IFNg shapes macrophage inflammatory responses by STAT1 isoform-specific epigenetic and transcriptional mechanisms

Interferon gamma (IFNg) is a pivotal cytokine that activates macrophages and shapes their response to subsequent inflammatory stimuli. Here, we investigated the distinct roles of STAT1 isoforms, STAT1alpha and STAT1beta, in IFNg-induced epigenetic remodelling and subsequent responses to lipopolysaccharide (LPS) in primary macrophages. We show that the STAT1 C-terminal TAD, which is missing in the STAT1beta isoform, is required for both H3K27 acetylation and deacetylation in response to IFNg. Notably, H3K27 deacetylation was associated with AP-1 motifs rather than STAT1 binding, suggesting indirect regulatory mechanisms. Functionally, IFNg pretreatment suppressed the induction of anti-inflammatory and virus response genes, including a subset of IFN-stimulated genes (ISGs), in response to LPS, while enhancing the expression of a distinct set of ISGs. Mechanistically, the STAT1 C-terminal TAD was critical for IFNg-mediated inhibition of LPS-induced enhancer activation at key regulatory genes, such as Il10 and Irak3, which are involved in negative feedback of toll-like receptor (TLR) signalling. Conversely, cooperative gene activation by IFNg and LPS was largely independent of the STAT1 C-terminal TAD, with notable exceptions, such as Ido1 and Tgtp1. Genome-wide analysis indicated that IRF1 and IRF8, rather than STAT1 homodimers, predominantly mediate in IFNg-induced H3K27 acetylation and transcription factor network analysis identified additional regulators integrating IFNg and LPS responses. Together, these findings reveal gene- and isoform-specific roles of STAT1 in coordinating IFNg-dependent chromatin remodelling and transcriptional cross-regulation, providing new insights into the control of inflammation and innate immunity.