Phase transition and lysosomal degradation of expanded CAG repeat RNA suppress global protein synthesis.

Phase transitions (PT) of biomolecules are heavily involved in neurodegenerative disorders. Almost all previous studies were focusing on the PT of misfolded proteins whereas RNA molecules containing expanded repeats such as the CAG repeats are also able to undergo PT in vitro, a process called RNA gelation. Meanwhile, the expanded CAG repeat (eCAGr) RNA forms condensates that are largely observed only in the nuclei and exhibit liquid-like properties without obvious gelation. Thus, whether eCAGr RNA gelation occurs in cells and what function it is involved in remained elusive. We recently discovered that eCAGr RNA forms solid-like RNA gels in the cytoplasm, but they are rapidly cleared by the lysosomes via an autophagy-independent but LAMP2C-depdent pathway, making their presence in the cytoplasm difficult to be observed. We further revealed that these RNA gels sequester EEF2 in the cells and thus suppress global protein synthesis. In vivo expression of eCAGr RNA alone without detectable protein expression in the mouse model led to neurodegeneration-relevant electrophysiological and behavioral phenotypes, demonstrating its possible pathogenic roles.

Gelation of cytoplasmic expanded CAG RNA repeats suppresses global protein synthesis.

RNA molecules with the expanded CAG repeat (eCAGr) may undergo sol-gel phase transitions, but the functional impact of RNA gelation is completely unknown. Here, we demonstrate that the eCAGr RNA may form cytoplasmic gel-like foci that are rapidly degraded by lysosomes. These RNA foci may significantly reduce the global protein synthesis rate, possibly by sequestering the translation elongation factor eEF2. Disrupting the eCAGr RNA gelation restored the global protein synthesis rate, whereas enhanced gelation exacerbated this phenotype. eEF2 puncta were significantly enhanced in brain slices from a knock-in mouse model and from patients with Huntington's disease, which is a CAG expansion disorder expressing eCAGr RNA. Finally, neuronal expression of the eCAGr RNA by adeno-associated virus injection caused significant behavioral deficits in mice. Our study demonstrates the existence of RNA gelation inside the cells and reveals its functional impact, providing insights into repeat expansion diseases and functional impacts of RNA phase transition.

Characterization of the extra copy of TPOX locus with tri-allelic pattern.

BACKGROUND: An STR locus with tri-allelic pattern is occasionally observed in routine forensic casework. The extra copy of TPOX locus with tri-allelic pattern in populations has been assumed to be inserted into an X chromosome, which took place forth before the Bantu expansion in Africa. Nonetheless, the exact location of the duplication and the form of rearrangement in the human genome has not been clarified yet. RESULTS: In this study, we investigated the extra copy of type 2 tri-allelic pattern at TPOX in various populations. While allele 10 is the major third allele in Africa, allele 11 appears more frequent in America and overwhelming in Chinese and Korean populations, which might attribute to the population substructures. Results from the investigation of family cases showed that the transmission of the extra allele had a similar genetic pattern of autosomal genes. Furthermore, a whole-genome sequencing followed by bioinformatics analysis revealed that the intact form of chromosomal duplication and rearrangement occurred ~ 407 kb away from the authentic TPOX locus on chromosome 2 in two cases. The breakpoints of the insertion were further validated in most other tri-allelic subjects, which can imply the identical origin from the ancestral extra copy. Nevertheless, de novo chromosomal duplication and rearrangement at thyroid peroxidase gene occur in populations. CONCLUSIONS: Instead of the extra allele 10 in African populations, the main third allele at TPOX with tri-allelic pattern is allele 11 in Chinese and Korean populations. The insertion of the extra copy into chromosome 2 occurs in most subjects with tri-allelic pattern at TPOX and demonstrates the transmission of the third allele from parents to offspring. The breakpoints of the ancestral extra copy are defined, which shows evidence of its inheritance from African populations. In addition, the simple validation method would help improve tri-allelic pattern calling, distinguish de novo chromosomal rearrangements, and also count the frequencies among different geographic regions. Therefore, the statistical interpretation of tri-allelic pattern at TPOX could be enhanced during forensic practice.

Targeting Gpr52 lowers mutant HTT levels and rescues Huntington's disease-associated phenotypes.

