Bacterial processing of glucose modulates C. elegans lifespan and healthspan

Controlled burn: interconnections between energy-spilling pathways and metabolic signaling in bacteria

Bacterial energy-spilling pathways-such as overflow metabolism and futile cycles-have been considered inefficient forms of metabolism that result from poor regulatory control or function as mechanisms to cope with excess energy. However, mounting evidence places these seemingly wasteful reactions at the fulcrum between metabolic signaling and stress adaptation in bacteria. Specifically, energy-spilling pathways may mediate the metabolic reprogramming observed when cells encounter growth-limiting constraints (i.e., nutrient limitation). Recent insights spotlight microbial metabolism as an intricate signaling network that coordinates physiological programming with energy and nutrient conditions. Such intracellular metabolic cross stalk is pivotal to survival in competitive, fluctuating environments that bacteria frequently encounter in nature. In light of this paradigm of metabolic signaling, energy-spilling pathways are increasingly recognized as regulatory strategies that enable metabolic rewiring in response to stress. Overflow metabolism or futile cycles may generate secondary metabolites with signaling properties, alter the flux of metabolic pathways and the rate of nutrient acquisition, or stimulate regulatory nodes to trigger specific metabolic programs in response to environmental challenges. Furthermore, the observation of such expensive pathways under laboratory conditions purported to be "energy limiting" may in fact suggest energy sufficiency, compelling us to rethink how we model energy limitation and starvation for bacteria.

Causal relationship between gut microbiota and ageing: A multi-omics Mendelian randomization study

INTRODUCTION

Observational studies and clinical trials have suggested a connection between gut microbiota and aging. However, the causal relationship between them remains undetermined.

OBJECTIVES

This study aimed to use bidirectional two-sample Mendelian randomization (TSMR) analysis to explore the causal relationship between gut microbiota and aging.

METHODS

Summary statistics from genome-wide association studies (GWAS) on gut microbiota and seven aging-related phenotypes were employed for TSMR analysis. Reverse Mendelian randomization (MR) analysis was performed to assess the potential for reverse causality. Additionally, the relationship between Akkermansia muciniphila and inflammation-related proteins and metabolites was further investigated. The effects of Akkermansia muciniphila on aging were also examined in Caenorhabditis elegans by measuring both lifespan and healthspan.

RESULTS

MR analysis of 207 microbial taxa and seven aging phenotypes revealed 44 causal relationships between the gut microbiota and aging. Akkermansia muciniphila was found to be causally linked to several aging-related traits, including mvAge, appendicular lean mass, and grip strength (P < 0.05). Reverse MR analysis identified 23 causal relationships, but no bidirectional causality was observed. Moreover, Akkermansia muciniphila is causally related to ST1A1, taurine bile acid, and mannose (P < 0.05). In Caenorhabditis elegans, treatment with Akkermansia muciniphila significantly extended lifespan (P < 0.05) and improved mobility in aging nematodes.

CONCLUSION

TSMR analysis uncovers multiple potential causal links between gut microbiota and aging, particularly Akkermansia muciniphila. Experimental results support its role in alleviating aging. This study provides a strong foundation for future research on gut microbiota's role in aging.

Environmental NaCl affects C. elegans development and aging

Sodium is an essential nutrient, but is toxic in excess. In humans, excessive dietary sodium can cause high blood pressure, which contributes to age-related diseases including stroke and heart disease. We used C. elegans to elucidate how sodium levels influence animal aging. Most experiments on this animal are conducted in standard culture conditions: Nematode Growth Medium (NGM) agar with a lawn of E. coli. Here, we report that the supplemental NaCl in standard NGM, 50 mM, accelerates aging and decreases lifespan. For comparison, we prepared NGM with reduced NaCl or excess NaCl. Considering reduced NaCl as a baseline, wild-type worms on standard NGM displayed normal development and fertility but reduced lifespan and health span, indicating toxicity in old animals. The long-lived mutants daf-2, age-1, and nuo-6, cultured on standard NGM, also displayed reduced lifespan. Thus, NaCl in standard NGM accelerates aging in multiple genetic backgrounds. Wild-type worms on excess NaCl displayed delayed development and reduced fertility, and reduced lifespan and health span, indicating toxicity in both young and old animals. These results suggest that young animals are relatively resistant to NaCl toxicity, but that aging causes progressive sensitivity, such that old animals display toxicity to both standard and excess NaCl. We investigated pathways that respond to NaCl. Young animals cultured with excess NaCl activated gpdh-1, a specific response to NaCl stress. Old animals cultured with excess NaCl activated gpdh-1 and hsp-6, a reporter for the mitochondrial unfolded protein response. Thus, excess NaCl activates multiple stress response pathways in older animals.

