Limb regeneration is impaired in an adult zebrafish model of diabetes mellitus

Animal models of obesity and diabetes mellitus

More than one-third of the worldwide population is overweight or obese and therefore at risk of developing type 2 diabetes mellitus. In order to mitigate this pandemic, safer and more potent therapeutics are urgently required. This necessitates the continued use of animal models to discover, validate and optimize novel therapeutics for their safe use in humans. In order to improve the transition from bench to bedside, researchers must not only carefully select the appropriate model but also draw the right conclusions. In this Review, we consolidate the key information on the currently available animal models of obesity and diabetes and highlight the advantages, limitations and important caveats of each of these models.

Oxidative stress-dependent MMP-13 activity underlies glucose neurotoxicity

BACKGROUND

A complication of diabetes is neuropathy, a condition of sensory axon degeneration that originates in the epidermis. The mechanisms remain unknown but reactive oxygen species (ROS) have been implicated in this condition. In this study, we assessed the role of ROS and a candidate downstream target, MMP-13 in glucose-induced sensory axon degeneration in zebrafish and mice.

METHODS

The effects of glucose on metabolism and sensory axon degeneration were assessed using qPCR and live imaging. ROS were analyzed using pentafluorobenzene-sulfonyl fluorescein and activation of the NF-κB stress response was determined using Tg(NF-κB:GFP) zebrafish. The role of MMP-13 and ROS in glucose-dependent axon degeneration was determined in zebrafish following treatment with the antioxidant, N-acetylcysteine and the MMP-13 inhibitor, DB04760. Neuropathic mice fed on a high-fat/high-sugar diet were treated with the MMP-13 inhibitor, CL-82198 to assess sensory recovery.

RESULTS

Glucose treatment of zebrafish induced metabolic changes that resemble diabetes. Sensory axon degeneration was mediated by ROS-induced MMP-13 and prevented upon antioxidant treatment or MMP-13 inhibition. MMP-13 inhibition also reversed neuropathy in diabetic mice.

CONCLUSION

We demonstrate that zebrafish are suitable to study glucose-induced neurotoxicity. Given the effects in zebrafish and mice, MMP-13 inhibition may be beneficial in the treatment of human diabetic neuropathy.

Ocular lesions in leptin receptor-deficient medaka (Oryzias latipes)

Ocular lesions in leptin receptor-deficient medaka were examined histopathologically at 10, 28, and 37 weeks post hatching. Leptin receptor-deficient medaka at 28 and 37 weeks old showed hyperglycemia and hypoinsulinemia. Histopathologically, vacuolation, swelling, fragmentation, and liquefaction of the lens fibers and dilatation of the retinal central veins, retinal capillaries, iridal veins and capillaries, and choroidal veins were observed in leptin receptor-deficient medaka at 28 and 37 weeks old. Thinning of the total retina, pigment epithelial layer, layer of rods and cones, outer granular layer, outer plexiform layer, inner granular layer, and inner plexiform layer was observed in leptin receptor-deficient medaka at 28 and 37 weeks compared with in control medaka. These histopathological characteristics in leptin receptor-deficient medaka are similar to characteristics in ocular lesions of rodent models for type II diabetes mellitus, making leptin receptor-deficient medaka a useful model of diabetic cataract and retinopathy.

Immune Suppressive and Bone Inhibitory Effects of Prednisolone in Growing and Regenerating Zebrafish Tissues

Glucocorticoids are widely used as therapeutic agents to treat immune-mediated diseases in humans because of their anti-inflammatory and immunosuppressive effects. However, glucocorticoids have various adverse effects, in particular rapid and pronounced bone loss associated with fractures in glucocorticoid-induced osteoporosis, a common form of secondary osteoporosis. In zebrafish, which are increasingly used to study processes of bone regeneration and disease, glucocorticoids show detrimental effects on bone tissue; however, the underlying cellular mechanisms are incompletely understood. Here, we show that treatment with the glucocorticoid prednisolone impacts on the number, activity and differentiation of osteoblasts, osteoclasts, and immune cells during ontogenetic growth, homeostasis, and regeneration of zebrafish bone. Macrophage numbers are reduced in both larval and adult tissues, correlating with decreased generation of myelomonocytes and enhanced apoptosis of these cells. In contrast, osteoblasts fail to proliferate, show decreased activity, and undergo incomplete differentiation. In addition, prednisolone treatment mitigates the number and recruitment of osteoclasts to sites of bone regeneration in adult fish. In combination, these effects delay bone growth and impair bone regeneration. Our study demonstrates the many-faceted effects of glucocorticoids in non-mammalian vertebrates and helps to further establish the zebrafish as a model to study glucocorticoid-induced osteoporosis. © 2017 American Society for Bone and Mineral Research.

Effect of diabetes status and hyperglycemia on global DNA methylation and hydroxymethylation

Type 2 diabetes mellitus (T2DM) is characterized by oxidative stress that could lead to chronic micro- and macrovascular complications. We hypothesized that some of the target organ damage is mediated by oxidative alterations in epigenetic mechanisms involving DNA methylation (5mC) and DNA hydroxymethylation (5hmC). We analyzed global DNA methylation and hydroxymethylation in peripheral blood cells in well-controlled and poorly controlled patients with T2DM and compared them with healthy controls. We also analyzed microarrays of DNA methylation and gene expression of other important tissues in the context of diabetes from the GEO database repository and then compared these results with our experimental gene expression data. DNA methylation and, more importantly, DNA hydroxymethylation levels were increased in poorly controlled patients compared to well-controlled and healthy individuals. Both 5mC and 5hmC measurements were correlated with the percentage of glycated hemoglobin, indicating a direct impact of hyperglycemia on changes over the epigenome. The analysis of methylation microarrays was concordant, and 5mC levels were increased in the peripheral blood of T2DM patients. However, the DNA methylation levels were the opposite of those in other tissues, such as the pancreas, adipose tissue and skeletal muscle. We hypothesize that a process of DNA oxidation associated with hyperglycemia may explain the DNA demethylation in which the activity of ten-eleven translocation (TET) proteins is not sufficient to complete the process. High levels of glucose lead to cellular oxidation, which triggers the process of DNA demethylation aided by TET enzymes, resulting in epigenetic dysregulation of the damaged tissues.

