Cellular basis of diabetic nephropathy: II. The transforming growth factor-beta system and diabetic nephropathy lesions in type 1 diabetes

Oxidative Stress in Type 2 Diabetes: Impacts from Pathogenesis to Lifestyle Modifications

Oxidative stress is a critical factor in the pathogenesis and progression of diabetes and its associated complications. The imbalance between reactive oxygen species (ROS) production and the body's antioxidant defence mechanisms leads to cellular damage and dysfunction. In diabetes, chronic hyperglycaemia and mitochondrial dysfunction contribute to increased ROS production, further exacerbating oxidative stress. This oxidative burden adversely affects various aspects of diabetes, including impaired beta-cell function and insulin resistance, leading to disrupted glucose regulation. Additionally, oxidative stress-induced damage to blood vessels and impaired endothelial function contribute to the development of diabetic vascular complications such as retinopathy, nephropathy, and cardiovascular diseases. Moreover, organs and tissues throughout the body, including the kidneys, nerves, and eyes, are vulnerable to oxidative stress, resulting in diabetic nephropathy, neuropathy, and retinopathy. Strategies to mitigate oxidative stress in diabetes include antioxidant therapy, lifestyle modifications, and effective management of hyperglycaemia. However, further research is necessary to comprehensively understand the underlying mechanisms of oxidative stress in diabetes and to evaluate the efficacy of antioxidant interventions in preventing and treating diabetic complications. By addressing oxidative stress, it might be possible to alleviate the burden of diabetes and improve patient outcomes.

Anti-diabetic and hypolipidemic effects of Cinnamon cassia bark extracts: an in vitro, in vivo, and in silico approach

The present investigation was aimed to study the anti-diabetic and hypolipidemic potential of Cinnamon cassia (Lauraceae family) bark in streptozotocin (STZ)-induced diabetic rats. The preliminary phytochemical analysis (hexane, petroleum ether, chloroform, ethanol, methanol, and aqueous extracts), GC-MS analysis (ethanol), in vitro (aqueous, ethanol and methanol), in vivo (ethanol) and in silico anti-diabetic activity with hypolipidemic effect of C. cassia bark was analysed. The ethanolic extract of the C. cassia bark has a fine inhibitory activity than the aqueous and methanolic extract. Out of 20 different compounds identified, seven compounds were biologically active, and 9-octadecenoic acid has highly interacted with PPARα/γ in docking studies. The levels of diabetic markers, enzymes, and lipid profiles were altered in STZ-induced rats, but after the treatment of C. cassia, the levels were returned to the normal. The study may prove the ethanolic extract of C. cassia has a powerful anti-diabetic and anti-hyperlipidemic activity.

Mesenchymal stem cells derived from the kidney can ameliorate diabetic nephropathy through the TGF-β/Smad signaling pathway

Diabetic nephropathy (DN) has been introduced as one of the main microvascular complications in diabetic patients, the most common cause of end-stage renal disease (ESRD). Based on the therapeutic potential of mesenchymal stem cells in tissue repair, we aimed to test the hypothesis that kidney stem cells (KSCs) might be effective in the kidney regeneration process. Stem cells from rat kidney were separated, and the surface stem cell markers were determined by flow cytometry analysis. Thirty-two Sprague Dawley rats were divided into four groups (control, control that received kidney stem cells, diabetic, diabetic treated with stem cells). To establish diabetic, model STZ (streptozotocin) (60 mg/kg) was used. The KSCs were injected into experimental groups via tail vein (2 × 106 cells/rat). In order to determine the impact of stem cells on the function and structure of the kidney, biochemical and histological parameters were measured. Further, the expression of miRNA-29a, miR-192, IL-1β, and TGF-β was determined through the real-time PCR technique. Phosphorylation of Smad2/3 was evaluated by using the standard western blotting. The KSCs significantly reduced blood nitrogen (BUN), serum creatinine (Scr), and 24-h urinary proteins in DN (P < 0.05). IL-1β and TGF-β significantly increased in the kidney of diabetic rats. In addition, the expression of miR-29a is significantly increased, whereas miR-192 decreased after treatment with KSCs (P < 0.05). Diabetic rats showed an increased level of phosphorylation of both Smad2 and Smad3 (P < 0.05). Periodic acid-Schiff (PAS) staining showed improved histopathological changes in the presence of KSCs. Stem cells derived from adult rat kidney may be an option for treating the early DN to improve the functions and structure of kidneys in rats with DN.

MicroRNA-10a/b inhibit TGF-β/Smad-induced renal fibrosis by targeting TGF-β receptor 1 in diabetic kidney disease

TGF-β/Smad signaling plays a vital role in the development of fibrosis in diabetic kidney disease (DKD). However, remedies targeting key elements in TGF-β/Smad signaling are lacking. Here, we found that TGF-β receptor 1 (TGFBR1), a key protein in TGF-β/Smad signaling, was upregulated in kidney from diabetic mice and patients with DKD. Induction of TGFBR1 was regulated by microRNA-10a and -10b (miR-10a/b) by a post-transcriptional mechanism. Furthermore, the decreased XRN2, an exoribonuclease, was identified to contribute to affecting miR-10a/b maturation in vitro. In streptozotocin (STZ)-induced DKD mice, preventing the reduction of miR-10a/b in the kidney by an in situ lentivirus-injection method attenuated collagen deposition and foot process effacement, whereas deprivation of miR-10a/b aggravated renal fibrosis. Mechanistically, manipulating miR-10a/b in the kidney influenced TGFBR1 protein expression, TGF-β/Smad signaling activation, and downstream pro-fibrotic genes expression including fibronectin (FN) and α-smooth muscle actin (α-SMA). In a cohort of patients diagnosed DKD, renal miR-10a/b expressions were downregulated, whereas both TGFBR1 and fibrosis were enhanced. Our finding suggests that overexpressing miR-10a/b in kidney may be a promising method for the treatment of fibrosis in DKD.

Diabetes mellitus among adults on highly active anti-retroviral therapy and its associated factors in Ethiopia: Systematic review and meta-analysis

BACKGROUND

Diabetes mellitus occurs as a comorbid illness among people living with HIV and, in particular those on Highly Active Anti-retroviral therapies (HAART). Previous studies have documented the prevalence of diabetes mellitus among adults on HAART; however, there is lack of comprehensive estimation. Hence, this study was aimed to estimate the pooled prevalence and associated factors of diabetes mellitus among adults on HAART in Ethiopia.

METHODS

Primary studies were exhaustively searched using Cochrane, PubMed, Google Scholar, Scopus and Web of science databases until February 2021. Eligible studies were selected and critically appraised for quality using the Joanna Briggs Institute (JBI) quality appraisal checklist. The required data were extracted and exported to Stata version 16 for meta-analysis. The overall prevalence of diabetes mellitus among adults on HAART was estimated using a weighted inverse random effect model. Sensitivity and sub-group analysis were conducted for evidence of heterogeneity. Trim and fill analysis was performed after Egger's test and funnel plot were indicating the presence of publication bias.

RESULTS

A total of 17 studies with 6,052 subjects on HAART were included. The pooled prevalence of diabetes mellitus among patients on HAART was 16.04% [95% Confidence Interval (CI); 11.6, 20.92]. Abnormal High Density Lipoprotein Cholesterol (HDL-C) [Adjusted Odd Ratio (AOR) = 4.68, 95% CI; 2.54, 6.82], Body Mass Index (BMI) ≥ 25 kg/m² [AOR = 7.41, 95% CI; 2.75, 12.08], ≥6 years ART [AOR = 8.14, 95% CI; 5.85, 30.43], hypertension [AOR = 3.29, 95% CI; 2.13, 4.45], age 35-44 years [AOR = 6.28; 95% CI; 4.20, 8.37, BMI ≥ 30 kg/m² [AOR = 7.81, 95% CI; 4.97, 10.64], educational status above diploma [AOR = 6.42, 95% CI; 1.28, 11.57] and age 45-55 years [AOR = 4.46, 95% CI; 2.81, 6.10] were positively associated with diabetes mellitus comorbidity among adults on HAART.

