ALS2/alsin deficiency in neurons leads to mild defects in macropinocytosis and axonal growth
ABSTRACT Loss of function mutations in the ALS2 gene account for a number of juvenile/infantile recessive motor neuron diseases, indicating that its gene product, ALS2/alsin, plays a crucial role in maintenance and survival for a subset of neurons. ALS2 acts as a guanine nucleotide exchange factor (GEF) for the small GTPase Rab5 and is implicated in endosome dynamics in cells. However, the role of ALS2 in neurons remains unclear. To elucidate the neuronal ALS2 functions, we investigate cellular phenotypes of ALS2-deficient primary cultured neurons derived from Als2-knockout (KO) mice. Here, we show that ALS2 deficiency results not only in the delay of axon outgrowth in hippocampal neurons, but also in a decreased level of the fluid phase horseradish peroxidase (HRP) uptake, which represents the activity for macropinocytic endocytosis, in cortical neurons. Thus, ALS2 may act as a modulator in neuronal differentiation and/or development through regulation of membrane dynamics.
- SourceAvailable from: Cristian Droppelmann[Show abstract] [Hide abstract]
ABSTRACT: Small GTPases participate in a broad range of cellular processes such as proliferation, differentiation, and migration. The exchange of GDP for GTP resulting in the activation of these GTPases is catalyzed by a group of enzymes called guanine nucleotide exchange factors (GEFs), of which two classes: Dbl-related exchange factors and the more recently described dedicator of cytokinesis proteins family exchange factors. Increasingly, deregulation of normal GEF activity or function has been associated with a broad range of disease states, including neurodegeneration and neurodevelopmental disorders. In this review, we examine this evidence with special emphasis on the novel role of Rho guanine nucleotide exchange factor (RGNEF/p190RhoGEF) in the pathogenesis of amyotrophic lateral sclerosis. RGNEF is the first neurodegeneration-linked GEF that regulates not only RhoA GTPase activation but also functions as an RNA binding protein that directly acts with low molecular weight neurofilament mRNA 3' untranslated region to regulate its stability. This dual role for RGNEF, coupled with the increasing understanding of the key role for GEFs in modulating the GTPase function in cell survival suggests a prominent role for GEFs in mediating a critical balance between cytotoxicity and neuroprotection which, when disturbed, contributes to neuronal loss.Frontiers in Cellular Neuroscience 09/2014; 8. DOI:10.3389/fncel.2014.00282 · 4.18 Impact Factor
Article: Protein clearing pathways in ALS.[Show abstract] [Hide abstract]
ABSTRACT: In the present review a large amount of experimental and clinical studies on ALS are discussed in an effort to dissect common pathogenic mechanisms which may provide novel information and potential therapeutic strategies for motor neuron degeneration.Protein clearing systems play a critical role in motor neuron survival during excitotoxic stress, aging and neurodegenerative disorders. Among various mechanisms which clear proteins from the cell recent studies indicate autophagy as the most prominent pathway to promote survival of motor neurons.Autophagy regulates the clearance of damaged mitochondria, endoplasmic reticulum and misfolded proteins in eukaryotic cells. Upon recruitment of the autophagy pathway, an autophagosome is produced and directed towards lysosomal degradation.Here we provide evidence that in both genetic and sporadic amyotrophic lateral sclerosis (ALS, the most common motor neuron disorder) a defect in the autophagy machinery is common. In fact, swollen, disrupted mitochondria and intracellular protein aggregates accumulate within affected motor neurons. These structures localize within double membrane vacuoles, autophagosomes, which typically cluster in perinuclear position. In keeping with this, when using autophagy inhibitors or suppressing autophagy promoting genes, motor symptoms and motor neuron death are accelerated. Conversely stimulation of autophagy alleviates motor neuron degeneration.Therefore, autophagy represents an important target when developing novel treatments in ALS.Archives italiennes de biologie 03/2011; 149(1):121-49. · 1.42 Impact Factor
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ABSTRACT: Abstract Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease of unknown cause, characterized by the selective and progressive death of both upper and lower motoneurons, leading to a progressive paralysis. Experimental animal models of the disease may provide knowledge of the pathophysiological mechanisms and allow the design and testing of therapeutic strategies, provided that they mimic as close as possible the symptoms and temporal progression of the human disease. The principal hypotheses proposed to explain the mechanisms of motoneuron degeneration have been studied mostly in models in vitro, such as primary cultures of fetal motoneurons, organotypic cultures of spinal cord sections from postnatal rodents and the motoneuron-like hybridoma cell line NSC-34. However, these models are flawed in the sense that they do not allow a direct correlation between motoneuron death and its physical consequences like paralysis. In vivo, the most widely used model is the transgenic mouse that bears a human mutant superoxide dismutase 1, the only known cause of ALS. The major disadvantage of this model is that it represents about 2%–3% of human ALS. In addition, there is a growing concern on the accuracy of these transgenic models and the extrapolations of the findings made in these animals to the clinics. Models of spontaneous motoneuron disease, like the wobbler and pmn mice, have been used aiming to understand the basic cellular mechanisms of motoneuron diseases, but these abnormalities are probably different from those occurring in ALS. Therefore, the design and testing of in vivo models of sporadic ALS, which accounts for >90% of the disease, is necessary. The main models of this type are based on the excitotoxic death of spinal motoneurons and might be useful even when there is no definitive demonstration that excitotoxicity is a cause of human ALS. Despite their difficulties, these models offer the best possibility to establish valid correlations between cellular alterations and motor behavior, although improvements are still necessary in order to produce a reliable and integrative model that accurately reproduces the cellular mechanisms of motoneuron degeneration in ALS.Molecular Neurodegeneration 01/2009; · 5.29 Impact Factor