Augmenting autophagy to treat acute kidney injury during endotoxemia in mice

MALAT1 DEREPRESSES MIR-433-3P-MEDIATED RPTOR SUPPRESSION TO IMPAIR AUTOPHAGY AND DRIVE PYROPTOSIS IN ENDOTOXEMIA

ABSTRACT

Objective: Autophagy elevation in endotoxemia plays a protective role by negatively regulating the pyroptosis of vascular endothelial cells, but the molecular mechanisms are still poorly understood. The present study aimed to identify the mechanism underlying autophagy and pyroptosis in endotoxemia. Methods: Bioinformatics analysis and whole-gene transcriptome sequencing prediction were used to identify the endotoxemia-related lncRNA-miRNA-mRNA axis of interest. Human umbilical vein endothelial cells (HUVECs) were activated by lipopolysaccharide (LPS) to mimic the inflammatory environment encountered in endotoxemia. Autophagy and pyroptosis of LPS-treated HUVECs were assessed in response to the knockdown of MALAT1 (metastasis-associated lung adenocarcinoma transcript 1)/miR-433-3p (miRNA-433-3p)/RPTOR (regulatory-associated protein of mTOR). The binding affinity of MALAT1, miR-433-3p, and RPTOR was detected by RNA pull-down and luciferase activity assays. The endothelial cell-specific RPTOR knockout mice were developed and rendered septic using LPS induction to verify the role of RPTOR in autophagy, pyroptosis, and inflammatory response in vivo . Results: The in vitro experiments indicated that LPS could stimulate HUVECs to highly express RPTOR, and its knockdown enhanced cellular autophagy and restricted pyroptosis to curb inflammatory responses. Mechanically, MALAT1 is competitively bound to miR-433-3p to release RPTOR expression, thereby promoting pyroptosis and aggravating endotoxemia. In vivo experiments further confirmed that the knockdown of RPTOR activated autophagy and curtailed pyroptosis in septic mice. Conclusion: MALAT1 is highly expressed in endotoxemia. MALAT1 promotes RPTOR expression by competitively absorbing miR-433-3p, inhibits LPS-activated HUVEC cell autophagy, promotes cell death, enhances LPS-induced inflammatory activation of vascular endothelial cells, and ultimately promotes the progression of endotoxemia.

Vascular injury associated with ethanol intake is driven by AT1 receptor and mitochondrial dysfunction

BACKGROUND

Renin-angiotensin (Ang II)-aldosterone system (RAAS) is crucial for the cardiovascular risk associated with excessive ethanol consumption. Disturbs in mitochondria have been implicated in multiple cardiovascular diseases. However, if mitochondria dysfunction contributes to ethanol-induced vascular dysfunction is still unknown. We investigated whether ethanol leads to vascular dysfunction via RAAS activation, mitochondria dysfunction, and mitochondrial reactive oxygen species (mtROS).

METHODS

Male C57/BL6J or mt-keima mice (6-8-weeks old) were treated with ethanol (20% vol./vol.) for 12 weeks with or without Losartan (10 mg/kg/day).

RESULTS

Ethanol induced aortic hypercontractility in an endothelium-dependent manner. PGC1α (a marker of biogenesis), Mfn2, (an essential protein for mitochondria fusion), as well as Pink-1 and Parkin (markers of mitophagy), were reduced in aortas from ethanol-treated mice. Disturb in mitophagy flux was further confirmed in arteries from mt-keima mice. Additionally, ethanol increased mtROS and reduced SOD2 expression. Strikingly, losartan prevented vascular hypercontractility, mitochondrial dysfunction, mtROS, and restored SOD2 expression. Both MnTMPyP (SOD2 mimetic) and CCCP (a mitochondrial uncoupler) reverted ethanol-induced vascular dysfunction. Moreover, L-NAME (NOS inhibitor) and EUK 134 (superoxide dismutase/catalase mimetic) did not affect vascular response in ethanol group, suggesting that ethanol reduces aortic nitric oxide (NO) and H2O2 bioavailability. These responses were prevented by losartan.

CONCLUSION

AT1 receptor modulates ethanol-induced vascular hypercontractility by promoting mitochondrial dysfunction, mtROS, and reduction of NO and H2O2 bioavailability. Our findings shed a new light in our understanding of ethanol-induced vascular toxicity and open perspectives of new therapeutic approaches for patients with disorder associated with abusive ethanol drinking.

Update on persistent acute kidney injury in critical illnesses

Acute kidney injury (AKI) affects about half of patients admitted to the intensive care unit (ICU), and worsens their short- and long-term outcomes. Apparently self-limiting AKI episodes initiate a progression toward chronic kidney disease (CKD) through cellular and molecular mechanisms that are yet to be explained. In particular, persistent AKI, defined in 2016 by the Acute Dialysis Quality Initiative as an AKI which lasts more than 48 h from its onset, has been correlated with higher morbidity and mortality, and with a higher progression to acute kidney disease (AKD) and CKD than transient AKI (i.e. AKI with a reversal within 48 h). This classification has been also used in the setting of solid organ transplantation, demonstrating similar outcomes. Due to its incidence and poor prognosis and because prompt interventions seem to change its course, persistent AKI should be recognized early and followed-up also after its recovery. However, while AKI and CKD are well-described syndromes, persistent AKI and AKD are relatively new entities. The purpose of this review is to highlight the key phases of persistent AKI in ICU patients in terms of both clinical and mechanistic features in order to offer to clinicians and researchers an updated basis from which to start improving patients' care and direct future research.

Epigenetic dysregulation of autophagy in sepsis-induced acute kidney injury: the underlying mechanisms for renoprotection

Sepsis-induced acute kidney injury (SI-AKI), a common critically ill, represents one of the leading causes of global death. Emerging evidence reveals autophagy as a pivotal modulator of SI-AKI. Autophagy affects the cellular processes of renal lesions, including cell death, inflammation, and immune responses. Herein, we conducted a systematic and comprehensive review on the topic of the proposed roles of autophagy in SI-AKI. Forty-one relevant studies were finally included and further summarized and analyzed. This review revealed that a majority of included studies (24/41, 58.5%) showed an elevation of the autophagy level during SI-AKI, while 22% and 19.5% of the included studies reported an inhibition and an elevation at the early stage but a declination of renal autophagy in SI-AKI, respectively. Multiple intracellular signaling molecules and pathways targeting autophagy (e.g. mTOR, non-coding RNA, Sirtuins family, mitophagy, AMPK, ROS, NF-Kb, and Parkin) involved in the process of SI-AKI, exerting multiple biological effects on the kidney. Multiple treatment modalities (e.g. small molecule inhibitors, temsirolimus, rapamycin, polydatin, ascorbate, recombinant human erythropoietin, stem cells, Procyanidin B2, and dexmedetomidine) have been found to improve renal function, which may be attributed to the elevation of the autophagy level in SI-AKI. Though the exact roles of autophagy in SI-AKI have not been well elucidated, it may be implicated in preventing SI-AKI through various molecular pathways. Targeting the autophagy-associated proteins and pathways may hint towards a new prospective in the treatment of critically ill patients with SI-AKI, but more preclinical studies are still warranted to validate this hypothesis.

Mitochondrial Dysfunction in the Cardio-Renal Axis

Cardiovascular disease (CVD) frequently complicates chronic kidney disease (CKD). The risk of all-cause mortality increases from 20% to 500% in patients who suffer both conditions; this is referred to as the so-called cardio-renal syndrome (CRS). Preclinical studies have described the key role of mitochondrial dysfunction in cardiovascular and renal diseases, suggesting that maintaining mitochondrial homeostasis is a promising therapeutic strategy for CRS. In this review, we explore the malfunction of mitochondrial homeostasis (mitochondrial biogenesis, dynamics, oxidative stress, and mitophagy) and how it contributes to the development and progression of the main vascular pathologies that could be affected by kidney injury and vice versa, and how this knowledge may guide the development of novel therapeutic strategies in CRS.

