Butyrate and propionate are microbial danger signals that activate the NLRP3 inflammasome in human macrophages upon TLR stimulation

New insights on metabolic reprogramming in macrophage plasticity

Macrophages are the first line of defense in the innate immune system. Macrophages have two subtypes: classically activated macrophages (M1) and alternatively activated macrophages (M2), with different phenotypes and functions. They play a critical role in defending against pathogens and maintaining internal homeostasis. Macrophages have great plasticity in their biological characteristics. Although the regulation of macrophage plasticity has not been fully elucidated, accumulated evidence supports that microenvironmental differences are the root cause for macrophage differentiation into different subtypes. These differences alter macrophage plasticity by modulating key metabolites, activating downstream gene transcription, and influencing phagocytosis, cytokine secretion, and immune regulation. Herein, we systematically summarize metabolic reprogramming, including glucose, lipid, amino acid, ion, vitamin, nucleotide, and butyrate metabolism, as key regulators affecting macrophage polarization, providing new insights for developing targeted drugs that modulate macrophage plasticity.

Updated insights into the molecular networks for NLRP3 inflammasome activation

Over the past decade, significant advances have been made in our understanding of how NACHT-, leucine-rich-repeat-, and pyrin domain-containing protein 3 (NLRP3) inflammasomes are activated. These findings provide detailed insights into the transcriptional and posttranslational regulatory processes, the structural-functional relationship of the activation processes, and the spatiotemporal dynamics of NLRP3 activation. Notably, the multifaceted mechanisms underlying the licensing of NLRP3 inflammasome activation constitute a focal point of intense research. Extensive research has revealed the interactions of NLRP3 and its inflammasome components with partner molecules in terms of positive and negative regulation. In this Review, we provide the current understanding of the complex molecular networks that play pivotal roles in regulating NLRP3 inflammasome priming, licensing and assembly. In addition, we highlight the intricate and interconnected mechanisms involved in the activation of the NLRP3 inflammasome and the associated regulatory pathways. Furthermore, we discuss recent advances in the development of therapeutic strategies targeting the NLRP3 inflammasome to identify potential therapeutics for NLRP3-associated inflammatory diseases. As research continues to uncover the intricacies of the molecular networks governing NLRP3 activation, novel approaches for therapeutic interventions against NLRP3-related pathologies are emerging.

Sodium-Coupled Monocarboxylate Absorption in the Airway Epithelium Is Facilitated by the SLC5A8 Co-Transporter

AIM

Amino acids, sugars, short-chain fatty acids (SCFA), vitamins, and other small molecules compose the extracellular metabolome on the airway lumen surface, but how the airway epithelium deals with these molecules has not been deeply studied. Due to the broad spectrum of metabolites transported by SLC5A8 and SLC5A12, we aim to determine if they are functionally expressed and participate in the absorption of Na+, short-chain fatty acids, and monocarboxylates in mouse and human airway epithelium.

METHODS

Tracheas isolated from male or female mice and human bronchial epithelial cells (HBECs) were used for electrophysiological studies in the Ussing chamber and to detect members of the SLC16 family by RT-PCR and bulk RNAseq. Additionally, cell lines expressing the human and murine SLC5A8 transporter were employed for uptake studies using a fluorescent lactate probe.

RESULTS

We showed for the first time that human and murine airway epithelium express a functional SLC5A8 transporter, facilitating the absorption of glucose metabolites and SCFAs. The Na+-coupled monocarboxylate transport was not additive with ENaC-mediated Na+ absorption in mouse trachea. We observed that valproate acts as an inhibitor of the murine but not of the human SLC5A8 transporter.

CONCLUSIONS

Our results demonstrate that several metabolites derived from bacterial and cellular metabolism can be transported from the airway lumen into the epithelial cells, participating in a homeostatic relation of the tissue with its environment.

