Kristina L. Go

Mitochondrial Dysfunction and Autophagy in Hepatic Ischemia/Reperfusion Injury

Ischemia/reperfusion (I/R) injury remains a major complication of liver resection, transplantation, and hemorrhagic shock. Although the mechanisms that contribute to hepatic I/R are complex and diverse involving the interaction of cell injury in hepatocytes, immune cells, and endothelium, mitochondrial dysfunction is a cardinal event culminating in hepatic reperfusion injury. Mitochondrial autophagy, so-called mitophagy, is a key cellular process that regulates mitochondrial homeostasis and eliminates damaged mitochondria in a timely manner. Growing evidence accumulates that I/R injury is attributed to defective mitophagy. This review aims to summarize the current understanding of autophagy and its role in hepatic I/R injury and highlight the various therapeutic approaches that have been studied to ameliorate injury.

Autophagy in Ischemic Livers: A Critical Role of Sirtuin 1/Mitofusin 2 Axis in Autophagy Induction

No-flow ischemia occurs during cardiac arrest, hemorrhagic shock, liver resection and transplantation. Recovery of blood flow and normal physiological pH, however, irreversibly injures the liver and other tissues. Although the liver has the powerful machinery for mitochondrial quality control, a process called mitophagy, mitochondrial dysfunction and subsequent cell death occur after reperfusion. Growing evidence indicates that reperfusion impairs mitophagy, leading to mitochondrial dysfunction, defective oxidative phosphorylation, accumulation of toxic metabolites, energy loss and ultimately cell death. The importance of acetylation/deacetylation cycle in the mitochondria and mitophagy has recently gained attention. Emerging data suggest that sirtuins, enzymes deacetylating a variety of target proteins in cellular metabolism, survival and longevity, may also act as an autophagy modulator. This review highlights recent advances of our understanding of a mechanistic correlation between sirtuin 1, mitophagy and ischemic liver injury.

Autophagy in the liver: cell's cannibalism and beyond.

Chronic liver disease and its progression to liver failure are induced by various etiologies including viral infection, alcoholic and nonalcoholic hepatosteatosis. It is anticipated that the prevalence of fatty liver disease will continue to rise due to the growing incidence of obesity and metabolic disorder. Evidence is accumulating to indicate that the onset of fatty liver disease is causatively linked to mitochondrial dysfunction and abnormal lipid accumulation. Current treatment options for this disease are limited. Autophagy is an integral catabolic pathway that maintains cellular homeostasis both selectively and nonselectively. As mitophagy and lipophagy selectively remove dysfunctional mitochondria and excess lipids, respectively, stimulation of autophagy could have therapeutic potential to ameliorate liver function in steatotic patients. This review highlights our up-to-date knowledge on mechanistic roles of autophagy in the pathogenesis of fatty liver disease and its vulnerability to surgical stress, with an emphasis on mitophagy and lipophagy.

Deacetylation of mitofusin-2 by sirtuin-1: A critical event in cell survival after ischemia

ABSTRACT Sirtuin-1 (SIRT1) is associated with longevity and cell survival. Recently, we unveiled a new role of SIRT1 in hepatic ischemia/reperfusion (I/R) injury and identified a novel interaction between SIRT1 and mitochondrial outer membrane protein mitofusin-2 (MFN2), in which SIRT1-dependent deacetylation of MFN2 regulates mitochondria and autophagy in the liver.

Orthotopic Patient-Derived Pancreatic Cancer Xenografts Engraft Into the Pancreatic Parenchyma, Metastasize, and Induce Muscle Wasting to Recapitulate the Human Disease

OBJECTIVE Limitations associated with current animal models serve as a major obstacle to reliable preclinical evaluation of therapies in pancreatic cancer (PC). In an effort to develop more reliable preclinical models, we have recently established a subcutaneous patient-derived xenograft (PDX) model. However, critical aspects of PC responsible for its highly lethal nature, such as the development of distant metastasis and cancer cachexia, remain underrepresented in the flank PDX model. The purpose of this study was to evaluate the degree to which an orthotopic PDX model of PC recapitulates these aspects of the human disease. METHODS Human PDX-derived PC tumors were implanted directly into the pancreas of NOD.Cg-Prkdc Il2rg/SzJ mice. Tumor growth, metastasis, and muscle wasting were then evaluated. RESULTS Orthotopically implanted PDX-derived tumors consistently incorporated into the murine pancreatic parenchyma metastasized to both the liver and lungs and induced muscle wasting directly proportional to the size of the tumor, consistent of the cancer cachexia syndrome. CONCLUSIONS Through the orthotopic implantation technique described, we demonstrate a highly reproducible model that recapitulates both local and systemic aspects of human PC.Objective Limitations associated with current animal models serve as a major obstacle to reliable preclinical evaluation of therapies in pancreatic cancer (PC). In an effort to develop more reliable preclinical models, we have recently established a subcutaneous patient-derived xenograft (PDX) model. However, critical aspects of PC responsible for its highly lethal nature, such as the development of distant metastasis and cancer cachexia, remain underrepresented in the flank PDX model. The purpose of this study was to evaluate the degree to which an orthotopic PDX model of PC recapitulates these aspects of the human disease. Methods Human PDX-derived PC tumors were implanted directly into the pancreas of NOD.Cg-Prkdcscid Il2rgtm1Wjl/SzJ mice. Tumor growth, metastasis, and muscle wasting were then evaluated. Results Orthotopically implanted PDX-derived tumors consistently incorporated into the murine pancreatic parenchyma, metastasized to both the liver and lungs and induced muscle wasting directly proportional to the size of the tumor, consistent of the cancer cachexia syndrome. Conclusions Through the orthotopic implantation technique described, we demonstrate a highly reproducible model that recapitulates both local and systemic aspects of human PC.

