Research on Saturated Fatty Acids and Brain Function

Background Introduction

Obesity and metabolic syndrome are major global health challenges today. Numerous studies have shown that excessive consumption of diets rich in saturated fats leads to obesity, accompanied by a series of metabolic complications such as insulin resistance and diabetes. However, obesity not only affects physical health but may also have significant impacts on brain function. Animal model studies have indicated that diet-induced obesity (DIO) can cause metabolic changes in the hippocampus, synaptic dysfunction, and impairments in learning and memory processes [1-3]. Surprisingly, short-term intake of high-fat, high-sugar diets in humans (only four days) is sufficient to significantly impair hippocampal-dependent learning and memory.

Obesity is often accompanied by a state of low-grade inflammation, and in the brain, neuroinflammation triggered by DIO is particularly notable. This inflammatory process involves the activation of microglia, known as microgliosis. Although literature on neuroinflammation induced by DIO is controversial, some studies report no significant cytokine overexpression in certain brain regions such as the hippocampus and cortex [5-9]. Thus, the specific mechanisms by which microglia are involved in DIO remain uncertain. This paper uses the BV2 cell model to study the response characteristics of microglia exposed to palmitate (a saturated fatty acid rich in high-fat diets and the brains of obese individuals).

Research Source

This research was jointly written by scientists Gabriela C. de Paula, Blanca I. Aldana, Roberta Battistella, Rosalía Fernández-Calle, Andreas Bjure, Iben Lundgaard, Tomas Deierborg, and João M. N. Duarte. The authors are primarily from the Department of Experimental Medical Science and the Wallenberg Centre for Molecular Medicine at Lund University, Sweden, and the Department of Drug Design and Pharmacology at the Faculty of Health and Medical Sciences, University of Copenhagen, Denmark. The paper was published in 2024 in the Journal of Neuroinflammation.

Research Process

Research Subjects and Experimental Methods

1. Cell Culture and Treatment

• BV2 microglial cells (from ATCC, Manassas, VA-USA, #CRL-2469) were cultured in Dulbecco’s modified Eagle medium (DMEM) containing 5 mmol/L glucose, 1 mmol/L pyruvate, and 4 mmol/L glutamine, supplemented with 10% fetal bovine serum (FBS) and 100 U/ml penicillin/streptomycin (P/S).

1. Cell Proliferation and Viability Testing

• Cell proliferation was determined by cell counting at six-hour intervals.
• Cell viability and apoptosis were assessed using the CyQuant MTT Cell Viability Assay Kit and the Caspase-Glo ³⁄₇ Activity Assay Kit.

1. Oxygen Consumption Rate (OCR) and Extracellular Acidification Rate (ECAR)

• OCR and ECAR were measured using the Seahorse XF96 Analyzer to assess cellular metabolic activity.

1. Quantitative Real-Time Polymerase Chain Reaction (qPCR)

• Total RNA from cells was extracted and cDNA was synthesized using a reverse transcription kit for qPCR analysis (specific genes such as TNF-α, IL-6, and IL-1β).

1. Proteomics Analysis

• Extracellular vesicles (EVs) secreted from treated BV2 cells were collected, and their proteomes were analyzed using mass spectrometry (MS).

1. Animal Experiments

• EVs secreted from BV2 cells treated with palmitate and control cells were injected into the lateral ventricles of mice to observe their effects on mouse behavior, cognition, and glucose tolerance.

Main Results

1. Palmitate Induces Microglial Proliferation but Does Not Increase Cytokine Expression

• After 24 hours of exposure to 200 µmol/L palmitate, BV2 cells showed an increased rate of proliferation, with no significant increase in cytokine expression levels such as TNF-α or IL-1β.

1. Reorganization of Metabolic Pathways

• Palmitate treatment significantly increased glycolytic activity in BV2 cells while decreasing mitochondrial respiratory capacity related to oxidative phosphorylation, indicating a reorganization of energy metabolism.

1. Changes in EVs Proteome

• Mass spectrometry analysis revealed that EVs secreted by BV2 cells treated with palmitate had distinctive proteome characteristics, including reduced content of ribosomal proteins and proteins related to protein metabolism.

1. Impact of EVs on Mouse Brain Function and Behavior

• Injection of EVs into the lateral ventricles of mice showed that mice receiving EVs treated with palmitate exhibited impaired memory (such as in the novel object recognition test) and depressive-like behavior (such as in the sucrose splash test), as well as reduced glucose tolerance.

Conclusions and Significance

This study demonstrates that BV2 cells exposed to palmitate transmit signals of metabolic reorganization through the secretion of specific EVs, which may lead to brain dysfunction. Although no significant overexpression of cytokines was observed, the changes in the proteome carried by EVs may play a key role in neuroinflammation and brain dysfunction. These findings provide new perspectives on brain dysfunction in the context of obesity and suggest that EVs could be new targets for intervention in obesity-related brain dysfunction.

Research Highlights

• Reorganization of Metabolic Pathways: Revealed the mechanism of metabolic conversion in microglia under palmitate treatment.
• Mediatory Role of EVs: Systematically studied and verified the role of microglial EVs secreted after exposure to palmitate in neurological dysfunction.
• Behavioral Impacts: Empirically confirmed the direct impact of EVs on memory and emotional behavior through mouse experiments.

Limitations and Prospects

Further validation using primary microglia cells is needed. The study was limited to proteomic statistics; future research should focus on other components of EVs such as metabolites, lipids, and nucleic acids. Additionally, exploring response differences across different age stages and designing more comprehensive research plans are important directions.