GLT1 overexpression reverses established neuropathic pain‐related behavior and attenuates chronic dorsal horn neuron activation following cervical spinal cord injury

Abstract

Development of neuropathic pain occurs in a major portion of traumatic spinal cord injury (SCI) patients, resulting in debilitating and often long-term physical and psychological burdens. Following SCI, chronic dysregulation of extracellular glutamate homeostasis has been shown to play a key role in persistent central hyperexcitability of superficial dorsal horn neurons that mediate pain neurotransmission, leading to various forms of neuropathic pain. Astrocytes express the major CNS glutamate transporter, GLT1, which is responsible for the vast majority of functional glutamate uptake, particularly in the spinal cord. In our unilateral cervical contusion model of mouse SCI that is associated with ipsilateral forepaw heat hypersensititvity (a form of chronic at-level neuropathic pain-related behavior), we previously reported significant and long-lasting reductions in GLT1 expression and functional GLT1-mediated glutamate uptake in cervical spinal cord dorsal horn. To therapeutically address GLT1 dysfunction following cervical contusion SCI, we injected an adeno-associated virus type 8 (AAV8)-Gfa2 vector into the superficial dorsal horn to increase GLT1 expression selectively in astrocytes. Compared to both contusion-only animals and injured mice that received AAV8-eGFP control injection, AAV8-GLT1 delivery increased GLT1 protein expression in astrocytes of the injured cervical spinal cord dorsal horn, resulting in a significant and persistent reversal of already-established heat hypersensitivity. Furthermore, AAV8-GLT1 injection significantly reduced expression of the transcription factor and marker of persistently increased neuronal activation, ΔFosB, in superficial dorsal horn neurons. These results demonstrate that focal restoration of GLT1 expression in the superficial dorsal horn is a promising target for treating chronic neuropathic pain following SCI.

Impaired sensitivity to pain stimuli in plasma membrane calcium ATPase 2 (PMCA2) heterozygous mice: a possible modality‐ and sex‐specific role for PMCA2 in nociception

“…Overactivation of DH projection neurons is a mechanism that underlies the manifestation of pain (41). Glutamate is the principal neurotransmitter that mediates the hyperexcitability of DH neurons, and dysregulation of extracellular glutamate homeostasis has been implicated in increased pain (34,(74)(75)(76)(77). Rapid and efficient clearance of glutamate in the CNS is mediated by astrocytes, which are the principal cell type that expresses GLAST and GLT1 (78).…”

Neuropathic pain following traumatic spinal cord injury: Models, measurement, and mechanisms

“…Neuronal hyperexcitability in the dorsal horn has also been implicated in SCI‐induced neuropathic pain (Zhang et al, ; Gwak et al, ; Gwak and Hulsebosch, ). This might occur through dysregulation of glutamate release, uptake, and receptor expression (Leem et al, ; Gwak et al, ; Putatunda et al, ; Falnikar et al, ); dendritic spine remodeling (Tan et al, ; Zhao et al, ); loss of local inhibitory (GABAergic) tone (Drew et al, ; Lu et al, ; Meisner et al, ; Berrocal et al, ; Lee‐Kubli et al, ); descending (particularly serotonergic) inhibitory input to spinal nociceptive circuitry (Hains et al, ; Kalous et al, ; Lin et al, ); or increased expression of the calcium channel subunit Ca v α2δ‐1 (Boroujerdi et al, ). The latter finding may partially explain the (small) benefit of gabapentinoids (which bind α2δ‐1) in neuropathic pain (Baastrup and Finnerup, ).…”

“…Widespread astrogliosis is also a feature of SCI (Carlton et al, ; Gwak and Hulsebosch, ; Gwak et al, ; Putatunda et al, ; Watson et al, ), and astroglial connexin hemichannels have been implicated in SCI pain (Chen et al, ). The astroglial glutamate reuptake transporter GLT1 is downregulated following SCI, and its overexpression reduces pain‐related behaviors and immunohistochemical markers of neuronal activity (Putatunda et al, ; Falnikar et al, ).…”

Improving the therapeutic efficacy of neural progenitor cell transplantation following spinal cord injury

“…In all cases, it is essential to generate the appropriate population of cells and to optimize survival and integration of the transplants. One consideration is the inclusion of therapeutic factors (using scaffolds, genetic modification of donor cells, or cotransplantation with other cell populations) to promote survival and integration, thus increasing the efficacy of the transplant [42], but it is also likely that NPC transplantation will be combined with other treatments such as neuroprotective drugs, exercise or electrical stimulation.…”