Epigenetic modification in neuropathic pain.

Neuropathic pain is characterized by complicated combination of positive (e.g., hyperalgesia and allodynia) and negative (e.g., hypoesthesia and hypoalgesia) symptoms, and is often refractory to conventional pharmacological agents, including morphine. Although the molecular mechanisms for positive symptoms are extensively studied, those for negative symptoms are poorly understood. There is convincing evidence that altered gene expression within peripheral and central nervous systems is a key mechanism for neuropathic pain; however, its transcriptional mechanisms are poorly understood. Epigenetic modifications, such as DNA methylation and histone modifications (e.g., acetylation, methylation, and phosphorylation), are known to cause stable gene expression via chromatin remodeling. These mechanisms have a role not only in the determination of developmental cell fates, but also in the physiological and pathological processes in nervous system. Moreover, epigenetic therapies using epigenetic modifying compounds are progressively advanced in the treatments of diverse diseases, including cancer and neurological diseases. Importantly, there is emerging evidence that a variety of genes undergo epigenetic regulation via DNA methylation and histone modifications within peripheral and central nervous systems, thereby contributing to the alterations in both pain sensitivity and pharmacological efficacy in neuropathic pain. In this review, we will highlight the epigenetic gene regulation underlying neuropathic pain, especially focusing on the negative symptoms. Moreover, we will discuss whether epigenetic mechanisms can serve as a potential target to treat neuropathic pain.