Loss of sirtuin 1 and mitofusin 2 contributes to enhanced ischemia/reperfusion injury in aged livers

Ischemia/reperfusion (I/R) injury is a causative factor contributing to morbidity and mortality during liver resection and transplantation. Livers from elderly patients have a poorer recovery from these surgeries, indicating reduced reparative capacity with aging. Mechanisms underlying this age‐mediated hypersensitivity to I/R injury remain poorly understood. Here, we investigated how sirtuin 1 (SIRT1) and mitofusin 2 (MFN2) are affected by I/R in aged livers. Young (3 months) and old (23–26 months) male C57/BL6 mice were subjected to hepatic I/R in vivo. Primary hepatocytes isolated from each age group were also exposed to simulated in vitro I/R. Biochemical, genetic, and imaging analyses were performed to assess cell death, autophagy flux, mitophagy, and mitochondrial function. Compared to young mice, old livers showed accelerated liver injury following mild I/R. Reperfusion of old hepatocytes also showed necrosis, accompanied with defective autophagy, onset of the mitochondrial permeability transition, and mitochondrial dysfunction. Biochemical analysis indicated a near‐complete loss of both SIRT1 and MFN2 after I/R in old hepatocytes, which did not occur in young cells. Overexpression of either SIRT1 or MFN2 alone in old hepatocytes failed to mitigate I/R injury, while co‐overexpression of both proteins promoted autophagy and prevented mitochondrial dysfunction and cell death after reperfusion. Genetic approaches with deletion and point mutants revealed that SIRT1 deacetylated K655 and K662 residues in the C‐terminus of MFN2, leading to autophagy activation. The SIRT1‐MFN2 axis is pivotal during I/R recovery and may be a novel therapeutic target to reduce I/R injury in aged livers.

Laparoscopic sleeve gastrectomy in patients with heart failure and left ventricular assist devices as a bridge to transplant

BACKGROUND Obesity is an epidemic that is closely associated with heart failure. The ultimate treatment for end-stage heart failure is cardiac transplantation. Patients with morbid obesity are often excluded from receiving donor organs. Many transplant centers use body mass index (BMI) >35 kg/m2 as a contraindication to listing for heart transplant. Left ventricular assist devices (LVADs) were developed as a bridge to transplant for many heart failure patients, but bariatric surgery for LVAD patients has not been well described. OBJECTIVES The purpose of our study was to evaluate the safety and efficacy of laparoscopic sleeve gastrectomy (LSG) in LVAD patients and the impact on heart failure recovery as a bridge to cardiac transplantation. SETTING University hospital. METHODS A retrospective study was conducted to evaluate the outcomes of patients with morbid obesity and LVADs who underwent LSG at a large academic medical center between 2013 and 2017. Age, BMI, percent excess weight loss, cardiac ejection fraction, listing status for transplantation, and success of transplant were reviewed. RESULTS Eleven patients were identified with morbid obesity and heart failure with LVAD support who underwent LSG. There were no perioperative deaths. Four patients (37%) achieved BMI <35 and were successfully listed for and received cardiac transplantation. An additional 3 patients (27%) achieved BMI <35 kg/m2 and are listed for cardiac transplantation. CONCLUSIONS LSG can be safely used in patients with morbid obesity and end-stage heart failure requiring LVAD support to lower their BMI and become eligible for cardiac transplantation.

Mitochondrial Damage and Mitophagy in Ischemia/Reperfusion-Induced Liver Injury

The liver is innately vulnerable to hypoxia and anoxia. Ischemia/reperfusion (I/R) injury is a major obstacle in liver resection and transplantation. However, therapeutic strategies to attenuate reperfusion injury remain disappointing largely due to the complex and multifactorial nature of I/R injury. One key mechanism contributing to I/R injury in the liver is the onset of mitochondrial permeability transition and subsequent mitochondrial dysfunction. Mitochondrial integrity is critical for hepatocyte survival and function after I/R. Key quality control machinery in mitochondria is mitophagy that clears damaged or abnormal mitochondria in a timely manner. Evidence is accumulating to indicate that defective mitophagy is an important factor culminating in I/R injury. Here, we highlight our current knowledge on mitochondrial dysfunction after I/R in the liver, role of mitophagy in reperfusion injury, and therapeutic potential of mitophagy. We also discuss mitochondrial dysfunction in aged and fatty livers and their sensitivity to I/R injury and describe the various therapeutic approaches that have been proposed to ameliorate injury.