Nerve injury-induced upregulation of apolipoprotein E in dorsal root ganglion participates in neuropathic pain in male mice.

Apolipoprotein E (ApoE) is an apolipoprotein involved in lipid metabolism and is primarily responsible for lipid transport and cholesterol homeostasis in the central nervous system (CNS). The aim of this study is to explore the role of ApoE in the pathological development of neuropathic pain. First, we examined the location of ApoE in the dorsal root ganglion (DRG) and spinal cord in male mice using immunohistochemistry, and found that ApoE was predominantly expressed in DRG satellite glial cells (SGCs) and macrophages and spinal cord astrocytes. Using a spinal nerve ligation (SNL)-induced neuropathic pain mouse model, we found that nerve injury caused an increase in ApoE expression in the injured DRGs, but not in the spinal cord after SNL surgery. Furthermore, we observed reduced SNL-induced pain hypersensitivity in ApoE knockout mice compared to wild-type mice. Moreover, an antisense oligonucleotide (ASO) targeting the Apoe gene sequence, which was microinjected into the DRG or administered intrathecally, not only reduced ApoE expression in DRG but also attenuated SNL-induced pain hypersensitivity. Finally, we found that a tyrosine kinase receptor AXL, which was previously demonstrated to contribute to neuropathic pain, may mediate ApoE function under neuropathic pain condition. In conclusion, our data suggest that ApoE in DRG promote pain hypersensitivity via the DRG membrane receptor AXL in neurons under neuropathic pain conditions. This study revealed a novel mechanism between lipid homeostasis and neuropathic pain.