G protein-coupled receptors for energy metabolites as new therapeutic targets. Nat Rev Drug Discov. 2012;11:603-619. [PMID: 22790105 DOI: 10.1038/nrd3777]

G-protein-coupled receptor 84 regulates acute inflammation in normal and diabetic skin wounds

Lipids have emerged as potent regulators of immune cell function. In the skin, adipocyte lipolysis increases the local pool of free fatty acids and is essential for coordinating early macrophage inflammation following injury. Here, we investigate G-protein-coupled receptor 84 (GPR84), a medium-chain fatty acid (MCFA) receptor, for its potential to propagate pro-inflammatory signaling after skin injury. GPR84 signaling was identified as a key component of regulating myeloid cell numbers and subsequent tissue repair through in vivo administration of a pharmacological antagonist and the MCFA decanoic acid. We found that impaired injury-induced dermal adipocyte lipolysis is a hallmark of diabetes, and lipidomic analysis demonstrated that MCFAs are significantly reduced in diabetic murine wounds. Furthermore, local administration of decanoic acid rescued myeloid cell numbers and tissue repair during diabetic wound healing. Thus, GPR84 is a readily targetable lipid signaling pathway for manipulating injury-induced tissue inflammation with beneficial effects on acute diabetic healing.

Clostridium butyricum upregulates GPR109A/AMPK/PGC-1α and ameliorates acute pancreatitis-associated intestinal barrier injury in mice

Acute pancreatitis frequently causes intestinal barrier damage, which aggravates pancreatitis. Although Clostridium butyricum exerts anti-inflammatory and protective effects on the intestinal barrier during acute pancreatitis, the underlying mechanism is unclear. The G protein-coupled receptors 109 A (GPR109A) and adenosine monophosphate-activated protein kinase (AMPK)/ peroxisome proliferator-activated receptor-gamma coactivator 1 alpha (PGC-1α) signaling pathways can potentially influence the integrity of the intestinal barrier. Our study generated acute pancreatitis mouse models via intraperitoneal injection of cerulein and lipopolysaccharides. After intervention with Clostridium butyricum, the model mice showed reduced small intestinal and colonic intestinal barrier damage, dysbiosis amelioration, and increased GPR109A/AMPK/PGC-1α expression. In conclusion, Clostridium butyricum could improve pancreatic and intestinal inflammation and pancreatic injury, and relieve acute pancreatitis-induced intestinal barrier damage in the small intestine and colon, which may be associated with GPR109A/AMPK/PGC-1α.

Short-Chain Fatty Acids and Human Health: From Metabolic Pathways to Current Therapeutic Implications

The gastrointestinal tract is home to trillions of diverse microorganisms collectively known as the gut microbiota, which play a pivotal role in breaking down undigested foods, such as dietary fibers. Through the fermentation of these food components, short-chain fatty acids (SCFAs) such as acetate, propionate, and butyrate are produced, offering numerous health benefits to the host. The production and absorption of these SCFAs occur through various mechanisms within the human intestine, contingent upon the types of dietary fibers reaching the gut and the specific microorganisms engaged in fermentation. Medical literature extensively documents the supplementation of SCFAs, particularly butyrate, in the treatment of gastrointestinal, metabolic, cardiovascular, and gut-brain-related disorders. This review seeks to provide an overview of the dynamics involved in the production and absorption of acetate, propionate, and butyrate within the human gut. Additionally, it will focus on the pivotal roles these SCFAs play in promoting gastrointestinal and metabolic health, as well as their current therapeutic implications.

Autoinducer-2 promotes the colonization of Lactobacillus rhamnosus GG to improve the intestinal barrier function in a neonatal mouse model of antibiotic-induced intestinal dysbiosis

BACKGROUND

Human health is seriously threatened by antibiotic-induced intestinal disorders. Herein, we aimed to determine the effects of Autoinducer-2 (AI-2) combined with Lactobacillus rhamnosus GG (LGG) on the intestinal barrier function of antibiotic-induced intestinal dysbiosis neonatal mice.

