histological damage. Throughout a period of 14 days, in areas of cortical tubular atrophy and interstitial fibrosis, loss of VEGFR-2 and platelet endothelial cell adhesion molecule-expressing peritubular capillaries was preceded by marked decreases in VEGF-A transcript and protein levels. Nephrotoxicity was associated with tissue hypoxia, especially in regenerating tubules, as assessed by an established in situ method. Despite the hypoxia, levels of HIF-1 alpha, a protein known to up-regulate VEGF-A, were reduced. During the course of nephrotoxicity, levels of pVHL, a factor that destabilizes HIF-1 alpha, increased significantly. We speculate that that down-regulation of VEGF-A may be functionally-implicated in the progressive attrition of peritubular capillaries in areas of tubular atrophy and interstitial fibrosis; VEGF-A down-regulation correlates with a loss of HIF-1 alpha expression which itself occurs in the face of increased tissue hypoxia.

Pathogenesis of renal ischemia/reperfusion injury: lessons from knockout mice

Ischemia/reperfusion-induced acute renal failure is a common clinical problem associated with a high morbidity and mortality. Upon hypoxic injury, the depletion of ATP causes mitochondrial dysfunction, and accumulation of intracellular sodium, calcium and reactive oxygen species. Subsequently, multiple enzyme systems including proteases, nitric oxide synthases, phospholipases and endonuclease are activated and responsible for cytoskeleton disruption, membrane damage, and DNA degradation, and eventually cell death. Ischemia/reperfusion injury also activates complement, cytokines, and chemokines, which are cytotoxic themselves, but also attract leukocytes into the ischemic area to cause further damage. The vascular endothelial cell injury and dysfunction prolong ischemia and induce vascular congestion, edema, and further infiltration of inflammatory cells. Many players in renal ischemia/reperfusion injury and their mechanisms have been investigated using genetically manipulated mouse models. In this review, we focus on the information gathered from these studies. Deficiency of the Na/Ca exchanger, inducible nitric oxide synthase, Caspase-1, A3 adenosine receptor, C3, C5, C6, Factor B, or midkine protects the kidney against I/R injury. Conversely, deficiency of the interleukin-1 receptor, osteopontin, C4, or recombination activation gene-1 is not protective, while the absence of adrenomedullin or endothelin receptor B delays the recovery of ischemia/reperfusion injury. The knowledge obtained from these studies provides new direction for designing potential therapeutic agents for treating ischemia/reperfusion injury.

Role of Insulin-Like Growth Factor-1 Signaling in Dental Fibroblast Apoptosis

BACKGROUND

Studies have shown that periodontal ligament fibroblasts (PDLF) and gingival fibroblasts (GF) respond differently to growth factors in the repair and regeneration of periodontal tissues. The goal of this study was to determine the effects of insulin-like growth factor-1 (IGF-1) signaling on cell apoptosis in PDLF compared to GF.

METHODS

The levels of apoptosis were compared between cultured PDLF and GF by DNA fragmentation assay and trypan blue exclusion assay, either in the presence or absence of IGF-1. The transcript level of upstream signaling molecules, such as IGF binding protein-5 (IGFBP-5), IGF-1 receptor (IGF-1R), and phosphoinositide 3-kinase (PI3K), was studied using reverse transcription-polymerase chain reaction (RT-PCR). Furthermore, the role of IGFBP-5 in IGF-1 signaling was verified by annexin-V staining using flow cytometric analysis.

RESULTS

IGF-1 significantly inhibited the level of DNA fragmentation and decreased trypan blue-positive cells in PDLF compared to GF during serum deprivation. The mRNA expression of IGFBP-5, IGF-1R, and PI3K was constitutively upregulated in PDLF compared to GF. In the presence of exogenous IGFBP-5, the annexin-V-positive cells were significantly decreased in GF after IGF-1 stimulation.

