Cold Storage Increases Albumin and Advanced Glycation-End Product-Albumin Levels in Kidney Transplants: A Possible Cause for Exacerbated Renal Damage

Cold Storage Followed by Transplantation Induces Immunoproteasome in Rat Kidney Allografts: Inhibition of Immunoproteasome Does Not Improve Function

Key Points

Cold storage (CS) increases the severity of graft dysfunction in a time-dependent manner, and prolonged CS decreases animal survival. CS plus transplant increases iproeasome levels/assembly in renal allografts; IFN-γ is a potential inducer of the iproteasome. Inhibiting iproteasome ex vivo during renal CS did not confer graft protection after transplantation.

Background

It is a major clinical challenge to ensure the long-term function of transplanted kidneys. Specifically, the injury associated with cold storage (CS) of kidneys compromises the long-term function of the grafts after transplantation. Therefore, the molecular mechanisms underlying CS-related kidney injury are attractive therapeutic targets to prevent injury and improve long-term graft function. Previously, we found that constitutive proteasome function was compromised in rat kidneys after CS followed by transplantation. Here, we evaluated the role of the immunoproteasome (i proteasome), a proteasome variant, during CS followed by transplantation.

Methods

Established in vivo rat kidney transplant model with or without CS containing vehicle or iproteasome inhibitor (ONX 0914) was used in this study. The i proteasome function was performed using rat kidney homogenates and fluorescent-based peptide substrate specific to β 5i subunit. Western blotting and quantitative RT-PCR were used to assess the subunit expression/level of the i proteasome (β 5i) subunit.

Results

We demonstrated a decrease in the abundance of the β 5i subunit of the i proteasome in kidneys during CS, but β 5i levels increased in kidneys after CS and transplant. Despite the increase in β 5i levels and its peptidase activity within kidneys, inhibiting β 5i during CS did not improve graft function after transplantation.

Summary

These results suggest that the pharmacologic inhibition of immunoproteasome function during CS does not improve graft function or outcome. In light of these findings, future studies targeting immunoproteasomes during both CS and transplantation may define the role of immunoproteasomes on short-term and long-term kidney transplant outcomes.

Normal Proteasome Function Is Needed to Prevent Kidney Graft Injury during Cold Storage Followed by Transplantation

Kidney transplantation is the preferred treatment for end-stage kidney disease (ESKD). However, there is a shortage of transplantable kidneys, and donor organs can be damaged by necessary cold storage (CS). Although CS improves the viability of kidneys from deceased donors, prolonged CS negatively affects transplantation outcomes. Previously, we reported that renal proteasome function decreased after rat kidneys underwent CS followed by transplantation (CS + Tx). Here, we investigated the mechanism underlying proteasome dysfunction and the role of the proteasome in kidney graft outcome using a rat model of CS + Tx. We found that the key proteasome subunits β5, α3, and Rpt6 are modified, and proteasome assembly is impaired. Specifically, we detected the modification and aggregation of Rpt6 after CS + Tx, and Rpt6 modification was reversed when renal extracts were treated with protein phosphatases. CS + Tx kidneys also displayed increased levels of nitrotyrosine, an indicator of peroxynitrite (a reactive oxygen species, ROS), compared to sham. Because the Rpt6 subunit appeared to aggregate, we investigated the effect of CS + Tx-mediated ROS (peroxynitrite) generation on renal proteasome assembly and function. We treated NRK cells with exogenous peroxynitrite and evaluated PAC1 (proteasome assembly chaperone), Rpt6, and β5. Peroxynitrite induced a dose-dependent decrease in PAC1 and β5, but Rpt6 was not affected (protein level or modification). Finally, serum creatinine increased when we inhibited the proteasome in transplanted donor rat kidneys (without CS), recapitulating the effects of CS + Tx. These findings underscore the effects of CS + Tx on renal proteasome subunit dysregulation and also highlight the significance of proteasome activity in maintaining graft function following CS + Tx.