Upregulation of OASIS/CREB3L1 in podocytes contributes to the disturbance of kidney homeostasis

Podocyte injury is involved in the onset and progression of various kidney diseases. We previously demonstrated that the transcription factor, old astrocyte specifically induced substance (OASIS) in myofibroblasts, contributes to kidney fibrosis, as a novel role of OASIS in the kidneys. Importantly, we found that OASIS is also expressed in podocytes; however, the pathophysiological significance of OASIS in podocytes remains unknown. Upon lipopolysaccharide (LPS) treatment, there is an increase in OASIS in murine podocytes. Enhanced serum creatinine levels and tubular injury, but not albuminuria and podocyte injury, are attenuated upon podocyte-restricted OASIS knockout in LPS-treated mice, as well as diabetic mice. The protective effects of podocyte-specific OASIS deficiency on tubular injury are mediated by protein kinase C iota (PRKCI/PKCι), which is negatively regulated by OASIS in podocytes. Furthermore, podocyte-restricted OASIS transgenic mice show tubular injury and tubulointerstitial fibrosis, with severe albuminuria and podocyte degeneration. Finally, there is an increase in OASIS-positive podocytes in the glomeruli of patients with minimal change nephrotic syndrome and diabetic nephropathy. Taken together, OASIS in podocytes contributes to podocyte and/or tubular injury, in part through decreased PRKCI. The induction of OASIS in podocytes is a critical event for the disturbance of kidney homeostasis.

Upregulation of transcription factor OASIS in podocytes contributes to podocyte and/or tubular injury through decreased PRKCi expression and is a critical event for the disturbance of kidney homeostasis.

Sepsis-induced AKI: From pathogenesis to therapeutic approaches

Sepsis is a heterogenous and highly complex clinical syndrome, which is caused by infectious or noninfectious factors. Acute kidney injury (AKI) is one of the most common and severe complication of sepsis, and it is associated with high mortality and poor outcomes. Recent evidence has identified that autophagy participates in the pathophysiology of sepsis-associated AKI. Despite the use of antibiotics, the mortality rate is still at an extremely high level in patients with sepsis. Besides traditional treatments, many natural products, including phytochemicals and their derivatives, are proved to exert protective effects through multiple mechanisms, such as regulation of autophagy, inhibition of inflammation, fibrosis, and apoptosis, etc. Accumulating evidence has also shown that many pharmacological inhibitors might have potential therapeutic effects in sepsis-induced AKI. Hence, understanding the pathophysiology of sepsis-induced AKI may help to develop novel therapeutics to attenuate the complications of sepsis and lower the mortality rate. This review updates the recent progress of underlying pathophysiological mechanisms of sepsis-associated AKI, focuses specifically on autophagy, and summarizes the potential therapeutic effects of phytochemicals and pharmacological inhibitors.

Molecular mechanisms and physiological functions of autophagy in kidney diseases

Autophagy is a highly conserved cellular progress for the degradation of cytoplasmic contents including micromolecules, misfolded proteins, and damaged organelles that has recently captured attention in kidney diseases. Basal autophagy plays a pivotal role in maintaining cell survival and kidney homeostasis. Accordingly, dysregulation of autophagy has implicated in the pathologies of kidney diseases. In this review, we summarize the multifaceted role of autophagy in kidney aging, maladaptive repair, tubulointerstitial fibrosis and discuss autophagy-related drugs in kidney diseases. However, uncertainty still remains as to the precise mechanisms of autophagy in kidney diseases. Further research is needed to clarify the accurate molecular mechanism of autophagy in kidney diseases, which will facilitate the discovery of a promising strategy for the prevention and treatment of kidney diseases.

PD-L1 maintains neutrophil extracellular traps release by inhibiting neutrophil autophagy in endotoxin-induced lung injury

Programmed death ligand 1 (PD-L1) is not only an important molecule in mediating tumor immune escape, but also regulates inflammation development. Here we showed that PD-L1 was upregulated on neutrophils in lipopolysaccharide (LPS)-induced acute respiratory distress syndrome (ARDS). Neutrophil specific knockout of PD-L1 reduced lung injury in ARDS model induced by intratracheal LPS injection. The level of NET release was reduced and autophagy is elevated by PD-L1 knockout in ARDS neutrophils both in vivo and in vitro. Inhibition of autophagy could reverse the inhibitory effect of PD-L1 knockout on NET release. PD-L1 interacted with p85 subunit of PI3K at the endoplasmic reticulum (ER) in neutrophils from ARDS patients, activating the PI3K/Akt/mTOR pathway. An extrinsic neutralizing antibody against PD-L1 showed a protective effect against ARDS. Together, PD-L1 maintains the release of NETs by regulating autophagy through the PI3K/Akt/mTOR pathway in ARDS. Anti-PD-L1 therapy may be a promising measure in treating ARDS.

When a calorie isn't just a calorie: a revised look at nutrition in critically ill patients with sepsis and acute kidney injury

PURPOSE OF REVIEW

To discuss how nutritional management could be optimized to promote protective metabolism in sepsis and associated acute kidney injury.

RECENT FINDINGS

Recent evidence suggests that sepsis is a metabolically distinct critical illness and that certain metabolic alterations, such as activation of fasting metabolism, may be protective in bacterial sepsis. These findings may explain the lack of survival benefit in recent randomized controlled trials of nutrition therapy for critical illness. These trials are limited by cohort heterogeneity, combining both septic and nonseptic critical illness, and the use of inaccurate caloric estimates to determine energy requirements. These energy estimates are also unable to provide information on specific substrate preferences or the capacity for substrate utilization. As a result, high protein feeding beyond the capacity for protein synthesis could cause harm in septic patients. Excess glucose and insulin exposures suppress fatty acid oxidation, ketogenesis and autophagy, of which emerging evidence suggest are protective against sepsis associated organ damage such as acute kidney injury.

SUMMARY

Distinguishing pathogenic and protective sepsis-related metabolic changes are critical to enhancing and individualizing nutrition management for critically ill patients.

Mitochondrial Dysfunction: An Emerging Link in the Pathophysiology of Cardiorenal Syndrome

The crosstalk between the heart and kidney is carried out through various bidirectional pathways. Cardiorenal syndrome (CRS) is a pathological condition in which acute or chronic dysfunction in the heart or kidneys induces acute or chronic dysfunction of the other organ. Complex hemodynamic factors and biochemical and hormonal pathways contribute to the development of CRS. In addition to playing a critical role in generating metabolic energy in eukaryotic cells and serving as signaling hubs during several vital processes, mitochondria rapidly sense and respond to a wide range of stress stimuli in the external environment. Impaired adaptive responses ultimately lead to mitochondrial dysfunction, inducing cell death and tissue damage. Subsequently, these changes result in organ failure and trigger a vicious cycle. In vitro and animal studies have identified an important role of mitochondrial dysfunction in heart failure (HF) and chronic kidney disease (CKD). Maintaining mitochondrial homeostasis may be a promising therapeutic strategy to interrupt the vicious cycle between HF and acute kidney injury (AKI)/CKD. In this review, we hypothesize that mitochondrial dysfunction may also play a central role in the development and progression of CRS. We first focus on the role of mitochondrial dysfunction in the pathophysiology of HF and AKI/CKD, then discuss the current research evidence supporting that mitochondrial dysfunction is involved in various types of CRS.

Current Status of Autophagy Enhancers in Metabolic Disorders and Other Diseases

Autophagy is pivotal in the maintenance of organelle function and intracellular nutrient balance. Besides the role of autophagy in the homeostasis and physiology of the individual tissues and whole organism in vivo, dysregulated autophagy has been incriminated in the pathogenesis of a variety of diseases including metabolic diseases, neurodegenerative diseases, cardiovascular diseases, inflammatory or immunological disorders, cancer and aging. Search for autophagy modulators has been widely conducted to amend dysregulation of autophagy or pharmacologically modulate autophagy in those diseases. Current data support the view that autophagy modulation could be a new modality for treatment of metabolic syndrome associated with lipid overload, human-type diabetes characterized by deposition of islet amyloid or other diseases including neurodegenerative diseases, infection and cardiovascular diseases. While clinically available bona fide autophagy modulators have not been developed yet, it is expected that on-going investigation will lead to the development of authentic autophagy modulators that can be safely administered to patients in the near future and will open a new horizon for treatment of incurable or difficult diseases.

