Correction of diabetic alterations by glucokinase.

Hyperglycemia is a common feature of diabetes mellitus. It results from a decrease in glucose utilization by the liver and peripheral tissues and an increase in hepatic glucose production. Glucose phosphorylation by glucokinase is an initial event in glucose metabolism by the liver. However, glucokinase gene expression is very low in diabetic animals. Transgenic mice expressing the P-enolpyruvate carboxykinase/glucokinase chimeric gene were generated to study whether the return of the expression of glucokinase in the liver of diabetic mice might prevent metabolic alterations. In contrast to nontransgenic mice treated with streptozotocin, mice with the transgene previously treated with streptozotocin showed high levels of both glucokinase mRNA and its enzyme activity in the liver, which were associated with an increase in intracellular levels of glucose 6-phosphate and glycogen. The liver of these mice also showed an increase in pyruvate kinase activity and lactate production. Furthermore, normalization of both the expression of genes involved in gluconeogenesis and ketogenesis in the liver and the production of glucose and ketone body by hepatocytes in primary culture were observed in streptozotocin-treated transgenic mice. Thus, glycolysis was induced while gluconeogenesis and ketogenesis were blocked in the liver of diabetic mice expressing glucokinase. This was associated with normalization of blood glucose, ketone bodies, triglycerides, and free fatty acids even in the absence of insulin. These results suggest that the expression of glucokinase during diabetes might be a new approach to the normalization of hyperglycemia.

Prevention of diabetic alterations in transgenic mice overexpressing Myc in the liver.

Recent studies have demonstrated that the overexpression of the c-myc gene in the liver of transgenic mice leads to an increase in both utilization and accumulation of glucose in the liver, suggesting that c-Myc transcription factor is involved in the control of liver carbohydrate metabolism in vivo. To determine whether the increase in c-Myc might control glucose homeostasis, an intraperitoneal glucose tolerance test was performed. Transgenic mice showed lower levels of blood glucose than control animals, indicating that the overexpression of c-Myc led to an increase of blood glucose disposal by the liver. Thus, the increase in c-Myc might counteract diabetic hyperglycemia. In contrast to control mice, transgenic mice treated with streptozotocin showed normalization of concentrations of blood glucose, ketone bodies, triacylglycerols and free fatty acids in the absence of insulin. These findings resulted from the normalization of liver metabolism in these animals. While low glucokinase activity was detected in the liver of diabetic control mice, high levels of both glucokinase mRNA and enzyme activity were noted in the liver of streptozotocin-treated transgenic mice, which led to an increase in intracellular levels of glucose 6-phosphate and glycogen. The liver of these mice also showed an increase in pyruvate kinase activity and lactate production. Furthermore, normalization of both the expression of genes involved in the control of gluconeogenesis and ketogenesis and the production of glucose and ketone bodies was observed in streptozotocin-treated transgenic mice. Thus, these results suggested that c-Myc counteracted diabetic alterations through its ability to induce hepatic glucose uptake and utilization and to block the activation of gluconeogenesis and ketogenesis.

Regulated expression of the obese gene product (leptin) in white adipose tissue and 3T3-L1 adipocytes.

A mutation within the obese gene was recently identified as the genetic basis for obesity in the ob/ob mouse. The obese gene product, leptin, is a 16-kDa protein expressed predominantly in adipose tissue. Consistent with leptin's postulated role as an extracellular signaling protein, human embryonic kidney 293 cells transfected with the obese gene secreted leptin with minimal intracellular accumulation. Upon differentiation of 3T3-L1 preadipocytes into adipocytes, the leptin mRNA was expressed concomitant with mRNAs encoding adipocyte marker proteins. A factor(s) present in calf serum markedly activated expression of leptin by fully differentiated 3T3-L1 adipocytes. A 16-hr fast decreased (by approximately 85%) the leptin mRNA level of adipose tissue of lean (ob/+ or +/+) mice but had no effect on the approximately 4-fold higher level in obese (ob/ob) littermates. Since the mutation at the ob locus fails to produce the functional protein, yet its cognate mRNA is overproduced, it appears that leptin is necessary for its own downregulation. Leptin mRNA was also suppressed in adipose tissue of rats during a 16-hr fast and was rapidly induced during a 4-hr refeeding period. Insulin deficiency provoked by streptozotocin also markedly down-regulated leptin mRNA and this suppression was rapidly reversed by insulin. These results suggest that insulin may regulate the expression of leptin.

