Differential roles of AMPKα1 and AMPKα2 in regulating 4-HNE-induced RPE cell death and permeability

Lipid peroxidation products such as 4-hydroxy-2-nonenal (4-HNE) cause dysfunction and death of retinal pigmented epithelial (RPE) cells, thereby leading to retinal degeneration. The molecular mechanisms underlying their action remain elusive however. In this study, the roles of AMP-activated protein kinase (AMPK) in 4-HNE-induced RPE cell dysfunction and viability were addressed. 4-HNE caused RPE cell death and down-regulated basal activity of AMPK as evidenced by decreased Thr(172) phosphorylation of AMPK alpha. Exposure of RPE cells to the AMPK inhibitor, compound C also led to cell death, indicating that RPE cell death is correlated with 4-HNE modulation of AMPK activity. ARPE19 cells express both AMPK alpha 1 and AMPK alpha 2 with predominant expression of the AMPK alpha 1 isoform. siRNA studies revealed that knockdown of AMPK alpha 1 expression sensitized RPE cells to 4-HNE. Intriguingly, knockdown of AMPK alpha 2 protected RPE cells from 4-HNE injury. Sub-lethal doses of 4-HNE induced an increase in RPE monolayer permeability, as measured by reduction in trans-epithelial resistance (TER). Knockdown of AMPK alpha 2 but not AMPK alpha 1 significantly restored RPE cell barrier function. No further protection was observed by knockdown of both AMPK alpha 1 and AMPK alpha 2. In contrast, knockdown of AMPK alpha 1 and/or AMPK alpha 2 did not reverse the 4-HNE's inhibitory effects on production of IL-8 and MCP-1. These data demonstrate that AMPK alpha 1 and AMPK alpha 2 play distinct roles in regulating 4-HNE effects on RPE function and viability. Therefore, selective modulation of AMPK alpha activity may benefit patients with retinal degeneration associated with RPE cell atrophy. (c) 2010 Elsevier Ltd. All rights reserved.