Nucleolin reorganization and nucleolar stress in Purkinje cells of mutant PCD mice

Abstract

The Purkinje cell (PC) degeneration (pcd) mouse harbors a mutation in Agtpbp1 gene that encodes for the cytosolic carboxypeptidase, CCP1. The mutation causes degeneration and death of PCs during the postnatal life, resulting in clinical and pathological manifestation of cerebellar ataxia. Monogenic biallelic damaging variants in the Agtpbp1 gene cause infantile-onset neurodegeneration and cerebellar atrophy, linking loss of functional CCP1 with human neurodegeneration. Although CCP1 plays a key role in the regulation of tubulin stabilization, its loss of function in PCs leads to a severe nuclear phenotype with heterochromatinization and accumulation of DNA damage. Therefore, the pcd mice provides a useful neuronal model to investigate nuclear mechanisms involved in neurodegeneration, particularly the nucleolar stress. In this study, we demonstrated that the Agtpbp1 gene mutation induces a p53-dependent nucleolar stress response in PCs, which is characterized by nucleolar fragmentation, nucleoplasmic and cytoplasmic mislocalization of nucleolin, and dysfunction of both pre-rRNA processing and mRNA translation. RT-qPCR analysis revealed reduction of mature 18S rRNA, with a parallel increase of its intermediate 18S-5'-ETS precursor, that correlates with a reduced expression of Fbl mRNA, which encodes an essential factor for rRNA processing. Moreover, nucleolar alterations were accompanied by a reduction of PTEN mRNA and protein levels, which appears to be related to the chromosome instability and accumulation of DNA damage in degenerating PCs. Our results highlight the essential contribution of nucleolar stress to PC degeneration and also underscore the nucleoplasmic mislocalization of nucleolin as a potential indicator of neurodegenerative processes.

Nna1 gene deficiency triggers Purkinje neuron death by tubulin hyperglutamylation and ER dysfunction

“…First, our studies in vivo and in vitro confirm that deficiency of deglutamylase Nna1 may result in PN apoptosis via free tubulin accumulation-induced abnormal ER stress and UPR ( Figure 6B). Second, another potentially relevant factor recently suggested (56) proposes that a nucleolar stress response may participate in PN degeneration in pcd mice.…”

The Childhood-Onset Neurodegeneration with Cerebellar Atrophy (CONDCA) Disease Caused by AGTPBP1 Gene Mutations: The Purkinje Cell Degeneration Mouse as an Animal Model for the Study of this Human Disease

“…Between two and four weeks of age, PCs rapidly degenerate, with only a few PCs remaining in lobule X of the cerebellar vermis, which is preserved for a few additional weeks (Figure 4A,B) [10,17,19,47]. The degeneration of a massive number of PCs in pcd mice sequentially involves an initial "preneurodegenerative" stage, from postnatal day (P) 15 to P20, during which both cytoplasmic and nuclear alterations occur [17,25,48,49], followed by a degenerative stage (P25- 45), in which all cerebellar PCs degenerate (Figure 4C,D) [17,48], leading to an alteration in cerebellar-related motor performance. Interestingly, heterozygous pcd mice show a significant reduction in the number of PCs at P300, an observation that supports the idea that heterozygosity of the AGTPBP1 mutation may influence the ageing process, causing moderate PC degeneration [50].…”

“…However, little is known about its potential role in the neuronal nucleus. We performed an extensive analysis of the effects of AGTPBP1-deficiency in the PC’s nuclear compartments involved in RNA transcription and processing and DNA damage repair, evaluating the impact of their dysfunction on neuronal homeostasis and survival [ 17 , 48 , 49 ]. During the pre-degenerative stage, in PCs, there is a progressive large-scale reorganisation of chromatin into large, transcriptionally silent, heterochromatin domains associated with the accumulation of DNA damage, which is one of the first signs of the PC pre-neurodegenerative stage of in pcd mice [ 17 ].…”

“…In addition to DNA damage and epigenetic changes in chromatin conformation, other nuclear compartments are affected in the mutant PCs. In particular, the disassembly of the Cajal bodies [ 61 ] and nucleolar disruption are directly correlated with the activation of nucleolar stress and defective ribosome biogenesis [ 48 , 49 ]. Nucleolar stress has been associated with several neurodegenerative human disorders, including Alzheimer’s and Parkinson’s diseases, ALS and spinal muscular atrophy, among others [ 62 , 63 , 64 , 65 , 66 , 67 , 68 ].…”

“…Copyright 2011 Brain Pathology. ( E – G ) Adapted with permission from [ 49 ]. Copyright 2019 Neurobiology of Disease.…”