Hsp27 associates with actin and limits injury in energy depleted renal epithelia

Structural and functional properties of proteins interacting with small heat shock proteins

Small heat shock proteins (sHsps) are ubiquitous molecular chaperones found in all domains of life, possessing significant roles in protein quality control in cells and assisting the refolding of non-native proteins. They are efficient chaperones against many in vitro protein substrates. Nevertheless, the in vivo native substrates of sHsps are not known. To better understand the functions of sHsps and the mechanisms by which they enhance heat resistance, sHsp-interacting proteins were identified using affinity purification under heat shock conditions. This paper aims at providing some insights into the characteristics of natural substrate proteins of sHsps. It seems that sHsps of prokaryotes, as well as sHsps of some eukaryotes, can bind to a wide range of substrate proteins with a preference for certain functional classes of proteins. Using Drosophila melanogaster mitochondrial Hsp22 as a model system, we observed that this sHsp interacted with the members of ATP synthase machinery. Mechanistically, Hsp22 interacts with the multi-type substrate proteins under heat shock conditions as well as non-heat shock conditions.

Heat shock proteins in the kidney

Heat shock proteins (Hsps) are essential to cell survival through their function as protein chaperones. The role they play in kidney health and disease is varied. Hsp induction may be either beneficial or detrimental to the kidney, depending on the specific Hsp, type of cell, and context. This review addresses the role of Hsps in the kidney, including during development, as osmoprotectants, and in various kidney disease models. Heat shock transcription factor, activated by a stress on renal cells, induces Hsp elaboration and separately regulates immune responses that can contribute to renal injury. Induced Hsps in the intracellular compartment are mostly beneficial in the kidney by stabilizing and restoring cell architecture and function through acting as protein chaperones. Intracellular Hsps also inhibit apoptosis and facilitate cell proliferation, preserving renal tubule viability after acute injury, but enhancing progression of cystic kidney disease and malignancy. Induced Hsps in the extracellular compartment, either circulating or located on outer cell membranes, are mainly detrimental through enhancing inflammation pathways to injury. Correctly harnessing these stress proteins promises the opportunity to alter the course of acute and chronic kidney disease.

Prediction of Nephrotoxicant Action and Identification of Candidate Toxicity-Related Biomarkers

A vast majority of pharmacological compounds and their metabolites are excreted via the urine, and within the complex structure of the kidney, the proximal tubules are a main target site of nephrotoxic compounds. We used the model nephrotoxicants mercuric chloride, 2-bromoethylamine hydrobromide, hexachlorobutadiene, mitomycin, amphotericin, and puromycin to elucidate time- and dose-dependent global gene expression changes associated with proximal tubular toxicity. Male Sprague–Dawley rats were dosed via intraperitoneal injection once daily for mercuric chloride and amphotericin (up to 7 doses), while a single dose was given for all other compounds. Animals were exposed to 2 different doses of these compounds and kidney tissues were collected on day 1, 3, and 7 postdosing. Gene expression profiles were generated from kidney RNA using 17K rat cDNA dual dye microarray and analyzed in conjunction with histopathology. Analysis of gene expression profiles showed that the profiles clustered based on similarities in the severity and type of pathology of individual animals. Further, the expression changes were indicative of tubular toxicity showing hallmarks of tubular degeneration/regeneration and necrosis. Use of gene expression data in predicting the type of nephrotoxicity was then tested with a support vector machine (SVM)-based approach. A SVM prediction module was trained using 120 profiles of total profiles divided into four classes based on the severity of pathology and clustering. Although mitomycin C and amphotericin B treatments did not cause toxicity, their expression profiles were included in the SVM prediction module to increase the sample size. Using this classifier, the SVM predicted the type of pathology of 28 test profiles with 100% selectivity and 82% sensitivity. These data indicate that valid predictions could be made based on gene expression changes from a small set of expression profiles. A set of potential biomarkers showing a time- and dose-response with respect to the progression of proximal tubular toxicity were identified. These include several transporters ( Slc21a2, Slc15, Slc34a2), Kim 1, IGFbp-1, osteopontin, α -fibrinogen, and Gstα.

A1 adenosine receptor attenuates intracerebral hemorrhage-induced secondary brain injury in rats by activating the P38-MAPKAP2-Hsp27 pathway

Background

This study was designed to determine the role of the A1 adenosine receptors in intracerebral hemorrhage (ICH)-induced secondary brain injury and the underlying mechanisms.

Methods

A collagenase-induced ICH model was established in Sprague–Dawley rats, and cultured primary rat cortical neurons were exposed to oxyhemoglobin at a concentration of 10 μM to mimic ICH in vitro. The A1 adenosine receptor agonist N(6)-cyclohexyladenosine and antagonist 8-phenyl-1,3-dipropylxanthine were used to study the role of A1 adenosine receptor in ICH-induced secondary brain injury, and antagonists of P38 and Hsp27 were used to study the underlying mechanisms of A1 adenosine receptor actions.

Results

The protein level of A1 adenosine receptor was significantly increased by ICH, while there was no significant change in protein levels of the other 3 adenosine receptors. In addition, the A1 adenosine receptor expression could be increased by N(6)-cyclohexyladenosine and decreased by 8-phenyl-1,3-dipropylxanthine under ICH conditions. Activation of the A1 adenosine receptor attenuated neuronal apoptosis in the subcortex, which was associated with increased phosphorylation of P38, MAPK, MAPKAP2, and Hsp27. Inhibition of the A1 adenosine receptor resulted in opposite effects. Finally, the neuroprotective effect of the A1 adenosine receptor agonist N(6)-cyclohexyladenosine was inhibited by antagonists of P38 and Hsp27.

Conclusions

This study demonstrates that activation of the A1 adenosine receptor by N(6)-cyclohexyladenosine could prevent ICH-induced secondary brain injury via the P38-MAPKAP2-Hsp27 pathway.

The impact of heat stress on intestinal function and productivity in grow-finish pigs

Heat stress is a physiological condition when animals can no longer regulate their internal euthermic temperature. When livestock such as pigs are subjected to this environmental stress, it can be detrimental to performance, health and well-being, and if severe enough even death. Growing pigs are particularly susceptible to heat stress and one of the major organs first affected by heat stress is the gastrointestinal tract. As a result, reductions in appetite, intestinal function and integrity and increased risk of endotoxemia can modify post-absorptive metabolism and tissue accretion. These changes in intestinal integrity may be a result of altered expression of tight junction proteins, increased circulating endotoxin concentrations and markers of cellular stress (heat shock and hypoxia response), which is evident as early on as 2 h after heat-stress onset. Due to restricted blood flow, the ileum is more severely affected compared with the colon. Interestingly, many of the negative effects of heat stress on intestinal integrity appear to be similar to those observed with pigs reared under reduced nutrient and caloric intakes. Altogether, these depress pig performance and health, and extend days to market. Despite this impact on the gastrointestinal tract, under heat-stress conditions, intestinal glucose transport pathways are upregulated. This review discussed how heat stress (directly and indirectly via reduced feed intake) affects intestinal integrity and how heat stress contributes to decreased growth performance in growing pigs.

