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

Potential osmoprotective roles of branchial heat shock proteins towards Na+, K+-ATPase in milkfish (Chanos chanos) exposed to hypotonic stress

In euryhaline teleosts, osmoregulatory mechanisms vary with osmotic stresses, and heat shock proteins (HSPs) play a central role in maintaining cellular homeostasis. The present study aimed to investigate the expression and potential roles of HSP70 and HSP90 in the gills of seawater (SW)- and freshwater (FW)-acclimated milkfish (Chanos chanos). Four HSP genes, including Cchsc70 (heat shock cognate 70), Cchsp70, Cchsp90α, and Cchsp90β, were analyzed in milkfish gills. Among these genes, only the mRNA abundance of branchial Cchsp90α was significantly lower in the FW-acclimated than in the SW-acclimated milkfish. Immunoblotting showed no significant difference in the relative protein abundance of branchial HSP70 and HSP90 between the two groups. The time-course experiments (from SW to FW) showed that the protein abundance of HSP70 and HSP90 at the 3 h and 6 h post-transfer and then declined gradually. To further illustrate the potential osmoregulatory roles of HSP70 and HSP90, their interaction with Na⁺, K⁺-ATPase (NKA, the primary driving force for osmoregulation) was analyzed using co-immunoprecipitation. The results showed the interaction between HSP70, HSP90 and NKA after acclimation to SW or FW increased within 3 h; and then returned to normal levels within 7 days. To our knowledge, the present study was the first to demonstrate that the interaction between HSP70, HSP90 and NKA changes with hypotonic stress in euryhaline teleosts. Before the transfer, no interaction was detected. When transferred to FW from SW, the interaction of HSP70 and HSP90 with NKA were detected. The results suggested that HSP70 and HSP90 participated in the acute responses of osmoregulatory mechanisms to protect branchial NKA from hypotonic stress in milkfish.

A CASPR1-ATP1B3 protein interaction modulates plasma membrane localization of Na+/K+-ATPase in brain microvascular endothelial cells

Contactin-associated protein 1 (CASPR1 or CNTNAP1) was recently reported to be expressed in brain microvascular endothelial cells (BMECs), the major component of the blood-brain barrier. To investigate CASPR1's physiological role in BMECs, here we used CASPR1 as a bait in a yeast two-hybrid screen to identify CASPR1-interacting proteins and identified the β3 subunit of Na⁺/K⁺-ATPase (ATP1B3) as a CASPR1-binding protein. Using recombinant and purified CASPR1, RNAi, GST-pulldown, immunofluorescence, immunoprecipitation, and Na⁺/K⁺-ATPase activity assays, we found that ATP1B3's core proteins, but not its glycosylated forms, interact with CASPR1, which was primarily located in the endoplasmic reticulum of BMECs. CASPR1 knockdown reduced ATP1B3 glycosylation and prevented its plasma membrane localization, phenotypes that were reversed by expression of full-length CASPR1. We also found that the CASPR1 knockdown reduces the plasma membrane distribution of the α1 subunit of Na⁺/K⁺-ATPase, which is the major component assembled with ATP1B3 in the complete Na⁺/K⁺-ATPase complex. The binding of CASPR1 with ATP1B3, but not the α1 subunit, indicated that CASPR1 binds with ATP1B3 to facilitate the assembly of Na⁺/K⁺-ATPase. Furthermore, the activity of Na⁺/K⁺-ATPase was reduced in CASPR1-silenced BMECs. Interestingly, shRNA-mediated CASPR1 silencing reduced glutamate efflux through the BMECs. These results demonstrate that CASPR1 binds with ATP1B3 and thereby contributes to the regulation of Na⁺/K⁺-ATPase maturation and trafficking to the plasma membrane in BMECs. We conclude that CASPR1-mediated regulation of Na⁺/K⁺-ATPase activity is important for glutamate transport across the blood-brain barrier.

