Intestinal barrier dysfunction: an evolutionarily conserved hallmark of aging

Influence of human gut microbiome on the healthy and the neurodegenerative aging

The gut microbiome plays a crucial role in host health throughout the lifespan by influencing brain function during aging. The microbial diversity of the human gut microbiome decreases during the aging process and, as a consequence, several mechanisms increase, such as oxidative stress, mitochondrial dysfunction, inflammatory response, and microbial gut dysbiosis. Moreover, evidence indicates that aging and neurodegeneration are closely related; consequently, the gut microbiome may serve as a novel marker of lifespan in the elderly. In this narrative study, we investigated how the changes in the composition of the gut microbiome that occur in aging influence to various neuropathological disorders, such as mild cognitive impairment (MCI), dementia, Alzheimer's disease (AD), and Parkinson's disease (PD); and which are the possible mechanisms that govern the relationship between the gut microbiome and cognitive impairment. In addition, several studies suggest that the gut microbiome may be a potential novel target to improve hallmarks of brain aging and to promote healthy cognition; therefore, current and future therapeutic interventions have been also reviewed.

Altered lactate/pyruvate ratio may be responsible for aging-associated intestinal barrier dysfunction in male rats

Some evidence points to a link between aging-related increased intestinal permeability and mitochondrial dysfunction in in-vivo models. Several studies have also demonstrated age-related accumulation of the of specific deletion 4834-bp of "common" mitochondrial DNA (mtDNA) in various rat tissues and suggest that this deletion may disrupt mitochondrial metabolism. The present study aimed to investigate possible associations among the mitochondrial DNA (mtDNA) common deletion, mitochondrial function, intestinal permeability, and aging in rats. The study was performed on the intestinal tissue from (24 months) and young (4 months) rats. mtDNA4834 deletion, mtDNA copy number, mitochondrial membrane potential, and ATP, lactate and pyruvate levels were analyzed in tissue samples. Zonulin and intestinal fatty acid-binding protein (I-FABP) levels were also evaluated in serum. Serum zonulin and I-FABP levels were significantly higher in 24-month-old rats than 4-month-old rats (p = 0.04, p = 0.026, respectively). There is not significant difference in mtDNA4834 copy levels was observed between the old and young intestinal tissues (p > 0.05). The intestinal mitochondrial DNA copy number was similar between the two age groups (p > 0.05). No significant difference was observed in ATP levels in the intestinal tissue lysates between old and young rats (p > 0.05). ATP levels in isolated mitochondria from both groups were also similar. Analysis of MMP using JC-10 in intestinal tissue mitochondria showed that mitochondrial membrane potentials (red/green ratios) were similar between the two age groups (p > 0.05). Pyruvate tended to be higher in the 24-month-old rat group and the L/P ratio was found to be approximately threefold lower in the intestinal tissue of the older rats compared to the younger rats (p < 0.002). The tissue lactate/pyruvate ratio (L/P) was three times lower in old rats than in young rats. Additionally, there were significant negative correlations between intestinal permeability parameters and L/P ratios. The intestinal tissues of aged rats are not prone to accumulate mtDNA common deletion, we suggest that this mutation does not explain the age-related increase in intestinal permeability. It seems to be more likely that altered glycolytic capacity could be a link to increased intestinal permeability with age. This observation strengthens assertions that the balance between glycolysis and mitochondrial metabolism may play a critical role in intestinal barrier functions.

Senolytic Treatment Improve Small Intestine Regeneration in Aging

Aging induces a series of alterations, specifically a decline in the stature and number of villi and crypts in the small intestine, thus compromising the absorbent capability of the villi. This investigation employed a senolytic combination of dasatinib and quercetin (D+Q) to examine its impact on the intestinal tract of elderly mice. Our findings demonstrate that D+Q treatment leads to a decrease in the expression of p21, p16, and Ki67, while concurrently triggering removal of apoptotic cells within the villi. Additionally, D+Q treatment exhibits the ability to promote growth in both the height and quantity of villi and crypts, along with stimulating nitric oxide (NO) production in aged mice. The study presented a model to assess strategies to alleviate age-related senescence in the intestinal tract of elderly mice. Importantly, D+Q showcases promising potential in enhancing intestinal functionality within the aging.

