Congenital DNA repair deficiency results in protection against renal ischemia reperfusion injury in mice

Removal of the catalytic subunit of DNA-protein kinase in the proximal tubules promotes DNA and tubular damage during kidney injury

Tubular epithelial cell damage can be repaired through a series of complex signaling pathways. An early event in many forms of tubular damage is the observation of DNA damage, which can be repaired by specific pathways depending upon the type of genomic alteration.. In this study, we report that the catalytic subunit of DNA protein kinase (DNA-PKcs), a central DNA repair enzyme involved in sensing DNA damage and performing double stranded DNA break repair, plays an important role in the extent of tubular epithelial cell damage following exposure to injurious acute and chronic stimuli. Selective loss of DNA-PKcs in the proximal tubules led to increased markers of kidney dysfunction, DNA damage, and tubular epithelial cell injury in multiple models of acute kidney injury, specifically bilateral renal ischemia-reperfusion injury and single dose of cisplatin (15 mg/kg IP). In contrast, in a mouse model of kidney fibrosis and chronic kidney disease (UUO),the protective effects of DNA-PKcs was not as obvious histologically from the tissue sections. In the absence of proximal tubular DNA-PKcs, there was reduced levels of fibrotic markers, α-SMA and fibronectin, which suggests that there may be a biphasic role of DNA-PKcs depending upon the conditions exerted upon the kidney. In conclusion, this study demonstrates that the catalytic subunit of DNA-PKcs plays a context-dependent role in the kidney to reduce DNA damage during exposure to various types of acute, but not chronic forms of injurious stimuli.

DNA damage is overcome by TRIP13 overexpression during cisplatin nephrotoxicity

Cisplatin is a commonly used chemotherapeutic agent to treat a wide array of cancers that is frequently associated with toxic injury to the kidney due to oxidative DNA damage and perturbations in cell cycle progression leading to cell death. In this study, we investigated whether thyroid receptor interacting protein 13 (TRIP13) plays a central role in the protection of the tubular epithelia following cisplatin treatment by circumventing DNA damage. Following cisplatin treatment, double-stranded DNA repair pathways were inhibited using selective blockers to proteins involved in either homologous recombination or non-homologous end joining. This led to increased blood markers of acute kidney injury (AKI) (creatinine and neutrophil gelatinase–associated lipocalin), tubular damage, activation of DNA damage marker (γ-H2AX), elevated appearance of G2/M blockade (phosphorylated histone H3 Ser10 and cyclin B1), and apoptosis (cleaved caspase-3). Conditional proximal tubule–expressing Trip13 mice were observed to be virtually protected from the cisplatin nephrotoxicity by restoring most of the pathological phenotypes back toward normal conditions. Our findings suggest that TRIP13 could circumvent DNA damage in the proximal tubules during cisplatin injury and that TRIP13 may constitute a new therapeutic target in protecting the kidney from nephrotoxicants and reduce outcomes leading to AKI.

Pre-Operative Fasting Provides Long Term Protection Against Chronic Renal Damage Induced by Ischaemia Reperfusion Injury in Wild Type and Aneurysm Prone Fibulin-4 Mice

OBJECTIVE

Renal ischaemia reperfusion injury (IRI) is inevitable during open repair of pararenal aortic aneurysms. Pre-operative fasting potently increases resistance against IRI. The effect of fasting on IRI was examined in a hypomorphic Fibulin-4 mouse model (Fibulin-4^+/R), which is predisposed to develop aortic aneurysms.

METHODS

Wild type (WT) and Fibulin-4^+/R mice were either fed ad libitum (AL) or fasted for two days before renal IRI induction by temporary clamping of the renal artery and vein of both kidneys. Six hours, 48 h, and seven days post-operatively, serum urea levels, renal histology, and mRNA expression levels of inflammatory and injury genes were determined to assess kidney function and damage. Additionally, matrix metalloproteinase activity in the kidney was assessed six months after IRI.

RESULTS

Two days of fasting improved survival the first week after renal IRI in WT mice compared with AL fed mice. Short term AL fed Fibulin-4^+/R mice showed improved survival and kidney function compared with AL fed WT mice, which could not be further enhanced by fasting. Both fasted WT and Fibulin-4^+/R mice showed improved survival, kidney function and morphology compared with AL fed mice six months after renal IRI. Fibulin-4^+/R kidneys of fasted mice showed reduced apoptosis together with increased matrix metalloprotease activity levels compared with AL fed Fibulin-4^+/R mice, indicative of increased matrix remodelling.

