Impact of Hypothermia and Oxygen Deprivation on the Cytoskeleton in Organ Preservation Models

Molecular Frontiers in Transplantation-Induced Ischemia-Reperfusion Injury

This Special Issue aims to summarize the most up-to-date research on ischemia-reperfusion and organ transplantation [...].

Superresolution Imaging of Cytoskeletal Networks in Fixed Brain Tissue

Emerging evidence suggests that neurodegeneration is directly linked to dysfunction of cytoskeleton; however, visualizing the organization of cytoskeletal structures in brain tissues remains challenging due to the limitation of resolution of light microscopy. Superresolution imaging overcomes this limitation and resolves subcellular structures below the diffraction barrier of light (20-200 nm), while retaining the advantages of fluorescent microscopy such as simultaneous visualization of multiple proteins and increased signal sensitivity and contrast. However, superresolution imaging approaches have been largely limited to very thin samples such as cultured cells growing as a single monolayer. Analysis of thicker tissue sections represents a technical challenge due to high background fluorescence and quality of the tissue preservation methods. Among superresolution microscopy approaches, structured illumination microscopy is one of the most compatible methods for analyzing thicker native tissue samples. We have developed a methodology that allows maximal preservation and quantitative analyses of cytoskeletal networks in tissue sections from a rodent brain. This methodology includes a specialized fixation protocol, tissue preparation, and image acquisition procedures optimized for the characterization of subcellular cytoskeletal structures using superresolution with structured illumination microscopy.

Cytoskeletal Arrest: An Anoxia Tolerance Mechanism

Polymerization of actin filaments and microtubules constitutes a ubiquitous demand for cellular adenosine-5′-triphosphate (ATP) and guanosine-5′-triphosphate (GTP). In anoxia-tolerant animals, ATP consumption is minimized during overwintering conditions, but little is known about the role of cell structure in anoxia tolerance. Studies of overwintering mammals have revealed that microtubule stability in neurites is reduced at low temperature, resulting in withdrawal of neurites and reduced abundance of excitatory synapses. Literature for turtles is consistent with a similar downregulation of peripheral cytoskeletal activity in brain and liver during anoxic overwintering. Downregulation of actin dynamics, as well as modification to microtubule organization, may play vital roles in facilitating anoxia tolerance. Mitochondrial calcium release occurs during anoxia in turtle neurons, and subsequent activation of calcium-binding proteins likely regulates cytoskeletal stability. Production of reactive oxygen species (ROS) formation can lead to catastrophic cytoskeletal damage during overwintering and ROS production can be regulated by the dynamics of mitochondrial interconnectivity. Therefore, suppression of ROS formation is likely an important aspect of cytoskeletal arrest. Furthermore, gasotransmitters can regulate ROS levels, as well as cytoskeletal contractility and rearrangement. In this review we will explore the energetic costs of cytoskeletal activity, the cellular mechanisms regulating it, and the potential for cytoskeletal arrest being an important mechanism permitting long-term anoxia survival in anoxia-tolerant species, such as the western painted turtle and goldfish.

Microtubule Stabilization Protects Hypothermia-Induced Damage to the Cytoskeleton and Barrier Integrity of the Corneal Endothelial Cells

