Distinct hsp70 domains mediate apoptosis-inducing factor release and nuclear accumulation

Molecular Mechanisms of Neuroprotection after the Intermittent Exposures of Hypercapnic Hypoxia

The review introduces the stages of formation and experimental confirmation of the hypothesis regarding the mutual potentiation of neuroprotective effects of hypoxia and hypercapnia during their combined influence (hypercapnic hypoxia). The main focus is on the mechanisms and signaling pathways involved in the formation of ischemic tolerance in the brain during intermittent hypercapnic hypoxia. Importantly, the combined effect of hypoxia and hypercapnia exerts a more pronounced neuroprotective effect compared to their separate application. Some signaling systems are associated with the predominance of the hypoxic stimulus (HIF-1α, A1 receptors), while others (NF-κB, antioxidant activity, inhibition of apoptosis, maintenance of selective blood-brain barrier permeability) are mainly modulated by hypercapnia. Most of the molecular and cellular mechanisms involved in the formation of brain tolerance to ischemia are due to the contribution of both excess carbon dioxide and oxygen deficiency (ATP-dependent potassium channels, chaperones, endoplasmic reticulum stress, mitochondrial metabolism reprogramming). Overall, experimental studies indicate the dominance of hypercapnia in the neuroprotective effect of its combined action with hypoxia. Recent clinical studies have demonstrated the effectiveness of hypercapnic-hypoxic training in the treatment of childhood cerebral palsy and diabetic polyneuropathy in children. Combining hypercapnic hypoxia with pharmacological modulators of neuro/cardio/cytoprotection signaling pathways is likely to be promising for translating experimental research into clinical medicine.

Point-of-care salivary oxidative and renal functional markers to assess kidney function in reperfusion-induced acute kidney injury in male rats

OBJECTIVES

Saliva is one of the most promising body fluids in the research of new biomarker for various diseases diagnosis. However, serial sampling in this condition is very dangerous and pose iatrogenic anemia with blood loss. This study was done to evaluate the cost-effectiveness of point-of-care salivary tests and identify the validity of salivary markers.

METHODS

Rats were randomly assigned to four experimental groups: (1) control (2) IR-3 h (3) IR-6 h (4) IR-24 h. Both renal pedicles were occluded for 55 min and then were declamped to allow reperfusion for 3, 6 and 24 h in IR groups. After reperfusion, all rats received pilocarpine 1 mg/kg to collect saliva. Plasma samples were also collected. Renal parameters including Cr, uric acid, and urea, malondialdehyde (MDA) levels, Bax/Bcl2 ratio, nitrite/nitrate ratio, corticosterone levels and oxidant/antioxidant ratio were measured in both plasma and salivary samples.

RESULTS

There were significant increased level of renal function parameters, MDA levels, Bax/Bcl2 ratio, nitrite/nitrate ratio and corticosterone in both saliva and plasma. The comparison of above parameters in both saliva and plasma showed significant correlation.

CONCLUSIONS

This study demonstrated that concentrations of indices specifically renal functional parameters increase in saliva in the IR-induced kidney injury in male rats and result indicate the potential of saliva as a tool to monitoring AKI. Measurement of salivary parameters may can become reliable diagnostic tests for patients with AKI.

Role of Iberin as an anti-apoptotic agent on renal ischemia-reperfusion injury in rats

Ischemia-reperfusion injury (IRI) is a major contributor to acute and chronic kidney failure, heart failure, and ischemic stroke. This study aimed to investigate the therapeutic potential of Iberin, known for its anti-inflammatory, antioxidant, and antiapoptotic properties, in a rat model of renal IRI. Twenty-four adult male rats were randomly divided into four groups: Group I (Sham group) underwent laparotomy without IRI induction; Group II (Control group) underwent laparotomy followed by renal artery clamping for 30 minutes to induce ischemia, followed by 2 hours of reperfusion; Group III (Iberin treatment group) received a pre-injection of Iberin (15 mg/kg) and underwent 30 minutes of ischemia followed by 2 hours of reperfusion; and Group IV (Vehicle-treated group) received the vehicle (ethanol) 1 hour prior to ischemia and reperfusion induction. Iberin was diluted with ethanol. Biomarkers associated with inflammation, oxidative stress, and apoptosis were measured using enzyme-linked immunosorbent assay. Iberin treatment significantly reduced levels of inflammatory cytokines interleukin-1β (IL-1β) and IL-6, Bcl-2-associated X protein (BAX), tumor necrosis factor α (TNF-α), nuclear factor kappa p56, high mobility group B1, and neutrophil gelatinase-associated lipocalin. Moreover, Iberin increased levels of heat shock protein and Bcl2 compared to the control and vehicle groups. Iberin treatment prolonged the ischemic tolerance of renal tissue, potentially preventing or delaying irreversible injuries. These findings highlight the potential of Iberin as a promising candidate for mitigating renal injury caused by ischemia-reperfusion, due to its ability to modulate inflammatory markers.

Permissive hypercapnia and hypercapnic hypoxia inhibit signaling pathways of neuronal apoptosis in ischemic/hypoxic rats

INTRODUCTION

In the present study, we aimed to test the hypothesis that hypercapnia, independently and/or in combination with hypoxia, can activate signaling pathways related to the inhibition of proapoptotic (caspase-dependent and caspase-independent) factors and the induction of antiapoptotic factors in facilitating adaptation to hypoxia/ischemia.

MATERIALS AND METHODS

Following exposure to permissive hypercapnia and/or normobaric hypoxia, the degree of apoptosis was evaluated in experimental ischemia models in vivo and in vitro. The percentages of caspase-3, apoptosis-inducing factor (AIF), Bax, and Bcl-2 in astrocytes and neurons derived from male Wistar rats were also calculated. In vitro, cells were subjected to various types of respiratory exposure (hypoxia and/or hypercapnia for 24 or 12 h) as well as further sublethal chemical hypoxia. The percentages of these molecules in nerve cells in the ischemic penumbra of the brain after photothrombotic injury were also calculated.

RESULTS

The degree of apoptosis was found to decrease in ischemic penumbra, mostly due to the hypercapnic component. It was also discovered that the levels of caspase-3, AIF, and Bax decreased in this region, whereas the Bcl-2 levels increased following exposure to hypercapnia and hypercapnic hypoxia.

