The small GTPase Arf6 is dysregulated in a mouse model for fragile X syndrome

Delayed recruitment of activity-dependent bulk endocytosis in Fmr1 knockout neurons

The presynapse performs an essential role in brain communication via the activity-dependent release of neurotransmitters. However, the sequence of events through which a presynapse acquires functionality is relatively poorly understood, which is surprising, since mutations in genes essential for its operation are heavily implicated in neurodevelopmental disorders. We addressed this gap in knowledge by determining the developmental trajectory of synaptic vesicle (SV) recycling pathways in primary cultures of rat hippocampal neurons. Exploiting a series of optical and morphological assays, we revealed that the majority of nerve terminals displayed activity-dependent calcium influx from 3 days in vitro (DIV), immediately followed by functional evoked exocytosis and endocytosis, although the number of responsive nerve terminals continued to increase until the second week in vitro. However, the most intriguing discovery was that activity-dependent bulk endocytosis (ADBE) was only observed from DIV 14 onwards. Importantly, optimal ADBE recruitment was delayed until DIV 21 in Fmr1 knockout neurons, which model Fragile X Syndrome (FXS). This implicates the delayed recruitment of ADBE as a potential contributing factor in the development of circuit dysfunction in FXS, and potentially other neurodevelopmental disorders.

Arf6 GTPase deficiency leads to porcine oocyte quality decline during aging

Arf6 is a member of ADP-ribosylation factor (Arf) family, which is widely implicated in the regulation of multiple physiological processes including endocytic recycling, cytoskeletal organization, and membrane trafficking during mitosis. In this study, we investigated the potential relationship between Arf6 and aging-related oocyte quality, and its roles on organelle rearrangement and cytoskeleton dynamics in porcine oocytes. Arf6 expressed in porcine oocytes throughout meiotic maturation, and it decreased in aged oocytes. Disruption of Arf6 led to the failure of cumulus expansion and polar body extrusion. Further analysis indicated that Arf6 modulated ac-tubulin for meiotic spindle organization and microtubule stability. Besides, Arf6 regulated cofilin phosphorylation and fascin for actin assembly, which further affected spindle migration, indicating the roles of Arf6 on cytoskeleton dynamics. Moreover, the lack of Arf6 activity caused the dysfunction of Golgi and ER for protein synthesis and signal transduction. Mitochondrial dysfunction was also observed in Arf6-deficient porcine oocytes, which was supported by the increased ROS level and abnormal membrane potential. In conclusion, our results reported that insufficient Arf6 was related to aging-induced oocyte quality decline through spindle organization, actin assembly, and organelle rearrangement in porcine oocytes.

α-Synuclein-dependent increases in PIP5K1γ drive inositol signaling to promote neurotoxicity

Anomalous aggregation of α-synuclein (α-Syn) is a pathological hallmark of many degenerative synucleinopathies including Lewy body dementia (LBD) and Parkinson's disease (PD). Despite its strong link to disease, the precise molecular mechanisms that link α-Syn aggregation to neurodegeneration have yet to be elucidated. Here, we find that elevated α-Syn leads to an increase in the plasma membrane (PM) phosphoinositide PI(4,5)P2, which precipitates α-Syn aggregation and drives toxic increases in mitochondrial Ca2+ and reactive oxygen species leading to neuronal death. Upstream of this toxic signaling pathway is PIP5K1γ, whose abundance and localization is enhanced at the PM by α-Syn-dependent increases in ARF6. Selective inhibition of PIP5K1γ or knockout of ARF6 in neurons rescues α-Syn aggregation and cellular phenotypes of toxicity. Collectively, our data suggest that modulation of phosphoinositide metabolism may be a therapeutic target to slow neurodegeneration for PD and other related neurodegenerative disorders.