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.

Animal Models of Diabetic Retinopathy

PURPOSE OF REVIEW

Diabetic retinopathy (DR) is one of the most common complications associated with chronic hyperglycemia seen in patients with diabetes mellitus. While many facets of DR are still not fully understood, animal studies have contributed significantly to understanding the etiology and progression of human DR. This review provides a comprehensive discussion of the induced and genetic DR models in different species and the advantages and disadvantages of each model.

RECENT FINDINGS

Rodents are the most commonly used models, though dogs develop the most similar morphological retinal lesions as those seen in humans, and pigs and zebrafish have similar vasculature and retinal structures to humans. Nonhuman primates can also develop diabetes mellitus spontaneously or have focal lesions induced to simulate retinal neovascular disease observed in individuals with DR. DR results in vascular changes and dysfunction of the neural, glial, and pancreatic β cells. Currently, no model completely recapitulates the full pathophysiology of neuronal and vascular changes that occur at each stage of diabetic retinopathy; however, each model recapitulates many of the disease phenotypes.

Coordination of Bactericidal and Iron Regulatory Functions of Hepcidin in Innate Antimicrobial Immunity in a Zebrafish Model

Hepcidin acts as both an antimicrobial peptide and a hormonal regulator of iron homeostasis; however, the biological significance of this dual-function in immune reactions remains elusive. In this study, we provide experimental evidence regarding the coordination of this dual-function in the innate antimicrobial immunity using a zebrafish model. The transcription of hepcidin gene was significantly upregulated in liver by Aeromonas hydrophila (A.h) DNA stimulation, which was accompanied by an increase of hepcidin protein and a decrease of iron concentration in serum. Thus, an enhanced bactericidal activity against A.h and Escherichia coli and inhibitory effects on A.h growth and OmpA expression were observed in A.h cells, the latter of which made the bacterium more susceptible to complement attack. The enhanced bacteriostatic activities in serum following the stimulation were dramatically impaired by neutralizing hepcidin or restoring iron to the samples. Immuno-protection assay showed that zebrafish administrated with A.h DNA or designed CpG-ODNs had a significantly enhanced defence against A.h and Vibrio alginolyticus infections, which was also eliminated by the neutralization of hepcidin. Results indicate that the induction of hepcidin leads to the decrease of iron in circulation, which eventually limits iron availability to invading microorganisms, thus contributing to host defence.

Development of a Novel Zebrafish Model for Type 2 Diabetes Mellitus

Obesity is a major cause of type 2 diabetes mellitus (T2DM) in mammals. We have previously established a zebrafish model of diet-induced obesity (DIO zebrafish) by overfeeding Artemia. Here we created DIO zebrafish using a different method to induce T2DM. Zebrafish were overfed a commercially available fish food using an automated feeding system. We monitored the fasting blood glucose levels in the normal-fed group (one feed/day) and overfed group (six feeds/day) over an 8-week period. The fasting blood glucose level was significantly increased in DIO zebrafish compared with that of normal-fed zebrafish. Intraperitoneal and oral glucose tolerance tests showed impaired glucose tolerance by overfeeding. Insulin production, which was determined indirectly by measuring the EGFP signal strength in overfed Tg(−1.0ins:EGFP)^sc1 zebrafish, was increased in DIO zebrafish. The anti-diabetic drugs metformin and glimepiride ameliorated hyperglycaemia in the overfed group, suggesting that this zebrafish can be used as a model of human T2DM. Finally, we conducted RNA deep sequencing and found that the gene expression profiling of liver-pancreas revealed pathways common to human T2DM. In summary, we developed a zebrafish model of T2DM that shows promise as a platform for mechanistic and therapeutic studies of diet-induced glucose intolerance and insulin resistance.

A synthetic Nitraria alkaloid, isonitramine protects pancreatic β-cell and attenuates postprandial hyperglycemia

OBJECTIVE

The extracts of Nitraria genus are composed of Nitraria alkaloids and have been used traditionally as a hypoglycemic medicine. However, the efficacy and precise mechanism of Nitraria alkaloids remain largely unknown.

METHODS

Previously, we reported the total synthesis of (+)-isonitramine, one of Nitraria alkaloids. In this study, we investigated the anti-diabetic potential of isonitramine in diabetes mellitus and its underlying molecular mechanism in carbohydrate catabolism in vitro and in vivo.

RESULTS

Isonitramine exerted significant inhibitory effect on α-glucosidases but not α-amylase in vitro. In zebrafish, isonitramine alleviated the streptozotocin (STZ)-induced postprandial hyperglycemia and protected the pancreatic damages against alloxan-induced oxidative stress in vivo. Also, isonitramine induced insulin without any toxicities and downregulated phosphoenolpyruvate carboxykinase (PEPCK), which catalyzes the first committed step in gluconeogenesis.

