Mitochondrial quality control in hepatic ischemia-reperfusion injury

Mitochondrial Transplantation: A Novel Therapy for Liver Ischemia/Reperfusion Injury

OBJECTIVE

To investigate the hepatoprotective effects of mitochondrial transplantation (MTx) in a murine liver ischemia/reperfusion (I/R) model.

BACKGROUND

Sequential liver ischemia, followed by reperfusion (I/R), is a pathophysiological process underlying hepatocellular injury in a number of clinical contexts, such as hemorrhagic shock/resuscitation, major elective liver surgery, and organ transplantation. A unifying pathogenic consequence of I/R is mitochondrial dysfunction. Restoration of mitochondria through transplantation (MTx) has emerged as a potential therapeutic in I/R. However, its role in liver I/R and its mechanisms of action remain poorly defined.

METHODS

We investigated the hepatoprotective effects of MTx in an in vivo mouse model of liver I/R and used in vivo imaging and various knockout and transgenic mouse models to determine the mechanism of protection.

RESULTS

We found that I/R-induced hepatocellular injury was prevented by MTx, as measured by plasma ALT, AST, and liver histology. In addition, I/R-induced pro-inflammatory cytokine release (IL-6, TNFα) was dampened by MTx, and anti-inflammatory IL-10 was enhanced. Moreover, MTx lowered neutrophil infiltration into both the liver sinusoids and lung bronchoalveolar lavage fluid, suggesting a local and distant reduction in inflammation. Using in vivo intravital imaging, we found that I/R-subjected Kupffer cells (KCs), rapidly sequestered transplanted mitochondria, and acidified mitochondria within lysosomal compartments. To specifically interrogate the role of KCs, we depleted KCs using the diphtheria toxin-inducible Clec4f/iDTR transgenic mouse, then induced I/R, and discovered that KCs are necessary for the beneficial effects of MTx. Finally, we induced I/R in the complement receptor of the immunoglobulin (CRIg) superfamily knockout mice and found that CRIg was required for mitochondria capture by KCs and mitochondria-mediated hepatoprotection.

CONCLUSIONS

In this study, we demonstrated that CRIg-dependent capture of mitochondria by I/R-subjected KCs is a hepatoprotective mechanism in vivo . These data progress knowledge on the mechanisms of MTx and open new avenues for clinical translation.

Research progress on the role of mitochondria in the process of hepatic ischemia-reperfusion injury

During liver ischemia-reperfusion injury, existing mechanisms involved oxidative stress, calcium overload, and the activation of inflammatory responses involve mitochondrial injury. Mitochondrial autophagy, a process that maintains the normal physiological activity of mitochondria, promotes cellular metabolism, improves cellular function, and facilitates organelle renewal. Mitochondrial autophagy is involved in oxidative stress and apoptosis, of which the PINK1-Parkin pathway is a major regulatory pathway, and the deletion of PINK1 and Parkin increases mitochondrial damage, reactive oxygen species production, and inflammatory response, playing an important role in mitochondrial quality regulation. In addition, proper mitochondrial permeability translational cycle regulation can help maintain mitochondrial stability and mitigate hepatocyte death during ischemia-reperfusion injury. This mechanism is also closely related to oxidative stress, calcium overload, and the aforementioned autophagy pathway, all of which leads to the augmentation of the mitochondrial membrane permeability transition pore opening and cause apoptosis. Moreover, the release of mitochondrial DNA (mtDNA) due to oxidative stress further aggravates mitochondrial function impairment. Mitochondrial fission and fusion are non-negligible processes required to maintain the dynamic renewal of mitochondria and are essential to the dynamic stability of these organelles. The Bcl-2 protein family also plays an important regulatory role in the mitochondrial apoptosis signaling pathway. A series of complex mechanisms work together to cause hepatic ischemia-reperfusion injury (HIRI). This article reviews the role of mitochondria in HIRI, hoping to provide new therapeutic clues for alleviating HIRI in clinical practice.