Multigenerational study of chemically induced cytotoxicity and proliferation in cultures of human proximal tubular cells

Primary cultures of human proximal tubular (hPT) cells are a useful experimental model to study transport, metabolism, cytotoxicity, and effects on gene expression of a diverse array of drugs and environmental chemicals because they are derived directly from the in vivo human kidney. To extend the model to investigate longer-term processes, primary cultures (P0) were passaged for up to four generations (P1-P4). hPT cells retained epithelial morphology and stained positively for cytokeratins through P4, although cell growth and proliferation successively slowed with each passage. Necrotic cell death due to the model oxidants tert-butyl hydroperoxide (tBH) and methyl vinyl ketone (MVK) increased with increasing passage number, whereas that due to the selective nephrotoxicant S-(1,2-dichlorovinyl)-l-cysteine (DCVC) was modest and did not change with passage number. Mitochondrial activity was lower in P2-P4 cells than in either P0 or P1 cells. P1 and P2 cells were most sensitive to DCVC-induced apoptosis. DCVC also increased cell proliferation most prominently in P1 and P2 cells. Modest differences with respect to passage number and response to DCVC exposure were observed in expression of three key proteins (Hsp27, GADD153, p53) involved in stress response. Hence, although there are some modest differences in function with passage, these results support the use of multiple generations of hPT cells as an experimental model.

Mice with an absent stress response are protected against ischemic renal injury

Inducible heat shock proteins (HSP), regulated by heat shock factor-1 (HSF-1), protect against renal cell injury in vitro. To determine whether HSPs ameliorate ischemic renal injury in vivo, HSF-1functional knock-out mice (HSF-KO) were compared with wild-type mice following bilateral ischemic renal injury. Following injury, the kidneys of wild-type mice had the expected induction of HSP70 and HSP25; a response absent in the kidneys of HSF-KO mice. Baseline serum creatinine was equivalent between strains. Serum creatinines at 24 hours reflow in HSF-KO mice were significantly lower than in the wild-type. Histology showed similar tubule injury in both strains after ischemic renal injury but increased medullary vascular congestion in wild-type compared with HSF-KO mice. Flow-cytometry of mononuclear cells isolated from kidneys showed no difference between strains in the number of CD4⁺ and CD8⁺ T cells in sham operated animals. At 1 hour of reflow, CD4⁺ and CD8⁺ cells were doubled in the kidneys of wild type but not HSF-KO mice. Foxp3⁺ T regulatory cells were significantly more abundant in the kidneys of sham-operated HSF-KO than wild-type mice. Suppression of CD25⁺Foxp3⁺ cells in HSF-KO kidneys with the anti-CD25 antibody PC61 reversed the protection against ischemic renal injury. Thus, HSF-KO mice are protected from ischemic renal injury by a mechanism that depends on an increase in the T regulatory cells in the kidney associated with altered T cell infiltration early in reflow. Hence, stress response activation may contribute to early injury by facilitating T cell infiltration into ischemic kidney.

Cell stress promotes the association of phosphorylated HspB1 with F-actin

Previous studies have suggested that the small heat shock protein, HspB1, has a direct influence on the dynamics of cytoskeletal elements, in particular, filamentous actin (F-actin) polymerization. In this study we have assessed the influence of HspB1 phosphorylation on its interaction(s) with F-actin. We first determined the distribution of endogenous non-phosphorylated HspB1, phosphorylated HspB1 and F-actin in neuroendocrine PC12 cells by immunocytochemistry and confocal microscopy. We then investigated a potential direct interaction between HspB1 with F-actin by precipitating F-actin directly with biotinylated phalloidin followed by Western analyses; the reverse immunoprecipitation of HspB1 was also carried out. The phosphorylation influence of HspB1 in this interaction was investigated by using pharmacologic inhibition of p38 MAPK. In control cells, HspB1 interacts with F-actin as a predominantly non-phosphorylated protein, but subsequent to stress there is a redistribution of HspB1 to the cytoskeletal fraction and a significantly increased association of pHspB1 with F-actin. Our data demonstrate HspB1 is found in a complex with F-actin both in phosphorylated and non-phosphorylated forms, with an increased association of pHspB1 with F-actin after heat stress. Overall, our study combines both cellular and biochemical approaches to show cellular localization and direct demonstration of an interaction between endogenous HspB1 and F-actin using methodolgy that specifically isolates F-actin.

Ezrin functionality and hypothermic preservation injury in LLC-PK1 cells

Renal epithelial cells from donor kidneys are susceptible to hypothermic preservation injury, which is attenuated when they over express the cytoskeletal linker protein ezrin. This study was designed to characterize the mechanisms of this protection. Renal epithelial cell lines were created from LLC-PK1 cells, which expressed mutant forms of ezrin with site directed alterations in membrane binding functionality. The study used cells expressing wild type ezrin, T567A, and T567D ezrin point mutants. The A and D mutants have constitutively inactive and active membrane binding conformations, respectively. Cells were cold stored (4 °C) for 6-24 h and reperfused for 1h to simulate transplant preservation injury. Preservation injury was assessed by mitochondrial activity (WST-1) and LDH release. Cells expressing the active ezrin mutant (T567D) showed significantly less preservation injury compared to wild type or the inactive mutant (T567A), while ezrin-specific siRNA knockdown and the inactive mutant potentiated preservation injury. Ezrin was extracted and identified from purified mitochondria. Furthermore, isolated mitochondria specifically bound anti-ezrin antibodies, which were reversed with the addition of exogenous recombinant ezrin. Recombinant wild type ezrin significantly reduced the sensitivity of the mitochondrial permeability transition pore (mPTP) to calcium, suggesting ezrin may modify mitochondrial function. In conclusion, the cytoskeletal linker protein ezrin plays a significant role in hypothermic preservation injury in renal epithelia. The mechanisms appear dependent on the molecule's open configuration (traditional linker functionality) and possibly a novel mitochondrial specific role, which may include modulation of mPTP function or calcium sensitivity.

Pathophysiology of acute kidney injury

Acute kidney injury (AKI) is the leading cause of nephrology consultation and is associated with high mortality rates. The primary causes of AKI include ischemia, hypoxia, or nephrotoxicity. An underlying feature is a rapid decline in glomerular filtration rate (GFR) usually associated with decreases in renal blood flow. Inflammation represents an important additional component of AKI leading to the extension phase of injury, which may be associated with insensitivity to vasodilator therapy. It is suggested that targeting the extension phase represents an area potential of treatment with the greatest possible impact. The underlying basis of renal injury appears to be impaired energetics of the highly metabolically active nephron segments (i.e., proximal tubules and thick ascending limb) in the renal outer medulla, which can trigger conversion from transient hypoxia to intrinsic renal failure. Injury to kidney cells can be lethal or sublethal. Sublethal injury represents an important component in AKI, as it may profoundly influence GFR and renal blood flow. The nature of the recovery response is mediated by the degree to which sublethal cells can restore normal function and promote regeneration. The successful recovery from AKI depends on the degree to which these repair processes ensue and these may be compromised in elderly or chronic kidney disease (CKD) patients. Recent data suggest that AKI represents a potential link to CKD in surviving patients. Finally, earlier diagnosis of AKI represents an important area in treating patients with AKI that has spawned increased awareness of the potential that biomarkers of AKI may play in the future.