Cold Storage Followed by Transplantation Induces Interferon-Gamma and STAT-1 in Kidney Grafts

Cold storage (CS)-mediated inflammation, a reality of donor kidney processing and transplantation, can contribute to organ graft failure. However, the mechanisms by which this inflammation is perpetuated during and after CS remain unclear. Here, we examined the immunoregulatory roles of signal transducer and activator of transcription (STAT) family proteins, most notably STAT1 and STAT3, with our in vivo model of renal CS and transplant. Donor rat kidneys were exposed to 4 h or 18 h of CS, which was then followed by transplantation (CS + transplant). STAT total protein level and activity (phosphorylation) were evaluated via Western blot analysis and mRNA expression was tabulated using quantitative RT-PCR after organ harvest on day 1 or day 9 post-surgery. In vivo assays were further corroborated via similar analyses featuring in vitro models, specifically proximal tubular cells (human and rat) as well as macrophage cells (Raw 264.7). Strikingly, gene expression of IFN-γ (a pro-inflammatory cytokine inducer of STAT) and STAT1 were markedly increased after CS + transplant. STAT3 dephosphorylation was additionally observed after CS, a result suggestive of dysregulation of anti-inflammatory signaling as phosphorylated STAT3 acts as a transcription factor in the nucleus to increase the expression of anti-inflammatory signaling molecules. In vitro, IFN-γ gene expression as well as amplification of downstream STAT1 and inducible nitric oxide synthase (iNOS; a hallmark of ischemia reperfusion injury) was remarkably increased after CS + rewarming. Collectively, these results demonstrate that aberrant induction of STAT1 is sustained in vivo post-CS exposure and post-transplant. Thus, Jak/STAT signaling may be a viable therapeutic target during CS to mitigate poor graft outcomes when transplanting kidneys from deceased donors.

Effect of Copper on the Function of Isolated Porcine Kidneys Stored Using Simple Hypothermia

Renal ischemia in the peri-transplant period causes a number of changes that adversely affect the initiation of normal vital functions in grafts after transplantation. To minimise the extent of ischemic damage, organs are stored in preservation fluid. The components of the fluid are supposed to ensure stabilisation of the cell cytoskeleton, protect against oxygen free radicals, reduce cell swelling, and ensure endothelial cell integrity. The aim of this study was to analyse the protective effect of Cu2+, as a component of Biolasol preservative fluid, in the prevention of nephron damage occurring during the graft storage period. Analyses of the effectiveness of copper in the presence of prolactin added to Biolasol fluid were also carried out. Forty isolated pig slaughter kidneys were used in the study, avoiding the use of laboratory animals. The kidneys were stored using simple hypothermia. After 2 h and 48 h of graft storage, selected biochemical indicators of renal function were determined in the collected perfusates. The addition of Cu2+ at a dose of 1 µg/L to the composition of Biolasol fluid was found to affect the generation of ischemic damage in the isolated pig kidney. The intensity of the occurrence of these processes is exacerbated by the presence of prolactin at a dose of 0.1 µg/L.

Aberrant activation of the complement system in renal grafts is mediated by cold storage

Aberrant complement activation leads to tissue damage during kidney transplantation, and it is recognized as an important target for therapeutic intervention. However, it is not clear whether cold storage (CS) triggers the complement pathway in transplanted kidneys. The goal of the present study was to determine the impact of CS on complement activation in renal transplants. Male Lewis and Fischer rats were used, and donor rat kidneys were exposed to 4 h or 18 h of CS followed by transplantation (CS + transplant). To study CS-induced effects, a group with no CS was included in which the kidney was removed and transplanted back to the same rat [autotransplantation (ATx)]. Complement proteins (C3 and C5b-9) were evaluated with Western blot analysis (reducing and nonreducing conditions) and immunostaining. Western blot analysis of renal extracts or serum indicated that the levels of C3 and C5b-9 increased after CS + transplant compared with ATx. Quite strikingly, intracellular C3 was profoundly elevated within renal tubules after CS + transplant but was absent in sham or ATx groups, which showed only extratubular C3. Similarly, C5b-9 immunofluorescence staining of renal sections showed an increase in C5b-9 deposits in kidneys after CS + transplant. Real-time PCR (SYBR green) showed increased expression of CD11b and CD11c, components of complement receptors 3 and 4, respectively, as well as inflammatory markers such as TNF-α. In addition, recombinant TNF-α significantly increased C3 levels in renal cells. Collectively, these results demonstrate that CS mediates aberrant activation of the complement system in renal grafts following transplantation.NEW & NOTEWORTHY This study highlights cold storage-mediated aberrant activation of complement components in renal allografts following transplantation. Specifically, the results demonstrate, for the first time, that cold storage functions in exacerbation of C5b-9, a terminal cytolytic membrane attack complex, in renal grafts following transplantation. In addition, the results indicated that cold storage induces local C3 biogenesis in renal proximal cells/tubules and that TNF-α promotes C3 biogenesis and activation in renal proximal tubular cells.