Molecular Insights into IQSEC2 Disease

Recent insights into IQSEC2 disease are summarized in this review as follows: (1) Exome sequencing of IQSEC2 patient DNA has led to the identification of numerous missense mutations that delineate at least six and possibly seven essential functional domains present in the IQSEC2 gene. (2) Experiments using IQSEC2 transgenic and knockout (KO) mouse models have recapitulated the presence of autistic-like behavior and epileptic seizures in affected animals; however, seizure severity and etiology appear to vary considerably between models. (3) Studies in IQSEC2 KO mice reveal that IQSEC2 is involved in inhibitory as well as stimulatory neurotransmission. The overall picture appears to be that mutated or absent IQSEC2 arrests neuronal development, resulting in immature neuronal networks. Subsequent maturation is aberrant, leading to increased inhibition and reduced neuronal transmission. (4) The levels of Arf6-GTP remain constitutively high in IQSEC2 knockout mice despite the absence of IQSEC2 protein, indicating impaired regulation of the Arf6 guanine nucleotide exchange cycle. (5) A new therapy that has been shown to reduce the seizure burden for the IQSEC2 A350V mutation is heat treatment. Induction of the heat shock response may be responsible for this therapeutic effect.

IQSEC2-related encephalopathy in male children: Novel mutations and phenotypes

The isoleucine–glutamine (IQ) motif and Sec7 domain-containing protein 2 (IQSEC2) gene, located at Xp11. 2, are associated with nervous system diseases, such as epilepsy, autism, and intellectual disabilities. Gender-related differences in the severity of phenotype severity have been described previously. Here, we report the details of seven male children with IQSEC2 mutations from different families. During this investigation, we explored the relationship between the genotype and phenotype of IQSEC2 mutations; to do so, we recruited seven children with pathogenic/likely pathogenic IQSEC2 mutations who were diagnosed with global developmental delay and/or epilepsy. Their clinical features were assessed, and Trio-based whole-exome sequencing (trio WES) was conducted in seven pedigrees. A variety of algorithms and computational tools were used to calculate the pathogenicity, protein stability, conservation, side chain properties, and protein-protein interactions of mutated proteins. The seven patients ranged in age from 18 months to 5 years. Among them, six children were found to have both developmental delay and epilepsy, and one child only exhibited developmental delay. Four novel mutations (c.316C > T, c.443_4 44dup, c.3235T > C, and c.1417G > T) were newly reported. Two patients did not have truncated aberrant proteins caused by missense mutations. Still, they did have severe phenotypes, such as early-onset epilepsy in infancy, because the mutations were located in domains like the pleckstrin homology and IQ calmodulin-binding motif domains. The bioinformatics analysis also proved that missense mutations may be located in the functional region, which affects protein stability and is harmful. In summary, severe phenotypes, such as early-onset epilepsy in infancy, occur in male patients with a missense mutation in specific domains (e.g., pleckstrin homology and IQ calmodulin-binding motif domains). Some female individuals with IQSEC2 mutations may be asymptomatic because of the skewed inactivation of the X chromosome.

Decoding competitive endogenous RNA regulatory network in postoperative cognitive dysfunction

Postoperative cognitive dysfunction (POCD) is a common postoperative neurological complication in elderly patients. Circular RNAs (circRNAs) are abundant in the mammalian brain and can probably regulate cognitive function. However, the competitive endogenous RNA (ceRNA) regulatory network in POCD remains illiterate. Transcriptomic signatures in the hippocampus of POCD mice derived from the Gene Expression Omnibus (GEO) dataset GSE190880, GSE95070, and GSE115440 were used to identify the circRNA, miRNA, and mRNA expression profiles of POCD mice compared with controls, respectively. A set of differentially expressed RNAs, including 119 circRNAs, 33 miRNAs, and 49 mRNAs were identified. Transcript validation showed the enhanced expression of circ_0001634, circ_0001345, and circ_0001493. A ceRNA regulatory network composed of three circRNAs, three miRNAs, and six mRNAs was established. The hub mRNAs in the ceRNA network were further found to be involved in the hormone catabolic process and regulation of canonical Wnt signaling pathway, revealing their crucial role in POCD. Finally, three miRNAs and four mRNAs were verified by qRT-PCR. These results based on bioinformatics and PCR array suggest that circ_0001634/miR-490-5p/Rbm47, circ_0001634/miR-490-5p/Sostdc1, circ_0001634/miR-7001-5p/Sostdc1, circ_0001345/miR-7001-5p/Sostdc1, and circ_0001493/miR-7001-5p/Sostdc1 may be novel diagnostic biomarkers and therapeutic targets for POCD.