CONCLUSION

Taken together, isonitramine inhibited α-glucosidase activity and PEPCK expression, while increased insulin expression, resulting in attenuating the postprandial hyperglycemia. Also, isonitramine protected the pancreas from ROS-mediated toxicities. Therefore, isonitramine may be a new drug candidate for the treatment of diabetes mellitus.

Improved regeneration and de novo bone formation in a diabetic zebrafish model treated with paricalcitol and cinacalcet

Bone changes related to diabetes have been well stablished, but few strategies have been developed to prevent this growing health problem. In our work, we propose to investigate the effects of calcitriol as well as of a vitamin D analog (paricalcitol) and a calcimimetic (cinacalcet), in fin regeneration and de novo mineralization in a zebrafish model of diabetes. Following exposure of diabetic transgenic Tg(ins:nfsb-mCherry) zebrafish to calcitriol, paricalcitol and cinacalcet, caudal fins were amputated to assess their effects on tissue regeneration. Caudal fin mineralized and regenerated areas were quantified by in vivo alizarin red staining. Quantitative real-time PCR was performed using RNA from the vertebral column. Diabetic fish treated with cinacalcet and paricalcitol presented increased regenerated and mineralized areas when compared with non-treated diabetic group, while no significant increase was observed in non-diabetic fish treated with both drugs. Gene expression analysis showed an up-regulation for runt-related transcription factor 2b (runx2b), bone gamma-carboxyglutamic acid-containing protein (bglap), insulin a (insa) and insulin b (insb) and a trend of increase for sp7 transcription factor (sp7) in diabetic groups treated with cinacalcet and paricalcitol. Expression of insra and vdra was up-regulated in both diabetic and nondiabetic fish treated with cinacalcet. In nondiabetic fish treated with paricalcitol and cinacalcet a similar increase in gene expression could be observed but not so pronounced. The increased mineralization and regeneration in diabetic zebrafish treated with cinacalcet and paricalcitol can be explained by increased osteoblastic differentiation and increased insulin expression indicating pro-osteogenic potential of both drugs.

In vitro, in vivo and in silico anti-hyperglycemic inhibition by sinigrin

OBJECTIVE

To evaluate the anti-hyperglycemic potential of sinigrin using in vitro, in silico and in vivo streptozotocin (STZ) induced hyperglycemic zebrafish model.

METHODS

The in vitro enzyme inhibition assay was carried out to determine the IC₅₀ value against α-glucosidase and α-amylase, in silico molecular docking was performed against both enzymes with PyRx tool and simulations were performed using GROMACS tool. Hyperglycemia was induced in zebrafishes using three intraperitoneal injections on alternating days for 1 week at 350 mg/kg of STZ. Hyperglycemic fishes were treated intraperitoneally with 50, 100 and 150 mg of sinigrin/kg of body weight for 24 h and glucose levels were measured.

RESULTS

The sinigrin showed very strong inhibition against α-glucosidase and α-amylase with 0.248 and 0.00124 μM while reference drug acarbose showed IC₅₀ value of 73.0700 and 0.0017 μM against α-glucosidase and α-amylase, respectively. Kinetic analysis revealed that sinigrin has the mixed type mode of inhibition against α-glucosidase. Molecular docking results revealed its strong binding affinity with α-glucosidase (-10.00 kcal/mol) and α-amylase (-8.10 kcal/mol). Simulations graphs confirmed its stability against both enzymes. Furthermore, in hyperglycemic zebrafishes most significant (P < 0.001) reduction of glucose was occurred at 150 mg/kg, moderate significant reduction of glucose was observed at 100 mg/kg and no any significant reduction of glucose was measured at 50 mg/kg.

CONCLUSIONS

It can be evident from the present results that sinigrin has potent anti-hyperglycemic activity and it may prove to be effective treatment for the hyperglycemia.

Diabetes, adult neurogenesis and brain remodeling: New insights from rodent and zebrafish models

The prevalence of diabetes rapidly increased during the last decades in association with important changes in lifestyle. Diabetes and hyperglycemia are well-known for inducing deleterious effects on physiologic processes, increasing for instance cardiovascular diseases, nephropathy, retinopathy and foot ulceration. Interestingly, diabetes also impairs brain morphology and functions such as (1) decreased neurogenesis (proliferation, differentiation and cell survival), (2) decreased brain volumes, (3) increased blood-brain barrier leakage, (4) increased cognitive impairments, as well as (5) increased stroke incidence and worse neurologic outcomes following stroke. Importantly, diabetes is positively associated with a higher risk to develop Alzheimer disease. In this context, we aim at reviewing the impact of diabetes on neural stem cell proliferation, newborn cell differentiation and survival in a homeostatic context or following stroke. We also report the effects of hyper- and hypoglycemia on the blood-brain barrier physiology through modifications of tight junctions and transporters. Finally, we discuss the implication of diabetes on cognition and behavior.

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.

Chronic hyperglycemia affects bone metabolism in adult zebrafish scale model

Type II diabetes mellitus is a metabolic disease characterized by chronic hyperglycemia that induce other pathologies including diabetic retinopathy and bone disease. The mechanisms implicated in bone alterations induced by type II diabetes mellitus have been debated for years and are not yet clear because there are other factors involved that hide bone mineral density alterations. Despite this, it is well known that chronic hyperglycemia affects bone health causing fragility, mechanical strength reduction and increased propensity of fractures because of impaired bone matrix microstructure and aberrant bone cells function. Adult Danio rerio (zebrafish) represents a powerful model to study glucose and bone metabolism. Then, the aim of this study was to evaluate bone effects of chronic hyperglycemia in a new type II diabetes mellitus zebrafish model created by glucose administration in the water. Fish blood glucose levels have been monitored in time course experiments and basal glycemia was found increased. After 1 month treatment, the morphology of the retinal blood vessels showed abnormalities resembling to the human diabetic retinopathy. The adult bone metabolism has been evaluated in fish using the scales as read-out system. The scales of glucose-treated fish didn't depose new mineralized matrix and shown bone resorption lacunae associated with an intense osteoclast activity. In addition, hyperglycemic fish scales have shown a significant decrease of alkaline phosphatase activity and increase of tartrate-resistant acid phosphatase activity, in association with alterations in other bone-specific markers. These data indicates an imbalance in bone metabolism, which leads to the osteoporotic-like phenotype visualized through scale mineral matrix staining. The zebrafish model of hyperglycemic damage can contribute to elucidate in vivo the molecular mechanisms of metabolic changes, which influence the bone tissues regulation in human diabetic patients.