Chemical genetic identification of GAK substrates reveals its role in regulating Na+/K+-ATPase

Novel GAK phosphorylation targets are identified using chemical genetic methods. One of the substrates is the α subunit of the Na⁺/K⁺-ATPase, phosphorylation of which is necessary for its surface trafficking from endosomes. Conserved functions of NAK family kinases are described.

Cyclin G–associated kinase (GAK) is a ubiquitous serine/threonine kinase that facilitates clathrin uncoating during vesicle trafficking. GAK phosphorylates a coat adaptor component, AP2M1, to help achieve this function. GAK is also implicated in Parkinson's disease through genome-wide association studies. However, GAK's role in mammalian neurons remains unclear, and insight may come from identification of further substrates. Employing a chemical genetics method, we show here that the sodium potassium pump (Na⁺/K⁺-ATPase) α-subunit Atp1a3 is a GAK target and that GAK regulates Na⁺/K⁺-ATPase trafficking to the plasma membrane. Whole-cell patch clamp recordings from CA1 pyramidal neurons in GAK conditional knockout mice show a larger change in resting membrane potential when exposed to the Na⁺/K⁺-ATPase blocker ouabain, indicating compromised Na⁺/K⁺-ATPase function in GAK knockouts. Our results suggest a modulatory role for GAK via phosphoregulation of substrates such as Atp1a3 during cargo trafficking.

Pandemonium Breaks Out: Disruption of Salicylic Acid-Mediated Defense by Plant Pathogens

Salicylic acid (SA) or 2-hydroxybenoic acid is a phenolic plant hormone that plays an essential role in plant defense against biotrophic and semi-biotrophic pathogens. In Arabidopsis, SA is synthesized from chorismate in the chloroplast through the ICS1 (isochorismate synthase I) pathway during pathogen infection. The transcription co-activator NPR1 (Non-Expresser of Pathogenesis-Related Gene 1), as the master regulator of SA signaling, interacts with transcription factors to induce the expression of anti-microbial PR (Pathogenesis-Related) genes. To establish successful infections, plant bacterial, oomycete, fungal, and viral pathogens have evolved at least three major strategies to disrupt SA-mediated defense. The first strategy is to reduce SA accumulation directly by converting SA into its inactive derivatives. The second strategy is to interrupt SA biosynthesis by targeting the ICS1 pathway. In the third major strategy, plant pathogens deploy different mechanisms to interfere with SA downstream signaling. The wide array of strategies deployed by plant pathogens highlights the crucial role of disruption of SA-mediated plant defense in plant pathogenesis. A deeper understanding of this topic will greatly expand our knowledge of how plant pathogens cause diseases and consequently pave the way for the development of more effective ways to control these diseases.

The role of Sigma-1 receptor in sex-specific heat shock response in an experimental rat model of renal ischaemia/reperfusion injury

We previously showed that female rats are more protected against renal ischaemia/reperfusion (I/R) injury than males, which is partly attributed to their more pronounced heat shock response. We recently described that Sigma-1 receptor (S1R) activation improves postischaemic survival and renal function. 17β-estradiol activates S1R, thus here we investigated the role of sex-specific S1R activation and heat shock response in severe renal I/R injury. Proximal tubular cells were treated with 17β-estradiol, which caused direct S1R activation and subsequent induction of heat shock response. Uninephrectomized female, male and ovariectomized female (Ovx) Wistar rats were subjected to 50-min renal ischaemia followed by 2 (T2) and 24 (T24) hours of reperfusion. At T24 renal functional, impairment was less severe and structural damage was less prominent in females versus males or Ovx. Postischaemic increase in S1R, pAkt, HSF-1, HSP72 levels were detected as early as at T2, while pHSP27 was elevated later at T24. Abundance of heat shock proteins was higher in healthy female rats and remained higher at T2 and T24 (female versus male or Ovx; resp.). We propose a S1R-dependent mechanism, which contributes to the relative renoprotection of females after I/R injury by enhancing the heat shock response.