High Nutritional Conditions Influence Feeding Plasticity in Pristionchus pacificus and Render Worms Non-Predatory

Developmental plasticity, the ability of a genotype to produce different phenotypes in response to environmental conditions, has been subject to intense studies in the last four decades. The self-fertilising nematode Pristionchus pacificus has been developed as a genetic model system for studying developmental plasticity due to its mouth-form polyphenism that results in alternative feeding strategies with a facultative predatory and non-predatory mouth form. Many studies linked molecular aspects of the regulation of mouth-form polyphenism with investigations of its evolutionary and ecological significance. Also, several environmental factors influencing P. pacificus feeding structure expression were identified including temperature, culture condition and population density. However, the nutritional plasticity of the mouth form has never been properly investigated although polyphenisms are known to be influenced by changes in nutritional conditions. For instance, studies in eusocial insects and scarab beetles have provided significant mechanistic insights into the nutritional regulation of polyphenisms but also other forms of plasticity. Here, we study the influence of nutrition on mouth-form polyphenism in P. pacificus through experiments with monosaccharide and fatty acid supplementation. We show that in particular glucose supplementation renders worms non-predatory. Subsequent transcriptomic and mutant analyses indicate that de novo fatty acid synthesis and peroxisomal beta-oxidation pathways play an important role in the mediation of this plastic response. Finally, the analysis of fitness consequences through fecundity counts suggests that non-predatory animals have an advantage over predatory animals grown in the glucose-supplemented condition.

Biological effects of Maillard reaction products: Use of Caenorhabditis elegans as an in vivo model

Maillard reaction products (MRPs), including melanoidins and volatile odor compounds, are associated with distinct flavors and colors during food processing and cooking. Although MRPs have health benefits, such as antioxidant activity, they are also associated with pathophysiological effects. Several in vivo models, especially rodents, are used to demonstrate physiological effects. Caenorhabditis elegans (C. elegans), an easy-to-rear free-living nematode with a short lifespan, has been used as a promising in vivo organism for the evaluation of functional properties in food components, including antiaging, antioxidant, and antiobesity properties. Furthermore, the high olfactory discrimination of this organism allows for the basic elucidation of behavior and regulation of aging. In this minireview, I discuss the various attributes of C. elegans that make it a promising in vivo model for studying the biological effects of MRPs.

Glucose-fed microbiota alters C. elegans intestinal epithelium and increases susceptibility to multiple bacterial pathogens

Overconsumption of dietary sugar can lead to many negative health effects including the development of Type 2 diabetes, metabolic syndrome, cardiovascular disease, and neurodegenerative disorders. Recently, the human intestinal microbiota, strongly associated with our overall health, has also been known to be affected by diet. However, mechanistic insight into the importance of the human intestinal microbiota and the effects of chronic sugar ingestion has not been possible largely due to the complexity of the human microbiome which contains hundreds of types of organisms. Here, we use an interspecies C. elegans/E. coli system, where E. coli are subjected to high sugar, then consumed by the bacterivore host C. elegans to become the microbiota. This glucose-fed microbiota results in a significant lifespan reduction accompanied by reduced healthspan (locomotion), reduced stress resistance, and changes in behavior and feeding. Lifespan reduction is also accompanied by two potential major contributors: increased intestinal bacterial density and increased concentration of reactive oxygen species. The glucose-fed microbiota accelerated the age-related development of intestinal cell permeability, intestinal distention, and dysregulation of immune effectors. Ultimately, the changes in the intestinal epithelium due to aging with the glucose-fed microbiota results in increased susceptibility to multiple bacterial pathogens. Taken together, our data reveal that chronic ingestion of sugar, such as a Western diet, has profound health effects on the host due to changes in the microbiota and may contribute to the current increased incidence of ailments including inflammatory bowel diseases as well as multiple age-related diseases.

