Pioglitazone normalizes insulin signaling in the diabetic rat retina through reduction in tumor necrosis factor α and suppressor of cytokine signaling 3

Insulin resistance is associated with the presence and severity of retinopathy in patients with type 2 diabetes

BACKGROUND

To assess the relationship between novel insulin resistance (IR) indices and the presence and severity of diabetic retinopathy (DR) in patients with type 2 diabetes.

METHODS

This is a cross-sectional study involving 2211 patients. The study outcomes were DR events. The study exposures were IR indices including estimated glucose disposal rate (eGDR), natural logarithm of glucose disposal rate (lnGDR), metabolic insulin resistance score (METS-IR), triglyceride glucose index-body mass index (TyG-BMI), triglyceride glucose index-waist-to-hip ratio (TyG-WHR), and triglyceride/high-density lipoprotein cholesterol(TG/HDL-c ratio). We used binary and multivariate ordered logistic regression models to estimate the association between different IR indices and the presence and severity of DR. Subject work characteristic curves were used to assess the predictive power of different IR indices for DR.

RESULTS

DR was present in 25.4% of participants. After adjusting for all covariates, per standard deviation (SD) increases in eGDR (ratio [OR] 0.38 [95% CI 0.32-0.44]), lnGDR (0.34 [0.27-0.42]) were negatively associated with the presence of DR. In contrast, per SD increases in METS-IR (1.97 [1.70-2.28]), TyG-BMI (1.94 [1.68-2.25]), TyG-WHR (2.34 [2.01-2.72]) and TG/HDL-c ratio (1.21 [1.08-1.36]) were positively associated with the presence of DR. eGDR was strongly associated with severity of DR. Of all variables, eGDR had the strongest diagnostic value for DR (AUC = 0.757).

CONCLUSIONS

Of the six IR indices, eGDR was significantly associated with the presence and severity of DR in patients with type 2 diabetes. eGDR has a good predictive value for DR. Thus, eGDR maybe a stronger marker of DR.

Protective Effect of Pioglitazone on Retinal Ganglion Cells in an Experimental Mouse Model of Ischemic Optic Neuropathy

The aim was to assess the protective effect of pioglitazone (PGZ) on retinal ganglion cells (RGCs) after anterior ischemic optic neuropathy (AION) in diabetic and non-diabetic mice. Adult C57BL/6 mice with induced diabetes were divided into three groups: group 1: oral PGZ (20 mg/kg) in 0.1% dimethyl sulfoxide (DMSO) for 4 weeks; group 2: oral PGZ (10 mg/kg) in 0.1% DMSO for 4 weeks; and group 3: oral DMSO only for 4 weeks (control group). Two weeks after treatment, AION was induced through photochemical thrombosis. For non-diabetic mice, adult C57BL/6 mice were divided into four groups after AION was induced: group 1: oral DMSO for 4 weeks; group 2: oral PGZ (20 mg/kg) in 0.1% DMSO for 4 weeks; group 3: oral PGZ (20 mg/kg) in 0.1% DMSO + peritoneal injection of GW9662 (one kind of PPAR-γ inhibitor) (1 mg/kg) for 4 weeks; group 4: peritoneal injection of GW9662 (1 mg/kg) for 4 weeks; One week after the induction of AION in diabetic mice, apoptosis in RGCs was much lower in group 1 (8.0 ± 4.9 cells/field) than in group 2 (24.0 ± 11.5 cells/field) and 3 (25.0 ± 7.7 cells/field). Furthermore, microglial cell infiltration in the retina (group 1: 2.0 ± 2.6 cells/field; group 2: 15.6 ± 3.5 cells/field; and group 3: 14.8 ± 7.5 cells/field) and retinal thinning (group 1: 6.7 ± 5.7 μm; group 2: 12.8 ± 6.1 μm; and group 3: 15.8 ± 5.8 μm) were also lower in group 1 than in the other two groups. In non-diabetic mice, preserved Brn3A⁺ cells were significantly greater in group 2 (2382 ± 140 Brn3A+ cells/mm², n = 7) than in group 1 (1920 ± 228 Brn3A+ cells/mm²; p = 0.03, n = 4), group 3 (1938 ± 213 Brn3A+ cells/mm²; p = 0.002, n = 4), and group 4 (2138 ± 126 Brn3A+ cells/mm²; p = 0.03, n = 4), respectively; PGZ confers protection to RGCs from damage caused by ischemic optic neuropathy in diabetic and non-diabetic mice.

Investigation of the correlation between diabetic retinopathy and prevalent and incident migraine in a national cohort study

Migraine is a disease characterized by cerebral vasodilation. While diabetes has previously been associated with a lower risk of migraine, it is not known if diabetic retinopathy (DR), a retinal peripheral vascular occlusive disease, is a potential biomarker of protection against migraine. Therefore, we aimed to examine diabetic retinopathy as a marker of prevalent and 5-year incident migraine. In a national cohort, we compared patients with diabetes attending DR screening from The Danish National Registry of Diabetic Retinopathy (cases, n = 205,970) to an age- and gender-matched group of patients without diabetes (controls, n = 1,003,170). In the cross-sectional study, a multivariable model demonstrated a lower prevalence of migraine among cases compared with controls (OR 0.83, 95% CI 0.81–0.85), with a lower risk in cases with DR than in those without (OR 0.69, 95% CI 0.65–0.72). In the prospective study, a lower risk of incident migraine was found in a multivariable model in cases (HR 0.76, 95% CI 0.70–0.82), but this did not depend upon the presence of DR. To conclude, in a national study of more than 1.2 million people, patients screened for DR had a lower risk of present migraine, but DR was not a protective marker of incident migraine.

Thiazolidinedione use and retinal fluid in the comparison of age-related macular degeneration treatments trials

Background

Thiazolidinediones, commonly used antidiabetic medications, have been associated with an increased risk of development of diabetic macular oedema and increased vascular endothelial cell permeability. Macular neovascularisation in age-related macular degeneration (AMD) and associated fluid leakage may be influenced by thiazolidinediones. This study aims to determine the association between thiazolidinedione usage and retinal morphological outcomes or visual acuity (VA) in patients treated with bevacizumab or ranibizumab for neovascular AMD (nAMD).

Methods

Secondary analysis of data from the Comparison of Age-related Macular Degeneration Treatments Trials. Participant self-reported diabetes status and thiazolidinedione usage at baseline. VA, intraretinal, subretinal and subretinal pigment epithelium fluid, and foveal thickness of retinal layers were evaluated at baseline and during 2-year follow-up. Comparisons of outcomes between thiazolidinedione usage groups were adjusted by macular neovascularisation lesion type in multivariable regression models.