METHODS

An antibiotic-induced intestinal dysbiosis neonatal mouse model was created using antibiotic cocktails, and the model mice were randomized into the control, AI-2, LGG, and LGG + AI-2 groups. Intestinal short-chain fatty acids and AI-2 concentrations were detected by mass spectrometry and chemiluminescence, respectively. The community composition of the gut microbiota was analyzed using 16S rDNA sequencing, and biofilm thickness and bacterial adhesion in the colon were assessed using scanning electron microscopy. Transcriptome RNA sequencing of intestinal tissues was performed, and the mRNA and protein levels of HCAR2 (hydroxycarboxylic acid receptor 2), claudin3, and claudin4 in intestinal tissues were determined using quantitative real-time reverse transcription PCR and western blotting. The levels of inflammatory factors in intestinal tissues were evaluated using enzyme-linked immunosorbent assays (ELISAs). D-ribose, an inhibitor of AI-2, was used to treat Caco-2 cells in vitro.

RESULTS

Compared with the control, AI-2, and LGG groups, the LGG + AI-2 group showed increased levels of intestinal AI-2 and proportions of Firmicutes and Lacticaseibacillus, but a reduced fraction of Proteobacteria. Specifically, the LGG + AI-2 group had considerably more biofilms and LGG on the colon surface than those of other three groups. Meanwhile, the combination of AI-2 and LGG markedly increased the concentration of butyric acid and promoted Hcar2, claudin3 and claudin4 expression levels compared with supplementation with LGG or AI-2 alone. The ELISAs revealed a significantly higher tumor necrosis factor alpha (TNF-α) level in the control group than in the LGG and LGG + AI-2 groups, whereas the interleukin 10 (IL-10) level was significantly higher in the LGG + AI-2 group than in the other three groups. In vitro, D-ribose treatment dramatically suppressed the increased levels of Hcar2, claudin3, and claudin4 in Caco-2 cells induced by AI-2 + LGG.

CONCLUSIONS

AI-2 promotes the colonization of LGG and biofilm formation to improve intestinal barrier function in an antibiotic-induced intestinal dysbiosis neonatal mouse model.

Ketosis prevents abdominal aortic aneurysm rupture through C-C chemokine receptor type 2 downregulation and enhanced extracellular matrix balance

Abdominal aortic aneurysms (AAAs) are prevalent with aging, and AAA rupture is associated with increased mortality. There is currently no effective medical therapy to prevent AAA rupture. The monocyte chemoattractant protein (MCP-1)/C-C chemokine receptor type 2 (CCR2) axis critically regulates AAA inflammation, matrix-metalloproteinase (MMP) production, and extracellular matrix (ECM) stability. We therefore hypothesized that a diet intervention that can modulate CCR2 axis may therapeutically impact AAA risk of rupture. Since ketone bodies (KBs) can trigger repair mechanisms in response to inflammation, we evaluated whether systemic ketosis in vivo could reduce CCR2 and AAA progression. Male Sprague-Dawley rats underwent surgical AAA formation using porcine pancreatic elastase and received daily β-aminopropionitrile to promote AAA rupture. Rats with AAAs received either a standard diet, ketogenic diet (KD), or exogenous KBs (EKB). Rats receiving KD and EKB reached a state of ketosis and had significant reduction in AAA expansion and incidence of rupture. Ketosis also led to significantly reduced aortic CCR2 content, improved MMP balance, and reduced ECM degradation. Consistent with these findings, we also observed that Ccr2-/- mice have significantly reduced AAA expansion and rupture. In summary, this study demonstrates that CCR2 is essential for AAA expansion, and that its modulation with ketosis can reduce AAA pathology. This provides an impetus for future clinical studies that will evaluate the impact of ketosis on human AAA disease.

Microbiota-Induced Epigenetic Alterations in Depressive Disorders Are Targets for Nutritional and Probiotic Therapies

Major depressive disorder (MDD) is a complex disorder and a leading cause of disability in 280 million people worldwide. Many environmental factors, such as microbes, drugs, and diet, are involved in the pathogenesis of depressive disorders. However, the underlying mechanisms of depression are complex and include the interaction of genetics with epigenetics and the host immune system. Modifications of the gut microbiome and its metabolites influence stress-related responses and social behavior in patients with depressive disorders by modulating the maturation of immune cells and neurogenesis in the brain mediated by epigenetic modifications. Here, we discuss the potential roles of a leaky gut in the development of depressive disorders via changes in gut microbiota-derived metabolites with epigenetic effects. Next, we will deliberate how altering the gut microbiome composition contributes to the development of depressive disorders via epigenetic alterations. In particular, we focus on how microbiota-derived metabolites such as butyrate as an epigenetic modifier, probiotics, maternal diet, polyphenols, drugs (e.g., antipsychotics, antidepressants, and antibiotics), and fecal microbiota transplantation could positively alleviate depressive-like behaviors by modulating the epigenetic landscape. Finally, we will discuss challenges associated with recent therapeutic approaches for depressive disorders via microbiome-related epigenetic shifts, as well as opportunities to tackle such problems.

