The effect of surgical weight loss on diabetes complications in individuals with class II/III obesity.

AIMS/HYPOTHESIS: The aim of this study was to determine the effect of bariatric surgery on diabetes complications in individuals with class II/III obesity (BMI > 35 kg/m2). METHODS: We performed a prospective cohort study of participants with obesity who underwent bariatric surgery. At baseline and 2 years following surgery, participants underwent metabolic phenotyping and diabetes complication assessments. The primary outcomes for peripheral neuropathy (PN) were a change in intra-epidermal nerve fibre density (IENFD, units = fibres/mm) at the distal leg and proximal thigh, the primary outcome for cardiovascular autonomic neuropathy (CAN) was a change in the expiration/inspiration (E/I) ratio, and the primary outcome for retinopathy was a change in the mean deviation on frequency doubling technology testing. RESULTS: Among 127 baseline participants, 79 completed in-person follow-up (age 46.0 ± 11.3 years [mean ± SD], 73.4% female). Participants lost a mean of 31.0 kg (SD 18.4), and all metabolic risk factors improved except for BP and total cholesterol. Following bariatric surgery, one of the primary PN outcomes improved (IENFD proximal thigh, +3.4 ± 7.8, p<0.01), and CAN (E/I ratio -0.01 ± 0.1, p=0.89) and retinopathy (deviation -0.2 ± 3.0, p=0.52) were stable. Linear regression revealed that a greater reduction in fasting glucose was associated with improvements in retinopathy (mean deviation point estimate -0.7, 95% CI -1.3, -0.1). CONCLUSIONS/INTERPRETATION: Bariatric surgery may be an effective approach to reverse PN in individuals with obesity. The observed stability of CAN and retinopathy may be an improvement compared with the natural progression of these conditions; however, controlled trials are needed.

mTORC1 regulates high levels of protein synthesis in retinal ganglion cells of adult mice.

Mechanistic target of rapamycin (mTOR) and mTOR complex 1 (mTORC1), linchpins of the nutrient sensing and protein synthesis pathways, are present at relatively high levels in the ganglion cell layer (GCL) and retinal ganglion cells (RGCs) of rodent and human retinas. However, the role of mTORCs in the control of protein synthesis in RGC is unknown. Here, we applied the SUrface SEnsing of Translation (SUnSET) method of nascent protein labeling to localize and quantify protein synthesis in the retinas of adult mice. We also used intravitreal injection of an adeno-associated virus 2 vector encoding Cre recombinase in the eyes of mtor- or rptor-floxed mice to conditionally knockout either both mTORCs or only mTORC1, respectively, in cells within the GCL. A novel vector encoding an inactive Cre mutant (CreΔC) served as control. We found that retinal protein synthesis was highest in the GCL, particularly in RGC. Negation of both complexes or only mTORC1 significantly reduced protein synthesis in RGC. In addition, loss of mTORC1 function caused a significant reduction in the pan-RGC marker, RNA-binding protein with multiple splicing, with little decrease of the total number of cells in the RGC layer, even at 25 weeks after adeno-associated virus-Cre injection. These findings reveal that mTORC1 signaling is necessary for maintaining the high rate of protein synthesis in RGCs of adult rodents, but it may not be essential to maintain RGC viability. These findings may also be relevant to understanding the pathophysiology of RGC disorders, including glaucoma, diabetic retinopathy, and optic neuropathies.

Insulin-like growth factor-2 regulates basal retinal insulin receptor activity.