Galacto-Oligosaccharides and the Elderly Gut: Implications for Immune Restoration and Health

The increasing prevalence of noncommunicable diseases in the aging population has been correlated with a decline in innate and adaptive immune responses; hence, it is imperative to identify approaches to improve immune function, prevent related disorders, and reduce or treat age-associated health complications. Prebiotic supplementation is a promising approach to modulate the gut microbiome and immune system, offering a potential strategy to maintain the integrity of immune function in older individuals. This review summarizes the current research on prebiotic galacto-oligosaccharide (GOS) immunomodulatory mechanisms mediated by bacterial-derived metabolites, including short-chain fatty acids and secondary bile acids, to maintain immune homeostasis. The potential applications of GOS as immunotherapy for age-related disease prevention in older individuals are also highlighted. This aligns with the global shift toward proactive healthcare and emphasizes the significance of early intervention in directing an individual's health trajectory.

Viral infection disrupts intestinal homeostasis via Sting-dependent NF-κB signaling in Drosophila

Host-microbe interactions influence intestinal stem cell (ISC) activity to modulate epithelial turnover and composition. Here, we investigated the functional impacts of viral infection on intestinal homeostasis and the mechanisms by which viral infection alters ISC activity. We report that Drosophila A virus (DAV) infection disrupts intestinal homeostasis in Drosophila by inducing sustained ISC proliferation, resulting in intestinal dysplasia, loss of gut barrier function, and reduced lifespan. We found that additional viruses common in laboratory-reared Drosophila also promote ISC proliferation. The mechanism of DAV-induced ISC proliferation involves progenitor-autonomous epidermal growth factor receptor (EGFR) signaling, c-Jun N-terminal kinase (JNK) activity in enterocytes, and requires Sting-dependent nuclear factor κB (NF-κB) (Relish) activity. We further demonstrate that activating Sting-Relish signaling is sufficient to induce ISC proliferation, promote intestinal dysplasia, and reduce lifespan in the absence of infection. Our results reveal that viral infection can significantly disrupt intestinal physiology, highlight a novel role for Sting-Relish signaling, and support a role for viral infection in aging.

Systematic-Narrative Hybrid Literature Review: Crosstalk between Gastrointestinal Renin-Angiotensin and Dopaminergic Systems in the Regulation of Intestinal Permeability by Tight Junctions

In the first part of this article, the role of intestinal epithelial tight junctions (TJs), together with gastrointestinal dopaminergic and renin-angiotensin systems, are narratively reviewed to provide sufficient background. In the second part, the current experimental data on the interplay between gastrointestinal (GI) dopaminergic and renin-angiotensin systems in the regulation of intestinal epithelial permeability are reviewed in a systematic manner using the PRISMA methodology. Experimental data confirmed the copresence of DOPA decarboxylase (DDC) and angiotensin converting enzyme 2 (ACE2) in human and rodent enterocytes. The intestinal barrier structure and integrity can be altered by angiotensin (1-7) and dopamine (DA). Both renin-angiotensin and dopaminergic systems influence intestinal Na+/K+-ATPase activity, thus maintaining electrolyte and nutritional homeostasis. The colocalization of B0AT1 and ACE2 indicates the direct role of the renin-angiotensin system in amino acid absorption. Yet, more studies are needed to thoroughly define the structural and functional interaction between TJ-associated proteins and GI renin-angiotensin and dopaminergic systems.

Lactobacillus rhamnosus GG Stimulates Dietary Tryptophan-Dependent Production of Barrier-Protecting Methylnicotinamide

BACKGROUND & AIMS

Lacticaseibacillus rhamnosus GG (LGG) is the world's most consumed probiotic but its mechanism of action on intestinal permeability and differentiation along with its interactions with an essential source of signaling metabolites, dietary tryptophan (trp), are unclear.

