Adenoviral gene transfer of hepatic stimulator substance confers resistance against hepatic ischemia-reperfusion injury by improving mitochondrial function

Preservation of Mitochondrial Health in Liver Ischemia/Reperfusion Injury

Liver ischemia-reperfusion injury (LIRI) is a major cause of the development of complications in different clinical settings such as liver resection and liver transplantation. Damage arising from LIRI is a major risk factor for early graft rejection and is associated with higher morbidity and mortality after surgery. Although the mechanisms leading to the injury of parenchymal and non-parenchymal liver cells are not yet fully understood, mitochondrial dysfunction is recognized as a hallmark of LIRI that exacerbates cellular injury. Mitochondria play a major role in glucose metabolism, energy production, reactive oxygen species (ROS) signaling, calcium homeostasis and cell death. The diverse roles of mitochondria make it essential to preserve mitochondrial health in order to maintain cellular activity and liver integrity during liver ischemia/reperfusion (I/R). A growing body of studies suggest that protecting mitochondria by regulating mitochondrial biogenesis, fission/fusion and mitophagy during liver I/R ameliorates LIRI. Targeting mitochondria in conditions that exacerbate mitochondrial dysfunction, such as steatosis and aging, has been successful in decreasing their susceptibility to LIRI. Studying mitochondrial dysfunction will help understand the underlying mechanisms of cellular damage during LIRI which is important for the development of new therapeutic strategies aimed at improving patient outcomes. In this review, we highlight the progress made in recent years regarding the role of mitochondria in liver I/R and discuss the impact of liver conditions on LIRI.

COX-2 Expression in Hepatocytes Improves Mitochondrial Function after Hepatic Ischemia-Reperfusion Injury

Cyclooxygenase 2 (COX-2) is a key enzyme in prostanoid biosynthesis. The constitutive hepatocyte expression of COX-2 has a protective role in hepatic ischemia-reperfusion (I/R) injury (IRI), decreasing necrosis, reducing reactive oxygen species (ROS) levels, and increasing autophagy and antioxidant and anti-inflammatory response. The physiopathology of IRI directly impacts mitochondrial activity, causing ATP depletion and being the main source of ROS. Using genetically modified mice expressing human COX-2 (h-COX-2 Tg) specifically in hepatocytes, and performing I/R surgery on the liver, we demonstrate that COX-2 expression has a beneficial effect at the mitochondrial level. Mitochondria derived from h-COX-2 Tg mice livers have an increased respiratory rate associated with complex I electron-feeding pathways compared to Wild-type (Wt) littermates, without affecting complex I expression or assembly. Furthermore, Wt-derived mitochondria show a loss of mitochondrial membrane potential (ΔΨm) that correlates to increased proteolysis of fusion-related OPA1 through OMA1 protease activity. All these effects are not observed in h-COX-2 Tg mitochondria, which behave similarly to the Sham condition. These results suggest that COX-2 attenuates IRI at a mitochondrial level, preserving the proteolytic processing of OPA1, in addition to the maintenance of mitochondrial respiration.

Role of Mitochondrial Pathways in Cell Apoptosis during He-Patic Ischemia/Reperfusion Injury

Hepatic ischemia-reperfusion injury is a major cause of post-operative hepatic dysfunction and liver failure after transplantation. Mitochondrial pathways can be either beneficial or detrimental to hepatic cell apoptosis during hepatic ischemia/reperfusion injury, depending on multiple factors. Hepatic ischemia/reperfusion injury may be induced by opened mitochondrial permeability transition pore, released apoptosis-related proteins, up-regulated B-cell lymphoma-2 gene family proteins, unbalanced mitochondrial dynamics, and endoplasmic reticulum stress, which are integral parts of mitochondrial pathways. In this review, we discuss the role of mitochondrial pathways in apoptosis that account for the most deleterious effect of hepatic ischemia/reperfusion injury.