Modulation of Sarco/Endoplasmic Reticulum Ca2+-ATPase 2 (SERCA2) function by acetylation following the treatment with histone deacetylase inhibitor suberoylanilide hydroxamic acid (SAHA)

Background: Acetylation and deacetylation at specific lysine (K) residues is mediated by histone acetylases (HATs) and deacetylases (HDACs), respectively. HATs and HDACs act on both histone and non-histone proteins, regulating various processes, including cardiac impulse propagation. Aim of the present work was to establish whether the function of the Ca2+ ATPase SERCA2, one of the major players in Ca2+ reuptake during excitation-contraction coupling in cardiac myocytes (CMs), could be modulated by direct K acetylation. Materials and methods: HL-1 atrial mouse cells (donated by Prof. Claycomb), zebrafish and Streptozotocin-induced diabetic rat CMs were treated with the pan-inhibitor of class I and II HDACs suberanilohydroxamic acid (SAHA) for 1.5 hour. Evaluation of SERCA2 acetylation was analyzed by co-immunoprecipitation. SERCA2 activity was measured on microsomes by pyruvate/NADH coupled reaction assay. SERCA2 mutants were obtained after cloning wild-type and mutated sequences into the pCDNA3 vector and transfected into HEK cells. Ca2+ transients in CMs (loading with Fluo3-AM, field stimulation, 0.5 Hz) and in transfected HEK cells (loading with FLUO-4, caffeine pulse) were recorded. Results: Co-Immunoprecipitation experiments performed on HL-1 cells demonstrated a significant increase in the acetylation of SERCA2 after SAHA-treatment (2.5 µM, n=3). This was associated with an increase in SERCA2 activity in microsomes obtained from HL-1 cells, after SAHA exposure (n=5). Accordingly, SAHA-treatment significantly shortened the Ca2+ reuptake time of adult zebrafish CMs. Further, SAHA 2.5 nM restored to control values the recovery time of Ca2+ transients decay in diabetic rat CMs. HDAC inhibition also improved contraction parameters, such as fraction of shortening, and increased pump activity in microsomes isolated from diabetic CMs (n=4). Notably, the K464, identified by bioinformatic tools as the most probable acetylation site on human SERCA2a, was mutated into Glutamine (Q) or Arginine (R) mimicking acetylation and deacetylation respectively. Measurements of Ca2+ transients in HEK cells revealed that the substitution of K464 with R significantly delayed the transient recovery time, thus indicating that deacetylation has a negative impact on SERCA2 function. Conclusions: Our results indicate that SERCA2 function can be improved by pro-acetylation interventions and that this mechanism of regulation is conserved among species. Therefore, the present work provides the basis to open the search for novel pharmacological tools able to specifically improve SERCA2 activity in diseases where its expression and/or function is impaired, such as diabetic cardiomyopathy.

Implications physiopathologiques de la Nestine lors du remodelage pulmonaire et cardiaque à la suite de l’infarctus du myocarde, du diabète et de l’hypertension pulmonaire