METHODS

Untargeted metabolomic and transcriptomic analyses were performed in LGG monocolonized germ-free mice fed trp-free or -sufficient diets. LGG-derived metabolites were profiled in vitro under anaerobic and aerobic conditions. Multiomic correlations using a newly developed algorithm discovered novel metabolites tightly linked to tight junction and cell differentiation genes whose abundances were regulated by LGG and dietary trp. Barrier-modulation by these metabolites were functionally tested in Caco2 cells, mouse enteroids, and dextran sulfate sodium experimental colitis. The contribution of these metabolites to barrier protection is delineated at specific tight junction proteins and enterocyte-promoting factors with gain and loss of function approaches.

RESULTS

LGG, strictly with dietary trp, promotes the enterocyte program and expression of tight junction genes, particularly Ocln. Functional evaluations of fecal and serum metabolites synergistically stimulated by LGG and trp revealed a novel vitamin B3 metabolism pathway, with methylnicotinamide (MNA) unexpectedly being the most robust barrier-protective metabolite in vitro and in vivo. Reduced serum MNA is significantly associated with increased disease activity in patients with inflammatory bowel disease. Exogenous MNA enhances gut barrier in homeostasis and robustly promotes colonic healing in dextran sulfate sodium colitis. MNA is sufficient to promote intestinal epithelial Ocln and RNF43, a master inhibitor of Wnt. Blocking trp or vitamin B3 absorption abolishes barrier recovery in vivo.

CONCLUSIONS

Our study uncovers a novel LGG-regulated dietary trp-dependent production of MNA that protects the gut barrier against colitis.

Chronic trans fatty acid consumption shortens lifespan in male Drosophila melanogaster on a high-sugar and high-fat diet

Aging entails the progressive decline in the body's self-regulation and functionality over time. Notably, obesity and aging exhibit parallel phenotypes, with obesity further accelerating the aging process across multiple dimensions and diminishing lifespan. In this study, we explored the impact of trans fatty acid (TFA) consumption on the overall health and lifespan of male Drosophila melanogaster under an isocaloric high-sugar and high-fat diet. Our results indicate that TFA intake results in a shortened lifespan, elevated body weight, and increased triglyceride levels in flies fed a high-sugar and high-fat diet with equivalent caloric intake. Additionally, TFA exposure induces oxidative stress, locomotor deficits, and damage to the intestinal barrier in flies. Collectively, chronic TFA consumption expedites the aging process and reduces the lifespan of male Drosophila melanogaster. These results contribute supplementary evidence regarding the adverse health effects associated with TFAs.

β-Nicotinamide mononucleotide supplementation prolongs the lifespan of prematurely aged mice and protects colon function in ageing mice

Ageing is defined as the degeneration of physiological functions in numerous tissues and organs of an organism, which occurs with age. As we age, the gut undergoes a series of changes and weaknesses that may contribute to overall ageing. Emerging evidence suggests that β-nicotinamide mononucleotide (NMN) plays a role in regulating intestinal function, but there is still a lack of literature on its role in maintaining the colon health of ageing mice. In our research, Zmpste24-/- mice proved that NMN prolonged their life span and delayed senescence. This study was designed to investigate the effects of long-term intervention on regulating colon function in ageing mice. Our results indicated that NMN improved the pathology of intestinal epithelial cells and intestinal permeability by upregulating the expression of intestinal tight junction proteins and the number of goblet cells, increasing the release of anti-inflammatory factors, and increasing beneficial intestinal bacteria. NMN increased the expression of the proteins SIRT1, NMNAT2, and NMNAT3 and decreased the expression of the protein P53. It also regulated the activity of ISCs by increasing Wnt/β-catenin and Lgr5. Our findings also revealed that NMN caused a significant increase in the relative abundance of Akkermansia muciniphila and Bifidobacterium pseudolongum and notable differences in metabolic pathways related to choline metabolism in cancer. In summary, NMN supplementation can delay frailty in old age, aid healthy ageing, and delay gut ageing.