The retinal insulin receptor (IR) exhibits basal kinase activity equivalent to that of the liver of fed animals, but unlike the liver, does not fluctuate with feeding and fasting; it also declines rapidly after the onset of insulin-deficient diabetes. The ligand(s) that determine basal IR activity in the retina has not been identified. Using a highly sensitive insulin assay, we found that retinal insulin concentrations remain constant in fed versus fasted rats and in diabetic versus control rats; vitreous fluid insulin levels were undetectable. Neutralizing antibodies against insulin-like growth factor 2 (IGF-2), but not insulin-like growth factor 1 (IGF-1) or insulin, decreased IR kinase activity in normal rat retinas, and depletion of IGF-2 from serum specifically reduced IR phosphorylation in retinal cells. Immunoprecipitation studies demonstrated that IGF-2 induced greater phosphorylation of the retinal IR than the IGF-1 receptor. Retinal IGF-2 mRNA content was 10-fold higher in adults than pups and orders of magnitude higher than in liver. Diabetes reduced retinal IGF-2, but not IGF-1 or IR, mRNA levels, and reduced IGF-2 and IGF-1 content in vitreous fluid. Finally, intravitreal administration of IGF-2 (mature and pro-forms) increased retinal IR and Akt kinase activity in diabetic rats. Collectively, these data reveal that IGF-2 is the primary ligand that defines basal retinal IR activity and suggest that reduced ocular IGF-2 may contribute to reduced IR activity in response to diabetes. These findings may have importance for understanding the regulation of metabolic and prosurvival signaling in the retina.

American Association of Clinical Endocrinology Clinical Practice Guideline: Developing a Diabetes Mellitus Comprehensive Care Plan-2022 Update.

OBJECTIVE: The objective of this clinical practice guideline is to provide updated and new evidence-based recommendations for the comprehensive care of persons with diabetes mellitus to clinicians, diabetes-care teams, other health care professionals and stakeholders, and individuals with diabetes and their caregivers. METHODS: The American Association of Clinical Endocrinology selected a task force of medical experts and staff who updated and assessed clinical questions and recommendations from the prior 2015 version of this guideline and conducted literature searches for relevant scientific papers published from January 1, 2015, through May 15, 2022. Selected studies from results of literature searches composed the evidence base to update 2015 recommendations as well as to develop new recommendations based on review of clinical evidence, current practice, expertise, and consensus, according to established American Association of Clinical Endocrinology protocol for guideline development. RESULTS: This guideline includes 170 updated and new evidence-based clinical practice recommendations for the comprehensive care of persons with diabetes. Recommendations are divided into four sections: (1) screening, diagnosis, glycemic targets, and glycemic monitoring; (2) comorbidities and complications, including obesity and management with lifestyle, nutrition, and bariatric surgery, hypertension, dyslipidemia, retinopathy, neuropathy, diabetic kidney disease, and cardiovascular disease; (3) management of prediabetes, type 2 diabetes with antihyperglycemic pharmacotherapy and glycemic targets, type 1 diabetes with insulin therapy, hypoglycemia, hospitalized persons, and women with diabetes in pregnancy; (4) education and new topics regarding diabetes and infertility, nutritional supplements, secondary diabetes, social determinants of health, and virtual care, as well as updated recommendations on cancer risk, nonpharmacologic components of pediatric care plans, depression, education and team approach, occupational risk, role of sleep medicine, and vaccinations in persons with diabetes. CONCLUSIONS: This updated clinical practice guideline provides evidence-based recommendations to assist with person-centered, team-based clinical decision-making to improve the care of persons with diabetes mellitus.

A validated analysis pipeline for mass spectrometry-based vitreous proteomics: new insights into proliferative diabetic retinopathy.

