Heat shock protein 27 associates with basolateral cell boundaries in heat-shocked and ATP-depleted epithelial cells

Regulation of Epithelial and Endothelial Barriers by Molecular Chaperones

The integrity and permeability of epithelial and endothelial barriers depend on the formation of tight junctions, adherens junctions, and a junction-associated cytoskeleton. The establishment of this junction-cytoskeletal module relies on the correct folding and oligomerization of its protein components. Molecular chaperones are known regulators of protein folding and complex formation in different cellular compartments. Mammalian cells possess an elaborate chaperone network consisting of several hundred chaperones and co-chaperones. Only a small part of this network has been linked, however, to the regulation of intercellular adhesions, and the systematic analysis of chaperone functions at epithelial and endothelial barriers is lacking. This review describes the functions and mechanisms of the chaperone-assisted regulation of intercellular junctions. The major focus of this review is on heat shock protein chaperones, their co-chaperones, and chaperonins since these molecules are the focus of the majority of the articles published on the chaperone-mediated control of tissue barriers. This review discusses the roles of chaperones in the regulation of the steady-state integrity of epithelial and vascular barriers as well as the disruption of these barriers by pathogenic factors and extracellular stressors. Since cytoskeletal coupling is essential for junctional integrity and remodeling, chaperone-assisted assembly of the actomyosin cytoskeleton is also discussed.

Junctional complexes in epithelial cells: sentinels for extracellular insults and intracellular homeostasis

The cell-cell and cell-ECM junctions within the epithelial tissues are crucial anchoring structures that provide architectural stability, mechanical resistance, and permeability control. Their indispensable role as signaling hubs orchestrating cell shape-related changes such as proliferation, differentiation, migration, and apoptosis has also been well recognized. However, growing amount of evidence now suggests that the multitasking nature of epithelial junctions extends well beyond anchorage-dependent or cell shape change-related biological processes. In this review, we discuss the emerging roles of junctional complexes in regulating innate immune defense, stress resistance, and intracellular proteostasis of the epithelial cells, with emphasis on the upstream regulation of epithelial junctions on various aspects of the epithelial barrier.

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.

Structure and properties of chimeric small heat shock proteins containing yellow fluorescent protein attached to their C-terminal ends

Recombinant chimeras of small heat shock proteins (sHsp) HspB1, HspB5, and HspB6 containing enhanced yellow fluorescent protein (EYFP) attached to their C-terminal ends were constructed and purified. Some properties of these chimeras were compared with the corresponding properties of the same chimeras containing EYFP attached to the N-terminal end of sHsp. The C-terminal fluorescent chimeras of HspB1 and HspB5 tend to aggregate and form a heterogeneous mixture of oligomers. The apparent molecular weight of the largest C-terminal chimeric oligomers was higher than that of the corresponding N-terminal chimeras or of the wild-type proteins; however, both homooligomers of N-terminal chimeras and homooligomers of C-terminal chimeras contained fewer subunits than the wild-type HspB1 or HspB5. Both N-terminal and C-terminal chimeras of HspB6 form small oligomers with an apparent molecular weight of 73-84 kDa. The C-terminal chimeras exchange their subunits with homologous wild-type proteins. Heterooligomers formed by the wild-type HspB1 (or HspB5) and the C-terminal chimeras of HspB6 differ in size and composition from heterooligomers formed by the corresponding wild-type proteins. As a rule, the N-terminal chimeras possess similar or slightly higher chaperone-like activity than the corresponding wild-type proteins, whereas the C-terminal chimeras always have a lower chaperone-like activity than the wild-type proteins. It is concluded that attachment of EYFP to either N-terminal or C-terminal ends of sHsp affects their oligomeric structure, their ability to form heterooligomers, and their chaperone-like activity. Therefore, the data obtained with fluorescent chimeras of sHsp expressed in the cell should be interpreted with caution.

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.

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.

