Deletion of Small GTPase H-Ras Rescues Memory Deficits and Reduces Amyloid Plaque-Associated Dendritic Spine Loss in Transgenic Alzheimer's Mice

Xenografted human iPSC-derived neurons with the familial Alzheimer's disease APPV717I mutation reveal dysregulated transcriptome signatures linked to synaptic function and implicate LINGO2 as a disease signaling mediator

Alzheimer's disease (AD) is the most common cause of dementia, and disease mechanisms are still not fully understood. Here, we explored pathological changes in human induced pluripotent stem cell (iPSC)-derived neurons carrying the familial AD APPV717I mutation after cell injection into the mouse forebrain. APPV717I mutant iPSCs and isogenic controls were differentiated into neurons revealing enhanced Aβ42 production, elevated phospho-tau, and impaired neurite outgrowth in APPV717I neurons. Two months after transplantation, APPV717I and control neural cells showed robust engraftment but at 12 months post-injection, APPV717I grafts were smaller and demonstrated impaired neurite outgrowth compared to controls, while plaque and tangle pathology were not seen. Single-nucleus RNA-sequencing of micro-dissected grafts, performed 2 months after cell injection, identified significantly altered transcriptome signatures in APPV717I iPSC-derived neurons pointing towards dysregulated synaptic function and axon guidance. Interestingly, APPV717I neurons showed an increased expression of genes, many of which are also upregulated in postmortem neurons of AD patients including the transmembrane protein LINGO2. Downregulation of LINGO2 in cultured APPV717I neurons rescued neurite outgrowth deficits and reversed key AD-associated transcriptional changes related but not limited to synaptic function, apoptosis and cellular senescence. These results provide important insights into transcriptional dysregulation in xenografted APPV717I neurons linked to synaptic function, and they indicate that LINGO2 may represent a potential therapeutic target in AD.

Loss of TREM2 exacerbates parenchymal amyloid pathology but diminishes CAA in Tg-SwDI mice

Alzheimer's disease (AD) is a progressive neurodegenerative disease, and it is the most common cause of dementia worldwide. Recent genome-wide association studies (GWAS) identified TREM2 (triggering receptor expressed on myeloid cells 2) as one of the major risk factors for AD. TREM2 is a surface receptor expressed on microglia and largely mediates microglial functions and immune homeostasis in the brain. The functions of TREM2 in AD pathogenesis, including in the formation of the key pathology parenchymal amyloid-β (Aβ) plaques, have been investigated by introducing Trem2 deficiency in AD mouse models. However, the role of TREM2 in cerebrovascular amyloidosis, in particular cerebral amyloid angiopathy (CAA) remains unexplored. CAA features Aβ deposition along the cerebral vessels, signifying an intersection between AD and vascular dysfunction. Using a well-characterized CAA-prone, transgenic mouse model of AD, Tg-SwDI (SwDI), we found that loss of TREM2 led to a marked increase in overall Aβ load in the brain, but a dramatic decrease in CAA in microvessel-rich regions, along with reduced microglial association with CAA. Transcriptomic analysis revealed that in the absence of Trem2 , microglia were activated but trapped in transition to the fully reactive state. Like microglia, perivascular macrophages were activated with upregulation of cell junction related pathways in Trem2 -deficient SwDI mice. In addition, vascular mural cells and astrocytes exhibited distinct responses to Trem2 deficiency, contributing to the pathological changes in the brain of Trem2 -null SwDI mice. Our study provides the first evidence that TREM2 differentially modulates parenchymal and vascular Aβ pathologies, which may have significant implications for both TREM2- and Aβ-targeting therapies for AD.

