Probiotic bacteria are normal inhabitants of a healthy human gut, conferring multiple beneficial effects on the gut and beyond. Under various disease states, the abundance and diversity of beneficial bacteria are significantly decreased, a process called dysbiosis. Among the intra- and extracellular components of probiotics, the extracellular vesicles (EVs) secreted by them have recently garnered significant attention as potential mediators of probiotics’ effects on host health. Further, these nanosized particles that encapsulate a wide range of bioactive molecules (proteins, lipids, RNA, and DNA) are standing out as key factors that could mediate gut microbiota–host communication and confer ameliorating effects in experimental inflammatory, metabolic, and cardiovascular disease models. However, a standard protocol of EV isolation from probiotic bacteria, not varying from lab to lab, must be established to achieve consistency in the experimental results in these pre-clinical models. Our current study compared two commonly used methods for EV isolation from biological samples, ultracentrifugation and precipitation, to develop a standard protocol for isolating EVs from the probiotics Lactobacillus acidophilus (LA), a Gram-positive bacterium, and Escherichia coli Nissle (EcN), a Gram-negative bacterium. The ultracentrifugation method gave ~1.5-fold higher EV yield for both LA and EcN compared to the precipitation method. Further, EcN released a higher level of EVs compared to LA. EVs were quantified and characterized by nanoparticle-tracking analysis (NTA) and by measuring the specific surface biomarkers using Western blot. Here, we describe our standardized step-by-step protocol for isolating EVs from probiotic bacteria and their characterization.

Growth Differentiation Factor 15 (GDF15), also known as non-steroidal anti-inflammatory drug-activated gene-1 (NAG-1) or macrophage inhibitory cytokine 1 (MIC-1), is a stress- and inflammation-induced cytokine distantly related to the TGF-β superfamily. Its highly elevated levels showed close association with various pathological conditions, making it an emerging biomarker of disease prognosis. However, most GDF15-mediated effects under normal physiology and various pathological conditions are poorly understood. This is partly because the only known GDF15 receptor is exclusively localized in the brain, and how GDF15 functions peripherally is currently unknown. Mounting recent evidence has shown GDF15’s critical role in fibrosis in multiple organs, such as the liver, lung, and kidney. Evidence further suggests that it can either contribute to fibrosis by promoting inflammation and fibroblast activation or confer protective effects by modulating the immune response and mitigating fibrosis severity. Thus, the exact role of GDF15 in fibrosis can vary depending on the organ involved and the specific disease context. For example, increased GDF15 in idiopathic pulmonary fibrosis (IPF) promotes fibrosis via fibroblast activation and collagen deposition. Conversely, GDF15 might have a protective role in liver fibrosis, with decreased GDF15 levels causing increased fibrosis severity, while GDF15 treatment ameliorates fibrosis. Due to its close association with fibrosis, GDF15 is being investigated as a potential biomarker for disease severity and monitoring treatment response. However, further research unraveling its mechanisms of action is needed to explore the potential of GDF15 as a therapeutic target for treating fibrosis, either by modulating its expression or utilizing its immunomodulatory properties. This review marshals the limited studies addressing the recently appreciated differential role of GDF15 in regulating the fibrotic process in different organs. The review also discusses the aspects of further research needed to highlight GDF 15 as a novel predictor and therapeutic target for fibrosis in different organs.

We have recently demonstrated that exosomal communication between endothelial progenitor cells (EPCs) and brain endothelial cells is compromised in hypertensive conditions, which might contribute to the poor outcomes of stroke subjects with hypertension. The present study investigated whether exercise intervention can regulate EPC–exosome (EPC-EX) functions in hypertensive conditions. Bone marrow EPCs from sedentary and exercised hypertensive transgenic mice were used for generating EPC-EXs, denoted as R-EPC-EXs and R-EPC-EX^ET. The exosomal microRNA profile was analyzed, and EX functions were determined in a co-culture system with N2a cells challenged by angiotensin II (Ang II) plus hypoxia. EX-uptake efficiency, cellular survival ability, reactive oxygen species (ROS) production, mitochondrial membrane potential, and the expressions of cytochrome c and superoxide-generating enzyme (Nox4) were assessed. We found that (1) exercise intervention improves the uptake efficiency of EPC-EXs by N2a cells. (2) exercise intervention restores miR-27a levels in R-EPC-EXs. (3) R-EPC-EX^ET improved the survival ability and reduced ROS overproduction in N2a cells challenged with Ang II and hypoxia. (4) R-EPC-EX^ET improved the mitochondrial membrane potential and decreased cytochrome c and Nox4 levels in Ang II plus hypoxia-injured N2a cells. All these effects were significantly reduced by miR-27a inhibitor. Together, these data have demonstrated that exercise-intervened EPC-EXs improved the mitochondrial function of N2a cells in hypertensive conditions, which might be ascribed to their carried miR-27a.

