SIL1 improves cognitive impairment in APP23/PS45 mice by regulating amyloid precursor protein processing and Aß generation.

SIL1, an endoplasmic reticulum (ER)-resident protein, is reported to play a protective role in Alzheimer's disease (AD). However, the effect of SIL1 on amyloid precursor protein (APP) processing remains unclear. In this study, the role of SIL1 in APP processing was explored both in vitro and in vivo. In the in vitro experiment, SIL1 was either overexpressed or knocked down in cells stably expressing the human Swedish mutant APP695. In the in vivo experiment, AAV-SIL1-EGFP or AAV-EGFP was microinjected into APP23/PS45 mice and their wild-type littermates. Western blotting (WB), immunohistochemistry, RNA sequencing (RNA-seq), and behavioral experiments were performed to evaluate the relevant parameters. Results indicated that SIL1 expression decreased in APP23/PS45 mice. Overexpression of SIL1 significantly decreased the protein levels of APP, presenilin-1 (PS1), and C-terminal fragments (CTFs) of APP in vivo and in vitro. Conversely, knockdown of SIL1 increased the protein levels of APP, ß-site APP cleavage enzyme 1 (BACE1), PS1, and CTFs, as well as APP mRNA expression in 2EB2 cells. Furthermore, SIL1 overexpression reduced the number of senile plaques in APP23/PS45 mice. Importantly, Y-maze and Morris Water maze tests demonstrated that SIL1 overexpression improved cognitive impairment in APP23/PS45 mice. These findings indicate that SIL1 improves cognitive impairment in APP23/PS45 mice by inhibiting APP amyloidogenic processing and suggest that SIL1 is a potential therapeutic target for AD by modulating APP processing.

ICA1 affects APP processing through the PICK1-PKCα signaling pathway.

AIMS: Islet cell autoantigen 1 (ICA1) is involved in autoimmune diseases and may affect synaptic plasticity as a neurotransmitter. Databases related to Alzheimer's disease (AD) have shown decreased ICA1 expression in patients with AD. However, the role of ICA1 in AD remains unclear. Here, we report that ICA1 expression is decreased in the brains of patients with AD and an AD mouse model. RESULTS: The ICA1 increased the expression of amyloid precursor protein (APP), disintegrin and metalloprotease 10 (ADAM10), and disintegrin and metalloprotease 17 (ADAM17), but did not affect protein half-life or mRNA levels. Transcriptome sequencing analysis showed that ICA1 regulates the G protein-coupled receptor signaling pathway. The overexpression of ICA1 increased PKCα protein levels and phosphorylation. CONCLUSION: Our results demonstrated that ICA1 shifts APP processing to non-amyloid pathways by regulating the PICK1-PKCα signaling pathway. Thus, this study suggests that ICA1 is a novel target for the treatment of AD.

Astrocyte-Ablation of Mtnr1b Increases Anxiety-Like Behavior in Adult Male Mice.

BACKGROUND: Astrocytes are essential for synaptic transmission, and their dysfunction can result in neuropsychiatric disorders such as anxiety and depression. Many studies have shown that global knockout of Melatonin receptor 2 (Mtnr1b) is associated with the development of various mental disorders. AIM: This study aimed to investigate the effects of astrocyte ablation of Mtnr1b on cognitive function and anxiety-like behavior in mice, as well as the potential biological mechanisms. METHODS: A conditional Cre-loxP system allowing deletion of Mtnr1b from astrocytes was developed to investigate the specific role Mtnr1b. Control and Mtnr1b cKO𝐺𝑓𝑎𝑝 mice were selected for cognitive function behavioral testing (Morris water maze test, novel object recognition test) and emotion-related behavioral testing (open field, elevated plus maze). After testing, brain tissue was collected and examined by immunofluorescence for the expression of neuronal nuclei (NeuN), glutamate decarboxylase 67 (GAD67), and vesicular glutamate transporter 1 (vGluT1). RNA-seq was performed on hippocampal tissue from control and Mtnr1b cKO𝐺𝑓𝑎𝑝 mice to identify differentially expressed genes. Additional confirmation of differential gene expression was performed using real-time quantitative polymerase chain reaction (qRT-PCR). RESULTS: Mtnr1b cKO𝐺𝑓𝑎𝑝 mice were not significantly different from control mice in the Morris water maze and novel object recognition tests. Results from the open field and elevated plus maze tests showed that Mtnr1b cKO𝐺𝑓𝑎𝑝 mice exhibited significantly more anxiety-like behavior than did controls. Immunofluorescence revealed that the number of mature neurons did not differ significantly between Mtnr1b cKO𝐺𝑓𝑎𝑝 mice and controls. The expression of GAD67 in the hippocampal CA1 and CA3 areas of Mtnr1b cKO𝐺𝑓𝑎𝑝 mice was significantly lower than in the control group, but no significant difference was detected for vGluT1 expression. RNA-seq and qRT-PCR results showed that Mtnr1b knockout in astrocytes led to a decrease in the levels of gamma-aminobutyric acid sub-type A (GABAA) receptors and Kir2.2. CONCLUSIONS: The astrocyte-specific knockout in Mtnr1b cKO𝐺𝑓𝑎𝑝 mice results in anxiety-like behavior, which is caused by down-regulation of gamma-aminobutyric acid-ergic (GABAergic) synaptic function.