CONCLUSION

Fibulin-4^+/R mice are naturally protected against the short-term, but not long-term, consequences of renal IRI. Pre-operative fasting protects against renal IRI and prevents (long-term) deterioration of kidney function and morphology in both WT and Fibulin-4^+/R mice. These data suggest that pre-operative fasting may decrease renal damage in patients undergoing open abdominal aneurysm repair.

Development of new method to enrich human iPSC-derived renal progenitors using cell surface markers

Cell therapy using renal progenitors differentiated from human embryonic stem cells (hESCs) or induced pluripotent stem cells (hiPSCs) has the potential to significantly reduce the number of patients receiving dialysis therapy. However, the differentiation cultures may contain undifferentiated or undesired cell types that cause unwanted side effects, such as neoplastic formation, when transplanted into a body. Moreover, the hESCs/iPSCs are often genetically modified in order to isolate the derived renal progenitors, hampering clinical applications. To establish an isolation method for renal progenitors induced from hESCs/iPSCs without genetic modifications, we screened antibodies against cell surface markers. We identified the combination of four markers, CD9⁻CD140a⁺CD140b⁺CD271⁺, which could enrich OSR1⁺SIX2⁺ renal progenitors. Furthermore, these isolated cells ameliorated renal injury in an acute kidney injury (AKI) mouse model when used for cell therapy. These cells could contribute to the development of hiPSC-based cell therapy and disease modeling against kidney diseases.

TRIP13-deficient tubular epithelial cells are susceptible to apoptosis following acute kidney injury

Damage to renal tubular epithelial cells by genetic, environmental, or biological insults can initiate complex signaling mechanisms that promote kidney repair and functional recovery. In this study, we demonstrated that thyroid receptor interacting protein 13 (TRIP13) is a critical modulator of tubular epithelial cell repair following ischemia‐reperfusion injury (IRI), a common type of renal stressor. In Trip13^Gt/Gthypomorph mice treated with unilateral renal IRI, persistent tubular epithelial cell damage was determined in the IRI-treated kidney throughout the 168 hours of experimental period compared to the contralateral kidneys. The damaged epithelial cells were associated with increased levels of DNA damage (ɣH2AX) and apoptotic markers (p53, cleaved caspase-7, and TUNEL-positive cells). Correspondingly, TRIP13 was found to directly interact with Tetratricopeptide Repeat Domain 5 (TTC5), a p53 co‐factor, and genetic knockdown of TRIP13 in murine inner medullary collecting duct cells in the presence of hydrogen peroxide showed increased activity of p53 at Serine 15. In all, these studies suggest that insufficient TRIP13 increased the susceptibility of damaged tubular epithelial cells to progress towards apoptotic cell death.

DNA repair in ischemic acute kidney injury

Ischemia-reperfusion injury (IRI) is a common cause of acute kidney injury leading to an induction of oxidative stress, cellular dysfunction, and loss of renal function. DNA damage, including oxidative base modifications and physical DNA strand breaks, is a consequence of renal IRI. Like many other organs in the body, a redundant and highly conserved set of endogenous repair pathways have evolved to selectively recognize the various types of cellular DNA damage and combat its negative effects on cell viability. Severe damage to the DNA, however, can trigger cell death and elimination of the injured tubular epithelial cells. In this minireview, we summarize the state of the current field of DNA damage and repair in the kidney and provide some expected and, in some cases, unexpected effects of IRI on DNA damage and repair in the kidney. These findings may be applicable to other forms of acute kidney injury and could provide new opportunities for renal research.

DNA damage response in nephrotoxic and ischemic kidney injury

DNA damage activates specific cell signaling cascades for DNA repair, cell cycle arrest, senescence, and/or cell death. Recent studies have demonstrated DNA damage response (DDR) in experimental models of acute kidney injury (AKI). In cisplatin-induced AKI or nephrotoxicity, the DDR pathway of ATR/Chk2/p53 is activated and contributes to renal tubular cell apoptosis. In ischemic AKI, DDR seems more complex and involves at least the ataxia telangiectasia mutated (ATM), a member of the phosphatidylinositol 3-kinase-related kinase (PIKK) family, and p53; however, while ATM may promote DNA repair, p53 may trigger cell death. Targeting DDR for kidney protection in AKI therefore relies on a thorough elucidation of the DDR pathways in various forms of AKI.

