Efferent signals from the central nervous system represent a key layer of regulation of white adipose tissue (WAT). However, the mechanism by which efferent neural signals control WAT metabolism remains to be better understood. Here, we exploit the volume fluorescence-imaging technique to visualize the neural arborizations in mouse inguinal WAT at single-fiber resolution. The imaging reveals a dense network of sympathetic arborizations that had been previously undetected by conventional methods, with sympathetic fibers being in close apposition to > 90% of adipocytes. We demonstrate that these sympathetic fibers originate from the celiac ganglia, which are activated by cold challenge. Sympathetic-specific deletion of TrkA receptor or pharmacologic ablation by 6-hydroxydopamine abolishes these intra-adipose arborizations and, as a result, cold-induced beiging of inguinal WAT. Furthermore, we find that local sympathetic arborizations function through beta-adrenergic receptors in this beiging process. These findings uncover an essential link connecting efferent neural signals with metabolism of individual adipocytes.
Highlights d The ImmuView procedure enables whole-tissue 3D assessment of mouse immune organs d A panicle-shaped sympathetic architecture is present in the spleen parenchyma d Sympathetic architecture suppresses the spleen antibacterial innate immunity d Norepinephrine inhibits the LPS-elicited innate immune response cell-intrinsically
Local immunity of the lung needs to be under tight control. However, how efferent neural signals influence lung immunity remains incompletely understood. Here, we report the development of a modified iDISCO-based protocol, iDISCO(ace), for whole-tissue 3D assessment of neural innervations and immune reactions in intact, unsectioned lung tissues. We observed that genetic, pharmacologic, or surgical removal of local sympathetic innervations promoted LPS-elicited innate immune response in the lung. Also, sympathetic ablation enhanced IL-33–elicited type 2 innate immunity. We further show that the sympathetic neurotransmitter norepinephrine, or specific agonists of the β2-adrenergic receptor, can inhibit the LPS- or IL-33–elicited immune response in a cell-intrinsic manner. Moreover, genetic deletion of the β2-adrenergic receptor produced immunomodulatory effects similar to those observed with sympathetic ablation. Together, this study elucidates the critical function of local sympathetic innervations in negatively modulating the lung innate immune responses.
Sympathetic innervation regulates energy balance, and the nerve density in the adipose tissues changes under various metabolic states, resulting in altered neuronal control and conferring resilience to metabolic challenges. However, the impact of the immune milieu on neuronal innervation is not known. Here, we examined the regulatory role on nerve plasticity by eosinophils and found they increased cell abundance in response to cold and produced nerve growth factor (NGF) in the white adipose tissues (WAT). Deletion of Ngf from eosinophils or depletion of eosinophils impairs cold-induced axonal outgrowth and beiging process. The spatial proximity between sympathetic nerves, IL-33–expressing stromal cells, and eosinophils was visualized in both human and mouse adipose tissues. At the cellular level, the sympathetic adrenergic signal induced calcium flux in the stromal cells and subsequent release of IL-33, which drove the up-regulation of IL-5 from group 2 innate lymphoid cells (ILC2s), leading to eosinophil accretion. We propose a feed-forward loop between sympathetic activity and type 2 immunity that coordinately enhances sympathetic innervation and promotes energy expenditure.
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