PARP1-LSD1 functional interplay controls transcription of SOD2 that protects human pro-inflammatory macrophages from death under an oxidative condition.

The function of macrophages makes them vulnerable to several sources of stress and damage, and thus there is a considerable requirement for some form of resilient molecular defence. Differentiation of human macrophages and their further pro-inflammatory (M1) polarization with bacterial endotoxin is associated with increased transcription of PARP1 and SOD2. The latter gene responded immediately to LPS with high NFκB-dependent expression rate, and the resulting enzyme made M1 macrophages resistant to hydrogen peroxide-induced oxidative stress and associated cell death. LPS-induced recruitment of RELA to SOD2 promoter was accompanied by release of PARP1 and LSD1 from chromatin and increased H3K4 di- and tri-methylation. PARP1 dissociation from SOD2 promoter occurred at an early stage of SOD2 transcriptional activation. This event contributed to the termination of mRNA synthesis at a later stage of macrophage polarization by allowing LSD1 to rebind to the SOD2 promoter. LSD1 removed transcription-promoting methylation of H3K4 and led to displacement of RELA. Analysis of temporal changes at the SOD2 promoter indicated a direct mutual interdependence between PARP1, LSD1, H3K4 methylation and the ongoing SOD2 transcription, which correlated positively with both PARP1 abundance on the chromatin and dimethylation of H3K4, but negatively with LSD1 and chromatin compaction in LPS-treated macrophages. Deficiency of LSD1 activity and maintenance of PARP1 at the SOD2 promoter substantially upregulated SOD2 level, thereby further increasing resistance of M1 macrophages to hydrogen peroxide. Inhibitors of LSD1 and PARP1 poisons that capture the latter enzyme on the chromatin seem to be prosurvival molecular tools protecting polarized macrophages from certain pro-oxidative conditions.
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