Augmenter of liver regeneration-mediated mitophagy protects against hepatic ischemia/reperfusion injury

Augmenter of liver regeneration (ALR) is an anti-apoptotic protein found mainly in mitochondria. It protects hepatocytes from ischemia-reperfusion (I/R) injury, but the underlying mechanism is not clear. We found that in rats, delivery of the ALR gene alleviated hepatic I/R injury during orthotopic liver transplantation as evidenced by reduced serum aminotransferase, oxidative stress and apoptosis, and increased expression of autophagy markers. In an in vitro hypoxia/reoxygenation (H/R) model, overexpression of the ALR gene activated autophagy and relieved defective mitophagy via the PINK1/Parkin pathway. Mechanistically, ALR transfection induced the expression of mitofusin 2 (Mfn2) in the H/R model, which led to PINK1 accumulation and mitochondrial translocation of Parkin. Deletion of Mfn2 abolished mitophagy activation induced by ALR transfection, promoted mitochondrial dysfunction, and eventually increased cell apoptosis. Mfn2 administration prevented the inhibition of mitophagy in ALR-knockout (KO) cells, thus attenuated mitochondrial dysfunction and cell apoptosis. In heterozygous ALR-knockout mice treated with a warm I/R injury, marked aggravation of liver injury was associated with mitophagy inhibition and reduction in Mfn2 expression. Taken together, our results confirm that ALR accelerated Parkin translocation and mitophagy via Mfn2, and protected hepatocytes from I/R-induced injury. Our findings provide a novel rationale for the treatment of hepatic I/R injury.

Downregulation of augmenter of liver regeneration impairs the therapeutic efficacy of liver epithelial progenitor cells against acute liver injury by enhancing mitochondrial fission

Cell-based therapeutic approaches have been proven to be effective strategies for the treatment of acute liver injury (ALI). However, widespread application of these procedures is limited by several key issues, including rapid loss of stemness in vitro, aberrant differentiation into undesirable cell types, and low engraftment in vivo. In this study, liver epithelial progenitor cells (LEPCs) were characterized and transfected with augmenter of liver regeneration (ALR). The results revealed that in ALI mice with CCl₄ , the transplantation of ALR-bearing LEPCs into the liver markedly protected mice against ALI by decreasing the levels of alanine aminotransferase (ALT) and aspartate aminotransferase (AST), thus relieving hepatic tissue injury and attenuating inflammatory infiltration. Mechanistically, the knockdown of ALR in LEPCs activated the phosphorylation of dynamin-related protein 1 (Drp1) at the S616 site and thereby enhanced mitochondrial fission. In contrast, the transfection of ALR into LEPCs significantly inhibited Drp1 phosphorylation, thereby favoring the maintenance of mitochondrial integrity and the preservation of adenosine triphosphate contents in LEPCs. Consequently, the ALR-bearing LEPCs transplanted into ALI mice exhibited substantially greater homing ability to the injured liver via the SDF-1/CXCR4 axis than that of LEPCs-lacking ALR. In conclusion, we demonstrated that the transplantation of ALR-transfected LEPCs protected mice against CCl₄ -induced ALI, thus offering immense curative potential in the clinic.

The Role of Mitochondria in Liver Ischemia-Reperfusion Injury: From Aspects of Mitochondrial Oxidative Stress, Mitochondrial Fission, Mitochondrial Membrane Permeable Transport Pore Formation, Mitophagy, and Mitochondria-Related Protective Measures

Ischemia-reperfusion injury (IRI) has indeed been shown as a main complication of hepatectomy, liver transplantation, trauma, and hypovolemic shock. A large number of studies have confirmed that microvascular and parenchymal damage is mainly caused by reactive oxygen species (ROS), which is considered to be a major risk factor for IRI. Under normal conditions, ROS as a kind of by-product of cellular metabolism can be controlled at normal levels. However, when IRI occurs, mitochondrial oxidative phosphorylation is inhibited. In addition, oxidative respiratory chain damage leads to massive consumption of adenosine triphosphate (ATP) and large amounts of ROS. Additionally, mitochondrial dysfunction is involved in various organs and tissues in IRI. On the one hand, excessive free radicals induce mitochondrial damage, for instance, mitochondrial structure, number, function, and energy metabolism. On the other hand, the disorder of mitochondrial fusion and fission results in further reduction of the number of mitochondria so that it is not enough to clear excessive ROS, and mitochondrial structure changes to form mitochondrial membrane permeable transport pores (mPTPs), which leads to cell necrosis and apoptosis, organ failure, and metabolic dysfunction, increasing morbidity and mortality. According to the formation mechanism of IRI, various substances have been discovered or synthesized for specific targets and cell signaling pathways to inhibit or slow the damage of liver IRI to the body. Here, based on the development of this field, this review describes the role of mitochondria in liver IRI, from aspects of mitochondrial oxidative stress, mitochondrial fusion and fission, mPTP formation, and corresponding protective measures. Therefore, it may provide references for future clinical treatment and research.