Idiopathic pulmonary fibrosis microenvironment: Novel mechanisms and research directions

Idiopathic Pulmonary Fibrosis (IPF) is a progressive interstitial lung disease marked by increasing dyspnea and respiratory failure. The underlying mechanisms remain poorly understood, given the complexity of its pathogenesis. This review investigates the microenvironment of IPF to identify novel mechanisms and therapeutic avenues. Studies have revealed that various cell types, including alveolar epithelial cells, fibroblasts, myofibroblasts, and immune cells, are integral to disease progression, engaging in cellular stress responses and inflammatory regulation via signaling pathways such as TGF-β, Wnt, mTOR, and ROS. Non-coding RNAs, particularly miRNAs, are critical in IPF and may serve as diagnostic and prognostic biomarkers. Regarding treatment, mesenchymal stem cells (MSCs) and their extracellular vesicles (EVs) or non-vesicular derivatives offer promise by modulating immune responses, enhancing tissue repair, and inhibiting fibrosis. Additionally, alterations in the lung microbiota are increasingly recognized as a contributing factor to IPF progression, offering fresh insights into potential treatments. Despite the encouraging results of MSC-based therapies, the precise mechanisms and clinical applications remain subjects of ongoing research. This review emphasizes the significance of the IPF microenvironment and highlights the need for further exploration to develop effective therapies that could enhance patient outcomes.

Diet-microbiome interactions in cancer

Diet impacts cancer in diverse manners. Multiple nutritional effects on tumors are mediated by dietary modulation of commensals, residing in mucosal surfaces and possibly also within the tumor microenvironment. Mechanistically understanding such diet-microbiome-host interactions may enable to develop precision nutritional interventions impacting cancer development, dissemination, and treatment responses. However, data-driven nutritional strategies integrating diet-microbiome interactions are infrequently incorporated into cancer prevention and treatment schemes. Herein, we discuss how dietary composition affects cancer-related processes through alterations exerted by specific nutrients and complex foods on the microbiome. We highlight how dietary timing, including time-restricted feeding, impacts microbial function in modulating cancer and its therapy. We review existing and experimental nutritional approaches aimed at enhancing microbiome-mediated cancer treatment responsiveness while minimizing adverse effects, and address challenges and prospects in integrating diet-microbiome interactions into precision oncology. Collectively, mechanistically understanding diet-microbiome-host interactomes may enable to achieve a personalized and microbiome-informed optimization of nutritional cancer interventions.

Intestinal-pulmonary axis: a 'Force For Good' against respiratory viral infections

Respiratory viral infections are a major global public health concern, and current antiviral therapies still have limitations. In recent years, research has revealed significant similarities between the immune systems of the gut and lungs, which interact through the complex physiological network known as the "gut-lung axis." As one of the largest immune organs, the gut, along with the lungs, forms an inter-organ immune network, with strong parallels in innate immune mechanisms, such as the activation of pattern recognition receptors (PRRs). Furthermore, the gut microbiota influences antiviral immune responses in the lungs through mechanisms such as systemic transport of gut microbiota-derived metabolites, immune cell migration, and cytokine regulation. Studies have shown that gut dysbiosis can exacerbate the severity of respiratory infections and may impact the efficacy of antiviral therapies. This review discusses the synergistic role of the gut-lung axis in antiviral immunity against respiratory viruses and explores potential strategies for modulating the gut microbiota to mitigate respiratory viral infections. Future research should focus on the immune mechanisms of the gut-lung axis to drive the development of novel clinical treatment strategies.

Gut microbiota in treating inflammatory digestive diseases: Current challenges and therapeutic opportunities

Accumulating evidence indicates that the gut microbiota is intricately involved in the initiation and progression of human diseases, forming a multidirectional regulatory axis centered on intestinal microbiota. This article illustrates the challenges in exploring the role of the gut microbiota in inflammatory digestive diseases, such as metabolic dysfunction-associated steatotic liver disease (MASLD) and inflammatory bowel disease (IBD), and summarizes the existing microbiome-focused treatment strategies (probiotics, prebiotics, symbiotics, fecal microbiota transplantation, and bacteriophages therapy), emerging technologies (gut microbiome-on-a-chip and artificial intelligence), as well as possible future research directions. Taken together, these therapeutic strategies and technologies present both opportunities and challenges, which require researchers and clinicians to test the rationality and feasibility of various therapeutic modalities in continuous practice.

Gut microbiota and inflammasome-mediated pyroptosis: a bibliometric analysis from 2014 to 2023

Background

The role of gut microbiota in inflammatory disease development and progression has been recognized more recently. Inflammasome-mediated pyroptosis in involved in these diseases. This complex relationship between gut microbiota and inflammasome-mediated pyroptosis provides an important field of research. Bibliometric analysis provides a comprehensive understanding of this relationship, offering valuable insights into emerging research trends.