BACKGROUND: Vitreous is an accessible, information-rich biofluid that has recently been studied as a source of retinal disease-related proteins and pathways. However, the number of samples required to confidently identify perturbed pathways remains unknown. In order to confidently identify these pathways, power analysis must be performed to determine the number of samples required, and sample preparation and analysis must be rigorously defined. METHODS: Control (n = 27) and proliferative diabetic retinopathy (n = 23) vitreous samples were treated as biologically distinct individuals or pooled together and aliquoted into technical replicates. Quantitative mass spectrometry with tandem mass tag labeling was used to identify proteins in individual or pooled control samples to determine technical and biological variability. To determine effect size and perform power analysis, control and proliferative diabetic retinopathy samples were analyzed across four 10-plexes. Pooled samples were used to normalize the data across plexes and generate a single data matrix for downstream analysis. RESULTS: The total number of unique proteins identified was 1152 in experiment 1, 989 of which were measured in all samples. In experiment 2, 1191 proteins were identified, 727 of which were measured across all samples in all plexes. Data are available via ProteomeXchange with identifier PXD025986. Spearman correlations of protein abundance estimations revealed minimal technical (0.99-1.00) and biological (0.94-0.98) variability. Each plex contained two unique pooled samples: one for normalizing across each 10-plex, and one to internally validate the normalization algorithm. Spearman correlation of the validation pool following normalization was 0.86-0.90. Principal component analysis revealed stratification of samples by disease and not by plex. Subsequent differential expression and pathway analyses demonstrated significant activation of metabolic pathways and inhibition of neuroprotective pathways in proliferative diabetic retinopathy samples relative to controls. CONCLUSIONS: This study demonstrates a feasible, rigorous, and scalable method that can be applied to future proteomic studies of vitreous and identifies previously unrecognized metabolic pathways that advance understanding of diabetic retinopathy.

mTORC1 and mTORC2 expression in inner retinal neurons and glial cells.

The retina is one of the most metabolically active tissues, yet the processes that control retinal metabolism remains poorly understood. The mTOR complex (mTORC) that drives protein and lipid biogenesis and autophagy has been studied extensively in regards to retinal development and responses to optic nerve injury but the processes that regulate homeostasis in the adult retina have not been determined. We previously demonstrated that normal adult retina has high rates of protein synthesis compared to skeletal muscle, associated with high levels of mechanistic target of rapamycin (mTOR), a kinase that forms multi-subunit complexes that sense and integrate diverse environmental cues to control cell and tissue physiology. This study was undertaken to: 1) quantify expression of mTOR complex 1 (mTORC1)- and mTORC2-specific partner proteins in normal adult rat retina, brain and liver; and 2) to localize these components in normal human, rat, and mouse retinas. Immunoblotting and immunoprecipitation studies revealed greater expression of raptor (exclusive to mTORC1) and rictor (exclusive for mTORC2) in normal rat retina relative to liver or brain, as well as the activating mTORC components, pSIN1 and pPRAS40. By contrast, liver exhibits greater amounts of the mTORC inhibitor, DEPTOR. Immunolocalization studies for all three species showed that mTOR, raptor, and rictor, as well as most other known components of mTORC1 and mTORC2, were primarily localized in the inner retina with mTORC1 primarily in retinal ganglion cells (RGCs) and mTORC2 primarily in glial cells. In addition, phosphorylated ribosomal protein S6, a direct target of the mTORC1 substrate ribosomal protein S6 kinase beta-1 (S6K1), was readily detectable in RGCs, indicating active mTORC1 signaling, and was preserved in human donor eyes. Collectively, this study demonstrates that the inner retina expresses high levels of mTORC1 and mTORC2 and possesses active mTORC1 signaling that may provide cell- and tissue-specific regulation of homeostatic activity. These findings help to define the physiology of the inner retina, which is key for understanding the pathophysiology of optic neuropathies, glaucoma and diabetic retinopathy.

New insights into the mechanisms of diabetic complications: role of lipids and lipid metabolism.

Diabetes adversely affects multiple organs, including the kidney, eye and nerve, leading to diabetic kidney disease, diabetic retinopathy and diabetic neuropathy, respectively. In both type 1 and type 2 diabetes, tissue damage is organ specific and is secondary to a combination of multiple metabolic insults. Hyperglycaemia, dyslipidaemia and hypertension combine with the duration and type of diabetes to define the distinct pathophysiology underlying diabetic kidney disease, diabetic retinopathy and diabetic neuropathy. Only recently have the commonalities and differences in the metabolic basis of these tissue-specific complications, particularly those involving local and systemic lipids, been systematically examined. This review focuses on recent progress made using preclinical models and human-based approaches towards understanding how bioenergetics and metabolomic profiles contribute to diabetic kidney disease, diabetic retinopathy and diabetic neuropathy. This new understanding of the biology of complication-prone tissues highlights the need for organ-specific interventions in the treatment of diabetic complications.