Inhibition of Drp1 SUMOylation by ALR protects the liver from ischemia-reperfusion injury

Hepatic ischemic reperfusion injury (IRI) is a common complication of liver surgery. Although an imbalance between mitochondrial fission and fusion has been identified as the cause of IRI, the detailed mechanism remains unclear. Augmenter of liver regeneration (ALR) was reported to prevent mitochondrial fission by inhibiting dynamin-related protein 1 (Drp1) phosphorylation, contributing partially to its liver protection. Apart from phosphorylation, Drp1 activity is also regulated by small ubiquitin-like modification (SUMOylation), which accelerates mitochondrial fission. This study aimed to investigate whether ALR-mediated protection from hepatic IRI might be associated with an effect on Drp1 SUMOylation. Liver tissues were harvested from both humans and from heterozygous ALR knockout mice, which underwent IRI. The SUMOylation and phosphorylation of Drp1 and their modulation by ALR were investigated. Hepatic Drp1 SUMOylation was significantly increased in human transplanted livers and IRI-livers of mice. ALR-transfection significantly decreased Drp1 SUMOylation, attenuated the IRI-induced mitochondrial fission and preserved mitochondrial stability and function. This study showed that the binding of transcription factor Yin Yang-1 (YY1) to its downstream target gene UBA2, a subunit of SUMO-E1 enzyme heterodimer, was critical to control Drp1 SUMOylation. By interacting with YY1, ALR inhibits its nuclear import and dramatically decreases the transcriptional level of UBA2. Consequently, mitochondrial fission was significantly reduced, and mitochondrial function was maintained. This study showed that the regulation of Drp1 SUMOylation by ALR protects mitochondria from fission, rescuing hepatocytes from IRI-induced apoptosis. These new findings provide a potential target for clinical intervention to reduce the effects of IRI during hepatic surgery.

Aging aggravates hepatic ischemia-reperfusion injury in mice by impairing mitophagy with the involvement of the EIF2α-parkin pathway

Hepatic ischemia-reperfusion (I/R) injury fundamentally influences the performance of aged liver grafts. The significance of mitophagy in the age dependence of sensitivity to I/R injury remains poorly understood. Here, we show that aging aggravated hepatic I/R injury with decreased mitophagy in mice. The enhancement of mitophagy resulted in significant protection against hepatic I/R injury. Parkin, an E3 ubiquitin ligase, was found depleted by I/R in aged livers. In oxygen-glucose deprivation reperfusion (OGD-Rep.)-treated L02 cells, parkin silencing impaired mitophagy and aggravated cell damage through a relative large mitochondrial membrane potential transition. The phosphorylation of the endoplasmic reticulum stress response protein EIF2α, which was also reduced in the aged liver, induced parkin expression both in vivo and vitro. Forty-six hepatic biopsy specimens from liver graft were collected 2 hours after complete revascularization, followed by immunohistochemical analyses. Parkin expression was negatively correlated to donor age and the peak level of aspartate aminotransferase within first week after liver transplantation. Our translational study demonstrates that aging aggravated hepatic I/R injury by impairing the age-dependent mitophagy function via an insufficient parkin expression and identifies a new strategy to evaluate the capacity of an aged liver graft in the process of I/R through the parkin expression.

Emerging therapeutic strategies for transplantation-induced acute kidney injury: protecting the organelles and the vascular bed

INTRODUCTION

Renal ischemia-reperfusion injury (IRI) is a significant clinical challenge faced by clinicians in a broad variety of clinical settings such as perioperative and intensive care. Renal IRI induced acute kidney injury (AKI) is a global public health concern associated with high morbidity, mortality, and health-care costs. Areas covered: This paper focuses on the pathophysiology of transplantation-related AKI and recent findings on cellular stress responses at the intersection of 1. The Unfolded protein response; 2. Mitochondrial dysfunction; 3. The benefits of mineralocorticoid receptor antagonists. Lastly, perspectives are offered to the readers. Expert opinion: Renal IRI is caused by a sudden and temporary impairment of blood flow to the organ. Defining the underlying cellular cascades involved in IRI will assist us in the identification of novel interventional targets to attenuate IRI with the potential to improve transplantation outcomes. Targeting mitochondrial function and cellular bioenergetics upstream of cellular damage may offer several advantages compared to targeting downstream inflammatory and fibrosis processes. An improved understanding of the cellular pathophysiological mechanisms leading to kidney injury will hopefully offer improved targeted therapies to prevent and treat the injury in the future.