CONCLUSION

The higher prevalence of diabetes mellitus was observed for adults on HAART. HDL-C, duration of ART, hypertension, overweight, obesity, age and educational status of participants increases the prevalence of diabetes mellitus. The study highlights the importance of timely screening of HDL-C level, blood pressure and BMI for adults on HAART.

Potential underlying genetic associations between keratoconus and diabetes mellitus

Background Keratoconus (KC) is the most common ectatic corneal disease, characterized by significantly localized thinning of the corneal stroma. Genetic, environmental, hormonal, and metabolic factors contribute to the pathogenesis of KC. Additionally, multiple comorbidities, such as diabetes mellitus, may affect the risk of KC. Main Body Patients with diabetes mellitus (DM) have been reported to have lower risk of developing KC by way of increased endogenous collagen crosslinking in response to chronic hyperglycemia. However, this remains a debated topic as other studies have suggested either a positive association or no association between DM and KC. To gain further insight into the underlying genetic components of these two diseases, we reviewed candidate genes associated with KC and central corneal thickness in the literature. We then explored how these genes may be regulated similarly or differentially under hyperglycemic conditions and the role they play in the systemic complications associated with DM. Conclusion Our comprehensive review of potential genetic factors underlying KC and DM provides a direction for future studies to further determine the genetic etiology of KC and how it is influenced by systemic diseases such as diabetes.

Oxyberberine, an absorbed metabolite of berberine, possess superior hypoglycemic effect via regulating the PI3K/Akt and Nrf2 signaling pathways

Berberine (BBR) is a promising anti-diabetic isoquinoline alkaloid from Rhizoma coptidis, while its bioavailability was extremely low. Here, the existing form and pharmacokinetics of BBR were comparatively characterized in conventional and antibiotic-induced pseudo germ-free (PGF) rats. Furthermore, we comparatively investigated the antidiabetic effect and potential mechanism of BBR and its intestinal oxidative metabolite oxyberberine (OBB) in STZ-induced diabetic rats. Results showed that BBR and OBB existed mainly as protein-bound form in blood, while protein-bound OBB was significantly depleted in PGF rats. Treatment with OBB and BBR effectively decreased clinical symptoms of diabetic rats, reduced blood glucose level, ameliorated the pancreatic damage, and mitigated oxidative stress and inflammatory markers. However, the anti-diabetes effect of BBR was obviously compromised by antibiotics. In addition, OBB exerted superior anti-diabetes effect to BBR of the same dose, significantly up-regulated the mRNA expression of Nrf2 signaling pathway and substantially promoted the pancreatic levels of PI3K/Akt signaling pathway. In conclusion, BBR and its absorbed oxidative metabolite OBB were mainly presented and transported in the protein-bound form in vivo. The gut microbiota may play an important role in the anti-diabetes effect of BBR through transforming itself into the superior hypoglycemic metabolite OBB. OBB possessed favorable hypoglycemic and pancreatic β-cells protective effects, which may stand a huge potential to be further developed into a promising anti-diabetes candidate.

Involvement of TGF-β and Autophagy Pathways in Pathogenesis of Diabetes: A Comprehensive Review on Biological and Pharmacological Insights

Despite recent advancements in clinical drugs, diabetes treatment still needs further progress. As such, ongoing research has attempted to determine the precise molecular mechanisms of the disorder. Specifically, evidence supports that several signaling pathways play pivotal roles in the development of diabetes. However, the exact molecular mechanisms of diabetes still need to be explored. This study examines exciting new hallmarks for the strict involvement of autophagy and TGF-β signaling pathways in the pathogenesis of diabetes and the design of novel therapeutic strategies. Dysregulated autophagy in pancreatic β cells due to hyperglycemia, oxidative stress, and inflammation is associated with diabetes and accompanied by dysregulated autophagy in insulin target tissues and the progression of diabetic complications. Consequently, several therapeutic agents such as adiponectin, ezetimibe, GABA tea, geniposide, liraglutide, guava extract, and vitamin D were shown to inhibit diabetes and its complications through modulation of the autophagy pathway. Another pathway, TGF-β signaling pathway, appears to play a part in the progression of diabetes, insulin resistance, and autoimmunity in both type 1 and 2 diabetes and complications in diabetes. Subsequently, drugs that target TGF-β signaling, especially naturally derived ones such as resveratrol, puerarin, curcumin, hesperidin, and silymarin, as well as Propolis, Lycopus lucidus, and Momordica charantia extracts, may become promising alternatives to current drugs in diabetes treatment. This review provides keen insights into novel therapeutic strategies for the medical care of diabetes.

Novel Interplay Between Smad1 and Smad3 Phosphorylation via AGE Regulates the Progression of Diabetic Nephropathy

Diabetic nephropathy (DN) is the major cause of end-stage renal failure and is associated with increased morbidity and mortality compared with other causes of renal diseases. We previously found that Smad1 plays a critical role in the development of DN both in vitro and in vivo. However, functional interaction between Smad1 and Smad3 signaling in DN is unclear. Here, we addressed the molecular interplay between Smad1 and Smad3 signaling under a diabetic condition by using Smad3-knockout diabetic mice. Extracellular matrix (ECM) protein overexpression and Smad1 activation were observed in the glomeruli of db/db mice but were suppressed in the glomeruli of Smad3^+/-; db/db mice. Smad3 activation enhanced the phosphorylation of Smad1 C-terminal domain but decreased the phosphorylation of linker domain, thus regulating Smad1 activation in advanced glycation end product-treated mesangial cells (MCs). However, forced phosphorylation of the Smad1 linker domain did not affect Smad3 activation in MCs. Phosphorylation of the Smad1 linker domain increased in Smad3^+/-; db/db mice and probucol-treated db/db mice, which was consistent with the attenuation of ECM overproduction. These results indicate that Smad3 expression and activation or probucol treatment alters Smad1 phosphorylation, thus suggesting new molecular mechanisms underlying DN development and progression.

Macrophages in diabetic nephropathy in patients with type 2 diabetes

Background

Inflammation plays a role in the development of diabetic nephropathy (DN) in type 2 diabetes. Although macrophages have been found in experimental models of DN, little is known regarding the presence of macrophages in patients with DN. Therefore, we investigated the presence and phenotype of glomerular and interstitial macrophages in relation to clinical and histopathological parameters in patients with DN.

Methods

Renal autopsy samples were obtained from 88 type 2 diabetic patients with histologically proven DN and stained for CD68 and CD163 as general and M2/anti-inflammatory markers of macrophages. Renal damage was scored based on histopathological classification of DN. Control renal autopsy samples were obtained from patients without renal abnormalities and from diabetic patients without DN. Positive cells per glomerulus were counted. Interstitial macrophages were counted semi-quantitatively.

Results

Macrophages were present in all groups. In the DN group, the mean number of CD68+ cells per glomerulus and CD163+ cells per glomerulus was 4.2 (range 0-19) and 2.1 (range 0-14.47), respectively. The distribution was similar between all histopathological classes. Glomerular CD163+ macrophages were positively associated with DN class, interstitial fibrosis and tubular atrophy, and glomerulosclerosis. Interstitial CD68+ macrophages were correlated with glomerular filtration rate stage and albuminuria.

Conclusions

Our results demonstrate that macrophages are present in the glomeruli and interstitium of type 2 diabetic patients with DN and of controls. Although patients and controls had similar numbers of glomerular macrophages, glomerular anti-inflammatory CD163+ macrophages were associated with pathological lesions in DN. Taken together with the correlation between interstitial macrophages and interstitial fibrosis and tubular atrophy, DN class, and renal function, this finding suggests that macrophages may play a role in DN progression. Therefore, targeting macrophages may be a promising new therapy for inhibiting the progression of DN.

