CARD9 Conveys Pancreatic Islet Sympathetic Nervous β2 Signals to Reshape Macrophage Creatine Metabolism in Type 1 Diabetes

Abstract Type 1 diabetes (T1D) is an autoimmune disorder marked by the injury of pancreatic β cells, during which sympathetic neurons in the endocrine region of pancreas are lost, whereas those in the exocrine regions surrounding islets remain intact. This abnormal sympathetic nervous signaling may disrupt the balance of the neuroendocrine‐immune network and contribute to the development of T1D, although its underlying molecular mechanisms are still elusive. Here, single‐cell omics and whole‐tissue immunostaining reveal a decrease in pancreatic sympathetic nerve density in T1D patients and T1D mouse models. Surgical and chemical desensitization of the sympathetic nervous system exacerbates T1D, while macrophage depletion mitigates this effect. Mechanistically, diminished norepinephrine (NE) release impairs β2‐adrenergic receptor (β2‐AR)‐PKA‐CREB1 signaling in islet macrophages, leading to downregulation of the adaptor caspase recruitment domain family member 9 (CARD9). Loss of CARD9 decreases SLC6A8‐mediated creatine uptake, shifts macrophages toward a pro‐inflammatory phenotype, and promotes sympathetic axon ferroptosis driven by decreased neurotrophic factor and anti‐inflammatory factor release. Conversely, β2‐AR agonist formoterol restores PKA‐CREB1‐CARD9 activation, preserves creatine metabolism, and maintains anti‐inflammatory macrophage polarization. These findings define a novel sympathetic‐macrophage‐creatine metabolic axis governed by CARD9 that links neural signals to immune and metabolic regulation in T1D, highlighting neuroimmune interactions as targets for therapies.