CONCLUSIONS

This integrative assessment of the rate of apoptosis/necrosis in astrocyte and neuron cultures shows that the combination of hypercapnia and hypoxia resulted in the maximum neuroprotective effect. The levels of apoptosis mediators in astrocyte and neuron cultures were calculated after modeling chemical hypoxia in vitro. These results show that the exposure models where permissive hypercapnia and normobaric hypoxia were combined also had the most pronounced inhibitory effects on apoptotic signaling pathways.

Oxidative stress and mitochondrial dysfunction following traumatic brain injury: From mechanistic view to targeted therapeutic opportunities

Traumatic brain injury (TBI) is one of the most prevalent causes of permanent physical and cognitive disabilities. TBI pathology results from primary insults and a multi-mechanistic biochemical process, termed as secondary brain injury. Currently, there are no pharmacological agents for definitive treatment of patients with TBI. This article is presented with the purpose of reviewing molecular mechanisms of TBI pathology, as well as potential strategies and agents against pathological pathways. In this review article, materials were obtained by searching PubMed, Scopus, Elsevier, Web of Science, and Google Scholar. This search was considered without time limitation. Evidence indicates that oxidative stress and mitochondrial dysfunction are two key mediators of the secondary injury cascade in TBI pathology. TBI-induced oxidative damage results in the structural and functional impairments of cellular and subcellular components, such as mitochondria. Impairments of mitochondrial electron transfer chain and mitochondrial membrane potential result in a vicious cycle of free radical formation and cell apoptosis. The results of some preclinical and clinical studies, evaluating mitochondria-targeted therapies, such as mitochondria-targeted antioxidants and compounds with pleiotropic effects after TBI, are promising. As a proposed strategy in recent years, mitochondria-targeted multipotential therapy is a new hope, waiting to be confirmed. Moreover, based on the available findings, biologics, such as stem cell-based therapy and transplantation of mitochondria are novel potential strategies for the treatment of TBI; however, more studies are needed to clearly confirm the safety and efficacy of these strategies.

NRF2 and Key Transcriptional Targets in Melanoma Redox Manipulation

Melanocytes are dendritic, pigment-producing cells located in the skin and are responsible for its protection against the deleterious effects of solar ultraviolet radiation (UVR), which include DNA damage and elevated reactive oxygen species (ROS). They do so by synthesizing photoprotective melanin pigments and distributing them to adjacent skin cells (e.g., keratinocytes). However, melanocytes encounter a large burden of oxidative stress during this process, due to both exogenous and endogenous sources. Therefore, melanocytes employ numerous antioxidant defenses to protect themselves; these are largely regulated by the master stress response transcription factor, nuclear factor erythroid 2-related factor 2 (NRF2). Key effector transcriptional targets of NRF2 include the components of the glutathione and thioredoxin antioxidant systems. Despite these defenses, melanocyte DNA often is subject to mutations that result in the dysregulation of the proliferative mitogen-activated protein kinase (MAPK) pathway and the cell cycle. Following tumor initiation, endogenous antioxidant systems are co-opted, a consequence of elevated oxidative stress caused by metabolic reprogramming, to establish an altered redox homeostasis. This altered redox homeostasis contributes to tumor progression and metastasis, while also complicating the application of exogenous antioxidant treatments. Further understanding of melanocyte redox homeostasis, in the presence or absence of disease, would contribute to the development of novel therapies to aid in the prevention and treatment of melanomas and other skin diseases.

Mechanisms of nucleophosmin (NPM)-mediated regulated cell death elucidated by Hsp70 during renal ischemia

Nucleophosmin (NPM), a nucleolar-based protein chaperone, promotes Bax-mediated mitochondrial injury and regulates cell death during acute kidney injury. However, the steps that transform NPM from an essential to a toxic protein during stress are unknown. To localize NPM-mediated events causing regulated cell death during ischemia, wild type (WT) and Hsp70 mutant proteins with characterized intracellular trafficking defects that restrict movement to either the nucleolar region (M45) or cytosol (985A) were expressed in primary murine proximal tubule epithelial cells (PTEC) harvested from Hsp70 null mice. After ischemia in vitro, PTEC survival was significantly improved and apoptosis reduced in rank order by selectively overexpressing WT > M45 > 985A Hsp70 proteins. Only Hsp70 with nuclear access (WT and M45) inhibited T95 NPM phosphorylation responsible for NPM translocation and also reduced cytosolic NPM accumulation. In contrast, WT or 985A > M45 significantly improved survival in Hsp70 null PTEC that expressed a cytosol-restricted NPM mutant, more effectively bound NPM, and also reduced NPM-Bax complex formation required for mitochondrial injury and cell death. Hsp70 knockout prevented the cytoprotective effect of suppressing NPM in ischemic PTEC and also increased cytosolic NPM accumulation after acute renal ischemia in vivo, emphasizing the inhibitory effect of Hsp70 on NPM-mediated toxicity. Distinct cytoprotective mechanisms by wild type and mutant Hsp70 proteins identify dual nuclear and cytosolic events that mediate NPM toxicity during stress-induced apoptosis and are rational targets for therapeutic AKI interventions. Antagonizing these early events in regulated cell death promotes renal cell survival during experimental AKI.

Function, Therapeutic Potential, and Inhibition of Hsp70 Chaperones

Hsp70s are among the most highly conserved proteins in all of biology. Through an iterative binding and release of exposed hydrophobic residues on client proteins, Hsp70s can prevent aggregation and promote folding to the native state of their client proteins. The human proteome contains eight canonical Hsp70s. Because Hsp70s are relatively promiscuous they play a role in folding a large proportion of the proteome. Hsp70s are implicated in disease through their ability to regulate protein homeostasis. In recent years, researchers have attempted to develop selective inhibitors of Hsp70 isoforms to better understand the role of individual isoforms in biology and as potential therapeutics. Selective inhibitors have come from rational design, forced localization, and serendipity, but the development of completely selective inhibitors remains elusive. In the present review, we discuss the Hsp70 structure and function, the known Hsp70 client proteins, the role of Hsp70s in disease, and current efforts to discover Hsp70 modulators.

