A non-canonical immunometabolic function of BRD3 during sepsis

Sepsis is a life-threatening condition characterized by a dysregulated host innate immune response to pathogen infection. Here, we identify a pathological role for bromodomain-containing 3 (BRD3) in driving septic shock by upregulating aconitate decarboxylase 1 (ACOD1) in monocytes and macrophages via a non-canonical pathway. Mechanistically, lipopolysaccharide triggers an interaction between BRD3 and tripartite motif containing 21 (TRIM21), which activates CREB binding lysine acetyltransferase (CREBBP) via its E3 ligase activity, facilitating CREBBP's binding to and acetylation of cyclic adenosine monophophate (cAMP)-response-element-binding protein 1 (CREB1). BRD3 then recognizes and phosphorylates acetylated CREB1 at the transcription-activating site, thereby upregulating ACOD1 transcription. In four murine models of infection, myeloid-specific Brd3 deletion (Brd3^Mye-/-) or pharmacological intervention using small-molecule inhibitor OTX015 confers significant protection, reducing systemic inflammation and organ injury, similar to the effects observed in Acod1^Mye-/- mice. In patients with sepsis, elevated BRD3 levels correlate with accelerated inflammation, increased disease severity, and a greater risk of in-hospital death. These findings establish BRD3 as a potential therapeutic target for managing infection-associated immune dysregulation.