Impaired tissue regeneration corresponds with altered expression of developmental genes that persists in the metabolic memory state of diabetic zebrafish

Beyond drug discovery: Exploring the physiological and methodological dimensions of zebrafish in diabetes research

Diabetes mellitus is a chronic disease that is now considered a global epidemic. Chronic diabetes conditions include type 1 and type 2 diabetes, both of which are normally irreversible. As a result of long-term uncontrolled high levels of glucose, diabetes can progress to hyperglycaemic pathologies, such as cardiovascular diseases, retinopathy, nephropathy and neuropathy, among many other complications. The complete mechanism underlying diabetes remains unclear due to its complexity. In this scenario, zebrafish (Danio rerio) have arisen as a versatile and promising animal model due to their good reproducibility, simplicity, and time- and cost-effectiveness. The Zebrafish model allows us to make progress in the investigation and comprehension of the root cause of diabetes, which in turn would aid in the development of pharmacological and surgical approaches for its management. The current review provides valuable reference information on zebrafish models, from the first zebrafish diabetes models using genetic, disease induction and chemical approaches, to the newest ones that further allow for drug screening and testing. This review aims to update our knowledge related to diabetes mellitus by gathering the most authoritative studies on zebrafish as a chemical, dietary and insulin induction, and genetic model for diabetes research.

Research Progress on the Construction and Application of a Diabetic Zebrafish Model

Diabetes is a metabolic disease characterized by high blood glucose levels. With economic development and lifestyle changes, the prevalence of diabetes is increasing yearly. Thus, it has become an increasingly serious public health problem in countries around the world. The etiology of diabetes is complex, and its pathogenic mechanisms are not completely clear. The use of diabetic animal models is helpful in the study of the pathogenesis of diabetes and the development of drugs. The emerging vertebrate model of zebrafish has many advantages, such as its small size, large number of eggs, short growth cycle, simple cultivation of adult fish, and effective improvement of experimental efficiency. Thus, this model is highly suitable for research as an animal model of diabetes. This review not only summarizes the advantages of zebrafish as a diabetes model, but also summarizes the construction methods and challenges of zebrafish models of type 1 diabetes, type 2 diabetes, and diabetes complications. This study provides valuable reference information for further study of the pathological mechanisms of diabetes and the research and development of new related therapeutic drugs.

Advances in Zebrafish for Diabetes Mellitus with Wound Model

Diabetic foot ulcers cause great suffering and are costly for the healthcare system. Normal wound healing involves hemostasis, inflammation, proliferation, and remodeling. However, the negative factors associated with diabetes, such as bacterial biofilms, persistent inflammation, impaired angiogenesis, inhibited cell proliferation, and pathological scarring, greatly interfere with the smooth progress of the entire healing process. It is this impaired wound healing that leads to diabetic foot ulcers and even amputations. Therefore, drug screening is challenging due to the complexity of damaged healing mechanisms. The establishment of a scientific and reasonable animal experimental model contributes significantly to the in-depth research of diabetic wound pathology, prevention, diagnosis, and treatment. In addition to the low cost and transparency of the embryo (for imaging transgene applications), zebrafish have a discrete wound healing process for the separate study of each stage, resulting in their potential as the ideal model animal for diabetic wound healing in the future. In this review, we examine the reasons behind the delayed healing of diabetic wounds, systematically review various studies using zebrafish as a diabetic wound model by different induction methods, as well as summarize the challenges and improvement strategies which provide references for establishing a more reasonable diabetic wound zebrafish model.