Hsp70 in cancer: A double agent in the battle between survival and death

The heat shock protein (Hsps) superfamily, also known as molecular chaperones, are highly conserved and present in all living organisms and play vital roles in protein fate. The HspA1A (Hsp70-1), called Hsp70 in this review, is expressed at low or undetectable levels in most unstressed normal cells, but numerous studies have shown that diverse types of tumor cells express Hsp70 at the plasma membrane that leads to resistance to programmed cell death and tumor progression. Hsp70 is released into the extracellular milieu in three forms including free soluble, complexed with cancer antigenic peptides, and exosome forms. Therefore, it seems to be a promising therapeutic target in human malignancies. However, a great number of studies have indicated that both intracellular and extracellular Hsp70 have a dual function. A line of evidence presented that intracellular Hsp70 has a cytoprotective function via suppression of apoptosis and lysosomal cell death (LCD) as well as that extracellular Hsp70 can promote tumorigenesis and angiogenesis. Other evidence showed intracellular Hsp70 can promote apoptosis and membrane-associated/extracellular Hsp70 can elicit antitumor innate and adaptive immune responses. Given the contradictory functions, as a "double agent," could Hsp70 be a promising tool in the future of targeted cancer therapies? To answer this question, in this review, we will discuss the functions of Hsp70 in cancers besides inhibition and stimulation strategies for targeting Hsp70 along with their challenges.

Quiescent hepatic stellate cells induce toxicity and sensitivity to doxorubicin in cancer cells through a caspase-independent cell death pathway: Central role of apoptosis-inducing factor

Hepatocellular carcinoma (HCC) is a major health problem worldwide and in the United States as its incidence has increased substantially within the past two decades. HCC therapy remains a challenge, primarily due to underlying liver disorders such as cirrhosis that determines treatment approach and efficacy. Activated hepatic stellate cells (A-HSCs) are the key cell types involved in hepatic fibrosis/cirrhosis. A-HSCs are important constituents of HCC tumor microenvironment (TME) and support tumor growth, chemotherapy resistance, cancer cell migration, and escaping immune surveillance. This makes A-HSCs an important therapeutic target in hepatic fibrosis/cirrhosis as well as in HCC. Although many studies have reported the role of A-HSCs in cancer generation and investigated the therapeutic potential of A-HSCs reversion in cancer arrest, not much is known about inactivated or quiescent HSCs (Q-HSCs) in cancer growth or arrest. Here we report that Q-HSCs resist cancer cell growth by inducing cytotoxicity and enhancing chemotherapy sensitivity. We observed that the conditioned media from Q-HSCs (Q-HSCCM) induces cancer cell death through a caspase-independent mechanism that involves an increase in apoptosis-inducing factor expression, nuclear localization, DNA fragmentation, and cell death. We further observed that Q-HSCCM enhanced the efficiency of doxorubicin, as measured by cell viability assay. Exosomes present in the conditioned media were not involved in the mechanism, which suggests the role of other factors (proteins, metabolites, or microRNA) secreted by the cells. Identification and characterization of these factors are important in the development of effective HCC therapy.

Hsp70: A Cancer Target Inside and Outside the Cell

Heat shock protein 70 (Hsp70) is the most ubiquitous stress-inducible chaperone. It accumulates in the cells in response to a wide variety of physiological and environmental insults including anticancer chemotherapy, thus allowing the cell to survive to lethal conditions. Intracellular Hsp70 is viewed as a cytoprotective protein. Indeed, this protein can inhibit key effectors of the apoptotic and autophagy machineries. In cancer cells, the expression of Hsp70 is abnormally high, and Hsp70 may participate in oncogenesis and in resistance to chemotherapy. In rodent models, Hsp70 overexpression increases tumor growth and metastatic potential. Depletion or inhibition of Hsp70 frequently reduces the size of the tumors and can even cause their complete involution. However, HSP70 is also found in the extra-cellular space where it may signal via membrane receptors or endosomes to alter gene transcription and cellular function. Overall, Hsp70 extracellular function is believed to be immnunogenic and the term chaperokine to define the extracellular chaperones such as Hsp70 has been advanced. In this chapter the knowledge to date, as well as some emerging paradigms about the intra- and extra-cellular functions of Hsp70, are presented. The strategies targeting Hsp70 that are being developed in cancer therapy will also be discussed.

Blocking peptides and molecular mimicry as treatment for kidney disease

Protein mimotopes, or blocking peptides, are small therapeutic peptides that prevent protein-protein interactions by selectively mimicking a native binding domain. Inexpensive technology facilitates straightforward design and production of blocking peptides in sufficient quantities to allow preventive and therapeutic trials in both in vitro and in vivo experimental disease models. The kidney is an ideal peptide target, since small molecules undergo rapid filtration and efficient bulk absorption by tubular epithelial cells. Because the half-life of peptides is markedly prolonged in the kidneys compared with the bloodstream, blocking peptides are an attractive tool for treating diverse renal diseases, including ischemia, proteinuric states, such as membranous nephropathy and focal and segmental glomerulosclerosis, and renal cell carcinoma. Therapeutic peptides represent one of the fastest-growing reagent classes for novel drug development in human disease, partly because of their ease of administration, high binding affinity, and minimal off-target effects. This review introduces the concepts of blocking peptide design, production, and administration and highlights the potential use of therapeutic peptides to prevent or treat specific renal diseases.

miR-146a is essential for lipopolysaccharide (LPS)-induced cross-tolerance against kidney ischemia/reperfusion injury in mice

MicroRNA-146a is one of most important microRNAs involved in development of endotoxin tolerance via (toll-like receptors) TLRs/ NF-κB pathway. In this study, we sought to identify the mechanistic role of miR-146a in mediating the protective effect of lipopolysaccharide (LPS) pretreatment on kidney ischemia/reperfusion injury. A locked nucleic acid–modified anti-miR-146a given before LPS treatment knocked down miR-146a expression and completely negated LPS-mediated protection against kidney ischemia/reperfusion injury. Knockdown of miR-146a resulted in significantly higher histopathological scores for tubular damage, expression of proinflammatory cytokines and chemokines, and neutrophil and macrophage infiltration. Furthermore, knockdown of miR-146a greatly up-regulated the protein levels of IL-1 receptor-associated kinase (IRAK-1) and tumor-necrosis factor (TNF) receptor-associated factor 6 (TRAF6), which are known target genes of miR-146a, leading to activation of NF-κB. Finally, elevation of nuclear translocation of NF-κB p65/p50 and caspase-3 expression, degradation of cytosolic IkBα and BcL-xL, and substantially exacerbation of tubular cell apoptosis were inversely correlated with miR-146a expression. Taken together, our results identify that miR146a exerts a kidney protective effect through negative regulation of acute inflammatory response by suppressing NF-κB activation and proinflammatory genes expression.

