Akkermansia muciniphila and its metabolite propionic acid maintains neuronal mitochondrial division and autophagy homeostasis during Alzheimer's disease pathologic process via GPR41 and GPR43

Akkermansia muciniphila reverses neuronal atrophy in Negr1 knockout mice with depression-like phenotypes

Genetic predispositions can shape the gut microbiome, which in turn modulates host gene expression and impacts host physiology. The complex interplay between host genetics and the gut microbiome likely contributes to the development of neuropsychiatric disorders, yet the mechanisms behind these interactions remain largely unexplored. In this study, we investigated the gut microbiota in Negr1 knockout (KO) mice, which exhibit anxiety- and depression-like behaviors, as NEGR1 (neuronal growth regulator 1) is a cell adhesion molecule linked to neuronal development and neuropsychiatric disorders. Our findings show significant early-life alterations in the gut microbiota composition of Negr1 KO mice, most notably a marked reduction in Akkermansia spp. along with reduced dendritic arborization and spine density in the nucleus accumbens (NAc) and the dentate gyrus (DG) of the hippocampus. Remarkably, daily administration of an Akkermansia strain isolated from wild-type mice reversed the neuronal structural abnormalities and ameliorated anxiety- and depression-like behaviors in Negr1 KO mice. Transcriptomic profiling revealed upregulation of mitochondrial genome-encoded genes in the NAc and hippocampus of Negr1 KO mice, along with a predisposition toward a pro-inflammatory state in the colon of Negr1 KO mice. The Akkermansia supplementation downregulated these mitochondrial genes in the NAc and hippocampus and upregulated genes involved in T cell activation and immune homeostasis in the colon. These findings demonstrate a novel gene-microbiome interaction in the pathophysiology of Negr1 KO mice, positioning Akkermansia spp. as a key mediator that improves neuronal atrophy and modulates anxiety- and depression-like behaviors. Our study provides compelling evidence for bidirectional interactions between host genetics and the gut microbiome in modulating neuropsychiatric phenotypes, offering new insights for addressing genetically influenced mental disorders.

Vitamin C supplementation mitigates mild cognitive impairment in mice subjected to D-galactose: Insights into intestinal flora and derived SCFAs

BACKGROUND

With the acceleration of population ageing, there has been increasing attention to ageing-related diseases, especially mild cognitive impairment (MCI). Vitamin C (VC), known as ascorbic acid, has demonstrated potential anti-ageing effects and may offer protection against MCI. The study sought to investigate the underlying mechanisms by which VC protects against MCI induced by D-galactose (D-gal).

APPROACHES

ICR mice were subjected to D-gal to elicit MCI and were subsequently administered VC for 8 weeks. The therapeutic effects of VC were assessed by behavioural evaluations and hippocampal pathology. To investigate the potential mechanisms, 16S rDNA sequencing, gas chromatography, and Spearman correlation analysis were employed.

RESULTS

VC supplementation significantly improved spatial learning and memory functions while mitigating hippocampal neuronal damage in D-gal-induced mice. Additionally, VC enhanced cognitive-related anti-inflammatory properties and antioxidant capacity. VC markedly mitigated the colonic pathological damage. Notably, VC led to increased microbial diversity, particularly the enrichment of genera that produce short-chain fatty acids (SCFAs), such as Akkermansia, Ruminococcus, and Butyricicoccus. Interestingly, levels of SCFAs (acetic acid, propionic acid, and butyric acid, etc.) were elevated following VC administration. The Spearman correlation analysis revealed that SCFAs levels were positively correlated with the abundance of the probiotics (Ruminococcus and Butyricicoccus) in response to VC.

CONCLUSIONS

VC supplementation may mitigate MCI, potentially through modulation of intestinal flora and SCFAs production. These results establish a foundation for the application of VC in the management of MCI and underscore its potential as a therapeutic strategy for ageing-related diseases.

Aberrant Reduction of Short-Chain Fatty Acid (SCFA) Receptor GPR41 and Transporter MCT4 in Prion-Infected Rodent and Cell Models