Materials and methods

Leveraging data spanning from 2014 to 2023 sourced from the Web of Science Core Collection, our analysis was conducted using advanced tools such as SCImago Graphica, VOSviewer, and CiteSpace software. Visualizations were created using GraphPad Prism software. We explored the nuanced aspects of research hotspots, collaborative networks, and developing trends in this field.

Results

A global bibliometric analysis identified 520 relevant studies spanning 41 countries and 887 institutions. Over the past decade, publication trends have shown consistent growth, with China and the United States leading the research output. Southern Medical University and Nanjing Medical University in China emerged as leading institutions in this filed. Prominent contributors include Jia Sun, Yuan Zhang, Wei Chen, Jing Wang, and Hongtao Liu from China, alongside Eicke Latz from Germany. High-impact journals such as Frontiers in Immunology and Nature Communications have been pivotal in disseminating research in this domain. Keyword analysis highlighted a primary focus on gut microbiota, NLRP3 inflammasome, pyroptosis pathways, and inflammatory diseases, themes that persist in recent studies. Furthermore, burst keyword analysis identified "butyrate" as the sole term currently experiencing a marked increase in research interest.

Conclusion

Research has been deeply focused on the gut microbiota and inflammasome triggered pyroptosis in years. Over the past decade, the exploration of how gut microbiota and NLRP3 or NLRP6 inflammasome-mediated pyroptosis has been an area of interest. Future investigations in this filed may primarily revolve around understanding the correlation between butyrate and NLRP3 inflammasome induced pyroptosis in relation to conditions. However, an in-depth analysis, through studies is crucial to uncover and elucidate the complex mechanisms linking these elements.

Recent advances in gut microbiota and thyroid disease: pathogenesis and therapeutics in autoimmune, neoplastic, and nodular conditions

This review synthesizes key findings from the past five years of experimental literature, elucidating the gut microbiome's significant influence on the pathogenesis of thyroid diseases. A pronounced shift in the gut microbiota composition has been consistently observed, with a significant reduction in bacteria such as Bifidobacterium, Bacillaceae, Megamonas, and Clostridium, and a notable increase in bacteria, including Bacteroides, Proteobacteria, Actinobacteria, Desulfobacterota, and Klebsiella. These alterations are implicated in the development and progression of thyroid diseases by impacting metabolic pathways including bile acid and cytokine production, including a decrease in short-chain fatty acids (SCFAs) that are crucial for immune regulation and thyroid hormone homeostasis. The review also highlights the therapeutic implications of probiotics in managing thyroid conditions. Evidence suggests that probiotic adjunct therapy can modulate the gut microbiota, leading to improvements in thyroid function and patient outcomes. The use of specific probiotic strains, such as Lactiplantibacillus plantarum 299v and Bifidobacterium longum, has demonstrated potential in enhancing the effects of traditional treatments and possibly restoring a balanced gut microbiota. Notably, fecal microbiota transplantation (FMT) has emerged as a promising intervention in Graves' Disease (GD), demonstrating the potential to recalibrate the gut microbiota, thereby influencing neurotransmitters and trace elements via the gut-brain and gut-thyroid axes. The integration of microbiome-based therapies with traditional treatments is anticipated to usher in a new era of personalized thyroid disease management, offering a more nuanced approach to patient care. By integrating this body of work, the review offers an innovative perspective on the gut microbiome's broad impact on thyroid diseases and the therapeutic applications of probiotics.

Pyroptosis the Emerging Link Between Gut Microbiota and Multiple Sclerosis

This review elucidates the pivotal role of pyroptosis, triggered by gut microbiota, in the development of multiple sclerosis (MS), emphasizing its significance within the gut-brain axis. Our comprehensive analysis of recent literature reveals how dysbiosis in the gut microbiota of MS patients-characterized by reduced microbial diversity and shifts in bacterial populations-profoundly impacts immune regulation and the integrity of the central nervous system (CNS). Pyroptosis, an inflammatory form of programmed cell death, significantly exacerbates MS by promoting the release of inflammatory cytokines and causing substantial damage to CNS tissues. The gut microbiota facilitates this detrimental process through metabolites such as short-chain fatty acids and neuroactive compounds, or self-structural products like lipopolysaccharides (LPS), which modulate immune responses and influence neuronal survival. This review highlights the potential of modulating gut microbiota to regulate pyroptosis, thereby suggesting that targeting this pathway could be a promising therapeutic strategy to mitigate inflammatory responses and preserve neuronal integrity in patients with MS.