The retinas of heterozygous male Ins2(Akita) mice exhibit vascular, neural, and glial abnormalities generally consistent with clinical observations and other animal models of diabetes. In light of the relatively early, spontaneous onset of the disease and the popularity of the C57BL/6J inbred strain as a background for the generation and study of other genetic alterations, combining the Ins2(Akita) mutation with other engineered mutations will be of great use for studying the molecular basis of retinal complications of diabetes.

Leucine is recognized as a nutrient signal; however, the long-term in vivo consequences of leucine signaling and the role of branched-chain amino acid (BCAA) metabolism in this signaling remain unclear. To investigate these questions, we disrupted the BCATm gene, which encodes the enzyme catalyzing the first step in peripheral BCAA metabolism. BCATm(-/-) mice exhibited elevated plasma BCAAs and decreased adiposity and body weight, despite eating more food, along with increased energy expenditure, remarkable improvements in glucose and insulin tolerance, and protection from diet-induced obesity. The increased energy expenditure did not seem to be due to altered locomotor activity, uncoupling proteins, sympathetic activity, or thyroid hormones but was strongly associated with food consumption and an active futile cycle of increased protein degradation and synthesis. These observations suggest that elevated BCAAs and/or loss of BCAA catabolism in peripheral tissues play an important role in regulating insulin sensitivity and energy expenditure.

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...

We describe a general way of introducing transgenes into the mouse germ line for comparing different sequences without the complications of variation in copy nuniber and insertion site. The method uses homologous recombination in embryonic stem (ES) cells to generate mice having a single copy of a transgene integrated into a chosen location in the genome. To test the method, a single copy murine bcl-2 cDNA driven by either a chicken 8-actin promoter or a human 18-actin promoter has been inserted immediately 5' to the X-linked hypoxanthine phosphoribosyltransferase locus by a directly selectable homologous recombination event. The level of expression of the targeted bcl-2 transgene in ES cells is identical in independently isolated homologous recombinants having the same promoter yet varies between the different promoters. In contrast, the expression of bcl-2 transgenes having the same (chicken ,B-actin) promoter varies drastically when they are independently integrated at random insertion sites. Both promoters direct broad expression of the single-copy transgene in mice derived from the respective targeted ES cells. In vitro and in vivo, the human f8-actin promoter consistently directed a higher level of transgene expression than the chicken f8-actin promoter.