A concise review of common animal models for the study of limb regeneration

Correct selection of an appropriate animal mode to closely mimic human extremity diseases or to exhibit desirable phenotypes of limb regeneration is the first critical step for all scientists in biomedical and regenerative researches. The commonly-used animals in limb regeneration and repairing studies, such as axolotl, mice, and rats, are discussed in the review and other models including cockroaches, dogs, and horses are also mentioned. The review weighs the general advantages, disadvantages, and precedent uses of each model in the context of limb and peripheral injury and subsequent regeneration. We hope that this review can provide the reader an overview of each model, from which to select one for their specific purpose.

Characterization of SIGIRR/IL-1R8 Homolog from Zebrafish Provides New Insights into Its Inhibitory Role in Hepatic Inflammation

Single Ig IL-1R-related molecule (SIGIRR, also called IL-1R8 or Toll/IL-1R [TIR]8), a negative regulator for Toll/IL-1R signaling, plays critical roles in innate immunity and various diseases in mammals. However, the occurrence of this molecule in ancient vertebrates and its function in liver homeostasis and disorders remain poorly understood. In this study, we identified a SIGIRR homology from zebrafish (Danio rerio [DrSIGIRR]) by using a number of conserved structural and functional hallmarks to its mammalian counterparts. DrSIGIRR was highly expressed in the liver. Ablation of DrSIGIRR by lentivirus-delivered small interfering RNA in the liver significantly enhanced hepatic inflammation in response to polyinosinic-polycytidylic acid [poly(I:C)] stimulation, as shown by the upregulation of inflammatory cytokines and increased histological disorders. In contrast, depletion of TIR domain-containing adaptor inducing IFN-β (TRIF) or administration of TRIF signaling inhibitor extremely abrogated the poly(I:C)-induced hepatic inflammation. Aided by the zebrafish embryo model, overexpression of DrSIGIRR in vivo significantly inhibited the poly(I:C)- and TRIF-induced NF-κB activations; however, knockdown of DrSIGIRR promoted such activations. Furthermore, pull-down and Duolink in situ proximity ligation assay assays showed that DrSIGIRR can interact with the TRIF protein. Results suggest that DrSIGIRR plays an inhibitory role in TRIF-mediated inflammatory reactions by competitive recruitment of the TRIF adaptor protein from its TLR3/TLR22 receptor. To our knowledge, this study is the first to report a functional SIGIRR homolog that existed in a lower vertebrate. This molecule is essential to establish liver homeostasis under inflammatory stimuli. Overall, the results will enrich the current knowledge about SIGIRR-mediated immunity and disorders in the liver.

Leptin signaling regulates glucose homeostasis, but not adipostasis, in the zebrafish

Leptin is the primary adipostatic factor in mammals. Produced largely by adipocytes in proportion to total adipose mass, the hormone informs the brain regarding total energy stored as triglycerides in fat cells. The hormone acts on multiple circuits in the brain to regulate food intake, autonomic outflow, and endocrine function to maintain energy balance. In addition to regulating adipose mass, mammalian leptin also plays a role in the regulation of glucose homeostasis and as a gating factor in reproductive competence. Leptin-deficient mice and people exhibit early onset profound hyperphagia and obesity, diabetes, and infertility. Although leptin and the leptin receptor are found in fish, the hormone is not expressed in adipose tissue, but is found in liver and other tissues. Here, we show that adult zebrafish lacking a functional leptin receptor do not exhibit hyperphagia or increased adiposity, and exhibit normal fertility. However, leptin receptor-deficient larvae have increased numbers of β-cells and increased levels of insulin mRNA. Furthermore, larval zebrafish have been shown to exhibit β-cell hyperplasia in response to high fat feeding or peripheral insulin resistance, and we show here that leptin receptor is required for this response. Adult zebrafish also have increased levels of insulin mRNA and other alterations in glucose homeostasis. Thus, a role for leptin in the regulation of β-cell mass and glucose homeostasis appears to be conserved across vertebrates, whereas its role as an adipostatic factor is likely to be a secondary role acquired during the evolution of mammals.

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.

Fishing for Nature's Hits: Establishment of the Zebrafish as a Model for Screening Antidiabetic Natural Products

Diabetes mellitus affects millions of people worldwide and significantly impacts their quality of life. Moreover, life threatening diseases, such as myocardial infarction, blindness, and renal disorders, increase the morbidity rate associated with diabetes. Various natural products from medicinal plants have shown potential as antidiabetes agents in cell-based screening systems. However, many of these potential "hits" fail in mammalian tests, due to issues such as poor pharmacokinetics and/or toxic side effects. To address this problem, the zebrafish (Danio rerio) model has been developed as a "bridge" to provide an experimentally convenient animal-based screening system to identify drug candidates that are active in vivo. In this review, we discuss the application of zebrafish to drug screening technologies for diabetes research. Specifically, the discovery of natural product-based antidiabetes compounds using zebrafish will be described. For example, it has recently been demonstrated that antidiabetic natural compounds can be identified in zebrafish using activity guided fractionation of crude plant extracts. Moreover, the development of fluorescent-tagged glucose bioprobes has allowed the screening of natural product-based modulators of glucose homeostasis in zebrafish. We hope that the discussion of these advances will illustrate the value and simplicity of establishing zebrafish-based assays for antidiabetic compounds in natural products-based laboratories.