The Probiotic Strain Lactobacillus acidophilus CL1285 Reduces Fat Deposition and Oxidative Stress and Increases Lifespan in Caenorhabditis elegans

Caenorhabditis elegans was recently shown to be a powerful model for studying and identifying probiotics with specific functions. Lactobacillus acidophilus CL1285, Lacticaseibacillus casei LBC80R, and Lacticaseibacillus rhamnosus CLR2, which are three bacteria that were marketed by Bio-K+, were evaluated using the nematode C. elegans to study fat accumulation, lifespan, and resistance to oxidative stress. Although the general effects of probiotics in terms of protection against oxidative stress were highlighted, the CL1285 strain had an interesting and specific feature, namely its ability to prevent fat accumulation in nematodes; this effect was verified by both the Oil Red and Nile Red methods. This observed phenotype requires daf-16 and is affected by glucose levels. In addition, in a daf-16- and glucose-dependent manner, CL1285 extended the lifespan of C. elegans; this effect was unique to CL1285 and not found in the other L. acidophilus subtypes in this study. Our findings indicate that L. acidophilus CL1285 impacts fat/glucose metabolism in C. elegans and provides a basis to further study this probiotic, which could have potential health benefits in humans and/or in mammals.

Glucose stockpile in the intestinal apical brush border in C. elegans

Revealing the mechanisms of glucose transport is crucial for studying pathological diseases caused by glucose toxicities. Numerous studies have revealed molecular functions involved in glucose transport in the nematode Caenorhabditis elegans, a commonly used model organism. However, the behavior of glucose in the intestinal lumen-to-cell remains elusive. To address that, we evaluated the diffusion coefficient of glucose in the intestinal apical brush border of C. elegans by using fluorescent glucose and fluorescence recovery after photobleaching. Fluorescent glucose taken in the intestine of worms accumulates in the apical brush border, and its diffusion coefficient of ∼10-8 cm2/s is two orders of magnitude slower than that in bulk. This result indicates that the intestinal brush border is a viscous layer. ERM-1 point mutations at the phosphorylation site, which shorten the microvilli length, did not significantly affect the diffusion coefficient of fluorescent glucose in the brush border. Our findings imply that glucose enrichment is dominantly maintained by the viscous layer composed of the glycocalyx and molecular complexes on the apical surface.

Oleic Acid Metabolism in Response to Glucose in C. elegans

A key response to glucose stress is an increased production of unsaturated fatty acids to balance the increase in saturated fatty acids in the membrane. The C. elegans homolog of stearoyl-CoA desaturase, FAT-7, introduces the first double bond into saturated C18 fatty acids yielding oleic acid, and is a critical regulatory point for surviving cold and glucose stress. Here, we incorporated 13C stable isotopes into the diet of nematodes and quantified the 13C-labelled fatty acid using GC-MS and HPLC/MS-MS to track its metabolic response to various concentrations of glucose. Previous work has analyzed the membrane composition of C. elegans when responding to mild glucose stress and showed few alterations in the overall fatty acid composition in the membrane. Here, in nematodes exposed to higher concentrations of glucose, a specific reduction in oleic acid and linoleic acid was observed. Using time courses and stable isotope tracing, the response of fatty acid metabolism to increasing levels of glucose stress is characterized, revealing the funneling of monounsaturated fatty acids to preserve the abundance of polyunsaturated fatty acids. Taken together, higher levels of glucose unveil a specific reduction in oleic and linolenic acid in the metabolic rewiring required to survive glucose stress.