Establishment of Zebrafish Models for Diabetes Mellitus and Its Microvascular Complications

Diabetes mellitus (DM) is a chronic metabolic disease known to cause several microvascular complications, including diabetic retinopathy, diabetic nephropathy, and diabetic neuropathy. Hyperglycemia plays a key role in inducing diabetic microvascular complications. A cohort of diabetic animal models has been established to study diabetes-related vascular diseases. However, the zebrafish model offers unique advantages in this field. The tiny size and huge offspring numbers of zebrafish make it amenable to perform large-scale analysis or screening. The easily accessible strategies for gene manipulation with morpholino or CRISPR/Cas9 and chemical/drug treatment through microinjection or skin absorption allow establishing the zebrafish DM models by a variety of means. In addition, the transparency of zebrafish embryos makes it accessible to perform in vivo high-resolution imaging of the vascular system. In this review, we focus on the strategies to establish diabetic or hyperglycemic models with zebrafish and the achievements and disadvantages of using zebrafish as a model to study diabetic microvascular complications.

Neonatal nephron loss during active nephrogenesis results in altered expression of renal developmental genes and markers of kidney injury

Preterm neonates are at a high risk for nephron loss under adverse clinical conditions. Renal damage potentially collides with postnatal nephrogenesis. Recent animal studies suggest that nephron loss within this vulnerable phase leads to renal damage later in life. Nephrogenic pathways are commonly reactivated after kidney injury supporting renal regeneration. We hypothesized that nephron loss during nephrogenesis affects renal development, which, in turn, impairs tissue repair after secondary injury. Neonates prior to 36 wk of gestation show an active nephrogenesis. In rats, nephrogenesis is ongoing until day 10 after birth. Mimicking the situation of severe nephron loss during nephrogenesis, male pups were uninephrectomized at day 1 of life (UNXd1). A second group of males was uninephrectomized at postnatal day 14 (UNXd14), after terminated nephrogenesis. Age-matched controls were sham operated. Three days after uninephrectomy transcriptional changes in the right kidney were analyzed by RNA-sequencing, followed by functional pathway analysis. In UNXd1, 1,182 genes were differentially regulated, but only 143 genes showed a regulation both in UNXd1 and UNXd14. The functional groups "renal development" and "kidney injury" were among the most differentially regulated groups and revealed distinctive alterations. Reduced expression of candidate genes concerning renal development (Bmp7, Gdnf, Pdgf-B, Wt1) and injury (nephrin, podocin, Tgf-β1) were detected. The downregulation of Bmp7 and Gdnf persisted until day 28. In UNXd14, Six2 was upregulated and Pax2 was downregulated. We conclude that nephron loss during nephrogenesis affects renal development and induces a specific regulation of genes that might hinder tissue repair after secondary kidney injury.

Propolis Can Improve Caudal Fin Regeneration in Zebrafish (Danio rerio) Induced by The Combined Administration of Alloxan and Glucose

Hyperglycemia, a primary symptom in diabetes mellitus, is associated with difficulties in wound healing and regeneration. This condition is due to the length of the inflammatory phase and free radicals. Furthermore, there is evidence that molecular pathogenesis is involved in impaired wound healing in diabetics. As an animal model, zebrafish have many shared orthologous genes with human that are involved in protein regulation of wound healing and regeneration. Little is known about natural drugs that may be used to treat complications of wound healing in diabetes. Propolis, however, is known to consist of various organic compounds such as phenols and flavonoids with antioxidant and anti-inflammatory activities. This research aims to study propolis' effect on caudal fin regeneration and relative expression of several genes belonging to Hedgehog, bone morphogenetic protein (BMP), and Wnt signaling hyperglycemic (HG) zebrafish. GC-MS analysis and antioxidant activity testing were performed on ethanolic extract of propolis (EEP). Caudal fin regeneration was analyzed using ImageJ; blood glucose levels were measured; and relative gene expression analysis of shha, igf2a, bmp2b, and col1a2 was performed by the real-time polymerase chain reaction method with the β-actin housekeeping gene. Impairment of caudal fin regeneration in zebrafish hyperglycemia was characterized by a low percentage of regeneration and decreased relative gene expression. EEP at 15 ppm could increase the percentage of caudal fin regeneration and the expression of shha, igf2a, bmp2b, and col1a2. Based on the results, it appears that phenols and flavonoids from the EEP can improve the caudal fin regeneration of HG zebrafish.