Results

Patients taking thiazolidinedione (n=30) had lower adjusted mean VA score at baseline (difference −6.2 letters; p=0.02), greater proportion with intraretinal fluid (IRF) at year 2 (75% vs 50%, adjusted OR 2.8; p=0.04), greater mean decrease in subretinal tissue complex thickness from baseline at year 1 (difference −75.1 um; p=0.02) and greater mean decrease in subretinal thickness at year 1 (difference −41.9 um; p=0.001) and year 2 (difference −43.3 um; p=0.001).

Conclusions

In this exploratory analysis, patients with diabetes taking thiazolidinediones and treated with bevacizumab or ranibizumab for nAMD had worse baseline mean VA, greater reductions in subretinal and subretinal tissue complex thickness from baseline, and greater proportions with IRF comparing to patients not taking thiazolidinediones.

Trial registration number

ClinicalTrials.gov NCT00593450.

The role of peroxisome proliferator-activated receptors in healthy and diseased eyes

Peroxisome Proliferator-Activated Receptors (PPARs) are a family of nuclear receptors that play essential roles in modulating cell differentiation, inflammation, and metabolism. Three subtypes of PPARs are known: PPAR-alpha (PPARα), PPAR-gamma (PPARγ), and PPAR-beta/delta (PPARβ/δ). PPARα activation reduces lipid levels and regulates energy homeostasis, activation of PPARγ results in regulation of adipogenesis, and PPARβ/δ activation increases fatty acid metabolism and lipolysis. PPARs are linked to various diseases, including but not limited to diabetes, non-alcoholic fatty liver disease, glaucoma and atherosclerosis. In the past decade, numerous studies have assessed the functional properties of PPARs in the eye and key PPAR mechanisms have been discovered, particularly regarding the retina and cornea. PPARγ and PPARα are well established in their functions in ocular homeostasis regarding neuroprotection, neovascularization, and inflammation, whereas PPARβ/δ isoform function remains understudied. Naturally, studies on PPAR agonists and antagonists, associated with ocular pathology, have also gained traction with the development of PPAR synthetic ligands. Studies on PPARs has significantly influenced novel therapeutics for diabetic eye disease, ocular neuropathy, dry eye, and age-related macular degeneration (AMD). In this review, therapeutic potentials and implications will be highlighted, as well as reported adverse effects. Further investigations are necessary before any of the PPARs ligands can be utilized, in the clinics, to treat eye diseases. Future research on the prominent role of PPARs will help unravel the complex mechanisms involved in order to prevent and treat ocular diseases.

Photoreceptor cells and RPE contribute to the development of diabetic retinopathy

Diabetic retinopathy (DR) is a leading cause of blindness. It has long been regarded as vascular disease, but work in the past years has shown abnormalities also in the neural retina. Unfortunately, research on the vascular and neural abnormalities have remained largely separate, instead of being integrated into a comprehensive view of DR that includes both the neural and vascular components. Recent evidence suggests that the most predominant neural cell in the retina (photoreceptors) and the adjacent retinal pigment epithelium (RPE) play an important role in the development of vascular lesions characteristic of DR. This review summarizes evidence that the outer retina is altered in diabetes, and that photoreceptors and RPE contribute to retinal vascular alterations in the early stages of the retinopathy. The possible molecular mechanisms by which cells of the outer retina might contribute to retinal vascular damage in diabetes also are discussed. Diabetes-induced alterations in the outer retina represent a novel therapeutic target to inhibit DR.

Targeted pharmacotherapy against neurodegeneration and neuroinflammation in early diabetic retinopathy

Diabetic retinopathy (DR), the most frequent complication of diabetes, is one of the leading causes of irreversible blindness in working-age adults and has traditionally been regarded as a microvascular disease. However, increasing evidence has revealed that synaptic neurodegeneration of retinal ganglion cells (RGCs) and activation of glial cells may represent some of the earliest events in the pathogenesis of DR. Upon diabetes-induced metabolic stress, abnormal glycogen synthase kinase-3β (GSK-3β) activation drives tau hyperphosphorylation and β-catenin downregulation, leading to mitochondrial impairment and synaptic neurodegeneration prior to RGC apoptosis. Moreover, glial cell activation triggers enhanced inflammation and oxidative stress, which may accelerate the deterioration of diabetic RGCs neurodegeneration. These findings have opened up opportunities for therapies, such as inhibition of GSK-3β, glial cell activation, glutamate excitotoxicity and the use of neuroprotective drugs targeting early neurodegenerative processes in the retina and halting the progression of DR before the manifestation of microvascular abnormalities. Such interventions could potentially remedy early neurodegeneration and help prevent vision loss in people suffering from DR.

Diabetic photoreceptors: Mechanisms underlying changes in structure and function

Based on clinical findings, diabetic retinopathy (DR) has traditionally been defined as a retinal microvasculopathy. Retinal neuronal dysfunction is now recognized as an early event in the diabetic retina before development of overt DR. While detrimental effects of diabetes on the survival and function of inner retinal cells, such as retinal ganglion cells and amacrine cells, are widely recognized, evidence that photoreceptors in the outer retina undergo early alterations in diabetes has emerged more recently. We review data from preclinical and clinical studies demonstrating a conserved reduction of electrophysiological function in diabetic retinas, as well as evidence for photoreceptor loss. Complementing in vivo studies, we discuss the ex vivo electroretinography technique as a useful method to investigate photoreceptor function in isolated retinas from diabetic animal models. Finally, we consider the possibility that early photoreceptor pathology contributes to the progression of DR, and discuss possible mechanisms of photoreceptor damage in the diabetic retina, such as enhanced production of reactive oxygen species and other inflammatory factors whose detrimental effects may be augmented by phototransduction.