Empagliflozin Enhances Autophagy, Mitochondrial Biogenesis, and Antioxidant Defense and Ameliorates Renal Ischemia/Reperfusion in Nondiabetic Rats

Background. Recent meta-analyses have shown that sodium-glucose cotransporter 2 (SGLT-2) inhibitors alleviate chronic kidney disease and acute kidney injury in diabetic patients. In this study, we aimed to investigate the effect of empagliflozin on renal ischemia/reperfusion (I/R) in nondiabetic rats and find the possible mechanisms. Experimental Approach. Eighteen male Wistar rats were randomly divided into three groups, including healthy control, ischemic control, and empagliflozin-treated group. Thirty minutes of bilateral renal ischemia was induced by clamping the renal hilum. Forty-eight hours after reopening the clamps, rats’ blood samples and tissue specimens were collected. Empagliflozin 10 mg/kg was administered by gavage, 2 hours before ischemia and 24 hours after the first dose. Results. I/R injury led to a significant rise in serum creatinine and blood urea nitrogen which was significantly decreased after treatment with empagliflozin. Empagliflozin also alleviated tubulointerstitial and glomerular damage and significantly decreased tissue histology scores. Empagliflozin decreased the increased levels of malondialdehyde, interleukin 1β, and tumor necrosis factor α. SGLT2 inhibition increased the decreased expression of nuclear factor erythroid 2-related factor 2 and PPARG coactivator 1 alpha that conduct antioxidant defense and mitochondrial biogenesis, respectively. Furthermore, empagliflozin markedly increased LC3-II/LC3-I and bcl2/bax ratios, showing its beneficial effect on activation of autophagy and inhibition of apoptosis. Despite its effects on diabetic nephropathy, empagliflozin did not activate the Sestrin2/AMP-activated protein kinase pathway in this study. Conclusion. Empagliflozin improved renal I/R injury in nondiabetic rats in this study by promoting autophagy and mitochondrial biogenesis and attenuation of oxidative stress, inflammation, and apoptosis.

Metabolic Reprogramming and Host Tolerance: A Novel Concept to Understand Sepsis-Associated AKI

Acute kidney injury (AKI) is a frequent complication of sepsis that increases mortality and the risk of progression to chronic kidney disease. However, the mechanisms leading to sepsis-associated AKI are still poorly understood. The recognition that sepsis induces organ dysfunction in the absence of overt necrosis or apoptosis has led to the consideration that tubular epithelial cells (TEC) may deploy defense mechanisms to survive the insult. This concept dovetails well with the notion that the defense against infection does not only depend on the capacity of the immune system to limit the microbial load (known as resistance), but also on the capacity of cells and tissues to limit tissue injury (known as tolerance). In this review, we discuss the importance of TEC metabolic reprogramming as a defense strategy during sepsis, and how this cellular response is likely to operate through a tolerance mechanism. We discuss the fundamental role of specific regulatory nodes and of mitochondria in orchestrating this response, and how this opens avenues for the exploration of targeted therapeutic strategies to prevent or treat sepsis-associated AKI.

Mechanisms of Caloric Restriction-Mediated Stress-Resistance in Acute Kidney Injury

Caloric restriction (CR)-mediated organ protection has been shown to be extremely efficient in rodent models of acute kidney injury (AKI). Limited understanding of the underlying mechanisms paired with a risk of malnourishment and feasibility problems has hindered the translation of this immense potential to the patient setting. In this mini-review, the current mechanistic concepts of CR-mediated stress-resistance as potential key targets for renal protection in AKI will be highlighted.

RIP3 impedes transcription factor EB to suppress autophagic degradation in septic acute kidney injury

Autophagy is an important renal-protective mechanism in septic acute kidney injury (AKI). Receptor interacting protein kinase 3 (RIP3) has been implicated in the renal tubular injury and renal dysfunction during septic AKI. Here we investigated the role and mechanism of RIP3 on autophagy in septic AKI. We showed an activation of RIP3, accompanied by an accumulation of the autophagosome marker LC3II and the autophagic substrate p62, in the kidneys of lipopolysaccharide (LPS)-induced septic AKI mice and LPS-treated cultured renal proximal tubular epithelial cells (PTECs). The lysosome inhibitor did not further increase the levels of LCII or p62 in LPS-treated PTECs. Moreover, inhibition of RIP3 attenuated the aberrant accumulation of LC3II and p62 under LPS treatment in vivo and in vitro. By utilizing mCherry-GFP-LC3 autophagy reporter mice in vivo and PTECs overexpression mRFP-GFP-LC3 in vitro, we observed that inhibition of RIP3 restored the formation of autolysosomes and eliminated the accumulated autophagosomes under LPS treatment. These results indicated that RIP3 impaired autophagic degradation, contributing to the accumulation of autophagosomes. Mechanistically, the nuclear translocation of transcription factor EB (TFEB), a master regulator of the lysosome and autophagy pathway, was inhibited in LPS-induced mice and LPS-treated PTECs. Inhibition of RIP3 restored the nuclear translocation of TFEB in vivo and in vitro. Co-immunoprecipitation further showed an interaction of RIP3 and TFEB in LPS-treated PTECs. Also, the expression of LAMP1 and cathepsin B, two potential target genes of TFEB involved in lysosome function, were decreased under LPS treatment in vivo and in vitro, and this decrease was rescued by inhibiting RIP3. Finally, overexpression of TFEB restored the autophagic degradation in LPS-treated PTECs. Together, the present study has identified a pivotal role of RIP3 in suppressing autophagic degradation through impeding the TFEB-lysosome pathway in septic AKI, providing potential therapeutic targets for the prevention and treatment of septic AKI.

Mitochondrial Metabolism in Acute Kidney Injury

The kidney is a highly metabolic organ that requires substantial adenosine triphosphate for the active transport required to maintain water and solute reabsorption. Aberrations in energy availability and energy utilization can lead to cellular dysfunction and death. Mitochondria are essential for efficient energy production. The pathogenesis of acute kidney injury is complex and varies with different types of injury. However, multiple distinct acute kidney injury syndromes share a common dysregulation of energy metabolism. Pathways of energy metabolism and mitochondrial dysfunction are emerging as critical drivers of acute kidney injury and represent new potential targets for treatment. This review shows the basic metabolic pathways that all cells depend on for life; describes how the kidney optimizes those pathways to meet its anatomic, physiologic, and metabolic needs; summarizes the importance of metabolic and mitochondrial dysfunction in acute kidney injury; and analyzes the mitochondrial processes that become dysregulated in acute kidney injury including mitochondrial dynamics, mitophagy, mitochondrial biogenesis, and changes in mitochondrial energy metabolism.

Pivotal role of endothelial cell autophagy in sepsis

Sepsis is a fatal organ dysfunction resulting from a disordered host response to infection. Endothelial cells (ECs) are usually the primary targets of inflammatory mediators in sepsis; damage to ECs plays a pivotal part in vital organ failure. In recent studies, autophagy was suggested to play a critical role in the ECs injury although the mechanisms by which ECs are injured in sepsis are not well elucidated. Autophagy is a highly conserved catabolic process that includes sequestrating plasma contents and transporting cargo to lysosomes for recycling the vital substrates required for metabolism. This pathway also counteracts microbial invasion to balance and retain homeostasis, especially during sepsis. Increasing evidence indicates that autophagy is closely associated with endothelial function. The role of autophagy in sepsis may or may not be favorable depending upon conditions. In the present review, the current knowledge of autophagy in the process of sepsis and its influence on ECs was evaluated. In addition, the potential of targeting EC autophagy for clinical treatment of sepsis was discussed.