Increased oxidative phosphorylation in response to acute and chronic DNA damage

Accumulation of DNA damage is intricately linked to aging, aging-related diseases and progeroid syndromes such as Cockayne syndrome (CS). Free radicals from endogenous oxidative energy metabolism can damage DNA, however the potential of acute or chronic DNA damage to modulate cellular and/or organismal energy metabolism remains largely unexplored. We modeled chronic endogenous genotoxic stress using a DNA repair-deficient Csa^-/-|Xpa^-/- mouse model of CS. Exogenous genotoxic stress was modeled in mice in vivo and primary cells in vitro treated with different genotoxins giving rise to diverse spectrums of lesions, including ultraviolet radiation, intrastrand crosslinking agents and ionizing radiation. Both chronic endogenous and acute exogenous genotoxic stress increased mitochondrial fatty acid oxidation (FAO) on the organismal level, manifested by increased oxygen consumption, reduced respiratory exchange ratio, progressive adipose loss and increased FAO in tissues ex vivo. In multiple primary cell types, the metabolic response to different genotoxins manifested as a cell-autonomous increase in oxidative phosphorylation (OXPHOS) subsequent to a transient decline in steady-state NAD+ and ATP levels, and required the DNA damage sensor PARP-1 and energy-sensing kinase AMPK. We conclude that increased FAO/OXPHOS is a general, beneficial, adaptive response to DNA damage on cellular and organismal levels, illustrating a fundamental link between genotoxic stress and energy metabolism driven by the energetic cost of DNA damage. Our study points to therapeutic opportunities to mitigate detrimental effects of DNA damage on primary cells in the context of radio/chemotherapy or progeroid syndromes.

Cell Therapy Using Human Induced Pluripotent Stem Cell-Derived Renal Progenitors Ameliorates Acute Kidney Injury in Mice

Acute kidney injury (AKI) is defined as a rapid loss of renal function resulting from various etiologies, with a mortality rate exceeding 60% among intensive care patients. Because conventional treatments have failed to alleviate this condition, the development of regenerative therapies using human induced pluripotent stem cells (hiPSCs) presents a promising new therapeutic option for AKI. We describe our methodology for generating renal progenitors from hiPSCs that show potential in ameliorating AKI. We established a multistep differentiation protocol for inducing hiPSCs into OSR1+SIX2+ renal progenitors capable of reconstituting three-dimensional proximal renal tubule-like structures in vitro and in vivo. Moreover, we found that renal subcapsular transplantation of hiPSC-derived renal progenitors ameliorated the AKI in mice induced by ischemia/reperfusion injury, significantly suppressing the elevation of blood urea nitrogen and serum creatinine levels and attenuating histopathological changes, such as tubular necrosis, tubule dilatation with casts, and interstitial fibrosis. To our knowledge, few reports demonstrating the therapeutic efficacy of cell therapy with renal lineage cells generated from hiPSCs have been published. Our results suggest that regenerative medicine strategies for kidney diseases could be developed using hiPSC-derived renal cells.

SIGNIFICANCE

This report is the first to demonstrate that the transplantation of renal progenitor cells differentiated from human induced pluripotent stem (iPS) cells has therapeutic effectiveness in mouse models of acute kidney injury induced by ischemia/reperfusion injury. In addition, this report clearly demonstrates that the therapeutic benefits come from trophic effects by the renal progenitor cells, and it identifies the renoprotective factors secreted by the progenitors. The results of this study indicate the feasibility of developing regenerative medicine strategy using iPS cells against renal diseases.

Tissue specific response to DNA damage: C. elegans as role model

The various symptoms associated with hereditary defects in the DNA damage response (DDR), which range from developmental and neurological abnormalities and immunodeficiency to tissue-specific cancers and accelerated aging, suggest that DNA damage affects tissues differently. Mechanistic DDR studies are, however, mostly performed in vitro, in unicellular model systems or cultured cells, precluding a clear and comprehensive view of the DNA damage response of multicellular organisms. Studies performed in intact, multicellular animals models suggest that DDR can vary according to the type, proliferation and differentiation status of a cell. The nematode Caenorhabditis elegans has become an important DDR model and appears to be especially well suited to understand in vivo tissue-specific responses to DNA damage as well as the impact of DNA damage on development, reproduction and health of an entire multicellular organism. C. elegans germ cells are highly sensitive to DNA damage induction and respond via classical, evolutionary conserved DDR pathways aimed at efficient and error-free maintenance of the entire genome. Somatic tissues, however, respond differently to DNA damage and prioritize DDR mechanisms that promote growth and function. In this mini-review, we describe tissue-specific differences in DDR mechanisms that have been uncovered utilizing C. elegans as role model.