Sitagliptin ameliorates diabetic nephropathy by blocking TGF-β1/Smad signaling pathway

Diabetic nephropathy (DN) is the leading cause of end-stage failure of the kidney, but the efficacy of current strategies available for the prevention of DN remains unsatisfactory. The purpose of this study was to assess whether sitagliptin (SIT) has therapeutic potential for prevention of DN and to investigate its possible mechanism. The effects of SIT on DN were investigated in rats with type 2 diabetes mellitus (T2DM) and rat mesangial cells (MCs) induced by high glucose. T2DM rats were administered at a dose of 10 mg/kg SIT. The kidney index, 24 h urinary protein, blood urea nitrogen (BUN), serum creatinine (Cr), accumulation of glycogen and collagens were investigated by different methods. MCs were administered with SIT at doses of 0.1, 1 and 10 µmol/ml. The possible mechanism of SIT on protection of diabetic kidney injury was examined by expression of transforming growth factor-β1 (TGF-β1)/Smad pathway. The results showed that the SIT-treated diabetic rats significantly reduced diabetic kidney injury by inhibiting the kidney index and attenuating 24 h urinary protein, reducing BUN and serum creatinine, inhibiting progressive renal fibrosis and increassing extracellular matrix including collagen IV and fibronectin. Further studies showed that inhibition of renal fibrosis in SIT-treated diabetic rats and MCs were associated with rebalancing of TGF-β1/Smad pathway. Sitagliptin may be a potent agent for preventing the progression of DN through inhabiting TGF-β1/Smad-mediated renal fibrosis.

Erectile dysfunction and its management in patients with diabetes mellitus

Diabetes can be described as a syndrome of multiple closely related conditions induced by a chronic state of hyperglycaemia resulting from defective insulin secretion, insulin action or both. Chronic complications associated with diabetes (including neuropathy, vascular disease, nephropathy and retinopathy) are common, and of these, erectile dysfunction (ED) deserves special attention. ED and its correlation with cardiovascular disease require careful evaluation and appropriate treatment. PDE5 inhibitors (PDE5is) are an important tool for the treatment of ED, with new drugs coming onto the market since the late 90s. This review offers an overview of PDE5is and their use in treating ED in diabetes. We underline the differences between different types of PDE5i, focusing on available doses, duration of action, T ½, side effects and selectivity profiles in relation to patients with diabetes. We also discuss the link between diabetes and ED in presence of various associated cofactors (obesity, hypertension and its pharmacological treatments, atherosclerosis, hyperhomocysteinaemia, neuropathy, nephropathy, hypogonadism and depression). Finally a number of past and ongoing clinical trials on the use of PDE5is in patients with diabetes are presented to offer an overview of the appropriate treatment of ED in this condition.

Differential Response to High Glucose in Skin Fibroblasts of Monozygotic Twins Discordant for Type 1 Diabetes

CONTEXT

Most epigenetic studies in diabetes compare normal cells in "high glucose" (HG) to cells in "normal glucose" (NG) and cells returned from HG to NG. Here we challenge this approach.

OBJECTIVE

The objective was to determine whether there were differences in gene expression in skin fibroblasts of monozygotic twins (MZT) discordant for type 1 diabetes (T1D).

DESIGN

Skin fibroblasts were grown in NG (5.5 mmol/L) and HG (25 mmol/L) for multiple passages.

SETTING

This study was conducted at the University of Minnesota.

PATIENTS

Patients were nine MZT pairs discordant for T1D.

MAIN OUTCOME MEASURE(S)

Gene expression was assessed by mRNA-Seq, using the Illumina HiSeq 2000 instrument. Pathway analysis tested directionally consistent group differences within the Kyoto Encyclopedia of Genes and Genomes pathways.

RESULTS

A total of 3308 genes were differentially expressed between NG and HG in T1D MZT vs 889 in non-T1D twins. DNA replication, proteasome, cell cycle, base excision repair, homologous recombination, pyrimidine metabolism, and spliceosome pathways had overrepresented genes with increased expression in T1D twins with P values ranging from 7.21 × 10(-10) to 1.39 × 10(-4). In a companion article, we demonstrate that these pathway changes are related to diabetic nephropathy risk. There were no pathways statistically significant differently expressed in nondiabetic twins in HG vs NG.

CONCLUSIONS

In vivo exposure to diabetes alters cells in a manner that markedly changes their in vitro responses to HG. These results highlight the importance of using cells directly derived from diabetic patients for studies examining the effects of HG in diabetes.

Synthesis of new thiazolylmethoxyphenyl pyrimidines and antihyperglycemic evaluation of the pyrimidines, analogues isoxazolines and pyrazolines

New thiazolylmethoxyphenyl pyrimidines (7a-g) have been conveniently synthesized with better yields by cyclocondensing 3-(4-((2-phenylthiazol-4-yl)methoxy)phenyl)-1-(4-substituted phenyl)prop-2-en-1-ones (4a-g) with thiourea in aqueous emulsion of tetradecyltrimethylammonium bromide (TTAB) at 80 °C. Antihyperglycemic activity of the new thiazolylmethoxyphenyl pyrimidines (7a-d), thiazolylmethoxyphenyl pyrazolines (5a-d) and thiazolylmethoxyphenyl isoxazolines (6a-d) has been evaluated in sucrose loaded rat model. Among these compounds; 5a, 5c, 6b, 7c and 7d have displayed noticeable antihyperglycemic activity. Pyrimidines and pyrazolines have displayed better antihyperglycemic activity than the analogues isoxazolines.

Highly precise plasmonic and colorimetric sensor based on enzymatic etching of nanospheres for the detection of blood and urinary glucose

A highly precise glucose sensor was developed based on plasmon peak shift induced by the glucose oxidase mediated etching of Au–Ag nanoparticles. The platform enabled quantitative glucose detection in human blood and urine samples.

Kolaviron improved resistance to oxidative stress and inflammation in the blood (erythrocyte, serum, and plasma) of streptozotocin-induced diabetic rats

AIMS

Bitter kola seed (Garcinia kola, family: Guttiferae) has been used as a social masticatory agent in Africa for several years and is believed to possess many useful medicinal properties. The present study evaluates the antioxidative, anti-inflammatory, and antilipidemic effects of kolaviron (an extract from the Garcinia kola seeds) in the blood of streptozotocin- (STZ) induced diabetic rats. METHODS. Diabetic rats were treated with kolaviron (100 mg/kg b·wt) orally, five times a week for a period of six weeks. Serum glucose and HBA(1C) concentrations were estimated in experimental groups. The activities of antioxidant enzymes: catalase (CAT), superoxide dismutase (SOD), and glutathione peroxidase (GPX) (in erythrocytes) as well as plasma concentration of malondialdehyde (MDA), a product of lipid peroxidation, oxygen radical absorbing capacity (ORAC) and ferric-reducing antioxidant power (FRAP) were investigated. Serum levels of proinflammatory cytokines and growth factor: interleukin- (IL-) 1, monocyte chemotactic protein-1 (MCP-1), and vascular endothelial growth factor (VEGF), respectively, were also analyzed.

RESULTS

Kolaviron treatment markedly improved antioxidant status and abated inflammatory response evidenced by reduction in the levels of proinflammatory cytokines and growth factor, lipid peroxidation product, and the restoration of activities of erythrocyte antioxidant enzymes in the blood of diabetic rats.

CONCLUSION

Kolaviron improved antioxidant status, reduced inflammation, and protected against hyperglycemic-induced oxidative damage in the blood of diabetic rats.

