Chemogenetic Schwann cell activation impairs early myelination and triggers adult demyelination in the peripheral nervous system

Schwann cells (SCs), the myelin-forming glia of the peripheral nervous system (PNS), are essential for nerve development and maintenance; however, the contribution of Ca²⁺ signaling to their maturation and long-term stability remains poorly understood. Here, we present a chemogenetic approach to selectively manipulate Gq-mediated Ca²⁺ signaling in SCs across developmental stages. By combining <i>Cre</i>-dependent expression of the excitatory DREADD hM3Dq with activation by clozapine-N-oxide, we achieved precise, temporally controlled stimulation of the canonical Gq-PLC-IP3-Ca²⁺ cascade. <i>In vitro</i>, hM3Dq activation in immature SCs elevated basal Ca²⁺ levels, amplified spontaneous oscillations, and suppressed voltage- and ligand-gated Ca²⁺ influx, completely blocking SC maturation and myelin protein expression without affecting survival or proliferation. <i>In vivo</i>, early postnatal activation severely impaired sciatic nerve myelination, resulting in thinner myelin sheaths, fewer myelinated axons, and abnormal Remak bundle organization. Conversely, activation in mature SCs induced progressive demyelination, axonal degeneration, and motor deficits in adult mice. Ultrastructural and biochemical analyses confirmed widespread myelin loss and reduced expression of key myelin proteins, accompanied by increased g-ratios and axonal pathology. These findings uncover a previously unrecognized, bidirectional role for sustained Gq signaling in SC biology-blocking developmental myelination and destabilizing mature myelin through Ca²⁺ dysregulation. Our study establishes excitatory DREADDs as a powerful tool for probing stage-specific signaling requirements in peripheral glia and highlights Ca²⁺ homeostasis as a critical determinant of PNS integrity, with implications for demyelinating neuropathies and regenerative therapies.