Exploring the Prospective Role of Propolis in Modifying Aging Hallmarks

Aging populations worldwide are placing age-related diseases at the forefront of the research agenda. The therapeutic potential of natural substances, especially propolis and its components, has led to these products being promising agents for alleviating several cellular and molecular-level changes associated with age-related diseases. With this in mind, scientists have introduced a contextual framework to guide future aging research, called the hallmarks of aging. This framework encompasses various mechanisms including genomic instability, epigenetic changes, mitochondrial dysfunction, inflammation, impaired nutrient sensing, and altered intercellular communication. Propolis, with its rich array of bioactive compounds, functions as a potent functional food, modulating metabolism, gut microbiota, inflammation, and immune response, offering significant health benefits. Studies emphasize propolis' properties, such as antitumor, cardioprotective, and neuroprotective effects, as well as its ability to mitigate inflammation, oxidative stress, DNA damage, and pathogenic gut bacteria growth. This article underscores current scientific evidence supporting propolis' role in controlling molecular and cellular characteristics linked to aging and its hallmarks, hypothesizing its potential in geroscience research. The aim is to discover novel therapeutic strategies to improve health and quality of life in older individuals, addressing existing deficits and perspectives in this research area.

Trametinib ameliorates aging-associated gut pathology in Drosophila females by reducing Pol III activity in intestinal stem cells

Pharmacological therapies are promising interventions to slow down aging and reduce multimorbidity in the elderly. Studies in animal models are the first step toward translation of candidate molecules into human therapies, as they aim to elucidate the molecular pathways, cellular mechanisms, and tissue pathologies involved in the anti-aging effects. Trametinib, an allosteric inhibitor of MEK within the Ras/MAPK (Ras/Mitogen-Activated Protein Kinase) pathway and currently used as an anti-cancer treatment, emerged as a geroprotector candidate because it extended lifespan in the fruit fly Drosophila melanogaster. Here, we confirm that trametinib consistently and robustly extends female lifespan, and reduces intestinal stem cell (ISC) proliferation, tumor formation, tissue dysplasia, and barrier disruption in guts in aged flies. In contrast, pro-longevity effects of trametinib are weak and inconsistent in males, and it does not influence gut homeostasis. Inhibition of the Ras/MAPK pathway specifically in ISCs is sufficient to partially recapitulate the effects of trametinib. Moreover, in ISCs, trametinib decreases the activity of the RNA polymerase III (Pol III), a conserved enzyme synthesizing transfer RNAs and other short, non-coding RNAs, and whose inhibition also extends lifespan and reduces gut pathology. Finally, we show that the pro-longevity effect of trametinib in ISCs is partially mediated by Maf1, a repressor of Pol III, suggesting a life-limiting Ras/MAPK-Maf1-Pol III axis in these cells. The mechanism of action described in this work paves the way for further studies on the anti-aging effects of trametinib in mammals and shows its potential for clinical application in humans.

Bazi Bushen capsule improves the deterioration of the intestinal barrier function by inhibiting NLRP3 inflammasome-mediated pyroptosis through microbiota-gut-brain axis

Purpose

The senescence-accelerated prone mouse 8 (SAMP8) is a widely used model for accelerating aging, especially in central aging. Mounting evidence indicates that the microbiota-gut-brain axis may be involved in the pathogenesis and progression of central aging-related diseases. This study aims to investigate whether Bazi Bushen capsule (BZBS) attenuates the deterioration of the intestinal function in the central aging animal model.