SIRT1 attenuates sepsis-induced acute kidney injury via Beclin1 deacetylation-mediated autophagy activation

Our previous studies showed that silent mating-type information regulation 2 homologue-1 (SIRT1, a deacetylase) upregulation could attenuate sepsis-induced acute kidney injury (SAKI). Upregulated SIRT1 can deacetylate certain autophagy-related proteins (Beclin1, Atg5, Atg7 and LC3) in vitro. However, it remains unclear whether the beneficial effect of SIRT1 is related to autophagy induction and the underlying mechanism of this effect is also unknown. In the present study, caecal ligation and puncture (CLP)-induced mice, and an LPS-challenged HK-2 cell line were established to mimic a SAKI animal model and a SAKI cell model, respectively. Our results demonstrated that SIRT1 activation promoted autophagy and attenuated SAKI. SIRT1 deacetylated only Beclin1 but not the other autophagy-related proteins in SAKI. SIRT1-induced autophagy and its protective effect against SAKI were mediated by the deacetylation of Beclin1 at K430 and K437. Moreover, two SIRT1 activators, resveratrol and polydatin, attenuated SAKI in CLP-induced septic mice. Our study was the first to demonstrate the important role of SIRT1-induced Beclin1 deacetylation in autophagy and its protective effect against SAKI. These findings suggest that pharmacologic induction of autophagy via SIRT1-mediated Beclin1 deacetylation may be a promising therapeutic approach for future SAKI treatment.

Dichloroacetate reverses sepsis-induced hepatic metabolic dysfunction

Metabolic reprogramming between resistance and tolerance occurs within the immune system in response to sepsis. While metabolic tissues such as the liver are subjected to damage during sepsis, how their metabolic and energy reprogramming ensures survival is unclear. Employing comprehensive metabolomic, lipidomic, and transcriptional profiling in a mouse model of sepsis, we show that hepatocyte lipid metabolism, mitochondrial tricarboxylic acid (TCA) energetics, and redox balance are significantly reprogrammed after cecal ligation and puncture (CLP). We identify increases in TCA cycle metabolites citrate, cis-aconitate, and itaconate with reduced fumarate and triglyceride accumulation in septic hepatocytes. Transcriptomic analysis of liver tissue supports and extends the hepatocyte findings. Strikingly, the administration of the pyruvate dehydrogenase kinase (PDK) inhibitor dichloroacetate reverses dysregulated hepatocyte metabolism and mitochondrial dysfunction. In summary, our data indicate that sepsis promotes hepatic metabolic dysfunction and that targeting the mitochondrial PDC/PDK energy homeostat rebalances transcriptional and metabolic manifestations of sepsis within the liver.

CaMKIV regulates mitochondrial dynamics during sepsis

Sepsis and shock states impose mitochondrial stress, and in response, adaptive mechanisms such as fission, fusion and mitophagy are induced to eliminate damaged portions of or entire dysfunctional mitochondria. The mechanisms underlying these events are being elucidated; yet a direct link between loss of mitochondrial membrane potential ΔΨm and the initiation of fission, fusion and mitophagy remains to be well characterized. The direct association between the magnitude of the ΔΨm and the capacity for mitochondria to buffer Ca²⁺ renders Ca²⁺ uniquely suited as the signal engaging these mechanisms in circumstances of mitochondrial stress that lower the ΔΨm. Herein, we show that the calcium/calmodulin-dependent protein kinase (CaMK) IV mediates an adaptive slowing in oxidative respiration that minimizes oxidative stress in the kidneys of mice subjected to either cecal ligation and puncture (CLP) sepsis or endotoxemia. CaMKIV shifts the balance towards mitochondrial fission and away from fusion by 1) directly phosphorylating an activating Serine616 on the fission protein DRP1 and 2) reducing the expression of the fusion proteins Mfn1/2 and OPA-1. CaMKIV, through its function as a direct PINK1 kinase and regulator of Parkin expression, also enables mitophagy. These data support that CaMKIV serves as a keystone linking mitochondrial stress with the adaptive mechanisms of mitochondrial fission, fusion and mitophagy that mitigate oxidative stress in the kidneys of mice responding to sepsis.

Autophagy in kidney homeostasis and disease

Autophagy is a conserved lysosomal pathway for the degradation of cytoplasmic components. Basal autophagy in kidney cells is essential for the maintenance of kidney homeostasis, structure and function. Under stress conditions, autophagy is altered as part of the adaptive response of kidney cells, in a process that is tightly regulated by signalling pathways that can modulate the cellular autophagic flux - mammalian target of rapamycin, AMP-activated protein kinase and sirtuins are key regulators of autophagy. Dysregulated autophagy contributes to the pathogenesis of acute kidney injury, to incomplete kidney repair after acute kidney injury and to chronic kidney disease of varied aetiologies, including diabetic kidney disease, focal segmental glomerulosclerosis and polycystic kidney disease. Autophagy also has a role in kidney ageing. However, questions remain about whether autophagy has a protective or a pathological role in kidney fibrosis, and about the precise mechanisms and signalling pathways underlying the autophagy response in different types of kidney cells and across the spectrum of kidney diseases. Further research is needed to gain insights into the regulation of autophagy in the kidneys and to enable the discovery of pathway-specific and kidney-selective therapies for kidney diseases and anti-ageing strategies.

The Yin and Yang of Alarmins in Regulation of Acute Kidney Injury

Acute kidney injury (AKI) is a major clinical burden affecting 20 to 50% of hospitalized and intensive care patients. Irrespective of the initiating factors, the immune system plays a major role in amplifying the disease pathogenesis with certain immune cells contributing to renal damage, whereas others offer protection and facilitate recovery. Alarmins are small molecules and proteins that include granulysins, high-mobility group box 1 protein, interleukin (IL)-1α, IL-16, IL-33, heat shock proteins, the Ca++ binding S100 proteins, adenosine triphosphate, and uric acid. Alarmins are mostly intracellular molecules, and their release to the extracellular milieu signals cellular stress or damage, generally leading to the recruitment of the cells of the immune system. Early studies indicated a pro-inflammatory role for the alarmins by contributing to immune-system dysregulation and worsening of AKI. However, recent developments demonstrate anti-inflammatory mechanisms of certain alarmins or alarmin-sensing receptors, which may participate in the prevention, resolution, and repair of AKI. This dual function of alarmins is intriguing and has confounded the role of alarmins in AKI. In this study, we review the contribution of various alarmins to the pathogenesis of AKI in experimental and clinical studies. We also analyze the approaches for the therapeutic utilization of alarmins for AKI.

The Role of PGC-1α and Mitochondrial Biogenesis in Kidney Diseases

Chronic kidney disease (CKD) is one of the fastest growing causes of death worldwide, emphasizing the need to develop novel therapeutic approaches. CKD predisposes to acute kidney injury (AKI) and AKI favors CKD progression. Mitochondrial derangements are common features of both AKI and CKD and mitochondria-targeting therapies are under study as nephroprotective agents. PGC-1α is a master regulator of mitochondrial biogenesis and an attractive therapeutic target. Low PGC-1α levels and decreased transcription of its gene targets have been observed in both preclinical AKI (nephrotoxic, endotoxemia, and ischemia-reperfusion) and in experimental and human CKD, most notably diabetic nephropathy. In mice, PGC-1α deficiency was associated with subclinical CKD and predisposition to AKI while PGC-1α overexpression in tubular cells protected from AKI of diverse causes. Several therapeutic strategies may increase kidney PGC-1α activity and have been successfully tested in animal models. These include AMP-activated protein kinase (AMPK) activators, phosphodiesterase (PDE) inhibitors, and anti-TWEAK antibodies. In conclusion, low PGC-1α activity appears to be a common feature of AKI and CKD and recent characterization of nephroprotective approaches that increase PGC-1α activity may pave the way for nephroprotective strategies potentially effective in both AKI and CKD.