Bioelectric impact of pathological angiogenesis on vascular function.

Pathological angiogenesis, as seen in many inflammatory, immune, malignant, and ischemic disorders, remains an immense health burden despite new molecular therapies. It is likely that further therapeutic progress requires a better understanding of neovascular pathophysiology. Surprisingly, even though transmembrane voltage is well known to regulate vascular function, no previous bioelectric analysis of pathological angiogenesis has been reported. Using the perforated-patch technique to measure vascular voltages in human retinal neovascular specimens and rodent models of retinal neovascularization, we discovered that pathological neovessels generate extraordinarily high voltage. Electrophysiological experiments demonstrated that voltage from aberrantly located preretinal neovascular complexes is transmitted into the intraretinal vascular network. With extensive neovascularization, this voltage input is substantial and boosts the membrane potential of intraretinal blood vessels to a suprahyperpolarized level. Coincident with this suprahyperpolarization, the vasomotor response to hypoxia is fundamentally altered. Instead of the compensatory dilation observed in the normal retina, arterioles constrict in response to an oxygen deficiency. This anomalous vasoconstriction, which would potentiate hypoxia, raises the possibility that the bioelectric impact of neovascularization on vascular function is a previously unappreciated pathophysiological mechanism to sustain hypoxia-driven angiogenesis.

Shared and distinct lipid-lipid interactions in plasma and affected tissues in a diabetic mouse model.

Lipids are ubiquitous metabolites with diverse functions; abnormalities in lipid metabolism appear to be related to complications from multiple diseases, including type 2 diabetes. Through technological advances, the entire lipidome has been characterized and researchers now need computational approaches to better understand lipid network perturbations in different diseases. Using a mouse model of type 2 diabetes with microvascular complications, we examined lipid levels in plasma and in renal, neural, and retinal tissues to identify shared and distinct lipid abnormalities. We used correlation analysis to construct interaction networks in each tissue, to associate changes in lipids with changes in enzymes of lipid metabolism, and to identify overlap of coregulated lipid subclasses between plasma and each tissue to define subclasses of plasma lipids to use as surrogates of tissue lipid metabolism. Lipid metabolism alterations were mostly tissue specific in the kidney, nerve, and retina; no lipid changes correlated between the plasma and all three tissue types. However, alterations in diacylglycerol and in lipids containing arachidonic acid, an inflammatory mediator, were shared among the tissue types, and the highly saturated cholesterol esters were similarly coregulated between plasma and each tissue type in the diabetic mouse. Our results identified several patterns of altered lipid metabolism that may help to identify pathogenic alterations in different tissues and could be used as biomarkers in future research into diabetic microvascular tissue damage.

Neurodegeneration in diabetic retinopathy: does it really matter?

The concept of diabetic retinopathy as a microvascular disease has evolved, in that it is now considered a more complex diabetic complication in which neurodegeneration plays a significant role. In this article we provide a critical overview of the role of microvascular abnormalities and neurodegeneration in the pathogenesis of diabetic retinopathy. A special emphasis is placed on the pathophysiology of the neurovascular unit (NVU), including the contributions of microvascular and neural elements. The potential mechanisms linking retinal neurodegeneration and early microvascular impairment, and the effects of neuroprotective drugs are summarised. Additionally, we discuss how the assessment of retinal neurodegeneration could be an important index of cognitive status, thus helping to identify individuals at risk of dementia, which will impact on current procedures for diabetes management. We conclude that glial, neural and microvascular dysfunction are interdependent and essential for the development of diabetic retinopathy. Despite this intricate relationship, retinal neurodegeneration is a critical endpoint and neuroprotection, itself, can be considered a therapeutic target, independently of its potential impact on microvascular disease. In addition, interventional studies targeting pathogenic pathways that impact the NVU are needed. Findings from these studies will be crucial, not only for increasing our understanding of diabetic retinopathy, but also to help to implement a timely and efficient personalised medicine approach for treating this diabetic complication.

