Equilibrative Nucleoside Transporter 1 is a Target to Modulate Neuroinflammation and Improve Functional Recovery in Mice with Spinal Cord Injury

Neuroinflammation plays a critical role in the neurological recovery of spinal cord injury (SCI). Adenosine can modulate neuroinflammation, whose uptake is mediated by nucleoside transporters. This study aimed to investigate the roles of equilibrative nucleoside transporter 1 (Ent1) in the inflammatory responses and functional recovery of SCI. Spinal cord contusion at the T10 dorsal portion was induced in mice to cause partial paralysis of the hindlimbs. Genetic deletion and pharmacological inhibition of Ent1 were used to evaluate the role of Ent1 in SCI. The outcomes were evaluated in terms of the Basso Mouse Scale (BMS), gait analysis, astrogliosis, microgliosis, and cytokine levels on day 14 post-injury. As a result, Ent1 deletion reduced neuroinflammation and improved the BMS score (4.88 +/- 0.35 in Ent1(-/-) vs. 3.78 +/- 1.09 in Ent1(+)(/+)) and stride length (3.74 +/- 0.48 cm in Ent1(-/-) vs. 2.82 +/- 0.78 cm in Ent1(+)(/+)) of mice with SCI. Along with the reduced lesion size, more preserved neurons were identified in the perilesional area of mice with Ent1 deletion (102 +/- 23 in Ent1(-/-) vs. 73 +/- 10 in Ent1(+)(/+)). The results of pharmacological inhibition were consistent with the findings of genetic deletion. Moreover, Ent1 inhibition decreased the protein level of complement 3 (an Al marker), but increased the levels of S100 calcium-binding protein a10 (an A2 marker) and transforming growth factor-beta, without changing the levels of inducible nitric oxide synthase (a M1 marker) and arginase 1 (a M2 marker) at the injured site. These findings indicate the important role of Ent1 in the pathogenesis and treatment of SCI.