CONCLUSIONS

The present study provides evidence that IGF-1 reduces apoptosis in cultured PDLF compared to GF. Upregulation of IGF-1R and PI3K in PDLF further suggests the activation of IGF signaling in PDLF. In addition, the anti-apoptotic effect of IGF-1 may be facilitated by the upregulation of IGFBP-5 in PDLF.

Activation of Src kinase in platelet-derived growth factor-B-dependent tubular regeneration after acute ischemic renal injury

We previously reported that the platelet-derived growth factor B-chain (PDGF-B)/PDGF receptor (PDGFR) axis is involved in tubular regeneration after ischemia/reperfusion injury of the kidney. In the present study, we examined the activation of Src tyrosine kinase, a crucially important signaling molecule for PDGFR, and assessed the role of Src in PDGF-B-dependent renal tubular regeneration afterischemia/reperfusion injury. Immunoblot using clone 28, a monoclonal antibody specific for the active form of Src kinases, demonstrated increased active Src expression in the injured rat kidney 6 hours after reperfusion with peak activation at 12 hours. In vitro kinase assay confirmed increased Src activity that concurred with PDGFR-beta activation as detected by the increment of receptor-phosphorylated tyrosine. Immunohistochemistry using clone 28 demonstrated that active Src was preferentially expressed in the S3 segment of the proximal tubule in reperfused kidney, where it is not normally expressed. This enhanced expression of active Src was co-localized with the increased PDGFR expression in the tubular cells that were undergoing cell proliferation cycle. Trapidil administration suppressed Src and PDGFR-beta activation in the reperfused kidney and resulted in deteriorated renal function. These findings suggest that active Src participates in PDGF-B-dependent regeneration of tubular cells from acute ischemic injury.

Cell death induced by acute renal injury: a perspective on the contributions of apoptosis and necrosis

In humans and experimental models of renal ischemia, tubular cells in various nephron segments undergo necrotic and/or apoptotic cell death. Various factors, including nucleotide depletion, electrolyte imbalance, reactive oxygen species, endonucleases, disruption of mitochondrial integrity, and activation of various components of the apoptotic machinery, have been implicated in renal cell vulnerability. Several approaches to limit the injury and augment the regeneration process, including nucleotide repletion, administration of growth factors, reactive oxygen species scavengers, and inhibition of inducers and executioners of cell death, proved to be effective in animal models. Nevertheless, an effective approach to limit or prevent ischemic renal injury in humans remains elusive, primarily because of an incomplete understanding of the mechanisms of cellular injury. Elucidation of cell death pathways in animal models in the setting of renal injury and extrapolation of the findings to humans will aid in the design of potential therapeutic strategies. This review evaluates our understanding of the molecular signaling events in apoptotic and necrotic cell death and the contribution of various molecular components of these pathways to renal injury.

Acute renal failure in the surgical setting

Acute renal failure (ARF) is an unwelcome complication of major surgical procedures that contributes to surgical morbidity and mortality. Acute renal failure associated with surgery may account for 18-47% of all cases of hospital-acquired ARF. The overall incidence of ARF in surgical patients has been estimated at 1.2%, although is higher in at-risk groups. Mortality of patients with ARF remains disturbingly high, ranging from 25% to 90%, despite advances in dialysis and intensive care support. Appreciation of at-risk surgical populations coupled with intensive perioperative care has the capacity to reduce the incidence of ARF and by implication mortality. Developments in understanding the pathophysiology of ARF may eventually result in newer therapeutic strategies to either prevent or accelerate recovery from ARF. At present the best form of treatment is prevention. In this review the epidemiology, pathophysiology, diagnosis, treatment and possible prevention of ARF will be discussed.

Cyclosporine or FK506 decrease mature epidermal growth factor protein expression and renal tubular regeneration in rat kidneys with ischemia/reperfusion injury

BACKGROUND

Epidermal growth factor (EGF) plays an important role in tubular regeneration in kidneys with ischemia/reperfusion (I/R) injury. This study was undertaken to evaluate the influence of cyclosporine A (CsA) or FK506 on mature EGF expression and tubular regeneration in rat kidneys with I/R injury.