Protein aggregation and glycation in Escherichia coli exposed to desiccation-rehydration stress

In natural environments, bacteria often enter a state of anhydrobiosis due to water loss. Multiple studies have demonstrated that desiccation may lead to protein aggregation and glycation both in vivo and in vitro. However, the exact effects of water-loss-induced proteotoxic stress and the interplay between protein glycation and aggregation in bacteria remain elusive. Our studies revealed that protein aggregates formation in Escherichia coli started during desiccation and continued during the rehydration stage. The aggregates were enriched in proteins prone to liquid-liquid phase separation. Although it is known that glycation may induce protein aggregation in vitro, the aggregates formed in E. coli contained low levels of glycation products compared to the soluble protein fraction. Carnosine, glycine betaine and trehalose diminished the formation of protein aggregates and glycation products, resulting in increased E. coli viability. Notably, although high concentrations of glycine-betaine and trehalose significantly enhanced protein aggregation, glycation was still inhibited and E. coli cells survived desiccation better than bacteria grown without osmolytes. Taken together, our results suggest that the aggregates might play protective functions during early desiccation-rehydration stress. Moreover, it seems glycation rather than protein aggregation is the main cause of E. coli death upon desiccation-rehydration stress.

Pasteurized Akkermansia muciniphila Reduces Fat Accumulation via nhr-49-Mediated Nuclear Hormone Signaling Pathway in Caenorhabditis elegans

Pasteurized Akkermansia muciniphila (p-AKK) is related to lipid metabolism and helps control obesity. The main goal of this study was to investigate the role and mechanism of p-AKK in lipid metabolism using Caenorhabditis elegans. The results showed that p-AKK increased the healthy lifespan of nematodes and helped maintain exercise ability in aging, suggesting a potential increase in energy expenditure. The overall fat deposition and triglyceride level were significantly decreased and the p-AKK anti-oxidative stress helped to regulate fatty acid composition. Additionally, the transcriptome results showed that p-AKK increased the expression of lipo-hydrolase and fatty acid β-oxidation-related genes, including lipl-4, nhr-49, acs-2 and acdh-8, while it decreased the expression of fat synthesis-related genes, including fat-7, elo-2 and men-1. These results partially explain the mechanisms underlying the fact that p-AKK decreases fat accumulation of C. elegans via nhr-49/acs-2-mediated signaling involved in fatty acid β-oxidation and synthesis.

Advanced Glycation End Products in Health and Disease

Advanced glycation end products (AGEs), formed through the nonenzymatic reaction of reducing sugars with the side-chain amino groups of lysine or arginine of proteins, followed by further glycoxidation reactions under oxidative stress conditions, are involved in the onset and exacerbation of a variety of diseases, including diabetes, atherosclerosis, and Alzheimer’s disease (AD) as well as in the secondary stages of traumatic brain injury (TBI). AGEs, in the form of intra- and interprotein crosslinks, deactivate various enzymes, exacerbating disease progression. The interactions of AGEs with the receptors for the AGEs (RAGE) also result in further downstream inflammatory cascade events. The overexpression of RAGE and the AGE-RAGE interactions are especially involved in cases of Alzheimer’s disease and other neurodegenerative diseases, including TBI and amyotrophic lateral sclerosis (ALS). Maillard reactions are also observed in the gut bacterial species. The protein aggregates found in the bacterial species resemble those of AD and Parkinson’s disease (PD), and AGE inhibitors increase the life span of the bacteria. Dietary AGEs alter the gut microbiota composition and elevate plasma glycosylation, thereby leading to systemic proinflammatory effects and endothelial dysfunction. There is emerging interest in developing AGE inhibitor and AGE breaker compounds to treat AGE-mediated pathologies, including diabetes and neurodegenerative diseases. Gut-microbiota-derived enzymes may also function as AGE-breaker biocatalysts. Thus, AGEs have a prominent role in the pathogenesis of various diseases, and the AGE inhibitor and AGE breaker approach may lead to novel therapeutic candidates.