Purpose: To determine the impact of hypothermia on the barrier function of donor corneal endothelium, thereby enhancing the success of corneal transplantation. Methods: Primary cultures of porcine endothelial cells were subjected to hypothermia (15 h; 4°C). The impact on microtubule assembly, peri-junctional actomyosin ring (PAMR), and ZO-1 was assessed by immunocytochemistry with and without pretreatment with a microtubule-stabilizing agent (Epothilone B; EpoB; 100 nM) and a p38 MAP kinase inhibitor (SB-203580; 20 μM). In addition, EpoB-loaded PLGA nanoparticles (ENPs) prepared by nanoprecipitation technique and coated with poly-L-lysine (PLL-ENPs) were administered one-time for sustained intracellular delivery of EpoB. Results: Exposure to hypothermia led to microtubule disassembly concomitant with the destruction of PAMR and the displacement of ZO-1 at the cellular periphery, suggesting a loss in barrier integrity. These adverse effects were attenuated by pretreatment with EpoB or SB-203580. PLL-ENPs possessed a zeta potential of ∼26 mV and a size of ∼110 nm. Drug loading and entrapment efficiency were 5% (w/w) and ∼87%, respectively, and PLL-ENPs showed a biphasic release in vitro: burst phase (1 day), followed by a sustained phase (∼4 weeks). Pretreatment with PLL-ENPs (0.4 mg/mL) for 24 h stabilized the microtubules and opposed the hypothermia-induced damage to PAMR and the redistribution of ZO-1. Conclusions: Hypothermia induces microtubule disassembly via activation of p38 MAP kinase and subsequently breaks down the barrier function of the endothelium. Sustained intracellular delivery of EpoB using nanoparticles has the potential to overcome endothelial barrier failure during prolonged cold storage of donor cornea.

High Throughput Proteomic Exploration of Hypothermic Preservation Reveals Active Processes within the Cell Associated with Cold Ischemia Kinetic

The demand for organs to be transplanted increases pressure on procurement centers, to the detriment of organ quality, increasing complications. New preservation protocols are urgently needed, requiring an in-depth understanding of ischemia-reperfusion mechanisms. We performed a proteomic analysis using LC-MS/MS-TOF data analyzed through R software and Cytoscape's ClueGO application, comparing the proteome of kidney endothelial cells, key cell type, subjected to 3, 6, 12, 19, and 24 h of cold ischemia and 6 h reperfusion. Critical pathways such as energy metabolism, cytoskeleton structure/transport system, and gene transcription/translation were modulated. Important time windows were revealed: a-during the first 3 h, central proteins were upregulated within these pathways; b-the majority of these upregulations were maintained until 12 h cold ischemia time (CIT); c-after that time, the overall decrease in protein expression was observed; d-at reperfusion, proteins expressed in response to cold ischemia were all downregulated. This shows that cold ischemia is not a simple slowing down of metabolism, as deep changes take place within the proteome on major pathways. Time-sensitive expression of key protein reveals possible quality biomarkers as well as potential targets for new strategies to maintain or optimize organ quality.

Assessing Kidney Graft Viability and Its Cells Metabolism during Machine Perfusion

Kidney transplantation is the golden treatment for end-stage renal disease. Static cold storage is currently considered the standard method of preservation, but dynamic techniques, such as machine perfusion (MP), have been shown to improve graft function, especially in kidneys donated by extended criteria donors and donation after circulatory death. With poor organ quality being a major reason for kidneys not being transplanted, an accurate, objective and reliable quality assessment during preservation could add value and support to clinicians’ decisions. MPs are emerging technologies with the potential to assess kidney graft viability and quality, both in the hypothermic and normothermic scenarios. The aim of this review is to summarize current tools for graft viability assessment using MP prior to implantation in relation to the ischemic damage.

Renal Procurement: Techniques for Optimizing the Quality of the Graft in the Cadaveric Setting

PURPOSE OF REVIEW

Kidney transplantation is the best treatment for end-stage renal disease. However, due to organ shortage, suboptimal grafts are increasingly being used.

RECENT FINDINGS

We carried out a review on the methods and techniques of organ optimization in the cadaveric setting. Donor care is the first link in a chain of care. Right after brain death, there is a set of changes, of which hormonal and hemodynamic changes are the most relevant. Several studies have been conducted to determine which drugs to administer, although in most cases, the results are not definitive. The main goal seems rather achieve a set of biochemical and hemodynamic objectives. The ischemia-reperfusion injury is a critical factor for kidney damage in transplantation. One of the ways found to deal with this type of injury is preconditioning. Local and remote ischemic preconditioning has been studied for various organs, but studies on the kidney are scarce. A new promising area is pharmacological preconditioning, which is taking its first steps. Main surgical techniques were established in the late twentieth century. Some minor new features have been introduced to deal with anatomical variations or the emergence of donation after circulatory death. Finally, after harvesting, it is necessary to ensure the best conditions for the kidneys until the time of transplantation. Much has evolved since static cold preservation, but the best preservation conditions are yet to be determined. Conservation in the cold has come to be questioned, and great results have appeared at temperatures closer to physiological.

