Suppression of autophagy in rat liver at late stage of polymicrobial sepsis. Shock. 2011;35:506-511. [PMID: 21263383 DOI: 10.1097/shk.0b013e31820b2f05]

Antiseptic effect of sea cucumber (Holothuria atra) against multi-organ failure induced by sepsis: Molecular and histopathological study

Sepsis is a systemic inflammatory response to infection and severe sepsis patients can develop acute lung and liver injury. The aim of the present study was to evaluate the efficacy of Holothuria atra methanolic body wall extract (HaE), as an antioxidant and anti-inflammatory agent against induced sepsis in a cecal ligation and puncture (CLP) rat model. In total, 30 males albino rats were divided into three groups (n=10 each) as follows: Sham (Sh), which was used as negative control; sepsis (Se), which was used as a positive control and was subjected to CLP surgery; and Ho, which was subjected to CLP and fed with 200 mg/kg (body weight) of HaE, once daily for 7 days. Subsequently, the expression of various genes was detected by polymerase chain reaction, while liver and lung tissues were examined by immunohistochemistry. The expression of Caspase-3 was significantly reduced in liver and lung tissues in the Ho group, while the expression levels of Gsta2, Cat and Sod1 genes were slightly reduced in the Ho group, when compared with the Se group. In addition, expression levels of tumor necrosis factor, interferon-γ, liver interleukin (IL)1b and lung IL1a were reduced in the Ho group compared with the Se group. Furthermore, histopathological changes were observed in liver tissues of the Se group, including congestion of hepatoportal blood vessel and focal hepatic necrosis, while lung tissues showed marked edema, hemorrhage and alveolar septal thickening. The Ho group showed apparent normal hepatic parenchyma and slight interstitial pneumonia. Immunohistochemical staining of caspase-3 in liver and lung tissues showed no expression in the Sh group, strong expression in the Se group and moderate expression in the Ho group. In conclusion, HaE demonstrated beneficial effect against induced sepsis, which may be attributed to its antioxidant and antiapoptotic activities.

Autophagy in sepsis: Degradation into exhaustion?

Autophagy is one of the innate immune defense mechanisms against microbial challenges. Previous in vitro and in vivo models of sepsis demonstrated that autophagy was activated initially in sepsis, followed by a subsequent phase of impairment. Autophagy modulation appears to be protective against multiple organ injuries in these murine sepsis models. This is achieved in part by preventing apoptosis, maintaining a balance between the productions of pro- and anti-inflammatory cytokines, and preserving mitochondrial functions. This article aims to discuss the role of autophagy in sepsis and the therapeutic potential of autophagy enhancers.

Atg7 Knockdown Augments Concanavalin A-Induced Acute Hepatitis through an ROS-Mediated p38/MAPK Pathway

Concanavalin A (ConA), a T-cell mitogen that induces acute autoimmune hepatitis, is widely used to model pathophysiological processes of human acute autoimmune liver disease. Although autophagy has been extensively studied in the past decade, little is known about its molecular mechanism underlying the regulation of ConA-induced acute hepatitis. In this study, we used a Cre-conditional atg7 KO mouse to investigate the effects of Atg7-associated autophagy on ConA-induced murine hepatitis. Our results demonstrated that atg7 deficiency in mice enhanced macrophage activation and increased pro-inflammatory cytokines upon ConA stimulation. Atg7 silencing resulted in accumulation of dysfunctional mitochondria, disruption of reactive oxygen species (ROS) degradation, and increase in pro-inflammatory cytokines in Raw264.7 cells. p38/MAPK and NF-κB levels were increased upon ConA induction due to Atg7 deficiency. Blocking ROS production inhibited ConA-induced p38/IκB phosphorylation and subsequent intracellular inflammatory responses. Hence, this study demonstrated that atg7 knockout in mice or Atg7 knockdown in cell culture augmented ConA-induced acute hepatitis and related cellular malfunction, indicating protective effects of Atg7 on regulating mitochondrial ROS via a p38/MAPK-mediated pathway. Collectively, our findings reveal that autophagy may attenuate macrophage-mediated inflammatory response to ConA and may be the potential therapeutic targets for acute liver injury.

