Brain Derived Neurotrophic Factor and Superior Collicular Extract Regulate the Expression of the 1.6 Subfamily of Voltage-gated Potassium Channels in the Developing Rat Retina in vitro.

PURPOSE: To evaluate the role of brain derived neurotrophic factor (BDNF) and superior collicular extract (SCE) on the expression of the 1.6 subfamily of voltage-gated potassium channels (VG Kv 1.6 channels) in retinal ganglion cells (RGCs) of rats in an in vitro model. METHODS: Neonatal retinal cultures were supplemented with trophic factors of interest, namely BDNF and SCE, at 0 DIV (days in vitro), 6 DIV and both 0 and 6 DIV. The expression of VG Kv 1.6 channels was evaluated by immunostaining with anti Kv 1.6 and immunofluorescence was measured by confocal scanning laser microscopy on 4, 6, 8, 10 and 12 DIV. The immunofluorescence indirectly measured the quantity of ion channels being expressed. RESULTS: RGCs were identified by their soma size. BDNF and SCE enhanced RGC survival by enhancing extensive neurite outgrowth, and increased the expression of VG Kv 1.6 channels; the effect of SCE was more significant than BDNF. Trophic factors also enhanced the survival of RGCs by increasing the expression of ion channels thereby contributing to spontaneous bursts of action potentials in the early stages of RGC development. CONCLUSION: The expression of delayed rectifier VG Kv 1.6 channels in RGCs may determine membrane excitability and responsiveness to trophic factors, this plays a key role in the refinement of developing retinal circuits.

Apolipoprotein E-Deficient Lipoproteins Induce Foam Cell Formation by Activation of PERK-EIF-2α Signaling Cascade.

Transformation of macrophages into foam cells by apolipoprotein (Apo) E-deficient, ApoB48-containing (E(-)/B48) lipoproteins has been shown to be associated with increased phosphorylation of eukaryotic initiation factor-2α (eIF-2α). The present report examined the causal relationship between eIF-2α phosphorylation and lipid accumulation in macrophages induced by E(-)/B48 lipoproteins. E(-)/B48 lipoproteins increased eIF-2α phosphorylation and cholesterol ester accumulation, while lipoprotein degradation decreased and lysosomal acid lipase and cathepsin B mRNA translation was inhibited in mouse peritoneal macrophages (MPMs). These responses were overcome by overexpression of a nonphosphorylatable eIF-2α mutant in MPMs. Incubation of MPMs with E(-)/B48 lipoproteins also increased the phosphorylation of RNA-dependent protein kinase-like endoplasmic reticulum kinase (PERK), but not other eIF-2α kinases. Overexpression of a nonphosphorylatable PERK mutant inhibited PERK and eIF-2α phosphorylation, and alleviated cholesterol ester accumulation induced by E(-)/B48 lipoproteins. PERK is an eIF-2α kinase activated by endoplasmic reticulum (ER) stress. Taken together, findings from this report suggest that induction of ER stress, i.e., activation of the PERK-eIF2α signaling cascade, is a mechanism by which E(-)/B48 lipoproteins down-regulate lysosomal hydrolase synthesis, inhibit lysosomal lipoprotein degradation, and increase intracellular lipoprotein and cholesterol ester accumulation, resulting in foam cell formation.