Large potentials of small heat shock proteins

Modern classification of the family of human small heat shock proteins (the so-called HSPB) is presented, and the structure and properties of three members of this family are analyzed in detail. Ubiquitously expressed HSPB1 (HSP27) is involved in the control of protein folding and, when mutated, plays a significant role in the development of certain neurodegenerative disorders. HSPB1 directly or indirectly participates in the regulation of apoptosis, protects the cell against oxidative stress, and is involved in the regulation of the cytoskeleton. HSPB6 (HSP20) also possesses chaperone-like activity, is involved in regulation of smooth muscle contraction, has pronounced cardioprotective activity, and seems to participate in insulin-dependent regulation of muscle metabolism. HSPB8 (HSP22) prevents accumulation of aggregated proteins in the cell and participates in the regulation of proteolysis of unfolded proteins. HSPB8 also seems to be directly or indirectly involved in regulation of apoptosis and carcinogenesis, contributes to cardiac cell hypertrophy and survival and, when mutated, might be involved in development of neurodegenerative diseases. All small heat shock proteins play important "housekeeping" roles and regulate many vital processes; therefore, they are considered as attractive therapeutic targets.

Hsp27-actin interaction

Hsp27 oligomer is reported to interact with F-actin as a barbed-end-capping protein. The present study determined the binding strength and stoichiometry of the interaction using fluorescence of probes attached to Hsp27 cysteine-137. The fluorescence of acrylodan attached to Hsp27 increased 4-5-fold upon interaction with F-actin. Titration of the fluorescence with F-actin yielded a weak binding constant (K_D^app = 5.3 μM) with an actin/Hsp27 stoichiometry between < 1 and 6. This stoichiometry is inconsistent with an F-actin end-capping protein. Pyrene attached to Hsp27 exhibited a large excimer fluorescence, in agreement with the known proximity of the cysteine-137's in the Hsp27 oligomer. Upon interaction with F-actin the pyrene-Hsp27 excimer fluorescence was largely lost, suggesting that Hsp27 interacts with F-actin as a monomer, consistent with the acrylodan-Hsp27 results. EM images of F-actin-Hsp27 demonstrated that Hsp27 is not a strong G-actin sequester. Thus, Hsp27, in vitro, is a weak F-actin side-binding protein.

The role of molecular microtubule motors and the microtubule cytoskeleton in stress granule dynamics

Stress granules (SGs) are cytoplasmic foci that appear in cells exposed to stress-induced translational inhibition. SGs function as a triage center, where mRNAs are sorted for storage, degradation, and translation reinitiation. The underlying mechanisms of SGs dynamics are still being characterized, although many key players have been identified. The main components of SGs are stalled 48S preinitiation complexes. To date, many other proteins have also been found to localize in SGs and are hypothesized to function in SG dynamics. Most recently, the microtubule cytoskeleton and associated motor proteins have been demonstrated to function in SG dynamics. In this paper, we will discuss current literature examining the function of microtubules and the molecular microtubule motors in SG assembly, coalescence, movement, composition, organization, and disassembly.

Regional differences in colonic mucosa-associated microbiota determine the physiological expression of host heat shock proteins

Cytoprotective heat shock proteins (Hsps) are critical for intestinal homeostasis and are known to be decreased in inflammatory bowel diseases. Signals responsible for maintenance of Hsp expression are incompletely understood. In this study, we find that Hsp25/27 and Hsp70 protein expressions are differentially regulated along the longitudinal length of the large intestine, being highest in the proximal colon and decreasing to the distal colon. This longitudinal gradient was similar in both conventionally colonized mouse colon as well as biopsies of human proximal and distal colon but was abolished in the colon of germ-free mice, suggesting a role of intestinal microbiota in the Hsp regional expression. Correspondingly, analysis of 16S ribosomal RNA genes of bacteria from each colonic segment indicated increased bacterial richness and diversity in the proximal colon. The mechanism of regulation is transcriptional, as Hsp70 mRNA followed a similar pattern to Hsp70 protein expression. Lysates of mucosa-associated bacteria from the proximal colon stimulated greater Hsp25 and Hsp70 mRNA transcription and subsequent protein expression in intestinal epithelial cells than did lysates from distal colon. In addition, transrectal administration of cecal contents stimulated Hsp25 and Hsp70 expression in the distal colon. Thus host-microbial interactions resulting in differential Hsp expression may have significant implications for the maintenance of intestinal homeostasis and possibly for development of inflammatory diseases of the bowel.

Curcumin activates the p38MPAK-HSP25 pathway in vitro but fails to attenuate diabetic nephropathy in DBA2J mice despite urinary clearance documented by HPLC

BACKGROUND

Curcumin has anti-inflammatory, anti-oxidant, and anti-proliferative properties, and depending upon the experimental circumstances, may be pro- or anti-apoptotic. Many of these biological actions could ameliorate diabetic nephropathy.

METHODS/DESIGN

Mouse podocytes, cultured in basal or high glucose conditions, underwent acute exposure to curcumin. Western blots for p38-MAPK, COX-2 and cleaved caspase-3; isoelectric focusing for HSP25 phosphorylation; and DNase I assays for F- to G- actin cleavage were performed for in vitro analyses. In vivo studies examined the effects of dietary curcumin on the development of diabetic nephropathy in streptozotocin (Stz)-induced diabetes in DBA2J mice. Urinary albumin to creatinine ratios were obtained, high performance liquid chromatography was performed for urinary curcuminoid measurements, and Western blots for p38-MAPK and total HSP25 were performed.

RESULTS

Curcumin enhanced the phosphorylation of both p38MAPK and downstream HSP25; inhibited COX-2; induced a trend towards attenuation of F- to G-actin cleavage; and dramatically inhibited the activation of caspase-3 in vitro. In curcumin-treated DBA2J mice with Stz-diabetes, HPLC measurements confirmed the presence of urinary curcuminoid. Nevertheless, dietary provision of curcumin either before or after the induction of diabetes failed to attenuate albuminuria.

CONCLUSIONS

Apart from species, strain, early differences in glycemic control, and/or dosing effects, the failure to modulate albuminuria may have been due to a decrement in renal HSP25 or stimulation of the 12/15 lipoxygenase pathway in DBA2J mice fed curcumin. In addition, these studies suggest that timed urine collections may be useful for monitoring curcumin dosing and renal pharmacodynamic effects.

