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 Thr172 phosphorylation of AMPKα. 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 AMPKα1 and AMPKα2 with predominant expression of the AMPKα1 isoform. siRNA studies revealed that knockdown of AMPKα1 expression sensitized RPE cells to 4-HNE. Intriguingly, knockdown of AMPKα2 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 AMPKα2 but not AMPKα1 significantly restored RPE cell barrier function. No further protection was observed by knockdown of both AMPKα1 and AMPKα2. In contrast, knockdown of AMPKα1 and/or AMPKα2 did not reverse the 4-HNE’s inhibitory effects on production of IL-8 and MCP-1. These data demonstrate that AMPKα1 and AMPKα2 play distinct roles in regulating 4-HNE effects on RPE function and viability. Therefore, selective modulation of AMPKα activity may benefit patients with retinal degeneration associated with RPE cell atrophy.

Research highlights
► Down-regulation of AMPKα activity by 4-HNE or compound C induces RPE cell death.
► Knockdown of AMPKα1 sensitizes RPE cells to 4-HNE, while AMPKα2 knockdown protects RPE cells from 4-HNE.
► AMPKα2 but not AMPKα1 mediates 4-HNE-induced increase in RPE cell permeability.
► AMPKα is dispensable for 4-HNE-induced reduction in cytokine production.
► These findings shed light on our understanding of the roles of lipid peroxidation in RPE cell atrophy.