Diabetic retinopathy remains a frightening prospect to patients and frustrates physicians. Destruction of damaged retina by photocoagulation remains the primary treatment nearly 50 years after its introduction. The diabetes pandemic requires new approaches to understand the pathophysiology and improve the detection, prevention, and treatment of retinopathy. This perspective considers how the unique anatomy and physiology of the retina may predispose it to the metabolic stresses of diabetes. The roles of neural retinal alterations and impaired retinal insulin action in the pathogenesis of early retinopathy and the mechanisms of vision loss are emphasized. Potential means to overcome limitations of current animal models and diagnostic testing are also presented with the goal of accelerating therapies to manage retinopathy in the face of ongoing diabetes. Diabetes 55:2401-2411, 2006 D espite years of clinical and laboratory investigation, diabetic retinopathy remains the leading cause of vision impairment and blindness among working-age adults, yet the fundamental cause(s) remains uncertain. Retinal photocoagulation to reduce neovascularization and macular edema was developed in the 1950s and is still the standard of care (1). The number of people worldwide at risk of developing vision loss from diabetes is predicted to double over the next 30 years (2), so it is imperative to develop better means to identify, prevent, and treat retinopathy in its earliest stages rather than wait for the onset of vision-threatening lesions. Progress in these areas requires a new perspective on the problem that includes the roles of the neural retina, impaired insulin action, and inflammation. In this way, established neurobiological principles can inform us how diabetes impairs vision, and knowledge of metabolism, inflammation, and regenerative medicine may lead to new treatments.This perspective will discuss how the unique anatomy and physiology of the retina may render it vulnerable to the metabolic derangements of diabetes and lead to impaired vision. The intent of this unconventional approach is to encourage consideration of new opportunities for investigations that will advance the field. NORMAL RETINAL STRUCTURE AND PHYSIOLOGY Topographic and cellular organization of the retina.It is instructive to consider the functional organization of the retina (literally a network) to better understand the impact of diabetes (http://webvision.med.utah.edu). The retina is a transparent layer of neural tissue between the retinal pigmented epithelium and the vitreous body. Normal vision depends on intact cell-cell communication among the neuronal, glial, microglial, vascular, and pigmented epithelial cells of the retina. The fundamental functions of the retina are to capture photons, convert the photochemical energy into electrical energy, integrate the resulting action potentials, and transmit them to the occipital lobe of the brain, where they are deciphered and interpreted into recognizable images. The retina is partitioned from the syst...

The minimal DNA sequence required for glucocorticoid induction of the phosphoenolpyruvate carboxykinase (PEPCK) gene in H4IIE rat hepatoma cells was defined. This novel glucocorticoid response unit (GRU) spans about 110 base pairs (bp) and includes two receptor-binding elements plus two accessory factor-binding elements. Purified glucocorticoid receptor bound to two regions (GR1 and GR2) between -395 and -349 bp relative to the transcription start site. Factors in crude rat liver nuclear extract bound to DNA in the regions -455 to -431 and -420 to -403 bp, which are designated accessory factor 1 (AF1) and accessory factor 2 (AF2) elements, respectively. Gel retardation analysis revealed that at least two proteins bound to AF1 and that they were distinct from the protein(s) that bound to AF2. Various combinations of GR1, GR2, AF1, and AF2 were fused to the chloramphenicol acetyltransferase (CAT) reporter gene and cotransfected with a glucocorticoid receptor expression plasmid (pSVGR1) into H4IIE cells to identify the functional GRU. Neither the glucocorticoid receptor binding region nor the accessory factor binding region alone was sufficient to confer glucocorticoid responsiveness. The two components of the glucocorticoid receptor binding region functioned independently, and each accounted for half of the maximal response, provided the accessory factor elements were present. Similarly, deletion of either AF1 or AF2 diminished glucocorticoid induction of the PEPCK gene to approximately half of the maximum. We propose that the complex PEPCK gene GRU provides the stringent regulation required of this critical enzyme in liver.

