No abstract

Despite widespread distribution of LAMP1 and the heterogeneous nature of LAMP1-labeled compartments, LAMP1 is routinely used as a lysosomal marker, and LAMP1-positive organelles are often referred to as lysosomes. In this study, we use immunoelectron microscopy and confocal imaging to provide quantitative analysis of LAMP1 distribution in various autophagic and endolysosomal organelles in neurons. Our study demonstrates that a significant portion of LAMP1-labeled organelles do not contain detectable lysosomal hydrolases including cathepsins D and B and glucocerebrosidase. A bovine serum albumin-gold pulse-chase assay followed by ultrastructural analysis suggests a heterogeneity of degradative capacity in LAMP1-labeled endolysosomal organelles. Gradient fractionation displays differential distribution patterns of LAMP1/2 and cathepsins D/B in neurons. We further reveal that LAMP1 intensity in familial amyotrophic lateral sclerosis-linked motor neurons does not necessarily reflect lysosomal deficits in vivo. Our study suggests that labeling a set of lysosomal hydrolases combined with various endolysosomal markers would be more accurate than simply relying on LAMP1/2 staining to assess neuronal lysosome distribution, trafficking, and functionality under physiological and pathological conditions.

Huntington's disease (HD) is caused by an expansion of the polyglutamine tract at the N terminus of huntingtin. This mutation reduces levels of BDNF in the striatum, likely by inhibiting cortical Bdnf gene expression and anterograde transport of BDNF from the cerebral cortex to the striatum. Substantial evidence suggests that this reduction of striatal BDNF plays a crucial role in HD pathogenesis. Here we report that overexpression of BDNF in the forebrain rescues many disease phenotypes in YAC128 mice that express a full-length human huntingtin mutant with a 128-glutamine tract. The Bdnf transgene, under the control of the promoter for ␣ subunit of Ca 2ϩ /calmodulindependent protein kinase II, greatly increased BDNF levels in the cerebral cortex and striatum. BDNF overexpression in YAC128 mice prevented loss and atrophy of striatal neurons and motor dysfunction, normalized expression of the striatal dopamine receptor D2 and enkephalin, and improved procedural learning. Furthermore, quantitative analyses of Golgi-impregnated neurons revealed a decreased spine density and abnormal spine morphology in striatal neurons of YAC128 mice, which was also reversed by increasing BDNF levels in the striatum. These results demonstrate that reduced striatal BDNF plays a crucial role in the HD pathogenesis and suggest that attempts to restore striatal BDNF level may have therapeutic effects to the disease.