Sinomenine hydrochloride protects against polymicrobial sepsis via autophagy

Sepsis, a systemic inflammatory response to infection, is the major cause of death in intensive care units (ICUs). The mortality rate of sepsis remains high even though the treatment and understanding of sepsis both continue to improve. Sinomenine (SIN) is a natural alkaloid extracted from Chinese medicinal plant Sinomenium acutum, and its hydrochloride salt (Sinomenine hydrochloride, SIN-HCl) is widely used to treat rheumatoid arthritis (RA). However, its role in sepsis remains unclear. In the present study, we investigated the role of SIN-HCl in sepsis induced by cecal ligation and puncture (CLP) in BALB/c mice and the corresponding mechanism. SIN-HCl treatment improved the survival of BALB/c mice that were subjected to CLP and reduced multiple organ dysfunction and the release of systemic inflammatory mediators. Autophagy activities were examined using Western blotting. The results showed that CLP-induced autophagy was elevated, and SIN-HCl treatment further strengthened the autophagy activity. Autophagy blocker 3-methyladenine (3-MA) was used to investigate the mechanism of SIN-HCl in vitro. Autophagy activities were determined by examining the autophagosome formation, which was shown as microtubule-associated protein light chain 3 (LC3) puncta with green immunofluorescence. SIN-HCl reduced lipopolysaccharide (LPS)-induced inflammatory cytokine release and increased autophagy in peritoneal macrophages (PM). 3-MA significantly decreased autophagosome formation induced by LPS and SIN-HCl. The decrease of inflammatory cytokines caused by SIN-HCl was partially aggravated by 3-MA treatment. Taken together, our results indicated that SIN-HCl could improve survival, reduce organ damage, and attenuate the release of inflammatory cytokines induced by CLP, at least in part through regulating autophagy activities.

T-cell autophagy deficiency increases mortality and suppresses immune responses after sepsis

BACKGROUND

Although the role of autophagy in sepsis has been characterized in several organs, its role in the adaptive immune system remains to be ascertained. This study aimed to investigate the role of autophagy in sepsis-induced T cell apoptosis and immunosuppression, using knockout mice with T cell specific deletion of autophagy essential gene Atg7.

METHODS AND RESULTS

Sepsis was induced in a cecal ligation and puncture (CLP) model, with T-cell-specific Atg7-knockout mice compared to control mice. Autophagic vacuoles examined by electron microscopy were decreased in the spleen after CLP. Autophagy proteins LC3-II and ATG7, and autophagosomes and autolysosomes stained by Cyto-ID Green and acridine orange were decreased in CD4+ and CD8+ splenocytes at 18 h and 24 h after CLP. This decrease in autophagy was associated with increased apoptosis of CD4+ and CD8+ after CLP. Moreover, mice lacking Atg7 in T lymphocytes showed an increase in sepsis-induced mortality, T cell apoptosis and loss of CD4+ and CD8+ T cells, in comparison to control mice. This was accompanied by suppressed cytokine production of Th1/Th2/Th17 by CD4+ T cells, reduced phagocytosis in macrophages and decreased bacterial clearance in the spleen after sepsis.

CONCLUSION

These results indicated that sepsis led to down-regulation of autophagy in T lymphocytes, which may result in enhanced apoptosis induction and decreased survival in sepsis. Autophagy may therefore play a protective role against sepsis-induced T lymphocyte apoptosis and immunosuppression.

Human placenta-derived mesenchymal stem cells promote hepatic regeneration in CCl4 -injured rat liver model via increased autophagic mechanism

Mesenchymal stem cells (MSCs) have great potential for cell therapy in regenerative medicine, including liver disease. Even though ongoing research is dedicated to the goal of bringing MSCs to clinical applications, further understanding of the complex underlying mechanisms is required. Autophagy, a type II programmed cell death, controls cellular recycling through the lysosomal system in damaged cells or tissues. However, it is still unknown whether MSCs can trigger autophagy to enhance regeneration and/or to provide a therapeutic effect as cellular survival promoters. We therefore investigated autophagy's activation in carbon tetrachloride (CCl4 )-injured rat liver following transplantation with chorionic plate-derived MSCs (CP-MSCs) isolated from placenta. The expression markers for apoptosis, autophagy, cell survival, and liver regeneration were analyzed. Whereas caspase 3/7 activities were reduced (p < .05), the expression levels of hypoxia-inducible factor-1α (HIF-1α) and factors for autophagy, survival, and regeneration were significantly increased by CP-MSCs transplantation. Decreased necrotic cells (p < .05) and increased autophagic signals (p < .005) were observed in CCl4 -treated primary rat hepatocytes during in vitro coculture with CP-MSCs. Furthermore, the upregulation of HIF-1α promotes the regeneration of damaged hepatic cells through an autophagic mechanism marked by increased levels of light chain 3 II (LC 3II). These results suggest that the administration of CP-MSCs promotes repair by systemically concomitant mechanisms involving HIF-1α and autophagy. These findings provide further understanding of the mechanisms involved in these processes and will help develop new cell-based therapeutic strategies for regenerative medicine in liver disease.

