Chieca, M.; Marini, M.; Baragli, M.; Bellantoni, E.; Bonacchi, L.; De Cesaris, F.; Tassorelli, C.; De Icco, R.; Greco, R.; Timotei, L.; Pulli, B.; Spinelli, G.; Souza Monteiro de Araujo, D.; Papini, A.; De Siena, G.; Scuffi, I.; Ferroni, G.; Pivotto, G.; Magi, A.; Nassini, R.; De Logu, F.

Medication-overuse headache (MOH) is one of the leading causes of chronic daily headache worldwide and arises from the repeated use of acute anti-migraine medications, including triptans. However, the cellular substrates and intracellular pathways driving this paradoxical chronification remain unknown. Here, using Schwann cell-selective silencing of the 5-HT1B/D receptor, we observed that acute triptan administration counteracts CGRP-induced, endosome-confined cAMP accumulation, preventing the development of periorbital mechanical allodynia in mice. In contrast, prolonged 5-HT1B/D activation in Schwann cells induces epigenetic and transcriptomic dysregulation associated with MOH in mice. Specifically, intronic hypermethylation-driven overexpression of BETAGLYCAN promotes activation of a non-canonical TGF-{beta}-dependent signaling cascade. The resulting TGF-{beta}3 upregulation establishes a feed-forward loop that sustains proalgesic paracrine communication between Schwann cells and primary sensory neurons. Analysis of plasma levels from patients with MOH confirmed elevated TGF-{beta}3 levels specifically associated with triptan-dependent MOH, supporting the translational relevance of these findings. Together, our data identify Schwann cell 5-HT1B/D signaling as a dual mediator of both the acute anti-migraine efficacy and the maladaptive mechanisms underlying MOH. These results provide a conceptual framework for strategies aimed at preserving the therapeutic benefits of triptans while limiting the adverse consequences of chronic administration.