Pioglitazone ameliorates high fat diet-induced hypertension and induces catechol o-methyl transferase expression in rats

Our study aimed to investigate the effect of pioglitazone (PIO) on the obesity-associated metabolic effects and whether this effect is associated with modulation of catechol O-methyl transferase (COMT) expression in the high fat diet (HFD) induced obese rats. Male Wistar rats fed HFD were used to evaluate the effect of PIO on obesity-associated hypertension and the expression of COMT. The HFD-induced obesity was confirmed by the change in body weights, the fasting serum insulin (FSI) which assessed by ELISA, homeostasis model assessment - insulin resistance (HOMA-IR), fasting blood glucose (FBG), oral glucose tolerance test (OGTT) and lipid profile which were determined by colorimetric methods. Plasma epinephrine (EP) and norepinephrine (NE) were determined by ELISA and the systolic blood pressure (SBP) was recorded using the tail-cuff method. COMT expression was assessed by quantitative real time-polymerase chain reaction (qRT-PCR), and western blotting. The HFD-induced obesity was associated with glucose intolerance, derangement of the lipid profile, increased SBP, reduced COMT expression with a concomitant increase in plasma catecholamines. Most importantly, treatment with PIO ameliorated the HFD-induced metabolic changes, improved the lipid profile, reduced SBP, increased COMT expression, and reduced plasma catecholamines. Treatment with PIO reversed HFD-induced glucose intolerance and the associated metabolic derangement. In addition, these effects of PIO were associated with up-regulating COMT expression with a subsequent reduction in plasma catecholamines levels.

Identification of novel differentially expressed genes in retinas of STZ-induced long-term diabetic rats through RNA sequencing

BACKGROUND

The aim of this research was to investigate the retinal transcriptome changes in long-term streptozotocin (STZ)-induced rats' retinas using RNA sequencing (RNA-seq), to explore the molecular mechanisms of diabetic retinopathy (DR), and to identify novel targets for the treatment of DR by comparing the gene expression profile we obtained.

METHODS

In this study, 6 healthy male SD rats were randomly divided into wild-type (WT) group and streptozotocin (STZ)-induced group, 3 rats each group. After 6 months, 3 normal retina samples and 3 DM retina samples (2 retinas from the same rat were considered as 1 sample) were tested and differentially expressed genes (DEGs) were measured by RNA-seq technology. Then, we did Gene Ontology (GO) enrichment analysis and KEGG (Kyoto Encyclopedia of Genes and Genomes) pathway analysis and validated the results of RNA-seq through qRT-PCR.

RESULTS

A total of 118 DEGs were identified, of which 72 were up-regulated and 46 were down-regulated. The enriched GO terms showed that 3 most significant enrichment terms were binding (molecular function), cell part (cellular component), and biological regulation (biological process). The results of the KEGG pathway analysis revealed a significant enrichment in cell adhesion molecules, PI3K-Akt signaling pathway, and allograft rejection, etc. CONCLUSION: Our research has identified specific DEGs and also speculated their potential functions, which will provide novel targets to explore the molecular mechanisms of DR.

Insulin Signal Transduction is Impaired in the Type 2 Diabetic Retina

Rates of type 2 diabetes are reaching epidemic levels. Yet, the tissue specific alterations due to insulin resistance are only recently being investigated. The goal of the present study was to evaluate retinal insulin signal transduction in a common mouse model of type 2 diabetes, the db/db mouse. Retinal lysates from five month old male db/db and db/+ (control) mice were collected and processed for Western blotting or ELISA analyses for insulin receptor, insulin receptor substrate-1 (IRS-1), Akt, tumor necrosis factor alpha (TNFα) and caspase 3 levels. Data demonstrate increased TNFα and IRS-1 phosphorylation on serine 307. This led to decreased Akt phosphorylation on serine 473 and increased cleavage of caspase 3. Taken together, the data suggest dysfunctional insulin signaling in the retina of the db/db mouse. insulin.

A locked immunometabolic switch underlies TREM2 R47H loss of function in human iPSC-derived microglia

Loss‐of‐function genetic variants of triggering receptor expressed on myeloid cells 2 (TREM2) are linked with an enhanced risk of developing dementias. Microglia, the resident immune cell of the brain, express TREM2, and microglial responses are implicated in dementia pathways. In a normal surveillance state, microglia use oxidative phosphorylation for their energy supply, but rely on the ability to undergo a metabolic switch to glycolysis to allow them to perform rapid plastic responses. We investigated the role of TREM2 on the microglial metabolic function in human patient iPSC‐derived microglia expressing loss of function variants in TREM2. We show that these TREM2 variant iPSC‐microglia, including the Alzheimer's disease R47H risk variant, exhibit significant metabolic deficits including a reduced mitochondrial respiratory capacity and an inability to perform a glycolytic immunometabolic switch. We determined that dysregulated PPARγ/p38MAPK signaling underlies the observed phenotypic deficits in TREM2 variants and that activation of these pathways can ameliorate the metabolic deficit in these cells and consequently rescue critical microglial cellular function such as β‐Amyloid phagocytosis. These findings have ramifications for microglial focussed‐treatments in AD.

PPARG Polymorphisms Are Associated with Unexplained Mild Vision Loss in Patients with Type 2 Diabetes Mellitus

Objectives

To investigate whether the presence of peroxisome proliferator-activated receptor gamma (PPARG) gene polymorphisms is associated with unexplained mild visual impairment (UMVI) in patients with type 2 diabetes mellitus (T2DM).

Methods

A total of 135 T2DM residents with UMVI and 133 with normal vision (NV; best-corrected visual acuity ≥ 20/25 in both eyes) were enrolled. UMVI was defined as best-corrected visual acuity (BCVA) < 20/25 and ≥ 20/63 in both eyes, with no visual impairment-causing diseases found. Four PPARG gene single-nucleotide polymorphisms (SNPs) (rs3856806, rs1801282, rs709158, and rs10865710) were assessed with the HAPLOVIEW 4.0 software to examine the statistical association of PPARG polymorphisms and UMVI in patients with T2DM.

Results

Four SNPs qualified the Hardy-Weinberg equilibrium (p > 0.05). The frequency of genotype GC at SNP rs10865710 was significantly higher in the UMVI group than in the NV group (p < 0.001; GG + GC versus CC) (OR = 8.94, 95% CI: 4.90-16.31), whereas genotype CC decreased the risk (OR = 0.07, 95% CI: 0.03-0.14). Genotype TT at SNP rs3856806 was strongly associated with UMVI (p < 0.0001, TT + TC versus CC) (OR = 4.74, 95% CI: 2.68-8.54), whereas genotype CC appeared to be protective for UMVI (OR = 0.55, 95% CI: 0.37-0.82).

Conclusions

Susceptibilities of PPARG variants may lead to differences in PPARG transcription, result in early function loss of retinal photoreceptor cells, and eventually cause UMVI.