Wild-Type Zebrafish (Danio rerio) Larvae as a Vertebrate Model for Diabetes and Comorbidities: A Review

Zebrafish have become a popular alternative to higher animals in biomedical and pharmaceutical research. The development of stable mutant lines to model target specific aspects of many diseases, including diabetes, is well reported. However, these mutant lines are much more costly and challenging to maintain than wild-type zebrafish and are simply not an option for many research facilities. As an alternative to address the disadvantages of advanced mutant lines, wild-type larvae may represent a suitable option. In this review, we evaluate organ development in zebrafish larvae and discuss established methods that use wild-type zebrafish larvae up to seven days post fertilization to test for potential drug candidates for diabetes and its commonly associated conditions of oxidative stress and inflammation. This provides an up to date overview of the relevance of wild-type zebrafish larvae as a vertebrate antidiabetic model and confidence as an alternative tool for preclinical studies. We highlight the advantages and disadvantages of established methods and suggest recommendations for future developments to promote the use of zebrafish, specifically larvae, rather than higher animals in the early phase of antidiabetic drug discovery.

Effect of adenosine monophosphate-activated protein kinase-p53-Krüppel-like factor 2a pathway in hyperglycemia-induced cardiac remodeling in adult zebrafish

Aims/Introduction

Diabetic cardiomyopathy is a type of myocardial disease. It causes left ventricular hypertrophy, followed by diastolic and systolic dysfunction, eventually leading to congestive heart failure. However, the underlying mechanism still requires further elucidation.

Materials and Methods

A high‐glucose zebrafish model was constructed by administering streptozocin intraperitoneally to enhance the development of cardiomyopathy and then treated with adenosine monophosphate‐activated protein kinase (AMPK) activator. Cardiac structure and function, and protein and gene expression were then analyzed. Cardiomyocytes (CMs) culture in vitro using lentivirus were used for detection of AMPK, p53 and Krüppel‐like factor 2a (klf2a) gene expression.

Results

In the hyperglycemia group, electrocardiogram findings showed arrhythmia, echocardiography results showed heart enlargement and dysfunction, and many differences, such as increased apoptosis and myocardial fiber loss, were observed. The phospho‐AMPK and klf2a expression were downregulated, and p53 expression was upregulated. Activation of phospho‐AMPK reduced p53 and increased klf2a expression, alleviated apoptosis in CMs and improved cardiac function in the hyperglycemic zebrafish. In vitro knockdown system of AMPK, p53 and klf2a using lentivirus illustrated an increased p53 expression and decreased klf2a expression in CMs by inhibiting AMPK. Repression of p53 and upregulation of klf2a expression were observed, but no changes in the expression of AMPK and its phosphorylated type.

Conclusions

In the model of streptozocin‐induced hyperglycemia zebrafish, the reduction of phosphorylated AMPK increased p53, which led to KLF2a decrease to facilitate apoptosis of CMs, inducing the cardiac remodeling and cardiac dysfunction. These results can be reversed by AMPK activator, which means the AMPK–p53–klf2a pathway might be a potential target for diabetic cardiomyopathy intervention.

Disruption of peripheral nerve development in a zebrafish model of hyperglycemia

Diabetes mellitus-induced hyperglycemia is associated with a number of pathologies such as retinopathy, nephropathy, delayed wound healing, and diabetic peripheral neuropathy (DPN). Approximately 50% of patients with diabetes mellitus will develop DPN, which is characterized by disrupted sensory and/or motor functioning, with treatment limited to pain management. Zebrafish ( Danio rerio) are an emerging animal model used to study a number of metabolic disorders, including diabetes. Diabetic retinopathy, nephropathy, and delayed wound healing have all been demonstrated in zebrafish. Recently, our laboratory has demonstrated that following the ablation of the insulin-producing β-cells of the pancreas (and subsequent hyperglycemia), the peripheral nerves begin to show signs of dysregulation. In this study, we take a different approach, taking advantage of the transdermal absorption abilities of zebrafish larvae to extend the period of hyperglycemia. Following 5 days of 60 mM d-glucose treatment, we observed motor axon defasciculation, disturbances in perineurial glia sheath formation, decreased myelination of motor axons, and sensory neuron mislocalization. This study extends our understanding of the structural changes of the peripheral nerve following induction of hyperglycemia and does so in an animal model capable of potential DPN drug discovery in the future.