The maximal cytoprotective function of the heat shock protein 27 is dependent on heat shock protein 70

Endogenous heat shock proteins (HSPs) 70 and 25/27 are induced in renal cells by injury from energy depletion. Transfected over-expression of HSPs 70 or 27 (human analogue of HSP25), provide protection against renal cell injury from ATP deprivation. This study examines whether over-expressed HSP27 depends on induction of endogenous HSPs, in particular HSP70, to afford protection against cell injury. LLC-PK1 cells transfected with HSP27 (27OE cells) were injured by ATP depletion for 2h and recovered for 4h in the presence of HSF decoy, HSP70 specific siRNA (siRNA-70) and their respective controls. Injury in the presence of HSF decoy, a synthetic oligonucleotide identical to the heat shock element, the nuclear binding site of HSF, decreased HSP70 induction by 80% without affecting the over-expression of transfected HSP27. The HSP70 stress response was completely ablated in the presence of siRNA-70. Protection against injury, provided by over-expression of HSP27, was reduced by treatment with HSF decoy and abolished by treatment with siRNA-70. Immunoprecipitation studies demonstrated association of HSP27 with actin that was not affected by either treatment with HSF decoy or siRNA. Therefore, HSP27 is dependent on HSP70 to provide its maximal cytoprotective effect, but not for its interaction with actin. This study suggests that, while it has specific action on the cytoskeleton, HSP 25/27 must have coordinated activity with other HSP classes, especially HSP70, to provide the full extent of resistance to injury from energy depletion.

Selective renal overexpression of human heat shock protein 27 reduces renal ischemia-reperfusion injury in mice

We have previously shown that exogenous and endogenous A(1) adenosine receptor (A(1)AR) activation protected against renal ischemia-reperfusion (IR) injury in mice by induction and phosphorylation of heat shock protein 27 (HSP27). With global overexpression of HSP27 in mice, however, there was a paradoxical increase in systemic inflammation with increased renal injury after an ischemic insult due to increased NK1.1 cytotoxicity. In this study, we hypothesized that selective renal expression of HSP27 in mice would improve renal function and reduce injury after IR. Mice were subjected to renal IR injury 2 days after intrarenal injection of saline or a lentiviral construct encoding enhanced green fluorescent protein (EGFP) or human HSP27 coexpressing EGFP (EGFP-huHSP27). Mice with kidney-specific reconstitution of huHSP27 had significantly lower plasma creatinine, renal necrosis, apoptosis, and inflammation as demonstrated by decreased proinflammatory cytokine mRNA induction and neutrophil infiltration. In addition, there was better preservation of the proximal tubule epithelial filamentous (F)-actin cytoskeleton in the huHSP27-reconstituted groups than in the control groups. Furthermore, huHSP27 overexpression led to increased colocalization with F-actin in renal proximal tubules. Taken together, these findings have important clinical implications, as they imply that kidney-specific expression of HSP27 through lentiviral delivery is a viable therapeutic option in attenuating the effects of renal IR.

Thiolutin inhibits endothelial cell adhesion by perturbing Hsp27 interactions with components of the actin and intermediate filament cytoskeleton

Thiolutin is a dithiole synthesized by Streptomyces sp. that inhibits endothelial cell adhesion and tumor growth. We show here that thiolutin potently inhibits developmental angiogenesis in zebrafish and vascular outgrowth from tissue explants in 3D cultures. Thiolutin is a potent and selective inhibitor of endothelial cell adhesion accompanied by rapid induction of HSPB1 (Hsp27) phosphorylation. The inhibitory effects of thiolutin on endothelial cell adhesion are transient, potentially due to a compensatory increase in Hsp27 protein levels. Accordingly, heat shock induction of Hsp27 limits the anti-adhesive activity of thiolutin. Thiolutin treatment results in loss of actin stress fibers, increased cortical actin as cells retract, and decreased cellular F-actin. Mass spectrometric analysis of Hsp27 binding partners following immunoaffinity purification identified several regulatory components of the actin cytoskeleton that associate with Hsp27 in a thiolutin-sensitive manner including several components of the Arp2/3 complex. Among these, ArpC1a is a direct binding partner of Hsp27. Thiolutin treatment induces peripheral localization of phosphorylated Hsp27 and Arp2/3. Hsp27 also associates with the intermediate filament components vimentin and nestin. Thiolutin treatment specifically ablates Hsp27 interaction with nestin and collapses nestin filaments. These results provide new mechanistic insights into regulation of cell adhesion and cytoskeletal dynamics by Hsp27.

Selective intrarenal human A1 adenosine receptor overexpression reduces acute liver and kidney injury after hepatic ischemia reperfusion in mice

Acute kidney injury (AKI) is frequent after liver ischemia reperfusion (IR) can potentiate liver injury and is often complicated by subsequent multiorgan dysfunction syndrome. AKI because of liver IR is characterized by early renal endothelial cell apoptosis and impaired vascular integrity with subsequent neutrophil infiltration, proximal tubule necrosis/inflammation, and filamentous (F) actin disintegration. We tested whether selective renal overexpression of human A(1) adenosine receptors (huA(1)AR) protects against both liver and kidney injury sustained after liver IR. Mice were subjected to liver IR or to sham surgery 48 h after unilateral intrarenal injection of lentivirus encoding enhanced green fluorescent protein (EGFP) or EGFP-huA(1)AR. Intrarenal lentiviral gene delivery caused a robust transgene expression in the injected kidney without significant expression in the contralateral kidney or in the liver. Mice injected with EGFP-huA(1)AR lentivirus were protected against hepatic IR-induced liver and kidney injury with reduced necrosis, inflammation, and apoptosis, and better preserved F-actin and vascular permeability compared with mice injected with EGFP lentivirus. Importantly, we show that removing the EGFP-huA(1)AR lentivirus-injected kidney before hepatic ischemia abolished both renal and hepatic protection after liver IR showing that the overexpression of huA(1)AR in the injected kidney has a crucial role in protecting the kidney and liver after liver IR. Therefore, our findings show that protecting the kidney reduces liver IR injury and selective overexpression of cytoprotective A(1)ARs in the kidney leads to protection of both liver and kidney after hepatic IR.

Partial attenuation of cytotoxicity and apoptosis by SOD1 in ischemic renal epithelial cells

Reactive oxygen species (ROS) contribute significantly to apoptosis in renal ischemia-reperfusion (IR) injury, however the exact mechanisms are not well understood. We used novel lentiviral vectors to over-express superoxide dismutase 1 (SOD1) in proximal tubular epithelial (LLC-PK(1)) cells and determined effects of SOD1 following ATP depletion-recovery, used as a model to simulate renal IR. SOD1 over-expression partially protected against cytotoxicity (P < 0.001) and decreased superoxide (O(2) (*-)) in ATP depleted cells. The ATP depletion-mediated increase in nuclear fragmentation, an index of apoptosis and activation of caspase-3 was also partially blocked by SOD1 (P < 0.05). However, SOD1 over-expression was insufficient to completely attenuate caspase-3, indicating that ROS other than cytoplasmic O(2) (*-) are involved in ATP depletion mediated injury. To test the contribution of hydrogen peroxide, a subset of enhanced green fluorescent protein (EGFP) and SOD1 (serum free and injured) cells were treated with polyethylene glycol-catalase (PEG-catalase). As expected there was 50% reduction in cytotoxicity and caspase-3 in SOD1 cells compared to EGFP cells; catalase treatment decreased both indices by an additional 28% following ATP depletion. To test the role of mitochondrial derived superoxide, we also treated a subset of LLC-PK(1) cells with the mitochondrial antioxidant, MitoTEMPO. Treatment with MitoTEMPO also decreased ATP depletion induced cytotoxicity in LLC-PK(1) cells in a dose dependant manner. These studies indicate that both SOD1 dependent and independent pathways are integral in protection against ATP depletion-recovery mediated cytotoxicity and apoptosis, however more studies are needed to delineate the signaling mechanisms involved.

