Coordinate Regulation of Mature Dopaminergic Axon Morphology by Macroautophagy and the PTEN Signaling Pathway

Macroautophagy is a conserved mechanism for the bulk degradation of proteins and organelles. Pathological studies have implicated defective macroautophagy in neurodegeneration, but physiological functions of macroautophagy in adult neurons remain unclear. Here we show that Atg7, an essential macroautophagy component, regulates dopaminergic axon terminal morphology. Mature Atg7-deficient midbrain dopamine (DA) neurons harbored selectively enlarged axonal terminals. This contrasted with the phenotype of DA neurons deficient in Pten – a key negative regulator of the mTOR kinase signaling pathway and neuron size – that displayed enlarged soma but unaltered axon terminals. Surprisingly, concomitant deficiency of both Atg7 and Pten led to a dramatic enhancement of axon terminal enlargement relative to Atg7 deletion alone. Similar genetic interactions between Atg7 and Pten were observed in the context of DA turnover and DA-dependent locomotor behaviors. These data suggest a model for morphological regulation of mature dopaminergic axon terminals whereby the impact of mTOR pathway is suppressed by macroautophagy

Macroautophagy deficiency mediates age-dependent neurodegeneration through a phospho-tau pathway

Background: Macroautophagy is an evolutionarily conserved mechanism for bulk intracellular degradation of proteins and organelles. Pathological studies have implicated macroautophagy defects in human neurodegenerative disorders of aging including Alzheimer’s disease and tauopathies. Neuronal deficiency of macroautophagy throughout mouse embryonic development results in neurodevelopmental defects and early postnatal mortality. However, the role of macroautophagy in mature CNS neurons, and the relationship with human disease neuropathology, remains unclear. Here we describe mice deficient in an essential macroautophagy component, Atg7, specifically within postnatal CNS neurons. Results: Postnatal forebrain-specific Atg7 conditional knockout (cKO) mice displayed age-dependent neurodegeneration and ubiquitin- and p62-positive inclusions. Phosphorylated tau was significantly accumulated in Atg7 cKO brains, but neurofibrillary tangles that typify end-stage human tauopathy were not apparent. A major tau kinase, glycogen synthase kinase 3β (GSK3β), was also accumulated in Atg7 cKO brains. Chronic pharmacological inhibition of tau phosphorylation, or genetic deletion of tau, significantly rescued Atg7-deficiency-mediated neurodegeneration, but did not suppress inclusion formation. Conclusions: These data elucidate a role for macroautophagy in the long-term survival and physiological function of adult CNS neurons. Neurodegeneration in the context of macroautophagy deficiency is mediated through a phospho-tau pathway

LRRK2 and RAB7L1 coordinately regulate axonal morphology and lysosome integrity in diverse cellular contexts

Leucine-rich repeat kinase 2 (LRRK2) has been linked to several clinical disorders including Parkinson’s disease (PD), Crohn’s disease, and leprosy. Furthermore in rodents, LRRK2 deficiency or inhibition leads to lysosomal pathology in kidney and lung. Here we provide evidence that LRRK2 functions together with a second PD-associated gene, RAB7L1, within an evolutionarily conserved genetic module in diverse cellular contexts. In C. elegans neurons, orthologues of LRRK2 and RAB7L1 act coordinately in an ordered genetic pathway to regulate axonal elongation. Further genetic studies implicated the AP-3 complex, which is a known regulator of axonal morphology as well as of intracellular protein trafficking to the lysosome compartment, as a physiological downstream effector of LRRK2 and RAB7L1. Additional cell-based studies implicated LRRK2 in the AP-3 complex-related intracellular trafficking of lysosomal membrane proteins. In mice, deficiency of either RAB7L1 or LRRK2 leads to prominent age-associated lysosomal defects in kidney proximal tubule cells, in the absence of frank CNS pathology. We hypothesize that defects in this evolutionarily conserved genetic pathway underlie the diverse pathologies associated with LRRK2 in humans and in animal models

Sonic Hedgehog Is a Chemoattractant for Midbrain Dopaminergic Axons

Midbrain dopaminergic axons project from the substantia nigra (SN) and the ventral tegmental area (VTA) to rostral target tissues, including the striatum, pallidum, and hypothalamus. The axons from the medially located VTA project primarily to more medial target tissues in the forebrain, whereas the more lateral SN axons project to lateral targets including the dorsolateral striatum. This structural diversity underlies the distinct functions of these pathways. Although a number of guidance cues have been implicated in the formation of the distinct axonal projections of the SN and VTA, the molecular basis of their diversity remains unclear. Here we investigate the molecular basis of structural diversity in mDN axonal projections. We find that Sonic Hedgehog (Shh) is expressed at a choice point in the course of the rostral dopaminergic projections. Furthermore, in midbrain explants, dopaminergic projections are attracted to a Shh source. Finally, in mice in which Shh signaling is inactivated during late neuronal development, the most medial dopaminergic projections are deficient

Spinal Cord Injury Reveals Multilineage Differentiation of Ependymal Cells

Spinal cord injury often results in permanent functional impairment. Neural stem cells present in the adult spinal cord can be expanded in vitro and improve recovery when transplanted to the injured spinal cord, demonstrating the presence of cells that can promote regeneration but that normally fail to do so efficiently. Using genetic fate mapping, we show that close to all in vitro neural stem cell potential in the adult spinal cord resides within the population of ependymal cells lining the central canal. These cells are recruited by spinal cord injury and produce not only scar-forming glial cells, but also, to a lesser degree, oligodendrocytes. Modulating the fate of ependymal progeny after spinal cord injury may offer an alternative to cell transplantation for cell replacement therapies in spinal cord injury