Effects of carotenoids on mitochondrial dysfunction

Oxidative stress, an imbalance between pro-oxidant and antioxidant status, favouring the pro-oxidant state is a result of increased production of reactive oxygen species (ROS) or inadequate antioxidant protection. ROS are produced through several mechanisms in cells including during mitochondrial oxidative phosphorylation. Increased mitochondrial-derived ROS are associated with mitochondrial dysfunction, an early event in age-related diseases such as Alzheimer's diseases (ADs) and in metabolic disorders including diabetes. AD post-mortem investigations of affected brain regions have shown the accumulation of oxidative damage to macromolecules, and oxidative stress has been considered an important contributor to disease pathology. An increase in oxidative stress, which leads to increased levels of superoxide, hydrogen peroxide and other ROS in a potentially vicious cycle is both causative and a consequence of mitochondrial dysfunction. Mitochondrial dysfunction may be ameliorated by molecules with antioxidant capacities that accumulate in mitochondria such as carotenoids. However, the role of carotenoids in mitigating mitochondrial dysfunction is not fully understood. A better understanding of the role of antioxidants in mitochondrial function is a promising lead towards the development of novel and effective treatment strategies for age-related diseases. This review evaluates and summarises some of the latest developments and insights into the effects of carotenoids on mitochondrial dysfunction with a focus on the antioxidant properties of carotenoids. The mitochondria-protective role of carotenoids may be key in therapeutic strategies and targeting the mitochondria ROS is emerging in drug development for age-related diseases.

Isosteviol plays a protective role on hepatic ischemia and reperfusion injury in mice through MAPK/NF-κB signaling pathway

Background

Hepatic ischemia and reperfusion (I/R) injury is of common occurrence during liver surgery and transplantation, isosteviol (ISV) is an acid hydrolysate of stevioside, the major component of Stevia rebaudiana. Stevioside and its metabolites have been shown to have varieties of pharmacological activities, However, the effect of ISV on hepatic I/R injury has not determined. The purpose of this paper is to study the effect of ISV on mice with hepatic I/R injury and further investigate its underlying mechanism.

Methods

The blood vessels supplying the left/middle lobe of the liver in mice were clamped to cause liver ischemia for 1h, and then removed the clamp to conduct reperfusion for 6 h. ISV or saline was injected intraperitoneally after reperfusion. The expression of tumor necrosis factor (TNF)-α, interleukin (IL)-1β, IL-6 and IL-10 in serum and tissues were evaluated by enzyme linked immunosorbent assay (ELISA) and quantitative real-time polymerase chain reaction (qRT-PCR). The infiltration of neutrophils and macrophages into the liver tissue was determined by flow cytometry and myeloperoxidase. Liver hematoxylin-eosin (HE) staining, terminal deoxynucleotidyl transferase mediated dUTP nick-end labeling (TUNEL) and Annexin V probe were used to determine liver injury and hepatocyte apoptosis. western blots (WB) was used to investigate the activation of nuclear factor kappa-B (NF-κB) and c-JunNH2 terminal kinase (JNK), p38 and extracellular regulated protein kinase (ERK), while the expression of apoptosis-related proteins B-cell lymphoma-2 (BCL-2), BCL2-associated X protein (BAX), caspase-3 was detected.

Results

ISV reduced aspartate aminotransferase (AST) and alanine aminotransferase (ALT) levels to alleviate liver injury. ISV significantly reduced the release of inflammatory cytokines and the accumulation of liver neutrophils and macrophages. Meanwhile, ISV can promote the expression of anti-apoptosis-related protein BCL-2 and inhibit the expression of pro-apoptotic protein BAX and the activation of the protease caspase-3, and reduce the occurrence of hepatocyte apoptosis. Finally, ISV can reduce the phosphorylation level and activation of NF-κB, JNK, p38 and ERK.

Conclusions

ISV inhibits the occurrence of inflammation and hepatocyte apoptosis through mitogen-activated protein kinase (MAPK)/NF-κB signaling pathway to relieve liver injury.

Focusing on Ischemic Reperfusion Injury in the New Era of Dynamic Machine Perfusion in Liver Transplantation

Liver transplantation is the most effective treatment for end-stage liver disease. Transplant indications have been progressively increasing, with a huge discrepancy between the supply and demand of optimal organs. In this context, the use of extended criteria donor grafts has gained importance, even though these grafts are more susceptible to ischemic reperfusion injury (IRI). Hepatic IRI is an inherent and inevitable consequence of all liver transplants; it involves ischemia-mediated cellular damage exacerbated upon reperfusion and its severity directly affects graft function and post-transplant complications. Strategies for organ preservation have been constantly improving since they first emerged. The current gold standard for preservation is perfusion solutions and static cold storage. However, novel approaches that allow extended preservation times, organ evaluation, and their treatment, which could increase the number of viable organs for transplantation, are currently under investigation. This review discusses the mechanisms associated with IRI, describes existing strategies for liver preservation, and emphasizes novel developments and challenges for effective organ preservation and optimization.