Methods

In our study, the SAMP8 mice were randomly divided into the model group, the BZ-low group (0.5 g/kg/d BZBS), the BZ-high group (1 g/kg/d BZBS) and the RAPA group (2 mg/kg/d rapamycin). Age-matched SAMR1 mice were used as the control group. Next, cognitive function was detected through Nissl staining and two-photon microscopy. The gut microbiota composition of fecal samples was analyzed by 16S rRNA gene sequencing. The Ileum tissue morphology was observed by hematoxylin and eosin staining, and the intestinal barrier function was observed by immunofluorescence. The expression of senescence-associated secretory phenotype (SASP) factors, including P53, TNF-α, NF-κB, IL-4, IL-6, and IL-10 was measured by real-time quantitative PCR. Macrophage infiltration and the proliferation and differentiation of intestinal cells were assessed by immunohistochemistry. We also detected the inflammasome and pyroptosis levels in ileum tissue by western blotting.

Results

BZBS improved the cognitive function and neuronal density of SAMP8 mice. BZBS also restored the intestinal villus structure and barrier function, which were damaged in SAMP8 mice. BZBS reduced the expression of SASP factors and the infiltration of macrophages in the ileum tissues, indicating a lower level of inflammation. BZBS enhanced the proliferation and differentiation of intestinal cells, which are essential for maintaining intestinal homeostasis. BZBS modulated the gut microbiota composition, by which BZBS inhibited the activation of inflammasomes and pyroptosis in the intestine.

Conclusion

BZBS could restore the dysbiosis of the gut microbiota and prevent the deterioration of intestinal barrier function by inhibiting NLRP3 inflammasome-mediated pyroptosis. These results suggested that BZBS attenuated the cognitive aging of SAMP8 mice, at least partially, by targeting the microbiota-gut-brain axis.

Smurfness-based two-phase model of ageing helps deconvolve the ageing transcriptional signature

Ageing is characterised at the molecular level by six transcriptional 'hallmarks of ageing', that are commonly described as progressively affected as time passes. By contrast, the 'Smurf' assay separates high-and-constant-mortality risk individuals from healthy, zero-mortality risk individuals, based on increased intestinal permeability. Performing whole body total RNA sequencing, we found that Smurfness distinguishes transcriptional changes associated with chronological age from those associated with biological age. We show that transcriptional heterogeneity increases with chronological age in non-Smurf individuals preceding the other five hallmarks of ageing that are specifically associated with the Smurf state. Using this approach, we also devise targeted pro-longevity genetic interventions delaying entry in the Smurf state. We anticipate that increased attention to the evolutionary conserved Smurf phenotype will bring about significant advances in our understanding of the mechanisms of ageing.

Gastrointestinal redox homeostasis in ageing

The gastrointestinal (GI) barrier acts as the primary interface between humans and the external environment. It constantly faces the risk of inflammation and oxidative stress due to exposure to foreign substances and microorganisms. Thus, maintaining the structural and functional integrity of the GI barrier is crucial for overall well-being, as it helps prevent systemic inflammation and oxidative stress, which are major contributors to age-related diseases. A healthy gut relies on maintaining gut redox homeostasis, which involves several essential elements. Firstly, it requires establishing a baseline electrophilic tone and an electrophilic mucosal gradient. Secondly, the electrophilic system needs to have sufficient capacity to generate reactive oxygen species, enabling effective elimination of invading microorganisms and rapid restoration of the barrier integrity following breaches. These elements depend on physiological redox signaling mediated by electrophilic pathways such as NOX2 and the H2O2 pathway. Additionally, the nucleophilic arm of redox homeostasis should exhibit sufficient reactivity to restore the redox balance after an electrophilic surge. Factors contributing to the nucleophilic arm include the availability of reductive substrates and redox signaling mediated by the cytoprotective Keap1-Nrf2 pathway. Future research should focus on identifying preventive and therapeutic strategies that enhance the strength and responsiveness of GI redox homeostasis. These strategies aim to reduce the vulnerability of the gut to harmful stimuli and address the decline in reactivity often observed during the aging process. By strengthening GI redox homeostasis, we can potentially mitigate the risks associated with age-related gut dyshomeostasis and optimize overall health and longevity.