Dynamic movements of Ro52 cytoplasmic bodies along microtubules

The RING-finger protein Ro52/TRIM21 is known as an autoantigen and is recognized by anti-Ro/SSA antibodies, which are commonly found in patients with Sjögren's syndrome and systemic lupus erythematosus. Recently, Ro52 has been shown to localize to distinct structures called cytoplasmic bodies and function as an E3 ubiquitin ligase. However, the Ro52 cytoplasmic bodies have not been well characterized. In this study, we investigated the Ro52 cytoplasmic bodies using fluorescence microscopy. This analysis revealed that the Ro52 cytoplasmic bodies are diffusely located in the cytoplasm and exist independently of TRIM5alpha cytoplasmic bodies. Our results further showed that the Ro52 cytoplasmic bodies are not stained with MitoTracker dye and are not colocalized with the proteasome subunit Rpt5, the caveolae component caveolin-1, the endosome markers (EEA1, Rab5, and Rab7), and the lysosome marker LAMP2. These results indicate that the Ro52 cytoplasmic bodies are not mitochondria, proteasome-enriched structures, caveolae, endosomes, or lysosomes. Importantly, the Ro52 cytoplasmic bodies are highly motile and are located along the microtubule network. These results suggest that the Ro52 cytoplasmic bodies are unidentified structures that are transported along the microtubule network.

Stress proteins and oxidative damage in a renal derived cell line exposed to inorganic mercury and lead

A close link between stress protein up-regulation and oxidative damage may provide a novel therapeutic tool to counteract nephrotoxicity induced by toxic metals in the human population, mainly in children, of industrialized countries. Here we analysed the time course of the expression of several heat shock proteins, glucose-regulated proteins and metallothioneins in a rat proximal tubular cell line (NRK-52E) exposed to subcytotoxic doses of inorganic mercury and lead. Concomitantly, we used morphological and biochemical methods to evaluate metal-induced cytotoxicity and oxidative damage. In particular, as biochemical indicators of oxidative stress we detected reactive oxygen species (ROS) and nitrogen species (RNS), total glutathione (GSH) and glutathione-S-transferase (GST) activity. Our results clearly demonstrated that mercury increases ROS and RNS levels and the expressions of Hsp25 and inducible Hsp72. These findings are corroborated by evident mitochondrial damage, apoptosis or necrosis. By contrast, lead is unable to up-regulate Hsp72 but enhances Grp78 and activates nuclear Hsp25 translocation. Furthermore, lead causes endoplasmic reticulum (ER) stress, vacuolation and nucleolar segregation. Lastly, both metals stimulate the over-expression of MTs, but with a different time course. In conclusion, in NRK-52E cell line the stress response is an early and metal-induced event that correlates well with the direct oxidative damage induced by mercury. Indeed, different chaperones are involved in the specific nephrotoxic mechanism of these environmental pollutants and work together for cell survival.

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.

HSP27 is involved in the pathogenesis of kidney tubulointerstitial fibrosis

We hypothesized that heat shock protein 27 (HSP27), a small heat shock protein with actin-remodeling properties, is involved in the pathogenesis of kidney tubulointerstitial fibrosis. We first examined its expression in the rat unilateral ureteral obstruction (UUO) model of kidney fibrosis and epithelial-to-mesenchymal transition (EMT). Immunoblot analyses showed that UUO resulted in significant upregulation of TGF-beta1, alpha-smooth muscle actin (alpha-SMA), total and phosphorylated HSP27, and phosphorylated p38MAPK. Immunofluorescence studies showed that HSP27 costained with TGF-beta1, alpha-SMA, and E-cadherin in areas of tubulointerstitial injury. We next attempted to translate these studies in an in vitro model of EMT using rat proximal tubular epithelial cells (NRK52E). TGF-beta1 (20 ng/ml) treatment resulted in EMT (upregulation of alpha-SMA and downregulation of E-cadherin) and significant upregulation of total and phosphorylated HSP27 and p38MAPK after 3 days. Real-time PCR analyses showed that HSP27, vimentin, and fibronectin increased whereas E-cadherin mRNA levels decreased. Double-staining immunofluorescence studies showed intracytoplasmic colocalization of HSP27 with both F-actin and E-cadherin in cells undergoing EMT. HSP27 overexpression by transient transfection significantly increased E-cadherin while decreasing E-cadherin repressor Snail levels. In aggregate, these studies show that HSP27 is involved in the pathogenesis of TGF-beta1-induced EMT and chronic tubulointerstitial fibrosis. HSP27 overexpression may delay injury by upregulating E-cadherin through downregulation of Snail.

