The Regulatory Roles of ATF2 and PPM1K in Macrophages

Abstract

The differentiation and activation of macrophages are critical regulatory programs that are central to host inflammation and defense against pathogens. The signaling pathways involved during these programs initiate a cascade of molecular events that result in distinct transcriptional profiles and metabolic adaptations, enabling macrophages to acquire diverse functions. However, the proteins involved during these processes, such as transcription factors (TFs) or phosphatases, are not well understood.

In this thesis, I demonstrated that the activity and expression of Activating Transcription Factor 2 (ATF2) is precisely regulated during monocyte-to-macrophage differentiation, and that its activation is linked to M1 polarization and bacterial infection. Mechanistically, ATF2 binds to the core promoter of PPM1A, a phosphatase that controls macrophage differentiation, to regulate its expression in macrophages. Functionally, overexpression of ATF2 (THP-ATF2) sensitized macrophages to M1 polarization, resulting in M1-like cell morphology, increased expression of MHC Class II, IL-1β and IP-10, and enhanced control of Mycobacterium tuberculosis (Mtb). Gene expression and metabolic profiling revealed that genetic overexpression or stimuli-induced activation of ATF2 alters the metabolic capacity of macrophages and primes these cells for glycolytic metabolism during M1 polarization or bacterial infection. These findings reveal that ATF2 plays key roles during macrophage differentiation and M1 polarization to enhance the functional capacities of macrophages.

Metal-dependent phosphatases (PPMs), such as PPM1A, have been shown to be involved in various cellular processes, including metabolism, apoptosis, proliferation, and inflammation. I profiled the mRNA expression of 11 PPMs during i) macrophage differentiation and ii) infection of macrophages with Mtb. Among these PPMs, PPM1K was strongly induced under both conditions, indicating its potential involvement in macrophage function. Gene expression analyses revealed that PPM1K upregulation was specific to live bacteria, rather than heat-killed (HK) bacteria. While PPM1K is upregulated during differentiation, genetic perturbations of PPM1K did not alter macrophage adherence or morphology. However, macrophages overexpressing PPM1K exhibited increased mitochondrial respiration and decreased glycolysis during Mtb infection, while their metabolism remained unaffected in response to HK-Mtb. Interestingly, the knockdown of PPM1K in macrophages reduced both mitochondrial respiration and glycolysis in response to either live or HK-Mtb. While these changes in metabolism did not majorly affect intracellular Mtb survival or macrophage cell death, these results indicate a potential role for PPM1K in the regulation of metabolic pathways in macrophages, which may have impact on other macrophage effector functions.