Hsp27 reduces cold ischemia-reperfusion injury in heart transplantation through regulation of NF-κB and PUMA signaling

BACKGROUND AND OBJECTIVE

Global myocardial ischemia-reperfusion (I/R) injury after heart transplantation is believed to impair graft function and aggravate episodes of both acute and chronic rejection. The 27-kDa heat shock protein (Hsp27) has a potent ability to alleviate I/R after cardiac transplantation. The aim of this study was to investigate the anti-I/R injury effect of Hsp27 to elucidate the underling mechanisms.

METHODS

Heart grafts from BALB/c mice were preserved in University of Wisconsin (UW) solution (control) or UW solution containing pAAV-Hsp27 (Hsp27 solution) at 4°C for 48 h and subsequently transplanted into syngeneic recipients for 72 h. The heart grafts were then collected for histopathological and gene expression analyses. An in vitro I/R model (H9c2 cells or H9c2/Hsp27 cells) was constructed. Then, protein and mRNA expression of Hsp27, p65, p53 upregulated modulator of apoptosis (PUMA), interleukin (IL)-6, IL-1β, and tumor necrosis factor (TNF)-α in heart tissues and H9c2 cells were detected with western blot and reverse transcription polymerase chain reaction analyses. Caspase-3 activity was detected using a commercial assay, while protein levels of IL-6, IL-1β, and TNF-α were detected using specific enzyme-linked immunosorbent assays. NF-κB activity was detected with an electrophoretic mobility shift assay. Cell apoptosis was detected with the terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling assay and flow cytometric analysis.

RESULTS

Cold I/R caused severe morphologic myocardial injury of heart grafts from wild type C57BL/c mice, whereas grafts from Hsp27 preservation showed less damage as demonstrated by decreased cell apoptosis/death and the preservation of the normal structure of the heart. Hsp27 inhibited I/R-induced injury as indicated by the reduction in cardiac troponin I activities and decreased cardiac tissue levels of the proinflammatory factors TNF-α, IL-1β, and IL-6. Hsp27 was further demonstrated to significantly inhibit nuclear translocation of p65 and p53 upregulated modulator of apoptosis (PUMA) expression.

CONCLUSIONS

These results suggested that the cardioprotective effect of Hsp27 could be due to the suppression of the myocardial inflammatory response and apoptosis by blocking the NF-κB-dependent pro-inflammatory and NF-κB-dependent PUMA signaling pathways.

Progress in research of augmenter of liver regeneration

Augmenter of liver regeneration (ALR), also known as hepatic stimulatory substance or hepatopoietin, is expressed ubiquitously in all organs, and exclusively in hepatocytes in the liver. Over the past decade, research indicates that ALR is able to promote growth of hepatocytes in the regenerating or injured liver, and plays an important role in hepatocyte transplantation, the pathogenesis of fulminant hepatitis, liver regeneration, and the development of hepatocellular carcinoma.

Hepatic stimulator substance resists hepatic ischemia/reperfusion injury by regulating Drp1 translocation and activation

Ischemia/reperfusion injury, induced by abnormal mitochondrial fission-related apoptosis, is a major concern in liver transplantation settings. Our previous studies have demonstrated that hepatic stimulator substance (HSS) is an antiapoptotic effector and could protect liver from ischemia/reperfusion injury. However, the underlying mechanism remains unclear. In the present study, we report that in vitro and in vivo HSS could regulate mitochondrial fission and hepatocyte apoptosis during liver ischemia/reperfusion injury by orchestrating the translocation and activation of dynamin-related protein 1 (Drp1). Using a mouse model of ischemia/reperfusion-induced liver injury, we found that HSS-haploinsufficient (HSS^+/- ) mice displayed exacerbated liver damage based on their increased serum aminotransferase levels, cell structural destruction, and apoptosis levels compared to wild-type (HSS^+/+ ) littermates. Disruption of HSS markedly increased cyclin-dependent kinase 1 (CDK1) and Bax expression, accompanied by elevated phosphorylated Drp1 and release of cytochrome c. In parallel in vitro studies, we found that HSS could inhibit the expression of CDK1 and that HSS inhibits hepatocyte apoptosis through its suppression of CDK1/cyclin B-mediated phosphorylation at Ser-616 of Drp1, thereby decreasing Drp1 accumulation in mitochondria and Drp1-mediated activation of the mitochondrial fission program. On the contrary, knockdown of HSS increased CDK1 as well as Drp1 phosphorylation and aggravated hepatocellular apoptosis. Mechanistic investigation showed that HSS was able to reduce the stability and translation of CDK1 mRNA by modulating the expression of several microRNAs (miRs), including miR-410-3p, miR-490-3p, and miR-582-5p.