Small heat shock protein Hsp27 is required for proper heart tube formation

The small heat shock protein Hsp27 has been shown to be involved in a diverse array of cellular processes, including cellular stress response, protein chaperone activity, regulation of cellular glutathione levels, apoptotic signaling, and regulation of actin polymerization and stability. Furthermore, mutation within Hsp27 has been associated with the human congenital neuropathy Charcot-Marie Tooth (CMT) disease. Hsp27 is known to be expressed in developing embryonic tissues; however, little has been done to determine the endogenous requirement for Hsp27 in developing embryos. In this study, we show that depletion of XHSP27 protein results in a failure of cardiac progenitor fusion resulting in cardia bifida. Furthermore, we demonstrate a concomitant disorganization of actin filament organization and defects in myofibril assembly. Moreover, these defects are not associated with alterations in specification or differentiation. We have thus demonstrated a critical requirement for XHSP27 in developing cardiac and skeletal muscle tissues.

Recruitment of phosphorylated small heat shock protein Hsp27 to nuclear speckles without stress

During stress, the mammalian small heat shock protein Hsp27 enters cell nuclei. The present study examines the requirements for entry of Hsp27 into nuclei of normal rat kidney (NRK) renal epithelial cells, and for its interactions with specific nuclear structures. We find that phosphorylation of Hsp27 is necessary for the efficient entry into nuclei during heat shock but not sufficient for efficient nuclear entry under control conditions. We further report that Hsp27 is recruited to an RNAse sensitive fraction of SC35 positive nuclear speckles, but not other intranuclear structures, in response to heat shock. Intriguingly, Hsp27 phosphorylation, in the absence of stress, is sufficient for recruitment to speckles found in post-anaphase stage mitotic cells. Additionally, pseudophosphorylated Hsp27 fused to a nuclear localization peptide (NLS) is recruited to nuclear speckles in unstressed interphase cells, but wildtype and nonphosphorylatable Hsp27 NLS fusion proteins are not. The expression of NLS-Hsp27 mutants does not enhance colony forming abilities of cells subjected to severe heat shock, but does regulate nuclear speckle morphology. These data demonstrate that phosphorylation, but not stress, mediates Hsp27 recruitment to an RNAse soluble fraction of nuclear speckles and support a site-specific role for Hsp27 within the nucleus.

Migratory marker expression in fibroblast foci of idiopathic pulmonary fibrosis

Background

Fibroblast foci (FF) are considered a relevant morphologic marker of idiopathic pulmonary fibrosis/usual interstitial pneumonia (IPF/UIP), and are recognised as sites where fibrotic responses are initiated and/or perpetuated in this severe disease. Despite their relevance, the cellular and molecular mechanisms responsible for the formation of FF and their role in tissue remodelling are poorly defined. In previous studies we have provided evidence of abnormal activation of the wnt-signaling-pathway in IPF/UIP that is centred on FF and the overlying epithelium. This important morphogenetic pathway is able to trigger epithelial-mesenchymal-transition (EMT), a mechanism involved in developmental and metastatic processes, which is also potentially involved in pulmonary fibrosis.

Methods

Since EMT is characterised by enhancement of migratory potential of cells, we investigated the molecular profile of FF in 30 biopsies of IPF/UIP and a variety of control samples, focussing on the immunohistochemical expression of three molecules involved in cell motility and invasiveness, namely laminin-5-γ2-chain, fascin, and heat-shock-protein-27.