Autophagy in kidney disease: Advances and therapeutic potential

Autophagy is a highly conserved intracellular catabolic process for the degradation of cytoplasmic components that has recently gained increasing attention for its importance in kidney diseases. It is indispensable for the maintenance of kidney homeostasis both in physiological and pathological conditions. Investigations utilizing various kidney cell-specific conditional autophagy-related gene knockouts have facilitated the advancement in understanding of the role of autophagy in the kidney. Recent findings are raising the possibility that defective autophagy exerts a critical role in different pathological conditions of the kidney. An emerging body of evidence reveals that autophagy exhibits cytoprotective functions in both glomerular and tubular compartments of the kidney, suggesting the upregulation of autophagy as an attractive therapeutic strategy. However, there is also accumulating evidence that autophagy could be deleterious, which presents a formidable challenge in developing therapeutic strategies targeting autophagy. Here, we review the recent advances in research on the role of autophagy during different pathological conditions, including acute kidney injury (AKI), focusing on sepsis, ischemia-reperfusion injury, cisplatin, and heavy metal-induced AKI. We also discuss the role of autophagy in chronic kidney disease (CKD) focusing on the pathogenesis of tubulointerstitial fibrosis, podocytopathies including focal segmental glomerulosclerosis, diabetic nephropathy, IgA nephropathy, membranous nephropathy, HIV-associated nephropathy, and polycystic kidney disease.

Autophagy Function and Regulation in Kidney Disease

Autophagy is a dynamic process by which intracellular damaged macromolecules and organelles are degraded and recycled for the synthesis of new cellular components. Basal autophagy in the kidney acts as a quality control system and is vital for cellular metabolic and organelle homeostasis. Under pathological conditions, autophagy facilitates cellular adaptation; however, activation of autophagy in response to renal injury may be insufficient to provide protection, especially under dysregulated conditions. Kidney-specific deletion of Atg genes in mice has consistently demonstrated worsened acute kidney injury (AKI) outcomes supporting the notion of a pro-survival role of autophagy. Recent studies have also begun to unfold the role of autophagy in progressive renal disease and subsequent fibrosis. Autophagy also influences tubular cell death in renal injury. In this review, we reported the current understanding of autophagy regulation and its role in the pathogenesis of renal injury. In particular, the classic mammalian target of rapamycin (mTOR)-dependent signaling pathway and other mTOR-independent alternative signaling pathways of autophagy regulation were described. Finally, we summarized the impact of autophagy activation on different forms of cell death, including apoptosis and regulated necrosis, associated with the pathophysiology of renal injury. Understanding the regulatory mechanisms of autophagy would identify important targets for therapeutic approaches.

Autophagy in Kidney Disease

Autophagy is a cellular homeostatic program for the turnover of cellular organelles and proteins, in which double-membraned vesicles (autophagosomes) sequester cytoplasmic cargos, which are subsequently delivered to the lysosome for degradation. Emerging evidence implicates autophagy as an important modulator of human disease. Macroautophagy and selective autophagy (e.g., mitophagy, aggrephagy) can influence cellular processes, including cell death, inflammation, and immune responses, and thereby exert both adaptive and maladaptive roles in disease pathogenesis. Autophagy has been implicated in acute kidney injury, which can arise in response to nephrotoxins, sepsis, and ischemia/reperfusion, and in chronic kidney diseases. The latter includes comorbidities of diabetes and recent evidence for chronic obstructive pulmonary disease-associated kidney injury. Roles of autophagy in polycystic kidney disease and kidney cancer have also been described. Targeting the autophagy pathway may have therapeutic benefit in the treatment of kidney disorders.

Effect of ATM on inflammatory response and autophagy in renal tubular epithelial cells in LPS-induced septic AKI

The aim of the present study was to explore the role of ataxia-telangiectasia mutated (ATM) in lipopolysaccharide (LPS)-induced in vitro model of septic acute kidney injury (AKI) and the association between ATM, tubular epithelial inflammatory response and autophagy. The renal tubular epithelial cell HK-2 cell line was cultured and passaged, with HK-2 cell injury induced by LPS. The effects of LPS on HK-2 cell morphology, viability, ATM expression and inflammation were observed. Lentiviral vectors encoding ATM shRNA were constructed to knock down ATM expression in HK-2 cells. The efficiency of ATM knockdown in HK-2 cells was detected by western blot analysis and reverse transcription-quantitative PCR (RT-qPCR). HK-2 cells transfected with the ATM shRNA lentivirus were used for subsequent experiments. Following ATM knockdown, corresponding controls were set up, and the effects of ATM on inflammation and autophagy were detected in HK-2 cells using RT-qPCR, western blotting and ELISA. After LPS stimulation, the HK-2 cells were rounded into a slender or fusiform shape with poorly defined outlines. LPS treatment reduced cell viability in a partly dose-dependent manner. LPS increased the expression of tumor necrosis factor-α, interleukin (IL)-1β and IL-6, with the levels reaching its highest value at 10 µg/ml. IL-6 and IL-1β expression increased with increasing LPS concentration. These findings suggest that LPS reduced HK-2 cell viability whilst increasing the expression of inflammatory factors. Following transfection with ATM shRNA, expression levels of key autophagy indicators microtubule associated protein 1 light chain 3α I/II ratio and beclin-1 in the two ATM shRNA groups were also significantly reduced compared with the NC shRNA group. In summary, downregulation of ATM expression in HK-2 cells reduced LPS-induced inflammation and autophagy in sepsis-induced AKI in vitro, suggesting that LPS may induce autophagy in HK-2 cells through the ATM pathway leading to the upregulation of inflammatory factors.

Prompt Administration of Antibiotics and Fluids in the Treatment of Sepsis: A Murine Trial

OBJECTIVES

Sepsis, the acute organ dysfunction caused by a dysregulated host response to infection, poses a serious public health burden. Current management includes early detection, initiation of antibiotics and fluids, and source control as necessary. Although observational data suggest that delays of even a few hours in the initiation of antibiotics or IV fluids is associated with survival, these findings are controversial. There are no randomized data in humans, and prior animal studies studied time from experimental manipulation, not from the onset of clinical features of sepsis. Using a recently developed murine cecal ligation and puncture model that precisely monitors physiologic deterioration, we hypothesize that incremental hourly delays in the first dose of antibiotics, in the first bolus of fluid resuscitation, or a combination of the two at a clinically relevant point of physiologic deterioration during polymicrobial sepsis will shorten survival.

DESIGN

Randomized laboratory animal experimental trial.

SETTING

University basic science laboratory.

SUBJECTS

Male C57BL/6J, female C57BL/6J, aged (40-50 wk old) male C57BL/6J, and BALB/C mice.

INTERVENTIONS

Mice (n = 200) underwent biotelemetry-enhanced cecal ligation and puncture and were randomized after meeting validated criteria for acute physiologic deterioration. Treatment groups consisted of a single dose of imipenem/cilastatin, a single bolus of 30 mL/kg fluid resuscitation, or a combination of the two. Mice were allocated to receive treatment at the time of meeting deterioration criteria, after a 2-hour delay or after a 4-hour delay.

MEASUREMENTS AND MAIN RESULTS

Hourly delays in the initiation of antibiotic therapy led to progressively shortened survival in our model (p < 0.001). The addition of fluid resuscitation was unable to rescue animals, which received treatment 4 hours after meeting enrollment criteria. Systemic inflammation was increased, and host physiology was increasingly deranged with hourly delays to antibiotics.

CONCLUSIONS

We conclude that antibiotic therapy is highly time sensitive, and efforts should be made to deliver this critical therapy as early as possible in sepsis, perhaps extending into the first point of medical contact outside the hospital.

