Impaired ATP7A-Mediated Copper Homeostasis in the Spinal Cord Promotes Morphine Tolerance

Abstract

Morphine tolerance remains a major clinical challenge in pain management, and its underlying mechanisms are still not fully understood. Here, we show that tolerance-inducing morphine administration persistently suppressed the P-type ATPase copper transporter ATP7A, resulting in copper accumulation within spinal dorsal horn neurons and a consequent increase in reactive oxygen species (ROS). Intrathecal delivery of the copper chelator ammonium tetrathiomolybdate markedly attenuated the development of morphine tolerance. Mechanistically, excess cytosolic copper promotes ROS production, leading to mitochondrial dysfunction and elevated mitochondrial ROS generation. Unexpectedly, we found that the transport of copper from the cytosol into mitochondria mitigated morphine-induced ROS accumulation. Pharmacological treatment with DC_AC50, a small molecule that enhances mitochondrial copper delivery by inhibiting the copper-trafficking proteins ATOX1 and CCS, effectively reduced morphine-evoked ROS levels. Conversely, inhibition of the mitochondrial copper chaperone COX17 exacerbated ROS buildup in both cytosolic and mitochondrial compartments following morphine exposure. Collectively, these findings identify spinal copper homeostasis as a previously unrecognized and potentially actionable therapeutic target for mitigating opioid tolerance.