Nfu1 Mediated ROS Removal Caused by Cd Stress in Tegillarca granosa

The blood clam Tegillarca granosa, a eukaryotic bottom-dwelling bivalve species has a strong ability to tolerate and accumulate cadmium. In our previous study, Nfu1 (iron-sulfur cluster scaffold protein), which is involved in Fe-S cluster biogenesis, was shown to be significantly up-regulated under Cd stress, as determined by proteomic analysis. To investigate the function of Nfu1 in cadmium (Cd) detoxification, the function of blood clam Nfu1 (designated as Tg-Nfu1) was investigated by integrated molecular and protein approaches. The full-length cDNA of Tg-Nfu1 is 1167 bp and encodes a protein of 272 amino acid residues. The deduced Tg-Nfu1 protein is 30 kDa contains a conserved Nfu-N domain and a Fe-S cluster binding motif (C-X-X-C). qRT-PCR analysis revealed that Tg-Nfu1 was ubiquitously expressed in all examined tissues; it was up-regulated in the hepatopancreas and gill, and kept a high level from 9 to 24 h after Cd exposure (250 μg/L). Western blot analysis further revealed that the Tg-Nfu1 protein was also highly expressed in the hepatopancreas and gill after 24 h of Cd stress. Further functional analysis showed that the production of ROS was increased and Cu/ZnSOD activity was inhibited in blood clam, treated with the specific Nfu1 siRNA and Cd stress, respectively. These results suggest that Tg-Nfu1 could protect blood clam from oxidative damage caused by Cd stress.

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.

RNA-seq analysis revealed ROS-mediated related genes involved in cadmium detoxification in the razor clam Sinonovacula constricta

The razor clam Sinonovacula constricta is a eukaryotic benthic intertidal bivalve species that is tolerant to different heavy metals, such as cadmium ion (Cd(2+)). However, the mechanism by which S. constricta responds to Cd(2+)-induced stress remains unclear. In this study, eight transcriptome libraries were constructed and sequenced using razor clams exposed to Cd(2+) for 12 and 48 h. A total of 18,330 unigenes with an average length of 500 bp were annotated. Among these 18,330 unigenes, 582 and 649 displayed differential expression profiles at 12 and 48 h in the gill, respectively. The corresponding differential unigenes in the hepatopancreas were 1056 and 382. Gene Ontology annotation revealed that these unigenes were highly pronounced in metabolic process, cellular process, binding, and catalytic activity. Notably, ROS production-related genes, such as heat shock proteins 32, metallothionein, and glutathione, were synchronously enriched in all experimental samples with induced expression profiles, which was also validated by qPCR. Our results highlighted the relation between immune regulation and Cd(2+)-induced stress in razor clam and provided new insights into the molecular mechanisms of heavy toxicology.

Heat Shock Proteins and Diabetes

Diabetes is a chronic disease, and its prevalence continues to rise and can increase the risk for the progression of microvascular (such as nephropathy, retinopathy and neuropathy) and also macrovascular complications. Diabetes is a condition in which the oxidative stress and inflammation rise. Heat shock proteins (HSPs) are a highly conserved family of proteins that are expressed by all cells exposed to environmental stress, and they have diverse functions. In patients with diabetes, the expression and levels of HSPs decrease, but these chaperones can aid in improving some complications of diabetes, such as oxidative stress and inflammation. (The suppression of some HSPs is associated with a generalized increase in tissue inflammation.) In this review, we summarize the current understanding of HSPs in diabetes as well as their complications, and we also highlight their potential role as therapeutic targets in diabetes.