Atg7 mediates renal tubular cell apoptosis in vancomycin nephrotoxicity through activation of PKC-δ

Recent studies have shown that autophagy exhibits a renoprotective role in various models of acute kidney injury (AKI). However, its role in vancomycin (Van)-induced AKI remains largely unclarified. This study was the first to indicate that autophagy was rapidly activated in both human kidney-2 cells and renal tissues, and mammalian target of rapamycin (mTOR) was inactivated via the suppression of ERK1/2 and mTOR during Van treatment. Interestingly, for both in vitro and in vivo experiments, the suppression of autophagy via chloroquine and PT-Atg7-KO significantly ameliorated Van-induced kidney injury and renal tubular cell apoptosis. Global gene expression analysis indicated that the expression levels of 6159 genes were induced by Van treatment in the kidney cortical tissues of PT-Atg7 wild-type mice, and 18 of them were notably suppressed in PT-Atg7-KO mice. These 18 genes were further classified as programmed cell death, protein binding, signal transduction, E3 ubiquitin ligase, nucleoside diphosphate kinase activity, and E1-like activating enzyme. Unexpectedly, following Van treatment, PKC-δ expression was found to be highest among the 4 genes related to cell death, which was remarkably suppressed in vitro and in PT-Atg7-KO mice. In addition, Atg7 could induce renal cell apoptosis during Van treatment via binding to PKC-δ. Likewise, the inhibition of PKCδ ameliorated Van-induced apoptosis in human kidney-2 cells and kidney tissues. Furthermore, the data showed that PT-Atg7-KO exerted a renoprotective effect against Van-induced nephrotoxicity, but this effect was lost after injection with myc-tagged PKCδ. Taken altogether, these results indicate that Van induces autophagy by suppressing the activation of the ERK1/2 and mTOR signaling pathway. In addition, Atg7 mediates Van-induced AKI through the activation of PKCδ. In sum, autophagy inhibition may serve as a novel therapeutic target for treating nephrotoxic AKI induced by Van.-Xu, X., Pan, J., Li, H., Li, X., Fang, F., Wu, D., Zhou, Y., Zheng, P., Xiong, L., Zhang, D. Atg7 mediates renal tubular cell apoptosis in vancomycin nephrotoxicity through activation of PKC-δ.

TSC1 deletion in fibroblasts alleviates lipopolysaccharide-induced acute kidney injury

Mechanistic target of rapamycin complex 1 (mTORC1) signaling is active in inflammation, but its involvement in septic acute kidney injury (AKI) has not been shown. mTORC1 activation (p-S6) in renal fibroblasts was increased in a mouse AKI model induced by 1.5 mg/kg lipopolysaccharide (LPS). Deletion of tuberous sclerosis complex 1 (TSC1), an mTORC1 negative regulator, in fibroblasts (Fibro-TSC1^-/-) inhibited the elevation of serum creatinine and blood urea nitrogen in AKI compared with that in TSC1^fl/fl control mice. Endothelin-1 (EDN1) and phospho-Jun-amino-terminal kinase (p-JNK) were up-regulated in Fibro-TSC1^-/- renal fibroblasts after LPS challenge. Rapamycin, an mTORC1 inhibitor, and bosentan, an EDN1 antagonist, eliminated the difference in renal function between TSC1^fl/fl and Fibro-TSC1^-/- mice after LPS injection. Rapamycin restored LPS-induced up-regulation of EDN1, endothelin converting enzyme-1 (ECE1), and p-JNK in TSC1-knockdown mouse embryonic fibroblasts (MEFs). SP600125, a Jun-amino-terminal kinase (JNK) inhibitor, attenuated LPS-induced enhancement of EDN1 and ECE1 in TSC1-knockdown MEFs without a change in phospho-S6 ribosomal protein (p-S6) level. The results indicate that mTORC1-JNK-dependent up-regulation of ECE1 elevated EDN1 in TSC1-knockout renal fibroblasts and contributed to improvement of renal function in Fibro-TSC1^-/- mice with LPS-induced AKI. Renal fibroblast mTORC1 plays an important role in septic AKI.

Translational Sepsis Research: Spanning the Divide

OBJECTIVE

Our knowledge of the molecular mechanisms of sepsis has attained exponential growth. Yet, the pillars of its care remain antibiotics, fluid resuscitation, and physiologic support of failing organ systems. The inability to bring biologic breakthroughs to the bedside is not for lack of effort. Over 60 clinical trials of novel therapies, each heavily supported by the momentum of biologic data suggesting clinical utility, have been conducted and have failed to identify benefit. This mass of "negative" clinical data abut an equally towering mound of knowledge of sepsis biology, which collectively have led investigators to ask, "what happened?"

DATA SOURCES

Review of published scientific literature via MEDLINE searches using key terms related to the article topics.

STUDY SELECTION

Original articles, review articles, and systematic reviews were considered.

DATA EXTRACTION

Articles were selected for inclusion based upon author consensus.

DATA SYNTHESIS

Here, we present a synthetic review of some of the challenges in translating experimental animal models of sepsis to the bedside. We commence with the concept that the heterogeneity in the kinetics of the sepsis response serves as an important, often underappreciated but surmountable, source of translational impedance. Upon this groundwork, we discuss distinctions between animal experimentation and clinical trial design in the elements for hypothesis testing: cohort selection, power and sample size, randomization and blinding, and timing of intervention. From this concept, we develop a contextual framework for advancing the paradigm of animal-based investigations to facilitate science that transitions from molecule to medicine.

CONCLUSIONS

A persistent divide exists between the laboratory and clinical research arenas, which may be addressable via systematic targeting of identified translational gaps.

Overexpression of homeodomain-interacting protein kinase 2 (HIPK2) attenuates sepsis-mediated liver injury by restoring autophagy

Sepsis is the leading cause of death in intensive care units worldwide. Autophagy has recently been shown to protect against sepsis-induced liver injury. Here, we investigated the roles of homeodomain-interacting protein kinase 2 (HIPK2) in the molecular mechanism of sepsis-induced liver injury. HIPK2 expression was reduced in sepsis-induced liver injury, and HIPK2 overexpression increased the survival rate and improved caecal ligation and puncture (CLP)-induced liver injury by reducing serum and liver aspartate transaminase (AST), alanine transaminase (ALT), and alkaline phosphatase (ALP) levels in mice with sepsis. HIPK2 overexpression significantly decreased CLP-induced release of inflammatory cytokines into the serum and attenuated oxidative stress-associated indicators in mice with CLP-induced liver injury, whereas HIPK2 knockdown produced the opposite results, suggesting that HIPK2 is a negative regulator of sepsis. Furthermore, HIPK2 overexpression inhibited lipopolysaccharide (LPS)-induced apoptosis of primary hepatocytes, increased the autophagic flux, and restored both autophagosome and autolysosome formation in the livers of CLP-induced mice by suppressing calpain signalling. Importantly, HIPK2 overexpression reduced the elevated cytosolic Ca²⁺ concentration in LPS-treated primary hepatocytes by interacting with calpain 1 and calmodulin. Finally, several anti-inflammatory drugs, including resveratrol, aspirin, vitamin E and ursolic acid, significantly increased the levels of the HIPK2 mRNA and protein by modulating promoter activity and the 3′-UTR stability of the HIPK2 gene. In conclusion, HIPK2 overexpression may improve sepsis-induced liver injury by restoring autophagy and thus might be a promising target for the clinical treatment of sepsis.

Sepsis-induced acute kidney injury

PURPOSE OF REVIEW

Sepsis is a common and frequently fatal condition in which mortality has been consistently linked to increasing organ dysfunction. For example, acute kidney injury (AKI) occurs in 40-50% of septic patients and increases mortality six to eight-fold. However, the mechanisms by which sepsis causes organ dysfunction are not well understood and hence current therapy remains reactive and nonspecific.

RECENT FINDINGS

Recent studies have challenged the previous notion that organ dysfunction is solely secondary to hypoperfusion, by showing, for example, that AKI occurs in the setting of normal or increased renal blood flow; and that it is characterized not by acute tubular necrosis or apoptosis, but rather by heterogeneous areas of colocalized sluggish peritubular blood flow and tubular epithelial cell oxidative stress. Evidence has also shown that microvascular dysfunction, inflammation, and the metabolic response to inflammatory injury are fundamental pathophysiologic mechanisms that may explain the development of sepsis-induced AKI.

SUMMARY

The implications of these findings are significant because in the context of decades of negative clinical trials in the field, the recognition that other mechanisms are at play opens the possibility to better understand the processes of injury and repair, and provides an invaluable opportunity to design mechanism-targeted therapeutic interventions.

The Nephroprotective Effect of MS-275 on Lipopolysaccharide (LPS)-Induced Acute Kidney Injury by Inhibiting Reactive Oxygen Species (ROS)-Oxidative Stress and Endoplasmic Reticulum Stress

Background

Histone deacetylase (HDAC) inhibitors can attenuate acute kidney injury (AKI)-mediated damage and reduce fibrosis in kidney disease models. The aim of the present study was to investigate the effects of the HDAC inhibitor MS-275 on lipopolysaccharide (LPS)-induced AKI and the associated mechanisms.