Protective effects of ezrin on cold storage preservation injury in the pig kidney proximal tubular epithelial cell line (LLC-PK1)

BACKGROUND

Renal damage caused by cold preservation and warm reperfusion has been well documented and involves tissue edema, cell swelling, ATP depletion, calcium toxicity, and oxidative stress. However, more common proximal mechanisms have not been identified, which may limit the development of effective clinical treatment strategies. Previous work indicates that many cytoskeletal structures are affected by cold preservation and reperfusion, including membrane-rich ezrin-associated complexes. The aim of this study was to investigate whether the sublamellar cytoskeletal protein ezrin is causally involved in cold preservation injury in renal tubule epithelial cells.

METHODS

We created a stably transfected cell line (LLC-EZ) using the pig kidney proximal tubular epithelial cell line (LLC-PK1), which constitutively overexpresses wild-type ezrin. These cells were cold stored in University of Wisconsin Solution and reperfused in vitro to model renal tubule preservation injury, which was assessed by biochemical, metabolic, functional, and structural endpoints.

RESULTS

Overexpression of ezrin increased cell viability (lactate dehydrogenase release), mitochondrial activity (ATP synthesis, dehydrogenase activity, and inner mitochondrial membrane potential), and protected the structure of cell membrane microvilli and mitochondria after cold storage preservation injury. Reperfusion-induced apoptosis was also significantly reduced in LLC-EZ cells overexpressing ezrin.

CONCLUSIONS

Enhanced ezrin expression protects tubule epithelial cells from cold storage preservation injury, possibly by membrane or mitochondrial mechanisms.

Hsp27 inhibits sublethal, Src-mediated renal epithelial cell injury

Disruption of cell contact sites in renal epithelial cells contributes to organ dysfunction after ischemia. We hypothesized that heat shock protein 27 (Hsp27), a known cytoprotectant protein, preserves cell architecture and cell contact site function during ischemic stress. To test this hypothesis, renal epithelial cells were subjected to transient ATP depletion, an in vitro model of ischemia-reperfusion injury. Compared with control, selective Hsp27 overexpression significantly preserved cell-cell junction function during metabolic stress as evidenced by reduced stress-mediated redistribution of the adherens junction protein E-cadherin, higher transepithelial electrical resistance, and lower unidirectional flux of lucifer yellow. Hsp27 overexpression also preserved paxillin staining within focal adhesion complexes and significantly decreased cell detachment during stress. Surprisingly, Hsp27, an F-actin-capping protein, only minimally reduced stress induced actin cytoskeleton collapse. In contrast to Hsp27 overexpression, siRNA-mediated knockdown had the opposite effect on these parameters. Since ischemia activates c-Src, a tyrosine kinase that disrupts both cell-cell and cell-substrate interactions, the relationship between Hsp27 and c-Src was examined. Although Hsp27 and c-Src did not coimmunoprecipitate and Hsp27 overexpression failed to inhibit whole cell c-Src activation during injury, manipulation of Hsp27 altered active c-Src accumulation at cell contact sites. Specifically, Hsp27 overexpression reduced, whereas Hsp27 knockdown increased active p-(416)Src detected at contact sites in intact cells as well as in a purified cell membrane fraction. Together, this evidence shows that Hsp27 overexpression prevents sublethal REC injury at cell contact sites possibly by a c-Src-dependent mechanism. Further exploration of the biochemical link between Hsp27 and c-Src could yield therapeutic interventions for ameliorating ischemic renal cell injury and organ dysfunction.

Kidney-specific reconstitution of the A1 adenosine receptor in A1 adenosine receptor knockout mice reduces renal ischemia-reperfusion injury

Genetic deletion of the adenosine A1 receptor (A1AR) increased renal injury following ischemia-reperfusion injury suggesting that receptor activation is protective in vivo. Here we tested this hypothesis by expressing the human-A(1)AR in A(1)AR knockout mice. Renal ischemia-reperfusion was induced in knockout mice 2 days after intrarenal injection of saline or a lentivirus encoding enhanced green fluorescent protein (EGFP) or EGFP-human-A(1)AR. We found that the latter procedure induced a robust expression of the reporter protein in the kidneys of knockout mice. Mice with kidney-specific human-A(1)AR reconstitution had significantly lower plasma creatinine, tubular necrosis, apoptosis, and tubular inflammation as evidenced by decreased leukocyte infiltration, pro-inflammatory cytokine, and intercellular adhesion molecule-1 expression in the kidney following injury compared to mice injected with saline or the control lentivirus. Additionally, there were marked disruptions of the proximal tubule epithelial filamentous (F)-actin cytoskeleton in both sets of control mice upon renal injury, whereas the reconstituted mice had better preservation of the renal tubule actin cytoskeleton, which co-localized with the human-A(1)ARs. Consistent with reduced renal injury, there was a significant increase in heat shock protein-27 expression, also co-localizing with the preserved F-actin cytoskeleton. Our findings suggest that selective expression of cytoprotective A(1)ARs in the kidney can attenuate renal injury.

Acute kidney injury in children

Acute kidney injury (AKI) (previously called acute renal failure) is characterized by a reversible increase in the blood concentration of creatinine and nitrogenous waste products and by the inability of the kidney to regulate fluid and electrolyte homeostasis appropriately. The incidence of AKI in children appears to be increasing, and the etiology of AKI over the past decades has shifted from primary renal disease to multifactorial causes, particularly in hospitalized children. Genetic factors may predispose some children to AKI. Renal injury can be divided into pre-renal failure, intrinsic renal disease including vascular insults, and obstructive uropathies. The pathophysiology of hypoxia/ischemia-induced AKI is not well understood, but significant progress in elucidating the cellular, biochemical and molecular events has been made over the past several years. The history, physical examination, and laboratory studies, including urinalysis and radiographic studies, can establish the likely cause(s) of AKI. Many interventions such as 'renal-dose dopamine' and diuretic therapy have been shown not to alter the course of AKI. The prognosis of AKI is highly dependent on the underlying etiology of the AKI. Children who have suffered AKI from any cause are at risk for late development of kidney disease several years after the initial insult. Therapeutic interventions in AKI have been largely disappointing, likely due to the complex nature of the pathophysiology of AKI, the fact that the serum creatinine concentration is an insensitive measure of kidney function, and because of co-morbid factors in treated patients. Improved understanding of the pathophysiology of AKI, early biomarkers of AKI, and better classification of AKI are needed for the development of successful therapeutic strategies for the treatment of AKI.