Occludin S490 Phosphorylation Regulates Vascular Endothelial Growth Factor-Induced Retinal Neovascularization.

Occludin is a transmembrane tight junction protein that contributes to diverse cellular functions, including control of barrier properties, cell migration, and proliferation. Vascular endothelial growth factor (VEGF) induces phosphorylation of occludin at S490, which is required for VEGF-induced endothelial permeability. Herein, we demonstrate that occludin S490 phosphorylation also regulates VEGF-induced retinal endothelial cell proliferation and neovascularization. Using a specific antibody, phospho-occludin was located in centrosomes in endothelial cell cultures, animal models, and human surgical samples of retinal neovessels. Occludin S490 phosphorylation was found to increase with endothelial tube formation in vitro and in vivo during retinal neovascularization after induction of VEGF expression. More important, expression of occludin mutated at S490 to Ala, completely inhibited angiogenesis in cell culture models and in vivo. Collectively, these data suggest a novel role for occludin in regulation of endothelial proliferation and angiogenesis in a phosphorylation-dependent manner. These findings may lead to methods of regulating pathological neovascularization by specifically targeting endothelial cell proliferation.

Incidence and Risk Factors for Developing Diabetic Retinopathy among Youths with Type 1 or Type 2 Diabetes throughout the United States.

PURPOSE: Despite the increasing prevalence of type 2 diabetes mellitus (T2DM) among children and adolescents, little is known about their risk of developing diabetic retinopathy (DR). We sought to identify risk factors for DR in youths with diabetes mellitus, to compare DR rates for youths with type 1 diabetes mellitus (T1DM) and those with T2DM, and to assess whether adherence to DR screening guidelines promoted by the American Academy of Ophthalmology, American Academy of Pediatrics, and American Diabetes Association adequately capture youths with DR. DESIGN: Retrospective observational longitudinal cohort study. PARTICIPANTS: Youths aged ≤21 years with newly diagnosed T1DM or T2DM who were enrolled in a large US managed-care network. METHODS: In this study of youths aged ≤21 years with newly diagnosed T1DM or T2DM who were under ophthalmic surveillance, we identified the incidence and timing of DR onset. Kaplan-Meier survival curves assessed the timing of initial diagnosis of DR for participants. Multivariable Cox proportional hazard regression modeling identified factors associated with the hazard of developing DR. Model predictors were age and calendar year at initial diabetes mellitus diagnosis, sex, race/ethnicity, net worth, and glycated hemoglobin A1c fraction (HbA1c). MAIN OUTCOME MEASURES: Hazard ratios (HRs) with 95% confidence intervals (CIs) for developing DR. RESULTS: Among the 2240 youths with T1DM and 1768 youths with T2DM, 20.1% and 7.2% developed DR over a median follow-up time of 3.2 and 3.1 years, respectively. Survival curves demonstrated that youths with T1DM developed DR faster than youths with T2DM (P < 0.0001). For every 1-point increase in HbA1c, the hazard for DR increased by 20% (HR = 1.20; 95% CI 1.06-1.35) and 30% (HR = 1.30; 95% CI 1.08-1.56) among youths with T1DM and T2DM, respectively. Current guidelines suggest that ophthalmic screening begin 3 to 5 years after initial diabetes mellitus diagnosis, at which point in our study, >18% of youths with T1DM had already received ≥1 DR diagnosis. CONCLUSIONS: Youths with T1DM or T2DM exhibit a considerable risk for DR and should undergo regular screenings by eye-care professionals to ensure timely DR diagnosis and limit progression to vision-threatening disease.

The neurovascular unit and the pathophysiologic basis of diabetic retinopathy.