Material/Methods

A LPS-induced model in 6–8 weeks-old mice was established by intraperitoneal injection of LPS (10 mg/kg), with pre-treatment of MS-275 (2 mg/kg/day) administered intraperitoneally for five days. In addition, HK-2 cells were exposed to LPS (1 μg/mL) at 0.1 nM, 1 nM, 10 nM, and 100 nM. For our in vitro MS-275 study, detection programs included histology, biochemical, immunohistochemistry, mRNA and protein expression as well as apoptosis.

Results

MS-275 ameliorated renal damage, enhanced the survival rate of the LPS-induced sepsis model, decreased the expressions of TNF-α, IL-1β, IL-6, COX-2, and NF-κBp65 nucleus translocation, suppressed the HDAC activity which was enhanced in septic AKI mice, and enhanced the acetylation of histone H3 and H4. Reactive oxygen species (ROS) production was enhanced in the kidney of LPS mice compared to control mice, while MS-275 suppressed the production of ROS in kidney tissue. In the in vitro studies, MS-275 reduced the LPS-induced apoptosis of HK-2 cells, inhibited ROS and MDA production, increased the production GSH and SOD activity, decreased the expressions of CHOP, GRP78, caspase3, and capase12, which was related to endoplasmic reticulum stress in LPS stimulated HK-2 cells.

Conclusions

MS-275 pre-treatment improved renal function and ameliorated histological alterations, inflammation, and ROS production in LPS-induced AKI mice and may act through inhibiting ROS-oxidative stress and endoplasmic reticulum stress.

Inhibition of autophagy with 3-methyladenine is protective in a lethal model of murine endotoxemia and polymicrobial sepsis

Here, the regulatory role of autophagy is examined in both an LPS-induced lethal endotoxic shock mouse model and cecal ligation and puncture (CLP) mouse model. Autophagy-inhibitor 3-methyladenine (3-MA) and autophagy-enhancer rapamycin were administrated to mice challenged with LPS or CLP. Animals challenged with LPS or CLP combined with 3-MA displayed increased survival after endotoxemia, but LPS combined with rapamycin worsened the endotoxic shock of the mice. Among the different organs studied, the lungs and intestines exhibited significant differences among LPS alone, LPS combined with 3-MA and LPS combined with rapamycin. LPS combined with 3-MA attenuated the inflammatory damages of these organs as compared with LPS alone. In contrast, LPS combined with rapamycin increased damage in these organs. Consistently, serum inflammatory mediators TNF-α and IL-6 were decreased by the treatment of LPS combined with 3-MA as compared with LPS alone, while administration of LPS combined with rapamycin increased the serum TNF-α and IL-6 levels. Similar results were found in mouse bone marrow-derived macrophages exposed to LPS. Moreover, the regulatory effect of autophagy to endotoxic shock is dependent on the TLR4 signaling pathway. Our results demonstrate the central role of autophagy in the regulation of endotoxic shock and its potential modulation for endotoxic shock treatment.

Bench-to-Bedside: A Translational Perspective on Murine Models of Sepsis

BACKGROUND

Considerable research effort has focused on the development of novel therapies for the treatment of sepsis, yet after decades of clinical trials, few significant advances have been achieved. This limitation persists despite a wealth of data yielded by basic science that has expanded our knowledge of the biology of this disease exponentially.

METHOD

Review of the English-language literature.

RESULTS

Translational researchers may address the resultant gap between the basic science laboratory and clinical research worlds. Herein, we review potential causes for the challenges of translating basic laboratory discovery into clinical benefit.

CONCLUSION

We propose conceptual platforms to further the development of translational sepsis research efforts.

Influence of autophagy on acute kidney injury in a murine cecal ligation and puncture sepsis model

The role of autophagy in the maintenance of renal homeostasis during sepsis is not well understood. We therefore aimed to determine the influence of autophagy on kidney during sepsis using a murine sepsis model, i.e. cecal ligation and puncture (CLP). In CLP treated animals, the number of autolysosomes observed by electron microscopy increased over time. The number of autophagosomes in CLP animals decreased relative sham operated controls at 24 hrs after CLP, indicating that autophagy flux is already diminishing by that time. Moreover, CLP induced an increase in LC3-II/LC3-I ratio at 6-8 hrs, demonstrated in western blots, as well as an increase in GFP-LC3 dots at 6-8 hrs and 24 hrs, using immunofluorescence and anti-LC3 and LAMP1 antibodies on tissue sections from GFP-LC3 transgenic mice. LC3-II/LC3-I ratio and the number of co-localized GFP-LC3 dots and LAMP1 signals (GFP LC3 + LAMP1 dots) in CLP mice at 24 hrs were significantly reduced compared with data obtained at 6-8 hrs. Notably, acceleration of autophagy by rapamycin resulted in improvement of renal function that was associated with improvement in the histologic severity of tubular epithelial injury in CLP treated animals. Autophagy in the kidney was significantly slowed in the kidney during the acute phase of sepsis; nonetheless, autophagy in kidney appears to play a protective role against sepsis.

Autophagy: A new treatment strategy for MSC-based therapy in acute kidney injury (Review)

Acute kidney injury (AKI) is a common and serious medical condition associated with poor health outcomes. Autophagy is a conserved multistep pathway that serves a major role in many biological processes and diseases. Recent studies have demonstrated that autophagy is induced in proximal tubular cells during AKI. Autophagy serves a pro‑survival or pro‑death role under certain conditions. Furthermore, mesenchymal stem cells (MSCs) have therapeutic potential in the repair of renal injury. This review summarizes the recent progress on the role of autophagy in AKI and MSCs‑based therapy for AKI. Further research is expected to prevent and treat acute kidney injury.

Necrostatin-1 attenuates sepsis-associated acute kidney injury by promoting autophagosome elimination in renal tubular epithelial cells

The aim of the present study was to investigate the protective effect of necrostatin‑1 (Nec‑1) in sepsis‑associated acute kidney injury (SA‑AKI). An SA‑AKI mouse model was established through an intraperitoneal injection of lipopolysaccharide (LPS), and Nec‑1 was administered to the mice prior to the establishment of SA‑AKI. Renal function and histological changes were evaluated, and the expression levels of microtubule‑associated protein light chain 3‑II (LC3‑II) and p62, as markers of autophagic flux, were detected. Autophagosomes and autolysosomes in renal tubular epithelial cells were also identified using electron microscopy. Pretreatment with Nec‑1 could attenuate the LPS‑induced increases in the concentrations of blood urea nitrogen (LPS+Nec‑1 vs. LPS group, 14.15±4.14 mmol/l vs. 32.54±5.46 mmol/l, respectively; P<0.001) and serum creatinine (11.50±1.67 µmol/l vs. 30.08±4.18 µmol/l, respectively; P<0.001). However, there were no significant differences in the rate of renal tubular epithelial cell necrosis between the groups. In the renal tissues of SA‑AKI mice, protein analysis showed that the LC3‑II and p62 proteins were increased, while a reverse transcription‑quantitative Reverse transcription‑polymerase chain reaction analysis detected no increase in LC3‑II or p62 mRNA. Additionally, a high number of autophagosomes, but not of autolysosomes, were observed by electron microscopy. When mice were pretreated with Nec‑1, the levels of LC3‑II and p62 decreased, and a large number of autolysosomes were observed by electron microscopy in the Nec‑1 pretreatment group. These results indicated that Nec‑1 improved autophagosome elimination, a process that is impaired by LPS, in renal tubular epithelial cells. This potentially enabled Nec‑1 to prevent SA‑AKI. Furthermore, the findings suggested that the protective effect of Nec‑1 may not have involved the inhibition of necroptosis, but may have occurred through the promotion of autophagosome elimination in renal tubular epithelial cells.