Akt Substrate of 160 kD Regulates Na+,K+-ATPase Trafficking in Response to Energy Depletion and Renal Ischemia

Renal ischemia and reperfusion injury causes loss of renal epithelial cell polarity and perturbations in tubular solute and fluid transport. Na(+),K(+)-ATPase, which is normally found at the basolateral plasma membrane of renal epithelial cells, is internalized and accumulates in intracellular compartments after renal ischemic injury. We previously reported that the subcellular distribution of Na(+),K(+)-ATPase is modulated by direct binding to Akt substrate of 160 kD (AS160), a Rab GTPase-activating protein that regulates the trafficking of glucose transporter 4 in response to insulin and muscle contraction. Here, we investigated the effect of AS160 on Na(+),K(+)-ATPase trafficking in response to energy depletion. We found that AS160 is required for the intracellular accumulation of Na(+),K(+)-ATPase that occurs in response to energy depletion in cultured epithelial cells. Energy depletion led to dephosphorylation of AS160 at S588, which was required for the energy depletion-induced accumulation of Na,K-ATPase in intracellular compartments. In AS160-knockout mice, the effects of renal ischemia on the distribution of Na(+),K(+)-ATPase were substantially reduced in the epithelial cells of distal segments of the renal tubules. These data demonstrate that AS160 has a direct role in linking the trafficking of Na(+),K(+)-ATPase to the energy state of renal epithelial cells.

Heat shock response and homeostatic plasticity

Heat shock response and homeostatic plasticity are mechanisms that afford functional stability to cells in the face of stress. Each mechanism has been investigated independently, but the link between the two has not been extensively explored. We explore this link. The heat shock response enables cells to adapt to stresses such as high temperature, metabolic stress and reduced oxygen levels. This mechanism results from the production of heat shock proteins (HSPs) which maintain normal cellular functions by counteracting the misfolding of cellular proteins. Homeostatic plasticity enables neurons and their target cells to maintain their activity levels around their respective set points in the face of stress or disturbances. This mechanism results from the recruitment of adaptations at synaptic inputs, or at voltage-gated ion channels. In this perspective, we argue that heat shock triggers homeostatic plasticity through the production of HSPs. We also suggest that homeostatic plasticity is a form of neuroprotection.

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.

[Role of AMP-activated protein kinase in renal ischemic preconditioning]

Kidney transplantation represents the best treatment of end-stage renal disease. In addition to the degree of human leukocyte antigen matching, long-term graft survival is influenced by the quality of the graft before its transplantation. Quality criteria include the level of ischemic damage caused by the transplantation per se. Renal ischemic preconditioning (IP) consists of different approaches to prevent ischemia/reperfusion (I/R) damage induced by the interruption and recovery of renal circulation, as observed during transplantation. Distinct animal models show promising results regarding the efficiency of PCI to preserve kidney structure and function in I/R conditions. Characterizing the cellular cascades involved in I/R led to the identification of putative targets of renal IP, including the adenosine monophosphate-activated protein kinase (AMPK). AMPK is a ubiquitous energy sensor, which has been implicated in the maintenance of epithelial cell polarization under energy deprivation. Among others, the anti-diabetic drug, metformin, is a potent activator of AMPK. Here, we summarize the in vitro and in vivo data about the role of AMPK in renal IP. Defining the pharmacological conditions of IP would help to improve the quality of the renal graft before its transplantation, thereby increasing its long-term survival.

Oxidative stress and apoptosis in a pig model of brain death (BD) and living donation (LD)

Background

As organ shortage is increasing, the acceptance of marginal donors increases, which might result in poor organ function and patient survival. Mostly, organ damage is caused during brain death (BD), cold ischemic time (CIT) or after reperfusion due to oxidative stress or the induction of apoptosis. The aim of this study was to study a panel of genes involved in oxidative stress and apoptosis and compare these findings with immunohistochemistry from a BD and living donation (LD) pig model and after cold ischemia time (CIT).

Methods

BD was induced in pigs; after 12 h organ retrieval was performed; heart, liver and kidney tissue specimens were collected in the BD (n = 6) and in a LD model (n = 6). PCR analysis for NFKB1, GSS, SOD2, PPAR-alpha, OXSR1, BAX, BCL2L1, and HSP 70.2 was performed and immunohistochemistry used to show apoptosis and nitrosative stress induced cell damage.

