One of the many interesting questions about Alzheimer's disease is why the relationship with being overweight or obese is tenuous in comparison to, say, type 2 diabetes. Why are there so many dramatically overweight people who do not develop Alzheimer's disease? As researchers here note, one can clearly point to Alzheimer's-adjacent mechanisms that obesity makes worse. Inflammatory dysfunction of the innate immune cells of the brain known as microglia has attracted a lot of attention in recent years, thought to contribute to all forms of neurodegeneration. Here, researchers look at one mechanism by which excess visceral fat tissue can harm microglia, giving rise to behaviors observed in the brains of Alzheimer's patients and animal models.
Increasing evidence suggests that metabolic disorders such as obesity are implicated in the development of Alzheimer's disease (AD). The pathological buildup of lipids in microglia is regarded as a key indicator in brain aging and the progression of AD, yet the mechanisms behind this process remain uncertain. The adipokine ANGPTL4 is strongly associated with obesity and is thought to play a role in the advancement of neurodegenerative diseases. This study utilized RNA sequencing to identify differential expression in lipid-accumulating BV2 microglia and investigated the potential mechanism through ANGPTL4 overexpression in BV2. Subsequently, animal models and clinical data were employed to further explore alterations in circulating ANGPTL4 levels in AD.
RNA sequencing results indicated a correlation between ANGPTL4 and microglial lipid accumulation. The overexpression of ANGPTL4 in microglia resulted in increased secretion of inflammatory factors, elevated oxidative stress levels, and diminished antiviral capacity. Furthermore, when simulating the coexistence of AD and obesity through combined treatment with Amyloid-Beta 1-42 peptide (Aβ) and Free Fatty Acids (FFA) in vitro, we observed a notable upregulation of ANGPTL4 expression, highlighting its potential role in the interplay between AD and obesity.
In vivo experiments, we also observed a significant increase in ANGPTL4 expression in the hippocampus and plasma of APP/PS1 mice compared to wild-type controls. This was accompanied by heightened microglial activation and reduced expression of longevity-related genes in the hippocampus. Clinical data from the UK Biobank indicated that plasma ANGPTL4 levels are elevated in patients with AD when compared to healthy controls. Moreover, significantly higher ANGPTL4 levels were observed in obese AD patients relative to their non-obese counterparts. Our findings suggest that ANGPTL4-mediated microglial aging may serve as a crucial link between AD and obesity, proposing ANGPTL4 as a potential biomarker for AD.
Link: https://doi.org/10.1016/j.nbd.2024.106741
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