Activation of autophagy is involved in the protective effect of 17β-oestradiol on endotoxaemia-induced multiple organ dysfunction in ovariectomized rats

Oestrogens have been reported to attenuate acute inflammation in sepsis. In this study, the effects of long-term oestrogen replacement with 17β-oestradiol (E2 ) on endotoxaemia-induced circulatory dysfunction and multiple organ dysfunction syndrome were evaluated in ovariectomized (Ovx) rats. E2 (50 μg/kg, s.c., 3 times/week) was administered for 8 weeks, followed by the induction of endotoxaemia by intravenous infusion of lipopolysaccharides (LPS; 30 mg/kg/4 hrs). Oestrogen deficiency induced by ovariectomy for 9 weeks augmented the LPS-induced damage, including endotoxic shock, myocardial contractile dysfunction, renal dysfunction and rhabdomyolysis. Cardiac levels of NF-κB p65, iNOS and oxidized glutathione, free radical production in skeletal muscles, myoglobin deposition in renal tubules, and plasma levels of plasminogen activator inhibitor-1, TNF-α, and IL-6 were more pronounced in the Ovx + LPS group than in the Sham + LPS group. Long-term treatment of E2 prevented this amplified damage in Ovx rats. Six hours after LPS initiation, activation of the autophagic process, demonstrated by increases in Atg12 and LC3B-II/LC3B-I ratios, and induction of haem oxygenase (HO)-1 and heat-shock protein (HSP) 70 protein expression in myocardium were increased significantly in the Ovx + E2  + LPS group. These results suggest that activation of autophagy and induction of HO-1 and HSP70 contribute to the protective effect of long-term E2 replacement on multiple organ dysfunction syndrome in endotoxaemia.

Cereblon deficiency confers resistance against polymicrobial sepsis by the activation of AMP activated protein kinase and heme-oxygenase-1

Cereblon (CRBN) has a pleiotropic role in important cellular processes and is a potential therapeutic target in several diseases, including mental retardation, cancer, and metabolic disorders. The role of CRBN in polymicrobial sepsis induced by cecal ligation and puncture (CLP) was investigated using CRBN-deficient (KO) mice. Survival following CLP was significantly higher in KO mice compared to wild-type (WT) controls (50% vs 0% at day 6 after CLP). The improved survival of KO mice was accompanied by reduced peripheral blood bacterial load and lung injury. Serum tumor necrosis factor (TNF)-α and high mobility group box 1 (HMGB1) concentrations were significantly lower in KO mice than in WT mice. Peritoneal macrophages from KO mice with CLP-induced septic mouse had higher levels of activation of AMPK and heme oxygenase-1 (HO-1). Forced expression of CRBN in macrophage of KO mice suppressed activation of 5' adenosine monophosphate-activated protein kinase (AMPK) and HO-1 and augmented expression of TNF-α and HMGB1 as inhibition of AMPK by compound C. These studies demonstrate the contribution of CRBN expression to the pathogenesis of CLP-induced sepsis and peritoneal macrophage responses and suggest a novel therapeutic modality for polymicrobial sepsis.

Mitofusin 2 Promotes Apoptosis of CD4+ T Cells by Inhibiting Autophagy in Sepsis

Apoptosis of CD4⁺ T cells is a primary pathophysiological mechanism of immune dysfunction in the pathogenesis of sepsis. Mitofusin 2 (Mfn2), an integral mitochondrial outer membrane protein, has been confirmed to be associated with cellular metabolism, proliferation, and apoptosis. The function of Mfn2 in CD4⁺ T cell apoptosis in sepsis is poorly understood. Here, we discovered increased in vivo Mfn2 expression, autophagy deficiency, and elevated cell apoptosis in murine splenic CD4⁺ T cells after cecal ligation and puncture (CLP). We also observed almost identical results in splenic CD4⁺ T cells upon lipopolysaccharide (LPS) stimulation in vitro. Furthermore, overexpression of Mfn2 resulted in impaired autophagy and increased apoptosis in Jurkat cells. Pharmacological inhibition of autophagy with 3-methyladenine enhanced Mfn2 overexpression-induced cell apoptosis. In addition, overexpression of Mfn2 downregulated phorbol myristate acetate (PMA)/ionomycin-, rapamycin- and starvation-induced autophagy in Jurkat T cells. Taken together, these data indicate a critical role of Mfn2 in CD4⁺ T cell apoptosis in sepsis and the underlying mechanism of autophagy deficiency.

Mechanisms of Organ Dysfunction in Sepsis

Sepsis-associated organ dysfunction involves multiple responses to inflammation, including endothelial and microvascular dysfunction, immune and autonomic dysregulation, and cellular metabolic reprogramming. The effect of targeting these mechanistic pathways on short- and long-term outcomes depends highly on the timing of therapeutic intervention. Furthermore, there is a need to understand the adaptive or maladaptive character of these mechanisms, to discover phase-specific biomarkers to guide therapy, and to conceptualize these mechanisms in terms of resistance and tolerance.

Autophagy is activated to protect renal tubular epithelial cells against iodinated contrast media‑induced cytotoxicity

With the steady increase in the use of various contrast‑related technologies in recent years, contrast‑induced nephropathy has received significant attention from clinicians and researchers. The present study aimed to determine the potential role of autophagy in iodinated contrast media (CM)‑induced cell injury and apoptosis in human proximal renal tubular epithelial HK‑2 cells. The present study used the iodinated CM iohexol (200 mg iodine/ml) to treat HK‑2 cells for 6 h, in order to establish a damaged cell model. The autophagy inhibitor 3‑methyladenine (3‑MA; 10 mM) was used to inhibit the formation of autophagosomes. Immunofluorescence assay and transmission electron microscopy (TEM) were used to observe the formation of autophagosomes in the cytoplasm. The protein expression levels of microtubule‑associated protein 1A/1B‑light chain 3 (LC3)‑II and autophagy‑related protein 7 (Atg7) were detected by western blotting. The cytotoxicity of CM was evaluated by MTT assay and lactate dehydrogenase release, and cell apoptosis was detected by flow cytometry. Increased formation of autophagosomes and autophagic vesicles was observed under TEM in HK‑2 cells following iohexol treatment for 6 h. Immunofluorescence assay demonstrated that iohexol increased LC3‑II expression in HK‑2 cells. Furthermore, the expression levels of LC3‑II and Atg7 in HK‑2 cells were significantly upregulated by iohexol administration; however, LC3‑II and Atg7 expression was decreased by 3‑MA treatment. These results provided evidence to suggest that autophagy is activated in response to iohexol‑induced cell injury and apoptosis, and may exert a renoprotective role in HK‑2 cells.

Autophagy Primes Neutrophils for Neutrophil Extracellular Trap Formation during Sepsis

RATIONALE

Neutrophils are key effectors in the host's immune response to sepsis. Excessive stimulation or dysregulated neutrophil functions are believed to be responsible for sepsis pathogenesis. However, the mechanisms regulating functional plasticity of neutrophils during sepsis have not been fully determined.

OBJECTIVES

We investigated the role of autophagy in neutrophil functions during sepsis in patients with community-acquired pneumonia.

METHODS

Neutrophils were isolated from patients with sepsis and stimulated with phorbol 12-myristate 13-acetate (PMA). The levels of reactive oxygen species generation, neutrophil extracellular trap (NET) formation, and granule release, and the autophagic status were evaluated. The effect of neutrophil autophagy augmentation was further evaluated in a mouse model of sepsis.

MEASUREMENTS AND MAIN RESULTS

Neutrophils isolated from patients who survived sepsis showed an increase in autophagy induction, and were primed for NET formation in response to subsequent PMA stimulation. In contrast, neutrophils isolated from patients who did not survive sepsis showed dysregulated autophagy and a decreased response to PMA stimulation. The induction of autophagy primed healthy neutrophils for NET formation and vice versa. In a mouse model of sepsis, the augmentation of autophagy improved survival via a NET-dependent mechanism.

CONCLUSIONS

These results indicate that neutrophil autophagy primes neutrophils for increased NET formation, which is important for proper neutrophil effector functions during sepsis. Our study provides important insights into the role of autophagy in neutrophils during sepsis.