Results

We provide evidence that in UIP these three molecules are abnormally expressed in discrete clusters of bronchiolar basal cells precisely localised in FF. These cellular clusters expressed laminin-5-γ2-chain and heat-shock-protein-27 at very high levels, forming characteristic three-layered lesions defined as "sandwich-foci" (SW-FF). Upon quantitative analysis SW-FF were present in 28/30 UIP samples, representing more than 50% of recognisable FF in 21/30, but were exceedingly rare in a wide variety of lung pathologies examined as controls. In UIP, SW-FF were often observed in areas of microscopic honeycombing, and were also found at the interface between normal lung tissue and areas of dense scarring.

Conclusion

These molecular abnormalities strongly suggest that SW-FF represent the leading edge of pulmonary remodelling, where abnormal migration and re-epithelialisation take place, and that abnormal proliferation and migration of bronchiolar basal cells have a major role in the remodelling process characterising IPF/UIP. Further investigations will assess their possible use as reliable markers for better defining the UIP-pattern in difficult cases.

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.

p38 MAPK/HSP25 signaling mediates cadmium-induced contraction of mesangial cells and renal glomeruli

The environmental pollutant cadmium affects human health, with the kidney being a primary target. In addition to proximal tubules, glomeruli and their contractile mesangial cells have also been identified as targets of cadmium nephrotoxicity. Glomerular contraction is thought to contribute to reduced glomerular filtration, a characteristic of cadmium nephrotoxicity. Because p38 MAPK/HSP25 signaling has been implicated in smooth muscle contraction, we examined its role in cadmium-induced contraction of mesangial cells. We report that exposure of mesangial cells to cadmium resulted in 1) cell contraction, 2) activation of MAP kinases, 3) increased HSP25 phosphorylation coincident with p38 MAP kinase activation, 4) sequential phosphorylation of the two phosphorylation sites of mouse HSP25 with Ser15 being phosphorylated before Ser86, 5) reduction of oligomeric size of HSP25, and 6) association of HSP25 with microfilaments. Exposure of isolated rat glomeruli to cadmium also resulted in contraction and increased HSP25 phosphorylation. The cadmium-induced responses were inhibited by the specific p38 MAP kinase inhibitor SB-203580, and cadmium-induced phosphorylation of HSP25 was inhibited by expression of a dominant-negative p38 MAP kinase mutant. These findings tentatively suggest that cadmium-induced nephrotoxicity results, in part, from glomerular contraction due to p38 MAP kinase/HSP25 signaling-dependent contraction of mesangial cells. With regard to the cellular action of HSP25, these data support a change in paradigm: in addition to its well-established cytoprotective function, HSP25 may also be involved in processes that ultimately lead to adverse effects, as is observed in the response of mesangial cells to cadmium.

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.

Luminal bacterial flora determines physiological expression of intestinal epithelial cytoprotective heat shock proteins 25 and 72

Heat shock proteins (HSP) 25 and 72 are expressed normally by surface colonocytes but not by small intestinal enterocytes. We hypothesized that luminal commensal microflora maintain the observed colonocyte HSP expression. The ability of the small intestine to respond to bacteria and their products and modulate HSPs has not been determined. The effects of luminal bacterial flora in surgically created midjejunal self-filling (SFL) vs. self-emptying (SEL) small-bowel blind loops on epithelial HSP expression were studied. HSP25 and HSP72 expression were assessed by immunoblot and immunohistochemistry. SFL were chronically colonized, whereas SEL contained levels of bacteria normal for the proximal small intestine. SFL creation significantly increased HSP25 and HSP72 expression relative to corresponding sections from SEL. Metronidazole treatment, which primarily affects anaerobic bacteria as well as a diet lacking fermentable fiber, significantly decreased SFL HSP expression. Small bowel incubation with butyrate ex vivo induced a sustained and significant upregulation of HSP25 and altered HSP72 expression, confirming the role of short-chain fatty acids. To determine whether HSPs induction altered responses to an injury, effects of the oxidant, monochloramine, on epithelial resistance and short-circuit current (I(sc)) responses to carbachol and glucose were compared. Increased SFL HSP expression was associated with protection against oxidant-induced decreases in transmural resistance and I(sc) responses to glucose, but not secretory responses to carbachol. In conclusion, luminal microflora and their metabolic byproducts direct expression of HSPs in gut epithelial cells, an effect that contributes to preservation of epithelial cell viability under conditions of stress.