Chaihuang-Yishen granule inhibits diabetic kidney disease in rats through blocking TGF-β/Smad3 signaling

OBJECTIVE

Increasing evidence shows that TGF-β1 is a key mediator in diabetic nephropathy (DN) and induces renal fibrosis positively by Smad3 but negatively by Smad7. However, treatment of DN by blocking the TGF-β/Smad pathway remains limited. The present study investigated the anti-fibrotic effect of a traditional Chinese medicine, Chaihuang-Yishen granule (CHYS), on DN.

RESEARCH DESIGN AND METHODS

Protective role of CHYS in DN was examined in an accelerated type 1 DN induced by streptozotocin in uninephrectomized Wistar rats. CHYS, at a dose of 0.56 g/kg body weight, was administered by a daily gastric gavage for 20 weeks and the therapeutic effect and potential mechanisms of CHYS on diabetic kidney injury were examined.

RESULTS

Treatment with CHYS attenuated diabetic kidney injury by significantly inhibiting 24-h proteinuria and progressive renal fibrosis including glomerulosclerotic index, tubulointerstitial fibrosis index, and upregulation of extracellular matrix (collagen I, IV, and fibronectin), despite the same levels of blood glucose. Further studies revealed that inhibition of renal fibrosis in CHYS-treated diabetic rats was associated with inhibition of TGF-β1/Smad3 signaling as demonstrated by upregulation of Smad7 but downregulation of TGF-β1, TGF-β receptors, activation of Smad3, and expression of miRNA-21.

CONCLUSIONS

CHYS may be a therapeutic agent for DN. CHYS attenuates DN by blocking TGF-β/Smad3-mediated renal fibrosis.

MicroRNA-29b inhibits diabetic nephropathy in db/db mice

Inflammation and its consequent fibrosis are two main features of diabetic nephropathy (DN), but target therapy on these processes for DN remains yet ineffective. We report here that miR-29b is a novel therapeutic agent capable of inhibiting progressive renal inflammation and fibrosis in type 2 diabetes in db/db mice. Under diabetic conditions, miR-29b was largely downregulated in response to advanced glycation end (AGE) product, which was associated with upregulation of collagen matrix in mesangial cells via the transforming growth factor-β (TGF-β)/Smad3-dependent mechanism. These pathological changes were reversed by overexpressing miR-29b, but enhanced by knocking-down miR-29b. Similarly, loss of renal miR-29b was associated with progressive diabetic kidney injury, including microalbuminuria, renal fibrosis, and inflammation. Restored renal miR-29b by the ultrasound-based gene therapy was capable of attenuating diabetic kidney disease. Further studies revealed that inhibition of Sp1 expression, TGF-β/Smad3-dependent renal fibrosis, NF-κB-driven renal inflammation, and T-bet/Th1-mediated immune response may be mechanisms associated with miR-29b treatment in db/db mice. In conclusion, miR-29b may play a protective role in diabetic kidney disease and may have therapeutic potential for diabetic kidney complication.

Role of microRNA 1207-5P and its host gene, the long non-coding RNA Pvt1, as mediators of extracellular matrix accumulation in the kidney: implications for diabetic nephropathy

Diabetic nephropathy is the most common cause of chronic kidney failure and end-stage renal disease in the Western World. One of the major characteristics of this disease is the excessive accumulation of extracellular matrix (ECM) in the kidney glomeruli. While both environmental and genetic determinants are recognized for their role in the development of diabetic nephropathy, epigenetic factors, such as DNA methylation, long non-coding RNAs, and microRNAs, have also recently been found to underlie some of the biological mechanisms, including ECM accumulation, leading to the disease. We previously found that a long non-coding RNA, the plasmacytoma variant translocation 1 (PVT1), increases plasminogen activator inhibitor 1 (PAI-1) and transforming growth factor beta 1 (TGF-β1) in mesangial cells, the two main contributors to ECM accumulation in the glomeruli under hyperglycemic conditions, as well as fibronectin 1 (FN1), a major ECM component. Here, we report that miR-1207-5p, a PVT1-derived microRNA, is abundantly expressed in kidney cells, and is upregulated by glucose and TGF-β1. We also found that like PVT1, miR-1207-5p increases expression of TGF-β1, PAI-1, and FN1 but in a manner that is independent of its host gene. In addition, regulation of miR-1207-5p expression by glucose and TGFβ1 is independent of PVT1. These results provide evidence supporting important roles for miR-1207-5p and its host gene in the complex pathogenesis of diabetic nephropathy.

Matrix Producing Cells in Chronic Kidney Disease: Origin, Regulation, and Activation

Chronic injury to the kidney causes kidney fibrosis with irreversible loss of functional renal parenchyma and leads to the clinical syndromes of chronic kidney disease (CKD) and end-stage renal disease (ESRD). Regardless of the type of initial injury, kidney disease progression follows the same pathophysiologic processes characterized by interstitial fibrosis, capillary rarefaction and tubular atrophy. Myofibroblasts play a pivotal role in fibrosis by driving excessive extracellular matrix (ECM) deposition. Targeting these cells in order to prevent the progression of CKD is a promising therapeutic strategy, however, the cellular source of these cells is still controversial. In recent years, a growing amount of evidence points to resident mesenchymal cells such as pericytes and perivascular fibroblasts, which form extensive networks around the renal vasculature, as major contributors to the pool of myofibroblasts in renal fibrogenesis. Identifying the cellular origin of myofibroblasts and the key regulatory pathways that drive myofibroblast proliferation and transdifferentiation as well as capillary rarefaction is the first step to developing novel anti-fibrotic therapeutics to slow or even reverse CKD progression and ultimately reduce the prevalence of ESRD. This review will summarize recent findings concerning the cellular source of myofibroblasts and highlight recent discoveries concerning the key regulatory signaling pathways that drive their expansion and progression in CKD.

Gene expression differences in skin fibroblasts in identical twins discordant for type 1 diabetes

Clinical studies suggest metabolic memory to hyperglycemia. We tested whether diabetes leads to persistent systematic in vitro gene expression alterations in patients with type 1 diabetes (T1D) compared with their monozygotic, nondiabetic twins. Microarray gene expression was determined in skin fibroblasts (SFs) of five twin pairs cultured in high glucose (HG) for ∼6 weeks. The Exploratory Visual Analysis System tested group differences in gene expression levels within KEGG (Kyoto Encyclopedia of Genes and Genomes) pathways. An overabundance of differentially expressed genes was found in eight pathways: arachidonic acid metabolism (P = 0.003849), transforming growth factor-β signaling (P = 0.009167), glutathione metabolism (P = 0.01281), glycosylphosphatidylinositol anchor (P = 0.01949), adherens junction (P = 0.03134), dorsal-ventral axis formation (P = 0.03695), proteasome (P = 0.04327), and complement and coagulation cascade (P = 0.04666). Several genes involved in epigenetic mechanisms were also differentially expressed. All differentially expressed pathways and all the epigenetically relevant differentially expressed genes have previously been related to HG in vitro or to diabetes and its complications in animal and human studies. However, this is the first in vitro study demonstrating diabetes-relevant gene expression differences between T1D-discordant identical twins. These SF gene expression differences, persistent despite the HG in vitro conditions, likely reflect "metabolic memory", and discordant identical twins thus represent an excellent model for studying diabetic epigenetic processes in humans.

Skin fibroblasts as a tool for identifying the risk of nephropathy in the type 1 diabetic population

Human fibroblasts in culture have been employed as an in vitro system to investigate some pathophysiological mechanisms of diabetes mellitus also associated with the development of diabetic nephropathy. In fact, there is increasing evidence that genetic factors either convey the risk of, or protect from, diabetic nephropathy and that the expression profiles and/or the behaviour of the cultured skin fibroblasts from type 1 diabetic patients could reflect these genetic influences. On the other hand, alterations could be attributable not only to changes in DNA sequence, but also to epigenetic factors. Our aim is to make a critical overview of the studies involving primary cultures of skin fibroblasts as tools to investigate the pathophysiology of diabetic nephropathy performed until now in this area. Cultured skin fibroblasts could be useful not only for the identification of patients at risk of developing diabetic renal disease, but also for a better understanding of the complex multifactorial mechanisms leading to the long-term complications in diabetes.

