Neuron type‐specific increase in lamin B1 contributes to nuclear dysfunction in Huntington’s disease

Abstract

Lamins are crucial proteins for nuclear functionality. Here, we provide new evidence showing that increased lamin B1 levels contribute to the pathophysiology of Huntington’s disease (HD), a CAG repeat‐associated neurodegenerative disorder. Through fluorescence‐activated nuclear suspension imaging, we show that nucleus from striatal medium‐sized spiny and CA1 hippocampal neurons display increased lamin B1 levels, in correlation with altered nuclear morphology and nucleocytoplasmic transport disruption. Moreover, ChIP‐sequencing analysis shows an alteration of lamin‐associated chromatin domains in hippocampal nuclei, accompanied by changes in chromatin accessibility and transcriptional dysregulation. Supporting lamin B1 alterations as a causal role in mutant huntingtin‐mediated neurodegeneration, pharmacological normalization of lamin B1 levels in the hippocampus of the R6/1 mouse model of HD by betulinic acid administration restored nuclear homeostasis and prevented motor and cognitive dysfunction. Collectively, our work points increased lamin B1 levels as a new pathogenic mechanism in HD and provides a novel target for its intervention.

Mislocalization of Nucleocytoplasmic Transport Proteins in Human Huntington’s Disease PSC-Derived Striatal Neurons

“…Aberrant nuclear architecture has been reported in several neurodegenerative disease models and our analysis of human neurones derived from different HD lines further supports the view that this is also a feature of HD (Edens et al, 2013;Frost et al, 2016;Gasset-Rosa et al, 2017;Alcalá-Vida et al, 2021). Lamin-B1 is a nuclear envelope protein that is highly expressed in neurons and provides structural support to the nucleus (Stuurman et al, 1998;Takamori et al, 2018).…”

“…Reduced RANGAP1 expression was observed in HD mice at late disease stages (Grima et al, 2017), whereas we found reduced RAN and RANGAP1 protein levels in our "young" PSC-derived neurones, suggesting that nuclear pore protein reduction may be an earlier phenotype than previously indicated through its links with aggregation. Interestingly increased lamin-B1 protein expression has been described in an HD mouse model, and further overexpression of lamin-B1 resulted in morphological changes in neurons (Alcalá-Vida et al, 2021). We did not observe increased lamin-B1 expression, possibly due to lower polyQ lengths of our neurons compared to the mouse model.…”

“…Next, we wanted to investigate whether high content imaging would provide a suitable platform to detect aberrations in the localization of proteins associated with nucleocytoplasmic transport. We focused on RAN, RANGAP1 and lamin-B1, which have previously been shown to mislocalize in several HD models (Gasset-Rosa et al, 2017;Grima et al, 2017;Veldman and Yang, 2017;Alcalá-Vida et al, 2021).…”

“…In both HD mouse and human post-mortem brain tissue, several NUPs and RANGAP1 have been shown to co-localize with mHTT, and mHTT has been shown to exhibit preferential binding to RANGAP1 (Hosp et al, 2015). Defects in NPCs and nucleocytoplasmic transport proteins have been described in human HD and disease models (Gasset-Rosa et al, 2017;Grima et al, 2017;Alcalá-Vida et al, 2021). These included a shift of RAN-GTP, RANGAP1 and the nucleoporins NUP62 and NUP88 from the nucleus to cytoplasm.…”

Isoform-Specific Reduction of the Basic Helix-Loop-Helix Transcription Factor TCF4 Levels in Huntington’s Disease

“…Considering (1) the functions of TCF4 in neurogenesis ( Schoof et al, 2020 ; Wang et al, 2020 ) and neural plasticity ( Kennedy et al, 2016 ; Thaxton et al, 2018 ; Badowska et al, 2020 ); (2) high expression of TCF4 in hippocampal neuroepithelium and its persistence in all mature hippocampal neuron subpopulations and astrocytes and similar high expression in cortical structures ( Jung et al, 2018 ; Kim et al, 2020 ); and (3) downregulation of TCF4 we show here in R6/1 mouse and HD patient hippocampus and cerebral cortex, allows to hypothesize that TCF4 might play a role in the impairment of cognitive functions in HD. In R6/1 mice, the motor and cognitive symptoms generally appear at 12–20 weeks of age ( Naver et al, 2003 ; Bolivar et al, 2004 ; Giralt et al, 2013 ), and treatment with papaverin (inhibitor of PDE10a) or betulinic acid improve these symptoms ( Giralt et al, 2013 ; Alcalá‐Vida et al, 2021 ). Importantly, both of these compounds affect PKA and cAMP levels, which are known to increase TCF4 transcriptional activity ( Sepp et al, 2017 ).…”