Results

In heart tissue of BD BAX, BCL2L1 and HSP 70.2 increased significantly after CIT. Only SOD2 was over-expressed after CIT in BD liver tissue. In kidney tissue, BCL2L1, NFKB, OXSR1, SOD2 and HSP 70.2 expression was significantly elevated in LD. Immunohistochemistry showed a significant increase in activated Caspase 3 and nitrotyrosine positive cells after CIT in BD in liver and in kidney tissue but not in heart tissue.

Conclusion

The up-regulation of protective and apoptotic genes seems to be divergent in the different organs in the BD and LD setting; however, immunohistochemistry revealed more apoptotic and nitrotyrosine positive cells in the BD setting in liver and kidney tissue whereas in heart tissue both BD and LD showed an increase.

The role of heat shock protein 90 in modulating ischemia-reperfusion injury in the kidney

INTRODUCTION

Kidney transplantation is the gold standard treatment for end-stage renal disease. Ischemia-reperfusion injury (IRI) is an unavoidable consequence of the transplantation procedure and is responsible for delayed graft function and poorer long-term outcomes.

AREAS COVERED

Pharmacological induction of heat shock protein (Hsp) expression is an emerging pre-conditioning strategy aimed at reducing IRI following renal transplantation. Hsp90 inhibition up-regulates protective Hsps (especially Hsp70) and potentially down-regulates NF-κB by disruption of the IκB kinase (IKK) complex. However, the clinical application of Hsp90 inhibitors is currently limited by their toxicity profile and the exact mechanism of protection conferred is unknown. Toll-like receptor 4 (TLR4) is a further regulator of NF-κB and recent studies suggest TLR4 plays a dominant role in mediating kidney damage following IRI. The full interaction of Hsps with TLRs is yet to be delineated and whether TLR4 signalling can be targeted by Hsp90 inhibition in IRI remains uncertain.

EXPERT OPINION

Pharmacological pre-conditioning by Hsp90 inhibition involves direct treatment to the kidney donor and/or organ, which aims to reduce injury prior to the onset of ischemia. The major challenges going forward are to establish the exact mechanism of protection offered by these drugs and the investgiation of less toxic analogues that could be safely translated into human studies.

Preactivation of AMPK by metformin may ameliorate the epithelial cell damage caused by renal ischemia

Alterations in epithelial cell polarity and in the subcellular distributions of epithelial ion transport proteins are key molecular consequences of acute kidney injury and intracellular energy depletion. AMP-activated protein kinase (AMPK), a cellular energy sensor, is rapidly activated in response to renal ischemia, and we demonstrate that its activity is upregulated by energy depletion in Madin-Darby canine kidney (MDCK) cells. We hypothesized that AMPK activity may influence the maintenance or recovery of epithelial cell organization in mammalian renal epithelial cells subjected to energy depletion. MDCK cells were ATP depleted through a 1-h incubation with antimycin A and 2-deoxyglucose. Immunofluoresence localization demonstrated that this regimen induces mislocalization of the Na-K-ATPase from its normal residence at the basolateral plasma membrane to intracellular vesicular compartments. When cells were pretreated with the AMPK activator metformin before energy depletion, basolateral localization of Na-K-ATPase was preserved. In MDCK cells in which AMPK expression was stably knocked down with short hairpin RNA, preactivation of AMPK with metformin did not prevent Na-K-ATPase redistribution in response to energy depletion. In vivo studies demonstrate that metformin activated renal AMPK and that treatment with metformin before renal ischemia preserved cellular integrity, preserved Na-K-ATPase localization, and led to reduced levels of neutrophil gelatinase-associated lipocalin, a biomarker of tubular injury. Thus AMPK may play a role in preserving the functional integrity of epithelial plasma membrane domains in the face of energy depletion. Furthermore, pretreatment with an AMPK activator before ischemia may attenuate the severity of renal tubular injury in the context of acute kidney injury.

