Neurobiology of Disease最新文献

Huntington's disease (HD) is caused by the expansion of a CAG repeat, encoding a string of glutamines (polyQ) in the first exon of the huntingtin gene (HTTex1). This mutant huntingtin protein (mHTT) with extended polyQ forms aggregates in cortical and striatal neurons, causing cell damage and death. The retina is part of the central nervous system (CNS), and visual deficits and structural abnormalities in the retina of HD patients have been observed. Defects in retinal structure and function are also present in the R6/2 and R6/1 HD transgenic mouse models that contain a gene fragment to express mHTTex1. We investigated whether these defects extend to the zQ175KI mouse model which is thought to be more representative of the human condition because it was engineered to contain the extended CAG repeat within the endogenous HTT locus. We found qualitatively similar phenotypes between R6/1 and zQ175KI retinae that include the presence of mHTT aggregates in retinal neurons, cone loss, downregulation of rod signaling proteins and abnormally elongated photoreceptor connecting cilia. In addition, we present novel findings that mHTT disrupts cell polarity in the photoreceptor cell layer and the retinal pigment epithelium (RPE). Furthermore, we show that the RPE cells from R6/1 mice contain mHTT nuclear inclusions, adding to the list of non-neuronal cells with mHTT aggregates and pathology. Thus, the eye may serve as a useful system to track disease progression and to test therapeutic intervention strategies for HD.

Background: Developmental and epileptic encephalopathies (DEE) are rare but severe neurodevelopmental disorders characterised by early-onset seizures often combined with developmental delay, behavioural and cognitive deficits. Treatment for DEEs is currently limited to seizure control and provides no benefits to the patients' developmental and cognitive outcomes. Genetic variants are the most common cause of DEE with KCNQ2 being one of the most frequently identified disease-causing genes. KCNQ2 encodes a voltage-gated potassium channel K_V7.2 widely expressed in the central nervous system and critically involved in the regulation of neuronal excitability. In this study, we aimed to characterise a KCNQ2 variant (K556E) found in a female patient with DEE using a heterologous expression system and a knock-in mouse model.

Methods: Wild-type KCNQ2 or K556E variant were expressed in Chinese Hamster Ovary (CHO) cells (with or without KCNQ3) and their biophysical properties assessed using patch clamp recordings. We further engineered a new Kcnq2 DEE mouse model (K557E) based on the K556E variant and characterised it using behavioural, electrophysiological, and transcriptome analysis.

Results: A mild loss of function was observed only when the mutant channel was co-expressed with KCNQ3 in the heterologous system. The heterozygous knock-in mice showed a reduced survival rate and increased susceptibility to induced seizures. Electrophysiology recordings in brain slices revealed a hyperexcitable phenotype for cortical layer 2/3 pyramidal neurons with retigabine (K_V7 channel opener) able to rescue both the increased sensitivity to chemically-induced seizures in vivo and neuronal excitability ex vivo. Whole-brain RNA sequencing revealed numerous differentially expressed genes and biological pathways pointing at dysregulation of early developmental processes.

Conclusions: Our study reports on a novel Kcnq2 DEE mouse model recapitulating aspects of the disease phenotype with the electrophysiological and transcriptome analysis providing insights into KCNQ2 DEE mechanisms that can be leveraged for future therapy development.

The accumulation of amyloid β-proteins (Aβ) in the extracellular space, forming insoluble plaques, is a primary pathological process underlying Alzheimer's disease (AD). Among the various Aβ species that appear during Aβ aggregation, Aβ oligomers are considered the most neurotoxic form. However, the precise mechanisms of their molecular functions within the Aβ aggregation cascade have not been clarified so far. This research aimed to uncover the structural and functional characteristics of globular-shaped Aβ oligomers (gAβO) under in vitro conditions. We performed thioflavin T (ThT) assays on low-molecular-weight (LMW) Aβ42, testing different concentrations of Aβ42 mature fibril (MF) seeds and gAβO. Fibril formation was continuously observed using high-speed atomic force microscopy (HS-AFM) in LMW Aβ42 with different sample conditions. Conformational changes of Aβ42 aggregates in the presence of gAβO was also evaluated using circular dichroism spectroscopy. The results of the ThT analysis and HS-AFM observation indicated that gAβO promoted fibril formation of LMW Aβ42 while gAβO itself did not form fibrous aggregates, indicating that gAβO would have a catalytic effects on LMW Aβ42 aggregation. We also showed that the molecular interaction of gAβO was altered by the presence and amount of MF seeds in the reaction buffers, indicating that complex interactions would exist among different Aβ species. The results of our present research demonstrated that gAβO would have significant roles to accelerate Aβ aggregation in AD pathogenesis. 225 < 250 words.