Conjugation with glucagon like peptide-1 enables targeted protein degradation

Lysosome-targeting chimeras (LYTACs) have emerged as a promising technique to extend the scope of targeted protein degradation to extracellular proteins, e.g., secreted proteins and membrane-anchored proteins. However, up to now, only a small number of lysosomal targeting receptors (LTRs), such as cation-independent mannose 6-phosphate receptor (CI-M6PR) and asialoglycoprotein receptor (ASGPR), were reported to build LYTACs for degradation of extracellular proteins. Therefore, it is important to explore more functionalized ligands for the relevant LTRs to expand the LYTAC framework. Herein, we demonstrate a new LTR ligand-glucagon like peptide 1 (GLP-1) based targeted degradation platform, termed GLP-1 receptor-targeting chimeras (GLP-1-LYTAC). GLP-1-LYTACs are formed by conjugating GLP-1 with targeted binder (such as antibody) through Click Chemistry, showing efficiently lysosomal degradation of both extracellular proteins (GFP and Neutravidin) as well as cell membrane proteins (EGFR and PD-L1). We believe that this novel GLP-1-LYTAC will open up a new dimension for targeted protein breakdown.

Ebola Virus Infection Induces HCAR2 Expression Leading to Cell Death

Ebola virus (EBOV) induces cell death not only in infected permissive cells but also in nonpermissive, bystander cells by employing different mechanisms. Hydroxycarboxylic acid receptor 2 (HCAR2) has been reported to be involved in apoptotic cell death. We previously reported an increase in the expression of HCAR2-specific mRNA in EBOV-infected individuals with fatal outcomes. Here, we report that infection with an EBOV lacking the VP30 gene (EBOVΔVP30) results in the upregulation of HCAR2 mRNA expression in human hepatocyte Huh7.0 cells stably expressing VP30. Transient overexpression of HCAR2 reduced the viability of Huh7.0 cells and human embryonic kidney cells. Phosphatidylserine externalization and cell membrane permeabilization by HCAR2 overexpression was also observed. Interestingly, coexpression of HCAR2 with EBOV VP40 further reduced cell viability in transfected cells compared to HCAR2 coexpression with other viral proteins. Our data suggest that HCAR2 may contribute to EBOV-induced cell death.

Rules and mechanisms governing G protein coupling selectivity of GPCRs

G protein-coupled receptors (GPCRs) convert extracellular stimuli into intracellular signaling by coupling to heterotrimeric G proteins of four classes: Gi/o, Gq, Gs, and G12/13. However, our understanding of the G protein selectivity of GPCRs is incomplete. Here, we quantitatively measure the enzymatic activity of GPCRs in living cells and reveal the G protein selectivity of 124 GPCRs with the exact rank order of their G protein preference. Using this information, we establish a classification of GPCRs by functional selectivity, discover the existence of a G12/13-coupled receptor, G15-coupled receptors, and a variety of subclasses for Gi/o-, Gq-, and Gs-coupled receptors, culminating in development of the predictive algorithm of G protein selectivity. We further identify the structural determinants of G protein selectivity, allowing us to synthesize non-existent GPCRs with de novo G protein selectivity and efficiently identify putative pathogenic variants.

The mechanism of oleic acid inhibiting platelet activation stimulated by collagen

BACKGROUND

Abnormal platelet activation is a key factor in the occurrence and development of thrombotic diseases. However, the physiological mechanisms that underlie platelet homeostasis remain unclear. Oleic acid, one of the most abundant lipids in the human diet, has potential antithrombotic effects. This study aimed to investigate the effects of oleic acid on platelet activation and thrombosis.

METHODS

Platelet aggregation, ATP release, and fibrinogen spread were evaluated to determine the role of oleic acid in platelet activation. A ferric chloride-induced carotid injury model was used to establish the effect of oleic acid on thrombus formation in vivo. Western blotting analysis and transfection experiments were performed to determine the mechanisms involved in this process.

RESULTS

Oleic acid inhibited platelet aggregation, granule release, and calcium mobilization. Furthermore, it inhibited the spread of platelets on fibrinogen. We also found that oleic acid delayed arterial thrombosis in mice, as demonstrated in a murine model of ferric chloride-induced carotid artery thrombosis. The molecular mechanism of its inhibition of platelet activity may be through the Syk-PLCγ2 and CaMKKβ/AMPKα/VASP pathways. In addition, we demonstrated that the phosphorylation of AMPK at Ser496 was an important mechanism of platelet activation.

