Chronic lithium treatment diminishes the female advantage in lifespan in Drosophila melanogaster

Pharmacology of Aging: Drosophila as a Tool to Validate Drug Targets for Healthy Lifespan

Finding effective therapies to manage age-related conditions is an emerging public health challenge. Although disease-targeted treatments are important, a preventive approach focused on aging can be more efficient. Pharmacological targeting of aging-related processes can extend lifespan and improve health in animal models. However, drug development and translation are particularly challenging in geroscience. Preclinical studies have survival as a major endpoint for drug screening, which requires years of research in mammalian models. Shorter-lived invertebrates can be exploited to accelerate this process. In particular, the fruit fly Drosophila melanogaster allows the validation of new drug targets using precise genetic tools and proof-of-concept experiments on drugs impacting conserved aging processes. Screening for clinically approved drugs that act on aging-related targets may further accelerate translation and create new tools for aging research. To date, 31 drugs used in clinical practice have been shown to extend the lifespan of flies. Here, we describe recent advances in the pharmacology of aging, focusing on Drosophila as a tool to repurpose these drugs and study age-related processes.

Dietary sucrose determines the regulatory activity of lithium on gene expression and lifespan in Drosophila melanogaster

The amount of dietary sugars and the administration of lithium both impact the lifespan of the fruit fly Drosophila melanogaster. It is noteworthy that lithium is attributed with insulin-like activity as it stimulates protein kinase B/Akt and suppresses the activity of glycogen synthase kinase-3 (GSK-3). However, its interaction with dietary sugar has largely remained unexplored. Therefore, we investigated the effects of lithium supplementation on known lithium-sensitive parameters in fruit flies, such as lifespan, body composition, GSK-3 phosphorylation, and the transcriptome, while varying the dietary sugar concentration. For all these parameters, we observed that the efficacy of lithium was significantly influenced by the sucrose content in the diet. Overall, we found that lithium was most effective in enhancing longevity and altering body composition when added to a low-sucrose diet. Whole-body RNA sequencing revealed a remarkably similar transcriptional response when either increasing dietary sucrose from 1% to 10% or adding 1 mM LiCl to a 1% sucrose diet, characterized by a substantial overlap of nearly 500 differentially expressed genes. Hence, dietary sugar supply is suggested as a key factor in understanding lithium bioactivity, which could hold relevance for its therapeutic applications.

Concentration-dependent effects of lithium on Daphnia magna: Life-history profiles and integrated biomarker response implementation

The growing use of lithium (Li) in industrial and energy applications and increasing demand worldwide has inevitably resulted in its wide dispersal, representing a significant threat to aquatic systems. Unfortunately, as a ubiquitous emerging contaminant, the comprehensive toxicological information regarding Li at multifarious levels is limited. To diminish this gap, this work was focused to explore Li-induced cascading effects on Daphnia magna as a key species in freshwater ecosystems. Specifically, the organisms were chronically exposed to gradient Li concentrations with emphasis on characterizing life-history traits from individual to population scale, primarily as observed by a markedly concentration-dependent decrease along exposure gradients. In parallel, a robust set of biomarkers relating to energy reserves, antioxidant and biotransformation enzymes, cellular damage, ionoregulation and neurotoxicity were assayed for further understanding potential underlying mechanisms. As a result, biomarker alterations were characterized by significant decreases in energy storage and enzymatic profiles of antioxidant and biotransformation systems, not only triggering an imbalance between reactive oxygen species (ROS) generation and elimination under Li exposure, but compromising the fecundity fitness of phenotypical costs. In contrast, malondialdehyde (MDA) levels were remarkably enhanced as a consequence of inefficient antioxidant and biotransformation capacity leading to lipid peroxidation (LPO). Additionally, Li exerted a dose-dependent biphasic effect on the activities of superoxide dismutase (SOD), Na+,K+-ATPase and acetylcholinesterase (AChE) by interfering with inherent balance. In terms of responsive patterns and dose-effect trends, the integrated biomarker response indices (IBRv2) and star plots were consistent with the differences in biomarker profiles, not only presenting comprehensively biological effects in a visualized form, but signaling the importance of progressive induced changes in an integrative way. Overall, these findings highlighted the need for elucidating Li-produced impacts from a comprehensive perspective, providing valuable insights into better understanding the toxicity of Li in relation to aquatic ecosystem functioning and ecological relevance.

Alterations in brain glycogen levels influence life-history traits and reduce the lifespan in female Drosophila melanogaster

Sexual dimorphism in lifespan, wherein females outlive males, is evident across all animal taxa. The longevity difference between sexes is controlled by multiple physiological processes with complex relationships to one another. In recent years, glycogen, the storage form of glucose, has been shown to cause rapid aging upon forced synthesis in healthy neurons. Glycogen in the form of corpora amylacea in the aging brain is also widely reported. While these studies did suggest a novel role for glycogen in aging, most of them have focused on pooled samples, and have not looked at sex-specific effects, if any. Given the widespread occurrence of sex-biased expression of genes and the underlying physiology, it is important to look at the sex-specific effects of metabolic processes. In the present study, using transgenic fly lines for the human glycogen synthase, we investigated the sex-specific effects of glycogen on stress resistance, fitness, and survival. We demonstrate that Drosophila melanogaster females with altered levels of glycogen in the brain display a shortened lifespan, increased resistance to starvation, and higher oxidative stress than male flies. The present study thus provides a novel insight into the sex-specific effect of glycogen in survival and aging and how differences in metabolic processes could contribute to sex-specific traits.

