Experimental acute lung injury induces multi-organ epigenetic modifications in key angiogenic genes implicated in sepsis-associated endothelial dysfunction

Karol Bomsztyk, Daniel Mar, Dowon An, Roya Sharifian, Michal Mikula, Sina A Gharib, William A Altemeier, W Conrad Liles, Oleg Denisenko

The Tie-2/angiopoietin (Tie-2/Ang) and vascular endothelial growth factor receptor-ligand systems (VEGFR/VEGF) are recognized to play important roles in the regulation of microvascular endothelial function. Downregulation of these genes during sepsis has been implicated in the pathogenesis of sepsis-related microvascular leak and multiple organ dysfunction syndrome (MODS). Mechanisms responsible for dysregulation of angiogenic genes in sepsis are poorly defined. Western blot, RT PCR and multiplex chromatin immunoprecipitation platform (Matrix ChIP) were used to investigate serum albumin leak, changes in gene expression and associated epigenetic alterations in a murine model of acute lung injury-induced sepsis (ALI-sepsis). Experimental ALI-sepsis induced microvascular leak and downregulation of expression of Angpt1 (Ang1), Tek (Tie-2) and Kdr (Vegfr2 or Flk-1) genes in lung, kidney and liver. These changes correlate with a decrease in RNA polymerase II (Pol II) density at these genes, with the greatest response observed in the lung. ALI-sepsis reduced levels of transcription-permissive histone H3 lysine acetylation (H3KAc) at these loci in all examined tissues. Decreases in permissive H3K4m3 and H3Km2 marks were detected only in lung. In contrast, only minimal alterations in transcription-repressive histone modifications (H3K27m3, H3K9m2, H3K9m3 and H4K20m3) were observed in all tissues. Our results demonstrate that decreases in transcription-permissive, but not increases in transcription-repressive, histone modifications at Angpt1, Tek and Kdr is a systemic, rather than a lung-restricted response, involving key end-organs in experimental ALI-sepsis. Given that ventilator-associated pneumonia is a major cause of sepsis in critically ill patients, elucidation of mechanisms mediating epigenetic alterations during sepsis provides fundamental new insights into the pathogenesis of sepsis-induced microvascular leak and subsequent end-organ injury/dysfunction.