Biological Mineralization of Methyl Orange by Pseudomonas aeruginosa

Due to its recalcitrant and carcinogenic nature, the presence of methyl orange (MO) in the environment is a serious threat to human and animal life and is also toxic to plants. MO being recalcitrant cannot be effectively reclaimed from industrial effluents through physical and chemical approaches. Biological methods on the other hand have the potential to degrade such dyes because of their compatibility with nature and low chances of adverse effects on the environment. Bacteria, due to their fast growth rate and capability of surviving in extreme environments can effectively be used for this purpose. In the current research study, Pseudomonas aeruginosa was isolated and characterized using 16rRNA from textile wastewater. In the preliminary tests it was found that Pseudomonas aeruginosa has the ability to degrade and mineralize methyl orange effectively. The physicochemical conditions were then optimized, in order to get maximum degradation of MO which was achieved at 37 °C, a pH of 7, a low salt concentration of 0.1 g/15 mL, a high carbon source of 0.6 g/15 mL, and 72 h experimental time. In a single set of experiments where all these optimum conditions were combined, 88.23% decolorization of the selected dye was achieved. At the end of the experimental cycle, the aliquots were homogenized and filtered. The filtrates were subjected to FTIR and GC-MS analysis where azo linkage breaking was confirmed from the FTIR spectra. The filtrates were then extracted with ethyl acetate and then passed through a silica gel column. On the basis of Rf value (TLC plates used) similar fraction were combined which were then subjected to NMR analysis. The compounds detected through GC-MS, peaks were not observed in proton and C-13 NMR. Instead, solvent and some impurity peaks were present, showing that complete mineralization of the dye had occurred due to the action of different bacterial enzymes such as azoreductase, peroxidases, and classes on MO. The prosed mechanism of complete mineralization is based on spectral data that needs to be verified by trapping the individual step products through the use of appropriate inhibitors of individual enzymes.

Increased fermentable carbohydrate intake alters colonic mucus barrier function through glycation processes and increased mast cell counts

Irritable bowel syndrome (IBS) is a functional gastrointestinal disorder for which dietary interventions can be a useful treatment. In recent years, the low-FODMAP approach is gaining traction in this regard. The fermentation of these non-absorbed carbohydrates by the gut microbiota can generate toxic glycating metabolites, such as methylglyoxal. These metabolites can have harmful effects by their role in the generation of advanced glycation end products (AGEs), which activates Receptor for AGEs (AGER). Mast cells can be stimulated by AGEs and play a role in IBS. We have treated mice with lactose or fructo-oligosaccharides (FOS), with or without co-administration of pyridoxamine and investigated the colonic mucus barrier. We have found that an increased intake of lactose and fructo-oligosaccharides induces a dysregulation of the colonic mucus barrier, increasing mucus discharge in empty colon, while increasing variability and decreasing average thickness mucus layer covering the fecal pellet. Changes were correlated with increased mast cell counts, pointing to a role for the crosstalk between these and goblet cells. Additionally, AGE levels in colonic epithelium were increased by treatment with the selected fermentable carbohydrates. Observed effects were prevented by co-treatment with anti-glycation agent pyridoxamine, implicating glycation processes in the negative impact of fermentable carbohydrate ingestion. This study shows that excessive intake of fermentable carbohydrates can cause colonic mucus barrier dysregulation in mice, by a process that involves glycating agents and increased mucosal mast cell counts.

p21-Activated kinase 1 (PAK1) in aging and longevity: An overview

The p21-activated kinases (PAKs) belong to serine/threonine kinases family, regulated by ∼21 kDa small signaling G proteins RAC1 and CDC42. The mammalian PAK family comprises six members (PAK1-6) that are classified into two groups (I and II) based on their domain architecture and regulatory mechanisms. PAKs are implicated in a wide range of cellular functions. PAK1 has recently attracted increasing attention owing to its involvement in oncogenesis, tumor progression, and metastasis as well as several life-limiting diseases and pathological conditions. In Caenorhabditis elegans, PAK1 functions limit the lifespan under basal conditions by inhibiting forkhead transcription factor DAF-16. Interestingly, PAK depletion extended longevity and attenuated the onset of age-related phenotypes in a premature-aging mouse model and delayed senescence in mammalian fibroblasts. These observations implicate PAKs as not only oncogenic but also aging kinases. Therefore, PAK-targeting genetic and/or pharmacological interventions, particularly PAK1-targeting, could be a viable strategy for developing cancer therapies with relatively no side effects and promoting healthy longevity. This review describes PAK family proteins, their biological functions, and their role in regulating aging and longevity using C. elegans. Moreover, we discuss the effect of small-molecule PAK1 inhibitors on the lifespan and healthspan of C. elegans.