CONCLUSION

Our data reveal a novel mechanism for HSS in regulating the mitochondrial fission machinery and further suggest that modulation of HSS may provide a therapeutic approach for combating liver damage. (Hepatology 2017;66:1989-2001).

Alleviation of Ischemia-Reperfusion Injury in Liver Steatosis by Augmenter of Liver Regeneration Is Attributed to Antioxidation and Preservation of Mitochondria

BACKGROUND

Fatty liver is one of the major impediments to liver surgery and liver transplantation because steatotic hepatocytes are more susceptible to ischemia-reperfusion injury (IRI). In this study, the effects of augmenter of liver regeneration (ALR) on hepatic IRI in steatotic mice were investigated.

METHODS

In vivo, liver steatosis of mice was induced by feeding a methionine-choline-deficient diet for 2 weeks. Three days before hepatic partial warm IRI, mice were transfected with the ALR-containing adenovirus. In an in vitro study, the protective effect of ALR on steatotic HepG2 cells was analyzed after hypoxia/reoxygenation (HR) treatment.

RESULTS

The transfection of the ALR gene into steatotic mice attenuated liver injury, inhibiting hepatic oxidative stress, increasing antioxidation capacities, promoting liver regeneration, and consequently suppressing cell apoptosis/death. Furthermore, resistance to HR injury was notably increased in ALR-transfected cells compared with the vector-transfected cells. The HR-induced rise in the mitochondrial reactive oxygen species was reduced, and cellular antioxidant activities were enhanced. The ALR transfection prevented cells from apoptosis, which can be attributed to the preservation of the mitochondrial membrane potential, enhancement of oxygen consumption rate and production of adenosine triphosphate.

CONCLUSIONS

ALR protects steatotic hepatocytes from IRI by attenuating oxidative stress and mitochondrial dysfunction, as well as improving antioxidant effect. ALR may be used as a potential therapeutic agent when performing surgery and transplantation of steatotic liver.

Pre-conditions for eliminating mitochondrial dysfunction and maintaining liver function after hepatic ischaemia reperfusion

The liver, the largest organ with multiple synthesis and secretion functions in mammals, consists of hepatocytes and Kupffer, stem, endothelial, stellate and other parenchymal cells. Because of early and extensive contact with the external environment, hepatic ischaemia reperfusion (IR) may result in mitochondrial dysfunction, autophagy and apoptosis of cells and tissues under various pathological conditions. Because the liver requires a high oxygen supply to maintain normal detoxification and synthesis functions, it is extremely susceptible to ischaemia and subsequent reperfusion with blood. Consequently, hepatic IR leads to acute or chronic liver failure and significantly increases the total rate of morbidity and mortality through multiple regulatory mechanisms. An increasing number of studies indicate that mitochondrial structure and function are impaired after hepatic IR, but that the health of liver tissues or liver grafts can be effectively rescued by attenuation of mitochondrial dysfunction. In this review, we mainly focus on the subsequent therapeutic interventions related to the conservation of mitochondrial function involved in mitigating hepatic IR injury and the potential mechanisms of protection. Because mitochondria are abundant in liver tissue, clarification of the regulatory mechanisms between mitochondrial dysfunction and hepatic IR should shed light on clinical therapies for alleviating hepatic IR‐induced injury.