Identification of differential gene expression during porcine conceptus rapid trophoblastic elongation and attachment to uterine luminal epithelium

Early embryonic development in the pig is characterized by a rapid elongation of the conceptus trophectoderm on days 11-12 of gestation. Initially, the conceptus trophoblast is morphologically rearranged from a 10-mm sphere into a tubular shape, transitioning into a thin filamentous form >150 mm in length in 2-3 h, followed by continued expansion within the uterine lumen for several days. Conceptus elongation is critical for establishing adequate placental surface area needed for embryo and fetal survival throughout gestation. The objective of this study was to characterize conceptus gene expression during trophoblastic elongation and the early attachment to the uterine endometrium on days 11-14 of gestation with the GeneChip Porcine Genome Array. In all, 3,759 different probe sets were statistically different in at least one comparison [spherical vs. tubular, spherical vs. day 12 filamentous (D12F), spherical vs. day 14 filamentous (D14F), tubular vs. D12F, tubular vs. D14F, and D12F vs. D14F]. When restricted to the spherical vs. D12F and D12F vs. D14F comparisons, 482 and 232 genes, respectively, were statistically different with greater than twofold change in expression. Utilization of k-means clustering, in addition to the Database for Annotation, Visualization, and Integrated Discovery (DAVID), identified genes of interest. Quantitative RT-PCR expression profiles for interferon-gamma (IFNG), heat shock protein 27 kDa (HSPB1), angiomotin, B-cell linker (BLNK), chemokine ligand 14 (CXCL14), parathyroid hormone-like hormone (PTHLH), and maspin were supportive of the GeneChip Porcine Genome Array data.

Oxidant-mediated apoptosis in proximal tubular epithelial cells following ATP depletion and recovery

Oxidant-mediated apoptosis has been implicated in renal injury due to ischemia reperfusion (IR); however, the apoptotic signaling pathways following IR have been incompletely defined. The purpose of this study was to examine the role of oxidants on cell death in a model of in vitro simulated IR injury in renal proximal tubular epithelial cells by analyzing the effects of a cell-permeable superoxide dismutase mimetic, manganese (III) tetrakis (1-methyl-4-pyridyl) porphyrin pentachloride (MnTmPyP). Renal proximal tubular epithelial cells were ATP depleted for 2, 4, or 6 h, followed by 2 h of recovery. We found that MnTmPyP was effective in attenuating cytotoxicity (P<0.001) and decreasing steady-state oxidant levels (P<0.001) and apoptotic cell death (P<0.001) following ATP depletion-recovery. MnTmPyP treatment prevented the early cytosolic release of cytochrome c and increased Bcl-2 protein levels following short durations of ATP depletion-recovery. After longer periods of ATP depletion-recovery, we observed a significant increase in TNF-alpha protein levels (P<0.001) and caspase-8 activation (P<0.001), both of which were decreased (P<0.001) by treatment with MnTmPyP. Our results suggest that oxidant mediated apoptosis via the mitochondrial pathway during the early phase of ATP depletion and by activation of the receptor-mediated apoptotic pathway following longer durations of injury.

20-HETE-mediated cytotoxicity and apoptosis in ischemic kidney epithelial cells

20-HETE, a metabolite of arachidonic acid, has been implicated as a mediator of free radical formation and tissue death following ischemia-reperfusion (IR) injury in the brain and heart. The present study examined the role of this pathway in a simulated IR renal injury model in vitro. Modified self-inactivating lentiviral vectors were generated to stably overexpress murine Cyp4a12 following transduction into LLC-PK(1) cells (LLC-Cyp4a12). We compared the survival of control and transduced LLC-PK(1) cells following 4 h of ATP depletion and 2 h of recovery in serum-free medium. ATP depletion-recovery of LLC-Cyp4a12 cells resulted in a significantly higher LDH release (P < 0.05) compared with LLC-enhanced green fluorescent protein (EGFP) cells. Treatment with the SOD mimetic MnTMPyP (100 microM) resulted in decreased cytotoxicity in LLC-Cyp4a12 cells. The selective 20-HETE inhibitor HET-0016 (10 microM) also inhibited cytotoxicity significantly (P < 0.05) in LLC-Cyp4a12 cells. Dihydroethidium fluorescence showed that superoxide levels were increased to the same degree in LLC-EGFP and LLC-Cyp4a12 cells after ATP depletion-recovery compared with control cells and that this increase was inhibited by MnTMPyP. There was a significant increase (P < 0.05) of caspase-3 cleavage, an effector protease of the apoptotic pathway, in the LLC-Cyp4a12 vs. LLC-EGFP cells (P < 0.05). This was abolished in the presence of HET-0016 (P < 0.05) or MnTMPyP (P < 0.01). These results demonstrate that 20-HETE overexpression can significantly exacerbate the cellular damage that is associated with renal IR injury and that the programmed cell death is mediated by activation of caspase-3 and is partially dependent on enhanced CYP4A generation of free radicals.

Small heat shock protein Hsp27 prevents heat-induced aggregation of F-actin by forming soluble complexes with denatured actin

Previously, we have shown that the small heat shock protein with apparent molecular mass 27 kDa (Hsp27) does not affect the thermal unfolding of F-actin, but effectively prevents aggregation of thermally denatured F-actin [Pivovarova AV, Mikhailova VV, Chernik IS, Chebotareva NA, Levitsky DI & Gusev NB (2005) Biochem Biophys Res Commun331, 1548-1553], and supposed that Hsp27 prevents heat-induced aggregation of F-actin by forming soluble complexes with denatured actin. In the present work, we applied dynamic light scattering, analytical ultracentrifugation and size exclusion chromatography to examine the properties of complexes formed by denatured actin with a recombinant human Hsp27 mutant (Hsp27-3D) mimicking the naturally occurring phosphorylation of this protein at Ser15, Ser78, and Ser82. Our results show that formation of these complexes occurs upon heating and accompanies the F-actin thermal denaturation. All the methods show that the size of actin-Hsp27-3D complexes decreases with increasing Hsp27-3D concentration in the incubation mixture and that saturation occurs at approximately equimolar concentrations of Hsp27-3D and actin. Under these conditions, the complexes exhibit a hydrodynamic radius of approximately 16 nm, a sedimentation coefficient of 17-20 S, and a molecular mass of about 2 MDa. It is supposed that Hsp27-3D binds to denatured actin monomers or short oligomers dissociated from actin filaments upon heating and protects them from aggregation by forming relatively small and highly soluble complexes. This mechanism might explain how small heat shock proteins prevent aggregation of denatured actin and by this means protect the cytoskeleton and the whole cell from damage caused by accumulation of large insoluble aggregates under heat shock conditions.

