Regulation of endosomal motility and degradation by amyotrophic lateral sclerosis 2/alsin.
Dysfunction of alsin, particularly its putative Rab5 guanine-nucleotide-exchange factor activity, has been linked to one form of juvenile onset recessive familial amyotrophic lateral sclerosis (ALS2). Multiple lines of alsin knockout (ALS2(-/-)) mice have been generated to model this disease. However, it remains elusive whether the Rab5-dependent endocytosis is altered in ALS2(-/-) neurons. To directly examine the Rab5-mediated endosomal trafficking in ALS2(-/-) neurons, we introduced green fluorescent protein (GFP)-tagged Rab5 into cultured hippocampal neurons to monitor the morphology and motility of Rab5-associated early endosomes. Here we report that Rab5-mediated endocytosis was severely altered in ALS2(-/-) neurons. Excessive accumulation of Rab5-positive vesicles was observed in ALS2(-/-) neurons, which correlated with a significant reduction in endosomal motility and augmentation in endosomal conversion to lysosomes. Consequently, a significant increase in endosome/lysosome-dependent degradation of internalized glutamate receptors was observed in ALS2(-/-) neurons. These phenotypes closely resembled the endosomal trafficking abnormalities induced by a constitutively active form of Rab5 in wild-type neurons. Therefore, our findings reveal a negatively regulatory mechanism of alsin in Rab5-mediated endosomal trafficking, suggesting that enhanced endosomal degradation in ALS2(-/-) neurons may underlie the pathogenesis of motor neuron degeneration in ALS2 and related motor neuron diseases.
Lai
Chen
C
Laboratory of Neurogenetics, National Institute on Aging, National Institutes of Health, Bethesda, MD 20892, USA. laichi@mail.nih.gov
Xie
Chengsong
C
Shim
Hoon
H
Chandran
Jayanth
J
Howell
Brian W
BW
Cai
Huaibin
H
D000690:Amyotrophic Lateral Sclerosis / Q000378:metabolism* / Q000473:pathology; D000818:Animals; D004705:Endocytosis / Q000187:drug effects; D011992:Endosomes / Q000187:drug effects / Q000378:metabolism*; D020662:Guanine Nucleotide Exchange Factors / Q000172:deficiency / Q000378:metabolism*; D006624:Hippocampus / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D051907:Lysosomal Membrane Proteins / Q000378:metabolism; D051379:Mice; D009474:Neurons / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D011499:Protein Processing, Post-Translational / Q000187:drug effects; D021381:Protein Transport / Q000187:drug effects; D017470:Receptors, Glutamate / Q000378:metabolism; D018350:alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid / Q000494:pharmacology; D020696:rab5 GTP-Binding Proteins / Q000378:metabolism; D052118:Lysosomal-Associated Membrane Protein 1
D020662:Guanine Nucleotide Exchange Factors; D051907:Lysosomal Membrane Proteins; D017470:Receptors, Glutamate; D018350:alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; D020696:rab5 GTP-Binding Proteins; C512358:Als2 protein, mouse; C052255:Lamp1 protein, mouse; D052118:Lysosomal-Associated Membrane Protein 1