Aag-initiated base excision repair promotes ischemia reperfusion injury in liver, brain, and kidney

Inflammation is accompanied by the release of highly reactive oxygen and nitrogen species (RONS) that damage DNA, among other cellular molecules. Base excision repair (BER) is initiated by DNA glycosylases and is crucial in repairing RONS-induced DNA damage; the alkyladenine DNA glycosylase (Aag/Mpg) excises several DNA base lesions induced by the inflammation-associated RONS release that accompanies ischemia reperfusion (I/R). Using mouse I/R models we demonstrate that Aag(-/-) mice are significantly protected against, rather than sensitized to, I/R injury, and that such protection is observed across three different organs. Following I/R in liver, kidney, and brain, Aag(-/-) mice display decreased hepatocyte death, cerebral infarction, and renal injury relative to wild-type. We infer that in wild-type mice, Aag excises damaged DNA bases to generate potentially toxic abasic sites that in turn generate highly toxic DNA strand breaks that trigger poly(ADP-ribose) polymerase (Parp) hyperactivation, cellular bioenergetics failure, and necrosis; indeed, steady-state levels of abasic sites and nuclear PAR polymers were significantly more elevated in wild-type vs. Aag(-/-) liver after I/R. This increase in PAR polymers was accompanied by depletion of intracellular NAD and ATP levels plus the translocation and extracellular release of the high-mobility group box 1 (Hmgb1) nuclear protein, activating the sterile inflammatory response. We thus demonstrate the detrimental effects of Aag-initiated BER during I/R and sterile inflammation, and present a novel target for controlling I/R-induced injury.

Rotterdam: main port for organ transplantation research in the Netherlands

This overview describes the full spectrum of current pre-clinical and clinical kidney-, liver-, heart- and lung transplantation research performed in Erasmus MC - University Medical Centre in Rotterdam, The Netherlands. An update is provided on the development of a large living donor kidney transplantation program and on optimization of kidney allocation, including the implementation of a domino kidney-donation program. Our current research efforts to optimize immunosuppressive regimens and find novel targets for immunosuppressive therapy, our recent studies on prevention of ischemia-reperfusion-induced graft injury, our newest findings on stimulation of tissue regeneration, our novel approaches to prevent rejection and viral infection, and our latest insights in the regulation of allograft rejection, are summarized.

A comparison of inflammatory, cytoprotective and injury gene expression profiles in kidneys from brain death and cardiac death donors

BACKGROUND

The superior long-term survival of kidneys from living donors (LDs) compared with kidneys from donation-after-brain-death (DBD) and donation-after-cardiac-death (DCD) donors is now well established. However, comparative studies on transcriptional changes that occur at organ retrieval and during and after cold ischemia (CI) are sparse.

METHODS

Using a rat model, we used qRT-PCR to examine expression levels of inflammatory, cytoprotective, and injury genes at different time points after organ retrieval. Cleaved caspase-3 was used to evaluate early apoptosis in DCD and DBD kidneys.

RESULTS

Immediately after retrieval, we found massive up-regulation of proinflammatory genes interleukin-1β, interleukin-6, tumor necrosis factor-α, monocyte chemotactic protein-1, P-selectin, and E-selectin in DBD compared with LD and DCD kidneys. A significant increase in the expression of injury markers Kim-1, p21, and the cytoprotective gene heme oxygenase-1 accompanied this. Bax was increased in DCD kidneys, and Bcl-2 was decreased in DBD kidneys. After 2 hr of CI in the LD group and 18 hr in the DBD and DCD groups, gene expression levels were similar to those found after retrieval. During 18 hr of cold storage, expression levels of these genes did not change. In DCD and DBD kidneys, early apoptosis increased after CI.

DISCUSSION/CONCLUSION

The gene expression profile in DBD kidneys represents an inflammatory and injury response to brain death. In contrast, DCD kidneys show only mild up-regulation of inflammatory and injury genes. These results may imply why delayed graft function in DCD kidneys does not have the deleterious effect it has on DBD kidneys.

Catheter-based induction of renal ischemia/reperfusion in swine: description of an experimental model

Several techniques to induce renal ischemia have been proposed: clamp, PVA particles, and catheter-balloon. We report the development of a controlled, single-insult model of unilateral renal ischemia/reperfusion (I/R) without contralateral nephrectomy, using a suitable model, the pig. This is a balloon-catheter-based model using a percutaneous, interventional radiology procedure. One angioplasty balloon-catheter was placed into the right renal artery and inflated for 120 min and reperfusion over 24 h. Serial serums were sampled from the inferior vena cava and urine was directly sampled from the bladder throughout the experiment, and both kidneys were excised after 24 h of reperfusion. Analyses of renal structure and function were performed by hematoxylin-eosin/periodic Acid-Schiff, serum creatinine (SCr), blood urea nitrogen (BUN), fractional excretion of ions, and glucose, SDS-PAGE analysis of urinary proteins, and serum neutrophil gelatinase-associated lipocalin (NGAL). Total nitrated protein was quantified to characterize oxidative stress. Acute tubular necrosis (ATN) was identified in every animal, but only two animals showed levels of SCr above 150% of baseline values. As expected, I/R increased SCr and BUN. Fractional sodium, potassium, chloride, and bicarbonate excretion were modulated during ischemia. Serum-nitrated proteins and NGAL had two profiles: decreased with ischemia and increased after reperfusion. This decline was associated with increased protein excretion during ischemia and early reperfusion. Altogether, these data show that the renal I/R model can be performed by percutaneous approach in the swine model. This is a suitable translational model to study new early renal ischemic biomarkers and pathophysiological mechanisms in renal ischemia.

