Neuronal regulation of tissue-resident macrophage maintenance and polarization

PROJECT SUMMARY The barrier tissues and body cavities are densely innervated by nociceptor sensory neurons (or nociceptors) that respond to noxious stimuli and mediate pain. Nociceptive innervation in the lung and peritoneal cavity begins as early as the embryonic development stage. Similarly, long-lived tissue-resident macrophages (TRMs), such as alveolar macrophages (AMs) in the lung and peritoneal macrophages (PMs) in the peritoneal cavity, start to populate at the very early stage of life and co-localize close to nerve fibers. However, it is unknown whether neurons can regulate TRM development and impact TRM abilities to respond to injury and inflammation. Upon activation, nociceptor nerve terminals secrete neuropeptides that act on their cognate receptors in macrophages for immunomodulation. The neuropeptide calcitonin gene-related peptide is dominantly secreted in our body by nociceptor sensory neurons. TRMs are well known to exhibit polarization (M1 or M2) depending upon the specific signals they encountered during their development or inflammatory conditions. While M1 macrophages are pro- inflammatory and damage the tissue during infection/injury, M2 macrophages exhibit tissue-protective type 2 inflammation and are crucial for resolving tissue damage and barrier dysfunction. Our preliminary data demonstrated that the nociceptors suppress the abundance of AMs and PMs at steady state, and lack of nociceptor signals polarize AMs and PMs to M1 type during activation with TLR ligands. By investigating AMs and PMs in ex vivo system and in vivo injury model, this R35 MIRA research program will determine the role of nociceptors and their subsets in the development and function of TRMs during steady-state and inflammation. Understanding neuron-TRM crosstalk is critical for determining the mechanism underlying loss of homeostasis, tissue damage, and pathogenesis of complex inflammatory diseases, such as sepsis. Specifically, this research program will address the following three key questions: 1) Do nociceptor neurons play a role in maintenance of TRMs at steady-state? 2) Do nociceptor signals involve in regulating the TRM polarization? 3) What is the role of neuropeptide receptor in TRM maintenance and M1/M2 polarization? Using both ‘loss and gain of function’ neuronal manipulating strategies in mice and using the neuropeptide deficient and neuropeptide receptor deficient mice, we will study the AMs and PMs to address these questions. Targeting the nervous system directly, or through downstream receptor signaling pathways in TRMs, will inform about the host-based strategy as a treatment modality for tissue damage and inflammatory diseases.