PURPOSE: To relate the concept of the retinal neurovascular unit and its alterations in diabetes to the pathophysiology of diabetic retinopathy. METHODS: Case illustrations and conceptual frameworks are presented that illustrate adaptive and maladaptive "dis-integration" of the retinal neurovascular unit with the progression of diabetes. RESULTS: Retinopathy treatment should address pathophysiologic processes rather than pathologic lesions as is current practice. CONCLUSIONS: Future improvements in the treatment of diabetic retinopathy requires deeper understanding of the cellular and molecular changes induced by diabetes, coupled with the use of quantitative phenotyping methods that assess the pathophysiologic processes.

Rates of Vitrectomy among Enrollees in a United States Managed Care Network, 2001-2012.

PURPOSE: To determine whether vitrectomy surgery rates have changed over the past decade and factors affecting the odds of undergoing this procedure. DESIGN: Retrospective, longitudinal cohort study. PARTICIPANTS: All enrollees 21 years of age or older between 2001 and 2012 in a United States managed care network. METHODS: Claims data from a managed care network were analyzed to identify all enrollees who underwent 1 vitrectomy or more each year from 2001 through 2012. Rates of vitrectomy per 1000 enrollees were computed each year from 2001 through 2012 for the entire group and separately for patients with and without diabetes mellitus. Multivariate logistic regression assessed factors affecting the odds of undergoing vitrectomy surgery. MAIN OUTCOME MEASURES: Annual rates of vitrectomy surgery from 2001 through 2012 and odds ratios (ORs) of undergoing a vitrectomy with 95% confidence intervals (CIs). RESULTS: Among the 11 161 907 eligible enrollees, 40 892 (0.4%) underwent vitrectomy over the 12-year period. The average age of those undergoing vitrectomy was 57±13 years. Overall vitrectomy rates increased 31% from 2001 to 2012 (from 1.47 to 1.92 per 1000 patients). During this same period, the vitrectomy rate among persons with diabetes mellitus decreased by 43% (from 5.84 to 3.31 per 1000 patients with diabetes). Women had 24% decreased odds of undergoing vitrectomy (adjusted odds ratio [OR], 0.76; 95% confidence interval [CI], 0.72-0.79). The odds of undergoing a vitrectomy were 17% greater for black persons (adjusted OR, 1.17; 95% CI, 1.07-1.27) and 7% higher for persons with diabetes (adjusted OR, 1.07; 95% CI, 1.01-1.14). CONCLUSIONS: Overall, we observed an increase in the vitrectomy rates per 1000 enrollees in this large managed care network over the course of the past decade. However, among persons with diabetes mellitus, vitrectomy rates declined substantially over this period. These changes may be explained, in part, by advances in surgical instrumentation and imaging methods to detect retinal diseases changing indications for surgery, improvements in diabetes care, and alternative treatment options for managing retinal conditions. These results may be useful for future planning of manpower needs and highlight the need for aggressive prevention of complications in black persons with diabetes.

Insulin-like growth factor 1 rescues R28 retinal neurons from apoptotic death through ERK-mediated BimEL phosphorylation independent of Akt.