Renal tubule necrosis and apoptosis modulation by A1 adenosine receptor expression

We have shown that A1 adenosine receptors (A1ARs) are cytoprotective against renal tubular necrosis and apoptosis both in vivo and in vitro. To study the role of A1AR numbers on renal epithelial cell survival, we stably overexpressed the human A1 receptor in a porcine renal tubule cell line and utilized primary cultures of proximal tubules obtained from A1AR knockout mice. Receptor-overexpressing cells were protected against peroxide-induced necrosis and tumor necrosis factor-alpha/cycloheximide-induced apoptosis. Conversely, cultured proximal tubule cells from receptor knockout mice showed more necrotic and apoptotic cell loss than corresponding cells from wild-type mice. Overexpression of the receptor resulted in a significantly higher baseline expression of both total and phosphorylated heat-shock protein (HSP)27; the latter due to A1 receptor enhancement of p38 and AP2 mitogen-activated protein kinase activities. The resistance to cell death in the porcine cells was reversed by selective A1 receptor antagonism and by a selective inhibitor of HSP synthesis. Receptor activation in wild-type mice in vivo led to increased total and phosphorylated HSP27, whereas receptor knockout mice showed decreased baseline and adenosine-mediated HSP phosphorylation. These studies show that endogenous A1AR activation produces cytoprotective effects in renal proximal tubules by modulating HSP27 signaling pathways.

Modulation of renal cell injury by heat shock proteins: lessons learned from the immature kidney

The mechanisms that underlie tolerance to injury in immature animals and tissues have been a subject of interest since 1670. Observations in neonatal units that premature infants are less prone to develop acute renal failure than adults in critical care units have prompted a series of investigations. Although initially attributed to metabolic adaptation such as increased glycolytic capacity and preservation of high energy phosphate, more recent studies have indicated a prominent role for the heat shock response. Observed modulations of injury by heat shock proteins in the immature kidney have significant implications for advancement of our understanding of renal cell injury in both adults and children.

Expression and distribution of HuR during ATP depletion and recovery in proximal tubule cells

Human antigen R (HuR) is a nucleocytoplasmic shuttling protein that binds to and stabilizes mRNAs containing adenine- and uridine-rich elements. Under normal growth conditions, the bulk of HuR is maintained in the nucleus, but under conditions of cell stress, HuR may become more prevalent in the cytosol, where it can stabilize mRNA and regulate gene expression. We have studied the behavior of HuR in LLC-PK1 proximal tubule cells subjected to ATP depletion and recovery. ATP depletion resulted in detectable net movement of HuR out of the nucleus, followed by net movement of HuR back into the nucleus on reversion to normal growth medium. In addition, HuR protein levels increased during energy depletion. This increase was inhibited by cycloheximide and was independent of HuR mRNA levels, since no change was noted in the quantity of HuR transcript. In contrast, recovery in normal growth medium resulted in increased HuR mRNA, while protein levels decreased to baseline. This suggested a mechanism by which previously injured cells maintained normal levels of HuR but were primed to rapidly translate increased amounts of protein on subsequent insults. Indeed, a second round of ATP depletion resulted in heightened HuR protein translation at a rate more rapid than during the first insult. Additionally, the second insult produced increased HuR levels in the cytoplasm while still maintaining high amounts in the nucleus, indicating that nuclear export may not be required on subsequent insults. These results suggest a role for HuR in protecting kidney epithelia from injury during ischemic stress.

Role of the renin-angiotensin system in the development of the ureteric bud and renal collecting system

Genetic, biochemical and physiological studies have demonstrated that the renin-angiotensin system (RAS) plays a fundamental role in kidney development. All of the components of the RAS are expressed in the metanephros. Mutations in the genes encoding components of the RAS in mice or pharmacological inhibition of RAS in animals or humans cause diverse congenital abnormalities of the kidney and lower urinary tract. The latter include renal vascular abnormalities, abnormal glomerulogenesis, renal papillary hypoplasia, hydronephrosis, aberrant UB budding, duplicated collecting system, and urinary concentrating defect. Thus, the actions of angiotensin (ANG) II during kidney development are pleiotropic both spatially and temporally. Whereas the role of ANG II in renovascular and glomerular development has received much attention, little is known about the potential role of ANG II and its receptors in the morphogenesis of the collecting system. In this review, we discuss recent genetic and functional evidence gathered from transgenic knockout mice and in vitro organ and cell culture implicating the RAS in the development of the ureteric bud and collecting ducts. A novel conceptual framework has emerged from this body of work which states that stroma-derived ANG II elicits activation of AT(1)/AT(2) receptors expressed on the ureteric bud to stimulate branching morphogenesis as well as collecting duct elongation and papillogenesis.

Molecular markers of trichloroethylene-induced toxicity in human kidney cells

Difficulties in evaluation of trichloroethylene (TRI)-induced toxicity in humans and extrapolation of data from laboratory animals to humans are due to the existence of multiple target organs, multiple metabolic pathways, sex-, species-, and strain-dependent differences in both metabolism and susceptibility to toxicity, and the lack or minimal amount of human data for many target organs. The use of human tissue for mechanistic studies is thus distinctly advantageous. The kidneys are one target organ for TRI and metabolism by the glutathione (GSH) conjugation pathway is responsible for nephrotoxicity. The GSH conjugate is processed further to produce the cysteine conjugate, S-(1,2-dichlorovinyl)-l-cysteine (DCVC), which is the penultimate nephrotoxic species. Confluent, primary cultures of human proximal tubular (hPT) cells were used as the model system. Although cells in log-phase growth, which are undergoing more rapid DNA synthesis, would give lower LD(50) values, confluent cells more closely mimic the in vivo proximal tubule. DCVC caused cellular necrosis only at relatively high doses (>100 muM) and long incubation times (>24 h). In contrast, both apoptosis and enhanced cellular proliferation occurred at relatively low doses (10-100 muM) and early incubation times (2-8 h). These responses were associated with prominent changes in expression of several proteins that regulate apoptosis (Bcl-2, Bax, Apaf-1, Caspase-9 cleavage, PARP cleavage) and cellular growth, differentiation and stress response (p53, Hsp27, NF-kappaB). Effects on p53 and Hsp27 implicate function of protein kinase C, the mitogen activated protein kinase pathway, and the cytoskeleton. The precise pattern of expression of these and other proteins can thus serve as molecular markers for TRI exposure and effect in human kidney.

Effects of small heat shock proteins on the thermal denaturation and aggregation of F-actin

Effect of recombinant chicken small heat shock protein with molecular mass 24 kDa (Hsp24) and recombinant human small heat shock protein with molecular mass 27 kDa (Hsp27) on the heat-induced denaturation and aggregation of skeletal F-actin was analyzed by means of differential scanning calorimetry and light scattering. All small heat shock proteins did not affect thermal unfolding of F-actin measured by differential scanning calorimetry, but effectively prevented aggregation of thermally denatured actin. Small heat shock protein formed stable complexes with denatured (but not with intact) F-actin. The size of these highly soluble complexes was smaller than the size of intact F-actin filaments. It is supposed that protective effect of small heat shock proteins on the cytoskeleton is at least partly due to prevention of aggregation of denatured actin.

