Weak Neuronal Glycolysis Sustains Cognition and Organismal Fitness

Neurology Biochemistry Basic Medical Sciences Life Sciences Medicine Cell Biology
Weak Glycolysis Cognitive Ability Organismal Fitness Bioenergetics Mitochondrial Stress NAD+ Reduction

This paper aims to explore the physiological importance of glycolysis in neuronal metabolic processes. For a long time, although neuronal activity mainly relies on glucose for energy, neurons have relatively weak glucose metabolism, mainly through glycolysis rather than other metabolic pathways. This phenomenon can be attributed to the sustained degradation of the key enzyme 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase-3 (PFKFB3), which promotes glycolysis. The physiological importance of the low levels of PFKFB3 in adult neurons is still unclear; however, understanding this “weak glycolysis” phenomenon is crucial for brain function.

Research Source

The paper was completed by Daniel Jimenez-Blasco and his research team, with authors affiliated with multiple research institutions, including the University of Salamanca in Spain, the University of Leuven in Belgium, and others. This paper was published in the journal Nature Metabolism, with the article DOI: https://doi.org/10.1038/s42255-024-01049-0.

Research Process

To unravel the physiological importance of low glycolysis in neurons, the research team used genetic engineering techniques to express PFKFB3 in mouse neurons, turning these neurons into active glycolytic cells. The research process included the following stages:

1. Construction of Mouse Models

The research team first used conditional Cdh1 gene knockout mice and crossed them with mice expressing the Cre recombinase under the control of the neuron-specific Camk2a (also known as CamkIIα) promoter, generating a mouse model with stabilized PFKFB3 protein in neurons, namely CamkIIα-Cdh1−/− mice. The team then designed a transgenic mouse (PFKFB3lox/+) with PFKFB3 introduced at the Rosa26 locus via homologous recombination, and crossed it with CamkIIα-Cre mice to generate CamkIIα-PFKFB3 mice.

2. Verification of Neuron-specific PFKFB3 Expression

Through Western Blot and immunocytochemistry, the research team verified the expression of PFKFB3 in different regions of the brain in CamkIIα-PFKFB3 mice, particularly in the cortex, hippocampus, and hypothalamus.

3. Determination of Glycolysis and PPP Flux

Using nuclear magnetic resonance spectroscopy and mass spectrometry techniques, the research team measured the glycolytic and pentose phosphate pathway (PPP) fluxes in mouse brains, showing that PFKFB3 expression significantly increased glycolytic flux but decreased PPP flux.

4. Mitochondrial Oxidative Stress and Energy Metabolism

The study also evaluated reactive oxygen species (ROS) levels in mitochondria using the Amplex Red assay and MitoSOX dye, finding that PFKFB3 expression caused mitochondrial oxidative stress. Measuring oxygen consumption rate (OCR) using the Seahorse device revealed that the mitochondrial oxidative stress induced by PFKFB3 expression led to the inactivation of complex I and disrupted energy metabolism.

5. Autophagy and Cognitive Function

The experiments showed that the NAD+ (nicotinamide adenine dinucleotide) reduction caused by activated glycolysis inhibited Sirtuin-mediated autophagy, leading to impaired cognitive function and metabolic syndrome in PFKFB3-expressing mice. Restoring NAD+ levels with NAD+ precursor compounds (NMN) successfully corrected these changes.

Main Results

  1. Impact on Glycolysis and PPP Flux: In the brains of PFKFB3-expressing mice, glycolytic flux increased while PPP flux decreased, leading to a reduction in reduced glutathione (GSH) levels.
  2. Mitochondrial Stress and Dysfunction: PFKFB3 expression caused the inactivation of mitochondrial complex I and oxidative stress, further leading to mitochondrial dysfunction.
  3. Changes in Autophagy Pathways: The decrease in NAD+ levels affected Sirtuin-dependent autophagy, resulting in impaired cognitive function in PFKFB3-expressing mice.

Conclusion and Significance

The study demonstrates that the low glycolytic nature of adult neurons is necessary for maintaining higher-order physiological functions. Excessive expression of PFKFB3 in neurons leads to mitochondrial oxidative stress and functional impairment, thereby damaging neuronal cognitive function and metabolic capacity. These findings provide new insights into understanding neuronal glycolytic changes and potential therapeutic approaches in diseases such as Alzheimer’s disease.

Research Highlights

  1. Revealed the weak glycolysis phenomenon in neurons and its physiological importance, providing critical insights into basic brain function in healthy and disease states.
  2. Applied various advanced methods, such as mass spectrometry analysis, nuclear magnetic resonance spectroscopy, and Seahorse technology, to comprehensively analyze the impact of glycolysis on neuronal function and mitochondrial health.
  3. Discovered new therapeutic targets, namely stabilizing PFKFB3 and NAD+ levels in neurons, which could potentially serve as therapeutic strategies for neurodegenerative diseases like Alzheimer’s disease.

This research significantly enhances our understanding of neuronal metabolic pathways and their impact on neurological diseases, holding profound scientific and clinical significance.