Pirfenidone for diabetic nephropathy

Pirfenidone is an oral antifibrotic agent that benefits diabetic nephropathy in animal models, but whether it is effective for human diabetic nephropathy is unknown. We conducted a randomized, double-blind, placebo-controlled study in 77 subjects with diabetic nephropathy who had elevated albuminuria and reduced estimated GFR (eGFR) (20 to 75 ml/min per 1.73 m²). The prespecified primary outcome was a change in eGFR after 1 year of therapy. We randomly assigned 26 subjects to placebo, 26 to pirfenidone at 1200 mg/d, and 25 to pirfenidone at 2400 mg/d. Among the 52 subjects who completed the study, the mean eGFR increased in the pirfenidone 1200-mg/d group (+3.3 ± 8.5 ml/min per 1.73 m²) whereas the mean eGFR decreased in the placebo group (-2.2 ± 4.8 ml/min per 1.73 m²; P = 0.026 versus pirfenidone at 1200 mg/d). The dropout rate was high (11 of 25) in the pirfenidone 2400-mg/d group, and the change in eGFR was not significantly different from placebo (-1.9 ± 6.7 ml/min per 1.73 m²). Of the 77 subjects, 4 initiated hemodialysis in the placebo group, 1 in the pirfenidone 2400-mg/d group, and none in the pirfenidone 1200-mg/d group during the study (P = 0.25). Baseline levels of plasma biomarkers of inflammation and fibrosis significantly correlated with baseline eGFR but did not predict response to therapy. In conclusion, these results suggest that pirfenidone is a promising agent for individuals with overt diabetic nephropathy.

Caldesmon over-expression in type 1 diabetic nephropathy

Substantial evidence supports a genetic susceptibility to develop nephropathy in type 1 diabetes and a key pathogenic role of actin cytoskeleton dysfunction in this complication. We previously reported that many cytoskeletal proteins were either up- or down-regulated in fibroblast cells from type 1 diabetic (T1DM) patients with nephropathy. The gene of one of these proteins, caldesmon, lies in a chromosomal region linked to nephropathy and its promoter region contains a single nucleotide polymorphism that is associated with nephropathy. Hence, we analyzed caldesmon gene and protein expression in cultured fibroblasts from T1DM patients with and without nephropathy and from control subjects. Caldesmon gene was studied in cells cultured under normal glucose levels by quantitative real-time RT-PCR. Caldesmon protein isoforms were quantified both under normal and high glucose conditions by two-dimensional electrophoresis. Caldesmon gene was over-expressed in fibroblasts from diabetic patients with nephropathy, in comparison to both those from diabetic patients without nephropathy and those from controls. We quantified six caldesmon protein isoforms, two of them were increased whereas another one was decreased only in fibroblasts from diabetic patients with nephropathy. None of these isoforms showed any difference in their relative abundance in response to high glucose. Variable results in response to high glucose were observed in the expression of other proteins in the three experimental groups. Our data lend further support to an involvement of caldesmon in the susceptibility to diabetic nephropathy in type 1 diabetes, independently from environmental glucose levels.

The protective role of Smad7 in diabetic kidney disease: mechanism and therapeutic potential

OBJECTIVE

Although Smad3 has been considered as a downstream mediator of transforming growth factor-β (TGF-β) signaling in diabetes complications, the role of Smad7 in diabetes remains largely unclear. The current study tests the hypothesis that Smad7 may play a protective role and has therapeutic potential for diabetic kidney disease.

RESEARCH DESIGN AND METHODS

Protective role of Smad7 in diabetic kidney disease was examined in streptozotocin-induced diabetic mice that have Smad7 gene knockout (KO) and in diabetic rats given Smad7 gene transfer using an ultrasound-microbubble-mediated technique.

RESULTS

We found that mice deficient for Smad7 developed more severe diabetic kidney injury than wild-type mice as evidenced by a significant increase in microalbuminuria, renal fibrosis (collagen I, IV, and fibronectin), and renal inflammation (interleukin-1β [IL-1β], tumor necrosis factor-α [TNF-α], monocyte chemoattractant protein-1 [MCP-1], intracellular adhesion molecule-1 [ICAM-1], and macrophages). Further studies revealed that enhanced renal fibrosis and inflammation in Smad7 KO mice with diabetes were associated with increased activation of both TGF-β/Smad2/3 and nuclear factor-κB (NF-κB) signaling pathways. To develop a therapeutic potential for diabetic kidney disease, Smad7 gene was transferred into the kidney in diabetic rats by an ultrasound-microbubble-mediated technique. Although overexpression of renal Smad7 had no effect on levels of blood glucose, it significantly attenuated the development of microalbuminuria, TGF-β/Smad3-mediated renal fibrosis such as collagen I and IV and fibronectin accumulation and NF-κB/p65-driven renal inflammation including IL-1β, TNF-α, MCP-1, and ICAM-1 expression and macrophage infiltration in diabetic rats.

CONCLUSIONS

Smad7 plays a protective role in diabetic renal injury. Overexpression of Smad7 may represent a novel therapy for the diabetic kidney complication.

Glycation and biomarkers of vascular complications of diabetes

Propensity to diabetic nephropathy (DN), retinopathy (DR), and cardiovascular disease (CVD) varies between individuals. Current biomarkers such as indicators of glycemia (HbA1c), retinal examinations, and albuminuria, cannot detect early tissue damage. HbAIc also doesn't reflect most glycative and oxidative chemical pathways that cause complications, and studies of new biomarkers to measure their end-products are needed. This review proposes the study of advanced glycation end products (AGEs) and oxidation end-products (OPs) in long-term diabetes outcome studies. AGEs integrate the activity of glycation pathways that form dicarbonyls, while OPs reflect superoxides, hydroxyl radicals, and peroxides. We discuss using these biomarkers to predict risk of development and progression of DN, DR, and CVD, and to determine if they confer risk independently of the level of HbA1c. We also discuss methods and guidelines to document sample quality in such studies. These studies have the potential to validate unique biomarkers during the early stages of diabetes in those who are at high risk of diabetic complications. Information on basic mechanisms responsible for complications could also stimulate development of therapeutic approaches to delay or arrest them. The ultimate goal is to predict those requiring aggressive therapies during the earliest stages, when prevention or reversal of complications is still possible.

Cellular basis of diabetic nephropathy: V. Endoglin expression levels and diabetic nephropathy risk in patients with Type 1 diabetes

Endoglin is an accessory receptor molecule that, in association with transforming growth factor beta (TGF-beta) family receptors Types I and II, binds TGF-beta1, TGF-beta3, activin A, bone morphogenetic protein (BMP)-2 and BMP-7, regulating TGF-beta dependent cellular responses. Relevant to diabetic nephropathy, endoglin, expressed in vascular endothelial and smooth muscle cells, fibroblasts, and mesangial cells, negatively regulates extracellular matrix (ECM). The aim of this study was to evaluate endoglin expression in cultured skin fibroblasts from patients with Type 1 diabetes with and without diabetic nephropathy. Kidney and skin biopsies were performed in 125 Type 1 diabetic patients. The 20 with the fastest rate of mesangial expansion (estimated by electron microscopy) and proteinuria ("fast-track") and the 20 with the slowest rate and normoalbuminuria ("slow-track"), along with 20 controls were studied. Endoglin mRNA expression was assessed by microarray and quantitative real-time polymerase chain reaction (QRT-PCR) and protein expression by Western blot. Age and sex distribution were similar among groups. Diabetes duration was similar (20+/-8 vs. 24+/-7 years), hemoglobin A1c lower (8.4+/-1.2% vs. 9.4+/-1.5%), and glomerular filtration rate higher (115+/-13 vs. 72+/-20 ml/min per 1.73 m2) in slow-track vs. fast-track patients. Microarray endoglin mRNA expression levels were higher in slow-track (1516.0+/-349.9) than fast-track (1211.0+/-274.9; P=.008) patients or controls (1223.1+/-422.9; P=.018). This was confirmed by QRT-PCR. Endoglin protein expression levels correlated with microarray (r=0.59; P=.044) and QRTPCR (r=0.61; P=.034) endoglin mRNA expression. These studies are compatible with the hypothesis that slow-track Type 1 diabetic patients, strongly protected from diabetic nephropathy, have distinct cellular behaviors that may be associated with reduced ECM production.

