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Jie Fan, Oday Alsarraf, Craig E Crosson; Sphingolipid Metabolism In Retinal Ischemic Preconditioning. Invest. Ophthalmol. Vis. Sci. 2016;57(12):4599. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Previous studies have shown that retinal neuroprotective actions of ischemic preconditioning (IPC) are associated with the reduction of HDAC activity and the generation of sphingosine-1-phosphate (S1P), a bioactive molecule involved in inhibiting apoptosis. This study investigates how sphingolipid metabolism and protein acetylation interact to limit ischemic retinal injury.
Cultured astrocytes from human optic nerve head were treated with FTY720, an S1P mimetic, and HDAC activity was evaluated. Unilateral retinal ischemic was induced in rats by elevating IOP to 160 mmHg for 45 minutes. Ischemic preconditioning (5 minutes) was induced in an identical fashion at times corresponding to 24 hours prior to ischemic retinal injury. Retinal localization of acetylated histone-H3 was determined by immunohistochemistry. Sphingosine and S1P were measured by LC-MS.
In astrocytes treated with FTY720 (100 μM), Class-I HDAC activity was significantly reduced by 27.8 ± 5.3%, when compared with control cultures. In rat retinas assayed 24 hours following ischemic injury, acetylated H3 staining was reduced in retinal ganglion cell layer (GCL) and inner nuclear layer (INL) when compared with control retinas. Associated with ischemic-induced reduction in acetylated histone H3 staining was an increase in Class-I HDAC activity of 21 ± 6.2%, and a reduction in S1P levels of 51.6 %. In rats subjected to IPC prior to ischemic injury, acetylated histone-H3 staining increased in the GCL and INL and was also visible in the outer nuclear layer, the increase in Class-I HDAC activity was blocked and the level of S1P was increased by 34.5%. This increase in S1P was associated with over a two fold rise in acid ceramidase activity.
Our results provide evidence that hypoacetylation associated with ischemic injury results from the increase in Class I HDAC activity and that neuroprotection induced by IPC is mediated in part by suppressing HDAC activity. This reduction in HDAC activity was associated with changes in sphingolipid metabolism that elevate the endogenous levels of S1P. Taken together these data support the idea that sphingolipid metabolism plays a central role in regulating HDAC activity and the retinal reponses to ischemic stress.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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