PNAS Jianwen Deng/Wang Chaoxia/Yun Yuan team revealed the mechanism of mitochondrial injury in inclusion somatic disease in the neuronal nucleus and potential therapeutic targets

Oligonucleotide repeat amplification has been linked
to more than 50 neuromuscular and neurological degenerative diseases.
The pathogenesis of these diseases is closely related
to the nucleotide repeating unit, the number of repeat amplifications, the composition of the repeating sequence, the gene located and the location of the gene.
Neuronal intranuclear inclusion disease (NIID) is a disease
characterized by the presence of eosinophilic inclusion bodies in the nucleus of the center, peripheral nerves, muscles, and other multi-organ tissues.
The disease was first reported in 1968, and it was not until 2019 that it was discovered that the causative variant of the disease was CGG repeated amplification [1-4]
of the NOTCH2NLC gene.
With the popularity of genetic diagnosis, the number of confirmed cases of NIID has gradually increased, and the heterogeneity of its clinical manifestations has also been reported by many times
.
In addition to the classic NIID in which episodic/progressive encephalopathy, peripheral neuropathy, and autonomic neuropathy are the main manifestations, a small number of NIID patients may present with idiopathic tremor, Alzheimer's disease, Parkinson's syndrome, "frostbite", and distal opharyngeal myopathy [5].

。 In recent years, two independent research teams have confirmed that CGG repeat amplification of the NOTCH2NLC gene produces polyglycine (polyG) toxic protein uN2CpolyG through upstream open reading frame (uORF) translation, which is involved in the pathogenic process of NIID [6-7].

At present, however, the pathogenesis of uN2CpolyG, a translation product of the NOTCH2NLC gene (CGG)_n, is unclear
.

On October 3, 2022, the team of Deng Jianwen/Wang Chaoxia/Yuan Yun, Department of Neurology, Peking University First Hospital, published a model entitled CGG repeat expansion in NOTCH2NLC causes mitochondrial dysfunction and progressive neurodegeneration in Drosophila at PNAS The research paper, the first to construct a NIID transgenic Drosophila model, elucidated the molecular mechanisms by which uN2CpolyG toxic proteins mediate mitochondrial dysfunction and neurodegeneration, and provides a potential therapeutic target for the disease
.


Drosophila melanogaster is a classic model animal, many important molecules in the history of life sciences were first discovered and functioned in fruit flies, and this animal is also one of the most commonly used animal models for the study of genetic diseases of
the nervous system.
To simulate the characteristics of NIID multisystem involvement, the team used the UAS/GAL4 system to construct a transgenic Drosophila model
in which specific tissues or systemic multi-tissue organs expressed uN2CpolyG protein.
It was found that Drosophila models expressing uN2CpolyG protein could replicate the main pathological features of NIID—inclusion body formation in the nucleus of neurons, progressive neuronal cell loss.
as well as disease phenotypes
such as movement disorders and shortened lifespan.
At the same time, the research group found that the mitochondrial volume increase was observed under electron microscopy in both transgenic Drosophila model and the muscle samples of NIID patients, and the uN2CpolyG protein could be located in the mitochondrial extracorporeal membrane and membrane gap in
the NIID patient muscle tissue, brain tissue and NIID cell model.
Binding to pre-mass spectrometry identification results and co-immunoprecipitation experiments showed that uN2CpolyG interacted with the mitochondrial RNA-binding protein LRPPRC, which may lead to LRPPRC aggregation and loss of function in the inclusion body, resulting in mitochondrial dysfunction
.
To verify the above speculations, the study overexpressed Bsf (the homologous gene of human LRPPRC) in uN2CpolyG transgenic fruit flies, and the results showed that it could significantly improve neuronal cell loss, suggesting that there is a functional deletion
of LRPPRC in NIID.
Further, RNA-seq and functional tests both showed the presence of mitochondrial oxidative phosphorylation dysfunction in transgenic Drosophila models and NIID patient samples, mainly manifested by the downregulation
of mitochondrial complex I-encoding gene expression.
The mitochondrial respiration ability of Drosophila models expressing uN2CpolyG toxic protein was significantly reduced compared with that of Drosophila in the control group, and the respiratory function of mitochondrial complex I was particularly significantly
altered.
In addition, the study found that mitochondrial ATP synthesis levels in uN2CpolyG Drosophila models were significantly reduced
compared to the control group.
These results suggest that mitochondrial complex I may be involved in the key pathogenic processes
of NIID.

Based on the above studies, mitochondria have been found to be one of the targets of uN2CpolyG toxic proteins, while idebenone (IDB) activates mitochondrial respiratory activity and promotes increased
ATP production.
The study further administered IDB treatment
to NIID transgenic Drosophila models and cell models.
IDB was found to alleviate mitochondrial oxidative phosphorylation disorders and improve neurodegenerative phenotypes
in NIID transgenic Drosophila models.

In summary, this study constructs a NIID (uN2CpolyG) transgenic Drosophila model to discover the molecular mechanisms by which uN2CpolyG toxic proteins mediate mitochondrial dysfunction and neurodegeneration, and provide potential therapeutic cues
for the disease.


Professor Wang Zhaoxia and Professor Deng Jianwen of the Department of Neurology, Peking University First Hospital are co-corresponding authors
of this paper.
Yu Jiaxi, a doctoral student at Peking University First Hospital, is the first author of
this paper.

Original link:

https://doi.
org/10.
1073/pnas.
2208649119

Plate Maker: Eleven

References

1.
H.
Ishiura et al.
, Noncoding CGG repeat expansions in neuronal intranuclear inclusion disease, oculopharyngodistal myopathy and an overlapping disease.
 Nat Genet 51, 1222-1232 (2019).
2.
Y.
Tian et al.
, Expansion of Human-Specific GGC Repeat in Neuronal Intranuclear Inclusion Disease-Related Disorders.
 Am J Hum Genet 105, 166-176 (2019).
3.
J.
Sone et al.
, Long-read sequencing identifies GGC repeat expansions in NOTCH2NLC associated with neuronal intranuclear inclusion disease.
 Nat Genet 51, 1215-1221 (2019).
4.
J.
Deng et al.
, Long-read sequencing identified repeat expansions in the 5'UTR of the NOTCH2NLC gene from Chinese patients with neuronal intranuclear inclusion disease.
 J Med Genet 56, 758-764 (2019).
5.
T.
Liufu et al.
, The polyG diseases: a new disease entity.
 Acta Neuropathol Commun 10, 79.
(2022).
6.
M.
Boivin et al.
, Translation of GGC repeat expansions into a toxic polyglycine protein in NIID defines a novel class of human genetic disorders: The polyG diseases.
 Neuron 109, 1825-1835 e1825 (2021).
7.
S.
Zhong et al.
, Upstream open reading frame with NOTCH2NLC GGC expansion generates polyglycine aggregates and disrupts nucleocytoplasmic transport: implications for polyglycine diseases.
 Acta Neuropathol 142, 1003-1023 (2021).
‍

Reprint Notice

【Non-original article】The copyright of this article belongs to the author of the article, welcome individuals to forward and share, without the author's permission is prohibited from reprinting, the author has all legal rights, violators will be prosecuted
.