G protein-coupled receptors orchestrating granulocytes in pemphigoid diseases

Granulocytes dominate the inflammatory infiltrate in many antibody-induced autoimmune diseases (AADs) and are often the primary effector cell population inflicting tissue injury in these diseases. This also includes Pemphigoid diseases (PDs). Granulocytes make their decisions mainly by integrating external stimuli they sense via cell surface receptors (CSRs). CSRs of granulocytes include multiple G protein-coupled receptors (GPCRs) and others. The CSR repertoire of granulocytes is partially dynamic and changes, e.g., with the state of maturation and activation. These dynamics are also part of the recently more appreciated molecular heterogeneity of neutrophil and eosinophil populations. Among the CSRs, GPCRs probably play a most important role in shaping granulocyte heterogeneity and in enabling granulocytes for their tasks in inflamed tissues. Profiling GPCR expression on murine bone marrow neutrophils, we have detected the expression of 240 GPCRs. Their expression levels were dynamic upon in vitro stimulation with immune complexes mimicking the situation in the dermis in PDs. Particularly, GPCRs activated by metabolites were markedly upregulated. Many of these metabolites, most prominently lactate, typically accumulate in inflamed tissues. In B02, we will profile the molecular phenotype of neutrophils and eosinophils in different tissues throughout the course of BP-like EBA at the single-cell transcriptomic level. Thus, we will distinguish granulocyte subpopulations, regulators of granulocytes, and granulocyte functions in PDs by a systems medicine approach. We will particularly focus on comprehensively profiling the GPCR repertoire (“GPCRome”) of granulocytes. We hypothesize that the GPCRome and its dynamics are most critical regulators of granulocyte activities in PDs. The dynamics in the GPCRome reflect the changing extracellular signals shaping granulocyte decisions in PDs and other AADs. We will systematically investigate the impact of select candidate GPCRs on neutrophil activities and, finally, skin inflammation in an in vivo model of PDs. With lactate generated in large amounts in inflamed tissues and its receptor GPR81 in vitro markedly induced in response to immune complex stimulation, our functional analyses will, among others, include a detailed investigation into the role of GPR81 in the regulation of neutrophil responses and in PDs.