Effects of streptozotocin-induced long-term diabetes on parietal cell function and morphology in rats

Gastric pathology is a common complication in diabetes mellitus. The aim of the study was to evaluate the functions and morphological changes of the parietal cells of the rat stomach after streptozotocin-induced diabetes. Diabetes mellitus was induced in Wistar rats by a single intraperitoneal injection of streptozotocin (60 mg/kg body weight). The rats were weighed weekly and sacrificed after 6 months. The glandular portion of the stomach was removed and processed for H(+)-K(+)-ATPase immunohistochemistry and light and electron microscopy studies. Acid secretion was measured in vivo. After 6 months of diabetes, the mean weight of the rats was significantly lower (P < 0.001) compared to control. The mean weight of the stomach to body weight percentage increased significantly (P < 0.001) compared to control. The blood glucose level in diabetic rats was significantly higher (P < 0.001) than in normal control. Diabetic rats showed significant (P < 0.001) decrease in basal and stimulated acid secretion when compared to control. Electron micrographs of the parietal cells of glandular stomach of diabetic rats revealed significant (P < 0.0002) reduction in the number of mitochondria and a small though not significant increase in the number of canaliculi in the parietal cells compared with normal. Immunohistochemistry showed reduced H(+)-K(+)-ATPase (P < 0.00001) compared to control. Long-term diabetes induces morphological as well as functional changes in gastric parietal cells. The decrease in the number of mitochondria accompanied by reduced in H(+)-K(+)-ATPase in parietal cells may explain the reduced acid secretion observed in diabetics.

Epithelial-to-mesenchymal transition in early transplant tubulointerstitial damage

It is unknown whether epithelial-to-mesenchymal transition (EMT) leads to tubulointerstitial fibrosis in renal transplants. In this study, interstitial fibrosis and markers of EMT were followed in protocol transplant biopsies in 24 patients. Tubulointerstitial damage (TID) increased from 34 to 54% between 1 and 3 mo after transplantation. Detection of EMT depended on the marker used; low levels of alpha-smooth muscle actin were found in 61% of biopsies, but the less specific marker S100 calcium binding protein-A4 (also known as Fsp1) suggested a higher incidence of EMT. The presence or development of TID did not correlate with EMT but instead significantly correlated with subclinical immune activity (P < 0.05). Among biopsies showing TID, microarray analysis revealed differential regulation of 127 genes at 1 mo and 67 genes at 3 mo compared with baseline; these genes were predominantly associated with fibrosis, tissue remodeling, and immune response. Of the 173 EMT-associated genes interrogated, however, only 8.1% showed an expression pattern consistent with EMT at 1 mo and 6.3% at 3 mo. The remainder were not differentially altered, or their changes in expression were opposite those expected to promote EMT. Quantitative reverse transcriptase-PCR revealed that the expression pattern of 12 EMT-associated genes was inconsistent over time, opposite that expected, or consistent with subclinical rejection or inflammation. In conclusion, EMT does not seem to play a significant role in the development of early allograft fibrosis.

Transgenic overexpression of brain natriuretic peptide prevents the progression of diabetic nephropathy in mice

AIMS/HYPOTHESIS

Brain natriuretic peptide (BNP) is a potent vasorelaxing and natriuretic peptide that is secreted from the heart and has cardioprotective properties. We have previously generated hypotensive transgenic mice (BNP-Tg mice) that overproduce BNP in the liver, which is released into the circulation. Using this animal model, we successfully demonstrated the amelioration of renal injury after renal ablation and in proliferative glomerulonephritis. Glomerular hyperfiltration is an early haemodynamic derangement, representing one of the key mechanisms of the pathogenesis of diabetic nephropathy. Based on the suggested involvement of increased endogenous natriuretic peptides, the aim of this study was to investigate their role in the development and progression of diabetic nephropathy.

MATERIALS AND METHODS

We evaluated the progression of renal injury and fibrogenesis in BNP-Tg mice with diabetes induced by streptozotocin. We also investigated the effect of BNP on high glucose-induced signalling abnormalities in mesangial cells.

RESULTS

After induction of diabetes, control mice exhibited progressively increased urinary albumin excretion with impaired renal function, whereas these changes were significantly ameliorated in BNP-Tg mice. Notably, diabetic BNP-Tg mice revealed minimal mesangial fibrogenesis with virtually no glomerular hypertrophy. Glomerular upregulation of extracellular signal-regulated kinase, TGF-beta and extracellular matrix proteins was also significantly inhibited in diabetic BNP-Tg mice. In cultured mesangial cells, activation of the above cascade under high glucose was abrogated by the addition of BNP.

CONCLUSIONS/INTERPRETATION

Chronic excess of BNP prevents glomerular injury in the setting of diabetes, suggesting that renoprotective effects of natriuretic peptides may be therapeutically applicable in preventing the progression of diabetic nephropathy.

Diabetic nephropathy is associated with gene expression levels of oxidative phosphorylation and related pathways

The in vitro behavior of skin fibroblasts from patients with or without diabetic nephropathy is associated with diabetic nephropathy risk. Here we compared skin fibroblast gene expression profiles from two groups of type 1 diabetic patients: 20 with very fast ("fast-track") versus 20 with very slow ("slow-track") rates of development of diabetic nephropathy lesions. Gene expression profiles of skin fibroblasts grown in 25 mmol/l glucose for 36 h were assessed by Affymetrix HG-U133A GeneChips to determine the proportion of genes in a given biological pathway that were directionally consistent in their group differences. Five pathways reached statistical significance. All had significantly greater proportions of genes with higher expression levels in the fast-track group. These pathways, the first four of which are closely related and have overlapping genes, included oxidative phosphorylation (P<0.001), electron transport system complex III (P=0.017), citrate cycle (P=0.037), propanoate metabolism (P=0.044), and transcription factors (P=0.046). These results support the concept that oxidative phosphorylation and related upstream pathways may be important in the pathogenesis of diabetic nephropathy. Whether these findings reflect inherent genetic cellular characteristics, "cell memory," or both requires further study.

Interaction of haemodynamic and metabolic pathways in the genesis of diabetic nephropathy

Clinical diabetic nephropathy is characterized by an earlier functional phase in which hyperglycaemia is accompanied by an increased glomerular filtration rate and microalbuminuria; the persistence of this high-flow and high-pressure state, added to a poor control of hyperglycaemia, fosters renal damage and proteinuria, accompanied by a decline in glomerular filtration rate and progression to end-stage renal disease. In this review, we present glucose transporter 1 (GLUT-1) as a novel link that connects the glomerular hyperfiltration (hypertension) state and the complex cascade of events that leads to nephropathy. The interplay between angiotensin II and nitric oxide, and its interactions with reactive oxygen species, are also discussed, in an attempt to provide an integrated view of the pathophysiology of diabetic nephropathy.

