Expression of expanded GGC repeats within NOTCH2NLC causes behavioral deficits and neurodegeneration in a mouse model of neuronal intranuclear inclusion disease

Abstract

GGC repeat expansions within NOTCH2NLC have been identified as the genetic cause of neuronal intranuclear inclusion disease (NIID). To understand the molecular pathogenesis of NIID, here, we established both a transgenic mouse model and a human neural progenitor cells (hNPCs) model. Expression of the NOTCH2NLC with expanded GGC repeats produced widespread intranuclear and perinuclear polyglycine (polyG), polyalanine (polyA), and polyarginine (polyR) inclusions, leading to behavioral deficits and severe neurodegeneration, which faithfully mimicked the clinical and pathological features associated with NIID. Furthermore, conserved alternative splicing events were identified between the NIID mouse and hNPC models, among which was the enrichment of the binding motifs of hnRNPM, an RNA binding protein known as alternative splicing regulator. Expanded NOTCH2NLC-polyG and NOTCH2NLC-polyA could interact with and sequester hnRNPM, while overexpression of hnRNPM could ameliorate the cellular toxicity. These results together suggested that dysfunction of hnRNPM could play an important role in the molecular pathogenesis of NIID.

GGC expansions in NOTCH2NLC contribute to Parkinson disease and dopaminergic neuron degeneration

“…In addition, eight PD patients and one healthy control were identified with intermediate-length NOTCH2NLC GGC repeat expansions (41-60 repeats), but the association between the intermediate-length NOTCH2NLC GGC repeat expansions and PD is not well established in our study. It had been reported that intermediate-length GGC repeat expansions in NOTCH2NLC may be associated with PD in two different studies, but such intermediate repeat Furthermore, widespread of NOTCH2NLC-polyG inclusions may cause neuronal death from proteotoxic stress, abnormalities in mitochondrial dysfunction, ubiquitin-proteasomal and autophagosomal-lysosomal systems, and neuroinflammation [17,[22][23][24][25]29].…”

“…Dementia-dominant and essential tremor-dominant phenotypes usually have a purer GGC repeat. There are also other possible mechanisms, including the toxicity of polyG-containing protein, the toxicity of repeat RNA, and the methylation status of NOTCH2NLC [17,22].…”

“…With the progress in genetic identification that has been made, molecular pathogenesis of NOTCH2NLC GGC repeat expansions is attracting considerable attention [22][23][24][25]. However, the pathology of PD patients with the NOTCH2NLC GGC repeat expansions is still poorly understood, and the role of NOTCH2NLC with expanded GGC repeats in substantia nigra (SN) dopaminergic neurons remains unclear [12,17].…”

“…Given that neurons are terminally differentiated cells that do divide, aging-related factors, includinggreater vulnerability and reduced protein homeostasis, make the neurons more susceptible to damage than glia cells. According to current reports, the potential mechanism of NOTCH2NLC-polyGmediated toxicity in our mouse model may be due to DNA repair alterations or nucleocytoplasmic transport disruption, which was explored in cell and mouse models of NIID, another neurodegenerative disorder caused by the same mutation in NOTCH2NLC[22][23][24][25]. In addition, like other misfolded proteins, accumulated NOTCH2NLC-polyG protein aggregates may recruit, through protein-protein interactions, other proteins such as RNA-binding proteins and transcription factors, thereby sequestering them from their functional locations and affecting their activities.…”

Native functions of short tandem repeats

“…Most of these new CGG repeatopathies reside within the 5’ UTRs, like the CGG repeat in FMR1 , and there is already evidence of convergent disease mechanisms triggered by these new repeats with those already established in Fragile X disorders. In one particularly notable example, a CGG repeat expansion in NOTCH2NLC leads to the creation of an AUG-initiated upstream open reading frame in the 5’ UTR that is generates a polyglycine-containing protein akin to FMRpolyG in FMR1 ( Liu et al, 2022 ; Boivin et al, 2021 ). This polyglycine protein is found within inclusions in patients with NIID and its generation is required to trigger inclusion formation and behavioral phenotypes in a mouse model of NOTCH2NLC associated NIID.…”