Knockdown of FABP5 mRNA decreases cellular cholesterol levels and results in decreased apoB100 secretion and triglyceride accumulation in ARPE-19 cells.

To maintain normal retinal function, retinal pigment epithelial (RPE) cells engulf photoreceptor outer segments (ROS) enriched in free fatty acids (FFAs). We have previously demonstrated fatty acid-binding protein 5 (FABP5) downregulation in the RPE/choroidal complex in a mouse model of aging and early age-related macular degeneration. FABPs are involved in intracellular transport of FFAs and their targeting to specific metabolic pathways. To elucidate the role of FABP5 in lipid metabolism, the production of the FABP5 protein in a human RPE cell line was inhibited using RNA interference technology. As a result, the levels of cholesterol and cholesterol ester were decreased by about 40%, whereas FFAs and triglycerides were increased by 18 and 67% after siRNA treatment, respectively. Some species of phospholipids were decreased in siRNA-treated cells. Cellular lipid droplets were evident and apoB secretion was decreased by 76% in these cells. Additionally, we discovered that ARPE-19 cells could synthesize and secrete Apolipoprotein B100 (apoB100), which may serve as a backbone structure for the formation of lipoprotein particles in these cells. Our results indicate that FABP5 mRNA knockdown results in the accumulation of cellular triglycerides, decreased cholesterol levels, and reduced secretion of apoB100 protein and lipoprotein-like particles. These observations indicated that FABP5 plays a critical role in lipid metabolism in RPE cells, suggesting that FABP5 downregulation in the RPE/choroid complex in vivo might contribute to aging and early age-related macular degeneration.

Plumbagin, a novel Nrf2/ARE activator, protects against cerebral ischemia.

Many phytochemicals function as noxious agents that protect plants against insects and other damaging organisms. However, at subtoxic doses, the same phytochemicals may activate adaptive cellular stress response pathways that can protect cells against a variety of adverse conditions. We screened a panel of botanical pesticides using cultured human and rodent neuronal cell models, and identified plumbagin as a novel potent activator of the nuclear factor E2-related factor 2 (Nrf2)/antioxidant response element (ARE) pathway. In vitro, plumbagin increases nuclear localization and transcriptional activity of Nrf2, and induces the expression of the Nrf2/ARE-dependent genes, such as heme oxygenase 1 in human neuroblastoma cells. Plumbagin specifically activates the Nrf2/ARE pathway in primary mixed cultures from ARE-human placental alkaline phosphatase reporter mice. Exposure of neuroblastoma cells and primary cortical neurons to plumbagin provides protection against subsequent oxidative and metabolic insults. The neuroprotective effects of plumbagin are abolished by RNA interference-mediated knockdown of Nrf2 expression. In vivo, administration of plumbagin significantly reduces the amount of brain damage and ameliorates-associated neurological deficits in a mouse model of focal ischemic stroke. Our findings establish precedence for the identification and characterization of neuroprotective phytochemicals based upon their ability to activate adaptive cellular stress response pathways.

Oxidized low density lipoproteins induce a pathologic response by retinal pigmented epithelial cells.

The accumulation of apolipoprotein B100 lipoproteins in Bruch membrane is an early event thought to promote age-related macular degeneration (AMD). Immunohistochemistry using an anti-oxidized low density lipoprotein antibody on 10 AMD specimens showed staining in Bruch membrane including basal deposits, a marker of AMD. To determine whether retinal pigmented epithelial cells develop a pathologic phenotype after interaction with lipoproteins, ARPE-19 cells were exposed to low density lipoproteins (LDL) or oxidized LDLs (oxLDL). Analysis using the Affymetrix U133 Plus 2.0 (Affymetrix, Inc., Santa Clara, CA, USA) gene chip showed physiological and pathological transcriptional responses after LDL and oxLDL treatment, respectively. LDL induced a down-regulation of cholesterol biosynthesis genes while oxLDL induced transcriptional alterations in genes related to lipid metabolism, oxidative stress, inflammation and apoptosis. Electrospray mass spectrometry showed that oxLDL, but not LDL induced large cellular increases of sphingomyelin, ceramides, and cholesteryl esters. With TUNEL labeling, oxLDL caused 14.6% apoptosis compared to <1% after LDL. Addition of an inhibitor of sphingomyelin synthase inhibited this apoptosis by 41%. These data support the hypothesis that oxidized lipoproteins are one trigger for initiating early events in the pathogenesis of AMD.

Diet-induced insulin resistance impairs hippocampal synaptic plasticity and cognition in middle-aged rats.

Overall dietary energy intake, particularly the consumption of simple sugars such as fructose, has been increasing steadily in Western societies, but the effects of such diets on the brain are poorly understood. Here, we used functional and structural assays to characterize the effects of excessive caloric intake on the hippocampus, a brain region important for learning and memory. Rats fed with a high-fat, high-glucose diet supplemented with high-fructose corn syrup showed alterations in energy and lipid metabolism similar to clinical diabetes, with elevated fasting glucose and increased cholesterol and triglycerides. Rats maintained on this diet for 8 months exhibited impaired spatial learning ability, reduced hippocampal dendritic spine density, and reduced long-term potentiation at Schaffer collateral--CA1 synapses. These changes occurred concurrently with reductions in levels of brain-derived neurotrophic factor in the hippocampus. We conclude that a high-calorie diet reduces hippocampal synaptic plasticity and impairs cognitive function, possibly through BDNF-mediated effects on dendritic spines.

Decline in daily running distance presages disease onset in a mouse model of ALS.

Amyotrophic lateral sclerosis (ALS) is characterized by progressive degeneration of lower motor neurons resulting in paralysis and death. Epidemiological and clinical findings suggest that a decline in athletic performance may presage the clinical onset of ALS, but this possibility has not been tested in an animal model. By placing running wheels in each mouse's cage to measure their exercise activity, we show that presymptomatic G93A SOD1 ALS mice are more active runners (15-20 km/day) than control mice (7-9 km/day). The ALS mice then exhibit a sharp decline in daily running distance 10-20 days prior to the onset of clinical disease. Within the group of ALS mice, there were no significant correlations between cumulative lifetime running distance and age at clinical disease onset or age at death, suggesting that amount of exercise did not affect the course of the disease process. Our data show that presymptomatic ALS mice have a propensity for running long distances, and then dramatically reduce the amount they run prior to the appearance of clinical symptoms. The monitoring of voluntary running distance may provide a valuable biomarker to evaluate the efficacy of potential therapeutic interventions for ALS in preclinical studies.

Neuroprotective actions of a histidine analogue in models of ischemic stroke.

Histidine is a naturally occurring amino acid with antioxidant properties, which is present in low amounts in tissues throughout the body. We recently synthesized and characterized histidine analogues related to the natural dipeptide carnosine, which selectively scavenge the toxic lipid peroxidation product 4-hydroxynonenal (HNE). We now report that the histidine analogue histidyl hydrazide is effective in reducing brain damage and improving functional outcome in a mouse model of focal ischemic stroke when administered intravenously at a dose of 20 mg/kg, either 30 min before or 60 min and 3 h after the onset of middle cerebral artery occlusion. The histidine analogue also protected cultured rat primary neurons against death induced by HNE, chemical hypoxia, glucose deprivation, and combined oxygen and glucose deprivation. The histidine analogue prevented neuronal apoptosis as indicated by decreased production of cleaved caspase-3 protein. These findings suggest a therapeutic potential for HNE-scavenging histidine analogues in the treatment of stroke and related neurodegenerative conditions.