Assessment of 115 candidate genes for diabetic nephropathy by transmission/disequilibrium test

Several lines of evidence, including familial aggregation, suggest that allelic variation contributes to risk of diabetic nephropathy. To assess the evidence for specific susceptibility genes, we used the transmission/disequilibrium test (TDT) to analyze 115 candidate genes for linkage and association with diabetic nephropathy. A comprehensive survey of this sort has not been undertaken before. Single nucleotide polymorphisms and simple tandem repeat polymorphisms located within 10 kb of the candidate genes were genotyped in a total of 72 type 1 diabetic families of European descent. All families had at least one offspring with diabetes and end-stage renal disease or proteinuria. As a consequence of the large number of statistical tests and modest P values, findings for some genes may be false-positives. Furthermore, the small sample size resulted in limited power, so the effects of some tested genes may not be detectable, even if they contribute to susceptibility. Nevertheless, nominally significant TDT results (P < 0.05) were obtained with polymorphisms in 20 genes, including 12 that have not been studied previously: aquaporin 1; B-cell leukemia/lymphoma 2 (bcl-2) proto-oncogene; catalase; glutathione peroxidase 1; IGF1; laminin alpha 4; laminin, gamma 1; SMAD, mothers against DPP homolog 3; transforming growth factor, beta receptor II; transforming growth factor, beta receptor III; tissue inhibitor of metalloproteinase 3; and upstream transcription factor 1. In addition, our results provide modest support for a number of candidate genes previously studied by others.

Aberrant expression and mutations of TGF-beta receptor type II gene in endometrial cancer

OBJECTIVE

Transforming growth factor beta (TGF-beta) is a multifunctional cytokine that strongly inhibits epithelial cell growth. Disabling of TGF-beta signaling is thought to be involved in development of a variety of tumors in which abnormal expression or function of TGF-beta receptor plays critical roles. In the present study, we examined aberrant expression and mutation of the gene TGF-beta receptor type II (TbetaRII) in endometrial cancers of endometrioid subtype.

METHODS AND RESULTS

Real-time PCR analysis using surgical tissue specimens of 27 endometrial cancers and 24 normal endometria revealed that endometrial cancers had significantly decreased levels of TbetaRII mRNA expression (mean level 2.44 +/- 2.65), compared to normal endometria (mean level 7.23 +/- 6.07) (P < 0.001). Methylation status of TbetaRII promoter containing 30 CpGs was examined by bisulfite sequencing analysis, and 98% (51/52) of the patients were found to have unmethylated TbetaRII promoter, indicating that promoter hypermethylation is not the major cause of decreased expression of TbetaRII in endometrial cancers. Mutational analysis revealed that 15.1% (8/53) of endometrial cancers had frameshift mutations at polyadenine repeats in exon 3 of the TbetaRII gene. Notably, these mutations were preferentially accumulated in patients with MSI-H phenotype (7/19:37%) (P < 0.001) or with those with methylated MLH1 promoters (6/16:38%) (P < 0.01). Thus, it appears that the TbetaRII gene is a target of mismatch repair deficiency.

CONCLUSION

Taken together, we found that the decreased expression of TbetaRII as well as frameshift mutation of TbetaRII via mismatch repair deficiency frequently occurs in this tumor type, possibly causing loss of receptor function and unresponsiveness of TGF-beta signaling that may lead to endometrial carcinogenesis.

Modulation of the TGFbeta/Smad signaling pathway in mesangial cells by CTGF/CCN2

Transforming growth factor-beta (TGFbeta) drives fibrosis in diseases such as diabetic nephropathy (DN). Connective tissue growth factor (CTGF; CCN2) has also been implicated in this, but the molecular mechanism is unknown. We show that CTGF enhances the TGFbeta/Smad signaling pathway by transcriptional suppression of Smad 7 following rapid and sustained induction of the transcription factor TIEG-1. Smad 7 is a known antagonist of TGFbeta signaling and TIEG-1 is a known repressor of Smad 7 transcription. CTGF enhanced TGFbeta-induced phosphorylation and nuclear translocation of Smad 2 and Smad 3 in mesangial cells. Antisense oligonucleotides directed against TIEG-1 prevented CTGF-induced downregulation of Smad 7. CTGF enhanced TGFbeta-stimulated transcription of the SBE4-Luc reporter gene and this was markedly reduced by TIEG-1 antisense oligonucleotides. Expression of the TGFbeta-responsive genes PAI-1 and Col III over 48 h was maximally stimulated by TGFbeta+CTGF compared to TGFbeta alone, while CTGF alone had no significant effect. TGFbeta-stimulated expression of these genes was markedly reduced by both CTGF and TIEG-1 antisense oligonucleotides, consistent with the endogenous induction of CTGF by TGFbeta. We propose that under pathological conditions, where CTGF expression is elevated, CTGF blocks the negative feedback loop provided by Smad 7, allowing continued activation of the TGFbeta signaling pathway.

Cellular basis of diabetic nephropathy: III. In vitro GLUT1 mRNA expression and risk of diabetic nephropathy in type 1 diabetic patients

AIMS/HYPOTHESIS

Altered glucose transporter expression has been implicated in the pathogenesis of diabetic nephropathy. There is increasing evidence that genetic factors convey risk of, or protection from, diabetic nephropathy and that the behaviour of cultured skin fibroblasts from type 1 diabetic patients may reflect these genetic influences. This study aimed to compare GLUT1 mRNA expression levels in skin fibroblasts from type 1 diabetic patients with either rapid ("fast-track", n=25) or slow ("slow-track", n=25) development of diabetic nephropathy and from non-diabetic normal control subjects (controls, n=25).

METHODS

Skin fibroblasts were cultured in Dulbecco's Modified Eagle's Medium with 25 mmol/l glucose for 36 h. Total RNA was isolated, and GLUT1 mRNA levels were estimated by microarray analysis and RT-PCR.

RESULTS

Levels of GLUT1 mRNA expression in skin fibroblasts from "slow-track" patients were greater than those from "fast-track" patients (p=0.02), as initially detected by microarray. GLUT1 mRNA expression levels were confirmed by RT-PCR to be higher in skin fibroblasts from "slow-track" patients (4.59+/-2.04) than in those from "fast-track" patients (3.34+/-1.2, p=0.02), and were also higher than in skin fibroblasts from control subjects (3.52+/-1.66, p=0.03). There was no statistically significant difference between levels of expression in the "fast-track" patients and the control subjects.

CONCLUSIONS/INTERPRETATION

This finding is consistent with the presence of cellular protection factors against diabetic nephropathy in the "slow-track" patients. These factors could be associated with the regulation of the GLUT1 pathway and may be genetically determined.

Diabetic nephropathy and transforming growth factor-beta: transforming our view of glomerulosclerosis and fibrosis build-up

The manifestations of diabetic nephropathy may be a consequence of the actions of certain cytokines and growth factors. Prominent among these is transforming growth factor beta (TGF-beta) because it promotes renal cell hypertrophy and stimulates extracellular matrix accumulation, the 2 hallmarks of diabetic renal disease. In tissue culture studies, cellular hypertrophy and matrix production are stimulated by high glucose concentrations in the culture media. High glucose, in turn, appears to act through the TGF-beta system because high glucose increases TGF-beta expression, and the hypertrophic and matrix-stimulatory effects of high glucose are prevented by anti-TGF-beta therapy. In experimental diabetes mellitus, several reports describe overexpression of TGF-beta or TGF-beta type II receptor in the glomerular and tubulointerstitial compartments. As might be expected, the intrarenal TGF-beta system is triggered, evidenced by activity of the downstream Smad signaling pathway. Treatment of diabetic animals with a neutralizing anti-TGF-beta antibody prevents the development of mesangial matrix expansion and the progressive decline in renal function. This antibody therapy also reverses the established lesions of diabetic glomerulopathy. Finally, the renal TGF-beta system is significantly up-regulated in human diabetic nephropathy. Although the kidney of a nondiabetic subject extracts TGF-beta1 from the blood, the kidney of a diabetic patient actually elaborates TGF-beta1 protein into the circulation. Along the same line, an increased level of TGF-beta in the urine is associated with worse clinical outcomes. In concert with TGF-beta, other metabolic mediators such as connective tissue growth factor and reactive oxygen species promote the accumulation of excess matrix. This fibrotic build-up also occurs in the tubulointerstitium, probably as the result of heightened TGF-beta activity that stimulates tubular epithelial and interstitial fibroblast cells to overproduce matrix. The data presented here strongly support the consensus that the TGF-beta system mediates the renal hypertrophy, glomerulosclerosis, and tubulointerstitial fibrosis of diabetic kidney disease.