Enhanced liver autophagic activity improves survival of septic mice lacking surfactant proteins A and D

Autophagy is a protective cellular mechanism in response to various stresses, including sepsis. Sepsis is defined as systemic inflammation by infection. Surfactant protein A and D (SP-A and SP-D) are involved in host defense, regulation of inflammation, and homeostasis, but their roles in the autophagic activity and relevant gene expression in sepsis are unclear. In this study, mice lacking SP-A and SP-D (SP-A/D KO mice) and background-matched wild-type (WT) C57BL/6 mice underwent either cecal ligation and puncture (CLP) or sham surgery. The results showed that SP-A/D KO mice had lower mortality than WT mice in CLP sepsis. Liver tissues showed marked pathological changes in both septic SP-A/D KO and WT mice 24 hrs after CLP treatment; and quantitative analysis of liver histopathology revealed significant difference between septic SP-A/D and septic WT mice. SP-A/D KO mice had higher basal and sepsis-induced level of autophagy than WT mice (p < 0.05), as judged by Western blot and electron microscopic analyses. The expression of 84 autophagy-related genes revealed differential basal and sepsis-induced gene expression between SP-A/D KO and WT mice. The expression increased in three genes and decreased in four genes in septic WT mice, as compared to septic SP-A/D KO mice (p < 0.05). Furthermore, differential responses to sepsis between SP-A/D KO and WT mice were found in six signaling pathways related to autophagy and apoptosis. Therefore, enhanced autophagic activity improves the survival of septic SP-A/D KO mice through the regulation of liver autophagy/apoptosis-related gene expression and signaling pathway activation.

Sepsis-induced Cardiac Mitochondrial Damage and Potential Therapeutic Interventions in the Elderly

The incidence of sepsis and its attendant mortality risk are significantly increased with aging. Thus, severe sepsis in the elderly is likely to become an emerging concern in critical care units. Cardiac dysfunction is an important component of multi-organ failure after sepsis. In our laboratory, utilizing a pneumonia-related sepsis animal model, our research has been focused on the mechanisms underlying sepsis-induced cardiac failure. In this review, based on findings from others and ours, we discussed age-dependent decay in mitochondria and the role of mitochondrial reactive oxygen species (mtROS) in sepsis-induced cardiac inflammation and autophagy. Our recent discovery of a potential signal transduction pathway that triggers myocardial mitochondrial damage is also discussed. Because of the significance of mitochondria damage in the aging process and in sepsis pathogenesis, we hypothesize that specific enhancing mitochondrial antioxidant defense by mitochondria-targeted antioxidants (MTAs) may provide important therapeutic potential in treating elder sepsis patients. In this review, we summarized the categories of currently published MTA molecules and the results of preclinical evaluation of MTAs in sepsis and aging models.

Complete activation of autophagic process attenuates liver injury and improves survival in septic mice

The accumulation of autophagosomes in the terminal step of the autophagic process has recently emerged as a potentially maladaptive process in the septic heart and lung. However, the role of autophagy in the septic liver has not been ascertained. This study was investigated by first examining the entire sequence of the autophagic process in the liver of septic mice. Second, a novel pharmacotherapeutic approach was utilized to treat sepsis with autophagy enhancer/inhibitor. Sepsis was induced by cecal ligation and puncture (CLP). C57BL/6 mice received autophagy enhancer carbamazepine (CBZ), autophagy inhibitor 3-methyladenine (inhibition of autophagosomal formation), or chloroquine (impairment of autophagosomal clearance). We found that the whole autophagic process was activated at 4 h after CLP; however, it did not proceed to completion during the 4- to 24-h time period, as indicated by accumulated autophagosomes and decreased autophagic flux. Carbamazepine, which induced complete activation of the autophagic process, improved CLP survival. This protective effect was also associated with decreased cell death, inflammatory responses, and hepatic injury. However, disruption of autophagosomal clearance with chloroquine abolished the above protective effects in CBZ-treated CLP mice. 3-Methyladenine, which resulted in inhibition of the autophagosomal formation, did not show any above beneficial effects in CLP mice. Impaired autophagosome-lysome fusion resulting in incomplete activation of autophagy may contribute to sepsis-induced liver injury. Treatment with CBZ may serve a protective role in the septic liver, possibly through the effect of complete activation of autophagic process.