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.

Role and regulation of intestinal epithelial heat shock proteins in health and disease

Mucosal injury and inflammation are cardinal manifestations of inflammatory bowel diseases (IBD), arising when the effects of cytotoxic factors and conditions overwhelm the cell's capacity for defense (i.e. cytoprotection) or repair. To date, most research in this area has focused primarily on agents and processes involved in producing tissue injury, with less consideration given to inherent mechanisms of cytoprotection and cellular repair. Therapeutic approaches to IBD reflect this bias, being largely directed towards down-regulating the inflammatory process by inhibiting the production of immune and inflammatory mediators. This review will focus on the cell's inherent ability to defend itself against cellular stress and injury through the production of evolutionarily conserved stress proteins called heat shock proteins (HSP). The physiological role of these proteins in maintaining intestinal epithelial cell structure and function will be reviewed, with emphasis on studies that examine the role of HSP in IBD. A clearer understanding of the innate cytoprotective mechanisms inherent in intestinal epithelial cells will foster the development of new insights into basic epithelial cell biology, which ultimately can be used to establish target-specific therapies directed at reducing or alleviating mucosal injury, thereby promoting tissue healing and repair.

Hsp72 interacts with paxillin and facilitates the reassembly of focal adhesions during recovery from ATP depletion

The cytoprotective effect of heat stress proteins on epithelial cell detachment, an important cause of acute, ischemic renal failure, was examined after ATP depletion by evaluating focal adhesion complex (FAC) integrity. The intracellular distribution of FAC proteins (paxillin, talin, and vinculin) was assessed by immunohistochemistry before, during, and after exposure of renal epithelial cells to metabolic inhibitors. The resulting ATP depletion caused reversible re-distribution of all three proteins from focal adhesions to the cytosol. Paxillin, a key adaptor protein, was selected as a surrogate marker for FAC integrity in subsequent studies. Prior heat stress increased hsp72, a molecular chaperone, in both the Triton X-100-soluble and -insoluble protein fractions. Compared with ATP depleted control, heat stress significantly decreased paxillin and hsp72 shift from the Triton X-100 soluble to the insoluble protein fraction (an established marker of denaturation and aggregation); increased paxillin-hsp72 interaction detected by co-immunoprecipitation; enhanced paxillin extractability from Triton X-100-insoluble precipitates, increased the reformation of focal adhesions, and improved cell attachment (p < 0.05). To determine whether hsp72 mediates protection afforded by heat stress, cells were infected with adenovirus containing human hsp72 or empty vector. Hsp72 overexpression increased its interaction with paxillin and improved focal adhesion reformation during recovery, mimicking the protective effects of heat stress. These data suggest that hsp72 facilitates the reassembly of focal adhesions and improves cell attachment by reducing paxillin denaturation and increasing its re-solubilization after ATP depletion.

Hsp27, Hsp70, and metallothionein in MDCK and LLC-PK1 renal epithelial cells: effects of prolonged exposure to cadmium

Cadmium is a widely distributed industrial and environmental toxin. The principal target organ of chronic sublethal cadmium exposure is the kidney. In renal epithelial cells, acute high-dose cadmium exposure induces differential expression of proteins, including heat shock proteins. However, few studies have examined heat shock protein expression in cells after prolonged exposure to cadmium at sublethal concentrations. Here, we assayed total cell protein, neutral red uptake, cell death, and levels of metallothionein and heat shock proteins Hsp27 and inducible Hsp70 in cultures of MDCK and LLC-PK1 renal epithelial cells treated with cadmium for 3 days. Treatment with cadmium at concentrations equal to or greater than 10 microM (LLC-PK1) or 25 microM (MDCK) reduced measures of cell vitality and induced cell death. However, a concentration-dependent increase in Hsp27 was detected in both cell types treated with as little as 5 microM cadmium. Accumulation of Hsp70 was correlated only with cadmium treatment at concentrations also causing cell death. Metallothionein was maximally detected in cells treated with cadmium at concentrations that did not reduce cell vitality, and further increases were not detected at greater concentrations. These results reveal that heat shock proteins accumulate in renal epithelial cells during prolonged cadmium exposure, that cadmium induces differential expression of heat shock protein in epithelial cells, and that protein expression patterns in epithelial cells are specific to the cadmium concentration and degree of cellular injury. A potential role for Hsp27 in the cellular response to sublethal cadmium-induced injury is also implicated by our results.