Il est reconnu que la protéine filamenteuse intermédiaire Nestine est exprimée lors du processus de cicatrisation et du remodelage fibrotique. De plus, nous avons identifié l’expression de la Nestine au sein de deux populations distinctes qui sont directement impliquées dans les réponses de fibroses réparative et réactive. Ainsi, une population de cellules souches neurales progénitrices résidentes du coeur de rat adulte exprime la Nestine et a été identifiée à titre de substrat de l’angiogenèse et de la neurogenèse cardiaque. Également, la Nestine est exprimée par les myofibroblastes cicatriciels cardiaques et il a été établi que la protéine filamenteuse intermédiaire joue un rôle dans la prolifération de ces cellules. Ainsi, l’objectif général de cette thèse était de mieux comprendre les évènements cellulaires impliqués dans la réponse neurogénique des cellules souches neurales progénitrices résidentes cardiaques Nestine(+) (CSNPRCN(+)) lors de la fibrose réparative cardiaque et d’explorer si l’apparition de fibroblastes Nestine(+) est associée avec la réponse de fibrose réactive secondaire du remodelage pulmonaire. Une première publication nous a permis d’établir qu’il existe une régulation à la hausse de l’expression de la GAP43 (growth associated protein 43) et que cet événement transitoire précède l’acquisition d’un phénotype neuronal par les CSNPRCN(+) lors du processus de cicatrisation cardiaque chez le rat ayant subi un infarctus du myocarde. De plus, la surimposition de la condition diabétique de type 1, via l’injection unique de Streptozotocine chez le rat, abolit la réponse neurogénique des CSNPRCN(+), qui est normalement induite à la suite de l’ischémie cardiaque ou de l’administration de 6-hydroxydopamine. Le second article a démontré que le développement aigu de la fibrose pulmonaire secondaire de l’infarctus du myocarde chez le rat est associé avec une augmentation de l’expression protéique de la Nestine et de l’apparition de myofibroblastes pulmonaires Nestine(+). Également, le traitement de fibroblastes pulmonaires avec des facteurs de croissances peptidiques pro-fibrotiques a augmenté l’expression de la Nestine par ces cellules. Enfin, le développement initial de la condition diabétique de type 1 chez le rat est associé avec une absence de fibrose réactive pulmonaire et à une réduction significative des niveaux protéiques et d’ARN messager de la Nestine pulmonaire. Finalement, la troisième étude représentait quant à elle un prolongement de la deuxième étude et a alors examiné le remodelage pulmonaire chronique chez un modèle établi d’hypertension pulmonaire. Ainsi, les poumons de rats adultes mâles soumis à l’hypoxie hypobarique durant 3 semaines présentent un remodelage vasculaire, une fibrose réactive et une augmentation des niveaux d’ARN messager et de la protéine Nestine. De plus, nos résultats ont démontré que la Nestine, plutôt que l’alpha-actine du muscle lisse, est un marqueur plus approprié des diverses populations de fibroblastes pulmonaires activés. Également, nos données suggèrent que les fibroblastes pulmonaires activés proviendraient en partie de fibroblastes résidents, ainsi que des processus de transition épithélio-mésenchymateuse et de transition endothélio-mésenchymateuse. Collectivement, ces études ont démontré que des populations distinctes de cellules Nestine(+) jouent un rôle majeur dans la fibrose réparative cardiaque et la fibrose réactive pulmonaire.

High glucose transactivates the EGF receptor and up-regulates serum glucocorticoid kinase in the proximal tubule

Background. Serum glucocorticoid regulated kinase (SGK-1) is induced in the kidney in diabetes mellitus. However, its role in the proximal tubule is unclear. This study determined the expression and functional role of SGK-1 in PTCs in high glucose conditions. As the epidermal growth factor (EGF) receptor is activated by both EGF and other factors implicated in diabetic nephropathy, the relationship of SGK-1 with EGFR activity was assessed. Methods. mRNA and protein expression of SGK-1 and mRNA expression of the sodium hydrogen exchanger NHE3 were measured in human PTCs exposed to 5 mmol/L (control) and 25 mmol/L (high) glucose. The effects of SGK-1 on cell growth, apoptosis, and progression through the cell cycle and NHE3 mRNA were examined following overexpression of SGK-1 in PTCs. The role of EGFR activation in observed changes was assessed by phospho-EGFR expression, and response to the EGFR blocker PKI166. SGK-1 expression was then assessed in vivo in a model of streptozotocin-induced diabetes mellitus type 2. Results. A total of 25 mmol/L glucose and EGF (10 ng/mL) increased SGK-1 mRNA (P < 0.005 and P < 0.002, respectively) and protein (both P < 0.02) expression. High glucose and overexpression of SGK-1 increased NHE3 mRNA (P < 0.05) and EGFR phosphorylation (P < 0.01), which were reversed by PKI166. SGK-1 overexpression increased PTC growth (P < 0.0001), progression through the cell cycle (P < 0.001), and increased NHE3 mRNA (P < 0.01), which were all reversed with PKI166. Overexpression of SGK-1 also protected against apoptosis induced in the PTCs (P < 0.0001). Up-regulation of tubular SGK-1 mRNA in diabetes mellitus was confirmed in vivo. Oral treatment with PKI166 attenuated this increase by 51%. No EGF protein was detectable in PTCs, suggestive of phosphorylation of the EGFR by high glucose and downstream induction of SGK-1. Conclusion. The effects of high glucose on PTC proliferation, reduced apoptosis and increased NHE3 mRNA levels are mediated by EGFR-dependent up-regulation of SGK-1.

