Astrocyte store-operated calcium entry is required for centrally mediated neuropathic pain.

INTRODUCTION

Acute injuries transition to chronic neuropathic pain through central sensitization (CS), which involves plastic changes to nociceptive networks within the central nervous system. Astrocytes are essential mediators of CS, and many neuromodulatory functions of astrocytes are regulated by complex Ca2+ signaling mechanisms. The role of astrocyte Ca2+ signaling in CS and the specific astrocyte Ca2+ channels involved are poorly defined.

OBJECTIVES

Our objective was to test the role of store-operated Ca2+ entry (SOCE), a highly conserved Ca2+ signaling mechanism that mediates Ca2+ influx in response to depletion of endoplasmic reticulum Ca2+ stores, in CS and neuropathic pain.

METHODS

We used a Drosophila model of CS based on the development of thermal allodynia 7 days after acute nerve injury, combined with a transcriptional reporter of intracellular Ca2+ mobilization. In vivo, astrocyte-specific RNAi was then used to test the role of Orai SOCE channels and Orai-activating Stim proteins in injury-induced astrocyte Ca2+ signaling and thermal allodynia.

RESULTS

Astrocytes exhibited Stim and Orai-dependent Ca2+ signaling 3 to 4 days postinjury. Astrocyte-specific suppression of Stim and Orai completely inhibited the development of thermal allodynia 7 days after injury and also inhibited the loss of GABAergic inhibitory neurons required for CS in flies as well as mammals. Finally, constitutive SOCE-mediated astrocyte Ca2+ signaling resulted in thermal allodynia even in the absence of injury.

CONCLUSION

Astrocyte SOCE is necessary and sufficient for CS and thermal allodynia in Drosophila, adding key new understanding to the conserved astrocyte Ca2+ signaling mechanisms involved in development of neuropathic pain.