Endotoxin Engages Mitochondrial Quality Control via an iNOS-Reactive Oxygen Species Signaling Pathway in Hepatocytes

Restoring the infected powerhouse: Mitochondrial quality control in sepsis

Sepsis is a dysregulated host response to an infection, characterized by organ failure. The pathophysiology is complex and incompletely understood, but mitochondria appear to play a key role in the cascade of events that culminate in multiple organ failure and potentially death. In shaping immune responses, mitochondria fulfil dual roles: they not only supply energy and metabolic intermediates crucial for immune cell activation and function but also influence inflammatory and cell death pathways. Importantly, mitochondrial dysfunction has a dual impact, compromising both immune system efficiency and the metabolic stability of end organs. Dysfunctional mitochondria contribute to the development of a hyperinflammatory state and loss of cellular homeostasis, resulting in poor clinical outcomes. Already in early sepsis, signs of mitochondrial dysfunction are apparent and consequently, strategies to optimize mitochondrial function in sepsis should not only prevent the occurrence of mitochondrial dysfunction, but also cover the repair of the sustained mitochondrial damage. Here, we discuss mitochondrial quality control (mtQC) in the pathogenesis of sepsis and exemplify how mtQC could serve as therapeutic target to overcome mitochondrial dysfunction. Hence, replacing or repairing dysfunctional mitochondria may contribute to the recovery of organ function in sepsis. Mitochondrial biogenesis is a process that results in the formation of new mitochondria and is critical for maintaining a pool of healthy mitochondria. However, exacerbated biogenesis during early sepsis can result in accumulation of structurally aberrant mitochondria that fail to restore bioenergetics, produce excess reactive oxygen species (ROS) and exacerbate the disease course. Conversely, enhancing mitophagy can protect against organ damage by limiting the release of mitochondrial-derived damage-associated molecules (DAMPs). Furthermore, promoting mitophagy may facilitate the growth of healthy mitochondria by blocking the replication of damaged mitochondria and allow for post sepsis organ recovery through enabling mitophagy-coupled biogenesis. The remaining healthy mitochondria may provide an undamaged scaffold to reproduce functional mitochondria. However, the kinetics of mtQC in sepsis, specifically mitophagy, and the optimal timing for intervention remain poorly understood. This review emphasizes the importance of integrating mitophagy induction with mtQC mechanisms to prevent undesired effects associated with solely the induction of mitochondrial biogenesis.

Ginsenoside Rg1 protects cardiac mitochondrial function via targeting GSTP1 to block S-glutathionylation of optic atrophy 1

Mitochondrial dysfunction is a fundamental challenge in myocardial injury. Ginsenoside Rg1 (Rg1) is a bioactive compound with pharmacological potential for cardiac protection. Optic atrophy 1 (OPA1) acts as a mitochondrial inner membrane protein that contributes to the structural integrity and function of mitochondria. This study investigated the protective role of Rg1 in septic cardiac injury from the perspective of OPA1 stability. Rg1 protected cardiac contractive function against endotoxin injury in mice by maintaining mitochondrial cristae structure. In cardiomyocytes, lipopolysaccharide (LPS) evoked mitochondrial fragmentation and destruction of mitochondrial biogenesis, which were prevented by Rg1, possibly due to the preservation of the integrity of cristae structure. In support, the beneficial effects of Rg1 on cardioprotection and mitochondrial biogenesis were diminished by OPA1 deficiency subjected to the LPS challenge. Mechanistically, LPS stimulation triggered intracellular glutathione destabilization that promoted S-glutathionylation of OPA1 at Cys551, leading to the dissociation of OPA1-Mitofilin. Rg1 interacted with GSTP1 to inhibit its S-glutathionylation of OPA1, thereby promoting OPA1-Mitofilin interaction and protecting mitochondrial cristae structure. These findings suggest that GSTP1/OPA1 axis may be a beneficial strategy for the treatment of myocardial injury, and expand the clinical application of Rg1.

iNOS contributes to heart failure with preserved ejection fraction through mitochondrial dysfunction and Akt S-nitrosylation

INTRODUCTION

Despite the high morbidity and mortality of heart failure with preserved fraction (HFpEF), there are currently no effective therapies for this condition. Moreover, the pathophysiological basis of HFpEF remains poorly understood.

OBJECTIVE

The aim of the present study was to investigate the role of inducible nitric oxide synthase (iNOS) and its underlying mechanism in a high-fat diet and N^ω-nitro-L-arginine methyl ester-induced HFpEF mouse model.

