Pathobiology of the autophagy-lysosomal pathway in the Huntington's disease brain.

Accumulated levels of mutant huntingtin protein (mHTT) and its fragments are considered contributors to the pathogenesis of Huntington's disease (HD). Although lowering mHTT by stimulating autophagy has been considered a possible therapeutic strategy, the role and competence of autophagy-lysosomal pathway (ALP) during HD progression in the human disease remains largely unknown. Here, we used multiplex confocal and ultrastructural immunocytochemical analyses of ALP functional markers in relation to mHTT aggresome pathology in striatum and the less affected cortex of HD brains staged from HD2 to HD4 by Vonsattel neuropathological criteria compared to controls.

Faulty autolysosome acidification in Alzheimer's disease mouse models induces autophagic build-up of Aβ in neurons, yielding senile plaques.

Autophagy is markedly impaired in Alzheimer's disease (AD). Here we reveal unique autophagy dysregulation within neurons in five AD mouse models in vivo and identify its basis using a neuron-specific transgenic mRFP-eGFP-LC3 probe of autophagy and pH, multiplex confocal imaging and correlative light electron microscopy. Autolysosome acidification declines in neurons well before extracellular amyloid deposition, associated with markedly lowered vATPase activity and build-up of Aβ/APP-βCTF selectively within enlarged de-acidified autolysosomes.

Axonal transport of late endosomes and amphisomes is selectively modulated by local Ca efflux and disrupted by PSEN1 loss of function.

Dysfunction and mistrafficking of organelles in autophagy- and endosomal-lysosomal pathways are implicated in neurodegenerative diseases. Here, we reveal selective vulnerability of maturing degradative organelles (late endosomes/amphisomes) to disease-relevant local calcium dysregulation. These organelles undergo exclusive retrograde transport in axons, with occasional pauses triggered by regulated calcium efflux from agonist-evoked transient receptor potential cation channel mucolipin subfamily member 1 (TRPML1) channels-an effect greatly exaggerated by exogenous agonist mucolipin synthetic agonist 1 (ML-SA1).

Endosomal Dysfunction Induced by Directly Overactivating Rab5 Recapitulates Prodromal and Neurodegenerative Features of Alzheimer's Disease.

Neuronal endosomal dysfunction, the earliest known pathobiology specific to Alzheimer's disease (AD), is mediated by the aberrant activation of Rab5 triggered by APP-β secretase cleaved C-terminal fragment (APP-βCTF). To distinguish pathophysiological consequences specific to overactivated Rab5 itself, we activate Rab5 independently from APP-βCTF in the PA-Rab5 mouse model. We report that Rab5 overactivation alone recapitulates diverse prodromal and degenerative features of AD.

mTOR hyperactivation in Down Syndrome underlies deficits in autophagy induction, autophagosome formation, and mitophagy.

Down syndrome (DS), a complex genetic disorder caused by chromosome 21 trisomy, is associated with mitochondrial dysfunction leading to the accumulation of damaged mitochondria. Here we report that mitophagy, a form of selective autophagy activated to clear damaged mitochondria is deficient in primary human fibroblasts derived from individuals with DS leading to accumulation of damaged mitochondria with consequent increases in oxidative stress. We identified two molecular bases for this mitophagy deficiency: PINK1/PARKIN impairment and abnormal suppression of macroautophagy.

Autophagy flux in CA1 neurons of Alzheimer hippocampus: Increased induction overburdens failing lysosomes to propel neuritic dystrophy.

Defective autophagy contributes to Alzheimer disease (AD) pathogenesis although evidence is conflicting on whether multiple stages are impaired. Here, for the first time, we have comprehensively evaluated the entire autophagic process specifically in CA1 pyramidal neurons of hippocampus from early and late-stage AD subjects and nondemented controls. CA1 neurons aspirated by laser capture microdissection were analyzed using a custom-designed microarray comprising 578 neuropathology- and neuroscience-associated genes.

BACE and gamma-secretase characterization and their sorting as therapeutic targets to reduce amyloidogenesis.

Secretases are named for enzymes processing amyloid precursor protein (APP), a prototypic type-1 membrane protein. This led directly to discovery of novel Aspartyl proteases (beta-secretases or BACE), a tetramer complex gamma-secretase (gamma-SC) containing presenilins, nicastrin, aph-1 and pen-2, and a new role for metalloprotease(s) of the ADAM family as a alpha-secretases. Recent advances in defining pathways that mediate endosomal-lysosomal-autophagic-exosomal trafficking now provide targets for new drugs to attenuate abnormal production of fibril forming products characteristic of AD.

Glucosylceramide synthase decrease in frontal cortex of Alzheimer brain correlates with abnormal increase in endogenous ceramides: consequences to morphology and viability on enzyme suppression in cultured primary neurons.

Abnormal increase in native long-chain ceramides (lcCer) in AD implicates roles in neuronal atrophy and cognitive dysfunction especially in view of divergent roles this second messenger plays in cell function. Since clearance is mediated by glucosylceramide synthase (GCS, EC 2.4.

Neurosecretases provide strategies to treat sporadic and familial Alzheimer disorders.

Recent discoveries on neurosecretases and their trafficking to release fibril-forming neuropeptides or other products, are of interest to pathology, cell signaling and drug discovery. Nomenclature arose from the use of amyloid precursor protein (APP) as a prototypic type-1 substrate leading to the isolation of beta-secretase (BACE), multimeric complexes (gamma-secretase, gamma-SC) for intramembranal cleavage, and attributing a new function to well-characterized metalloproteases of the ADAM family (alpha-secretase) for normal APP turnover. While purified alpha/beta-secretases facilitate drug discovery, gamma-SC presents greater challenges for characterization and mechanisms of catalysis.

APP processing enzymes (secretases) as therapeutic targets: insights from the use of transgenics (Tgs) and transfected cells.

Secretases degrade amyloid precursor protein (APP) releasing fragments (beta-peptides A beta, A beta x) that assemble to form hallmark extracellular deposits in Alzheimer's disease (AD) correlating with disease severity. As such, secretases supply targets for therapeutic intervention and form the focus of this overview. Progress in elucidating secretases and their modes of catalysis come from exploiting the use of transgenics or transfected cells.

Brain damage results in down-regulation of N-acetylaspartate as a neuronal osmolyte.

N-acetyl-L-aspartate (NAA) is present in the vertebrate brain, where its concentration is one of the highest of all free amino acids. Although NAA is synthesized and stored primarily in neurons, it is not hydrolyzed in these cells. However, after its regulated release into extracellular fluid, neuronal NAA is hydrolyzed by amidohydrolase II that is present in oligodendrocytes.