Ezrin functionality and hypothermic preservation injury in LLC-PK1 cells

Cold Saline Perfusion before Ischemia-Reperfusion Is Harmful to the Kidney and Is Associated with the Loss of Ezrin, a Cytoskeletal Protein, in Rats

Background: Organ protection for transplantation is perfusion with ice-cold preservation solutions, although saline is also used in animal experiments and living donor transplantations. However, ice-cold perfusion can contribute to initial graft injury. Our aim was to test if cytoskeletal damage of parenchymal cells is caused by saline itself or by the ice-cold solution. Methods: F344 rat kidneys were flushed with cold (4 °C) saline, ischemic and sham kidneys were not perfused. In a separate set, F344 kidneys were flushed with saline or preservation solution at 4 or 15 °C. Ischemia time was 30 min. Results: Renal injury was significantly more severe following cold ischemia (CI) than after ischemia-reperfusion without flushing (ischemia/reperfusion (I/R)). Functional and morphologic damage was accompanied by severe loss of ezrin from glomerular and tubular epithelial cells after CI. Moreover, saline caused serious injury independently from its temperature, while the perfusion solution was more beneficial, especially at 4 °C. Conclusions: Flushing the kidney with ice-cold saline can cause more severe injury than ischemia-reperfusion at body temperature even during a short (30 min) ischemia. Saline perfusion can prolong recovery from ischemia in kidney transplantation, which can be prevented by using preservation solutions.

High glucose induces phosphorylation and oxidation of mitochondrial proteins in renal tubular cells: A proteomics approach

Mitochondrial dysfunction has been thought to play roles in the pathogenesis of diabetic nephropathy (DN). However, precise mechanisms underlying mitochondrial dysfunction in DN remained unclear. Herein, mitochondria were isolated from renal tubular cells after exposure to normal glucose (5.5 mM glucose), high glucose (25 mM glucose), or osmotic control (5.5 mM glucose + 19.5 mM mannitol) for 96 h. Comparative proteomic analysis revealed six differentially expressed proteins among groups that were subsequently identified by tandem mass spectrometry (nanoLC-ESI-ETD MS/MS) and confirmed by Western blotting. Several various types of post-translational modifications (PTMs) were identified in all of these identified proteins. Interestingly, phosphorylation and oxidation were most abundant in mitochondrial proteins whose levels were exclusively increased in high glucose condition. The high glucose-induced increases in phosphorylation and oxidation of mitochondrial proteins were successfully confirmed by various assays including MS/MS analyses. Moreover, high glucose also increased levels of phosphorylated ezrin, intracellular ATP and ROS, all of which could be abolished by a p38 MAPK inhibitor (SB239063), implicating a role of p38 MAPK-mediated phosphorylation in high glucose-induced mitochondrial dysfunction. These data indicate that phosphorylation and oxidation of mitochondrial proteins are, at least in part, involved in mitochondrial dysfunction in renal tubular cells during DN.

Donor gluconate rescues livers from uncontrolled donation after cardiac death

BACKGROUND

Ischemia from organ preservation or donation causes cells and tissues to swell owing to loss of energy-dependent mechanisms of control of cell volume. These volume changes cause substantial preservation injury, because preventing these changes by adding cell impermeants to preservation solutions decreases preservation injury. The objective of this study was to assess if this effect could be realized early in uncontrolled donation after cardiac death (DCD) livers by systemically loading donors with gluconate immediately after death to prevent accelerated swelling injury during the warm ischemia period before liver retrieval.

METHODS

Uncontrolled DCD rat livers were cold-stored in University of Wisconsin solution for 24 hours and reperfused on an isolated perfused liver (IPL) device for 2 hours or transplanted into a rat as an allograft for 7 days. Donors were pretreated with a solution of the impermeant gluconate or a saline control immediately after cardiac death. Livers were retrieved after 30 minutes.

RESULTS

In vivo, gluconate infusion in donors immediately before or after cardiac death prevented DCD-induced increases in total tissue water, decreased vascular resistance, increased oxygen consumption and synthesis of adenosine triphosphate, increased bile production, decreased lactate dehydrogenase release, and decreased histology injury scores after reperfusion on the IPL relative to saline-treated DCD controls. In the transplant model, donor gluconate pretreatment significantly decreased both alanine aminotransferase the first day after transplantation and total bilirubin the seventh day after transplantation.

CONCLUSION

Cell and tissue swelling plays a key role in preservation injury of uncontrolled DCD livers, which can be mitigated by early administration of gluconate solutions to the donor immediately after death.