Excessive arachidonic acid induced actin bunching remodeling and podocyte injury via a PKA-c-Abl dependent pathway

Recent studies have shown that serum secretory phospholipase A2 group IB (sPLA2-IB) is associated with proteinuric kidney diseases and plays a pivotal role in podocyte injury via its natural receptor. Arachidonic acid (AA), as a major metabolite of sPLA2-IB, regulates the actin bungling remodeling and contributes to the podocyte injury. However, the underlying mechanism of AA in the regulation of podocyte actin remodeling and human podocyte injury is unclear. Here, we reported that AA induced F-actin cytoskeletal ring formation and promoted protein kinase A (PKA), nephrin and c-Abl phosphorylation. Moreover, AA promoted c-Abl translocation from the nucleus to the cytoplasm and increased the recruitment of c-Abl to p-nephrin by the interaction between them. H89 (PKA inhibitor) provided protection against AA-induced F-actin bunching remodeling, down-regulated nephrin phosphorylation, and suppressed the c-Abl translocation and activation. STI571 (c-Abl inhibitor) also improved the AA associated F-actin bunching remodeling. In addition, H89 and STI571 both alleviated apoptosis and adhesion damage of podocyte. These results indicate that an excess of AA treatment is detrimental to the podocyte actin cytoskeleton and promotes podocyte injury due to the activation of PKA-c-Abl signaling.

Preventing acute kidney injury during transplantation: the application of novel oxygen carriers

INTRODUCTION

Delayed graft function (DGF) has a significant impact on kidney transplantation outcome. One of the underlying pivotal mechanisms is organ preservation and associated hypothermia and biochemical alteration.

AREAS COVERED

This paper focuses on organ preservation and its clinical consequences and describes 1. A comprehensive presentation of the pathophysiological mechanism involved in delayed graft function development; 2. The impact on endothelial cells and microvasculature integrity and the consequences on transplanted organ outcome; 3. The reassessment of dynamic organ preservation motivated by the growing use of extended criteria donors and the interest in the potential of normothermia; 4. The role of oxygenation during dynamic preservation; and 5. Novel oxygen carriers and their proof of concept in transplantation, among which M101 (HEMO₂life®) is currently the most extensively investigated.

EXPERT OPINION

Metabolic disturbances and imbalance of oxygen supply during preservation highlight the importance of providing oxygen. Normothermia, permitted by recent advances in machine perfusion technology, appears to be the leading edge of preservation technology. Several oxygen transporters are compatible with normothermia; however, only M101 also demonstrates compatibility with standard hypothermic preservation.

Barriers and Advances in Kidney Preservation

Despite the fact that a significant fraction of kidney graft dysfunctions observed after transplantation is due to ischemia-reperfusion injuries, there is still no clear consensus regarding optimal kidney preservation strategy. This stems directly from the fact that as of yet, the mechanisms underlying ischemia-reperfusion injury are poorly defined, and the role of each preservation parameter is not clearly outlined. In the meantime, as donor demography changes, organ quality is decreasing which directly increases the rate of poor outcome. This situation has an impact on clinical guidelines and impedes their possible harmonization in the transplant community, which has to move towards changing organ preservation paradigms: new concepts must emerge and the definition of a new range of adapted preservation method is of paramount importance. This review presents existing barriers in transplantation (e.g., temperature adjustment and adequate protocol, interest for oxygen addition during preservation, and clear procedure for organ perfusion during machine preservation), discusses the development of novel strategies to overcome them, and exposes the importance of identifying reliable biomarkers to monitor graft quality and predict short and long-term outcomes. Finally, perspectives in therapeutic strategies will also be presented, such as those based on stem cells and their derivatives and innovative models on which they would need to be properly tested.