Hellström Mats, Harvey Alan R
School of Anatomy, Physiology and Human Biology, The University of Western Australia, Crawley, WA 6009, Australia.
School of Anatomy, Physiology and Human Biology, The University of Western Australia, Crawley, WA 6009, Australia.
Int J Biochem Cell Biol. 2014 Nov;56:66-73. doi: 10.1016/j.biocel.2014.04.018. Epub 2014 May 4.
In this paper we present a brief review of studies that have reported therapeutic benefits of elevated cAMP on plasticity and regeneration after injury to the central nervous system (CNS). We also provide new data on the cellular mechanisms by which elevation of cyclic adenosine monophosphate (cAMP) promotes cytokine driven regeneration of adult CNS axons, using the visual system as the experimental model. cAMP is a second messenger for many intracellular signalling pathways. Elevation of cAMP in the eye by intravitreal injection of the cell permeant analogue (8-(4-chlorophenylthio)-adenosine-3',5'-cyclic monophosphate; CPT-cAMP), when added to recombinant ciliary neurotrophic factor (rCNTF), significantly enhances rCNTF-induced regeneration of adult rat retinal ganglion cell (RGC) axons into peripheral nerve (PN) grafted onto transected optic nerve. This effect is mediated to some extent by protein kinase A (PKA) signalling, but CPT-cAMP also acts via PI3K/Akt signalling to reduce suppressor of cytokine signalling protein 3 (SOCS3) activity in RGCs. Another target for cAMP is the exchange protein activated by cAMP (Epac), which can also mediate cAMP-induced axonal growth. Here we describe some novel results and discuss to what extent the pro-regenerative effects of CPT-cAMP on adult RGCs are mediated via Epac as well as via PKA-dependent pathways. We used the established PN-optic nerve graft model and quantified the survival and regenerative growth of adult rat RGCs after intravitreal injection of rCNTF in combination with a selective activator of PKA and/or a specific activator of Epac. Viable RGCs were identified by βIII-tubulin immunohistochemistry and regenerating RGCs retrogradely labelled and quantified after an injection of fluorogold into the distal end of the PN grafts, 4 weeks post-transplantation. The specific agonists of either PKA or Epac were both effective in enhancing the effects of rCNTF on RGC axonal regeneration, but interestingly, injections that combined rCNTF with both agonists were significantly less effective. The results are discussed in relation to previous CPT-cAMP studies on RGCs, and we also consider the need to modulate cAMP levels in order to obtain the most functionally effective regenerative response after CNS trauma. This article is part of a directed issue entitled: Regenerative Medicine: the challenge of translation.
在本文中，我们简要回顾了一些研究，这些研究报道了环磷酸腺苷（cAMP）升高对中枢神经系统（CNS）损伤后可塑性和再生的治疗益处。我们还提供了新的数据，以细胞机制为切入点，利用视觉系统作为实验模型，研究环磷酸腺苷（cAMP）升高促进成年中枢神经系统轴突细胞因子驱动再生的机制。cAMP是许多细胞内信号通路的第二信使。通过玻璃体内注射细胞渗透性类似物（8-（4-氯苯基硫代）-腺苷-3'，5'-环磷酸；CPT-cAMP）提高眼内cAMP水平，当与重组睫状神经营养因子（rCNTF）联合使用时，可显著增强rCNTF诱导的成年大鼠视网膜神经节细胞（RGC）轴突向移植到横断视神经上的周围神经（PN）的再生。这种作用在一定程度上由蛋白激酶A（PKA）信号介导，但CPT-cAMP也通过PI3K/Akt信号发挥作用，以降低RGC中细胞因子信号抑制蛋白3（SOCS3）的活性。cAMP的另一个靶点是cAMP激活的交换蛋白（Epac），它也可以介导cAMP诱导的轴突生长。在这里，我们描述了一些新的结果，并讨论了CPT-cAMP对成年RGC的促再生作用在多大程度上是通过Epac以及PKA依赖性途径介导的。我们使用已建立的PN-视神经移植模型，在玻璃体内注射rCNTF并联合PKA的选择性激活剂和/或Epac的特异性激活剂后，对成年大鼠RGC的存活和再生生长进行定量分析。移植4周后，通过βIII-微管蛋白免疫组织化学鉴定存活的RGC，并在向PN移植物远端注射荧光金后，对逆行标记和定量的再生RGC进行分析。PKA或Epac的特异性激动剂均能有效增强rCNTF对RGC轴突再生的作用，但有趣的是，将rCNTF与两种激动剂联合注射的效果明显较差。我们结合之前关于RGC的CPT-cAMP研究对结果进行了讨论，并且我们还考虑了调节cAMP水平的必要性，以便在中枢神经系统创伤后获得功能上最有效的再生反应。本文是名为“再生医学：转化的挑战”的定向专题的一部分。