NEW & NOTEWORTHY Zebrafish are emerging as a robust model system for the study of diabetic complications such as retinopathy, nephropathy, and impaired wound healing. We present a novel model of diabetic peripheral neuropathy in zebrafish in which the integrity of the peripheral nerve is dysregulated following the induction of hyperglycemia. By using this model, future studies can focus on elucidating the underlying molecular mechanisms currently unknown.

The promise of zebrafish as a model of metabolic syndrome

Metabolic syndrome is a cluster including hyperglycaemia, obesity, hypertension, and hypertriglyceridaemia as a result of biochemical and physiological alterations and can increase the risk of cardiovascular disease and diabetes. Fundamental research on this disease requires validated animal models. One potential animal model that is rapidly gaining in popularity is zebrafish (Danio rerio). The use of zebrafish as an animal model conveys several advantages, including high human genetic homology, transparent embryos and larvae that allow easier visualization. This review discusses how zebrafish models contribute to the development of metabolic syndrome studies. Different diseases in the cluster of metabolic syndrome, such as hyperglycaemia, obesity, diabetes, and hypertriglyceridaemia, have been successfully studied using zebrafish; and the model is promising for hypertension and cardiovascular metabolic-related diseases due to its genetic similarity to mammals. Genetic mutation, chemical induction, and dietary alteration are among the tools used to improve zebrafish models. This field is expanding, and thus, more effective and efficient techniques are currently developed to fulfil the increasing demand for thorough investigations.

Acute effects of hyperglycemia on the peripheral nervous system in zebrafish (Danio rerio) following nitroreductase-mediated β-cell ablation

Diabetic peripheral neuropathy (DPN) is estimated to affect 50% of diabetic patients. Although DPN is highly prevalent, molecular mechanisms remain unknown and treatment is limited to pain relief and glycemic control. We provide a novel model of acute DPN in zebrafish ( Danio rerio) larvae. Beginning 5 days postfertilization (dpf), zebrafish expressing nitroreductase in their pancreatic β-cells were treated with metronidazole (MTZ) for 48 h and checked for β-cell ablation 7 dpf. In experimental design, this was meant to serve as proof of concept that β-cell ablation and hyperglycemia are possible at this time point, but we were surprised to find changes in both sensory and motor nerve components. Compared with controls, neurod+ sensory neurons were often observed outside the dorsal root ganglia in MTZ-treated fish. Fewer motor nerves were properly ensheathed by nkx2.2a+ perineurial cells, and tight junctions were disrupted along the motor nerve in MTZ-treated fish compared with controls. Not surprisingly, the motor axons of the MTZ-treated group were defasciculated compared with the control group, myelination was attenuated, and there was a subtle difference in Schwann cell number between the MTZ-treated and control group. All structural changes occurred in the absence of behavioral changes in the larvae at this time point, suggesting that peripheral nerves are influenced by acute hyperglycemia before becoming symptomatic. Moving forward, this novel animal model of DPN will allow us to access the molecular mechanisms associated with the acute changes in the hyperglycemic peripheral nervous system, which may help direct therapeutic approaches.