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

The purpose of the study was to determine whether Hsp27 interacts with actin and could protect against selected manifestations of injury from energy depletion in renal epithelia. LLC-PK1 cells were stably transfected to overexpress human Hsp27 tagged with green fluorescence protein (GFP). Transfected expression of the labeled Hsp27 did not reduce endogenous Hsp25 levels in the cells compared with either nontransfected cells or cells transfected with GFP alone used as the transfectant control (G). By fluorescence energy transfer (FRET) between GFP-tagged Hsp27 and rhodamine phalloidin-decorated actin, minimal interaction was found in uninjured control cells. In ATP-depleted cells, Hsp27 was associated closely with F-actin at lateral cell boundaries and with aggregated actin within the cell body. Less Hsp27 interaction with actin was found during recovery; but when adjusted for total phalloidin fluorescence, FRET between Hsp27 and F-actin did not change between 2-h ATP depletion and 4-h recovery. Where Hsp27 association with actin persisted during recovery, it was principally with the residual aggregates of actin in the cell body. Detachment of Na,K-ATPase from the cytoskeleton at 2-h ATP depletion was significantly less in Hsp27 cells compared with transfectant control G cells but not at 4-h ATP depletion. Detachment of ezrin from the cytoskeleton during ATP depletion was nearly complete and was not prevented in the Hsp27 cells. Protection of the Hsp27 cells was not attributable to preservation of cellular ATP levels. Hsp27 appears to have specific actions in renal epithelia subjected to energy depletion, including interacting with actin to preserve architecture in specific intracellular domains.

Site-specific alteration of actin assembly visualized in living renal epithelial cells during ATP depletion

Disruption of normal actin organization in renal tubular epithelial cells is an important element of renal injury induced by ischemia. Studies of fixed cells indicate that the cytoskeleton is disrupted by both ischemia and ATP depletion in a site-specific manner. However, few studies have examined these effects in living cells, and the relationship between the time course of ATP reduction and alteration of the cytoskeleton remains unclear. Here, time-lapse video images of cultured renal epithelial cells expressing an enhanced green fluorescent protein (EGFP)-actin fusion protein were obtained, and the kinetics of fluorescence actin distribution before and during ATP depletion is quantified and compared with measured ATP levels. This study found that assembly of lamellar actin is inhibited rapidly as cellular ATP levels are reduced, whereas disruption of actin in stress fibers is more gradual and persistent. Actin associated with focal adhesions is largely resistant to ATP depletion in these experiments, and, consistent with previous studies, particulate aggregates of actin were formed within the cytoplasm of ATP-depleted cells. Most surprisingly, time-lapse imaging of EGFP-actin distribution, quantitative fluorescence imaging of phalloidin-stained cells, and ultrastructural studies indicate that assembly of actin filaments occurs at sites of epithelial cell-cell attachment in ATP-depleted cells. This assembly is initiated early during ATP depletion and continues after ATP levels are maximally reduced. Assembly of actin at sites of cell-cell attachment may be an element of the pathology of injury induced by ischemia, or alternatively, could reflect the function of a protective mechanism. These studies directly demonstrate site-specific alteration of actin assembly in living epithelial cells during ATP depletion. The results also reveal that actin reorganization continues after ATP levels are maximally decreased and that epithelial cell-cell attachments are sites of actin assembly in ATP-depleted cells.