PDF, English (Dissertation) - main document Restricted access: Repository staff only until 6 November 2025. Login+Download (6MB) | Terms of use

Abstract

Macrophages are vital innate immune cells in maintaining tissue homeostasis. When their functions are disrupted, macrophages can contribute to disease progression and severity by exacerbating tissue-damaging, pro-inflammatory responses. This is particularly evident in complex diseases such as cancer, metabolic dysfunction-associated steatohepatitis (MASH), and bacterial infections. Understanding macrophage activation and polarization is crucial for developing targeted therapeutic strategies. Chromatin remodelers, like the high mobility group A1 (HMGA1) protein, are central to regulation of gene expression. HMGA1, binds to AT- rich DNA promoter regions and interacts with other proteins to modulate gene expression. HMGA1 enhances the transcription of pro-inflammatory genes across various cell types and malignancies. Despite this, the specific role of HMGA1 in macrophages remains underexplored. This research offers a detailed examination of HMGA1’s influence on macrophage activation, polarization, and immune responses. To elucidate the role of HMGA1 in macrophages within various disease contexts, I first investigated its macrophage-specific expression across different conditions, including inflammation, MASH and hepatocellular carcinoma (HCC). Next, to determine the specific functional role of HMGA1 in macrophages, I employed a loss of function approach using Cre recombinase technology to generate two macrophage specific Hmga1 knockout mouse lines: Hmga1fl/fl LysMCre and Hmga1fl/fl Csf1rCre. After evaluation of the knockout efficiency in the mouse lines, I determined that the Hmga1fl/fl Csf1rCre is a better model to deplete HMGA1. Furthermore, by qRT- PCR of bone marrow derived macrophages (BMDMs), I found that loss of Hmga1 influenced the expression of M1 (pro-inflammatory) related genes, but not the expression of M2-associated (anti-inflammatory) genes. This observation was also corroborated by flow cytometry and bulk RNA sequencing, which indicated that HMGA1 fine-tunes the pro-inflammatory gene signature in BMDMs. The function of macrophage-specific HMGA1 was investigated in three disease models: tumor development, infection and MASH. In a B16GP33 subcutaneous tumor model, the results showed a significant increase of the tumor size and volume in the macrophage specific Hmga1 depleted mice compared to the controls. Flow cytometry analysis showed an increase in the M-MDSC and Treg cell populations, while NK cells and cytotoxic CD8+ T cells were reduced. These findings suggested that Hmga1 deletion in macrophages promotes an immunosuppressive phenotype within the tumor microenvironment (TME) of the subcutaneous tumors. To test the effect of macrophage-Hmga1 deletion on bacterial infection, an in vitro bacterial killing assay using pathogenic E. coli showed that macrophages from Hmga1fl/fl Csf1rCre mice exhibited reduced bacterial killing ability compared to Hmga1fl/fl control macrophages. In addition, I investigated the effect of Hmga1 depletion in macrophages on liver steatosis and MASH development by feeding Hmga1fl/fl LysMCre mice with WD for 3 and 6 months. At the selected time points, the Hmga1 depleted mice were not protected from weight gain, steatosis development or liver damage. However, a difference in the myeloid cell migration into the liver was detected in the knockout group, suggesting that HMGA1 depletion influenced myeloid cell dynamics in the liver. Overall, this study underscores HMGA1’s critical role in fine-tuning macrophage polarization and function across different disease contexts. HMGA1 influences TME remodeling and bacterial killing capacity in vitro. These findings provide valuable insights into macrophage behavior and highlight the possibility for therapeutic strategies targeting HMGA1.