Transglutaminase inhibition ameliorates experimental diabetic nephropathy

Diabetic nephropathy is characterized by excessive extracellular matrix accumulation resulting in renal scarring and end-stage renal disease. Previous studies have suggested that transglutaminase type 2, by formation of its protein crosslink product epsilon-(gamma-glutamyl)lysine, alters extracellular matrix homeostasis, causing basement membrane thickening and expansion of the mesangium and interstitium. To determine whether transglutaminase inhibition can slow the progression of chronic experimental diabetic nephropathy over an extended treatment period, the inhibitor NTU281 was given to uninephrectomized streptozotocin-induced diabetic rats for up to 8 months. Effective transglutaminase inhibition significantly reversed the increased serum creatinine and albuminuria in the diabetic rats. These improvements were accompanied by a fivefold decrease in glomerulosclerosis and a sixfold reduction in tubulointerstitial scarring. This was associated with reductions in collagen IV accumulation by 4 months, along with reductions in collagens I and III by 8 months. This inhibition also decreased the number of myofibroblasts, suggesting that tissue transglutaminase may play a role in myofibroblast transformation. Our study suggests that transglutaminase inhibition ameliorates the progression of experimental diabetic nephropathy and can be considered for clinical application.

Do changes in transglutaminase activity alter latent transforming growth factor beta activation in experimental diabetic nephropathy?

Background. Diabetic nephropathy is the leading cause of end-stage kidney failure worldwide. It is characterized by excessive extracellular matrix accumulation. Transforming growth factor beta 1 (TGF-ß1) is a fibrogenic cytokine playing a major role in the healing process and scarring by regulating extracellular matrix turnover, cell proliferation and epithelial mesanchymal transdifferentiation. Newly synthesized TGF-ß is released as a latent, biologically inactive complex. The cross-linking of the large latent TGF-ß to the extracellular matrix by transglutaminase 2 (TG2) is one of the key mechanisms of recruitment and activation of this cytokine. TG2 is an enzyme catalyzing an acyl transfer reaction leading to the formation of a stable e(?-glutamyl)-lysine cross-link between peptides.Methods. To investigate if changes in TG activity can modulate TGF-ß1 activation, we used the mink lung cell bioassay to assess TGF-ß activity in the streptozotocin model of diabetic nephropathy treated with TG inhibitor NTU281 and in TG2 overexpressing opossum kidney (OK) proximal tubular epithelial cells.Results. Application of the site-directed TG inhibitor NTU281 caused a 25% reduction in kidney levels of active TGF-ß1. Specific upregulation of TG2 in OK proximal tubular epithelial cells increased latent TGF-ß recruitment and activation by 20.7% and 19.7%, respectively, in co-cultures with latent TGF-ß binding protein producing fibroblasts.Conclusions. Regulation of TG2 directly influences the level of active TGF-ß1, and thus, TG inhibition may exert a renoprotective effect by targeting not only a direct extracellular matrix deposition but also TGF-ß1 activation and recruitment.

Somatic cell gene therapy for diabetes mellitus: engineering a surrogate B-cell

Improved methods of insulin delivery are required for the treatment of insulin-dependent diabetes mellitus (IDDM) to achieve a more physiological profile of glucose homeostasis. Somatic cell gene therapy offers the prospect that insulin could be delivered by an autologous cell implant, engineered to secrete insulin in response to glucose. This study explores the feasibility of manipulating somatic cells to behave as a surrogate insulin-secreting β-cells. Initial studies were conducted using mouse pituitary AtT20 cells as a model, since these cells possess an endogenous complement of enzymes capable of processing proinsulin to mature insulin. Glucose sensitive insulin secretion was conferred to these cells by transfection with plasmids containing the human preproinsulin gene (hppI-1) and the GLUT2 gene for the glucose transporter isoform 2. Insulin secretion was responsive to changes in the glucose concentration up to about 50μM. Further studies to up-rate this glucose sensitivity into the mM range will require manipulation of the hexokinase and glucokinase enzymes. Intraperitoneal implantation of the manipulated AtT20 cells into athymic nude mice with streptozotocin-induced diabetes resulted in decreased plasma glucose concentrations. The cells formed vascularised tumours in vivo which were shown to contain insulin-secreting cells. To achieve proinsulin processing in non-endocrine cells, co-transfection with a suitable enzyme, or mutagenesis of the proinsulin itself are necessary. The mutation of the human preproinsulin gene to the consensus sequence for cleavage by the subtilisin-like serine protease, furin, was carried out. Co-transfection of human fibroblasts with wild-type proinsulin and furin resulted in 58% conversion to mature insulin by these cells. Intraperitoneal implantation of the mature-insulin secreting human fibroblasts into the diabetic nude mouse animal model gave less encouraging results than the AtT20 cells, apparently due to poor vascularisation. Cell aggregations removed from the mice at autopsy were shown to contain insulin secreting cells only at the periphery. This thesis provides evidence that it is possible to construct, by cellular engineering, a glucose-sensitive insulin-secreting surrogate β-cell. Therefore, somatic cell gene therapy offers a feasible alternative for insulin delivery in IDDM patients.