METHODS

The selective iNOS inhibitor L-NIL was used to examine the effects of short-term iNOS inhibition, whereas the long-term effects of iNOS deficiency were evaluated using iNOS-null mice. Cardiac and mitochondrial function, oxidative stress and Akt S-nitrosylation were then measured.

RESULTS

The results demonstrated that both pharmacological inhibition and iNOS knockout mitigated mitochondrial dysfunction, oxidative stress and Akt S-nitrosylation, leading to an ameliorated HFpEF phenotype in mice. In vitro, iNOS directly induced Akt S-nitrosylation at cysteine 224 residues , leading to oxidative stress, while inhibiting insulin-mediated glucose uptake in myocytes.

CONCLUSION

Altogether, the present findings suggested an important role for iNOS in the pathophysiological development of HFpEF, indicating that iNOS inhibition may represent a potential therapeutic strategy for HFpEF.

The Interplay of Oxidative Stress and ROS Scavenging: Antioxidants as a Therapeutic Potential in Sepsis

Oxidative stress resulting from the disproportion of oxidants and antioxidants contributes to both physiological and pathological conditions in sepsis. To combat this, the antioxidant defense system comes into the picture, which contributes to limiting the amount of reactive oxygen species (ROS) leading to the reduction of oxidative stress. However, a strong relationship has been found between scavengers of ROS and antioxidants in preclinical in vitro and in vivo models. ROS is widely believed to cause human pathology most specifically in sepsis, where a small increase in ROS levels activates signaling pathways to initiate biological processes. An inclusive understanding of the effects of ROS scavenging in cellular antioxidant signaling is essentially lacking in sepsis. This review compiles the mechanisms of ROS scavenging as well as oxidative damage in sepsis, as well as antioxidants as a potent therapeutic. Direct interaction between ROS and cellular pathways greatly affects sepsis, but such interaction does not provide the explanation behind diverse biological outcomes. Animal models of sepsis and a number of clinical trials with septic patients exploring the efficiency of antioxidants in sepsis are reviewed. In line with this, both enzymatic and non-enzymatic antioxidants were effective, and results from recent studies are promising. The usage of these potent antioxidants in sepsis patients would greatly impact the field of medicine.

Capsaicin Prevents Contrast-Associated Acute Kidney Injury through Activation of Nrf2 in Mice

Capsaicin, a transient receptor potential vanilloid 1 channel agonist, possesses antioxidative properties through activating nuclear factor-erythroid 2-related factor 2 (Nrf2). As oxidative stress is a major contributor to the development of contrast-associated acute kidney injury (CA-AKI), we investigated the protective effect of capsaicin against CA-AKI via Nrf2. C57BL/6J mice were treated with dehydration and iodixanol to establish the model of CA-AKI. For pretreatment, capsaicin (0.3 mg/kg) was given via intraperitoneal injection one hour before iodixanol injection. Nrf2-specific siRNA was given through the tail vein to knock down Nrf2. The CA-AKI mouse model had remarkable mitochondrial fragmentation and dysfunction and apoptosis of tubular cells, overproduction of superoxide in renal tubules, increased renal malondialdehyde, tubular epithelial cell injury, and renal dysfunction. Importantly, pretreatment with capsaicin significantly ameliorated tubular cell injury and renal dysfunction with decreased superoxide, renal malondialdehyde, and apoptotic tubular cells and improved mitochondrial morphology and function in the CA-AKI mouse model. The expression of Nrf2 was increased in the kidney from the CA-AKI mouse model and was further enhanced by capsaicin. Administration of siRNA through the tail vein successfully decreased Nrf2 expression in the kidney, and knockdown of Nrf2 by siRNA abolished the beneficial effects of capsaicin on CA-AKI. The present study demonstrated a protective effect of capsaicin pretreatment against CA-AKI via Nrf2.

Paeoniflorin ameliorates lipopolysaccharide-induced acute liver injury by inhibiting oxidative stress and inflammation via SIRT1/FOXO1a/SOD2 signaling in rats