A Genome-Wide Screen in Saccharomyces cerevisiae Reveals a Critical Role for Oxidative Phosphorylation in Cellular Tolerance to Lithium Hexafluorophosphate

Lithium hexafluorophosphate (LiPF₆) is one of the leading electrolytes in lithium-ion batteries, and its usage has increased tremendously in the past few years. Little is known, however, about its potential environmental and biological impacts. In order to improve our understanding of the cytotoxicity of LiPF₆ and the specific cellular response mechanisms to it, we performed a genome-wide screen using a yeast (Saccharomyces cerevisiae) deletion mutant collection and identified 75 gene deletion mutants that showed LiPF₆ sensitivity. Among these, genes associated with mitochondria showed the most enrichment. We also found that LiPF₆ is more toxic to yeast than lithium chloride (LiCl) or sodium hexafluorophosphate (NaPF₆). Physiological analysis showed that a high concentration of LiPF₆ caused mitochondrial damage, reactive oxygen species (ROS) accumulation, and ATP content changes. Compared with the results of previous genome-wide screening for LiCl-sensitive mutants, we found that oxidative phosphorylation-related mutants were specifically hypersensitive to LiPF₆. In these deletion mutants, LiPF₆ treatment resulted in higher ROS production and reduced ATP levels, suggesting that oxidative phosphorylation-related genes were important for counteracting LiPF₆-induced toxicity. Taken together, our results identified genes specifically involved in LiPF₆-modulated toxicity, and demonstrated that oxidative stress and ATP imbalance maybe the driving factors in governing LiPF₆-induced toxicity.

Sexual dimorphism in oxidant-induced adaptive homeostasis in multiple wild-type D. melanogaster strains

Sexual dimorphism includes the physical and reproductive differences between the sexes, including differences that are conserved across species, ranging from the common fruit fly, Drosophila melanogaster, to humans. Sex-dependent variations in adaptive homeostasis, and adaptive stress responses may offer insight into the underlying mechanisms for male and female survival differences and into differences in chronic disease incidence and severity in humans. Earlier work showed sex-specific differences in adaptive responses to oxidative stressors in hybrid laboratory strains of D. melanogaster. The present study explored whether this phenomenon is also observed in wild-type D. melanogaster strains Oregon-R (Or-R) and Canton-S (Ca-S), as well as the common mutant reference strain w[1118], in order to better understand whether such findings are descriptive of D. melanogaster in general. Flies of each strain were pretreated with non-damaging, adaptive concentrations of hydrogen peroxide (H₂O₂) or of different redox cycling agents (paraquat, DMNQ, or menadione). Adaptive homeostasis, and changes in the expression of the Proteasome and overall cellular proteasomal proteolytic capacity were assessed. Redox cycling agents exhibited a male-specific adaptive response, whereas H₂O₂ exposure provoked female-specific adaptation. These findings demonstrate that different oxidants can elicit sexually dimorphic adaptive homeostatic responses in multiple fly strains. These results (and those contained in a parallel study [1]) highlight the need to address sex as a biological variable in fundamental science, clinical research, and toxicology.

Is lithium biologically an important or toxic element to living organisms? An overview

Industrialized world is exposing living organisms to different chemicals and metals such as lithium (Li). Due to their use in common household items to industrial applications, it is imperative to examine their bioavailability. Lithium belongs to the group IA and also has wider uses such as in batteries, air conditioners to atomic reactors. Lithium occurs naturally in soil and water, mostly at low concentrations, and enters the food chain. It is not one of the essential minerals though various studies indicate that low levels of Li have beneficial effects on living organisms, whereas high levels expose them to toxicity and related detrimental effects. This review suggests that Li could be biologically important to living organism depending upon its concentration/exposure. Little is known about its biological importance and molecular understanding of its accumulation and mode of action, which might have future implications for Li's long-term effects on living organisms.

Lithium Promotes Longevity through GSK3/NRF2-Dependent Hormesis

The quest to extend healthspan via pharmacological means is becoming increasingly urgent, both from a health and economic perspective. Here we show that lithium, a drug approved for human use, promotes longevity and healthspan. We demonstrate that lithium extends lifespan in female and male Drosophila, when administered throughout adulthood or only later in life. The life-extending mechanism involves the inhibition of glycogen synthase kinase-3 (GSK-3) and activation of the transcription factor nuclear factor erythroid 2-related factor (NRF-2). Combining genetic loss of the NRF-2 repressor Kelch-like ECH-associated protein 1 (Keap1) with lithium treatment revealed that high levels of NRF-2 activation conferred stress resistance, while low levels additionally promoted longevity. The discovery of GSK-3 as a therapeutic target for aging will likely lead to more effective treatments that can modulate mammalian aging and further improve health in later life.