Galanin regulates blood glucose level in the zebrafish: a morphological and functional study

The present study has demonstrated the galaninergic innervation of the endocrine pancreas including sources of the galaninergic nerve fibers, and the influence of galanin receptor agonists on blood glucose level in the zebrafish. For the first time, a very abundant galaninergic innervation of the endocrine pancreas during development is shown, from the second day post-fertilization to adulthood. The fibers originated from ganglia consisting of galanin-IR, non-adrenergic (non-sensory) neurons located rostrally to the pancreatic tissue. The ganglia were found on the dorsal side of the initial part of the anterior intestinal segment, close to the intestinal branch of the vagus nerve. The galanin-IR neurons did not show immunoreactivity for applied antibodies against tyrosine hydroxylase, choline acetyltransferase, and vesicular acetylcholine transporter. Intraperitoneal injections of galanin analog NAX 5055 resulted in a statistically significant increase in the blood glucose level. Injections of another galanin receptor agonist, galnon, also caused a rise in blood glucose level; however, it was not statistically significant. The present findings suggest that, like in mammals, in the zebrafish galanin is involved in the regulation of blood glucose level. However, further studies are needed to elucidate the exact mechanism of the galanin action.

Diabetic pdx1-mutant zebrafish show conserved responses to nutrient overload and anti-glycemic treatment

Diabetes mellitus is characterized by disrupted glucose homeostasis due to loss or dysfunction of insulin-producing beta cells. In this work, we characterize pancreatic islet development and function in zebrafish mutant for pdx1, a gene which in humans is linked to genetic forms of diabetes and is associated with increased susceptibility to Type 2 diabetes. Pdx1 mutant zebrafish have the key diabetic features of reduced beta cells, decreased insulin and elevated glucose. The hyperglycemia responds to pharmacologic anti-diabetic treatment and, as often seen in mammalian diabetes models, beta cells of pdx1 mutants show sensitivity to nutrient overload. This unique genetic model of diabetes provides a new tool for elucidating the mechanisms behind hyperglycemic pathologies and will allow the testing of novel therapeutic interventions in a model organism that is amenable to high-throughput approaches.

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.

Animal Models of Diabetic Retinopathy

Diabetic retinopathy (DR) is one of today's main causes of blindness in numerous developed countries worldwide. The underlying pathogenesis of DR is complex and not well understood, thus impeding development of specific, effective treatment modalities. Consequently, the use of animal models of DR is of critical importance for investigating the pathogenesis of and treatment for DR. While rats and mice are the most commonly used animal models of DR, the zebrafish now appears to be a promising model. Nonhuman primates and humans have similar eye structures, and both can develop spontaneous diabetes mellitus (DM). Although various traditionally used animal models of DR undergo a number of pathological changes similar to those of human DR, several human variations, e.g. retinal neovascularization, cannot yet be fully mimicked in any existing animal model of DM. Since both the animal models and the methods chosen for inducing DR have great influence on experimental results, a clear understanding of available animal models is vital for planning an experimental design. In this review, we summarize the mechanisms, methodologies and pros and cons of the most commonly used animal models of DR.

Specialized insulin is used for chemical warfare by fish-hunting cone snails

More than 100 species of venomous cone snails (genus Conus) are highly effective predators of fish. The vast majority of venom components identified and functionally characterized to date are neurotoxins specifically targeted to receptors, ion channels, and transporters in the nervous system of prey, predators, or competitors. Here we describe a venom component targeting energy metabolism, a radically different mechanism. Two fish-hunting cone snails, Conus geographus and Conus tulipa, have evolved specialized insulins that are expressed as major components of their venoms. These insulins are distinctive in having much greater similarity to fish insulins than to the molluscan hormone and are unique in that posttranslational modifications characteristic of conotoxins (hydroxyproline, γ-carboxyglutamate) are present. When injected into fish, the venom insulin elicits hypoglycemic shock, a condition characterized by dangerously low blood glucose. Our evidence suggests that insulin is specifically used as a weapon for prey capture by a subset of fish-hunting cone snails that use a net strategy to capture prey. Insulin appears to be a component of the nirvana cabal, a toxin combination in these venoms that is released into the water to disorient schools of small fish, making them easier to engulf with the snail's distended false mouth, which functions as a net. If an entire school of fish simultaneously experiences hypoglycemic shock, this should directly facilitate capture by the predatory snail.

Metabolic insights from zebrafish genetics, physiology, and chemical biology

Metabolic diseases—atherosclerotic cardiovascular disease, type 2 diabetes mellitus, obesity, and non-alcoholic fatty liver disease––have reached pandemic proportions. Across gene, cell, organ, organism, and social-environmental scales, fundamental discoveries of the derangements that occur in these diseases are required to develop effective new treatments. Here we will review genetic, physiological, pathological and chemical biological discoveries in the emerging zebrafish model for studying metabolism and metabolic diseases. We present a synthesis of recent studies using forward and reverse genetic tools to make new contributions to our understanding of lipid trafficking, diabetes pathogenesis and complications, and to β-cell biology. The technical and physiological advantages and the pharmacological potential of this organism for discovery and validation of metabolic disease targets are stressed by our summary of recent findings. We conclude by arguing that metabolic research using zebrafish will benefit from adoption of conventional blood and tissue metabolite measurements, employment of modern imaging techniques, and development of more rigorous metabolic flux methods.