Acute liver injury (ALI) is a poor prognosis and high mortality complication of sepsis. Paeoniflorin (PF) has remarkable anti-inflammatory effects in different disease models. Here, we explored the protective effect and underlying molecular mechanisms of PF against lipopolysaccharide (LPS)-induced ALI. Sprague-Dawley rats received intraperitoneal (i.p.) injection of PF for 7 days, 1 h after the last administration, and rats were injected i.p. 10 mg/kg LPS. PF improved liver structure and function, reduced hepatic reactive oxygen species (ROS) and methane dicarboxylic aldehyde (MDA) levels, and increased superoxide dismutase (SOD) activity. Western blot analysis suggested that PF significantly inhibited expression of inflammatory cytokines (TNF-α, IL-1β, and IL-18) and inhibited activation of the NLRP3 inflammasome. PF or mitochondrial ROS scavenger (mito-TEMPO) significantly improved liver mitochondrial function by scavenging mitochondrial ROS (mROS), restoring mitochondrial membrane potential loss and increasing level of ATP and enzyme activity of complex I and III. In addition, PF increased expression of sirtuin-1 (SIRT1), forkhead box O1 (FOXO1a) and manganese superoxide dismutase (SOD2), and increased FOXO1a nuclear retention. However, the inhibitor of SIRT1 (EX527) abolished the protective effect of PF. Taken together, PF promotes mROS clearance to inhibit mitochondrial damage and activation of the NLRP3 inflammasome via SIRT1/FOXO1a/SOD2 signaling.

Oxidative Stress and Redox Signaling in the Pathophysiology of Liver Diseases

The increased production of derivatives of molecular oxygen and nitrogen in the form of reactive oxygen species (ROS) and reactive nitrogen species (RNS) lead to molecular damage called oxidative stress. Under normal physiological conditions, the ROS generation is tightly regulated in different cells and cellular compartments. Any disturbance in the balance between the cellular generation of ROS and antioxidant balance leads to oxidative stress. In this article, we discuss the sources of ROS (endogenous and exogenous) and antioxidant mechanisms. We also focus on the pathophysiological significance of oxidative stress in various cell types of the liver. Oxidative stress is implicated in the development and progression of various liver diseases. We narrate the master regulators of ROS-mediated signaling and their contribution to liver diseases. Nonalcoholic fatty liver diseases (NAFLD) are influenced by a "multiple parallel-hit model" in which oxidative stress plays a central role. We highlight the recent findings on the role of oxidative stress in the spectrum of NAFLD, including fibrosis and liver cancer. Finally, we provide a brief overview of oxidative stress biomarkers and their therapeutic applications in various liver-related disorders. Overall, the article sheds light on the significance of oxidative stress in the pathophysiology of the liver. © 2022 American Physiological Society. Compr Physiol 12:3167-3192, 2022.

Genetic BACH1 deficiency alters mitochondrial function and increases NLRP3 inflammasome activation in mouse macrophages

BTB-and-CNC homologue 1 (BACH1), a heme-regulated transcription factor, mediates innate immune responses via its functional role in macrophages. BACH1 has recently been shown to modulate mitochondrial metabolism in cancer cells. In the current study, we utilized a proteomics approach and demonstrate that genetic deletion of BACH1 in mouse macrophages is associated with decreased levels of various mitochondrial proteins, particularly mitochondrial complex I. Bioenergetic studies revealed alterations of mitochondrial energy metabolism in BACH1−/− macrophages with a shift towards increased glycolysis and decreased oxidative phosphorylation. Moreover, these cells exhibited enhanced mitochondrial membrane potential and generation of mitochondrial reactive oxygen species (mtROS) along with lower levels of mitophagy. Notably, a higher inducibility of NLRP3 inflammasome activation in response to ATP and nigericin following challenge with lipopolysaccharide (LPS) was observed in BACH1-deficient macrophages compared to wild-type cells. Mechanistically, pharmacological inhibition of mtROS markedly attenuated inflammasome activation. In addition, it is shown that inducible nitric oxide synthase and cyclooxygenase-2, both of which are markedly induced by LPS in macrophages, are directly implicated in BACH1-dependent regulation of NLRP3 inflammasome activation. Taken together, the current findings indicate that BACH1 is critical for immunomodulation of macrophages and may serve as a target for therapeutic approaches in inflammatory disorders.