Targeting Hsp70: A possible therapy for cancer

In all organisms, heat-shock proteins (HSPs) provide an ancient defense system. These proteins act as molecular chaperones by assisting proper folding and refolding of misfolded proteins and aid in the elimination of old and damaged cells. HSPs include Hsp100, Hsp90, Hsp70, Hsp40, and small HSPs. Through its substrate-binding domains, Hsp70 interacts with wide spectrum of molecules, ranging from unfolded to natively folded and aggregated proteins, and provides cytoprotective role against various cellular stresses. Under pathophysiological conditions, the high expression of Hsp70 allows cells to survive with lethal injuries. Increased Hsp70, by interacting at several points on apoptotic signaling pathways, leads to inhibition of apoptosis. Elevated expression of Hsp70 in cancer cells may be responsible for tumorigenesis and for tumor progression by providing resistance to chemotherapy. In contrast, inhibition or knockdown of Hsp70 reduces the size of tumors and can cause their complete regression. Moreover, extracellular Hsp70 acts as an immunogen that participates in cross presentation of MHC-I molecules. The goals of this review are to examine the roles of Hsp70 in cancer and to present strategies targeting Hsp70 in the development of cancer therapeutics.

Combined use of heat-shock protein 70 and glutamine synthetase is useful in the distinction of typical hepatocellular adenoma from atypical hepatocellular neoplasms and well-differentiated hepatocellular carcinoma

Well-differentiated hepatocellular carcinoma can mimic high-grade dysplastic nodule in cirrhotic liver and hepatocellular adenoma in non-cirrhotic liver. This study evaluates the efficacy of combined use of heat-shock protein 70 (HSP70), glutamine synthetase (GS) and glypican-3 in this setting. Immunohistochemistry for these three markers was done in 17 typical hepatocellular adenoma, 15 high-grade dysplastic nodules, 20 atypical hepatocellular neoplasms (14 clinically atypical and 6 pathologically atypical), 14 very well-differentiated hepatocellular carcinoma, and 43 well-differentiated hepatocellular carcinoma. All three markers were negative in typical adenomas. HSP70 was positive in 10, 71, and 67% of atypical neoplasms, very well-differentiated and well-differentiated HCC, respectively, while GS was positive in 60, 50, and 60% of atypical neoplasms, very well-differentiated and well-differentiated hepatocellular carcinoma, respectively. Glypican-3 was negative in all atypical neoplasms and very well-differentiated hepatocellular carcinoma, and was positive in 27% of well-differentiated hepatocellular carcinoma. Positive staining with at least one marker (HSP70 and/or GS) was seen in 85% of very well-differentiated hepatocellular carcinoma, which was similar to well-differentiated hepatocellular carcinoma (78%, P=0.4), and pathologically atypical cases (100%, P=0.5), but significantly higher compared with clinically atypical cases (43%. P=0.03) and none of typical adenomas (P<0.001). Positive staining with both GS and HSP70 was seen significantly more often in hepatocellular carcinoma compared with atypical neoplasms (45 vs 10%, P=0.004). Both these markers were also more often expressed in very well-differentiated hepatocellular carcinoma compared with atypical cases (38 vs 10%, P=0.06). In conclusion, the combined use of GS and HSP70 can be useful in the diagnosis of very well-differentiated hepatocellular carcinoma. These stains can also help in the distinction of typical adenoma from atypical hepatocellular neoplasms. Glypican-3 has low sensitivity and is not useful in this setting.

Hep88 mAb-mediated paraptosis-like apoptosis in HepG2 cells via downstream upregulation and activation of caspase-3, caspase-8 and caspase-9

Hepatocellular carcinoma (HCC) is a leading cause of cancer death worldwide. Presently, targeted therapy via monoclonal antibodies to specific tumor-associated antigens is being continuously developed. Hep88 mAb has proven to exert tumoricidal effects on the HepG2 cell via a paraptosis-like morphology. To verify the pathway, we then demonstrated downstream up-regulation of caspase-3, caspase-8 and caspase-9, assessingmRNA expression by real-time PCR and associated enzyme activity by colorimetric assay. Active caspase-3 determination was also accomplished by flow cytometry. Active caspase-3 expression was increased by Hep88 mAb treatment in a dose-and time-dependent manner. All of the results indicated that Hep88 mAb induced programmed cell death in the HepG2 cell line from paraptosis-like to apoptosis by downstream induction of caspases. These conclusions imply that Hep88mAb might be a promising tool for the effective treatment of HCC in the future.

Cyclosporine A increases hair follicle growth by suppressing apoptosis-inducing factor nuclear translocation: a new mechanism

Cyclosporine A (CsA) enhances hair growth through caspase-dependent pathways by retarding anagen-to-catagen phase transition in the hair follicle growth cycle. Whether apoptosis-inducing factor (AIF), a protein that induces caspase-independent apoptosis, can regulate the hair follicle cycle in response to CsA is currently unclear. Here, we show that the pro-hair growth properties of CsA are in part due to blockage of AIF nuclear translocation. We first isolate hair follicles from murine dorsal skin. We then used Western blot, immunohistochemistry and immunofluorescence to evaluate the expression and localization of AIF in hair follicles. We also determined whether modulation of AIF was responsible for the effects of CsA at the anagen-to-catagen transition. AIF was expressed in hair follicles during the anagen, catagen and telogen phases. There was significant nuclear translocation of AIF as hair follicles transitioned from anagen to late catagen phase; this was inhibited by CsA, likely due to reduced cyclophilin A expression and attenuated AIF release from mitochondria. However, we note that AIF translocation was not completely eliminated, which likely explains why the transition to catagen phase was severely retarded by CsA, rather than being completely inhibited. We speculate that blockade of the AIF signalling pathway is a critical event required for CsA-dependent promotion of hair growth in mice. The study of AIF-related signalling pathways may provide insight into hair diseases and suggest potential novel therapeutic strategies.

mReg2 inhibits nuclear entry of apoptosis-inducing factor in mouse insulinoma cells

We have reported earlier that murine-regenerating gene mReg2 protects MIN6 mouse insulinoma cells from ER stress and caspase-mediated apoptosis. In apoptotic cells, DNA damage is induced by the nuclear translocation of mitochondrial apoptosis-inducing factor (AIF). Here we tested the hypothesis that mReg2 may regulate Scythe and/or hsp70 which influence the nuclear import of AIF. Treatment with thapsigargin (Tg) or doxorubicin induced an increase in nuclear AIF in MIN6 cells carrying the empty transfection vector (MIN6-VC) but not in cells overexpressing mReg2 (MIN6-mReg2). On one hand, nuclear Scythe was higher in the nucleus of MIN6-mReg2 compared with that in MIN6-VC cells. mReg2 did not alter the expression of AIF or Scythe. On the other hand, mReg2 induced the expression of hsp70 which is known to promote cytosolic retention of AIF. We conclude that mReg2 inhibits AIF-mediated apoptosis by promoting the nuclear presence of Scythe and inducing hsp70.