Association of Retinopathy and Insulin Resistance: NHANES 2005-2008

Purpose: In animal models, insulin resistance without severe hyperglycemia is associated with retinopathy; however, corroborating data in humans are lacking. This study aims to investigate the prevalence of retinopathy in a population without diabetes and evaluate the association of insulin resistance and retinopathy within this group.Methods: The study population included 1914 adults age ≥40 without diabetes who were assigned to the morning, fasted group in the National Health and Nutrition Examination Survey 2005-2008, conducted by the Centers for Disease Control. Retinopathy was determined using fundus photos independently graded by a reading center and insulin resistance was determined using the homeostatic model of insulin resistance.Results: Prevalence of retinopathy in those without diabetes was survey design adjusted 9.4% (174/1914). In multivariable analyses, retinopathy was associated with insulin resistance (HOMA-IR OR: 1.09, 95% CI: 1.03, 1.16; p = .0030), male gender (OR: 1.39, 95% CI: 1.04, 1.85; p = .0267), and age (OR: 1.03, 95% CI: 1.01, 1.05; p = .0203).Conclusions: Insulin resistance in the absence of overt hyperglycemia could be an early driver of retinopathy.

Citreoviridin induces myocardial apoptosis through PPAR-γ-mTORC2-mediated autophagic pathway and the protective effect of thiamine and selenium

Citreoviridin (CIT), a mycotoxin and ATP synthase inhibitor, is regarded as one of aetiology factors of cardiac beriberi and Keshan disease. Thiamine (VB1) and selenium (Se) improve the recovery of these two diseases respectively. The underlying mechanisms of cardiotoxic effect of CIT and cardioprotective effect of VB1 and Se have not been fully elucidated. In this study, we found that ectopic ATP synthase was more sensitive to CIT treatment than mitochondrial ATP synthase in H9c2 cardiomyocytes. CIT inhibited the transcriptional activity of peroxisome proliferator activated receptor gamma (PPAR-γ) in mice hearts and H9c2 cells. PPAR-γ agonist attenuated the inhibitory effect of CIT on mechanistic target of rapamycin complex 2 (mTORC2) and stimulatory effect of CIT on autophagy in cardiomyocytes. CIT induced apoptosis through lysosomal-mitochondrial axis in cardiomyocytes. PPAR-γ agonist and autophagy inhibitor alleviated CIT-induced apoptosis and accelerated cardiac biomarker. VB1 and Se accelerated the basal transcriptional activity of PPAR-γ in mice hearts and H9c2 cells. Furthermore, VB1 and Se reversed the effect of CIT on PPAR-γ, autophagy and apoptosis. Our findings defined PPAR-γ-mTORC2-autophagy pathway as the key link between CIT cardiotoxicity and cardioprotective effect of VB1 and Se. The present study would shed new light on the pathogenesis of cardiomyopathy and the cardioprotective mechanism of micronutrients.

GDF10 blocks hepatic PPARγ activation to protect against diet-induced liver injury

OBJECTIVE

Growth differentiation factors (GDFs) and bone-morphogenic proteins (BMPs) are members of the transforming growth factor β (TGFβ) superfamily and are known to play a central role in the growth and differentiation of developing tissues. Accumulating evidence, however, demonstrates that many of these factors, such as BMP-2 and -4, as well as GDF15, also regulate lipid metabolism. GDF10 is a divergent member of the TGFβ superfamily with a unique structure and is abundantly expressed in brain and adipose tissue; it is also secreted by the latter into the circulation. Although previous studies have demonstrated that overexpression of GDF10 reduces adiposity in mice, the role of circulating GDF10 on other tissues known to regulate lipid, like the liver, has not yet been examined.

METHODS

Accordingly, GDF10^-/- mice and age-matched GDF10^+/+ control mice were fed either normal control diet (NCD) or high-fat diet (HFD) for 12 weeks and examined for changes in liver lipid homeostasis. Additional studies were also carried out in primary and immortalized human hepatocytes treated with recombinant human (rh)GDF10.

RESULTS

Here, we show that circulating GDF10 levels are increased in conditions of diet-induced hepatic steatosis and, in turn, that secreted GDF10 can prevent excessive lipid accumulation in hepatocytes. We also report that GDF10^-/- mice develop an obese phenotype as well as increased liver triglyceride accumulation when fed a NCD. Furthermore, HFD-fed GDF10^-/- mice develop increased steatosis, endoplasmic reticulum (ER) stress, fibrosis, and injury of the liver compared to HFD-fed GDF10^+/+ mice. To explain these observations, studies in cultured hepatocytes led to the observation that GDF10 attenuates nuclear peroxisome proliferator-activated receptor γ (PPARγ) activity; a transcription factor known to induce de novo lipogenesis.

CONCLUSION

Our work delineates a hepatoprotective role of GDF10 as an adipokine capable of regulating hepatic lipid levels by blocking de novo lipogenesis to protect against ER stress and liver injury.

New anti-hyperglycaemic agents for type 2 diabetes and their effects on diabetic retinopathy

There has been an increase in the range of non-insulin anti-hyperglycaemic agents used to treat type 2 diabetes. With the globally rising rates of type 2 diabetes and complications such as diabetic retinopathy, it is important for ophthalmologists to be aware of these new agents and their impacts on diabetic retinopathy and diabetic macular oedema. We conducted a review of the literature to determine if there were any beneficial or harmful effects of the currently used anti-hyperglycaemic agents on diabetic retinopathy or diabetic macular oedema. Our review of the current literature found that apart from thiazolidinediones, anti-hyperglycaemic agents have been reported to have beneficial or neutral effects on diabetic eye complications. Thiazolidinediones (pioglitazone is the only one currently available) have been linked to incident or worsening diabetic macular oedema, although the rate is believed to be low. Glucagon-like peptide 1 (GLP1) agonists (incretins) in general are beneficial except semaglutide which is associated with increased rates of diabetic retinopathy complications. These results have implications for selection of anti-hyperglycaemic agents for patients with diabetic retinopathy or macular oedema. Further studies need to be conducted to identify if reported beneficial effects are independent of the impact of glycaemic control. Early worsening of retinopathy with tight glycaemic control should also be noted in interpretation of future studies.