The BBZDR/Wor Rat Model for Investigating the Complications of Type 2 Diabetes Mellitus

Congenic and inbred strains of rats offer researchers invaluable insight into the etiopathogenesis of diabetes and associated complications. The inbred Bio-Breeding Zucker diabetic rat (BBZDR)/Wor rat strain is a relatively new and emerging model of type 2 diabetes. This strain was created by classical breeding methods used to introgress the defective leptin receptor gene (Lepr(fa)) from insulin-resistant Zucker fatty rats into the inbred BBDR/Wor strain background. The diabetic male BBZDR/Wor rat is homozygous for the fatty mutation and shares the genetic background of the original BB strain. Although lean littermates are phenotypically normal, obese juvenile BBZDR/Wor rats are hyperlipidemic and hyperleptinemic, become insulin resistant, and ultimately develop hyperglycemia. Furthermore, the BBZDR/Wor rat is immune competent and does not develop autoimmunity. Similar to patients with clinical diabetes, the BBZDR/Wor rat develops complications associated with hyperglycemia. The BBZDR/Wor rat is a model system that fully encompasses the ability to study the complications that affect human type 2 diabetic patients. In this review, recent work that has evaluated type 2 diabetic complications in BBZDR/Wor rats is discussed, including the authors' preliminary unpublished studies on cardiovascular disease.

Enhanced expression of transforming growth factor-beta isoforms in the neural tube of embryos derived from diabetic mice exposed to cyclophosphamide

We analyzed the expression pattern of transforming growth factor-beta isoforms (TGF-beta1, TGF-beta2 and TGF-beta3) in the developing brain of embryos derived from the normal and diabetic mice exposed to cyclophosphamide (CP), a cytotoxic teratogen. The CP-treated diabetic embryos showed significantly more TGF-beta1 and TGF-beta2 immunoreactive cells in the regions of telencephalon and diencephalon in comparison to that of CP-treated non-diabetic embryos. Moreover, no cells expressing TGF-beta isoforms were detectable in the developing brain of normal and diabetic embryos. The mRNA expression levels of TGF-beta isoforms were found to be significantly increased in the developing brain of CP-treated diabetic embryos compared to that of CP-treated non-diabetic embryos as measured by quantitative real time reverse transcription-polymerase chain reaction. The enhanced expression levels of TGF-beta isoforms appear to be associated with the increased frequency of neural tube defects observed in the diabetic embryos exposed to CP.

Microalbuminuria and hypertension with focus on type 1 and type 2 diabetes

Microalbuminuria and hypertension with Over the past decade, there has been considerable focus on the concept of microalbuminuria, not only because it predicts renal disease in type 1 and type 2 diabetes, but also because it relates to premature mortality in the diabetic and in the general population. More importantly, intervention at this stage is now possible with the perspective of preserving glomerular filtration rate (GFR) and ameliorating cardiovascular disease and ensuing strong end-points. INITIAL STUDIES: The concept of microalbuminuria was introduced about 20 years ago and since then there has been a multitude of studies and papers on this subject using the original definition, but not always, in the US. Before that time it was suggested, mainly from the US, that diabetic renal disease was an untreatable relentlessly progressive condition.

GENETIC STUDIES

There is an overwhelming number of studies on genetics and diabetes and also covering the genetics of diabetic complications including nephropathy. However, so far the results are extremely disappointing. Patients at risk cannot be identified and genetic analyses are of no value as a guide to treatment. The notion that the development of complications is controlled mainly by a special genetic pattern is increasingly doubtful. In genetic studies, it is rather phenotypic well-accepted risk factors that dominate. STRUCTURAL BASIS OF MICROALBUMINURIA: Patients with microalbuminuria have significant abnormalities in the kidney, including glomeruli. This is quite clear in patients with type 1 diabetes, but is also seen in type 2 diabetes, where on the other hand, other risk factors such as hypertension and dyslipidaemia also seem to be of importance, including loss of autoregulation. Renal biopsies are generally not indicated in the management of diabetic patients. MICROALBUMINURIA AND EARLY MORTALITY: It is quite clear that microalbuminuria predicts early mortality both in type 1 and type 2 diabetes. The association to other risk factors may partly explain this--but this does not account for the whole picture. Endothelial dysfunction as well as inflammatory and arteriosclerotic abnormalities in blood vessels may be a relevant hypothesis that needs to be further explored along with other possibilities. CLINICAL COURSE AND ASSOCIATED ABNORMALITIES: The risk factor for progression in normoalbuminuric patients to microalbuminuria is higher than normal albumin excretion (strongest factor), poor glycaemic control, elevated blood pressure, and to some extent smoking. The clinical course of microalbuminuria is usually progressive, but with the more effective intervention now available we encounter that the so-called natural history (without intervention) is increasingly difficult to study. Microalbuminuria is clearly associated with a number of abnormalities, almost in all organs, but GFR is generally well preserved in spite of more advanced structural lesions. Therefore, microalbuminuria is an important marker for more pronounced diabetic vascular disease in general as well as for nephropathy. Regression to normoalbuminuria only rarely occurs during standard unchanged nonintensive treatment. TREATMENT STRATEGIES: The best possible glycaemic control is important in preventing and ameliorating the course of normo- and micro-albuminuria. Another major treatment strategy, especially in microalbuminuric patients, is antihypertensive treatment including inhibition of the renal angiotensin aldosterone system. Numerous new studies are available, both in type 1 and type 2 diabetes, documenting that not only microalbuminuria but also renal and cardiovascular complications in these patient are also far better controlled by early detection and treatment. Therefore, screening for microalbuminuria should be a strategy in all diabetes management followed by effective intervention as outlined in this paper.

Diabetes and nephropathy

PURPOSE OF REVIEW

Diabetic nephropathy is the single most common disorder leading to renal failure. Its annual incidence has more than doubled in the past decade to reach 44% of all end-stage renal disease, despite recent therapeutic advances. Thus, research into diabetic nephropathy pathophysiology that could lead to new treatment approaches is urgently needed and this review aims to summarize the work performed in this area in the past year.

RECENT FINDINGS

There have been advances in the understanding of diabetic nephropathy pathology. Clearly, structural changes may be advanced before any clinical findings are apparent. Not all functional consequences of the condition are explained by current structural analyses. Genetic studies have connected the disorder risk to multiple candidate genes and a few genetic loci, but the exact genetic predisposition or protectors are not fully described. Perturbations in multiple metabolic pathways are associated with diabetic nephropathy in animals and humans, but their relative importance requires further work. Glycemia and blood pressure control are crucial for diabetic nephropathy prevention and treatment, but new modalities are needed.

SUMMARY

Recent advances in molecular biology and genetics will bring new insights to the mechanisms involved in diabetic nephropathy development. This will allow early identification of patients at risk of, or safe from, diabetic nephropathy and will hopefully lead to preventive strategies, based on the understanding of the pathophysiology of the disorder. Meanwhile, aggressive implementation of proven therapies to prevent (glycemic control) and slow (antihypertensive therapy, especially with renin-angiotensin system blockers) the progression of diabetic nephropathy are strongly recommended.