METHODS

Two separate studies were performed. First, the expression of EGF and tubular regeneration was observed in rat kidneys with I/R injury on days 1, 2, 3, 5, and 7. Second, the dose-dependent response of EGF expression and tubular regeneration to CsA (5, 10, and 20 mg/kg) or FK506 (0.25, 0.5, and 1.0 mg/kg) was observed in rat kidneys with I/R injury. I/R injury was induced by clamping both renal arteries for 45 min, and CsA or FK506 was injected just after release of vascular clamps. Rats were sacrificed on day 1 for evaluation of EGF expression, and on day 2 for evaluation of BudU-positive cells. Renal function, tubular injury score, EGF expression assessed by immunoblotting, levels of CsA and FK506 in whole blood, and immunostaining for BrdU was studied.

RESULTS

EGF expression was maximal on day 1 (cortex, 29-fold; medulla, 31-fold compared with sham-operated controls), and renal tubular regeneration measured with the number of BrdU-positive cells was maximal on days 2 and 3 in kidney with I/R injury, and thereafter the level of EGF and the number of BrdU-positive cells decreased progressively. CsA or FK506 treatment to ischemic rat kidneys reduced the expression of EGF and the number of BrdU-positive cells in a dose-dependent manner.

CONCLUSIONS

CsA or FK506 treatment delays recovery from acute tubular necrosis, and this may be associated with decreased EGF expression by CsA or FK506.

Mechanism of the process formation; podocytes vs. neurons

In this review article we discuss the common mechanism for cellular process formation. Besides the podocyte, the mechanism of process formation, including cytoskeletal organization and signal transduction, etc., has been studied using neurons and glias as model systems. There has been an accumulation of data showing common cell biological features of the podocyte and the neuron: 1) Both cells possess long and short cell processes equipped with highly organized cytoskeletal systems; 2) Both show cytoskeletal segregation; microtubules (MTs) and intermediate filaments (IFs) in podocyte primary processes and in neurites, while actin filaments (AFs) are abundant in podocyte foot processes in neuronal synaptic regions; 3) In both cells, process formation is mechanically dependent on MTs, whose assembly is regulated by various microtubule- associated proteins (MAPs); 4) In both cells, process formation is positively regulated by PP2A, a Ser/Thr protein phosphatase; 5) In both cells, process formation is accelerated by laminin, an extracellular matrix protein. In addition, recent data from our and other laboratories have shown that podocyte processes share many features with neuronal dendrites: 1) Podocyte processes and neuronal dendrites possess MTs with mixed polarity, namely, plus-end-distal and minus-end-distal MTs coexist in these processes; 2) To establish the mixed polarity of MTs, both express CHO1/MKLP1, a kinesin-related motor protein, and when its expression is inhibited formation of both podocyte processes and neuronal dendrites is abolished; 3) The elongation of both podocyte processes and neuronal dendrites is supported by rab8-regulated basolateral-type membrane transport; 4) Both podocyte processes and neuronal dendrites express synaptopodin, an actin-associated protein, in a development-dependent manner; interestingly, in both cells, synaptopodin is localized not in the main shaft of processes but in thin short projections from the main shaft. We propose that the podocyte process and the neuronal dendrite share many features, while the neuronal axon should be thought of as an exceptionally differentiated cellular process.

Endocan is a novel chondroitin sulfate/dermatan sulfate proteoglycan that promotes hepatocyte growth factor/scatter factor mitogenic activity