High tissue glucose alters intersomitic blood vessels in zebrafish via methylglyoxal targeting the VEGF receptor signaling cascade

Hyperglycemia causes micro- and macrovascular complications in diabetic patients. Elevated glucose concentrations lead to increased formation of the highly reactive dicarbonyl methylglyoxal (MG), yet the early consequences of MG for development of vascular complications in vivo are poorly understood. In this study, zebrafish were used as a model organism to analyze early vascular effects and mechanisms of MG in vivo. High tissue glucose increased MG concentrations in tg(fli:EGFP) zebrafish embryos and rapidly induced several additional malformed and uncoordinated blood vessel structures that originated out of existing intersomitic blood vessels (ISVs). However, larger blood vessels, including the dorsal aorta and common cardinal vein, were not affected. Expression silencing of MG-degrading enzyme glyoxalase (glo) 1 elevated MG concentrations and induced a similar vascular hyperbranching phenotype in zebrafish. MG enhanced phosphorylation of vascular endothelial growth factor (VEGF) receptor 2 and its downstream target Akt/protein kinase B (PKB). Pharmacological inhibitors for VEGF receptor 2 and Akt/PKB as well as MG scavenger aminoguanidine and glo1 activation prevented MG-induced hyperbranching of ISVs. Taken together, MG acts on smaller blood vessels in zebrafish via the VEGF receptor signaling cascade, thereby describing a new mechanism that can explain vascular complications under hyperglycemia and elevated MG concentrations.

Choosing preclinical study models of diabetic retinopathy: key problems for consideration

Diabetic retinopathy (DR) is the most common complication of diabetes mellitus in the eye. Although the clinical treatment for DR has already developed to a relative high level, there are still many urgent problems that need to be investigated in clinical and basic science. Currently, many in vivo animal models and in vitro culture systems have been applied to solve these problems. Many approaches have also been used to establish different DR models. However, till now, there has not been a single study model that can clearly and exactly mimic the developmental process of the human DR. Choosing the suitable model is important, not only for achieving our research goals smoothly, but also, to better match with different experimental proposals in the study. In this review, key problems for consideration in choosing study models of DR are discussed. These problems relate to clinical relevance, different approaches for establishing models, and choice of different species of animals as well as of the specific in vitro culture systems. Attending to these considerations will deepen the understanding on current study models and optimize the experimental design for the final goal of preventing DR.

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.

Hyperglycemia induces memory impairment linked to increased acetylcholinesterase activity in zebrafish (Danio rerio)

Diabetes mellitus, which causes hyperglycemia, affects the central nervous system and can impairs cognitive functions, such as memory. The aim of this study was to investigate the effects of hyperglycemia on memory as well as on the activity of acethylcholinesterase. Hyperglycemia was induced in adult zebrafish by immersion in glucose 111mM by 14 days. The animals were divided in 4 groups: control, glucose-treated, glucose-washout 7-days and glucose-washout 14-days. We evaluated the performance in inhibitory avoidance task and locomotor activity. We also determined acethylcholinesterase activity and gene expression from whole brain. In order to counteract the effect of hyperglycemia underlined by effects on acethylcholinesterase activity, we treated the animals with galantamine (0.05ng/g), an inhibitor of this enzyme. Also we evaluated the gene expression of insulin receptor and glucose transporter from zebrafish brain. The hyperglycemia promoted memory deficit in adult zebrafish, which can be explained by increased AChE activity. The ache mRNA levels from zebrafish brain were decrease in 111mM glucose group and returned to normal levels after 7 days of glucose withdrawal. Insulin receptors (insra-1, insra-2, insrb-1 and insrb-2) and glut-3 mRNA levels were not significantly changed. Our results also demonstrated that galantamine was able to reverse the memory deficit caused by hyperglycemia, demonstrating that these effects involve modulation of AChE activity. These data suggest that the memory impairment induced by hyperglycemia is underlined by the cholinergic dysfunction caused by the mechanisms involving the control of acetylcholinesterase function and gene expression.

An assay for lateral line regeneration in adult zebrafish

Due to the clinical importance of hearing and balance disorders in man, model organisms such as the zebrafish have been used to study lateral line development and regeneration. The zebrafish is particularly attractive for such studies because of its rapid development time and its high regenerative capacity. To date, zebrafish studies of lateral line regeneration have mainly utilized fish of the embryonic and larval stages because of the lower number of neuromasts at these stages. This has made quantitative analysis of lateral line regeneration/and or development easier in the earlier developmental stages. Because many zebrafish models of neurological and non-neurological diseases are studied in the adult fish and not in the embryo/larvae, we focused on developing a quantitative lateral line regenerative assay in adult zebrafish so that an assay was available that could be applied to current adult zebrafish disease models. Building on previous studies by Van Trump et al. that described procedures for ablation of hair cells in adult Mexican blind cave fish and zebrafish (Danio rerio), our assay was designed to allow quantitative comparison between control and experimental groups. This was accomplished by developing a regenerative neuromast standard curve based on the percent of neuromast reappearance over a 24 hr time period following gentamicin-induced necrosis of hair cells in a defined region of the lateral line. The assay was also designed to allow extension of the analysis to the individual hair cell level when a higher level of resolution is required.