Ameliorative effects of indomethacin at different concentrations on endothelial insulin resistance through two distinct pathways

Indomethacin (IDMT), a non-selective inhibitor of cycloxygenase-2 (COX-2), plays important roles in anti-inflammation and analgesia and it is commonly used to treat the patients with rheumatic and rheumatoid arthritis. Besides, various literatures reported that IDMT is a synthetic ligand of peroxisome proliferator activated receptor gamma (PPARγ). Rosiglitazone (RSG), an insulin-sensitizer, is also a synthetic ligand and applied clinically to cure the patients with type 2 diabetes mellitus. However, up to date little is known about whether IDMT ameliorates endothelial insulin resistance (IR). Accordingly, the purpose of this study is to investigate the effects of IDMT on endothelial IR and its underlying mechanism. Our present results showed that IDMT improved the endothelial IR induced by high glucose and fat concentration (HG/HF) in a concentration and time-dependent manner. Intriguingly, we further identified that 0.25 mM of IDMT noticeably induced the expression levels of PPARγ, AKT and endothelial nitric oxide synthase (eNOS) but failed to notably reverse the increases in expression levels of COX-2, inhibitory κB kinase (IKK) and tumor necrosis factor alpha (TNFα) induced by HG/HF; whereas 1.0 mM of IDMT exerted opposite effects compared with 0.25 mM of IDMT. Therefore, we conclude that IDMT ameliorates the endothelial IR induced by HG/HF through two distinct pathways, i.e., a lower concentration of IDMT through a PPARγ-AKT-eNOS pathway while a higher concentration mainly via an IKK-COX-2/TNFα pathway. The findings might provide a novel clinical use for IDMT to cure IR-related disorders.

Critical role of endoplasmic reticulum stress in chronic endothelial activation-induced visual deficits in tie2-tumor necrosis factor mice

Diabetic retinopathy (DR) is the leading cause of vision loss among working-age adults. The interplay between hyperglycemia and endothelial activation in inducing endoplasmic reticulum (ER) stress pathways and visual deficits in DR is not fully understood. To address this, we used a mouse model of chronic vascular activation using endothelial-specific tumor necrosis factor-α (TNF-α)-expressing (tie2-TNF) mice to induce diabetes with streptozotocin. At 4 weeks post streptozotocin, a significant 2-fold to 10-fold increase in retinal neurovascular inflammatory gene transcript response in tie2-TNF mice was further increased in diabetic tie2-TNF mice. A decrease in visual acuity and scotopic b-wave amplitude in tie2-TNF mice was further accentuated in diabetic tie2-TNF mice and these changes correlated with a multi-fold increase in retinal ER stress markers and a reduction in adherens junctions. Cultured retinal endothelial cells showed a significant decrease in trans-endothelial resistance as well as VE-cadherin expression under TNF-α and high glucose stress. These changes were partly rescued by tauroursodeoxycholic acid, a potent ER stress inhibitor. Taken together, constant endothelial activation induced by TNF-α further exacerbated by hyperglycemia results in activation of ER stress and chronic proinflammation in a feed forward loop ultimately resulting in endothelial junction protein alterations leading to visual deficits in the retina. Inhibition of ER stress and endothelial activation may prove to be a novel therapeutic target in DR.

Epac1 Restores Normal Insulin Signaling through a Reduction in Inflammatory Cytokines

We have previously reported that Epac1 reduced inflammatory cytokines, which is protective to the diabetic retina. We have also published that impaired insulin signaling occurs in the diabetic retina. A reduction in interleukin-1 beta (IL-1β) and tumor necrosis factor alpha (TNFα) by Epac1 could potentially restore normal insulin signal transduction. Confocal microscopy was performed to localize the insulin receptor in the retina of Epac1 floxed and endothelial cell-specific Epac1 knockout mice. Whole retinal lysates from Epac1 floxed and endothelial cell-specific Epac1 knockout mice were used to investigate proteins involved in the insulin signaling cascade. Primary human REC were cultured in normal and high glucose followed by Epac1 agonist treatment or transfection with IL-1β or TNFα siRNA for protein analyses of insulin signaling proteins. Decreased expression of the insulin receptor was observed in the Epac1 knockout mouse retinal vasculature compared to floxed littermates. Work in mice showed that loss of Epac1 decreased insulin signaling proteins. Treatment with an Epac1 agonist decreased p38 and JNK signaling and increased insulin signaling, as did inhibition of IL-1β or TNFα using siRNA when added to REC grown in high glucose. Taken together, Epac1 can restore normal insulin signaling in the retinal vasculature through reductions in inflammatory cytokines.

miRNA15a regulates insulin signal transduction in the retinal vasculature

We previously reported that tumor necrosis factor alpha (TNFα) could inhibit insulin signal transduction in retinal cells. We recently found that miR15a/16 also reduced TNFα in retinal endothelial cells (REC) and in vascular specific miR15a/16 knockout mice. Since in silico programs suggested that miR15a could directly bind the insulin receptor, we wanted to determine whether miR15a altered insulin signal transduction. We used a luciferase-based binding assay to determine whether miR15a directly bound the insulin receptor. We then used Western blotting, ELISA, and qPCR to investigate whether miR15a altered insulin signaling proteins in REC and in both miR15a/16 endothelial cell knockout and overexpressing mice. We also treated some REC with resveratrol to determine if resveratrol could increase miR15a expression, since resveratrol is protective to the diabetic retina. We found that miR15a directly bound the 3'UTR of the insulin receptor. Treatment with resveratrol increased miR15a expression in REC grown in high glucose. While total insulin receptor levels were not altered, insulin signal transduction was reduced in REC grown in high glucose and was restored with treatment with resveratrol. miR15a knockout mice had reduced insulin receptor phosphorylation and Akt2 levels, with increased insulin receptor substrate 1 (IRS-1) phosphorylation on serine 307, a site known to inhibit insulin signaling. In contrast, overexpression of miR15a increased insulin signal transduction. Taken together, these data suggest that miR15a binds the insulin receptor and indirectly regulates insulin receptor actions. It also offers an additional mechanism by which resveratrol is protective to the diabetic retina.

Optimization, Biopharmaceutical Profile and Therapeutic Efficacy of Pioglitazone-loaded PLGA-PEG Nanospheres as a Novel Strategy for Ocular Inflammatory Disorders

PURPOSE

The main goal of this study was to encapsulate Pioglitazone (PGZ), in biodegradable polymeric nanoparticles as a new strategy for the treatment of ocular inflammatory processes.

METHODS

To improve their biopharmaceutical profile for the treatment of ocular inflammatory disorders, nanospheres (NSs) of PGZ were formulated by factorial design with poly (lactic-co-glycolic acid) polyethylene glycol (PLGA-PEG). Interactions drug-polymer have been carried out by spectroscopic (X-ray spectroscopy, FTIR) and thermal methods (DSC). The PGZ-NSs were tested for their in vitro release profile, cytotoxicity, and ocular tolerance (HET-CAM® test); ex vivo corneal permeation, and in vivo inflammatory prevention and bioavailability.

