The lipid peroxidation product 4-hydroxy-2,3-nonenal increases AP-1-binding activity through caspase activation in neurons

The transcription factor activator protein-1 (AP-1) is activated in respons e to physiological activity in neuronal circuits and in response to neurona l injury associated with various acute and chronic neurodegenerative condit ions. The membrane lipid peroxidation product 4-hydroxy-2,3-nonenal (HNE) i s increasingly implicated in the disruption of neuronal calcium homeostasis that occurs in various paradigms of neuronal excitotoxicity and apoptosis. The possible mechanistic links between lipid peroxidation and alterations in gene transcription during neuronal apoptosis have not previously been ex amined. We now report that exposure of cultured rat cortical neurons to an apoptotic concentration of HNE results in a large increase in AP-I DNA-bind ing activity. The protein synthesis inhibitor cycloheximide blocked the ind uction of AP-1, consistent with a requirement for induction of expression o f AP-I family members. The broad-spectrum caspase inhibitor N-benzyloxycarb onyl-Val-Ala-Asp-fluoromethyl ketone and the caspase-3 inhibitor N-acetyl-A sp-Glu-Val-Asp-aldehyde blocked HNE-induced increases in AP-I DNA-binding a ctivity, demonstrating a requirement for caspase activation in the activati on of AP-1, HNE induced phosphorylation of c-Jun N-terminal kinase (JNK), w hich was prevented by caspase inhibitors, indicating that HNE was acting at or upstream of JNK phosphorylation. The intracellular calcium chelator BAP TA-acetoxymethyl ester completely prevented stimulation of AP-1 DNA-binding by HNE, indicating a requirement for calcium. Moreover, agents that suppre ss mitochondrial calcium uptake (ruthenium red) and membrane permeability t ransition (cyclosporin A) attenuated AP-1 activation by HNE, suggesting a c ontribution of mitochondrial alterations to AP-I activation, Collectively, our data suggest a scenario in which HNE disrupts neuronal calcium homeosta sis and perturbs mitochondrial function, resulting in caspase activation. A ctivated caspases, in turn, induce activation of JNK, resulting in stimulat ion of AP-I DNA-binding protein production. This transcriptional pathway in duced by HNE may modulate the cell death process.