Proteoglycans that modulate the activities of growth factors, chemokines, and coagulation factors regulate in turn the vascular endothelium with respect to processes such as inflammation, hemostasis, and angiogenesis. Endothelial cell-specific molecule-1 is mainly expressed by endothelial cells and regulated by pro-inflammatory cytokines (Lassalle, P., Molet, S., Janin, A., Heyden, J. V., Tavernier, J., Fiers, W., Devos, R., and Tonnel, A. B. (1996) J. Biol. Chem. 271, 20458-20464). We demonstrate that this molecule is secreted as a soluble dermatan sulfate (DS) proteoglycan. This proteoglycan represents the major form either secreted by cell lines or circulating in the human bloodstream. Because this proteoglycan is specifically secreted by endothelial cells, we propose to name it endocan. The glycosaminoglycan component of endocan consists of a single DS chain covalently attached to serine 137. Endocan dose-dependently increased the hepatocyte growth factor/scatter factor (HGF/SF)-mediated proliferation of human embryonic kidney cells, whereas the nonglycanated form of endocan did not. Moreover, DS chains purified from endocan mimicked the endocan-mediated increase of cell proliferation in the presence of HGF/SF. Overall, our results demonstrate that endocan is a novel soluble dermatan sulfate proteoglycan produced by endothelial cells. Endocan regulates HGF/SF-mediated mitogenic activity and may support the function of HGF/SF not only in embryogenesis and tissue repair after injury but also in tumor progression.

Increased renal angiopoietin-1 expression in folic acid-induced nephrotoxicity in mice

Growth factors affect epithelial regeneration after acute renal injury, but less is known regarding the expression of vascular growth factors in this setting. A mouse model of folic acid (FA)-induced nephrotoxicity was used to study the expression of angiopoietins (Ang), factors that bind the Tie-2 receptor and modulate endothelial growth. Tubular damage was detected 1 d after FA administration; in the next 14 d, most tubules regenerated but patchy atrophy, with interstitial fibrosis, was also observed. Ang-1 immunostaining was detected between cortical tubules and in the vasa rectae of vehicle-treated animals. FA-induced nephropathy was associated with the acquisition of Ang-1 immunostaining in renal arterial walls and in a subset of injured cortical tubules that failed to stain with periodic acid-Schiff stain, which indicated that they were distal tubules. Renal Ang-1 protein levels were significantly increased after FA administration, compared with time-matched control values, as assessed by Western blotting. Capillaries between regenerating tubules expressed both Tie-2 and platelet-endothelial cell adhesion molecule. A subset of these endothelia expressed proliferating cell nuclear antigen, whereas capillary proliferation was absent in control samples. Therefore, FA-induced nephropathy is associated with increased Ang-1 protein expression in renal epithelia and arteries. In addition, Tie-2-expressing capillaries near damaged cortical tubules undergo proliferation. Further experiments are required to establish whether these events are functionally related.

Hepatocyte growth factor prevents the development of chronic allograft nephropathy in rats

Long-term renal isografts in humans and laboratory animals exhibit features similar to those of chronic allograft nephropathy (CAN), indicating that antigen-independent factors, such as acute renal ischemia, are likely to be involved in the development of CAN. Hepatocyte growth factor (HGF) has been demonstrated to play a renotropic role in renal regeneration and protection from acute ischemic injury. This study was thus conducted to investigate the effect of HGF on the development of CAN, using an established rat model. HGF was administered daily (100 microg/d, intravenously) for 4 wk after engraftment. Control animals received saline solution. Allografts from control animals exhibited early evidence of severe structural collapse and necrotic cell death in the proximal tubules and outer medulla, with mononuclear cell infiltration, within 1 wk after engraftment. This was followed by sequential upregulation of adhesion molecules and cytokines, accompanied by dense macrophage infiltration. Fibrogenic events, as indicated by marked increases in transforming growth factor-beta1 expression and the accumulation of smooth muscle alpha-actin, occurred during the same period. Control animals ultimately developed features typical of CAN, with functional deterioration and severe histologic changes; a survival rate of 50.6% by 32 wk was observed. In contrast, remarkably little early injury and no late fibrogenic events were observed for the HGF-treated group. All treated animals survived, with well preserved graft function, during the 32-wk follow-up period. These results indicate that renal protection and recovery from early allograft injury with HGF treatment greatly contribute to a reduction of susceptibility to the subsequent development of CAN in a rat model. The potential application of HGF in the prevention of CAN warrants further attention.

