Verrier Jonathan D, Kochanek Patrick M, Jackson Edwin K
Department of Pharmacology and Chemical Biology (J.D.V., E.K.J.), Department of Critical Care Medicine (P.M.K.), and Safar Center for Resuscitation Research (P.M.K.), University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania.
Department of Pharmacology and Chemical Biology (J.D.V., E.K.J.), Department of Critical Care Medicine (P.M.K.), and Safar Center for Resuscitation Research (P.M.K.), University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania
J Pharmacol Exp Ther. 2015 Aug;354(2):175-83. doi: 10.1124/jpet.115.225219. Epub 2015 May 21.
The 3',5'-cAMP-adenosine pathway (3',5'-cAMP→5'-AMP→adenosine) and the 2',3'-cAMP-adenosine pathway (2',3'-cAMP→2'-AMP/3'-AMP→adenosine) are active in the brain. Oligodendrocytes participate in the brain 2',3'-cAMP-adenosine pathway via their robust expression of 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNPase; converts 2',3'-cAMP to 2'-AMP). Because Schwann cells also express CNPase, it is conceivable that the 2',3'-cAMP-adenosine pathway exists in the peripheral nervous system. To test this and to compare the 2',3'-cAMP-adenosine pathway to the 3',5'-cAMP-adenosine pathway in Schwann cells, we examined the metabolism of 2',3'-cAMP, 2'-AMP, 3'-AMP, 3',5'-cAMP, and 5'-AMP in primary rat Schwann cells in culture. Addition of 2',3'-cAMP (3, 10, and 30 µM) to Schwann cells increased levels of 2'-AMP in the medium from 0.006 ± 0.002 to 21 ± 2, 70 ± 3, and 187 ± 10 nM/µg protein, respectively; in contrast, Schwann cells had little ability to convert 2',3'-cAMP to 3'-AMP or 3',5'-cAMP to either 3'-AMP or 5'-AMP. Although Schwann cells slightly converted 2',3'-cAMP and 2'-AMP to adenosine, they did so at very modest rates (e.g., 5- and 3-fold, respectively, more slowly compared with our previously reported studies in oligodendrocytes). Using transected myelinated rat sciatic nerves in culture medium, we observed a time-related increase in endogenous intracellular 2',3'-cAMP and extracellular 2'-AMP. These findings indicate that Schwann cells do not have a robust 3',5'-cAMP-adenosine pathway but do have a 2',3'-cAMP-adenosine pathway; however, because the pathway mostly involves 2'-AMP formation rather than 3'-AMP, and because the conversion of 2'-AMP to adenosine is slow, metabolism of 2',3'-cAMP mostly results in the accumulation of 2'-AMP. Accumulation of 2'-AMP in peripheral nerves postinjury could have pathophysiological consequences.
3',5'-环磷酸腺苷-腺苷途径（3',5'-环磷酸腺苷→5'-单磷酸腺苷→腺苷）和2',3'-环磷酸腺苷-腺苷途径（2',3'-环磷酸腺苷→2'-单磷酸腺苷/3'-单磷酸腺苷→腺苷）在大脑中具有活性。少突胶质细胞通过其对2',3'-环核苷酸3'-磷酸二酯酶（CNPase；将2',3'-环磷酸腺苷转化为2'-单磷酸腺苷）的强烈表达参与大脑的2',3'-环磷酸腺苷-腺苷途径。由于雪旺细胞也表达CNPase，因此可以推测2',3'-环磷酸腺苷-腺苷途径存在于外周神经系统中。为了验证这一点并比较雪旺细胞中2',3'-环磷酸腺苷-腺苷途径与3',5'-环磷酸腺苷-腺苷途径，我们检测了原代培养的大鼠雪旺细胞中2',3'-环磷酸腺苷、2'-单磷酸腺苷、3'-单磷酸腺苷、3',5'-环磷酸腺苷和5'-单磷酸腺苷的代谢情况。向雪旺细胞中添加2',3'-环磷酸腺苷（3、10和30 μM）后，培养基中2'-单磷酸腺苷的水平分别从0.006±0.002增加到21±2、70±3和187±10 nM/μg蛋白质；相比之下，雪旺细胞将2',3'-环磷酸腺苷转化为3'-单磷酸腺苷或将3',5'-环磷酸腺苷转化为3'-单磷酸腺苷或5'-单磷酸腺苷的能力较弱。尽管雪旺细胞能将2',3'-环磷酸腺苷和2'-单磷酸腺苷轻微转化为腺苷，但其转化速率非常低（例如，分别比我们之前在少突胶质细胞中的研究慢5倍和3倍）。使用培养培养基中的横断有髓大鼠坐骨神经，我们观察到内源性细胞内2',3'-环磷酸腺苷和细胞外2'-单磷酸腺苷随时间增加。这些发现表明，雪旺细胞没有强大的3',5'-环磷酸腺苷-腺苷途径，但确实有2',3'-环磷酸腺苷-腺苷途径；然而，由于该途径主要涉及2'-单磷酸腺苷的形成而非3'-单磷酸腺苷，并且由于2'-单磷酸腺苷向腺苷的转化缓慢，2',3'-环磷酸腺苷的代谢主要导致2'-单磷酸腺苷的积累。损伤后外周神经中2'-单磷酸腺苷的积累可能具有病理生理后果。