RESULTS

The optimized system showed a negative surface charge of -13.9 mV, an average particle size (Z_av) of around 160 nm, a polydispersity index (PI) below 0.1, and a high encapsulation efficiency (EE) of around 92%. According to the DSC results, the drug was incorporated into the NSs polymeric matrix. The drug release was sustained for up to 14 h. PGZ-NSs up to 10 μg/ml exhibited no retinoblastoma cell toxicity. The ex vivo corneal and scleral permeation profiles of PGZ-NSs showed that retention and permeation through the sclera were higher than through the cornea. Ocular tolerance in vitro and in vivo demonstrated the non-irritant character of the formulation.

CONCLUSION

The in vivo anti-inflammatory efficacy of developed PGZ-NSs indicates this colloidal system could constitute a new approach to prevent ocular inflammation.

HuoXueJieDu Formula Alleviates Diabetic Retinopathy in Rats by Inhibiting SOCS3-STAT3 and TIMP1-A2M Pathways

HuoXueJieDu (HXJD) formula exerts protective effects against diabetic retinopathy (DR) in rats, but its underlying mechanism remains unknown. In the present study, the diabetic rats were established using streptozocin. The administration of HXJD was initiated at 20 weeks after diabetes induction and continued for 12 weeks. Whole genome expression profiles in rat retinas were examined using microarray technology. Differential gene expression and pathway enrichment analysis were conducted on the microarray data, with validation through real-time PCR and immunohistochemical staining. The results showed that 170 genes and several IPA canonical pathways related to inflammation, matrix metabolism, and phototransduction were regulated by HXJD. PCR validation of selected genes, including SOCS3, STAT3, TIMP1, and A2M, confirmed the gene expression changes influenced by HXJD. In addition, the immunohistochemical staining results suggested that critical members of the SOCS3-STAT3 pathway were also affected by HXJD. Taken together, these results indicated that SOCS3-STAT3 and TIMP1-A2M pathways might mediate the alleviation of HXJD activities in rats with diabetic retinopathy.

Comparative RNA-Seq transcriptome analyses reveal distinct metabolic pathways in diabetic nerve and kidney disease

Treating insulin resistance with pioglitazone normalizes renal function and improves small nerve fibre function and architecture; however, it does not affect large myelinated nerve fibre function in mouse models of type 2 diabetes (T2DM), indicating that pioglitazone affects the body in a tissue-specific manner. To identify distinct molecular pathways regulating diabetic peripheral neuropathy (DPN) and nephropathy (DN), as well those affected by pioglitazone, we assessed DPN and DN gene transcript expression in control and diabetic mice with or without pioglitazone treatment. Differential expression analysis and self-organizing maps were then used in parallel to analyse transcriptome data. Differential expression analysis showed that gene expression promoting cell death and the inflammatory response was reversed in the kidney glomeruli but unchanged or exacerbated in sciatic nerve by pioglitazone. Self-organizing map analysis revealed that mitochondrial dysfunction was normalized in kidney and nerve by treatment; however, conserved pathways were opposite in their directionality of regulation. Collectively, our data suggest inflammation may drive large fibre dysfunction, while mitochondrial dysfunction may drive small fibre dysfunction in T2DM. Moreover, targeting both of these pathways is likely to improve DN. This study supports growing evidence that systemic metabolic changes in T2DM are associated with distinct tissue-specific metabolic reprogramming in kidney and nerve and that these changes play a critical role in DN and small fibre DPN pathogenesis. These data also highlight the potential dangers of a 'one size fits all' approach to T2DM therapeutics, as the same drug may simultaneously alleviate one complication while exacerbating another.

The peroxisome proliferator-activated receptor pan-agonist bezafibrate suppresses microvascular inflammatory responses of retinal endothelial cells and vascular endothelial growth factor production in retinal pigmented epithelial cells

A randomized clinical trial showed the beneficial effects of the selective peroxisome proliferator-activated receptor (PPAR)-α agonist, fenofibrate, in reducing the progression of diabetic retinopathy independent of serum lipid levels. All subtypes of PPAR (PPAR-α, PPAR-γ, and PPAR-β/δ) have been reported to play a key role in microvascular inflammation and angiogenesis. Therefore, the agonistic function of fenofibrate against the PPAR-α has been suggested to contribute to its medicinal effect. Furthermore, bezafibrate is a fibrate drug commonly used as a lipid-lowering agent to treat hyperlipidemia and acts as a pan-agonist of all PPARs subtypes. However, the effects of bezafibrate in diabetic retinopathy remain unclear. Therefore, the purpose of this study was to investigate the effects of bezafibrate on retinal microvascular inflammation. Bezafibrate was not cytotoxic against human retinal microvascular endothelial cells (HRMECs) and human retinal pigment epithelial cells (ARPE-19 cells) treated with <100 and 200μM bezafibrate, respectively. In HRMECs, the expression levels of tumor necrosis factor (TNF)-α-induced monocyte chemoattractant protein (MCP)-1, intercellular adhesion molecule (ICAM)-1, and vascular cell adhesion molecule (VCAM)-1 were significantly suppressed by bezafibrate in a dose-dependent manner. TNF-α-induced nuclear translocation of nuclear factor (NF)-κB p65 and cell migration were also significantly inhibited in bezafibrate-treated HRMECs. Furthermore, bezafibrate treatment significantly suppressed interleukin (IL)-1β-induced vascular endothelial growth factor (VEGF) production in ARPE-19 cells. These results suggest that bezafibrate has beneficial effects on retinal microvascular inflammation. Our study demonstrates the therapeutic potential of bezafibrate for managing diabetic retinopathy.

