Background: The gut-brain axis and the intestinal microbiota are emerging as key players in health and disease. Shifts in intestinal microbiota composition affect a variety of systems; however, evidence of their direct impact on cognitive functions is still lacking. We tested whether faecal microbiota transplant (FMT) from aged donor mice into young adult recipients altered the hippocampus, an area of the central nervous system (CNS) known to be affected by the ageing process and related functions. Results: Young adult mice were transplanted with the microbiota from either aged or age-matched donor mice. Following transplantation, characterization of the microbiotas and metabolomics profiles along with a battery of cognitive and behavioural tests were performed. Label-free quantitative proteomics was employed to monitor protein expression in the hippocampus of the recipients. We report that FMT from aged donors led to impaired spatial learning and memory in young adult recipients, whereas anxiety, explorative behaviour and locomotor activity remained unaffected. This was paralleled by altered expression of proteins involved in synaptic plasticity and neurotransmission in the hippocampus. Also, a strong reduction of bacteria associated with short-chain fatty acids (SCFAs) production (Lachnospiraceae, Faecalibaculum, and Ruminococcaceae) and disorders of the CNS (Prevotellaceae and Ruminococcaceae) was observed. Finally, the detrimental effect of FMT from aged donors on the CNS was confirmed by the observation that microglia cells of the hippocampus fimbria, acquired an ageing-like phenotype; on the contrary, gut permeability and levels of systemic and local (hippocampus) cytokines were not affected. Conclusion: These results demonstrate that age-associated shifts of the microbiota have an impact on protein expression and key functions of the CNS. Furthermore, these results highlight the paramount importance of the gut-brain axis in ageing and provide a strong rationale to devise therapies aiming to restore a young-like microbiota to improve cognitive functions and the declining quality of life in the elderly.

Cadmium (Cd) is a highly toxic environmental pollutant released from the smelting and refining of metals and cigarette smoking. Oral exposure to cadmium may result in adverse effects on a number of tissues, including the central nervous system (CNS). In fact, its toxicity has been related to neurological disorders, as well as neurodegenerative diseases such as Alzheimer’s and Parkinson’s diseases. Under normal conditions, Cd barely reaches the brain in adults because of the presence of the blood–brain barrier (BBB); however, it has been demonstrated that Cd-dependent BBB alteration contributes to pathogenesis of neurodegeneration. However, the mechanism underlying Cd-dependent BBB alteration remain obscure. Here, we investigated the signaling pathway of Cd-induced tight junction (TJ), F-actin, and vimentin protein disassembly in a rat brain endothelial cell line (RBE4). RBE4 cells treated with 10 μM cadmium chloride (CdCl₂) showed a dose- and time-dependent significant increase in reactive oxygen species (ROS) production. This phenomenon was coincident with the alteration of the TJ zonula occludens-1 (ZO-1), F-actin, and vimentin proteins. The Cd-dependent ROS increase elicited the upregulation of GRP78 expression levels, a chaperone involved in endoplasmic reticulum (ER) stress that induces caspase-3 activation. Further signal profiling by the pannexin-1 (PANX1) specific inhibitor ¹⁰Panx revealed a PANX1-independent increase in ATP spillage in Cd-treated endothelial cells. Our results point out that a ROS-dependent ER stress-mediated signaling pathway involving caspase-3 activation and ATP release is behind the BBB morphological alterations induced by Cd.

Sarcopenia is characterised by a progressive loss of skeletal muscle mass and physical function as well as related metabolic disturbances. While fibre-rich diets can influence metabolic health outcomes, the impact on skeletal muscle mass and function is yet to be determined, and the moderating effects by physical activity (PA) need to be considered. The aim of the present study was to examine links between fibre intake, skeletal muscle mass and physical function in a cohort of older adults from the NU-AGE study. In 981 older adults (71 ± 4 years, 58% female), physical function was assessed using the short-physical performance battery test and handgrip strength. Skeletal muscle mass index (SMI) was derived using dual-energy X-ray absorptiometry (DXA). Dietary fibre intake (FI) was assessed by 7-day food record and PA was objectively determined by accelerometery. General linear models accounting for covariates including PA level, protein intake and metabolic syndrome (MetS) were used. Women above the median FI had significantly higher SMI compared to those below, which remained in fully adjusted models (24.7 ± 0.2% vs. 24.2 ± 0.1%, p = 0.011, η²p = 0.012). In men, the same association was only evident in those without MetS (above median FI: 32.4 ± 0.3% vs. below median FI: 31.3 ± 0.3%, p = 0.005, η²p = 0.035). There was no significant impact of FI on physical function outcomes. The findings from this study suggest a beneficial impact of FI on skeletal muscle mass in older adults. Importantly, this impact is independent of adherence to guidelines for protein intake and PA, which further strengthens the potential role of dietary fibre in preventing sarcopenia. Further experimental work is warranted in order to elucidate the mechanisms underpinning the action of dietary fibre on the regulation of muscle mass.

During Salmonella Typhimurium infection, intestinal CX₃CR1⁺ cells can either extend transepithelial cellular processes to sample luminal bacteria or, very early after infection, migrate into the intestinal lumen to capture bacteria. However, until now, the biological relevance of the intraluminal migration of CX₃CR1⁺ cells remained to be determined. We addressed this by using a combination of mouse strains differing in their ability to carry out CX₃CR1-mediated sampling and intraluminal migration. We observed that the number of S. Typhimurium traversing the epithelium did not differ between sampling-competent/migration-competent C57BL/6 and sampling-deficient/migration-competent BALB/c mice. In contrast, in sampling-deficient/migration-deficient CX₃CR1^−/− mice the numbers of S. Typhimurium penetrating the epithelium were significantly higher. However, in these mice the number of invading S. Typhimurium was significantly reduced after the adoptive transfer of CX₃CR1⁺ cells directly into the intestinal lumen, consistent with intraluminal CX₃CR1⁺ cells preventing S. Typhimurium from infecting the host. This interpretation was also supported by a higher bacterial fecal load in CX₃CR1^+/gfp compared with CX₃CR1^gfp/gfp mice following oral infection. Furthermore, by using real-time in vivo imaging we observed that CX₃CR1⁺ cells migrated into the lumen moving through paracellular channels within the epithelium. Also, we reported that the absence of CX₃CR1-mediated sampling did not affect Ab responses to a noninvasive S. Typhimurium strain that specifically targeted the CX₃CR1-mediated entry route. These data showed that the rapidly deployed CX₃CR1⁺ cell–based mechanism of immune exclusion is a defense mechanism against pathogens that complements the mucous and secretory IgA Ab–mediated system in the protection of intestinal mucosal surface.