Neuronal nerve processes in the tumor microenvironment were highlighted recently. However, the origin of intra-tumoral nerves remains poorly known, in part because of technical difficulties in tracing nerve fibers via conventional histological preparations. Here, we employ three-dimensional (3D) imaging of cleared tissues for a comprehensive analysis of sympathetic innervation in a murine model of pancreatic ductal adenocarcinoma (PDAC). Our results support two independent, but coexisting, mechanisms: passive engulfment of pre-existing sympathetic nerves within tumors plus an active, localized sprouting of axon terminals into non-neoplastic lesions and tumor periphery. Ablation of the innervating sympathetic nerves increases tumor growth and spread. This effect is explained by the observation that sympathectomy increases intratumoral CD163+ macrophage numbers, which contribute to the worse outcome. Altogether, our findings provide insights into the mechanisms by which the sympathetic nervous system exerts cancer-protective properties in a mouse model of PDAC.

Recent evidence has highlighted the presence of neuronal nerve processes in the tumor microenvironment. However, the origin of intra-tumoral nerves remains poorly known, in part because of technical difficulties in tracing nerve fibers via regular histological preparations.Here, we employed three-dimensional (3D) imaging of cleared tissues for a comprehensive analysis of sympathetic innervation in pancreatic ductal adenocarcinoma (PDAC). The results support two independent, but coexisting, mechanisms: passive engulfment of pre-existing nerves within tumors and active, localized sprouting of nerve terminals into non-neoplastic lesions and tumor periphery. Nerve ablation revealed an inverse correlation between sympathetic innervation and tumor growth and spread. Furthermore, sympathectomy increased CD163 + macrophage levels, which contributed to worse outcomes. Altogether, our findings revealed protective properties of the sympathetic nervous system in PDAC immunity and progression that could pave the way for new treatments.