Uncovering the regeneration strategies of zebrafish organs: a comprehensive systems biology study on heart, cerebellum, fin, and retina regeneration

Background

Regeneration is an important biological process for the restoration of organ mass, structure, and function after damage, and involves complex bio-physiological mechanisms including cell differentiation and immune responses. We constructed four regenerative protein-protein interaction (PPI) networks using dynamic models and AIC (Akaike’s Information Criterion), based on time-course microarray data from the regeneration of four zebrafish organs: heart, cerebellum, fin, and retina. We extracted core and organ-specific proteins, and proposed a recalled-blastema-like formation model to uncover regeneration strategies in zebrafish.

Results

It was observed that the core proteins were involved in TGF-β signaling for each step in the recalled-blastema-like formation model and TGF-β signaling may be vital for regeneration. Integrins, FGF, and PDGF accelerate hemostasis during heart injury, while Bdnf shields retinal neurons from secondary damage and augments survival during the injury response. Wnt signaling mediates the growth and differentiation of cerebellum and fin neural stem cells, potentially providing a signal to trigger differentiation.

Conclusion

Through our analysis of all four zebrafish regenerative PPI networks, we provide insights that uncover the underlying strategies of zebrafish organ regeneration.

Zebrafish as a Model for the Study of Microvascular Complications of Diabetes and Their Mechanisms

Diabetes mellitus (DM) is a crucial metabolic disease that leads to severe disorders. These include macrovascular complications such as myocardial infarction, stroke, and peripheral artery disease and microvascular complications including diabetic nephropathy, neuropathy, and retinopathy. Diabetes mellitus, along with its associated organ pathologies, is one of the key problems in today's medicine. Zebrafish is an upcoming disease model organism in diabetes research. Its glucose metabolism and the pathways of reactive metabolite formation are very similar to those of humans. Moreover, several physiological and pathophysiological pathways that also exist in humans and other mammals have been identified in this species or are currently under intense investigation. Zebrafish offer sophisticated imaging techniques and allow simple and fast genetic and pharmacological approaches with a high throughput. In this review, we highlight achievements and mechanisms concerning microvascular complications discovered in zebrafish, and we discuss the advantages and disadvantages of zebrafish as a model for studying diabetic complications.

Zebrafish Pancreas Development and Regeneration: Fishing for Diabetes Therapies

The zebrafish pancreas shares its basic organization and cell types with the mammalian pancreas. In addition, the developmental pathways that lead to the establishment of the pancreatic islets of Langherhans are generally conserved from fish to mammals. Zebrafish provides a powerful tool to probe the mechanisms controlling establishment of the pancreatic endocrine cell types from early embryonic progenitor cells, as well as the regeneration of endocrine cells after damage. This knowledge is, in turn, applicable to refining protocols to generate renewable sources of human pancreatic islet cells that are critical for regulation of blood sugar levels. Here, we review how previous and ongoing studies in zebrafish and beyond are influencing the understanding of molecular mechanisms underlying various forms of diabetes and efforts to develop cell-based approaches to cure this increasingly widespread disease.

Alternate Immersion in an External Glucose Solution Differentially Affects Blood Sugar Values in Older Versus Younger Zebrafish Adults

Recently, zebrafish have been used to examine hyperglycemia-induced complications (retinopathy and neuropathy), as would occur in individuals with diabetes. Current models to induce hyperglycemia in zebrafish include glucose immersion and streptozotocin injections. Both are effective, although neither is reported to elevate blood sugar values for more than 1 month. In this article, we report differences in hyperglycemia induction and maintenance in young (4-11 months) versus old (1-3 years) zebrafish adults. In particular, older fish immersed in an alternating constant external glucose solution (2%) for 2 months displayed elevated blood glucose levels for the entire experimental duration. In contrast, younger adults displayed only transient hyperglycemia, suggesting the fish were acclimating to the glucose exposure protocol. However, modifying the immersion protocol to include a stepwise increasing glucose concentration (from 1% → 2%→3%) resulted in maintained hyperglycemia in younger zebrafish adults for up to 2 months. Glucose-exposed younger fish collected after 8 weeks of exposure also displayed a significant decrease in wet weight. Taken together, these data suggest different susceptibilities to hyperglycemia in older and younger fish and that stepwise increasing glucose concentrations of 1% are required for maintenance of hyperglycemia in younger adults, with higher concentrations of glucose resulting in greater increases in blood sugar values.