Hypothermic Machine Perfusion Decreases Renal Cell Apoptosis During Ischemia/Reperfusion Injury via the Ezrin/AKT Pathway

This study aimed to explore the potential mechanisms of hypothermic machine perfusion (HMP)-a more efficient way to preserve kidneys from donors after cardiac death than static cold storage (CS), then to provide the basis for further improving donor quality. Twelve healthy male New Zealand rabbits (12 weeks old, weighing 3.0 ± 0.3 kg) were randomly divided into two groups: the HMP group and CS group (n = 6). Rabbits' left kidney was subjected to 35 min of warm ischemic time by clamping the left renal pedicle and 1 h of reperfusion. The kidneys were then hypothermically (4-8°C) preserved in vivo for 4 h with HCA-II solution using HMP or CS methods. Then rabbits underwent a right nephrectomy and the kidney tissues were collected after 24 h of reperfusion. TUNEL staining was performed on paraffin sections to detect apoptosis, and the expressions of cleaved caspase-3, ezrin, AKT, and p-AKT in frozen kidney tissues were detected by Western blotting. The ezrin expression was further confirmed by immunohistochemistry analysis. The apoptosis rate and expression of cleaved caspase-3 in the HMP group were significantly lower than the CS group (P < 0.001 and P = 0.002), meanwhile the expression of cleaved caspase-3 in the HMP and CS groups was significantly increased compared with the normal group (P = 0.035 and P < 0.001), and the expression of ezrin and p-AKT in the HMP group was significantly higher than the CS group (P = 0.005, 0.014). HMP decreased the renal cell apoptosis rate during ischemia/reperfusion injury via the ezrin/AKT pathway.

Phosphorylation dynamics of radixin in hypoxia-induced hepatocyte injury

The most prominent ezrin-radixin-moesin protein in hepatocytes is radixin, which is localized primarily at the canalicular microvilli and appears to be important in regulation of cell polarity and in localizing the multidrug resistance-associated protein 2 (Mrp-2) function. Our aim was to investigate how hypoxia affects radixin distribution and Mrp-2 function. We created wild-type and mutant constructs (in adenoviral vectors), which were expressed in WIF-B cells. The cellular distribution of Mrp-2 and radixin was visualized by fluorescence microscopy, and a 5-chloromethylfluorescein diacetate (CMFDA) assay was used to measure Mrp-2 function. Under usual conditions, cells infected with wild-type radixin, nonphosphorylatable radixin-T564A, and radixin-T564D (active phospho-mimicking mutant) were found to be heavily expressed in canalicular membrane compartment vacuoles, typically colocalizing with Mrp-2. In contrast, after hypoxia for 24 h, both endogenous and overexpressed wild-type radixin and the radixin-T564A mutant were found to be translocated to the cytoplasmic space. However, distribution of the radixin-T564D mutant, which mimics constant phosphorylation, was remarkably different, being associated with canalicular membranes even in hypoxic conditions. This dominant-active construct also prevented dissociation of radixin from the plasma membrane. Hypoxia also led to Mrp-2 mislocalization and caused Mrp-2 to be dissociated from radixin; the radixin phospho-mimicking mutant (T564D) abrogated this effect of hypoxia. Finally, hypoxia diminished the secretory response (measured using the CMFDA assay) in WIF-B cells, and the dominant-active construct (radixin-T567D) rescued this phenotype. Taken collectively, these findings suggest that radixin regulates Mrp-2 localization and function in hepatocytes and is important in hypoxic liver injury.

Moesin functionality in hypothermic liver preservation injury

The objective of this study was to determine how expression and functionality of the cytoskeletal linker protein moesin is involved in hepatic hypothermic preservation injury. Mouse livers were cold stored in University of Wisconsin (UW) solution and reperfused on an isolated perfused liver (IPL) device for one hour. Human hepatocytes (HepG2) and human or murine sinusoidal endothelial cells (SECs) were cold stored and rewarmed to induce hypothermic preservation injury. The cells were transfected with: wild type moesin, an siRNA duplex specific for moesin, and the moesin mutants T558D and T558A. Tissue and cell moesin expression and its binding to actin were determined by Western blot. Liver IPL functional outcomes deteriorated proportional to the length of cold storage, which correlated with moesin disassociation from the actin cytoskeleton. Cell viability (LDH and WST-8) in the cell models progressively declined with increasing preservation time, which also correlated with moesin disassociation. Transfection of a moesin containing plasmid or an siRNA duplex specific for moesin into HepG2 cells resulted in increased and decreased moesin expression, respectively. Overexpression of moesin protected while moesin knock-down potentiated preservation injury in the HepG2 cell model. Hepatocytes expressing the T558A (inactive) and T558D (active) moesin binding mutants demonstrated significantly more and less preservation injury, respectively. Cold storage time dependently caused hepatocyte detachment from the matrix and cell death, which was prevented by the T558D active moesin mutation. In conclusion, moesin is causally involved in hypothermic liver cell preservation injury through control of its active binding molecular functionality.