Fine Mapping of Genetic Variants in BIN1, CLU, CR1 and PICALM for Association with Cerebrospinal Fluid Biomarkers for Alzheimer's Disease

Recent genome-wide association studies of Alzheimer's disease (AD) have identified variants in BIN1, CLU, CR1 and PICALM that show replicable association with risk for disease. We have thoroughly sampled common variation in these genes, genotyping 355 variants in over 600 individuals for whom measurements of two AD biomarkers, cerebrospinal fluid (CSF) 42 amino acid amyloid beta fragments (Aβ42) and tau phosphorylated at threonine 181 (ptau181), have been obtained. Association analyses were performed to determine whether variants in BIN1, CLU, CR1 or PICALM are associated with changes in the CSF levels of these biomarkers. Despite adequate power to detect effects as small as a 1.05 fold difference, we have failed to detect evidence for association between SNPs in these genes and CSF Aβ42 or ptau181 levels in our sample. Our results suggest that these variants do not affect risk via a mechanism that results in a strong additive effect on CSF levels of Aβ42 or ptau181

The role of protein kinase C[gamma] in mammalian central nervous system function : a genetic approach

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Biology, 1994.On t.p., "[gamma]" appears as the lower case Greek letter.Includes bibliographical references.by Asa Abeliovich.Ph.D

CRISPR Transcriptional Activation Analysis Unmasks an Occult γ-Secretase Processivity Defect in Familial Alzheimer’s Disease Skin Fibroblasts

Summary: Mutations in presenilin (PSEN) 1 and 2, which encode components of the γ-secretase (GS) complex, cause familial Alzheimer’s disease (FAD). It is hypothesized that altered GS-mediated processing of the amyloid precursor protein (APP) to the Aβ42 fragment, which is accumulated in diseased brain, may be pathogenic. Here, we describe an in vitro model system that enables the facile analysis of neuronal disease mechanisms in non-neuronal patient cells using CRISPR gene activation of endogenous disease-relevant genes. In FAD patient-derived fibroblast cultures, CRISPR activation of APP or BACE unmasked an occult processivity defect in downstream GS-mediated carboxypeptidase cleavage of APP, ultimately leading to higher Aβ42 levels. These data suggest that, selectively in neurons, relatively high levels of BACE1 activity lead to substrate pressure on FAD-mutant GS complexes, promoting CNS Aβ42 accumulation. Our results introduce an additional platform for analysis of neurological disease. : Availability of facile cell-based models is a challenge in the study of neurodegenerative diseases. Using CRISPR activation, Inoue et al. demonstrate that activation of the APP and/or BACE1 genes unmasks a γ-secretase carboxypeptidase deficiency in patient fibroblasts, promoting Aβ42 accumulation. Keywords: CRISPR/Cas9, synergistic activation mediator, Alzheimer’s disease, amyloid precursor protein, β-amyloid, BACE1, presenilin, fibroblast, induced neuronal cells, γ-secretase processivit

Overexpression of WT DJ-1 Inhibits Aggregation of αSyn In Vivo

<div><p>(A) CAD murine neuroblastoma cells were transfected with Flag-αSyn along with WT DJ-1, L166P clinical mutant, or vector alone, and were differentiated in vitro via serum withdrawal. Cells were subsequently treated with 2 mM FeCl₂ (Fe), 5 μM lactacystin (LC), or media alone (0). Triton X-100-soluble (Tx-100 sol) and Triton X-100-insoluble (Tx-100 insol) fractions were analyzed by Western blotting. Upon FeCl₂ treatment, αSyn accumulates in the Triton X-100-insoluble fraction, and accumulation of insoluble αSyn is inhibited by overexpression of WT DJ-1 (left) but not the L166P clinical mutant (right).</p> <p>(B) Triton X-100-insoluble αSyn as quantified by NIH Image J of a Western blot (from [A]).</p> <p>(C) Heterozygous (+/–) and DJ-1 deficient (–/–) ES cells were differentiated using the embryoid body protocol. Cells were transfected with Flag-αSyn (F-αSyn), and, after 48 h, treated with 2 mM FeCl₂ or with media alone for 18 h. Cell lysates were analyzed by Western blotting for αSyn or β-actin. In the Triton X-100-soluble fraction (Tx-100 sol), DJ-1 accumulated to a similar extent in the knockout and control cells. In contrast, αSyn accumulation in the insoluble pool (Tx-100 insol) was detectable only in the knockout cells, and this was further promoted by FeCl₂ treatment.</p> <p>(D) CAD cells transfected with Flag-αSyn (F-αSyn) along with WT DJ-1 (or vector alone) were treated with 2 mM FeCl₂ or media alone for 18 h. Triton X-100-soluble cell lysates were immunoprecipitated with a mouse monoclonal antibody for the Flag epitope and Western blotted for DJ-1. FeCl₂ treatment induces association of Flag-αSyn with WT DJ-1. Lysates represent 20% input of the immunoprecipitation (IP α-Flag). The Triton X-100 soluble pool of DJ-1 is reduced by αSyn overexpression (but not vector control), particularly in the context of FeCl₂ treatment (bottom).</p> <p>(E) DJ-1 colocalizes with αSyn in the Triton X-100-insoluble fraction upon FeCl₂ treatment. The Western blot from (A) was stripped and reprobed for DJ-1.</p></div