Impact of age and sex on neuroinflammation following SARS-CoV-2 infection in a murine model

Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), the etiological agent for the worldwide COVID-19 pandemic, is known to infect people of all ages and both sexes. Senior populations have the greatest risk of severe disease, and sexual dimorphism in clinical outcomes has been reported in COVID-19. SARS-CoV-2 infection in humans can cause damage to multiple organ systems, including the brain. Neurological symptoms are widely observed in patients with COVID-19, with many survivors suffering from persistent neurological and cognitive impairment, potentially accelerating Alzheimer's disease. The present study aims to investigate the impact of age and sex on the neuroinflammatory response to SARS-CoV-2 infection using a mouse model. Wild-type C57BL/6 mice were inoculated, by intranasal route, with SARS-CoV-2 lineage B.1.351 variant known to infect mice. Older animals and in particular males exhibited a significantly greater weight loss starting at 4 dpi. In addition, male animals exhibited higher viral RNA loads and higher titers of infectious virus in the lung, which was particularly evident in males at 16 months of age. Notably, no viral RNA was detected in the brains of infected mice, regardless of age or sex. Nevertheless, expression of IL-6, TNF-α, and CCL-2 in the lung and brain was increased with viral infection. An unbiased brain RNA-seq/transcriptomic analysis showed that SARS-CoV-2 infection caused significant changes in gene expression profiles in the brain, with innate immunity, defense response to virus, cerebravascular and neuronal functions, as the major molecular networks affected. The data presented in this study show that SARS-CoV-2 infection triggers a neuroinflammatory response despite the lack of detectable virus in the brain. Age and sex have a modifying effect on this pathogenic process. Aberrant activation of innate immune response, disruption of blood-brain barrier and endothelial cell integrity, and supression of neuronal activity and axonogenesis underlie the impact of SARS-CoV-2 infection on the brain. Understanding the role of these affected pathways in SARS-CoV-2 pathogenesis helps identify appropriate points of therapeutic interventions to alleviate neurological dysfunction observed during COVID-19.

Evidence of Clinical Efficacy and Pharmacological Mechanisms of Resveratrol in the Treatment of Alzheimer's Disease

BACKGROUND

To evaluate the efficacy and pharmacological mechanisms of resveratrol in Alzheimer's disease (AD) patients.

METHODS

We conducted a thorough exploration of existing randomized controlled trials concerning the treatment of Alzheimer's disease patients using resveratrol, utilizing accessible open databases. Quantitative variables were represented as a standardized mean difference (SMD), accompanied by a 95% confidence interval (CI). Additionally, we examined the potential targets and plausible pathways associated with the impact of resveratrol on Alzheimer's disease using network pharmacology techniques.

RESULTS

Our meta-analysis comprised five trials involving 271 AD patients, of whom 139 received resveratrol treatment and 132 received placebo treatment. Compared with placebo therapy, resveratrol treatment resulted in a significant improvement in Alzheimer's Disease Cooperative Study- Activities of Daily Living (ADAS-ADL) scores (SMD=0.51; 95% CI, 0.24 to 0.78) and cerebrospinal fluid (CSF) Aβ40 (SMD=0.84; 95% CI, 0.21 to 1.47) and plasma Aβ40 levels (SMD=0.43; 95% CI, 0.07 to 0.79). However, the improvement in the resveratrol-treated group compared with the placebo treatment group on the Mini-Mental State Examination (MMSE) score, CSF Aβ42 and plasma Aβ42 levels, and brain volume was not significant. There were no noteworthy statistical variances in the occurrence of adverse effects noted between the two groups. The outcomes of network pharmacology divulged that the principal enriched interaction pathway between resveratrol and Alzheimer's disease is primarily concentrated within the PI3K signaling pathways. Resveratrol's potential key targets for the treatment of AD include MAKP1, HRAS, EGFR, and MAPK2K1.

CONCLUSION

While having a high safety profile, resveratrol has efficacy in AD patients to a certain extent, and more data are required to validate the efficacy of resveratrol for the treatment of AD in the future. Suppression of the PI3K signaling pathways could hold significant importance in the treatment of AD patients using resveratrol.