Biphasic regulation by dexamethasone of IL-1- and LPS-stimulated endothelial prostacyclin production

Activation of glucocorticoid receptors in Müller glia is protective to retinal neurons and suppresses microglial reactivity

Reactive microglia and macrophages are prevalent in damaged retinas. Glucocorticoid signaling is known to suppress inflammation and the reactivity of microglia and macrophages. In the vertebrate retina, the glucocorticoid receptor (GCR) is known to be activated and localized to the nuclei of Müller glia (Gallina et al., 2014). Accordingly, we investigated how signaling through GCR influences the survival of neurons using the chick retina in vivo as a model system. We applied intraocular injections of GCR agonist or antagonist, assessed microglial reactivity, and the survival of retinal neurons following different damage paradigms. Microglial reactivity was increased in retinas from eyes that were injected with vehicle, and this reactivity was decreased by GCR-agonist dexamethasone (Dex) and increased by GCR-antagonist RU486. We found that activation of GCR suppresses the reactivity of microglia and inhibited the loss of retinal neurons resulting from excitotoxicity. We provide evidence that the protection-promoting effects of Dex were maintained when the microglia were selectively ablated. Similarly, intraocular injections of Dex protected ganglion cells from colchicine-treatment and protected photoreceptors from damage caused by retinal detachment. We conclude that activation of GCR promotes the survival of ganglion cells in colchicine-damaged retinas, promotes the survival of amacrine and bipolar cells in excitotoxin-damaged retinas, and promotes the survival of photoreceptors in detached retinas. We propose that suppression of microglial reactivity is secondary to activation of GCR in Müller glia, and this mode of signaling is an effective means to lessen the damage and vision loss resulting from different types of retinal damage.

Comparison of the potency of various serotypes of E. coli lipopolysaccharides in stimulating PGI2 production and suppressing ACE activity in cultured human umbilical vein endothelial cells

We investigated the potency of various serotypes of lipopolysaccharides (LPS) by examining LPS-induced stimulation of PGI2 production and suppression of ACE activity in cultured human umbilical vein endothelial cells (HUVEC). HUVEC which had been incubated with E. coli 055:B5 and 0111:B4 for 24 h produced more prostacyclin (PGI2) in response to thrombin than HUVEC incubated with E. coli 026:B6. Also, angiotensin converting enzyme activity (ACE) in cell lysates of HUVEC incubated for 24 h with 055:B5 or 0111:B4 was suppressed significantly compared to control HUVEC or HUVEC incubated with 026:B6. From these experimental results, E. coli 055:B5 and 0111:B4 appear to be more potent than 026:B6. It is concluded that this difference in potency among various serotypes of LPS should be taken into account when experiments are designed to examine the effect of LPS on endothelial cell function.