The Role of Protein Tyrosine Phosphatase Non-Receptor Type 23 (PTPN23) in Regulating Macrophage Function Across Mucosal Organs

Mucosal organs, like the gut, the lungs, or the bladder, are in constant contact with the environment through the food we eat, the air we breathe, and the microbes that colonize our body surfaces. Therefore, a regulatory network that can distinguish harmless from harmful agents is essential. One important immune cell type in these mucosal tissues are macrophages. Macrophages can sense their environment, engulf bacteria and dead cells, communicate with other immune cells, and coordinate immune responses to maintain tissue homeostasis. To fulfill these roles, they can adopt either pro- or anti-inflammatory properties. Protein tyrosine phosphatase non-receptor type 23 (PTPN23) is a protein involved in coordinating a process called endosomal sorting complexes required for transport (ESCRT). The ESCRT pathway internalizes receptors from the cell surface and thereby controls their activity. As a result, ESCRT is involved in many processes that regulate cell proliferation, migration, and activation of multiple signaling pathways. Given the pivotal role of PTPN23, this project focused on studying its role in macrophages across different mucosal tissues. Since high expression of PTPN23 has been reported especially in intestinal macrophages, we focused primarily on intestinal diseases. We used a mouse model with a macrophage-specific knockout of PTPN23 (KO) mice and treated them with dextran sulfate sodium (DSS) to disrupt the colon epithelial layer. Compared to wild-type (WT) mice, KO mice showed a protective effect, with less weight loss and reduced epithelial damage, while the overall immune cell composition remained largely unchanged. We also analyzed the microbiome, as it is known to influence intestinal infections, but found no difference in the bacterial composition of the stool between KO and WT mice. Next, we investigated whether this protective effect was also seen during bacterial infection of the gut. We infected the same mice with Citrobacter rodentium, a bacterium that mimics human pathogenic Escherichia coli infections. In this model, no difference was observed between the genotypes. Single-cell RNA sequencing of colon immune cells revealed a macrophage subpopulation present in KO but not in WT mice. This subpopulation was defined by the expression of the gene glycoprotein non-metastatic melanoma protein B (GPNMB), which has been associated with tissue repair in other organs. We confirmed that colon tissue from KO mice showed higher Gpnmb expression than WT mice. To determine whether the protective effect of PTPN23 KO in intestinal macrophages was local or was also present in other mucosal organs, we infected the same mice with Legionella pneumophila, which can cause lung infections. In this model, no difference between KO and WT mice was observed. Additionally, we infected mice with uropathogenic Escherichia coli to study urinary tract infections (UTIs), where we observed a potential protective effect of PTPN23 depletion in macrophages. Taken together, our data show that PTPN23 in intestinal macrophages plays a protective role in the gut, potentially by promoting a tissue-repairing macrophage subpopulation. This effect appears specific to infections that damage the epithelial layer, as no differences were observed during bacterial infections of the intestine or lung. Understanding this tissue-specific role of PTPN23 in macrophages opens the door for further research into how intestinal macrophages regulate tissue repair and immune homeostasis, as well as the specific contribution of PTPN23 to these processes. $\textit{Full-text embargoed until: 2026-11-14}$