Hepatocyte growth factor: renotropic role and potential therapeutics for renal diseases

Hepatocyte growth factor (HGF), a ligand for the c-Met receptor tyrosine kinase, has mitogenic, motogenic, anti-apoptotic, and morphogenic (for example, induction of branching tubulogenesis) activities for renal tubular cells, while it has angiogenic and angioprotective actions for endothelial cells. Stromal cells such as mesangial cells, endothelial cells, and macrophages are sources of renal HGF; thus, HGF mediates epithelial-stromal and endothelial-mesangial interactions in the kidney. In response to acute renal injury, the expression of HGF increases in the injured kidney and in distant intact organs such as the lung and spleen. Locally and systemically increased HGF supports renal regeneration, possibly not only by enhancing cell growth but also by promoting morphogenesis of renal tissue. During progression of chronic renal failure/renal fibrosis, the expression of HGF decreases in a manner reciprocal to the increase in expression of transforming growth factor-beta (TGF-beta), a key player in tissue fibrosis. A decrease in endogenous HGF, as well as increase in TGF-beta, augments susceptibility to the onset of chronic renal failure/renal fibrosis. On the other hand, supplements of exogenous HGF have preventive and therapeutic effects in cases of acute and chronic renal failure/renal fibrosis in laboratory animals. HGF prevents epithelial cell death and enhances regeneration and remodeling of renal tissue with injury or fibrosis. A renotropic system underlies the vital potential of the kidney to regenerate, while an impaired renotropic system may confer susceptibility to the onset of renal diseases. Thus, HGF supplementation may be one therapeutic strategy to treat subjects with renal diseases, as it enhances the intrinsic ability of the kidney to regenerate.

Identification of a novel nuclear guanosine triphosphate-binding protein differentially expressed in renal disease

A novel guanosine triphosphate-binding protein, chronic renal failure gene (CRFG), was discovered by differential display PCR to be regulated differentially in renal disease. Within the rat kidney, CRFG mRNA was localized to the outer medulla and was highly expressed in epithelial cells. The specific renal expression of CRFG mRNA in the outer medulla was reduced dramatically in several rat models of renal disease, including diabetic nephropathy, partial nephrectomy, ischemia, and anti-Thy1.1-induced nephritis. CRFG was localized selectively in the nucleus of human and rodent cells, as determined by immunocytochemistry and green fluorescence fusion protein. Cellular mRNA levels of CRFG were also increased after serum administration, when cells proliferate. These data suggest that CRFG may be involved in regulating guanosine triphosphate-dependent nuclear events that are associated with cell proliferation and that are important in normal renal function and essential for growth and development.

Upregulation of ciliary neurotrophic factor (CNTF) and CNTF receptor alpha in rat kidney with ischemia-reperfusion injury

Ciliary neurotrophic factor (CNTF) is presumed to play a role as a survival factor in neuronal cells, but little is known about its role in the kidney. To investigate this, the expression of CNTF and CNTF receptor alpha (CNTFR alpha) was analyzed in the ischemic rat kidney. An ischemia/reperfusion (I/R) injury was induced by clamping both renal arteries for 45 min. Animals were killed at 1, 2, 3, 5, 7, 14, and 28 d after ischemia. The expression of CNTF and CNTFR alpha was monitored by reverse transcription-PCR, in situ hybridization, immunoblotting, immunohistochemistry, and electron microscopy. In sham-operated rat kidneys, CNTF expression was weak and limited to the descending thin limb of the loop of Henle. With I/R injury, CNTF mRNA and protein expressions were strikingly increased as compared with the sham-operated rat kidney, and the immunoreactivity of CNTF was mainly observed in the regenerating proximal tubules. The expression of CNTFR alpha mRNA was also increased after I/R injury, and its location and expression patterns were similar to the expression of CNTF. These findings suggest a possible role of CNTF as a growth factor during renal tubular repair processes after I/R injury and an autocrine or paracrine function of CNTF acting against CNTFR alpha.