Heat shock proteins in multiple myeloma

Heat shock proteins are molecular chaperones with a central role in protein folding and cellular protein homeostasis. They also play major roles in the development of cancer and in recent years have emerged as promising therapeutic targets. In this review, we discuss the known molecular mechanisms of various heat shock protein families and their involvement in cancer and in particular, multiple myeloma. In addition, we address the current progress and challenges in pharmacologically targeting these proteins as anti-cancer therapeutic strategies.

Heat shock protein 72 suppresses apoptosis by increasing the stability of X-linked inhibitor of apoptosis protein in renal ischemia/reperfusion injury

X-linked inhibitor of apoptosis protein (XIAP) negatively regulates apoptotic pathways at a post-mitochondrial level. XIAP functions by directly binding and inhibiting activation of specific caspases. Upon apoptotic stimuli, mitochondrial second mitochondria-derived activator of caspases (Smac)/direct IAP-binding protein with low PI (DIABLO) is released into the cytosol, which results in displacement of XIAP from caspases. Heat shock protein 72 (HSP72), an anti-apoptotic protein, prevents mitochondrial injury resulting from acute renal ischemia/reperfusion (I/R), its role in Smac/DIABLO and XIAP signaling remains to be elucidated. In the present study, the hypothesis that HSP72 prevents XIAP degradation in vivo and in vitro was assessed. To this purpose, a rat model of I/R injury was used to investigate the renoprotective role of HSP72 by treatment with geranylgeranylacetone (GGA), a specific inducer of HSP72. The mechanism of the cytoprotective properties of HSP72 was also investigated in vitro using adenovirus-mediated overexpression of HSP72 in adenosine triphosphate (ATP)-depleted human kidney 2 (HK-2) cells. Pre-conditioning rats with GGA attenuated renal tubular cell damage, reduced cell apoptosis, preserved XIAP protein content and improved renal function following I/R injury. An in vitro study was performed in which cells were transiently exposed to 5 mM sodium cyanide in a glucose-free medium in order to induce apoptosis. Compared with the control, overexpression of HSP72 inhibited Smac/DIABLO release from the mitochondria and increased levels of XIAP and pro-caspase 3 in ATP-depleted HK-2 cells. In addition, HSP72 interacted with Smac/DIABLO. The present data demonstrates that HSP72 preserves renal function in I/R injury through its anti-apoptotic effects, which act by suppressing mitochondrial Smac/DIABLO release and preserving XIAP protein content.

Conditional knockout of proximal tubule mitofusin 2 accelerates recovery and improves survival after renal ischemia

Proximal tubule (PT) cells are critical targets of acute ischemic injury. Elimination of the mitochondrial fusion protein mitofusin 2 (Mfn2) sensitizes PT cells to apoptosis in vitro. However, the role of PT Mfn2 in ischemic AKI in vivo is unknown. To test its role, we evaluated the effects of conditional KO of PT Mfn2 (cKO-PT-Mfn2) on animal survival after transient bilateral renal ischemia associated with severe AKI. Forty-eight hours after ischemia, 28% of control mice survived compared with 86% of cKO-PT-Mfn2 animals (P<0.001 versus control). Although no significant differences in histologic injury score, apoptosis, or necrosis were detected between genotypes, cKO-PT-Mfn2 kidneys exhibited a 3.5-fold increase in cell proliferation restricted to the intrarenal region with Mfn2 deletion. To identify the signals responsible for increased proliferation, primary PT cells with Mfn2 deficiency were subjected to stress by ATP depletion in vitro. Compared with normal Mfn2 expression, Mfn2 deficiency significantly increased PT cell proliferation and persistently activated extracellular signal-regulated kinase 1/2 (ERK1/2) during recovery from stress. Furthermore, stress and Mfn2 deficiency decreased the interaction between Mfn2 and Ras detected by immunoprecipitation, and purified Mfn2 dose-dependently decreased Ras activity in a cell-free assay. Ischemia in vivo also reduced the Mfn2-RAS interaction and increased both RAS and p-ERK1/2 activity in the renal cortical homogenates of cKO-PT-Mfn2 mice. Our results suggest that, in contrast to its proapoptotic effects in vitro, selective PT Mfn2 deficiency accelerates recovery of renal function and enhances animal survival after ischemic AKI in vivo, partly by increasing Ras-ERK-mediated cell proliferation.

Molecular chaperones and protein folding as therapeutic targets in Parkinson's disease and other synucleinopathies

Changes in protein metabolism are key to disease onset and progression in many neurodegenerative diseases. As a prime example, in Parkinson's disease, folding, post-translational modification and recycling of the synaptic protein α-synuclein are clearly altered, leading to a progressive accumulation of pathogenic protein species and the formation of intracellular inclusion bodies. Altered protein folding is one of the first steps of an increasingly understood cascade in which α-synuclein forms complex oligomers and finally distinct protein aggregates, termed Lewy bodies and Lewy neurites. In neurons, an elaborated network of chaperone and co-chaperone proteins is instrumental in mediating protein folding and re-folding. In addition to their direct influence on client proteins, chaperones interact with protein degradation pathways such as the ubiquitin-proteasome-system or autophagy in order to ensure the effective removal of irreversibly misfolded and potentially pathogenic proteins. Because of the vital role of proper protein folding for protein homeostasis, a growing number of studies have evaluated the contribution of chaperone proteins to neurodegeneration. We herein review our current understanding of the involvement of chaperones, co-chaperones and chaperone-mediated autophagy in synucleinopathies with a focus on the Hsp90 and Hsp70 chaperone system. We discuss genetic and pathological studies in Parkinson's disease as well as experimental studies in models of synucleinopathies that explore molecular chaperones and protein degradation pathways as a novel therapeutic target. To this end, we examine the capacity of chaperones to prevent or modulate neurodegeneration and summarize the current progress in models of Parkinson's disease and related neurodegenerative disorders.

