Zinc Modulates Neurturin– <scp>AKT</scp> Signaling to Promote Parasympathetic Innervation in Developing Submandibular Salivary Glands

Zinc (Zn²⁺), an essential trace element, has been increasingly recognized for its crucial role in neural development and regeneration. Although its function in central nervous system neurogenesis is well documented, its involvement in parasympathetic innervation remains insufficiently characterized. In this study, we examined the neurochemical interplay between Zn²⁺ and the neurotrophic factor neurturin (NRTN) during submandibular salivary gland (SMG) development, with particular emphasis on the PI3K/AKT signaling axis involved in parasympathetic innervation. Employing an ex vivo embryonic mouse SMG organ culture system combined with a bioengineered agarose-based hydrogel for sustained Zn²⁺ delivery, we demonstrate that zinc supplementation markedly enhances both epithelial branching morphogenesis and neurite outgrowth. Mechanistic investigations revealed that Zn²⁺ activates the PI3K/AKT pathway and promotes epithelial and neuronal development, even in the presence of pharmacological inhibitors targeting PI3K or AKT. NRTN, a critical neurotrophic factor implicated in parasympathetic innervation, was identified as an upstream activator of AKT, and its signaling activity was substantially enhanced by Zn²⁺. Notably, co-administration of Zn²⁺ and NRTN restored SMG morphogenesis and neuronal extension despite PI3K/AKT pathway inhibition, indicating a robust compensatory mechanism. This synergistic interaction reveals a previously unrecognized crosstalk between metal ion-mediated and neurotrophin-dependent signaling pathways during peripheral organ development. Collectively, this work broadens the current understanding of zinc's biological functions beyond the central nervous system and highlights its therapeutic potential in regenerative approaches targeting salivary gland dysfunction and related disorders involving compromised autonomic innervation.