Epigenetic Studies Point to DNA Replication/Repair Genes as a Basis for the Heritable Nature of Long Term Complications in Diabetes

Metabolic memory (MM) is defined as the persistence of diabetic (DM) complications even after glycemic control is pharmacologically achieved. Using a zebrafish diabetic model that induces a MM state, we previously reported that, in this model, tissue dysfunction was of a heritable nature based on cell proliferation studies in limb tissue and this correlated with epigenetic DNA methylation changes that paralleled alterations in gene expression. In the current study, control, DM, and MM excised fin tissues were further analyzed by MeDIP sequencing and microarray techniques. Bioinformatics analysis of the data found that genes of the DNA replication/DNA metabolism process group (with upregulation of the apex1, mcm2, mcm4, orc3, lig1, and dnmt1 genes) were altered in the DM state and these molecular changes continued into MM. Interestingly, DNA methylation changes could be found as far as 6-13 kb upstream of the transcription start site for these genes suggesting potential higher levels of epigenetic control. In conclusion, DNA methylation changes in members of the DNA replication/repair process group best explain the heritable nature of cell proliferation impairment found in the zebrafish DM/MM model. These results are consistent with human diabetic epigenetic studies and provide one explanation for the persistence of long term tissue complications as seen in diabetes.

Use of zebrafish as a model to investigate the role of epigenetics in propagating the secondary complications observed in diabetes mellitus

Diabetes mellitus (DM) is classified as a disease of metabolic dysregulation predicted to affect over 400 million individuals world-wide by 2030. The debilitating aspects of this disease are the long term complications involving microvascular and macrovascular pathologies. These long term complications are related to the clinical phenomenon of metabolic memory (MM) that is defined as the persistence of diabetic complications even after glycemic control has been pharmacologically achieved. The persistent nature of MM has invoked involvement of epigenetic processes. Current research with the DM/MM zebrafish model as described in this review as well as human and mammalian studies has established that changes in DNA methylation patterns appear to contribute to tissue dysfunctions associated with DM. This review will describe studies on an adult zebrafish model of type I diabetes mellitus that allows analysis of both the hyperglycemic (HG or DM) phase and MM phase of the disease. The review will discuss the model in regards to: 1) its hyperglycemic phase, 2) its MM phase, 3) biochemical õpathways underlying changes in DNA methylation patterns observed in the model, 4) loci specific changes in DNA methylation patterns, and 5) strengths of the adult zebrafish model as compared to other MM animal models.

Inhibition of poly-ADP ribose polymerase enzyme activity prevents hyperglycemia-induced impairment of angiogenesis during wound healing

We previously reported a zebrafish model of type I diabetes mellitus (DM) that can be used to study the hyperglycemic (HG) and metabolic memory (MM) states within the same fish. Clinically, MM is defined as the persistence of diabetic complications even after glycemic control is pharmacologically achieved. In our zebrafish model, MM occurs following β-cell regeneration, which returns fish to euglycemia. During HG, fish acquire tissue deficits reflective of the complications seen in patients with DM and these deficits persist after fish return to euglycemia (MM). The unifying mechanism for the induction of diabetic complications involves a cascade of events that is initiated by the HG stimulation of poly-ADP ribose polymerase enzyme (Parp) activity. Additionally, recent evidence shows that the HG induction of Parp activity stimulates changes in epigenetic mechanisms that correlate with the MM state and the persistence of complications. Here we report that wound-induced angiogenesis is impaired in DM and remains impaired when fish return to a euglycemic state. Additionally, inhibition of Parp activity prevented the HG-induced wound angiogenesis deficiency observed. This approach can identify molecular targets that will provide potential new avenues for therapeutic discovery as angiogenesis imbalances are associated with all HG-damaged tissues.