See Huang and Gitler (doi:10.1093/brain/awy112) for a scientific commentary on this article.Lowering the levels of disease-causing proteins is an attractive treatment strategy for neurodegenerative disorders, among which Huntington's disease is an appealing disease for testing this strategy because of its monogenetic nature. Huntington's disease is mainly caused by cytotoxicity of the mutant HTT protein with an expanded polyglutamine repeat tract. Lowering the soluble mutant HTT may reduce its downstream toxicity and provide potential treatment for Huntington's disease. This is hard to achieve by small-molecule compound drugs because of a lack of effective targets. Here we demonstrate Gpr52, an orphan G protein-coupled receptor, as a potential Huntington's disease drug target. Knocking-out Gpr52 significantly reduces mutant HTT levels in the striatum and rescues Huntington's disease-associated behavioural phenotypes in a knock-in Huntington's disease mouse model expressing endogenous mutant Htt. Importantly, a novel Gpr52 antagonist E7 reduces mutant HTT levels and rescues Huntington's disease-associated phenotypes in cellular and mouse models. Our study provides an entry point for Huntington's disease drug discovery by targeting Gpr52.

Suppression of MAPK11 or HIPK3 reduces mutant Huntingtin levels in Huntington's disease models.

Most neurodegenerative disorders are associated with accumulation of disease-relevant proteins. Among them, Huntington disease (HD) is of particular interest because of its monogenetic nature. HD is mainly caused by cytotoxicity of the defective protein encoded by the mutant Huntingtin gene (HTT). Thus, lowering mutant HTT protein (mHTT) levels would be a promising treatment strategy for HD. Here we report two kinases HIPK3 and MAPK11 as positive modulators of mHTT levels both in cells and in vivo. Both kinases regulate mHTT via their kinase activities, suggesting that inhibiting these kinases may have therapeutic values. Interestingly, their effects on HTT levels are mHTT-dependent, providing a feedback mechanism in which mHTT enhances its own level thus contributing to mHTT accumulation and disease progression. Importantly, knockout of MAPK11 significantly rescues disease-relevant behavioral phenotypes in a knockin HD mouse model. Collectively, our data reveal new therapeutic entry points for HD and target-discovery approaches for similar diseases.

Conformation-dependent recognition of mutant HTT (huntingtin) proteins by selective autophagy.

Protein misfolding is the common theme for neurodegenerative disorders including Huntington disease (HD), which is mainly caused by cytotoxicity of the mutant HTT (huntingtin) protein (mHTT). The soluble mHTT has an expanded polyglutamine (polyQ) stretch that may adopt multiple conformations, among which the one recognized by the polyQ antibody 3B5H10 is the most toxic due to unknown mechanisms. In a recent study, we showed that the 3B5H10-recognized mHTT species has a slower degradation rate due to its resistance to selective macroautophagy/autophagy. In HD mouse brain tissues as well as HD patient fibroblasts and post-mortem brain tissues, the 3B5H10-recognized mHTT species lacks Lys63-polyubiquitination and SQSTM1/p62 interaction, which are essential for cargo recognition by selective autophagy. Collectively, we discovered that the mHTT protein is subject to conformation-dependent recognition by selective autophagy, which is more selective than what we perceived: the process can be selective among different conformations of the same protein, leading to conformation-dependent differences in protein degradation and toxicity.

A toxic mutant huntingtin species is resistant to selective autophagy.

Protein misfolding is a common theme in neurodegenerative disorders including Huntington's disease (HD). The HD-causing mutant huntingtin protein (mHTT) has an expanded polyglutamine (polyQ) stretch that may adopt multiple conformations, and the most toxic of these is the one recognized by antibody 3B5H10. Here we show that the 3B5H10-recognized mHTT species has a slower degradation rate due to its resistance to selective autophagy in human cells and brains, revealing mechanisms of its higher toxicity.

Characterization of phenolic compounds from Rhododendron alutaceum.

A new phenolic glycoside, 3'-keto rhododendrin and a new sesquilignan, alutaceuol, together with twelve known phenolic compounds, were isolated from the leaves of Rhododendron alutaceum. Their structures were elucidated by extensive spectroscopic data analysis and comparison with literature values. In addition, the detailed analysis of 2D NMR data led us to conclude that the chemical shifts of dihydrobuddlenol B need to be revised.

[Studies on the chemical constituents from Rhododendron delavayi].

OBJECTIVE: To study the chemical constituents of the leaves from Rhododendron delavayi. METHODS: The compounds were isolated and purified using column chromatography with silical gel and Sephadex LH-20, and their structures wer identified by their physical and spectral data. RESULTS: Eight compounds were isolated and elucidated as 3',4',7-trihydroxy-3,5-dimethoxyflavone (1), 3',4',5,7-tetrahydroxy-3-methoxyflavone(2), quercetin-3-O-beta-D-arabinopyranoxide(3), catechin(4), epicatechin (5), epicatechin-(2beta-->O-->7,4beta-->8)-ent-epicatechin(6), (2S)-4-(3,4-dihydroxyphenyl) -2-butanol(7), (3,4-dihydroxyphenyl)-2-ethanol(8). CONCLUSION: Compounds 2,3,6,7,8 are isolated from this plant for the first time.