Mounting evidence shows that short-chain fatty acids (SCFAs), derived mainly from intestinal bacteria, play a significant role in maintaining the homeostasis of the immune system and the central nervous system (CNS). SCFAs, directly or indirectly mediated by SCFA receptors and transporters in neuronal cells, participate in the pathophysiological processes of various neurodegenerative diseases, but their roles in prion diseases are rarely addressed. Here, the abnormal changes in SCFA receptors and transporters in a prion-infected cell line and in the brains of several prion-scrapie-infected rodent models were evaluated by various methods. Markedly decreased GPR41 and MCT4 levels were observed in the brains of scrapie-infected rodents at the terminal stage and in the prion-infected cell line, whereas GPR43 and MCT1 levels did not change significantly. Morphological assays identified close colocalization of both GPR41 and MCT4 with NeuN-positive cells, while only a low amount was observed with Iba1-positive and GFAP-positive cells in the brains of prion-infected mice. Reduction of HO-1, an antioxidative agent in Nrf2 signaling, was observed in the brains of both prion-infected rodent models and the prion-infected cell line. Reductions of GPR41 and MCT4 in the prion-infected cell line were reversible after the removal of prion replication and stimulation with SCFA (sodium propionate) or a GPR41 agonist, accompanied by recovering the HO-1 level and improving cell viability. Our data presented here demonstrate a correlation between alterations in GPR41/MCT4 expression and the shifts in cellular composition that accompany prion pathogenesis. Furthermore, we explore the potential association between SCFA signaling and prion neurotoxicity, identifying it as a crucial area for future research endeavors.

The Role of G Protein-Coupled Receptors in the Regulation of Orthopaedic Diseases by Gut Microbiota

Exercise and diet modulate the gut microbiota, which is involved in the regulation of orthopaedic diseases and synthesises a wide range of metabolites that modulate cellular function and play an important role in bone development, remodelling and disease. G protein-coupled receptors (GPCRs), the largest family of transmembrane receptors in the human body, interact with gut microbial metabolites to regulate relevant pathological processes. This paper provides a review of different dietary and exercise effects on the pathogenic gut microbiota and their metabolites associated with GPCRs in orthopaedic diseases. RESULTS: Generally, metabolites produced by gut microbiota contribute to the maintenance of bone health by activating the corresponding GPCRs, which are involved in bone metabolism, regulation of immune response, and maintenance of gut flora homeostasis. Exercise and diet can influence gut microbiota, and an imbalance in gut microbiota homeostasis can trigger a series of adverse immune and metabolic responses by affecting GPCR function, ultimately leading to the onset and progression of various orthopaedic diseases. Understanding these relationships is crucial for elucidating the pathogenesis of orthopaedic diseases and developing personalised probiotic-based therapeutic strategies. In the future, we should further explore how to prevent and treat orthopaedic diseases through GPCR-based modulation of gut microbes and their interactions. The development of substances that precisely modulate gut microbes through different exercises and diets will provide more effective interventions to improve bone health in patients.

The multifaceted roles of Akkermansia muciniphila in neurological disorders

Gut commensals regulate neurological disorders through dynamic bidirectional communication along the gut-brain axis. Recent evidence has highlighted the well-documented beneficial role of the commensal gut bacterium Akkermansia muciniphila and its components in promoting host health. However, numerous clinical studies have demonstrated a paradoxical role of A. muciniphila in individuals with various neurological conditions. In this opinion article, we review the correlation between the prevalence of this gut commensal and the development of several disorders, including stroke, multiple sclerosis (MS), Parkinson's disease (PD), and Alzheimer's disease (AD). We focus on the potential mechanisms by which A. muciniphila may contribute to these diseases. An in-depth understanding of these correlations and the underlying pathogenic mechanisms could shed new light on the mechanisms of disease pathogenesis and provide a logical rationale for developing new therapies for these neurological conditions.

The Oral-Gut Microbiome-Brain Axis in Cognition

Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterized by cognitive decline and neuronal loss, affecting millions worldwide. Emerging evidence highlights the oral microbiome-a complex ecosystem of bacteria, fungi, viruses, and protozoa as a significant factor in cognitive health. Dysbiosis of the oral microbiome contributes to systemic inflammation, disrupts the blood-brain barrier, and promotes neuroinflammation, processes increasingly implicated in the pathogenesis of AD. This review examines the mechanisms linking oral microbiome dysbiosis to cognitive decline through the oral-brain and oral-gut-brain axis. These interconnected pathways enable bidirectional communication between the oral cavity, gut, and brain via neural, immune, and endocrine signaling. Oral pathogens, such as Porphyromonas gingivalis, along with virulence factors, including lipopolysaccharides (LPS) and gingipains, contribute to neuroinflammation, while metabolic byproducts, such as short-chain fatty acids (SCFAs) and peptidoglycans, further exacerbate systemic immune activation. Additionally, this review explores the influence of external factors, including diet, pH balance, medication use, smoking, alcohol consumption, and oral hygiene, on oral microbial diversity and stability, highlighting their role in shaping cognitive outcomes. The dynamic interplay between the oral and gut microbiomes reinforces the importance of microbial homeostasis in preserving systemic and neurological health. The interventions, including probiotics, prebiotics, and dietary modifications, offer promising strategies to support cognitive function and reduce the risk of neurodegenerative diseases, such as AD, by maintaining a diverse microbiome. Future longitudinal research is needed to identify the long-term impact of oral microbiome dysbiosis on cognition.