High dietary taurine inhibits myocardial apoptosis during an atherogenic diet: association with increased myocardial HSP70 and HSF-1 but not caspase 3

BACKGROUND AND AIM

Apoptosis is a major cause of myocyte death, and taurine is anti-apoptotic. Heat shock protein 70 (HSP70) (which is regulated by heat shock factor-HSF-1) is also anti-apoptotic, and caspase 3 stimulates the apoptotic pathway. This study investigated whether taurine affects atherogenic diet-induced myocardial apoptosis, and whether HSP70, HSF-1 and caspase 3 are involved.

METHODS

New Zealand white rabbits were divided into 3 groups for 4 weeks according to their diet. Group 1 (control) was fed a normal rabbit diet; Group 2 (MC) received a normal rabbit diet with 1% methionine plus 0.5% cholesterol. Group 3 received MC diet + 2.5% taurine (MCT).

RESULTS

The atherogenic diet did not affect myocardial HSP70 or HSF-1 protein, but increased myocardial apoptotic nuclei to 40% (p < 0.01) versus 7% in con and 12% in MCT (p < 0.01). However, in MCT, myocardial HSP70 expression increased by 42.7% versus con and MC (p = 0.016), HSF-1 by 12% versus con and MC (p < 0.05), and total nuclei count increased by 37% versus MC (p < 0.05). Caspase 3 subunits remained unchanged in all groups, and HSP70 was increased approximately twofold in endothelial layer of arterioles (p = 0.01).

CONCLUSION

This study shows that taurine could reduce myocardial apoptotic nuclei and thus confer myocardial cytoprotection via stimulating myocardial HSP70 via HSF-1 and caspase 3-independent mechanisms.

Nucleophosmin, a critical Bax cofactor in ischemia-induced cell death

We hypothesized that nucleophosmin (NPM), a nucleolar phosphoprotein, is critical for Bax-mediated cell death. To test this hypothesis, Bax activation was induced by metabolic stress. During stress, nucleolar NPM translocated into the cytosol, NPM-Bax complexes formed, and both NPM and Bax accumulated in mitochondria. Expression of a cytosol-restricted NPM mutant (NPM-ΔNLS), but not a nucleus-restricted NPM mutant, increased NPM-Bax complex formation, mitochondrial NPM and Bax accumulation, mitochondrial membrane injury, caspase 3 activation, and ischemia-induced cell death. Coexpression of NPM-ΔNLS with constitutively active Bax mutants caused nearly universal cell death in the absence of metabolic stress, whereas expression of active Bax or NPM-ΔNLS alone did not. A Bax peptide that disrupts NPM-Bax interaction significantly reduced cell death caused by exposure to metabolic inhibitors in vitro and preserved kidney function after ischemia in vivo. Thus, NPM-Bax interaction enhances mitochondrial Bax accumulation, organelle injury, and cell death. NPM-Bax complex formation is a novel target for preventing ischemic tissue injury.

Mitochondria in traumatic brain injury and mitochondrial-targeted multipotential therapeutic strategies

Traumatic brain injury (TBI) is a major health and socioeconomic problem throughout the world. It is a complicated pathological process that consists of primary insults and a secondary insult characterized by a set of biochemical cascades. The imbalance between a higher energy demand for repair of cell damage and decreased energy production led by mitochondrial dysfunction aggravates cell damage. At the cellular level, the main cause of the secondary deleterious cascades is cell damage that is centred in the mitochondria. Excitotoxicity, Ca(2+) overload, reactive oxygen species (ROS), Bcl-2 family, caspases and apoptosis inducing factor (AIF) are the main participants in mitochondria-centred cell damage following TBI. Some preclinical and clinical results of mitochondria-targeted therapy show promise. Mitochondria- targeted multipotential therapeutic strategies offer new hope for the successful treatment of TBI and other acute brain injuries.

Co-induction of the heat shock response ameliorates disease progression in a mouse model of human spinal and bulbar muscular atrophy: implications for therapy

Spinal and bulbar muscular atrophy, also known as Kennedy's disease, is an adult-onset hereditary neurodegenerative disorder caused by an expansion of the polyglutamine repeat in the first exon in the androgen receptor gene. Pathologically, the disease is defined by selective loss of spinal and bulbar motor neurons causing bulbar, facial and limb weakness. Although the precise disease pathophysiology is largely unknown, it appears to be related to abnormal accumulation of the pathogenic androgen receptor protein within the nucleus, leading to disruption of cellular processes. Using a mouse model of spinal and bulbar muscular atrophy that exhibits many of the characteristic features of the human disease, in vivo physiological assessment of muscle function revealed that mice with the pathogenic expansion of the androgen receptor develop a motor deficit characterized by a reduction in muscle force, abnormal muscle contractile characteristics, loss of functional motor units and motor neuron degeneration. We have previously shown that treatment with arimoclomol, a co-inducer of the heat shock stress response, delays disease progression in the mutant superoxide dismutase 1 mouse model of amyotrophic lateral sclerosis, a fatal motor neuron disease. We therefore evaluated the therapeutic potential of arimoclomol in mice with spinal and bulbar muscular atrophy. Arimoclomol was administered orally, in drinking water, from symptom onset and the effects established at 18 months of age, a late stage of disease. Arimoclomol significantly improved hindlimb muscle force and contractile characteristics, rescued motor units and, importantly, improved motor neuron survival and upregulated the expression of the vascular endothelial growth factor which possess neurotrophic activity. These results provide evidence that upregulation of the heat shock response by treatment with arimoclomol may have therapeutic potential in the treatment of spinal and bulbar muscular atrophy and may also be a possible approach for the treatment of other neurodegenerative diseases.

Inhibition of HSP70: a challenging anti-cancer strategy

HSP70 is a chaperone that accumulates in the cells after many different stresses promoting cell survival in response to the adverse conditions. In contrast to normal cells, most cancer cells abundantly express HSP70 at the basal level to resist to various insults at different stages of tumorigenesis and during anti-cancer treatment. This cancer cells addiction for HSP70 is the rational for its targeting in cancer therapy. Much effort has been dedicated in the last years for the active search of HSP70 inhibitors. Additionally, the recent clinical trials on highly promising inhibitors of another stress protein, HSP90, showed compensatory increase in HSP70 levels and raised the question of necessity to combine HSP90 inhibitors with simultaneous inhibition of HSP70. Here we analyzed the recent advancement in creation of novel HSP70 inhibitors and different strategies for their use in anti-cancer therapy.