Investigation of potential intervention targets to improve insulin action: a therapeutic approach

Impaired insulin action (insulin resistance) is a key factor in the pathogenesis of diabetes mellitus. To investigate therapeutic targets against insulin resistance, this thesis explores the mechanism of action of pharmacological agents and exogenous peptides known or suspected to modify insulin action. These included leptin, a hormone primarily involved in the regulation of body weight; sibutramine, an antiobesity agent; plant-derived compounds (pinitol and chamaemeloside) and agents known to affect insulin sensitivity, e.g. metformin, tolbutamide, thiazolidinediones, vanadyl sulphate and thioctic acid. Models used for investigation included the L6 skeletal muscle cell line and isolated skeletal muscles. In vivo studies were undertaken to investigate glycaemia, insulinaemia, satiety and body weight in streptozotocin-induced diabetic mice and obese (ob/ob) mice. Leptin acutely altered insulin action in skeletal muscle cells via the short form of the leptin receptor. This direct action of leptin was mediated via a pathway involving PI 3-kinase but not Jak2. The active metabolites of sibutramine had antidiabetic properties in vivo and directly improved insulin sensitivity in vitro. This effect appeared to be conducted via a non-PI 3-kinase-mediated increase in protein synthesis with facilitated glucose transport, and was independent of the serotonin and noradrenaline reuptake inhibition produced by sibutramine. Pinitol (a methyl inositol) had an insulin mimetic effect and was an effective glucose-lowering agent in insulinopenic states, acting directly on skeletal muscle. Conversely chamaemeloside appeared to improve glucose tolerance without directly altering glucose transport. Metformin directly increased basal glucose uptake independently of PI 3-kinase, possibly via an increase in the intrinsic activity of glucose transporters. Neither tolbutamide nor thiazolidinediones directly altered insulin sensitivity in L6 skeletal muscle cells: however vanadyl sulphate and thioctic acid increased glucose transport but appeared to exert toxic effects at therapeutic concentrations. Examination of glucose transport in skeletal muscle in this thesis has identified various components of post-receptor insulin signalling pathways which may be targeted to ameliorate insulin resistance. Type 2 Diabetes Mellitus Obesity L6 Skeletal Muscle Cells Glucose Transport Insulin Signalling 2