Insulin-like growth factor 1 (IGF-1) can provide long-term neurotrophic support by activation of Akt, inhibition of FoxO nuclear localization and suppression of Bim gene transcription in multiple neuronal systems. However, MEK/ERK activation can also promote neuron survival through phosphorylation of BimEL. We explored the contribution of the PI3K/Akt/FoxO and MEK/ERK/BimEL pathways in IGF-1 stimulated survival after serum deprivation (SD) of R28 cells differentiated to model retinal neurons. IGF-1 caused rapid activation of Akt leading to FoxO1/3-T32/T24 phosphorylation, and prevented FoxO1/3 nuclear translocation and Bim mRNA upregulation in response to SD. IGF-1 also caused MAPK/MEK pathway activation as indicated by ERK1/2-T202/Y204 and Bim-S65 phosphorylation. Overexpression of FoxO1 increased Bim mRNA expression and amplified the apoptotic response to SD without shifting the serum response curve. Inhibition of Akt activation with LY294002 or by Rictor knockdown did not block the protective effect of IGF-1, while inhibition of MEK activity with PD98059 prevented Bim phosphorylation and blocked IGF-1 protection. In addition, knockdown of Bim expression was protective during SD, while co-silencing of FoxO1 and Fox03 expression had little effect. Thus, the PI3K/Akt/FoxO pathway was not essential for protection from SD-induced apoptosis by IGF-1 in R28 cells. Instead, IGF-1 protection was dependent on activation of the MEK/ERK pathway leading to BimEL phosphorylation, which is known to prevent Bax/Bak oligomerization and activation of the intrinsic mitochondrial apoptosis pathway. These studies demonstrate the requirement of the MEK/ERK pathway in a model of retinal neuron cell survival and highlight the cell specificity for IGF-1 signaling in this response.

Phosphatase control of 4E-BP1 phosphorylation state is central for glycolytic regulation of retinal protein synthesis.

Control of protein synthesis in insulin-responsive tissues has been well characterized, but relatively little is known about how this process is regulated in nervous tissues. The retina exhibits a relatively high protein synthesis rate, coinciding with high basal Akt and metabolic activities, with the majority of retinal ATP being derived from aerobic glycolysis. We examined the dependency of retinal protein synthesis on the Akt-mTOR signaling and glycolysis using ex vivo rat retinas. Akt inhibitors significantly reduced retinal protein synthesis but did not affect glycolytic lactate production. Surprisingly, the glycolytic inhibitor 2-deoxyglucose (2-DG) markedly inhibited Akt1 and Akt3 activities, as well as protein synthesis. The effects of 2-DG, and 2-fluorodeoxyglucose (2-FDG) on retinal protein synthesis correlated with inhibition of lactate production and diminished ATP content, with all these effects reversed by provision of d-mannose. 2-DG treatment was not associated with increased AMPK, eEF2, or eIF2α phosphorylation; instead, it caused rapid dephosphorylation of 4E-BP1. 2-DG reduced total mTOR activity by 25%, but surprisingly, it did not reduce mTORC1 activity, as indicated by unaltered raptor-associated mTOR autophosphorylation and ribosomal protein S6 phosphorylation. Dephosphorylation of 4E-BP1 was largely prevented by inhibition of PP1/PP2A phosphatases with okadaic acid and calyculin A, and inhibition of PPM1 phosphatases with cadmium. Thus, inhibition of retinal glycolysis diminished Akt and protein synthesis coinciding with accelerated dephosphorylation of 4E-BP1 independently of mTORC1. These results demonstrate a novel mechanism regulating protein synthesis in the retina involving an mTORC1-independent and phosphatase-dependent regulation of 4E-BP1.

Multimodal characterization of proliferative diabetic retinopathy reveals alterations in outer retinal function and structure.

