Adcock Kathryn H, Brown David J, Shearer Morven C, Shewan Derryck, Schachner Melitta, Smith George M, Geller Herbert M, Fawcett James W
Centre for Brain Repair and Department of Physiology, University of Cambridge, Robinson Way, Cambridge CB2 2PY, UK.
Eur J Neurosci. 2004 Sep;20(6):1425-35. doi: 10.1111/j.1460-9568.2004.03573.x.
Axon regeneration in vivo is blocked at boundaries between Schwann cells and astrocytes, such as occur at the dorsal root entry zone and around peripheral nerve or Schwann cell grafts. We have created a tissue culture model of these boundaries in Schwann cell - astrocyte monolayer co-cultures. Axon behaviour resembles that in vivo, with axons showing a strong preference for Schwann cells over astrocytes. At boundaries between the two cell types, axons growing on astrocytes cross readily onto Schwann cells, but only 15% of axons growing on Schwann cells are able to cross onto astrocytes. Treatment with chondroitinase or chlorate to reduce inhibition by proteoglycans did not change this behaviour. The neural adhesion molecule L1 is present on Schwann cells and not astrocytes, and manipulation of L1 by application of an antibody, L1-Fc in solution, or adenoviral transduction of L1 into astrocytes increased the proportion of axons able to cross onto astrocytes to 40-50%. Elevating cAMP levels increased crossing from Schwann cells onto astrocytes in live and fixed cultures, and had a co-operative effect with NT-3 but not with NGF. Inactivation of Rho with a cell-permeant form of C3 exoenzyme also increased crossing from Schwann cells to astrocytes. Our experiments indicate that the preference of axons for Schwann cells is largely mediated by the presence of L1 on Schwann cells but not astrocytes, and that manipulation of growth cone signalling pathways can allow axons to disregard boundaries between the two cell types.
轴突在体内的再生在施万细胞与星形胶质细胞之间的边界处受阻,例如在背根进入区以及周围神经或施万细胞移植物周围。我们在施万细胞 - 星形胶质细胞单层共培养物中创建了这些边界的组织培养模型。轴突的行为类似于在体内的情况,轴突表现出对施万细胞的强烈偏好超过星形胶质细胞。在两种细胞类型之间的边界处,在星形胶质细胞上生长的轴突很容易交叉到施万细胞上,但在施万细胞上生长的轴突只有15%能够交叉到星形胶质细胞上。用软骨素酶或氯酸盐处理以减少蛋白聚糖的抑制作用并没有改变这种行为。神经粘附分子L1存在于施万细胞而不是星形胶质细胞上,通过应用抗体、溶液中的L1-Fc或通过腺病毒将L1转导到星形胶质细胞中对L1进行操作,可使能够交叉到星形胶质细胞上的轴突比例增加到40 - 50%。提高cAMP水平增加了在活细胞和固定培养物中从施万细胞到星形胶质细胞的交叉,并且与NT-3有协同作用,但与NGF没有协同作用。用细胞渗透性形式的C3外切酶使Rho失活也增加了从施万细胞到星形胶质细胞的交叉。我们的实验表明,轴突对施万细胞的偏好很大程度上是由施万细胞而非星形胶质细胞上存在L1介导的,并且对生长锥信号通路的操作可以使轴突无视两种细胞类型之间的边界。