# Deficiency of HMGN2 enhances antibacterial activity of macrophages by promoting H3 histone modification-mediated CD14/iNOS expression

## TL;DR

This study shows that reducing HMGN2 in macrophages boosts their ability to fight bacteria by increasing CD14 and nitric oxide production through epigenetic changes.

## Contribution

The study reveals a novel regulatory mechanism of HMGN2 in macrophage antibacterial activity via histone modification and CD14 expression.

## Key findings

- HMGN2 knockout enhances macrophage bactericidal and phagocytic capabilities.
- HMGN2 deficiency promotes CD14 expression through H3 histone modifications.
- CD14 upregulation activates MAPK pathways to increase nitric oxide production.

## Abstract

High-mobility group nucleosomal-binding domain 2 (HMGN2) is a widely recognized chromatin-structural protein within the nucleus of eukaryotes. It has been demonstrated to be implicated in immune responses during bacterial infection. Nevertheless, the regulatory mechanism of HMGN2 in the antibacterial process of macrophages remains unclear. In this research, distinct alterations in HMGN2 expression in macrophages were observed subsequent to microbial stimulation. To investigate the role of HMGN2 in macrophages during infection, the CRISPR-Cas9 technology was employed to construct an HMGN2-knockout RAW264.7 cell line. It was verified that HMGN2 knockout could significantly enhance the bactericidal and phagocytic capabilities of macrophages. The mechanistic investigation revealed that cluster of differentiation 14 (CD14) was transcriptionally promoted in HMGN2-knockout macrophages. HMGN2 knockout regulates CD14 expression by augmenting histone epigenetic modification levels on the CD14 gene promoter, including H3K4me3, H3K9ac, and H3K27ac. Moreover, HMGN2 knockout can activate the CD14-mediated mitogen-activated protein kinase (MAPK) signaling pathways to facilitate nitric oxide (NO) production. This study uncovers a crucial role of HMGN2 in the macrophage-mediated host immune response. HMGN2 is anticipated to serve as a therapeutic target for the treatment of infectious diseases.

Diagram Comparing the Effects of HMGN2-Wild Type (HMGN2-WT) and HMGN2-Deficiency on Macrophage Bactericidal Function. The left panel shows that under bacterial infection, CD14 mediates the activation of the MAPK pathway in macrophages, which further induces the phosphorylation of p38, JNK, and ERK. Ultimately, this regulates the occurrence of phagocytosis and the production of nitric oxide (NO), both of which are involved in the bactericidal process. The right panel shows the cellular changes in the state of HMGN2-deficiency: under the same infection conditions, histone modification in the CD14 gene promoter region of macrophages is altered, promoting the upregulation of CD14 expression. Enhanced CD14 expression drives the improvement of cellular phagocytic function and mediates the increased expression level of NO by activating the MAPK signaling pathway, ultimately enhancing the bactericidal capacity of macrophages. Green arrows indicate increased activity or upregulated expression level.

Diagram comparing HMGN2-WT and HMGN2-deficiency effects on cellular pathways. The left panel shows MAPK activation leading to phosphorylation of p38, JNK, and ERK, enhancing phagocytosis and nitric oxide (NO) production. The right panel illustrates increased phagocytosis, higher CD14 expression, and altered transcription factors in HMGN2-deficiency. The activation of iNOS and expression of specific histone markers are shown, with arrows indicating increased activity or expression levels.