Insulin gene therapy for the treatment of diabetes mellitus

Currently available treatments for insulin-dependent diabetes mellitus are often inadequate in terms of both efficacy and patient compliance. Gene therapy offers the possibility of a novel and improved method by which exogenous insulin can be delivered to a patient. This was approached in the present study by constructing a novel insulin-secreting cell line. For the purposes of this work immortalized cell lines were used. Fibroblasts and pituitary cells were transfected with the human preproisinulin gene to create stable lines of proinsulin- and insulin-secreting cells. The effect of known β-cell secretagogues on these cells were investigated, and found mostly to have no stimulatory effect, although IBMX, arginine and ZnSO4 each increased the rate of secretion. Cyclosporin (CyA) is currently the immunosuppresant of choice for transplant recipients; the effect of this treatment on endogenous β-cell function was assessed both in vivo and in vitro. Therapeutic doses of CyA were found to reduce plasma insulin concentrations and to impair glucose tolerance. The effect of immunoisolation on insulin release by HIT T15 cells was also investigated. The presence of an alginate membrane was found to severely impair insulin release. For the first implantation of the insulin-secreting cells, the animal model selected was the athymic nude mouse. This animal is immunoincompetent, and hence the use of an immunosuppressive regimen is circumvented. Graft function was assessed by measurement of plasma human C peptide concentrations, using a highly specific assay. Intraperitoneal implantation of genetically manipulated insulin-secreting pituitary cells into nude mice subsequently treated with a large dose of streptozotocin (STZ) resulted in a significantly delayed onset of hyperglycaemia when compared to control animals. Consumption of a ZnSO4 solution was shown to increase human C peptide release by the implant. Ensuing studies in nude mice examined the efficacy of different implantation sites, and included histochemical examination of the tumours. Aldehyde fuchsin staining and immunocytochemical processing demonstrated the presence of insulin containing cells within the excised tissue. Following initial investigations in nude mice, implantation studies were performed in CyA-immunosuppressed normal and STZ-diabetic mice. Graft function was found to be less efficacious, possibly due to the subcutaneous implantation site, or to the immunosuppresive regimen. Histochemical and transmission electron microscopic analysis of the tumour-like cell clusters found at autopsy revealed necrosis of cells at the core, but essentially normal cell morphology, with dense secretory granules in peripheral cells. The thesis provides evidence that gene therapy offers a feasibly new approach to insulin delivery.

Elevated ε-(γ-glutamyl)lysine in human diabetic nephropathy results from increased expression and cellular release of tissue transglutaminase

Introduction: Diabetic nephropathy (DN) is the leading cause of chronic kidney failure, however the mechanisms underlying the characteristic expansion of the extracellular matrix (ECM) in diabetic kidneys remain controversial and unclear. In non-diabetic kidney scarring the protein crosslinking enzyme tissue transglutaminase (tTg) has been implicated in this process by the formation of increased ε-(γ-glutamyl)lysine bonds between ECM components in both experimental and human disease. Studies in db/db diabetic mice and in streptozotocin-treated rats have suggested a similar mechanism, although the relevance of this to human disease has not been addressed. Methods: We have undertaken a retrospective analysis of renal biopsies from 16 DN patients with type 2 diabetes mellitus using an immunohistochemical and immunofl uorescence approach, with tTg and ε-(γ-glutamyl)lysine crosslink quantified by confocal microscopy. Results: Immunofl uorescent analysis of human biopsies (confocal microscopy) showed increases in levels of tTg (+1,266%, p <0.001) and ε-(γ-glutamyl)lysine (+486%, p <0.001) in kidneys with DN compared to normal. Changes were predominantly in the extracellular periglomerular and peritubular areas. tTg staining correlated with e-(?-glutamyl)lysine (r = 0.615, p <0.01) and renal scarring (Masson's trichrome, r = 0.728, p <0.001). Significant changes in e-(?-glutamyl)lysine were also noted intracellularly in some (=5%) tubular epithelial cells. This is consistent with cells undergoing a novel transglutaminase-mediated cell death process in response to Ca influx and subsequent activation of intracellular tTg. Conclusion: Changes in tTg and ε-(γ- glutamyl)lysine occur in human DN. Cellular export of tTg may therefore be a factor in the perpetuation of DN by crosslinking and stabilisation of the ECM, while intracellular activation may lead to cell death contributing towards tubular atrophy. Copyright © 2004 S. Karger AG, Basel.

Increases in renal ε-(γ-glutamyl)-lysine crosslinks result from compartment-specific changes in tissue transglutaminase in early experimental diabetic nephropathy:Pathologic implications

