Department of Neuroscience/Physiology, New York University Langone Medical Center, New York, New York 10016, USA.
J Neurosci. 2011 May 25;31(21):7817-30. doi: 10.1523/JNEUROSCI.6412-10.2011.
In the hallmark neuritic dystrophy of Alzheimer's disease (AD), autophagic vacuoles containing incompletely digested proteins selectively accumulate in focal axonal swellings, reflecting defects in both axonal transport and autophagy. Here, we investigated the possibility that impaired lysosomal proteolysis could be a basis for both of these defects leading to neuritic dystrophy. In living primary mouse cortical neurons expressing fluorescence-tagged markers, LC3-positive autophagosomes forming in axons rapidly acquired the endo-lysosomal markers Rab7 and LAMP1 and underwent exclusive retrograde movement. Proteolytic clearance of these transported autophagic vacuoles was initiated after fusion with bidirectionally moving lysosomes that increase in number at more proximal axon levels and in the perikaryon. Disrupting lysosomal proteolysis by either inhibiting cathepsins directly or by suppressing lysosomal acidification slowed the axonal transport of autolysosomes, late endosomes, and lysosomes and caused their selective accumulation within dystrophic axonal swellings. Mitochondria and other organelles lacking cathepsins moved normally under these conditions, indicating that the general functioning of the axonal transport system was preserved. Dystrophic swellings induced by lysosomal proteolysis inhibition resembled in composition those in several mouse models of AD and also acquired other AD-like features, including immunopositivity for ubiquitin, amyloid precursor protein, and hyperphosphorylated neurofilament proteins. Restoration of lysosomal proteolysis reversed the affected movements of proteolytic Rab7 vesicles, which in turn essentially cleared autophagic substrates and reversed the axonal dystrophy. These studies identify the AD-associated defects in neuronal lysosomal proteolysis as a possible basis for the selective transport abnormalities and highly characteristic pattern of neuritic dystrophy associated with AD.
在阿尔茨海默病（AD）的标志性神经突营养不良中，含有未完全消化的蛋白质的自噬空泡选择性地在局灶性轴突肿胀中积累，反映了轴突运输和自噬的缺陷。在这里，我们研究了溶酶体蛋白水解缺陷可能是导致这两种缺陷导致神经突营养不良的基础的可能性。在表达荧光标记物的活原代小鼠皮质神经元中，形成轴突中的 LC3 阳性自噬体迅速获得内溶酶体标记物 Rab7 和 LAMP1，并进行了特异性逆行运动。这些被转运的自噬体的蛋白水解清除是在与双向移动的溶酶体融合后开始的，溶酶体在更近端的轴突水平和胞体中数量增加。通过直接抑制组织蛋白酶或抑制溶酶体酸化来破坏溶酶体蛋白水解会减缓自噬溶酶体、晚期内体和溶酶体的轴突运输，并导致它们在营养不良的轴突肿胀中选择性积累。在这些条件下，缺乏组织蛋白酶的线粒体和其他细胞器正常移动，表明轴突运输系统的一般功能得以保留。溶酶体蛋白水解抑制诱导的营养不良肿胀在组成上类似于几种 AD 小鼠模型中的那些，并且还获得了其他 AD 样特征，包括泛素、淀粉样前体蛋白和磷酸化神经丝蛋白的免疫阳性。溶酶体蛋白水解的恢复逆转了受影响的溶酶体 Rab7 囊泡的运动，这反过来又基本上清除了自噬底物并逆转了轴突营养不良。这些研究确定了与 AD 相关的神经元溶酶体蛋白水解缺陷是与 AD 相关的选择性转运异常和特征性神经突营养不良的可能基础。