Role of mitofusin 2 in the renal stress response

The role of mitofusin 2 (MFN2), a key regulator of mitochondrial morphology and function in the renal stress response is unknown. To assess its role, the MFN2 floxed gene was conditionally deleted in the kidney of mice (MFN2 cKO) by Pax2 promoter driven Cre expression (Pax2Cre). MFN2 cKO caused severe mitochondrial fragmentation in renal epithelial cells that are critical for normal kidney tubular function. However, despite a small (20%) decrease in nephron number, newborn cKO pups had organ or tubular function that did not differ from littermate Cre-negative pups. MFN2 deficiency in proximal tubule epithelial cells in primary culture induced mitochondrial fragmentation but did not significantly alter ATP turnover, maximal mitochondrial oxidative reserve capacity, or the low level of oxygen consumption during cyanide exposure. MFN2 deficiency also did not increase apoptosis of tubule epithelial cells under non-stress conditions. In contrast, metabolic stress caused by ATP depletion exacerbated mitochondrial outer membrane injury and increased apoptosis by 80% in MFN2 deficient vs. control cells. Despite similar stress-induced Bax 6A7 epitope exposure in MFN2 deficient and control cells, MFN2 deficiency significantly increased mitochondrial Bax accumulation and was associated with greater release of both apoptosis inducing factor and cytochrome c. In conclusion, MFN2 deficiency in the kidney causes mitochondrial fragmentation but does not affect kidney or tubular function during development or under non-stress conditions. However, MFN2 deficiency exacerbates renal epithelial cell injury by promoting Bax-mediated mitochondrial outer membrane injury and apoptosis.

(S)-ZJM-289, a nitric oxide-releasing derivative of 3-n-butylphthalide, protects against ischemic neuronal injury by attenuating mitochondrial dysfunction and associated cell death

Pharmacological compounds that release nitric oxide (NO) have been recognized as the potential therapeutic agents for acute stroke. (S)-ZJM-289 is a novel NO-releasing derivative of 3-n-butylphthalide (NBP) with enhanced anti-platelet and anti-thrombotic actions. The present study was performed to investigate the neuroprotective effects and related mechanisms of (S)-ZJM-289 on ischemic neuronal injury in vitro and in vivo. Primary cortical neuronal cultures were exposured to oxygen-glucose deprivation followed by recovery (OGD/R), a model of ischemia-like injury, and treated with (S)-ZJM-289 before OGD. In vitro results showed that (S)-ZJM-289 attenuated OGD/R-induced neuronal injury, which was associated with the maintenance of mitochondrial integrity and function by alleviating intracellular calcium overload and reactive oxygen species (ROS) accumulation, preventing mitochondrial membrane depolarization and preserving respiratory chain complexes activities. Moreover, (S)-ZJM-289 treatment suppressed mitochondrial release of cytochrome c (cyt c) and nuclear translocation of apoptosis-inducing factor (AIF), thereby blocking mitochondria-mediated cell death, which may be partially mediated by up-regulation of Hsp70. The neuroprotection by (S)-ZJM-289 was also studied using a model of middle cerebral artery occlusion (MCAO). Oral administration of (S)-ZJM-289 at the onset of reperfusion for 3d significantly reduced the brain infarct size, improved neurological deficit and prevented neuronal loss and apoptosis. In current study, (S)-ZJM-289 appears to be more potent in ischemic neuroprotection than NBP, in particular at the lower doses, which may be due to the synergistic action of NBP and NO. These findings point to that (S)-ZJM-289 could be an attractive alternative to NBP in preventing the process of ischemia/reperfusion (I/R) injury.

Apoptosis-inducing factor: structure, function, and redox regulation

Apoptosis-inducing factor (AIF) is a flavin adenine dinucleotide-containing, NADH-dependent oxidoreductase residing in the mitochondrial intermembrane space whose specific enzymatic activity remains unknown. Upon an apoptotic insult, AIF undergoes proteolysis and translocates to the nucleus, where it triggers chromatin condensation and large-scale DNA degradation in a caspase-independent manner. Besides playing a key role in execution of caspase-independent cell death, AIF has emerged as a protein critical for cell survival. Analysis of in vivo phenotypes associated with AIF deficiency and defects, and identification of its mitochondrial, cytoplasmic, and nuclear partners revealed the complexity and multilevel regulation of AIF-mediated signal transduction and suggested an important role of AIF in the maintenance of mitochondrial morphology and energy metabolism. The redox activity of AIF is essential for optimal oxidative phosphorylation. Additionally, the protein is proposed to regulate the respiratory chain indirectly, through assembly and/or stabilization of complexes I and III. This review discusses accumulated data with respect to the AIF structure and outlines evidence that supports the prevalent mechanistic view on the apoptogenic actions of the flavoprotein, as well as the emerging concept of AIF as a redox sensor capable of linking NAD(H)-dependent metabolic pathways to apoptosis.

Apoptosis and acute kidney injury

Improved mechanistic understanding of renal cell death in acute kidney injury (AKI) has generated new therapeutic targets. Clearly, the classic lesion of acute tubular necrosis is not adequate to describe the consequences of renal ischemia, nephrotoxin exposure, or sepsis on glomerular filtration rate. Experimental evidence supports a pathogenic role for apoptosis in AKI. Interestingly, proximal tubule epithelial cells are highly susceptible to apoptosis, and injury at this site contributes to organ failure. During apoptosis, well-orchestrated events converge at the mitochondrion, the organelle that integrates life and death signals generated by the BCL2 (B-cell lymphoma 2) protein family. Death requires the 'perfect storm' for outer mitochondrial membrane injury to release its cellular 'executioners'. The complexity of this process affords new targets for effective interventions, both before and after renal insults. Inhibiting apoptosis appears to be critical, because circulating factors released by the injured kidney induce apoptosis and inflammation in distant organs including the heart, lung, liver, and brain, potentially contributing to the high morbidity and mortality associated with AKI. Manipulation of known stress kinases upstream of mitochondrial injury, induction of endogenous, anti-apoptotic proteins, and improved understanding of the timing and consequences of renal cell apoptosis will inevitably improve the outcome of human AKI.