Cloning, characterization, and heat stress-induced redistribution of a protein homologous to human hsp27 in the zebrafish Danio rerio

Hsp27 is a small heat shock protein (shsp) regulating stress tolerance and increasingly thought to play roles in tissue homeostasis and differentiation. The zebrafish Danio rerio is an important model for the study of developmental processes, but little is known regarding shsps in this animal. Here, we report the sequence, expression, regulation, and function of a zebrafish protein (zfHsp27) homologous to human Hsp27. zfHsp27 contains three conserved phosphorylatable serines and a cysteine important for regulation of apoptosis, but it lacks much of a C-terminal tail domain and shows low homology in two putative actin interacting domains that are features of mammalian Hsp27. zfHsp27 mRNA is most abundant in adult skeletal muscle and heart and is upregulated during early embryogenesis. zfHsp27 expressed in mammalian fibroblasts was phosphorylated in response to heat stress and anisomycin, and this phosphorylation was prevented by treatment with SB202190, an inhibitor of p38 MAPK. Expression of zfHsp27 and human Hsp27 in mammalian fibroblasts promoted a similar degree of tolerance to heat stress. zfHsp27 fusion proteins entered the nucleus and associated with the cytoskeleton of heat stressed cells in vitro and in zebrafish embryos. These results reveal conservation in regulation and function of mammalian and teleost Hsp27 proteins and define zebrafish as a new model for the study of Hsp27 function.

HSP70 binding modulates detachment of Na-K-ATPase following energy deprivation in renal epithelial cells

The molecular mechanisms associated with reestablishment of renal epithelial polarity after injury remain incompletely delineated. Stress proteins may act as molecular chaperones, potentially modulating injury or enhancing recovery. We tested whether overexpression of heat shock protein 70 (HSP70) would stabilize Na-K-ATPase attachment to the cytoskeleton, under conditions of ATP depletion, and whether a direct association existed between Na-K-ATPase and HSP70 in cultured renal epithelial cells. LLC-PK1 cells were transfected with a tagged HSP70 (70FLAG) or vector alone (VA). Detachment of Na-K-ATPase was detected in Triton soluble lysate after ATP depletion. 70FLAG cells demonstrated a significant (P < 0.01) decrease in detachment of Na-K-ATPase after either 2 or 4 h of ATP depletion. Interactions between HSP70 and Na-K-ATPase were determined by coimmunoprecipitation of 70FLAG and Na-K-ATPase, by direct and competitive binding assays and by immunocytochemical localization. Binding of HSP70 and Na-K-ATPase increased dramatically following injury. Interactions were: 1) reversible; 2) reciprocal to changes in the HSP70 binding protein clathrin; and 3) present only when ATP turnover was inhibited in cell lysate, an established characteristic of HSP binding. These studies indicate that 1) overexpression of HSP70 is associated with decreased detachment of Na-K-ATPase from the cytoskeleton following injury; 2) HSP70 binds to Na-K-ATPase; and 3) binding of HSP70 to Na-K-ATPase is dynamic and specific, increasing in response to injury and decreasing during recovery. Interaction between the molecular chaperone HSP70 and damaged or displaced Na-K-ATPase may represent a fundamental cellular mechanism underlying maintenance and recovery of renal tubule polarity following energy deprivation.

Resistance to ischemic acute renal failure in the Brown Norway rat: a new model to study cytoprotection

BACKGROUND

An in vivo model of intrinsic resistance to ischemia could be invaluable to define how specific pathways to injury or putative protectors from injury affect the severity of acute renal failure (ARF). The purpose of this study was to determine whether separate rat strains had differential sensitivity to renal ischemia, characterize the extent of protection, and begin to define differences in gene expression that might impact on the severity of ARF.

METHODS

The sensitivity to 45 minutes of renal ischemia in Sprague-Dawley rat (SD) was compared with 2 lines of Brown-Norway rats (BN/Mcw, BN/Hsd). Constitutive and inducible stress protein expression was compared between strains.

RESULTS

At 24 hours' reperfusion, SD rats had higher creatinine (3.4 mg/dL), elevated Na and water excretion, and proximal tubule necrosis. Both strains of BN rats were resistant to loss of renal function (Scr = 0.9 mg/dL at 24 hours' reflow) and had preserved renal morphology. BN rats had no redistribution of Na,K-ATPase into detergent-soluble cortical extracts found early (15 minutes) after ischemia in SD rats. Hsc73 expression did not differ between strains and was not induced by ischemia. Compared with SD, induction of Hsp25 and 72 by renal ischemia was blunted in both BN strains. Constitutive Hsp25 was higher in both BN-Mcw and BN-Hsd compared with SD rat kidney. Constitutive Hsp72 was significantly higher only in BN-Mcw kidneys. Immunohistochemistry showed baseline Hsp72 and 25 expression was increased in proximal tubules of BN-Mcw versus SD.

CONCLUSION

BN rat kidney is resistant to ischemic injury and provides a new model for studying cytoprotective mechanisms. Initial study of strain-specific gene expression suggests particular stress proteins are among the potential mechanisms contributing to protection against ARF.

p38 mitogen-activated protein kinase protects glomerular epithelial cells from complement-mediated cell injury

In the passive Heymann nephritis (PHN) model of rat membranous nephropathy, complement C5b-9 causes sublytic injury of glomerular epithelial cells (GEC). We previously showed that sublytic concentration of C5b-9 triggers a variety of biological events in GEC. In the current study, we demonstrate that complement activates p38 MAPK in GEC and address the role of p38 in complement-mediated cell injury. When cultured rat GEC were stimulated with complement, p38 kinase activity and phosphorylation were increased by approximately 2.4-fold, compared with control. Treatment with p38 inhibitors significantly augmented complement-mediated cytotoxicity. In contrast, when the constitutively active mutant of transforming growth factor-beta-activated kinase 1 (TAK1), a kinase upstream of p38, was expressed in GEC in an inducible manner, cytotoxicity was significantly reduced, compared with uninduced cells. p38 inhibitors abolished the protective effect of TAK1 expression. By analogy to cultured cells, p38 activity was also increased in glomeruli from rats with PHN and treatment with the p38 inhibitor FR-167653 increased proteinuria. Complement induced phosphorylation of MAPK-associated protein kinase-2 (MAPKAPK-2), a kinase downstream of p38 in GEC. Heat shock protein (HSP27) is a cytoskeleton-interacting substrate of MAPKAPK-2. Overexpression of the wild-type HSP27, but not a non-phosphorylatable mutant, markedly reduced complement-mediated GEC injury. In summary, complement activates p38 MAPK in GEC in vitro and in glomeruli from rats with PHN. The activation of p38 MAPK appears to be cytoprotective for GEC against complement-mediated GEC injury. Phosphorylation of HSP27 may mediate this cytoprotection.