Detecting soluble polyQ oligomers and investigating their impact on living cells using split-GFP

Neurodegenerative diseases and neuroinflammation-induced apoptosis

Neuroinflammation represents a critical pathway in the brain for the clearance of foreign bodies and the maintenance of homeostasis. When the neuroinflammatory process is dysregulate, such as the over-activation of microglia, which results in the excessive accumulation of free oxygen and inflammatory factors in the brain, among other factors, it can lead to an imbalance in homeostasis and the development of various diseases. Recent research has indicated that the development of numerous neurodegenerative diseases is closely associated with neuroinflammation. The pathogenesis of neuroinflammation in the brain is intricate, involving alterations in numerous genes and proteins, as well as the activation and inhibition of signaling pathways. Furthermore, excessive inflammation can result in neuronal cell apoptosis, which can further exacerbate the extent of the disease. This article presents a summary of recent studies on the relationship between neuronal apoptosis caused by excessive neuroinflammation and neurodegenerative diseases. The aim is to identify the link between the two and to provide new ideas and targets for exploring the pathogenesis, as well as the prevention and treatment of neurodegenerative diseases.

Disruption of the nascent polypeptide-associated complex leads to reduced polyglutamine aggregation and toxicity

The nascent polypeptide-associate complex (NAC) is a heterodimeric chaperone complex that binds near the ribosome exit tunnel and is the first point of chaperone contact for newly synthesized proteins. Deletion of the NAC induces embryonic lethality in many multi-cellular organisms. Previous work has shown that the deletion of the NAC rescues cells from prion-induced cytotoxicity. This counterintuitive result led us to hypothesize that NAC disruption would improve viability in cells expressing human misfolding proteins. Here, we show that NAC disruption improves viability in cells expressing expanded polyglutamine and also leads to delayed and reduced aggregation of expanded polyglutamine and changes in polyglutamine aggregate morphology. Moreover, we show that NAC disruption leads to changes in de novo yeast prion induction. These results indicate that the NAC plays a critical role in aggregate organization as a potential therapeutic target in neurodegenerative disorders.

The Molecular Basis of Spinocerebellar Ataxia Type 7

Spinocerebellar ataxia (SCA) type 7 (SCA7) is caused by a CAG trinucleotide repeat expansion in the ataxin 7 (ATXN7) gene, which results in polyglutamine expansion at the amino terminus of the ATXN7 protein. Although ATXN7 is expressed widely, the best characterized symptoms of SCA7 are remarkably tissue specific, including blindness and degeneration of the brain and spinal cord. While it is well established that ATXN7 functions as a subunit of the Spt Ada Gcn5 acetyltransferase (SAGA) chromatin modifying complex, the mechanisms underlying SCA7 remain elusive. Here, we review the symptoms of SCA7 and examine functions of ATXN7 that may provide further insights into its pathogenesis. We also examine phenotypes associated with polyglutamine expanded ATXN7 that are not considered symptoms of SCA7.

Huntington's Disease: Mechanisms of Pathogenesis and Therapeutic Strategies

Huntington's disease is a late-onset neurodegenerative disease caused by a CAG trinucleotide repeat in the gene encoding the huntingtin protein. Despite its well-defined genetic origin, the molecular and cellular mechanisms underlying the disease are unclear and complex. Here, we review some of the currently known functions of the wild-type huntingtin protein and discuss the deleterious effects that arise from the expansion of the CAG repeats, which are translated into an abnormally long polyglutamine tract. Finally, we outline some of the therapeutic strategies that are currently being pursued to slow down the disease.

Introducing inducible fluorescent split cholesterol oxidase to mammalian cells

Cholesterol oxidase (COase) is a bacterial enzyme catalyzing the first step in the biodegradation of cholesterol. COase is an important biotechnological tool for clinical diagnostics and production of steroid drugs and insecticides. It is also used for tracking intracellular cholesterol; however, its utility is limited by the lack of an efficient temporal control of its activity. To overcome this we have developed a regulatable fragment complementation system for COase cloned from Chromobacterium sp. The enzyme was split into two moieties that were fused to FKBP (FK506-binding protein) and FRB (rapamycin-binding domain) pair and split GFP fragments. The addition of rapamycin reconstituted a fluorescent enzyme, termed split GFP-COase, the fluorescence level of which correlated with its oxidation activity. A rapid decrease of cellular cholesterol induced by intracellular expression of the split GFP-COase promoted the dissociation of a cholesterol biosensor D4H from the plasma membrane. The process was reversible as upon rapamycin removal, the split GFP-COase fluorescence was lost, and cellular cholesterol levels returned to normal. These data demonstrate that the split GFP-COase provides a novel tool to manipulate cholesterol in mammalian cells.