Genome-wide DNA methylation analysis identifies a metabolic memory profile in patient-derived diabetic foot ulcer fibroblasts

Diabetic foot ulcers (DFUs) are a serious complication of diabetes. Previous exposure to hyperglycemic conditions accelerates a decline in cellular function through metabolic memory despite normalization of glycemic control. Persistent, hyperglycemia-induced epigenetic patterns are considered a central mechanism that activates metabolic memory; however, this has not been investigated in patient-derived fibroblasts from DFUs. We generated a cohort of patient-derived lines from DFU fibroblasts (DFUF), and site- and age-matched diabetic foot fibroblasts (DFF) and non-diabetic foot fibroblasts (NFF) to investigate global and genome-wide DNA methylation patterns using liquid chromatography/mass spectrometry and the Illumina Infinium HumanMethylation450K array. DFFs and DFUFs demonstrated significantly lower global DNA methylation compared to NFFs (p = 0.03). Hierarchical clustering of differentially methylated probes (DMPs, p = 0.05) showed that DFFs and DFUFs cluster together and separately from NFFs. Twenty-five percent of the same probes were identified as DMPs when individually comparing DFF and DFUF to NFF. Functional annotation identified enrichment of DMPs associated with genes critical to wound repair, including angiogenesis (p = 0.07) and extracellular matrix assembly (p = 0.035). Identification of sustained DNA methylation patterns in patient-derived fibroblasts after prolonged passage in normoglycemic conditions demonstrates persistent metabolic memory. These findings suggest that epigenetic-related metabolic memory may also underlie differences in wound healing phenotypes and can potentially identify therapeutic targets.

Epigenetics in kidney development and renal disease

The study of epigenetics is intimately linked and inseparable from developmental biology. Many of the genes that imprint epigenetic information on chromatin function during the specification of cell lineages in the developing embryo. These include the histone methyltransferases and their cofactors of the Polycomb and Trithorax gene families. How histone methylation is established and what regulates the tissue and locus specificity of histone methylation is an emerging area of research. The embryonic kidney is used as a model to understand how DNA-binding proteins can specify cell lineages and how such proteins interact directly with the histone methylation machinery to generate a unique epigenome for particular tissues and cell types. In adult tissues, histone methylation marks must be maintained for normal gene expression patterns. In chronic and acute renal disease, epigenetic marks are being characterized and correlated with the establishment of metabolic memory, in part to explain the persistence of pathologies even when optimal treatment modalities are used. Thus, the state of the epigenome in adult cells must be considered when attempting to alleviate or alter gene expression patterns in disease.

Parp inhibition prevents ten-eleven translocase enzyme activation and hyperglycemia-induced DNA demethylation

Studies from human cells, rats, and zebrafish have documented that hyperglycemia (HG) induces the demethylation of specific cytosines throughout the genome. We previously documented that a subset of these changes become permanent and may provide, in part, a mechanism for the persistence of complications referred to as the metabolic memory phenomenon. In this report, we present studies aimed at elucidating the molecular machinery that is responsible for the HG-induced DNA demethylation observed. To this end, RNA expression and enzymatic activity assays indicate that the ten-eleven translocation (Tet) family of enzymes are activated by HG. Furthermore, through the detection of intermediates generated via conversion of 5-methyl-cytosine back to the unmethylated form, the data were consistent with the use of the Tet-dependent iterative oxidation pathway. In addition, evidence is provided that the activity of the poly(ADP-ribose) polymerase (Parp) enzyme is required for activation of Tet activity because the use of a Parp inhibitor prevented demethylation of specific loci and the accumulation of Tet-induced intermediates. Remarkably, this inhibition was accompanied by a complete restoration of the tissue regeneration deficit that is also induced by HG. The ultimate goal of this work is to provide potential new avenues for therapeutic discovery.