Combined Transcriptome and Proteome Leukocyte's Profiling Reveals Up-Regulated Module of Genes/Proteins Related to Low Density Neutrophils and Impaired Transcription and Translation Processes in Clinical Sepsis

Sepsis is a global health emergency, which is caused by various sources of infection that lead to changes in gene expression, protein-coding, and metabolism. Advancements in "omics" technologies have provided valuable tools to unravel the mechanisms involved in the pathogenesis of this disease. In this study, we performed shotgun mass spectrometry in peripheral blood mononuclear cells (PBMC) from septic patients (N=24) and healthy controls (N=9) and combined these results with two public microarray leukocytes datasets. Through combination of transcriptome and proteome profiling, we identified 170 co-differentially expressed genes/proteins. Among these, 122 genes/proteins displayed the same expression trend. Ingenuity Pathway Analysis revealed pathways related to lymphocyte functions with decreased status, and defense processes that were predicted to be strongly increased. Protein-protein interaction network analyses revealed two densely connected regions, which mainly included down-regulated genes/proteins that were related to the transcription of RNA, translation of proteins, and mitochondrial translation. Additionally, we identified one module comprising of up-regulated genes/proteins, which were mainly related to low-density neutrophils (LDNs). LDNs were reported in sepsis and in COVID-19. Changes in gene expression level were validated using quantitative real-time PCR in PBMCs from patients with sepsis. To further support that the source of the upregulated module of genes/proteins found in our results were derived from LDNs, we identified an increase of this population by flow cytometry in PBMC samples obtained from the same cohort of septic patients included in the proteomic analysis. This study provides new insights into a reprioritization of biological functions in response to sepsis that involved a transcriptional and translational shutdown of genes/proteins, with exception of a set of genes/proteins related to LDNs and host-defense system.

An in vitro tumorigenesis model based on live-cell-generated oxygen and nutrient gradients

The tumor microenvironment (TME) is multi-cellular, spatially heterogenous, and contains cell-generated gradients of soluble molecules. Current cell-based model systems lack this complexity or are difficult to interrogate microscopically. We present a 2D live-cell chamber that approximates the TME and demonstrate that breast cancer cells and macrophages generate hypoxic and nutrient gradients, self-organize, and have spatially varying phenotypes along the gradients, leading to new insights into tumorigenesis.

Renal Dopamine Receptors and Oxidative Stress: Role in Hypertension

Significance: The kidney plays an important role in the long-term control of blood pressure. Oxidative stress is one of the fundamental mechanisms responsible for the development of hypertension. Dopamine, via five subtypes of receptors, plays an important role in the control of blood pressure by various mechanisms, including the inhibition of oxidative stress. Recent Advances: Dopamine receptors exert their regulatory function to decrease the oxidative stress in the kidney and ultimately maintain normal sodium balance and blood pressure homeostasis. An aberration of this regulation may be involved in the pathogenesis of hypertension. Critical Issues: Our present article reviews the important role of oxidative stress and intrarenal dopaminergic system in the regulation of blood pressure, summarizes the current knowledge on renal dopamine receptor-mediated antioxidation, including decreasing reactive oxygen species production, inhibiting pro-oxidant enzyme nicotinamide-adenine dinucleotide phosphate (NADPH) oxidase, and stimulating antioxidative enzymes, and also discusses its underlying mechanisms, including the increased activity of G protein-coupled receptor kinase 4 (GRK4) and abnormal trafficking of renal dopamine receptors in hypertensive status. Future Directions: Identifying the mechanisms of renal dopamine receptors in the regulation of oxidative stress and their contribution to the pathogenesis of hypertension remains an important research focus. Increased understanding of the role of reciprocal regulation between renal dopamine receptors and oxidative stress in the regulation of blood pressure may give us novel insights into the pathogenesis of hypertension and provide a new treatment strategy for hypertension.

Resveratrol ameliorates disorders of mitochondrial biogenesis and mitophagy in rats continuously exposed to benzo(a)pyrene from embryonic development through adolescence

Exposure to benzo(a)pyrene (BaP) is associated with poor neurodevelopment in children and memory impairment in adults. Previous research has demonstrated that mitochondrial damage plays an important role in BaP-induced neurotoxicity. Of interest, increasing evidence has suggested that resveratrol (RSV) can alleviate nerve cell damage, however the exact mechanisms of biological activity in mitochondria are not fully understood. In the current study, Wistar rats were exposed to BaP (1, 2, 4 mg/kg) and/or RSV (15, 30 mg/kg) during embryonic development and adolescence, and learning and memory ability, mitochondrial damage, and the expression of proteins associated with mitochondrial biogenesis and mitophagy were evaluated. These studies indicated that 2 and 4 mg/kg BaP could induce disorders of mitochondrial biogenesis and mitophagy, which leads to abnormal nerve cell development. However, pretreatment with 30 mg/kg RSV alleviated cell damage and the disorder of mitochondrial biogenesis by activating the AMPK/PGC-1α signaling pathway and promoting mitophagy. These findings suggested that RSV had utility in promoting mitochondrial homeostasis against BaP-induced nerve cell damage in the hippocampus of rats.