Pathophysiologic Features and Prevention of Human and Experimental Acute Tubular Necrosis

Abstract.Acute renal failure (ARF) remains a common and potentially devastating disorder that affects as many as 5% of all hospitalized patients, with a higher prevalence in patients in critical care units. The focus of this article is on categorizing recent pathophysiologic and clinically relevant developments in the field. The vascular and tubular factors in the pathogenesis of ARF, together with the potential mechanisms of recovery and repair of the injured kidney, are discussed. A number of experimental and clinical interventions to prevent. ARF are summarized. Although the clinical treatment of these patients is still largely supportive and many recent clinical trials showed rather negative results, it is hoped that basic research will provide therapeutic tools to improve the grim prognosis of this disease in the future.

Up-regulation of galectin-3 in acute renal failure of the rat

Galectin-3, a multifunctional beta-galactoside-binding lectin, is known to participate in development, oncogenesis, cell-to-cell attachment, and inflammation. We studied to determine whether galectin-3 is associated with cell injury and regeneration in two types of acute renal failure (ARF), namely ischemic and toxic ARF. In ischemia/reperfusion renal injury in rats (bilateral renal pedicles clamped for 40 minutes), galectin-3 mRNA began to increase at 2 hours and extended by 6.2-fold at 48 hours (P: < 0.01 versus normal control rats), and then decreased by 28 days after injury. In addition, a significant negative correlation between galectin-3 mRNA expression and serum reciprocal creatinine was shown at 48 hours after injury (n = 13, r = -0.94, P: < 0.0001). In folic acid-induced ARF, galectin-3 mRNA was found to be up-regulated at 2 hours after injury and increased levels continued until at least 7 days post-injury. In immunohistochemistry, at 2 hours following reperfusion, galectin-3 began to develop in proximal convoluted tubules. From 6 hours up to 48 hours, galectin-3 was also found in proximal straight tubules, distal tubules, thick ascending limbs, and collecting ducts. In later stages of regeneration, galectin-3 expressions were found in macrophages. In conclusion, we demonstrated that galectin-3 expressions were markedly up-regulated in both ischemic and toxic types of ARF. Galectin-3 may play an important role in acute tubular injury and the following regeneration stage.

Cell cycle regulatory proteins in renal disease: role in hypertrophy, proliferation, and apoptosis

The response to glomerular and tubulointerstitial cell injury in most forms of renal disease includes changes in cell number (proliferation and apoptosis) and cell size (hypertrophy). These events typically precede and may be responsible for the accumulation of extracellular matrix proteins that leads to a decrease in renal function. There is increasing evidence showing that positive (cyclins and cyclin-dependent kinases) and negative (cyclin-dependent kinase inhibitors) cell cycle regulatory proteins have a critical role in regulating these fundamental cellular responses to immune and nonimmune forms of injury. Data now show that altering specific cell cycle proteins affects renal cell proliferation and improves renal function. Equally exciting is the expanding body of literature showing novel biological roles for cell cycle proteins in the regulation of cell hypertrophy and apoptosis. With increasing understanding of the role for cell cycle regulatory proteins in renal disease comes the hope for potential therapeutic interventions.

Apoptotic mechanisms in acute renal failure

It has been generally accepted that a catastrophic breakdown of regulated cellular homeostasis, known as necrosis, is the mode of cellular injury in various forms of acute renal failure. One of the major advances in our understanding of cell death has been the recognition that the pathways traditionally associated with apoptosis as described in the landmark study by Kerr, Wyllie, and Currie in 1972 maybe very critical in the form of cell injury associated with necrosis. The pathway that is followed by the cell varies with both nature and severity of insults and may evolve from an apoptotic to a necrotic form of cell death. It is also likely that there are some common pathways that are shared and regulated in the two modes of cell death. In this review, we first describe evidence for the role of apoptotic pathways in ischemic acute renal failure, and then consider the potential mechanisms that may participate in this model of acute renal tubular injury. We then summarize the current information of apoptotic pathways related to other common causes of acute renal failure including endotoxin-induced, toxic acute renal failure and transplant rejection. A better understanding of the mechanisms of apoptosis could lead to safer and more specific therapeutic interventions for acute renal failure.