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Presenilins 1 and 2 (PS1 and PS2) are the catalytic subunits of the &lgr;-secretase complex, and genes encoding mutant PS1 and PS2 variants cause familial forms of Alzheimer's disease. Lee et al. (2010) recently reported that loss of PS1 activity lead to impairments in autophagosomal function as a consequence of lysosomal alkalinization, caused by failed maturation of the proton translocating V0a1 subunit of the vacuolar (H)-ATPase and targeting to the lysosome. We have reexamined these issues in mammalian cells and in brains of mice lacking PS (PScdko) and have been unable to find evidence that the turnover of autophagic substrates, vesicle pH, V0a1 maturation, or lysosome function is altered compared with wild-type counterparts. Collectively, our studies fail to document a role for presenilins in regulating cellular autophagosomal function. On the other hand, our transcriptome studies of PScdko mouse brains reveal, for the first time, a role for PS in regulating lysosomal biogenesis. [ABSTRACT FROM AUTHOR]

To elucidate the pathogenic mechanisms in Huntington's disease (HD) elicited by expression of full-length human mutant huntingtin (fl-mhtt), a bacterial artificial chromosome (BAC)-mediated transgenic mouse model (BACHD) was developed expressing fl-mhtt with 97 glutamine repeats under the control of endogenous htt regulatory machinery on the BAC. BACHD mice exhibit progressive motor deficits, neuronal synaptic dysfunction, and late-onset selective neuropathology, which includes significant cortical and striatal atrophy and striatal dark neuron degeneration. Power analyses reveal the robustness of the behavioral and neuropathological phenotypes, suggesting BACHD as a suitable fl-mhtt mouse model for preclinical studies. Additional analyses of BACHD mice provide novel insights into how mhtt may elicit neuropathogenesis. First, unlike previous fl-mhtt mouse models, BACHD mice reveal that the slowly progressive and selective pathogenic process in HD mouse brains can occur without early and diffuse nuclear accumulation of aggregated mhtt (i.e., as detected by immunostaining with the EM48 antibody). Instead, a relatively steady-state level of predominantly full-length mhtt and a small amount of mhtt N-terminal fragments are sufficient to elicit the disease process. Second, the polyglutamine repeat within fl-mhtt in BACHD mice is encoded by a mixed CAA-CAG repeat, which is stable in both the germline and somatic tissues including the cortex and striatum at the onset of neuropathology. Therefore, our results suggest that somatic repeat instability does not play a necessary role in selective neuropathogenesis in BACHD mice. In summary, the BACHD model constitutes a novel and robust in vivo paradigm for the investigation of HD pathogenesis and treatment. [ABSTRACT FROM AUTHOR]