Inhibition of HMGB1 protects the retina from ischemia-reperfusion, as well as reduces insulin resistance proteins

The role of inflammation in diabetic retinal amage is well accepted. While a number of cytokines and inflammatory mediators are responsible for these changes, upstream regulators are less well studied. Additionally, the role for these upstream mediators in retinal health is unclear. In this study, we hypothesized that inhibition of high mobility group box 1 (HMGB1) could restore normal insulin signaling in retinal endothelial cells (REC) grown in high glucose, as well as protect the retina against ischemia/reperfusion (I/R)-induced retinal damage. REC were grown in normal (5mM) or high glucose (25mM) and treated with Box A or glycyrrhizin, two different HMGB1 inhibitors. Western blotting was done for HMGB1, toll-like receptor 4 (TLR4), insulin receptor, insulin receptor substrate-1 (IRS-1), and Akt. ELISA analyses were done for tumor necrosis factor alpha (TNFα) and cleaved caspase 3. In addition, C57/B6 mice were treated with glycyrrhizin, both before and after ocular I/R. Two days following I/R, retinal sections were processed for neuronal changes, while vascular damage was measured at 10 days post-I/R. Results demonstrate that both Box A and glycyrrhizin reduced HMGB1, TLR4, and TNFα levels in REC grown in high glucose. This led to reduced cleavage of caspase 3 and IRS-1^Ser307 phosphorylation, and increased insulin receptor and Akt phosphorylation. Glycyrrhizin treatment significantly reduced loss of retinal thickness and degenerate capillary numbers in mice exposed to I/R. Taken together, these results suggest that inhibition of HMGB1 can reduce retinal insulin resistance, as well as protect the retina against I/R-induced damage.

Autophagy in Diabetic Retinopathy

Autophagy is an important homeostatic cellular process encompassing a number of consecutive steps indispensable for degrading and recycling cytoplasmic materials. Basically autophagy is an adaptive response that under stressful conditions guarantees the physiological turnover of senescent and impaired organelles and, thus, controls cell fate by various cross-talk signals. Diabetic retinopathy (DR) is a serious microvascular complication of diabetes and accounts for 5% of all blindness. Although, various metabolic disorders have been linked with the onset of DR, due to the complex character of this multi-factorial disease, a connection between any particular defect and DR becomes speculative. Diabetes increases inflammation, advanced glycation end products (AGEs) and oxidative stress in the retina and its capillary cells. Particularly, a great number of evidences suggest a mutual connection between oxidative stress and other major metabolic abnormalities implicated in the development of DR. In addition, the intricate networks between autophagy and apoptosis establish the degree of cellular apoptosis and the progression of DR. Growing data underline the crucial role of reactive oxygen species (ROS) in the activation of autophagy. Depending on their delicate balance both redox signaling and autophagy, being detrimental or beneficial, retain opposing effects. The molecular mechanisms of autophagy are very complex and involve many signaling pathways cooperating at various steps. This review summarizes recent advances of the possible molecular mechanisms in autophagic process that are involved in pathophysiology of DR. In-depth analysis on the molecular mechanisms leading to autophagy in the retinal pigment epithelial (RPE) will be helpful to plan new therapies aimed at preventing or improving the progression of DR.

IRS proteins and diabetic complications

IRS proteins are cellular adaptor molecules that mediate many of the key metabolic actions of insulin. When tyrosine is phosphorylated by the activated insulin receptor, IRS proteins recruit downstream effectors, such as phosphoinositide 3-kinase and mitogen-activated protein kinase, in order to elicit cellular responses such as glucose uptake, lipid metabolism and cell proliferation. There are two main IRS proteins in humans (IRS1 and IRS2), both of which are widely expressed. Given their central role in the insulin signalling pathway, it is not surprising that male mice lacking Irs1 or Irs2 present with elevated blood glucose or type 2 diabetes, respectively. For reasons yet to be identified, female Irs2 (-/-) mice do not develop type 2 diabetes. A number of organs are affected by complications of diabetes; macrovascular complications include stroke and coronary artery disease, while nephropathy, neuropathy and retinopathy fall into the category of microvascular complications. Given the serious consequences of these complications on patient morbidity and mortality, it is essential to identify the molecular pathogenesis underlying diabetic complications, with a view to improving therapeutic intervention and patient outcomes. A number of recently published papers have converged on the hypothesis that the loss of insulin signalling and IRS proteins is instrumental to the development and/or progression of diabetic complications. This review will summarise some highlights from the published work in which this hypothesis is discussed.

The progress in understanding and treatment of diabetic retinopathy

Diabetic retinopathy is the most frequently occurring complication of diabetes mellitus and remains a leading cause of vision loss globally. Its aetiology and pathology have been extensively studied for half a century, yet there are disappointingly few therapeutic options. Although some new treatments have been introduced for diabetic macular oedema (DMO) (e.g. intravitreal vascular endothelial growth factor inhibitors ('anti-VEGFs') and new steroids), up to 50% of patients fail to respond. Furthermore, for people with proliferative diabetic retinopathy (PDR), laser photocoagulation remains a mainstay therapy, even though it is an inherently destructive procedure. This review summarises the clinical features of diabetic retinopathy and its risk factors. It describes details of retinal pathology and how advances in our understanding of pathogenesis have led to identification of new therapeutic targets. We emphasise that although there have been significant advances, there is still a pressing need for a better understanding basic mechanisms enable development of reliable and robust means to identify patients at highest risk, and to intervene effectively before vision loss occurs.

Role of Peroxisome Proliferator-Activated Receptor γ in Ocular Diseases

Peroxisome proliferator-activated receptor γ (PPAR γ), a member of the nuclear receptor superfamily, is a ligand-activated transcription factor that plays an important role in the control of a variety of physiological processes. The last decade has witnessed an increasing interest for the role played by the agonists of PPAR γ in antiangiogenesis, antifibrosis, anti-inflammation effects and in controlling oxidative stress response in various organs. As the pathologic mechanisms of major blinding diseases, such as age-related macular degeneration (AMD), diabetic retinopathy (DR), keratitis, and optic neuropathy, often involve neoangiogenesis and inflammation- and oxidative stress-mediated cell death, evidences are accumulating on the potential benefits of PPAR γ to improve or prevent these vision threatening eye diseases. In this paper we describe what is known about the role of PPAR γ in the ocular pathophysiological processes and PPAR γ agonists as novel adjuvants in the treatment of eye diseases.

Skeletal muscle insulin resistance in salt-sensitive hypertension: role of angiotensin II activation of NFκB

Background

We have previously shown that in hypertensive Dahl salt-sensitive (DS) rats, impaired endothelium-dependent relaxation to acetylcholine and to insulin is mechanistically linked to up-regulation of angiotensin (Ang) II actions and the production of reactive oxygen species (ROS) and to activation of the proinflammatory transcription factor (NF)κB. Here we investigated whether Ang II activation of NFκB contributed to insulin resistance in the skeletal muscle of this animal model.

Methods

DS rats were fed either a normal (NS, 0.5% NaCl) or high (HS, 4% NaCl) salt diet for 6 weeks. In addition, 3 separate groups of HS rats were given angiotensin receptor 1 blocker candesartan (ARB, 10 mg/kg/day in drinking water), antioxidant tempol (1 mmol/L in drinking water) or NFκB inhibitor PDTC (150 mg/kg in drinking water).

