Retinal gene expression and visually evoked behavior in diabetic long evans rats.

PURPOSE: Patients with diabetic retinopathy may experience severe vision loss due to macular edema and neovascularization secondary to vascular abnormalities. However, before these abnormalities become apparent, there are functional deficits in contrast sensitivity, color perception, and dark adaptation. The goals of this study are to evaluate early changes (up to 3 months) in retinal gene expression, selected visual cycle proteins, and optokinetic tracking (OKT) in streptozotocin (STZ)-induced diabetic rats. METHODS: Retinal gene expression in diabetic Long Evans rats was measured by whole genome microarray 7 days, 4 weeks, and 3 months after the onset of hyperglycemia. Select gene and protein changes were probed by polymerase chain reaction (PCR) and immunohistochemistry, respectively, and OKT thresholds were measured using a virtual optokinetics system. RESULTS: Microarray analysis showed that the most consistently affected molecular and cellular functions were cell-to-cell signaling and interaction, cell death, cellular growth and proliferation, molecular transport, and cellular movement. Further analysis revealed reduced expression of several genes encoding visual cycle proteins including lecithin/retinol acyltransferase (LRAT), retinal pigment epithelium (RPE)-specific protein 65 kDa (RPE65), and RPE retinal G protein-coupled receptor (RGR). These molecular changes occurred simultaneously with a decrease in OKT thresholds by 4 weeks of diabetes. Immunohistochemistry revealed a decrease in RPE65 in the RPE layer of diabetic rats after 3 months of hyperglycemia. CONCLUSIONS: The data presented here are further evidence that inner retinal cells are affected by hyperglycemia simultaneously with blood retinal barrier breakdown, suggesting that glial and neuronal dysfunction may underlie some of the early visual deficits in persons with diabetes.

Strain-dependent increases in retinal inflammatory proteins and photoreceptor FGF-2 expression in streptozotocin-induced diabetic rats.

PURPOSE: Inflammation is thought to play a role in disease progression and vision loss in diabetic retinopathy (DR). However, the level of inflammation and the role of cytokines and growth factors in the early stages of this disease are poorly understood. Streptozotocin (STZ)-induced hyperglycemia in rats is widely used as a model of diabetic retinopathy, and therefore this model was used to better define the inflammatory response and the impact of the genetic background. METHODS: The expression of a panel of 57 inflammatory proteins and growth factors in the retina of three rat strains was compared by using a highly sensitive flow cytometry-based assay. Hyperglycemia was induced in Brown Norway (BN), Long-Evans (LE), and Sprague-Dawley (SD) rats, and protein expression in the retina was measured 4 weeks and 3 months later. RESULTS: The data revealed a subtle, but reproducible, inflammatory response in the retina of SD, but not in those of BN or LE, rats. Upregulation of fibroblast growth factor (FGF)-2 in the photoreceptor nuclear layer coincided with the inflammatory response in SD rats and may constitute a neuroprotective mechanism. Reduced expression of genes involved in the phototransduction pathway indicates altered photoreceptor function. CONCLUSIONS: Taken together, these data show that inflammatory changes in the diabetic rat retina are highly strain dependent, and SD rats exhibit low-level inflammation similar to that observed in diabetic patients. Therefore, SD rats may be a good model for the study of early inflammatory changes in human diabetic retinopathy.

Opposing activities of two novel members of the IL-1 ligand family regulate skin inflammation.

The interleukin (IL)-1 family members IL-1alpha, -1beta, and -18 are potent inflammatory cytokines whose activities are dependent on heterodimeric receptors of the IL-1R superfamily, and which are regulated by soluble antagonists. Recently, several new IL-1 family members have been identified. To determine the role of one of these family members in the skin, transgenic mice expressing IL1F6 in basal keratinocytes were generated. IL1F6 transgenic mice exhibit skin abnormalities that are dependent on IL-1Rrp2 and IL-1RAcP, which are two members of the IL-1R family. The skin phenotype is characterized by acanthosis, hyperkeratosis, the presence of a mixed inflammatory cell infiltrate, and increased cytokine and chemokine expression. Strikingly, the combination of the IL-1F6 transgene with an IL1F5 deficiency results in exacerbation of the skin phenotype, demonstrating that IL-1F5 has antagonistic activity in vivo. Skin from IL1F6 transgenic, IL1F5(-/-) pups contains intracorneal and intraepithelial pustules, nucleated corneocytes, and dilated superficial dermal blood vessels. Additionally, expression of IL1RL2, -1F5, and -1F6 is increased in human psoriatic skin. In summary, dysregulated expression of novel agonistic and antagonistic IL-1 family member ligands can promote cutaneous inflammation, revealing potential novel targets for the treatment of inflammatory skin disorders.

Characterization of the inflammatory response to a highly selective PDE4 inhibitor in the rat and the identification of biomarkers that correlate with toxicity.

The primary toxicity associated with repeated oral administration of the PDE4 inhibitor IC542 to the rat is an inflammatory response leading to tissue damage primarily in the gastrointestinal tract and mesentery. Although necrotizing vasculitis is frequently seen with other PDE4 inhibitors, blood vessel injury was rare following IC542 administration and was always associated with inflammation in the surrounding tissue. The incidence and severity of the histologic changes in these studies correlated with elevated peripheral blood leukocytes, serum IL-6, haptoglobin, and fibrinogen, and with decreased serum albumin. By monitoring haptoglobin, fibrinogen and serum albumin changes in IC542-treated rats, it was possible to identify rats with early histologic changes that were reversible. Since PDE4 inhibition is generally associated with anti-inflammatory activity, extensive inflammation in multiple tissues was unexpected with IC542. Co-administration of dexamethasone completely blocked IC542-induced clinical and histologic changes in the rat, confirming the toxicity resulted from inflammatory response. In addition, IC542 augmented release of the proinflammatory cytokine IL-6 in LPS-activated whole blood from rats but not monkeys or humans. The effect of IC542 on IL-6 release from rat leukocytes in vitro is consistent with the proinflammatory response observed in vivo and demonstrates species differences to PDE4 inhibition.

Characterization of the in vivo function of TNF-alpha-related apoptosis-inducing ligand, TRAIL/Apo2L, using TRAIL/Apo2L gene-deficient mice.

To define the normal physiological role for the TRAIL/Apo2L in vivo, we generated TRAIL/Apo2L gene-targeted mice. These mice develop normally and show no defects in lymphoid or myeloid cell homeostasis or function. Although TRAIL/Apo2L kills transformed cells in vitro, TRAIL/Apo2L(-/-) mice do not spontaneously develop overt tumors at an early age. However, in the A20 B cell lymphoma-transferred tumor model, TRAIL/Apo2L(-/-) mice are clearly more susceptible to death from overwhelming tumor burden, due to increased lymphoma load in the liver. A20 tumors are susceptible to TRAIL/Apo2L killing in vitro, indicating that TRAIL/Apo2L may act directly to control A20 cells in vivo. Despite the fact that TRAIL binds osteoprotegerin and osteoprotegerin-transgenic mice are osteopetrotic, TRAIL/Apo2L(-/-) mice show no evidence of altered gross bone density, and no alterations in frequency or in vitro differentiation of bone marrow precursor osteoclasts. Moreover, leucine zipper TRAIL has no toxicity when repeatedly administered to osteoprotegerin(-/-) mice. Thus, TRAIL/Apo2L is important in controlling tumors in vivo, but is not an essential regulator of osteoprotegerin-mediated biology, under normal physiological conditions.