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Unravelling the enigma of selective vulnerability in neurodegeneration: motor neurons resistant to degeneration in ALS show distinct gene expression characteristics and decreased susceptibility to excitotoxicity.

ABSTRACT: A consistent clinical feature of amyotrophic lateral sclerosis (ALS) is the sparing of eye movements and the function of external sphincters, with corresponding preservation of motor neurons in the brainstem oculomotor nuclei, and of Onuf's nucleus in the sacral spinal cord. Studying the differences in properties of neurons that are vulnerable and resistant to the disease process in ALS may provide insights into the mechanisms of neuronal degeneration, and identify targets for therapeutic manipulation. We used microarray analysis to determine the differences in gene expression between oculomotor and spinal motor neurons, isolated by laser capture microdissection from the midbrain and spinal cord of neurologically normal human controls. We compared these to transcriptional profiles of oculomotor nuclei and spinal cord from rat and mouse, obtained from the GEO omnibus database. We show that oculomotor neurons have a distinct transcriptional profile, with significant differential expression of 1,757 named genes (q < 0.001). Differentially expressed genes are enriched for the functional categories of synaptic transmission, ubiquitin-dependent proteolysis, mitochondrial function, transcriptional regulation, immune system functions, and the extracellular matrix. Marked differences are seen, across the three species, in genes with a function in synaptic transmission, including several glutamate and GABA receptor subunits. Using patch clamp recording in acute spinal and brainstem slices, we show that resistant oculomotor neurons show a reduced AMPA-mediated inward calcium current, and a higher GABA-mediated chloride current, than vulnerable spinal motor neurons. The findings suggest that reduced susceptibility to excitotoxicity, mediated in part through enhanced GABAergic transmission, is an important determinant of the relative resistance of oculomotor neurons to degeneration in ALS.

SUBMITTER: Brockington A

PROVIDER: S-EPMC3535376 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:ALS is a uniformly fatal neurodegenerative disease in which motor neurons in the spinal cord and brain stem are selectively lost. Individual motor - groups of motor neurons innervating single muscles - show widely varying degrees of disease resistance: in the final stages of ALS, nearly all voluntary movement is lost but eye movement and eliminative and sexual functions remain relatively unimpaired. These functions are controlled by motor neurons of the oculomotor (III), trochlear (IV) and abducens (VI) nuclei in the midbrain and brainstem, and by Onuf's nucleus in the lumbosacral spinal cord, respectively. Correspondingly, in ALS autopsies the oculomotor and Onuf's nuclei are almost completely preserved. We used microarray profiling of isolated wildtype mouse motor neurons to identify genes whose expression was characteristic of both oculomotor and Onuf's nuclei but not of vulnerable lumbar spinal neurons, or vice versa. Three wild-type C57BL/6J P7 male animals were perfused with 30% sucrose, lumbosacral spinal cord and midbrain regions were rapidly recovered, embedded in OCT compound, and frozen in liquid nitrogen. 12 um-thick cryosections were mounted on RNAse-free, PEN-foil covered glass slides (Zeiss), fixed for 2 min in 100% EtOH, rinsed in 50% EtOH, stained with 1% cresyl violet for 2 min, rinsed with 50% EtOH, dehydrated in graded solutions of ethanol and air dried prior to LCM using PALM Microbeam system (Zeiss). From each animal, ~200 DL, L5, and oculomotor motor neurons were collected directly in lysis buffer. RNA was purified using Absolutely RNA, NanoPrep kit (Stratagene, La Jolla, CA). RNA integrity was assessed on the Bioanalyzer 2100 (Agilent Technologies, Santa Clara, CA). At least 1.5 ng of purified RNA was the starting material used in the WT-Ovation Pico RNA Amplification System (Nugen, San Carlos,CA) with the FL-Ovation cDNA Biotin Module V2 (Nugen) to generate labeled probe. 10 ug of biotinylated cRNA from three independent samples for each motor neuron group isolated by LCM was hybridized to on Affymetrix (Santa Clara, CA) Mouse Genome 430 2.0 Arrays. Gene ontology and pathway analysis was performed using DAVID Bioinformatics Resources 6.7 (National Institute of Allergy and Infectious Diseases, NIH, Bethesda, MD).

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Unravelling the enigma of selective vulnerability in neurodegeneration: motor neurons resistant to degeneration in ALS show distinct gene expression characteristics and decreased susceptibility to excitotoxicity.

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