Results

DS rats manifested an increase in soleus muscle Ang II content, ROS production and phosopho-IκBα/IκBα ratio, ARB or tempol reduced ROS and phospho-IκBα/IκBα ratio. Hypertensive DS rats also manifested a reduction in glucose infusion rate, impaired insulin-induced Akt phosphorylation and Glut-4 translocation in the soleus muscle, which were prevented with treatment of either ARB, tempol, or PDTC. Data from the rat diabetes signaling pathway PCR array showed that 8 genes among 84 target genes were altered in the muscle of hypertensive rats with the increase in gene expression of ACE1 and 5 proinflammatory genes, and decrease of 2 glucose metabolic genes. Incubation of the muscle with NFκB SN50 (a specific peptide inhibitor of NFκB) ex vivo reversed changes in hypertension-induced gene expression.

Conclusion

The current findings strongly suggest that the activation of NFκB inflammatory pathway by Ang II play a critical role in skeletal muscle insulin resistance in salt-sensitive hypertension.

Sodium salicylate reduced insulin resistance in the retina of a type 2 diabetic rat model

Sodium salicylate has been reported to reduce markers of diabetic retinopathy in a type 1 rat model. Because rates of type 2 diabetes are on the rise, we wanted to determine whether salicylate could improve insulin resistance in a type 2 rat model, as well as improve retinal function. We treated lean and obese BBZDR/Wor type 2 diabetic rats with salicylate in their chow for 2 months. Prior to salicylate treatment, rats underwent an electroretinogram to measure retinal function. After 2 months of treatment, rats underwent an additional electroretinogram prior to sacrifice. In addition to the animal model, we also treated retinal endothelial cells (REC) and rat Müller cells with salicylate and performed the same analyses as done for the rat retinal lysates. To investigate the role of salicylate in insulin signaling, we measured TNFα and caspase 3 levels by ELISA, as well as performed Western blotting for insulin receptor substrate 1, insulin receptor, SOCS3, and pro- and anti-apoptotic markers. Data demonstrated that salicylate significantly improved retinal function, as well as reduced TNFα and SOCS3-induced insulin resistance in all samples. Overall, results suggest that salicylate is effective in reducing insulin resistance in the retina of type 2 diabetic rat models.

Pioglitazone alters monocyte populations and stimulates recent thymic emigrants in the BBDZR/Wor type 2 diabetes rat model

BACKGROUND

Type 2 diabetes is commonly characterized by insulin deficiency and decreased sensitivity of insulin receptors, leading to a chronic state of hyperglycemia in individuals. Disease progression induces changes in the immune profile that engenders a chronic inflammatory condition. Thiazolidinedione (TDZ) drugs, such as Pioglitazone (Pio), aid in controlling disease symptoms. While the mechanisms by which Pio controls hyperglycemia are beginning to be understood, relatively little is known about the effects of Pio on suppression of the systemic immune phenotype, attributed to visceral adipose tissue and macrophages.

METHODS

Here, we utilize the recently developed BBDZR/Wor type 2 diabetes rat model to test our hypothesis that a selective in vivo growth of CD3(+)T cells in the spleen contributes to the increase in T lymphocytes, including Tregs, independent of visceral adipose tissue. We investigated the systemic effects of Pio on multifactorial aspects of the disease-induced immune phenotype both in vivo and in vitro in normal, non-diabetic animals and in disease.

RESULTS

Our work revealed that Pio reversed the lymphopenic status of diabetic rats, in part by an increase in CD3(+) T lymphocytes and related subsets. Moreover, we found evidence that Pio caused a selective growth of newly differentiated T lymphocytes, based on the presence of recent thymic emigrants in vivo. To investigate effects of Pio on the inflammatory milieu, we examined the production of the signature cytokines TNF-α and IL-1β and found they were reduced by Pio-treatment, while the levels of IL-4, an anti-inflammatory mediator, were significantly increased in a Pio-dependent manner. The increase in IL-4 production, although historically attributed to macrophages from visceral adipose tissue under other conditions, came also from CD3(+) T lymphocytes from the spleen, suggesting splenocytes contribute to the Pio-induced shift towards an anti-inflammatory phenotype.

CONCLUSIONS

We show for the first time that Pio treatment significantly suppresses the systemic inflammatory status in the BBDZR/Wor type 2 diabetes rat model by the selective growth of newly differentiated CD3(+) T cells and by increasing CD3(+)IL-4 production in immigrant spleen lymphocytes.

Pioglitazone restores IGFBP-3 levels through DNA PK in retinal endothelial cells cultured in hyperglycemic conditions

PURPOSE

Previously, we reported that pioglitazone prevented insulin resistance and cell death in type 2 diabetic retina by reducing TNFα and suppressor of cytokine signaling 3 (SOCS3) levels. Numerous reports suggest prominent vasoprotective effects of insulin growth factor binding protein-3 (IGFBP-3) in diabetic retinopathy. We hypothesized that pioglitazone protects against retinal cell apoptosis by regulating IGFBP-3 levels, in addition to reducing TNFα. The current study explored potential IGFBP-3 regulatory pathways by pioglitazone in retinal endothelial cells cultured in high glucose.

METHODS

Primary human retinal endothelial cells (REC) were grown in normal (5 mM) and high glucose (25 mM) and treated with pioglitazone for 24 hours. Cell lysates were processed for Western blotting and ELISA analysis to evaluate IGFBP-3, TNFα, and cleaved caspase 3 protein levels.

RESULTS

Our results show that treatment with pioglitazone restored the high glucose-induced decrease in IGFBP-3 levels. This regulation was independent of TNFα actions, as reducing TNFα levels with siRNA did not prevent pioglitazone from increasing IGFBP-3 levels. Pioglitazone required protein kinase A (PKA) and DNA-dependent protein kinase (DNA PK) activity to regulate IGFBP-3, as specific inhibitors for each protein prevented pioglitazone-mediated normalization of IGFBP-3 in high glucose. Insulin growth factor binding protein-3 activity was increased and apoptosis decreased by pioglitazone, which was eliminated when serine site 156 of IGFBP-3 was mutated suggesting a key role of this phosphorylation site in pioglitazone actions.

CONCLUSIONS

Our findings suggest that pioglitazone mediates regulation of IGFBP-3 via activation of PKA/DNA PK pathway in hyperglycemic retinal endothelial cells.