Renoprotective effect of erythropoietin in rats subjected to ischemia/reperfusion injury: gender differences

BACKGROUND

Renal ischemia reperfusion injury induces gender-dependent heat-shock protein 72 expression, which maintains membrane localization of renal Na(+)/K(+)ATPase-α1. The erythropoietin has a protecting effect against ischemia reperfusion injury in various organs. In this study, we investigated whether erythropoietin exerts a beneficial effect against post-ischemic renal injury. Furthermore, we studied the erythropoietin signaling on heat-shock protein 72 and Na(+)/K(+)ATPase-α1 expression and localization.

METHODS

In male and female Wistar rats, rHuEPO (1000 IU/bwkg intraperitoneal) or vehicle was administered 24 hours prior to unilateral left renal ischemia reperfusion (50 minutes). Kidneys were subsequently removed at hours 2 or 24 of the reperfusion; sham-operated rats served as controls (C) (n = 8/group). We measured serum erythropoietin, renal function, evaluated histological injury, and observed heat-shock protein 72 as well as Na(+)/K(+)ATPase-α1 protein level and localization. Additional groups were followed for 7-day survival.

RESULTS

Erythropoietin treatment was associated with better post-ischemic survival and less impaired renal function in males while diminishing the renal structural damage in both sexes. Endogenous erythropoietin was higher in males and increased in both genders after erythropoietin treatment. The erythropoietin treatment elevated protein levels of heat-shock protein 72 and Na(+)/K(+)ATPase-α1 in 24 hours in males, whereas in females, the already higher expression of heat-shock protein 72 and Na(+)/K(+)ATPase-α1 was not increased. Moreover, erythropoietin prevented ischemia reperfusion induced Na(+)/K(+)ATPase-α1 translocation from the basolaterale membrane in males.

CONCLUSION

Erythropoietin diminishes gender difference in the susceptibility to renal post-ischemic injury and reduces post-ischemic structural damage while preserving kidney function, particularly in males. This additional protection may be associated with a heat-shock protein 72-mediated effect on Na(+)/K(+)ATPase-α1 expression and translocation.

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.

Pseudomonas syringae hijacks plant stress chaperone machinery for virulence

Plant heat shock protein Hsp70 is the major target of HopI1, a virulence effector of pathogenic Pseudomonas syringae. Hsp70 is essential for the virulence function of HopI1. HopI1 directly binds Hsp70 through its C-terminal J domain and stimulates Hsp70 ATP hydrolysis activity in vitro. In plants, HopI1 forms large complexes in association with Hsp70 and induces and recruits cytosolic Hsp70 to chloroplasts, the site of HopI1 localization. Deletion of a central P/Q-rich repeat region disrupts HopI1 virulence but not Hsp70 interactions or association with chloroplasts. Thus, HopI1 must not only bind Hsp70 through its J domain, but likely actively affects Hsp70 activity and/or specificity. At high temperature, HopI1 is dispensable for P. syringae pathogenicity, unless excess Hsp70 is provided. A working hypothesis is that Hsp70 has a defense-promoting activity(s) that HopI1 or high temperature can subvert. Enhanced susceptibility of Hsp70-depleted plants to nonpathogenic strains of P. syringae supports a defense-promoting role for Hsp70.

Protective effect of post-ischaemic viral delivery of heat shock proteins in vivo

Heat shock proteins (HSPs) function as molecular chaperones involved in protein folding, transport and degradation and, in addition, they can promote cell survival both in vitro and in vivo after a range of stresses. Although some in vivo studies have suggested that HSP27 and HSP70 can be neuroprotective, current evidence is limited, particularly when HSPs have been delivered after an insult. The effect of overexpressing HSPs after transient occlusion of the middle cerebral artery in rats was investigated by delivering an attenuated herpes simplex viral vector (HSV-1) engineered to express HSP27 or HSP70 30 mins after tissue reperfusion. Magnetic resonance imaging scans were used to determine lesion size and cerebral blood flow at six different time points up to 1 month after stroke. Animals underwent two sensorimotor tests at the same time points to assess the relationship between lesion size and function. Results indicate that post-ischaemic viral delivery of HSP27, but not of HSP70, caused a statistically significant reduction in lesion size and induced a significant behavioural improvement compared with controls. This is the first evidence of effective post-ischaemic gene therapy with a viral vector expressing HSP27 in an experimental model of stroke.