Lipopolysaccharide stimulates p62-dependent autophagy-like aggregate clearance in hepatocytes

Impairment of autophagy has been associated with liver injury. TLR4-stimulation by LPS upregulates autophagy in hepatocytes, although the signaling pathways involved remain elusive. The objective of this study was to determine the signaling pathway leading to LPS-stimulated autophagy in hepatocytes. Cell lysates from livers of wild type (WT; C57BL/6) mice given LPS (5 mg/kg-IP) and hepatocytes from WT, TLR4ko, and MyD88ko mice treated with LPS (100 ng/mL) up to 24 h were collected. LC3II, p62/SQSTM1, Nrf2, and beclin1 levels were determined by immunoblot, immunofluorescence, and qPCR. Autophagy-like activation was measured by GFP-LC3-puncta formation and LC3II-expression. Beclin1, Nrf2, p62, MyD88, and TIRAP were knocked-down using siRNA. LC3II-expression increased in both liver and hepatocytes after LPS and was dependent on TLR4. Beclin1 expression did not increase after LPS in hepatocytes and beclin1-knockdown did not affect LC3II levels. In hepatocytes given LPS, expression of p62 increased and p62 colocalized with LC3. p62-knockdown prevented LC3II puncta formation. LPS-induced LC3II/p62-puncta also required MyD88/TIRAP signaling and localization of both Nrf2 and NF κ B transcription factors to the nucleus to upregulate p62-expression. Therefore, TLR4-activation by LPS in hepatocytes induces a p62-mediated, not beclin1-mediated, autophagy-like clearance pathway that is hepatoprotective by clearing aggregate-prone or misfolded proteins from the cytosol and preserving energy homeostasis under stress.

Anthracyclines induce DNA damage response-mediated protection against severe sepsis

Severe sepsis remains a poorly understood systemic inflammatory condition with high mortality rates and limited therapeutic options in addition to organ support measures. Here we show that the clinically approved group of anthracyclines acts therapeutically at a low dose regimen to confer robust protection against severe sepsis in mice. This salutary effect is strictly dependent on the activation of DNA damage response and autophagy pathways in the lung, as demonstrated by deletion of the ataxia telangiectasia mutated (Atm) or the autophagy-related protein 7 (Atg7) specifically in this organ. The protective effect of anthracyclines occurs irrespectively of pathogen burden, conferring disease tolerance to severe sepsis. These findings demonstrate that DNA damage responses, including the ATM and Fanconi Anemia pathways, are important modulators of immune responses and might be exploited to confer protection to inflammation-driven conditions, including severe sepsis.

Bioenergetic failure correlates with autophagy and apoptosis in rat liver following silver nanoparticle intraperitoneal administration

BACKGROUND

Deposition and accumulation of silver nanoparticles (Ag-nps) in the liver have been shown to induce hepatotoxicity in animal studies. The hepatotoxicity may include oxidative stress, abnormalities in energy metabolism, and cell death. Studies have indicated that autophagy is an intracellular event involving balance of energy, nutrients, and turnover of subcellular organelles. The present study was undertaken to test the hypothesis that autophagy plays a role in mediating hepatotoxicity in animal after exposure to Ag-nps. Focus was placed on interrelationship between energy metabolism, autophagy, apoptosis and hepatic dysfunction.

METHODS

Sprague Dawley rats were intraperitoneally injected with Ag-nps (10-30 nm in diameter) at concentration of 500 mg kg(-1). All animals were sacrificed on days 1, 4, 7, 10 and 30 after exposure and blood and liver tissues were collected for further studies.

RESULTS

Uptake of Ag-nps was quite prompt and not proportional to the blood Ag concentration. Declination of ATP (-64% in days 1) and autophagy (determined by LC3-II protein expression and morphological evaluation) increased and peaked on the first day. The ATP content remained at low level even though the autophagy has been activated. Apoptosis (based on caspase-3 protein expression and TUNEL-positive cells staining) began to rise sigmoidally at days 1 and 4, reached a peak level at day 7, and remained at the same levels during days 7-30 post exposure. Meanwhile, autophagy exhibited a gradual decrease from days 1-10 and the decrease at day 30 was statistically significant as compared to day 0 (sham group). Inflammatory reaction (histopathological evaluation) was found at day 10 and preceded to an advanced degree at day 30 when liver function was impaired.

CONCLUSIONS

These results indicate that following Ag-nps administration, autophagy was induced; however, failure to preserve autophagy compounded with energy reduction led to apoptosis and the eventual impairment of liver function. The study provides an in-vivo evidence of hepatotoxicity by continuous exposure of Ag-nps in rats.

Kinetics and protective role of autophagy in a mouse cecal ligation and puncture-induced sepsis

Introduction

It is not well understood whether the process of autophagy is accelerated or blocked in sepsis, and whether it is beneficial or harmful to the immune defense mechanism over a time course during sepsis. Our aim was to determine both the kinetics and the role of autophagy in sepsis.

