Fruit Flies Shed New Light on Memory and Aging

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The brain is a complex organ responsible for many critical functions, including the formation and retrieval of our memories. As we age, the brain undergoes changes that can affect cognitive abilities, including our memory. Understanding the mechanisms that underlie these changes is critical for developing therapies for age-related cognitive decline. 

“Over the last two decades there has been growing recognition that lactate, the end product of glycolysis, serves many functions, including acting as a source of energy, a signaling molecule, and even as an epigenetic regulator.”

Lactate & LDH

Lactate is a molecule that is produced during the metabolism of glucose in the body. It is a byproduct of anaerobic metabolism, which occurs when there is insufficient oxygen supply to meet the energy demands of the body. Lactate can be used as an energy source by some cells, such as the heart and skeletal muscles, and it can also be transported to the liver where it can be converted back into glucose.

Lactate dehydrogenase (LDH), on the other hand, is an enzyme that catalyzes the conversion of pyruvate to lactate (the reverse reaction of lactate production) and is also involved in other metabolic processes. This enzyme is found in many tissues of the body, including the heart, liver and skeletal muscles, and is released into the bloodstream when tissues are damaged. LDH is often used as a diagnostic marker for various medical conditions, such as heart attacks, liver disease and certain cancers. High levels of LDH in the blood may indicate tissue damage or cell death, while low levels may indicate a deficiency in the enzyme.

The Study

Recently, researchers investigated the role of LDH in memory formation and aging using Drosophila melanogaster (fruit flies) as a model organism. In a new study, researchers Ariel K. Frame, J. Wesley Robinson, Nader H. Mahmoudzadeh, Jason M. Tennessen, Anne F. Simon, and Robert C. Cumming from Western University and Indiana University used genetic manipulation techniques to alter LDH expression in the neurons or glia of fruit flies to investigate its effects on aging and memory. Their research paper was published in Aging’s Volume 15, Issue 4, and entitled, “Aging and memory are altered by genetically manipulating lactate dehydrogenase in the neurons or glia of flies.”

“The astrocyte-neuron lactate shuttle hypothesis posits that glial-generated lactate is transported to neurons to fuel metabolic processes required for long-term memory.”

Lactate shuttling is a process in which lactate is transported from one cell or tissue to another for use as an energy source or as a signaling molecule. Previous research has shown that LDH is expressed in both neurons and glia in the brain, and that it may play a role in regulating synaptic plasticity and memory formation. The authors of the current research paper aimed to test the hypothesis that alterations in LDH expression in the brain may contribute to age-related cognitive decline.

“D. melanogaster serves as a good model for understanding the role of glia-neuron lactate shuttling in central nervous system (CNS) function and cognitive behaviour.”

To test this hypothesis, the researchers genetically manipulated LDH expression in the neurons or glia of fruit flies (dLDH) and assessed the impact on memory formation and aging. Specifically, they used RNA interference (RNAi) to either knock down or overexpress dLDH in either neurons or glia. They then assessed the effects of these manipulations on two different memory tasks at different ages, courtship memory and aversive olfactory memory, and also assessed survival, negative geotaxis, brain neutral lipids (the core component of lipid droplets), and brain metabolites.

Results

Their results showed that dLDH manipulation had differential effects on fruit flies depending on the cell type in which it was altered. In neurons, both upregulation and downregulation of dLDH resulted in memory impairment and decreased survival with age. In contrast, downregulation of dLDH in glial cells caused age-related memory impairment, without altering survival. Upregulating dLDH expression in glial cells lowered survival without disrupting memory. Both neuronal and glial dLDH upregulation increased neutral lipid accumulation.

“We provide evidence that altered lactate metabolism with age affects the tricarboxylic acid (TCA) cycle, 2-hydroxyglutarate (2HG), and neutral lipid accumulation.”

The results of this study may provide new insights into the role of LDH in memory formation and aging in humans. The findings suggest that LDH may be a potential target for developing therapies to combat age-related cognitive decline. Additionally, the study highlights the importance of considering cell-type specificity when investigating the role of genes and enzymes in complex biological processes. A limitation of the study is that it was conducted in fruit flies, which may not fully capture the complexity of memory formation and aging in humans. However, fruit flies have been shown to be a valuable model organism for studying many aspects of brain function, and the findings of this study may provide a foundation for future research in mammals.

“Collectively, our findings indicate that the direct alteration of lactate metabolism in either glia or neurons affects memory and survival but only in an age-dependent manner.”

Conclusion

In conclusion, the study provides new insights into the role of LDH in memory formation and aging. The findings suggest that LDH may play a critical role in regulating energy metabolism in the brain, which in turn affects synaptic plasticity and memory formation. The study also highlights the importance of considering cell-type specificity when investigating the role of genes and enzymes in complex biological processes. Future research in mammals may be needed to further explore the implications of these findings for human health and the potential for developing therapies for age-related cognitive decline. Nonetheless, this study provides an important step forward in understanding the complex interplay between lactate metabolism, memory and aging.

“In this study we demonstrate the importance of maintaining appropriate levels of dLdh in D. melanogaster glia and neurons for maintenance of long-term courtship memory and survival with age (Figure 6). In addition, our results implicate lipid metabolism, 2HG accumulation, and changes in TCA cycle activity as factors underlying the age-related impacts of perturbed dLdh expression, which likely modifies glia-neuron lactate shuttling in the fly brain.”

Click here to read the full research paper published by Aging.

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Aging is an open-access, peer-reviewed journal that has been publishing high-impact papers in all fields of aging research since 2009. These papers are available to readers (at no cost and free of subscription barriers) in bi-monthly issues at Aging-US.com.

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