Persistent impaired glucose metabolism in a zebrafish hyperglycemia model

Diabetes mellitus (DM) affects over 10% of the world's population. Hyperglycemia is the main feature for the diagnosis of this disease. The zebrafish (Danio rerio) is an established model organism for the study of various metabolic diseases. In this paper, hyperglycemic zebrafish, when immersed in a 111 mM glucose solution for 14 days, developed increased glycation of proteins from the eyes, decreased mRNA levels of insulin receptors in the muscle, and a reversion of high blood glucose level after treatment with anti-diabetic drugs (glimepiride and metformin) even after 7 days of glucose withdrawal. Additionally, hyperglycemic zebrafish developed an impaired response to exogenous insulin, which was recovered after 7 days of glucose withdrawal. These data suggest that the exposure of adult zebrafish to high glucose concentration is able to induce persistent metabolic changes probably underlined by a hyperinsulinemic state and impaired peripheral glucose metabolism.

Impact of a combined high cholesterol diet and high glucose environment on vasculature

AIMS

Vascular complications are the leading cause of mortality and morbidity in patients with diabetes. However, proper animal models of diabetic vasculopathy that recapitulate the accelerated progression of vascular lesions in human are unavailable. In the present study, we developed a zebrafish model of diabetic vascular complications and the methodology for quantifying vascular lesion formation real-time in the living diabetic zebrafish.

METHODS AND RESULTS

Wild type zebrafish (AB) and transgenic zebrafish lines of fli1:EGFP, lyz:EGFP, gata1:dsRed, double transgenic zebrafish of gata1:dsRed/fli1:EGFP were exposed to high cholesterol diet and 3% glucose (HCD-HG) for 10 days. The zebrafish model with HCD-HG treatment was characterized by significantly increased tissue levels of insulin, glucagon, glucose, total triglyceride and cholesterol. Confocal microscopic analysis further revealed that the diabetic larvae developed clearly thickened endothelial layers, distinct perivascular lipid depositions, substantial accumulations of inflammatory cells in the injured vasculature, and a decreased velocity of blood flow. Moreover, the vascular abnormalities were improved by the treatment of pioglitazone and metformin.

CONCLUSION

A combination of high cholesterol diet and high glucose exposure induces a rapid onset of vascular complications in zebrafish similar to the early atherosclerotic vascular injuries in mammalian diabetic models, suggesting that zebrafish may be used as a novel animal model for diabetic vasculopathy.

Animal models of diabetic retinopathy: doors to investigate pathogenesis and potential therapeutics

Effective and validated animal models are valuable to investigate the pathogenesis and potential therapeutics for human diseases. There is much concern for diabetic retinopathy (DR) in that it affects substantial number of working population all around the world, resulting in visual deterioration and social deprivation. In this review, we discuss animal models of DR based on different species of animals from zebrafish to monkeys and prerequisites for animal models. Despite criticisms on imprudent use of laboratory animals, we hope that animal models of DR will be appropriately utilized to deepen our understanding on the pathogenesis of DR and to support our struggle to find novel therapeutics against catastrophic visual loss from DR.

Imaging beta cell regeneration and interactions with islet vasculature in transparent adult zebrafish

Blood vessel networks provide nutrients and gaseous exchange that are essential for functions. Pancreatic islet capillaries deliver oxygen to endocrine cells while transporting hormones to organs and peripheral locations throughout the body. We have developed a zebrafish diabetes model in which adult islets can be followed in vivo during beta cell regeneration while calibrating changes in beta cell mass and fasting blood glucose levels. After genetic ablation, beta cells are initially dysfunctional or dying, and blood glucose levels increase fourfold. During a 2-week period, hyperglycemia eventually normalizes as beta cell mass regenerates. We show that mCherry-fluorescent, insulin-positive beta cells re-emerge in close contact with the vascular endothelium. Alterations in the dense vascular network of zebrafish islets were visualized by the expression of green fluorescent protein (GFP) in endothelial cells derived from the Fli transcription factor promoter. The rapid destruction and regeneration of beta cell mass was evaluated in the same animal over time, providing a functional model for investigating the interactions of islet cell types with vascular cells as well as the consequences of hyperglycemia on other tissues. Regenerating adult zebrafish can be utilized as vertebrate, metabolically active models for generating new insights into treatments for type 2 diabetes.

A novel, reliable method for repeated blood collection from aquarium fish

Collecting blood from laboratory animals is necessary for a wide variety of scientific studies, but the small size of the zebrafish makes this common procedure challenging. We developed a novel, minimally invasive method to collect repeated blood samples from adult zebrafish. This method minimizes trauma to the zebrafish and yields a low mortality rate of 2.3%. The maximum volume of blood that can be collected using this technique is approximately 2% of body weight. To avoid blood loss anemia and hemorrhagic death, we recommend that the total blood sample volume collected over repeat bleeds should be ≤0.4% of body weight per week, and ≤1% of body weight per 2 weeks. Additionally, we applied this method to the study of zebrafish glycolipid metabolism by measuring blood glucose and plasma triacylglyceride levels weekly over a 5-week period in both control and overfed zebrafish. The overfed fish developed significantly increased fasting blood glucose levels compared with normally fed fish. This new method of blood collection is essential for zebrafish or other small aquarium fish research requiring repeated blood samples, and increases the utility of the zebrafish as a model animal in hematological studies of human diseases.