DNA damage leads to progressive replicative decline but extends the life span of long-lived mutant animals

Human-nucleotide-excision repair (NER) deficiency leads to different developmental and segmental progeroid symptoms of which the pathogenesis is only partially understood. To understand the biological impact of accumulating spontaneous DNA damage, we studied the phenotypic consequences of DNA-repair deficiency in Caenorhabditis elegans. We find that DNA damage accumulation does not decrease the adult life span of post-mitotic tissue. Surprisingly, loss of functional ERCC-1/XPF even further extends the life span of long-lived daf-2 mutants, likely through an adaptive activation of stress signaling. Contrariwise, NER deficiency leads to a striking transgenerational decline in replicative capacity and viability of proliferating cells. DNA damage accumulation induces severe, stochastic impairment of development and growth, which is most pronounced in NER mutants that are also impaired in their response to ionizing radiation and inter-strand crosslinks. These results suggest that multiple DNA-repair pathways can protect against replicative decline and indicate that there might be a direct link between the severity of symptoms and the level of DNA-repair deficiency in patients.

The role of DNA damage and repair in aging through the prism of Koch-like criteria

Since the first publication on Somatic Mutation Theory of Aging (Szilárd, 1959), a great volume of knowledge in the field has been accumulated. Here we attempted to organize the evidence "for" and "against" the hypothesized causal role of DNA damage and mutation accumulation in aging in light of four Koch-like criteria. They are based on the assumption that some quantitative relationship between the levels of DNA damage/mutations and aging rate should exist, so that (i) the longer-lived individuals or species would have a lower rate of damage than the shorter-lived, and (ii) the interventions that modulate the level of DNA damage and repair capacity should also modulate the rate of aging and longevity and vice versa. The analysis of how the existing data meets the proposed criteria showed that many gaps should still be filled in order to reach a clear-cut conclusion. As a perspective, it seems that the main emphasis in future studies should be put on the role of DNA damage in stem cell aging.

Cockayne syndrome group B protein prevents the accumulation of damaged mitochondria by promoting mitochondrial autophagy

Cells from Cockayne syndrome patients and a mouse model of the disease show increased metabolism as a result of impaired autophagy-mediated removal of damaged mitochondria.

Cockayne syndrome (CS) is a devastating autosomal recessive disease characterized by neurodegeneration, cachexia, and accelerated aging. 80% of the cases are caused by mutations in the CS complementation group B (CSB) gene known to be involved in DNA repair and transcription. Recent evidence indicates that CSB is present in mitochondria, where it associates with mitochondrial DNA (mtDNA). We report an increase in metabolism in the CSB^m/m mouse model and CSB-deficient cells. Mitochondrial content is increased in CSB-deficient cells, whereas autophagy is down-regulated, presumably as a result of defects in the recruitment of P62 and mitochondrial ubiquitination. CSB-deficient cells show increased free radical production and an accumulation of damaged mitochondria. Accordingly, treatment with the autophagic stimulators lithium chloride or rapamycin reverses the bioenergetic phenotype of CSB-deficient cells. Our data imply that CSB acts as an mtDNA damage sensor, inducing mitochondrial autophagy in response to stress, and that pharmacological modulators of autophagy are potential treatment options for this accelerated aging phenotype.

Disorders of nucleotide excision repair: the genetic and molecular basis of heterogeneity

Mutations in genes on the nucleotide excision repair pathway are associated with diseases, such as xeroderma pigmentosum, Cockayne syndrome and trichothiodystrophy, that involve skin cancer and developmental and neurological symptoms. These mutations cause the defective repair of damaged DNA and increased transcription arrest but, except for skin cancer, the links between repair and disease have not been obvious. Widely different clinical syndromes seem to result from mutations in the same gene, even when the mutations result in complete loss of function. The mapping of mutations in recently solved protein structures has begun to clarify the links between the molecular defects and phenotypes, but the identification of additional sources of clinical variability is still necessary.