Na+/K+ -ATPase stabilization by Hsp70 in the outer stripe of the outer medulla in rats during recovery from a low-protein diet

A low-protein (LP) diet induces injury from energy depletion in renal epithelial cells. Overexpression of heat-shock proteins has been implicated in the restoration of the cytoskeletal anchorage of Na(+)/K(+)-ATPase. We tested if Hsp70 stabilizes renal Na(+)/K(+)-ATPase attachment to the cytoskeleton from the cortex and the outer stripe of the outer medulla (OSOM) in rats during recovery from a LP diet. Rats were fed with a LP diet (8% protein) for 14 days, and then the rats were recovered with a 24% protein (RP) diet. The control group received a 24% protein (NP) diet. Increased Na(+)/K(+)-ATPase dissociation was demonstrated in soluble fraction from OSOM with lower ATP content as a result of LP diet vs NP. Meanwhile, decreased Hsp70 levels in the same fraction were shown. Translocation of Hsp70 to the cytoskeletal injured fraction associated with stabilization of Na(+)/K(+)-ATPase was shown in OSOM from LP after in vitro co-incubation of the cytoskeletal fraction of LP and non-cytoskeletal fraction of RP. These effects were abolished by the addition of the anti-Hsp70 antibody. Absence of Na(+)/K(+)-ATPase detachment from its cytoskeletal anchorage was demonstrated in proximal duct segments from cortex in LP. Co-immunoprecipitation showed that the amount of Na(+)/K(+)-ATPase co-precipitating with Hsp70 increased in the OSOM as a result of the LP diet. In the cortex tissues from rats fed the LP and the RP diet, the interaction of both proteins were similar to the control groups. Our results indicate that Hsp70 has a critical role in protecting the integrity of the cytoskeletal anchorage of Na(+)/K(+)-ATPase during recovery from ATP-depleted injury resulting from LP in OSOM.

Alpha-lipoic Acid modulates heat shock factor-1 expression in streptozotocin-induced diabetic rat kidney

Increased oxidative stress and impaired heat shock protein (HSP) synthesis may contribute to diabetic nephropathy. The question of whether 8-week thiol antioxidant alpha-lipoic acid (LA) supplementation modulates HSP response and oxidative stress was studied in the kidney of streptozotocin-induced diabetic (SID) and nondiabetic rats. SID caused a histological mesangial expansion, tubular dilatation, and increased levels of transforming growth factor-beta (TGF-beta), a mediator of glomerulosclerosis. SID increased 4-hydroxynonenal (4-HNE) protein adduct formation, a marker of lipid peroxidation, and heme oxygenase-1 (HO-1), also a marker of oxidative stress. Moreover, SID increased the DNA-binding activity of heat shock factor-1 (HSF-1) and expression of heat shock protein 60 (HSP60). In contrast, LA supplementation partially reversed histological findings of glomerulosclerosis and decreased TGF-beta. LA also increased HSF-1 and decreased HO-1 protein expression, without affecting 4-HNE protein adduct levels. At the mRNA level, LA increased expression of HSF-1, HSP90, and glucose-regulated protein (GRP75) in both control and diabetic animals and HSP72 in SID rats. However, LA supplementation did not affect these HSPs at the protein level. These findings suggest that in addition to its antiglomerulosclerotic effects, LA can induce cytoprotective response in SID.