This study was undertaken to examine the interaction of platelet size and age in determining in vitro platelet function. Baboon megakaryocytes were labeled in vivo by the injection of 75Se- methionine. Blood was collected when the label was predominantly associated with younger platelets (day 2) and with older platelets (day 9). Size-dependent platelet subpopulations were prepared on both days by counterflow centrifugation. The reactivity of each platelet subpopulation was determined on both days by measuring thrombin-induced aggregation. Platelets were fixed after partial aggregation had occurred by the addition of EDTA/formalin. After removal of the aggregated platelets by differential centrifugation, the supernatant medium was assayed for remaining platelets and 75Se radioactivity. Comparing day 2 and day 9, no significant difference was seen in the rate of aggregation of a given subpopulation. However, aggregation was more rapid in the larger platelet fractions than in the smaller ones on both days. A greater percentage of the 75Se radioactivity appeared in the platelet aggregates on day 2 than on day 9. This effect was independent of platelet size, as it occurred to a similar extent in the unfractionated platelets and in each of the size-dependent platelet subpopulations. The data indicate that young platelets are more active than older platelets. This study demonstrates that size and age are both determinants of platelet function, but by independent mechanisms.

Promoter elements important for basal and cyclic AMP (cAMP)-regulated expression of the phosphoenolpyruvate carboxykinase (PEPCK) Analysis of the expression of fusion genes, in which the coding sequence of a reporter gene is placed under the control of putative regulatory elements of a test gene, has resulted in the identification of various cis-acting elements of eucaryotic and viral genes which interact with trans-acting factors to control transcription in mammalian cells (8,28,30). The two classes of cis-acting elements which have been identified are termed promoter and enhancer elements. Promoter elements are characterized by their dependence on position and orientation with respect to the transcription start site (8,28,30). These are typified by the CAAT, SP1, and TATA elements. Enhancer elements are characterized by their ability to exert effects relatively independently of distance from and orientation to the transcription start site (41). Enhancers may be constitutively active, as in the cases of the simian virus 40 enhancer (34) and the basal-level enhancers of the human metallothionein Ila gene (16, 40), or they may be regulatable, as exemplified by the metalregulatory elements of the human metallothionein IIa gene (22,23) and the steroid hormone response elements (22,23,37). Typically, deletion of a regulatable enhancer sequence affects regulated expression but has little or no effect on basal expression of the gene.The gene encoding phosphoenolpyruvate carboxykinase (PEPCK) is regulated at the transcriptional level by a number of hormones (3,10,24,39

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Objective: It is uncertain to what degree the relationship between breastfeeding and later cognitive development is a true biological effect, or is confounded by psychosocial factors. The study aim was to further investigate this relationship and the effect of duration of breast feeding on cognitive development. Methods:A total of 3880 children were followed from birth. Breastfeeding duration was measured by questionaire at 6 months of age and a Peabody Picture Vocabulary Test Revised (PPVT-R) was administered at 5 years. PPVT-R scores were adjusted for the effects of a large array of biological and psychosocial confounders. The relationship between breastfeeding and the mean PPVT-R scores were examined using analysis of variance and multiple linear regression. Results:A strong positive relationship was demonstrated between breastfeeding and the PPVT-R scores with increasing scores with increased duration of breastfeeding. After adjusting for a wide range of biological and social factors, the adjusted mean for those breastfed for 6 months or more was 8.2 points higher for females and 5.8 points for males when compared to those never breastfed. Conclusion:These findings suggest a significant benefit to child development is conferred by breastfeeding and is related independently to longer periods of breastfeeding. Keywords: breastfeeding; child development; intelligence; Peabody; cohort studies A substantial body of evidence suggests a benefit on cognitive development in infants as a result of breastfeeding. [1][2][3][4][5][6][7] Several population studies have been conducted in term infants, the majority of which show a positive effect on cognitive development in breastfed infants. [2][3][4][5] This positive association is by no means universal or necessarily indicative of a causal association. Several studies have shown that a large number of social and parental educational factors that could reasonably be expected to influence child development independently effect the incidence of breastfeeding. [2-4] Studies by Silva et al. [8] Jacobson et al.,[9] and Wigg et al. [10] suggest that once con-founders such as social advantage, maternal education and intelligence, and the quality of a child's developmental experiences were taken into account, the differences between bottle and breastfed groups were no longer statistically significant. A number of criticisms including lack of statistical power, [8] populations initially selected for other exposures [9,10] and the timing and quality of measurement of intervening variables [9] can be made of these studies. Pollock [4] selected a cohort of relatively advantaged mothers, and after controlling for factors associated with the likelihood of breastfeeding, demonstrated that infants breastfed for at least 3 months had small though statistically significant improvements in mean picture vocabulary scores at 5 years and ability scores at 10 years.If the association between breastfeeding and infant cognitive development is causal, two possible explanations have been su...