The role of proteasome dysfunction in the mechanisms of motor neuron degeneration in a mouse model of familial amyotrophic lateral sclerosis

Cheroni, Cristina (2008). The role of proteasome dysfunction in the mechanisms of motor neuron degeneration in a mouse model of familial amyotrophic lateral sclerosis. PhD thesis The Open University.

DOI: https://doi.org/10.21954/ou.ro.0000ea29

Abstract

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease characterized by the loss of the motor neurons. One consistent neuropathological feature of ALS patients and models of the disease is the formation of proteinaceous inclusion bodies; for this reason, alterations in the proteolytic ubiquitin-proteasome pathway (UPP) have been suggested to be implicated.

The purpose of this thesis was to analyze the role of the UPP in ALS pathogenesis studying the G93A mouse model. The activity of UPP was evaluated in G93A mice carrying the Ub^G76V-GFP reporter protein for proteasomal functionality. Furthermore, the expression of different constitutive proteasome and immunoproteasome subunits was measured during disease progression.

In symptomatic G93A lumbar spinal cord, a mild increase of Ub^G76V-GFP protein, but not of its transcript, was found in the motor neuronal population and was partly associated with high levels of ubiquitin and perikarial presence of phosphorylated neurofilaments. At the end stage, the increase of the reporter protein was prevalent in other neurons besides motor neurons, but also the mRNA levels were augmented.

Constitutive catalytic subunits of the 20S proteasome were reduced in end stage G93A lumbar spinal cord, while an increase of their inducible counterparts and a decrease of the non-catalytic as subunit were evident at the symptomatic phase. Components of 19S and 11S complexes were significantly reduced prior to symptom onset. The changes in proteasome composition were accompanied by a substantial increase of glial markers and TNFα.

Altogether, these data suggest that a subtle dysfunction of the ubiquitin-proteasome pathway occurs in the spinal cord of a mouse model of ALS in a phase in which the first signs of motor impairment are detectable. This pairs with alterations in the transcriptional rate of various proteasome subunits, resulting in a decrease of constitutive proteasome and an increase of immunoproteasome.