Octopamine mediates thermal preconditioning of the locust ventilatory central pattern generator via a cAMP/protein kinase A signaling pathway

We investigated the role of biogenic amines in generating thermoprotection of the ventilatory motor pattern circuitry in Locusta migratoria. Levels of octopamine (OA) and dopamine (DA) in the metathoracic ganglion decreased during heat stress. We measured the thermosensitivity of central pattern generation in response to a ramped increase of temperature in semi-intact preparations. OA, DA, and tyramine (TA) were either bath applied or injected into the locust hemocoel 4-8 h before testing. Neither TA nor DA modified the thermotolerance of ventilatory motor pattern generation. However, OA treatment by bath applications (10(-4) M OA) or by injections into the hemocoel (2 microg/10 microl OA) mimicked heat shock preconditioning and improved the thermotolerance of the motor pattern by increasing the failure temperature and by decreasing the time taken to recover operation after a return to room temperature. Heat shock-induced thermoprotection was eradicated in locusts preinjected with epinastine (Oct betaR antagonist). Neuropil injections of the cAMP agonist and protein kinase A (PKA) activator, Sp-cAMPs, both conferred thermoprotection in control locusts and rescued thermoprotection in epinastine-treated HS locusts. Similar injections of the PKA inhibitor Rp-cAMPs blocked the thermoprotective effect of bath-applied OA. Octopamine-mediated thermoprotection was also abolished with neuropil injections of cycloheximide or actinomycin D, indicating a requirement for transcription and translation. We conclude that OA has a crucial role in triggering protein synthesis-dependent physiological adaptations to protect CNS function during heat stress by activating a cAMP/PKA pathway.

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.

Transcriptomic changes in developing kidney exposed to chronic hypoxia

cDNA arrays compared gene expression in kidneys of neonatal mice subjected to 1, 2, and 4 weeks of chronic constant (CCH) or intermittent (CIH) hypoxia with normoxic littermates. Five to twenty percent of genes were regulated in each condition, with greater changes in CCH. Up-regulation of 42% of the solute carriers after 1 week of CCH suggests a strong activation of pH controlling pathways. Significant reduction in expression change of genes important in growth, development, and aging as a function of time indicates reduced maturation rate in CIH and CCH treatments. Regulated genes showed gender dependence in CCH, being higher in females than males at 1 week and higher in males than females thereafter. Transcriptional control was enhanced in CCH but not in CIH. Thus, CCH and CIH both alter gene expression and retard maturation with the more profound changes occurring in CCH than in CIH.

Sex differences in heat shock protein 72 expression and localization in rats following renal ischemia-reperfusion injury

Previously, we demonstrated gender differences in Na-K-ATPase (NKA) expression and function after renal ischemia-reperfusion (I/R) injury (Sex differences in the alterations of Na(+), K(+)-ATPase following ischemia-reperfusion injury in the rat kidney. J Physiol 555: 471-480, 2004). Postischemic membrane destruction causes inhibition of NKA, whereas heat shock protein (HSP) 72 helps to preserve it. We tested the sex differences in postischemic expression of HSP72 and colocalization with NKA. The left renal pedicle of uninephrectomized female (F) and male (M) Wistar rats was clamped for 55 min followed by 2 (T2), 16 (T16), and 24 h (T24) of reperfusion. Uninephrectomized, sham-operated F and M rats served as controls. Postischemic blood urea nitrogen (BUN), serum creatinine, and renal histology were analyzed. HSP72 mRNA expression was detected by RT-PCR, protein levels by Western blot analysis. Fluorescent immunohistochemistry was performed to evaluate the localization of HSP72 and NKA alpha(1)-subunit. Postischemic BUN and creatinine were higher, and renal histology showed more rapid progression in M vs. F (P < 0.05). HSP72 mRNA expression was higher in F vs. M in control and in all I/R groups (P < 0.05). Similar changes were observed in HSP72 protein levels (F vs. M, P < 0.05, control, T2, T16, T24, respectively). Immunohistochemical localization of HSP72 and NKA alpha(1) was similar in control F and M. In postischemic F kidneys, the majority of NKA alpha(1) and HSP72 was colocalized on the basolateral membrane of tubular cells, whereas in M prominent staining was observed in the cytosol and apical domain. This study indicates that in female kidneys the higher basal and postischemic levels of HSP72 and different colocalization with NKA might contribute to the gender differences in renal I/R injury.