Hexokinase regulates Bax-mediated mitochondrial membrane injury following ischemic stress

Hexokinase (HK), the rate-limiting enzyme in glycolysis, controls cell survival by promoting metabolism and/or inhibiting apoptosis. Since HK isoforms I and II have mitochondrial targeting sequences, we attempted to separate the protective effects of HK on cell metabolism from those on apoptosis. We exposed renal epithelial cells to metabolic stress causing ATP depletion in the absence of glucose and found that this activated glycogen synthase kinase 3β (GSK3β) and Bax caused mitochondrial membrane injury and apoptosis. ATP depletion led to a progressive HK II dissociation from mitochondria, released mitochondrial apoptosis inducing factor and cytochrome c into the cytosol, activated caspase-3, and reduced cell survival. Compared with control, adenoviral-mediated HK I or II overexpression improved cell survival following stress, but did not prevent GSK3β or Bax activation, improve ATP content, or reduce mitochondrial fragmentation. HK I or HK II overexpression increased mitochondria-associated isoform-specific HK content, and decreased mitochondrial membrane injury and apoptosis after stress. In vivo, HK II localized exclusively to the proximal tubule. Ischemia reduced total renal HK II content and dissociated HK II from proximal tubule mitochondria. In cells overexpressing HK II, Bax and HK II did not interact before or after stress. While the mechanism by which HK antagonizes Bax-mediated apoptosis is unresolved by these studies, one possible scenario is that the two proteins compete for a common binding site on the outer mitochondrial membrane.

Induction of heat shock protein 70 inhibits ischemic renal injury

Heat shock protein 70 (Hsp70) is a potent antiapoptotic agent. Here, we tested whether it directly regulates renal cell survival and organ function in a model of transient renal ischemia using Hsp70 knockout, heterozygous, and wild-type mice. The kidney cortical Hsp70 content inversely correlated with tubular injury, apoptosis, and organ dysfunction after injury. In knockout mice, ischemia caused changes in the activity of Akt and glycogen synthase kinase 3-β (kinases that regulate the proapoptotic protein Bax), increased active Bax, and activated the proapoptotic protease caspase 3. As these changes were significantly reduced in the wild-type mice, we tested whether Hsp70 influences ischemia-induced apoptosis. An Hsp70 inducer, geranylgeranylacetone, increased Hsp70 expression in heterozygous and wild-type mice, and reduced both ischemic tubular injury and organ dysfunction. When administered after ischemia, this inducer also decreased tubular injury and organ failure in wild-type mice but did not protect the knockout mice. ATP depletion in vitro caused greater mitochondrial Bax accumulation and death in primary proximal tubule cells harvested from knockout compared with wild-type mice and altered serine phosphorylation of a Bax peptide at the Akt-specific target site. In contrast, lentiviral-mediated Hsp70 repletion decreased mitochondrial Bax accumulation and rescued Hsp70 knockout cells from death. Thus, increasing Hsp70 either before or after ischemic injury preserves renal function by attenuating acute kidney injury.

Hsp70: anti-apoptotic and tumorigenic protein

Heat shock protein 70 (Hsp70) is a powerful chaperone whose expression is induced in response to a wide variety of physiological and environmental insults, including anticancer chemotherapy, thus allowing the cell to survive to lethal conditions. Hsp70 cytoprotective properties may be explained by its anti-apoptotic function. Indeed, this protein can inhibit key effectors of the apoptotic machinery at the pre- and postmitochondrial level. In cancer cells, the expression of Hsp70 is abnormally high, and Hsp70 may participate in oncogenesis and in resistance to chemotherapy. In rodent models, Hsp70 overexpression increases tumor growth and metastatic potential. Depletion or inhibition of Hsp70 frequently reduces the size of the tumors and even can cause their complete involution. But Hsp70 can also be found in the extracellular medium. Its role is then immunogenic and the term chaperokine to define the extracellular chaperones has been advanced. Hsp70 tumorigenic functions as well as the strategies that are being developed in cancer therapy in order to inhibit Hsp70 are commented in this chapter.

Inhibition of the JNK/Bim pathway by Hsp70 prevents Bax activation in UV-induced apoptosis

Here we studied the mechanism by which heat shock protein 70 (Hsp70) prevents Bax activation during ultraviolet (UV)-induced apoptosis. UV treatment led to c-Jun N-terminal kinase (JNK) phosphorylation, Bim redistribution and subsequent Bax activation. Bim depletion caused a smaller reduction in apoptosis than that by JNK inhibition, indicating that Bim activation is not entirely responsible for induction of apoptosis and other mechanisms are involved. Hsp70 knockdown resulted in high levels of activated JNK and Bax, while Hsp70 overexpression inhibited these processes. These findings demonstrate that Hsp70 prevented Bax activation via inhibiting the JNK/Bim pathway. Simultaneously, increased binding of Hsp70 to Bax was observed. Collectively, our results for the first time demonstrate that Hsp70 prevents Bax activation both by inhibiting the JNK/Bim pathway and by interacting with Bax in UV-induced apoptosis.

Heat shock proteins: cellular and molecular mechanisms in the central nervous system

Emerging evidence indicates that heat shock proteins (HSPs) are critical regulators in normal neural physiological function as well as in cell stress responses. The functions of HSPs represent an enormous and diverse range of cellular activities, far beyond the originally identified roles in protein folding and chaperoning. HSPs are now understood to be involved in processes such as synaptic transmission, autophagy, ER stress response, protein kinase and cell death signaling. In addition, manipulation of HSPs has robust effects on the fate of cells in neurological injury and disease states. The ongoing exploration of multiple HSP superfamilies has underscored the pluripotent nature of HSPs in the cellular context, and has demanded the recent revamping of the nomenclature referring to these families to reflect a re-organization based on structure and function. In keeping with this re-organization, we first discuss the HSP superfamilies in terms of protein structure, regulation, expression and distribution in the brain. We then explore major cellular functions of HSPs that are relevant to neural physiological states, and from there we discuss known and proposed HSP impacts on major neurological disease states. This review article presents a three-part discussion on the array of HSP families relevant to neuronal tissue, their cellular functions, and the exploration of therapeutic targets of these proteins in the context of neurological diseases.