Metabolic Syndrome Triggered by Fructose Diet Impairs Neuronal Function and Vascular Integrity in ApoE-KO Mouse Retinas: Implications of Autophagy Deficient Activation

Abstract

Metabolic syndrome is a disorder characterized by a constellation of clinical findings such as elevated blood glucose, hyperinsulinemia, dyslipidemia, hypertension, and obesity. A positive correlation has been found between metabolic syndrome or its components and retinopathy, mainly at microvascular level, in patients without a history of diabetes. Here, we extend the investigations beyond the vascular component analyzing functional changes as well as neuronal and glial response in retinas of Apolipoprotein E knockout (ApoE-KO) mice fed with 10% w/v fructose diet. Given that autophagy dysfunction is implicated in retinal diseases related to hyperglycemia and dyslipidemia, the activation of this pathway was also analyzed. Two months of fructose intake triggered metabolic derangements in ApoE-KO mice characterized by dyslipidemia, hyperglycemia and hyperinsulinemia. An increased number of TUNEL positive cells, in addition to the ganglion cell layer, was observed in the inner nuclear layer in retina. Vascular permeability, evidenced by albumin–Evans blue leakage and extravasation of albumin was also detected. Furthermore, a significant decrease of the glial fibrillary acidic protein expression was confirmed by Western blot analysis. Absence of both Müller cell gliosis and pro-angiogenic response was also demonstrated. Finally, retinas of ApoE-KO FD mice showed defective autophagy activation as judged by LC3B mRNA and p62 protein levels correlating with the increased cell death. These results demonstrated that FD induced in ApoE-KO mice biochemical alterations compatible with metabolic syndrome associated with neuronal impairment and mild vascular alterations in the retina.

Transcriptional analysis reveals that the intracellular lipid accumulation impairs gene expression profiles involved in insulin response-associated cardiac functionality

“…Finally, in previous studies we found that ApoE-KO mice had higher levels of circulating cholesterol, triglycerides, LDL-cholesterol, and HDL-cholesterol, and increased fasting plasma insulin levels 28 . The increase in fasting insulin was detected at 6 months of age, while the alteration in the lipid profile (high levels of total cholesterol, HDL and LDL cholesterol) was found at 4 months of age and lasted until 6 months of age 28 , 43 , these remaining lipoproteins can undergo lipolysis, generating small-dense LDL, which in turn promotes the formation of aggregated LDL 44 . In the present study, we found that ApoE-KO mice (6 months of age) had increased lipid accumulation in the myocardium detected by BODIPY-stained lipid droplet (Supplementary Fig.…”

“…As animal model, we used male C57BL/6J wild-type mice (Wt) and male Apolipoprotein E-deficient (ApoE-KO) mice on the same background (The Jackson Laboratories, Bar Harbor, ME, United States) 28 . We chose to use male mice to avoid fluctuations in the lipid profiles caused by hormonal cycling.…”

“…We chose to use male mice to avoid fluctuations in the lipid profiles caused by hormonal cycling. The ApoE-KO mice naturally develop metabolic syndrome, including hypercholesterolemia and elevated fasting insulin levels 28 . The mice were housed at a temperature of 22 ± 1 °C and were subjected to a 12-h light/12-h dark cycle with free access to water and food (normal commercial mice chow diet).…”

Retinal neurodegeneration in metabolic syndrome: a spectral optical coherence tomography study

“…Bruch membrane and basal membrane of retinal vessels were found thickened leading to an ischemic state which plays a role in cell damage. In contrast, Paz et al [22] showed changes in astrocyte integrity without any Müller cell reactivation via in vivo animal model of MetS. They also demonstrated an increased rate of apoptosis in the GCL and inner nuclear layer.…”

Etiological Roles of p75NTR in a Mouse Model of Wet Age-Related Macular Degeneration

“…The obtained cryosections were stored at −20 • C under dry conditions. Immunostaining was performed as described previously [34]. Briefly, cryosections were washed with PBS, blocked with 2% of BSA in PBS containing 0.1% Tween-20 for 1 h, and then incubated ON at 4 • C with the following primary antibodies, respectively: rabbit polyclonal anti-GFAP (1/1000; Dako, Carpinteria, CA, USA), mouse β3 tubulin (1/500; ab78078, Abcam), and goat anti-p75 NTR (1/500; R&D system).…”