PURPOSE: To identify changes in retinal function and structure in persons with proliferative diabetic retinopathy (PDR), including the effects of panretinal photocoagulation (PRP). DESIGN: Cross-sectional study. PARTICIPANTS: Thirty adults who underwent PRP for PDR, 15 adults with untreated PDR, and 15 age-matched controls. METHODS: Contrast sensitivity, frequency doubling perimetry (FDP), Humphrey visual fields, photostress recovery, and dark adaptation were assessed. Fundus photography and macular spectral-domain optical coherence tomography (SD OCT) were performed. To quantify retinal layer thicknesses, SD OCT scans were segmented semiautomatically. MAIN OUTCOME MEASURES: Visual function measures were compared among patients with PDR and PRP, untreated patients with PDR, and controls. Mean retinal layer thicknesses were compared between groups. Correlation analyses were performed to evaluate associations between visual function measures and retinal layer thicknesses. RESULTS: A significant reduction of FDP mean deviation (MD) was exhibited in PRP-treated patients with PDR (MD ± standard deviation, -8.20±5.76 dB; P < 0.0001) and untreated patients (-5.48±4.48 dB; P < 0.0001) relative to controls (1.07±2.50 dB). Reduced log contrast sensitivity compared with controls (1.80±0.14) also was observed in both PRP-treated patients (1.42±0.17; P < 0.0001) and untreated patients (1.56±0.20; P = 0.001) with PDR. Compared with controls, patients treated with PRP demonstrated increased photostress recovery time (151.02±104.43 vs. 70.64±47.14 seconds; P = 0.001) and dark adaptation speed (12.80±5.15 vs. 9.74±2.56 minutes; P = 0.022). Patients who underwent PRP had diffusely thickened nerve fiber layers (P = 0.024) and diffusely thinned retinal pigment epithelium (RPE) layers (P = 0.009) versus controls. Untreated patients with PDR also had diffusely thinned RPE layers (P = 0.031) compared with controls. CONCLUSIONS: Patients with untreated PDR exhibited inner retinal dysfunction, as evidenced by reduced contrast sensitivity and FDP performance, accompanied by alterations in inner and outer retinal structure. Patients who underwent PRP had more profound changes in outer retinal structure and function. Distinguishing the effects of PDR and PRP may guide the development of restorative vision therapies for patients with advanced diabetic retinopathy.

Impaired coronary and retinal vasomotor function to hyperoxia in Individuals with Type 2 diabetes.

PURPOSE: Adults with diabetes are at a high risk of developing coronary heart disease. The purpose of this study was to assess coronary artery vascular function non-invasively in individuals with and without Type 2 diabetes and to compare these coronary responses to another microvascular bed (i.e. retina). We hypothesized that individuals with diabetes would have impaired coronary reactivity and that these impairments would be associated with impairments in retinal reactivity. METHODS: Coronary blood velocity (Transthoracic Doppler Echocardiography) and retinal diameters (Dynamic Vessel Analyzer) were measured continuously during five minutes of breathing 100% oxygen (i.e. hyperoxia) in 15 persons with Type 2 diabetes and 15 age-matched control subjects. Using fundus photographs, retinal vascular calibers were also measured (central retinal arteriole and venule equivalents). RESULTS: Individuals with diabetes compared to controls had impaired coronary (-2.34±16.64% vs. -14.27±10.58%, P=0.03) and retinal (arteriole: -0.04±3.34% vs. -3.65±5.07%, P=0.03; venule: -1.65±3.68% vs. -5.23±5.47%, P=0.05) vasoconstrictor responses to hyperoxia, and smaller central arteriole-venule equivalent ratios (0.83±0.07 vs. 0.90±0.07, P=0.014). Coronary reactivity was associated with central retinal arteriole equivalents (r=-0.516, P=0.005) and retinal venular reactivity (r=0.387, P=0.034). CONCLUSION: Diabetes impairs coronary and retinal microvascular function to hyperoxia. Impaired vasoconstrictor responses may be part of a systemic diabetic vasculopathy, which may contribute to adverse cardiovascular events in individuals with diabetes.

Retinal Failure in Diabetes: a Feature of Retinal Sensory Neuropathy.

Physiologic adaptations mediate normal responses to short-term and long-term stresses to ensure organ function. Organ failure results if adaptive responses fail to resolve persistent stresses or maladaptive reactions develop. The retinal neurovascular unit likewise undergoes adaptive responses to diabetes resulting in a retinal sensory neuropathy analogous to other sensory neuropathies. Vision-threatening diabetic retinal neuropathy results from unremitting metabolic and inflammatory stresses, leading to macular edema and proliferative diabetic retinopathy, states of "retinal failure." Current regulatory strategies focus primarily on the retinal failure stages, but new diagnostic modalities and understanding of the pathophysiology of diabetic retinopathy may facilitate earlier treatment to maintain vision in persons with diabetes.