Kinesin-3 KIF1A (UNC-104 in C. elegans) is the major axonal transporter of synaptic vesicles and mutations in this molecular motor are linked to KIF1A-associated neurological disorders (KAND), encompassing Charcot-Marie-Tooth disease, amyotrophic lateral sclerosis and hereditary spastic paraplegia. UNC-104 binds to lipid bilayers of synaptic vesicles via its C-terminal PH (pleckstrin homology) domain. Since this interaction is relatively weak and non-specific, we hypothesize that other, more specific, interaction schemes exist. From the literature, it is evident that UNC-104 regulator SYD-2 interacts with UNC-10 and that UNC-10 itself interacts with RAB-3 bound to synaptic vesicles. RT-PCR and Western blot experiments expose genetic relationships between unc-10 and syd-2, but not between unc-10 and rab-3. Also, neither unc-10 nor rab-3 affects UNC-104 expression. However, co-immunoprecipitation and bimolecular fluorescence complementation (BiFC) assays reveal functional interactions between UNC-104, SYD-2, UNC-10 and RAB-3. Though both SNB-1 and RAB-3 are actively transported by UNC-104, motility of RAB-3 is facilitated in the presence of SYD-2 and UNC-10. Deletion of UNC-104's PH domain did not affect UNC-104/RAB-3 colocalization, but significantly affected UNC-104/SNB-1 colocalization. Similarly, motility of RAB-3-labeled vesicles is only slightly altered in nematodes carrying a point mutation in the PH domain, whereas movement of SNB-1 is significantly reduced in this mutant. Western blots from purified fractions of synaptic vesicles reveal strong reduction of UNC-104 in rab-3/unc-10 double mutants. Our findings suggest that the UNC-10/SYD-2 complex acts as a functional linker to connect UNC-104 to RAB-3-containing vesicles. Thus, this linker complex contributes to the specificity of motor/cargo interactions.

The observation that the risk of developing Alzheimer's disease is reduced in individuals with high premorbid cognitive functioning, higher educational attainment, and occupational status has led to the 'cognitive reserve' hypothesis. This hypothesis suggests that individuals with greater cognitive reserve can tolerate a more significant burden of neuropathological changes before the onset of cognitive decline. The underpinnings of cognitive reserve remain poorly understood, although a shared genetic basis between measures of cognitive reserve and Alzheimer's disease has been suggested. Using the largest samples to date and novel statistical tools, we aimed to investigate shared genetic variants between Alzheimer's disease, and measures of cognitive reserve; cognition and educational attainment to identify molecular and neurobiological foundations. We applied the causal mixture model (MiXeR) to estimate the number of trait-influencing variants shared between Alzheimer's disease, cognition, and educational attainment, and condFDR/conjFDR to identify shared loci. To provide biological insights loci were functionally characterized. Subsequently, we constructed a Structural Equation Model (SEM) to determine if the polygenic foundation of cognition has a direct impact on Alzheimer's disease risk, or if its effect is mediated through established risk factors for the disease, using a case-control sample from the UK Biobank. Univariate MiXeR analysis (after excluding chromosome 19) revealed that Alzheimer's disease was substantially less polygenic (450 trait-influencing variants) compared to cognition (11,100 trait-influencing variants), and educational attainment (12,700 trait-influencing variants). Bivariate MiXeR analysis estimated that Alzheimer's disease shared approximately 70 % of trait-influencing variants with cognition, and approximately 40 % with educational attainment, with mixed effect directions. Using condFDR analysis, we identified 18 loci jointly associated with Alzheimer's disease and cognition and 6 loci jointly associated with Alzheimer's disease and educational attainment. Genes mapped to shared loci were associated with neurodevelopment, expressed in early life, and implicated the dendritic tree and phosphatidylinositol phosphate binding mechanisms. Spatiotemporal gene expression analysis of the identified genes showed that mapped genes were highly expressed during the mid-fetal period, further suggesting early neurodevelopmental stages as critical periods for establishing cognitive reserve which affect the risk of Alzheimer's disease in old age. Furthermore, our SEM analysis showed that genetic variants influencing cognition had a direct effect on the risk of developing Alzheimer's disease, providing evidence in support of the neurodevelopmental hypothesis of the disease.