Enteroendocrine cells (EECs) are specialized secretory cells in the gut epithelium that differentiate from intestinal stem cells (ISCs). Mature EECs secrete incretin hormones that stimulate pancreatic insulin secretion and regulate appetite. Decreased EEC numbers and impaired secretion of the incretin glucagon-like peptide-1 (GLP1) have been implicated in obesity-associated metabolic complications. Gut microbial metabolites of dietary tryptophan (TRP) were recently shown to modulate ISC proliferation and differentiation. However, their specific effects on EEC differentiation are not known. We hypothesized that the gut microbial metabolites of dietary tryptophan counteract impaired GLP1 production and function in obesity by stimulating EEC differentiation from ISCs. We utilized complementary models of human and rat intestines to determine the effects of obesity or TRP metabolites on EEC differentiation. EEC differentiation was assessed by the EEC marker chromogranin A (CHGA) levels in the intestinal mucosa of normal versus obese rats. The effects of TRP metabolites on EEC differentiation were determined in human intestinal organoids treated with indole, a primary TRP metabolite, or the culture supernatant of Lactobacillus acidophilus grown in TRP media (LA-CS-TRP). Our results showed that the mRNA and protein levels of CHGA, the EEC marker, were significantly decreased (~60%) in the intestinal mucosa of high-fat-diet-induced obese rat intestines. The expression of the transcription factors that direct the ISC differentiation towards the EEC lineage was also decreased in obesity. In human organoids, treatment with indole or LA-CS-TRP significantly increased (more than 2-fold) CHGA levels, which were blocked by the aryl hydrocarbon receptor (AhR) antagonist CH-223191. Thus, the stimulation of EEC differentiation by colonic microbial metabolites highlights a novel therapeutic role of TRP metabolites in obesity and associated metabolic disorders.

Vascular cognitive impairment and dementia (VCID) encompass a spectrum of cognitive syndromes ranging from mild cognitive impairment to vascular dementia, accounting for approximately 15–20% of all dementia cases and representing the second most common form of dementia. Despite its high prevalence and clinical burden, effective therapeutic strategies remain lacking. Increasing evidence indicates that vascular dysfunction plays a central role in the pathogenesis of VCID by compromising cerebrovascular integrity, impairing endothelial function, and disrupting neurovascular coupling, which collectively contribute to cognitive decline. Stem cells have emerged as promising candidates for promoting vascular repair and neurovascular coupling. Notably, extracellular vesicles (EVs) derived from stem cells exert reparative and protective effects by transferring bioactive molecules that enhance endothelial function and preserve the blood–brain barrier (BBB) function to affected regions. This review summarizes the current knowledge of VCID from a vascular perspective, highlights recent advances in understanding stem cells and their derived EVs in promoting vascular repair and alleviating cognitive decline, and discusses future directions for translating these insights into innovative therapeutic strategies for VCID.

Creatine transporter (CrT1) mediates cellular uptake of creatine (Cr), a nutrient pivotal in maintaining energy homeostasis in various tissues including intestinal epithelial cells (IECs). The impact of CrT1 deficiency on the pathogenesis of various psychiatric and neurological disorders has been extensively investigated. However, there are no studies on its regulation in IECs in health and disease. Current studies have determined differential expression of CrT1 along the length of the mammalian intestine and its dysregulation in inflammatory bowel disease (IBD)-associated inflammation and Adherent Invasive E. coli (AIEC) infection. CrT1 mRNA and protein levels in normal intestines and their alterations in inflammation and following AIEC infection were determined in vitro in model IECs (Caco-2/IEC-6) and in vivo in SAMP1/YitFc mice, a model of spontaneous ileitis resembling human IBD. CrT1 is differentially expressed in different regions of mammalian intestines with its highest expression in jejunum. In vitro, CrT1 function (Na⁺-dependent ¹⁴C-Cr uptake), expression and promoter activity significantly decreased following TNFα/IL1β treatments and AIEC infection. SAMP1 mice and ileal organoids generated from SAMP1 mice also showed decreased CrT1 mRNA and protein compared to AKR controls. Our studies suggest that Cr deficiency in IECs secondary to CrT1 dysregulation could be a key factor contributing to IBD pathogenesis.