Methods

We examined autophagosome and autolysosome formation in a cecal ligation and puncture (CLP) mouse model of sepsis (in C57BL/6N mice and GFP-LC3 transgenic mice), using western blotting, immunofluorescence, and electron microscopy. We also investigated the effect of chloroquine inhibition of autophagy on these processes.

Results

Autophagy, as demonstrated by increased LC3-II/LC3-I ratios, is induced in the liver, heart, and spleen over 24 h after CLP. In the liver, autophagosome formation peaks at 6 h and declines by 24 h. Immunofluorescent localization of GFP-LC3 dots (alone and with lysosome-associated membrane protein type 1 (LAMP1)), as well as electron microscopic examination, demonstrate that both autophagosomes and autolysosomes are increased after CLP, suggesting that intact autophagy mechanisms operate in the liver in this model. Furthermore, inhibition of autophagy process by chloroquine administration immediately after CLP resulted in elevated serum transaminase levels and a significant increase in mortality.

Conclusions

All autophagy-related processes are properly activated in the liver in a mouse model of sepsis; autophagy appears to play a protective role in septic animals.

Ultrastructural pathology and interorganelle cross talk in hepatotoxicity

Mitochondria, endoplasmic reticulum (ER), cytoplasmic lipid droplets (CLD), and Golgi vesicles use cross talk to control hepatocyte metabolism, growth, and stress. Interpretation of ultrastructural change requires knowledge of how cross talk pathways function, how differential activation of hepatocellular signals influences organelle structure, and how organelles position themselves to become central hubs for stress responses. Mitochondria, by coupling energy production to pathways for protection, form critical platforms for innate signaling. Mitochondrial outer and inner membranes activate channels and signals to translocate peptides that drive oxidative phosphorylation, β-oxidation of fatty acids, and calcium ion (Ca(2+)) flux. In cell stress, mitochondrial signals initiate fusion and fission, reactive oxygen species (ROS) control, autophagy, apoptosis, and senescence. Specialized tethering proteins tie mitochondria to ER to support translocation of metabolites. For Ca(2+) translocation, ER pores are connected to mitochondrial voltage-dependent anion channels, and for mitochondrial fission, unique membrane proteins pull ER to mitochondria. In toxic injury, cytosolic cytokines translocate to alter metabolism. Toxic effects on ER lipid synthesis lead to Golgi vesicle reduplication and transport of perilipin and other protein cargos into CLDs. How cellular proteostasis, oxidative homeostasis, and ion balance are maintained depend upon the effectiveness of mitochondrial ROS defense responses, unfolded protein responses in mitochondria and ER, and other organelle defenses.

The decline of autophagy contributes to proximal tubular dysfunction during sepsis

Severe sepsis associated with overproduction of tumor necrosis factor α and reactive oxygen species leads to energy depletion and cellular damage. Both reactive oxygen species and damaged organelles induce autophagy for recycling nutrients to combat pathological stress. To study whether autophagy plays a beneficial role in the pathogenesis of renal failure during sepsis, rats were subjected to cecal ligation and puncture (CLP) or sham operation. Temporal relationship of autophagy and renal dysfunction were examined in vivo. The results showed that the level of lipidated microtubule-associated protein light chain 3 (LC3-II), a marker of autophagy, elevated transiently at 3 h but declined at 9 h until 18 h after CLP. Light chain 3 aggregation in renal tissue showed a similar trend to the change of LC3-II protein. High levels of blood urea nitrogen and creatinine as well as low tubular sodium reabsorption occurred at 18 h after CLP. The distribution of autophagy located primarily in angiotensin-converting enzyme-positive, which is concentrated in proximal tubule, but calbindin D28k (calcium-binding protein D28K, a marker of distal tubule)-negative cells in renal cortex. Therefore, NRK-52E (proximal tubule epithelial cell line) cells were used to further examine cell viability and DNA fragmentation after silencing or inducing autophagy. We found that knockdown of Atg7 (autophagy-related gene 7) exaggerates, whereas preincubation of rapamycin (an autophagy inducer) diminishes tumor necrosis factor α-induced cell death. These results suggest that the decline of sepsis-induced autophagy contributes to the proximal tubular dysfunction, and maintenance of sufficient autophagy prevents cell death. These data open prospects for therapies that activate autophagy during sepsis.

Autophagy: cellular defense to excessive inflammation

Autophagy can orchestrate a variety of cellular responses to dangerous stimuli. Our understanding of the physiologic roles of autophagy has recently expanded; in addition to its other roles, autophagy now appears to play an essential role in regulating inflammatory responses. This review describes recent findings concerning the roles and mechanisms of autophagy in controlling excessive inflammation.