Hepatic stimulator substance inhibits calcium overflow through the mitochondria-associated membrane compartment during nonalcoholic steatohepatitis

Nonalcoholic fatty liver disease is considered a disorder of the endoplasmic reticulum (ER) and mitochondria. Recent studies have shown that the ER and mitochondrial membranes overlap by 15-20%, a region referred to as the 'mitochondria-associated ER membrane' (MAM). Some proteins, including sarco/ER calcium ATPase (SERCA), are located in the MAM and have an important role in Ca²⁺ signaling and homeostasis between the ER and the mitochondria. Our previous study showed that hepatic stimulator substance (HSS) inhibits the ER stress induced by reactive oxygen species, thus reducing mitochondrial damage. However, the mechanism underlying the protective effect of HSS on the ER and ER-mitochondrial interaction remains unclear. In this study, we confirmed that the exogenous expression of HSS protected the liver from steatosis in mice with nonalcoholic steatohepatitis. More importantly, the protection provided by HSS allowed SERCA in the MAM compartment to function well, preventing the extensive influx of cytosolic free Ca²⁺ to the mitochondria, thus preserving the mitochondrial functions from calcium overload and relieving palmitic-acid-induced hepatocyte steatosis. Our results suggest that the protective effect of HSS on SERCA expression is associated with the maintenance of calcium homeostasis within the MAM, thus ameliorating the disordered Ca²⁺ communication between the ER and mitochondria.

Hydroxysafflor yellow A attenuates ischemia/reperfusion-induced liver injury by suppressing macrophage activation

Hydroxysafflor yellow A (HSYA), a major constituent in the hydrophilic fraction of the safflower plant, can retard the progress of hepatic fibrosis. However, the anti-inflammatory properties and the underlying mechanisms of HSYA on I/R-induced acute liver injury are unknown. Inhibiting macrophage activation is a potential strategy to treat liver ischemia/reperfusion (I/R) injury. In this study, we investigated the therapeutic effect of HSYA on liver I/R injury and the direct effect of HSYA on macrophage activation following inflammatory conditions. The therapeutic effects of HSYA on I/R injury were tested in vivo using a mouse model of segmental (70%) hepatic ischemia. The mechanisms of HSYA were examined in vitro by evaluating migration and the cytokine expression profile of the macrophage cell line RAW264.7 exposed to acute hypoxia and reoxygenation (H/R). Results showed that mice pretreated with HSYA had reduced serum transaminase levels, attenuated inflammation and necrosis, reduced expression of inflammatory cytokines, and less macrophage recruitment following segmental hepatic ischemia. In vitro HSYA pretreated RAW264.7 macrophages displayed reduced migratory response and produced less inflammatory cytokines. In addition, HSYA pretreatment down-regulated the expression of matrix matalloproteinase-9 and reactive oxygen species, and inhibited NF-κB activation and P38 phosphorylation in RAW264.7 cells. Thus, these data suggest that HSYA can reduce I/R-induced acute liver injury by directly attenuating macrophage activation under inflammatory conditions.

Enhanced endoplasmic reticulum SERCA activity by overexpression of hepatic stimulator substance gene prevents hepatic cells from ER stress-induced apoptosis

Although the potential pathogenesis of nonalcoholic fatty liver disease (NAFLD) is unclear, increasing evidence indicates that endoplasmic reticulum (ER) stress may link free fatty acids to NAFLD. Since we previously reported that hepatic stimulator substance (HSS) could protect the liver from steatosis, this study is aimed to investigate whether HSS protection could be related with its inhibition on ER stress. The HSS gene was stably transfected into BEL-7402 hepatoma cells and effectively expressed in ER. The palmitic acid (PA)-induced heptocyte lipotoxicity was reproduced in the HSS-transfected cells, and HSS alleviation of the ER stress and apoptosis were subsequently examined. The results showed that PA treatment led to a heavy accumulation of fatty acids within the cells and a remarkable increase in reactive oxygen species (ROS). However, in the HSS-expressing cells, production of ROS was inhibited and ER stress-related marker glucose-regulated protein 78 (GRP-78), sterol regulatory element-binding protein (SREBP), anti-phospho-PRK-1ike ER kinase (p-PERK), anti-phospho-eukaryotic initiation factor 2α (p-eIF2α), and anti-C/EBP homologous protein (CHOP) were downregulated compared with the wild-type or mutant HSS-transfected cells. Furthermore, PA treatment severely impaired the activity of sarco-endoplasmic reticulum Ca(2+)-ATPase (SERCA), leading to imbalanced calcium homeostasis during ER stress, which could be rescued in the HSS-trasfected cells. The protection provided by HSS to the SERCA is identical to that observed with N-acetyl-l-cysteine (NAC) and sodium dimercaptopropane sulfonate (Na-DMPS), which are two typical free radical scavengers. As a consequence, the rate of ER stress-mediated apoptosis in the HSS-expressing cells was significantly reduced. In conclusion, the protective effect of HSS against ER stress may be associated with the removal of ROS to restore the activity of the SERCA.