A zebrafish model of diabetes mellitus and metabolic memory

Diabetes mellitus currently affects 346 million individuals and this is projected to increase to 400 million by 2030. Evidence from both the laboratory and large scale clinical trials has revealed that diabetic complications progress unimpeded via the phenomenon of metabolic memory even when glycemic control is pharmaceutically achieved. Gene expression can be stably altered through epigenetic changes which not only allow cells and organisms to quickly respond to changing environmental stimuli but also confer the ability of the cell to "memorize" these encounters once the stimulus is removed. As such, the roles that these mechanisms play in the metabolic memory phenomenon are currently being examined. We have recently reported the development of a zebrafish model of type I diabetes mellitus and characterized this model to show that diabetic zebrafish not only display the known secondary complications including the changes associated with diabetic retinopathy, diabetic nephropathy and impaired wound healing but also exhibit impaired caudal fin regeneration. This model is unique in that the zebrafish is capable to regenerate its damaged pancreas and restore a euglycemic state similar to what would be expected in post-transplant human patients. Moreover, multiple rounds of caudal fin amputation allow for the separation and study of pure epigenetic effects in an in vivo system without potential complicating factors from the previous diabetic state. Although euglycemia is achieved following pancreatic regeneration, the diabetic secondary complication of fin regeneration and skin wound healing persists indefinitely. In the case of impaired fin regeneration, this pathology is retained even after multiple rounds of fin regeneration in the daughter fin tissues. These observations point to an underlying epigenetic process existing in the metabolic memory state. Here we present the methods needed to successfully generate the diabetic and metabolic memory groups of fish and discuss the advantages of this model.

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

As previously reported by our laboratory, streptozocin-induced diabetes mellitus (DM) in adult zebrafish results in an impairment of tissue regeneration as monitored by caudal fin regeneration. Following streptozocin withdrawal, a recovery phase occurs to reestablish euglycemia, via pancreatic beta-cell regeneration. However, DM-associated impaired fin regeneration continues indefinitely in the metabolic memory (MM) state, allowing for subsequent molecular analysis of the underlying mechanisms of MM. This study focuses on elucidating the molecular basis that explains the DM-associated impaired fin regeneration and why it persists into the MM state with the aim of better understanding MM. Using a combination of microarray analysis and bioinformatics approaches, our study found that of the 14,900 transcripts analyzed, aberrant expression of 71 genes relating to tissue developmental and regeneration processes were identified in DM fish and the altered expression of these 71 genes persisted in MM fish. Key regulatory genes of major development and signal transduction pathways were identified among this group of 71. The aberrant expression of key regulatory genes in the DM state that persist into the MM state provides a plausible explanation on how hyperglycemia induced impaired fin regeneration in the adult zebrafish DM/MM model.

Metabolic memory and chronic diabetes complications: potential role for epigenetic mechanisms

Recent estimates indicate that diabetes mellitus currently affects more than 10 % of the world's population. Evidence from both the laboratory and large scale clinical trials has revealed that prolonged hyperglycemia induces chronic complications which persist and progress unimpeded even when glycemic control is pharmaceutically achieved via the phenomenon of metabolic memory. The epigenome is comprised of all chromatin modifications including post translational histone modification, expression control via miRNAs and the methylation of cytosine within DNA. Modifications of these epigenetic marks not only allow cells and organisms to quickly respond to changing environmental stimuli but also confer the ability of the cell to "memorize" these encounters. As such, these processes have gained much attention as potential molecular mechanisms underlying metabolic memory and chronic diabetic complications. Here we present a review of the very recent literature published pertaining to this subject.

Arthroplasty in veterans: analysis of cartilage, bone, serum, and synovial fluid reveals differences and similarities in osteoarthritis with and without comorbid diabetes

Osteoarthritis patients with diabetes who receive total knee arthroplasty are more vulnerable to complications, including aseptic loosening and need for revision surgery. To elucidate mechanisms related to arthroplasty failure in diabetes, we examined serum and synovial fluid markers as well as collagen crosslinks in bone and cartilage of 20 patients (10 with diabetes, 10 controls without) undergoing this procedure. Hemoglobin A1c, body mass index, bone alkaline phosphatase, leptin, osteocalcin, and pyridinium were analyzed along with tissue content of the crosslinks hydroxylysylpyridinoline, lysylpyridinoline, and pentosidine. Pentosidine levels in tissue specimens from diabetic subjects were higher than in control subjects. Osteocalcin levels negatively correlated with hydroxylysylpyridinoline levels in cartilage. Osteocalcin levels also negatively correlated with pentosidine levels in cartilage, but only in subjects with diabetes. This study suggests potential metabolic mechanisms for arthroplasty failure in patients with diabetes.

Heritable transmission of diabetic metabolic memory in zebrafish correlates with DNA hypomethylation and aberrant gene expression

Metabolic memory (MM) is the phenomenon whereby diabetes complications persist and progress after glycemic recovery is achieved. Here, we present data showing that MM is heritable and that the transmission correlates with hyperglycemia-induced DNA hypomethylation and aberrant gene expression. Streptozocin was used to induce hyperglycemia in adult zebrafish, and then, following streptozocin withdrawal, a recovery phase was allowed to reestablish a euglycemic state. Blood glucose and serum insulin returned to physiological levels during the first 2 weeks of the recovery phase as a result of pancreatic β-cell regeneration. In contrast, caudal fin regeneration and skin wound healing remained impaired to the same extent as in diabetic fish, and this impairment was transmissible to daughter cell tissue. Daughter tissue that was never exposed to hyperglycemia, but was derived from tissue that was, did not accumulate AGEs or exhibit increased levels of oxidative stress. However, CpG island methylation and genome-wide microarray expression analyses revealed the persistence of hyperglycemia-induced global DNA hypomethylation that correlated with aberrant gene expression for a subset of loci in this daughter tissue. Collectively, the data presented here implicate the epigenetic mechanism of DNA methylation as a potential contributor to the MM phenomenon.