Diabetic nephropathy (DN) is characterized by an early, progressive expansion and sclerosis of the glomerular mesangium leading to glomerulosclerosis. This is associated with parallel fibrosis of the renal interstitium. In experimental renal scarring, the protein cross-linking enzyme, tissue transglutaminase (tTg), is up-regulated and externalized causing an increase in its crosslink product, e-(γ-glutamyl)-lysine, in the extracellular space. This potentially contributes to the extracellular matrix (ECM) accumulation central to tissue fibrosis by increasing deposition and inhibiting breakdown. We investigated if a similar mechanism may contribute to the ECM expansion characteristic of DN using the rat streptozotocin model over 120 days. Whole kidney e-(γ-glutamyl)-lysine (HPLC analysis) was significantly increased from Day 90 (+337%) and peaked at Day 120 (+650%) (p <0.05). Immunofluorescence showed this increase to be predominantly extracellular in the peritubular interstitial space, but also in individual glomeruli. Total kidney transglutaminase (Tg) was not elevated. However, using a Tg in situ activity assay, increased Tg was detected in both the extracellular interstitial space and glomeruli by Day 60, with a maximal 53% increase at Day 120 (p <0.05). Using a specific anti-tTg antibody, immunohistochemistry showed a similar increase in extracellular enzyme in the interstitium and glomeruli. To biochemically characterize glomerular changes, glomeruli were isolated by selective sieving. In line with whole kidney measurement, there was an increase in glomerular e-(γ-glutamyl) lysine (+ 361%); however, in the glomeruli this was associated with increases in Tg activity (+228%) and tTg antigen by Western blotting (+215%). Importantly, the ratio of glomerular e-(γ-glutamyl) lysine to hydroxyproline increased by 2.2-fold. In DN, changes in the kidney result in increased translocation of tTg to the extracellular environment where high Ca2+ and low GTP levels allow its activation. In the tubulointerstitium this is independent of increased tTg production, but dependent in the glomerulus. This leads to excessive ECM cross-linking, contributing to the renal fibrosis characteristic of progressive DN.

β-cell-specific glucocorticoid reactivation attenuates inflammatory β-cell destruction

Progression and severity of type 1 diabetes is dependent upon inflammatory induction of nitric oxide production and consequent pancreatic β-cell damage. Glucocorticoids (GCs) are highly effective anti-inflammatory agents but have been precluded in type 1 diabetes and in islet transplantation protocols because they exacerbated insulin resistance and suppressed β-cell insulin secretion at the high-doses employed clinically. In contrast, physiological-range elevation of GC action within β-cells ameliorated lipotoxic β-cell failure in transgenic mice overexpressing the intracellular enzyme 11β-hydroxysteroid dehydrogenase type 1 (MIP-HSD1^tg/+ mice). Here, we tested the hypothesis that elevated β-cell 11beta-HSD1 protects against the β-cell destruction elicited by streptozotocin (STZ), a toxin that dose-dependently mimics aspects of inflammatory and autoimmune β-cell destruction. MIP-HSD1^tg/+ mice exhibited an episodic protection from the severe hyperglycemia caused by a single high dose of STZ associated with higher and sustained β-cell survival, maintained β-cell replicative potential, higher plasma and islet insulin levels, reduced inflammatory macrophage infiltration and increased anti-inflammatory T regulatory cell content. MIP-HSD1^tg/+ mice also completely resisted mild hyperglycemia and insulitis induced by multiple low-dose STZ administration. In vitro, MIP-HSD1^tg/+ islets exhibited attenuated STZ-induced nitric oxide production, an effect reversed with a specific 11beta-HSD1 inhibitor. GC regeneration selectively within β-cells protects against inflammatory β-cell destruction, suggesting therapeutic targeting of 11beta-HSD1 may ameliorate processes that exacerbate type 1 diabetes and that hinder islet transplantation.

Alterações hepáticas na expressão gênica e atividade da catalase e superóxido dimutase em ratos diabéticos induzidos por estreptozootocina

The correlation between the type 1 diabetes mellitus and oxidative stress have been described in several studies, however its underlying mechanisms are not fully elucidated. The present work aimed to evaluate the effects of four weeks of streptozootocin-induced (STZ) diabetes in the redox homeostasis of rat hepatocytes. Thus, the liver of male Wistar rats from control and diabetic groups were collected and the activity and expression of antioxidant enzymes, as well the main markers of oxidative stress and content of H2O2 in these tissues were measured. The diabetes induced the activity of superoxide dismutase (SOD) and the gene expression of its mitochondrial isoform, SOD2. However, the expression of SOD1, the cytoplasmic isoform, was reduced by this disease. The activity and expression of catalase (CAT), as well the expression of glutathione peroxidase 1 (GPX1) and peroxiredoxin 4 (PRX4) were drastically reduced in the hepatocytes of diabetics rats. Even with this debility in the peroxidases mRNA expression, the content of H2O2 was reduced in the liver of diabetics rats when compared to the control group. The diabetes caused an increase of lipid peroxidation and a decrease of protein thiol content, showing that this disease causes distinct oxidative effects in different cell biomolecules. Our results indicate that four week of diabetes induced by STZ is already enough to compromise the enzymatic antioxidant systems of the hepatocytes.