CONCLUSIONS

Our study showed that oleic acid inhibits platelet activation and reduces thrombogenesis by inhibiting the phosphorylation of multiple signaling molecules, offering new insights into the research and development of antiplatelet drugs. Video Abstract.

Niacin modulates depressive-like behavior in experimental colitis through GPR109A-dependent mechanisms

AIMS

Depression is one of the common neurological comorbidities in patients with inflammatory bowel disease (IBD). The current study aimed to investigate the potential impact of niacin on colitis-induced depressive-like behavior in rats.

MATERIALS AND METHODS

Animals were given 5 % dextran sulfate sodium (DSS) in drinking water for one week to induce colitis. Niacin (80 mg/kg), with or without mepenzolate bromide (GPR109A blocker), was administered once per day throughout the experimental period. Rats were tested for behavioral changes using open field and forced swimming tests.

KEY FINDINGS

Niacin significantly ameliorated DSS-induced behavioral deficits and alleviated macroscopic and microscopic colonic inflammatory changes. It also augmented the hippocampal levels of ZO-1, occludin, and claudin-5 proteins, indicating the ability of niacin to restore the blood-brain barrier (BBB) integrity. Moreover, niacin decreased hippocampal IL-1ꞵ and NF-ĸB contents but increased GSH, Sirt-1, Nrf-2, HO-1 concentrations. All these beneficial effects were partially abolished by the co-administration of mepenzolate bromide.

SIGNIFICANCE

The neuroprotective effect of niacin against DSS-induced depressive-like behavior was partially mediated through GPR109A-mediated mechanisms. Such mechanisms are also involved in modulating neuronal oxidative stress and inflammation via Sirt-1/Nrf-2/HO-1 signaling pathways.

Whole-Blood Metabolomics of a Rat Model of Repetitive Concussion

Mild traumatic brain injury (mTBI) and repetitive mTBI (RmTBI) are silent epidemics, and so far, there is no objective diagnosis. The severity of the injury is solely based on the Glasgow Coma Score (GCS) scale. Most patients suffer from one or more behavioral abnormalities, such as headache, amnesia, cognitive decline, disturbed sleep pattern, anxiety, depression, and vision abnormalities. Additionally, most neuroimaging modalities are insensitive to capture structural and functional alterations in the brain, leading to inefficient patient management. Metabolomics is one of the established omics technologies to identify metabolic alterations, mostly in biofluids. NMR-based metabolomics provides quantitative metabolic information with non-destructive and minimal sample preparation. We employed whole-blood NMR analysis to identify metabolic markers using a high-field NMR spectrometer (800 MHz). Our approach involves chemical-free sample pretreatment and minimal sample preparation to obtain a robust whole-blood metabolic profile from a rat model of concussion. A single head injury was given to the mTBI group, and three head injuries to the RmTBI group. We found significant alterations in blood metabolites in both mTBI and RmTBI groups compared with the control, such as alanine, branched amino acid (BAA), adenosine diphosphate/adenosine try phosphate (ADP/ATP), creatine, glucose, pyruvate, and glycerphosphocholine (GPC). Choline was significantly altered only in the mTBI group and formate in the RmTBI group compared with the control. These metabolites corroborate previous findings in clinical and preclinical cohorts. Comprehensive whole-blood metabolomics can provide a robust metabolic marker for more accurate diagnosis and treatment intervention for a disease population.

A Multi-Omics and Human Biomonitoring Approach to Assessing the Effectiveness of Fortified Balanced Energy-Protein Supplementation on Maternal and Newborn Health in Burkina Faso: A Study Protocol

Fortified balanced energy-protein (BEP) supplementation is a promising intervention for improving maternal health, birth outcomes and infant growth in low- and middle-income countries. This nested biospecimen sub-study aimed to evaluate the physiological effect of multi-micronutrient-fortified BEP supplementation on pregnant and lactating women and their infants. Pregnant women (15-40 years) received either fortified BEP and iron-folic acid (IFA) (intervention) or IFA only (control) throughout pregnancy. The same women were concurrently randomized to receive either a fortified BEP supplement during the first 6 months postpartum in combination with IFA for the first 6 weeks (i.e., intervention) or the postnatal standard of care, which comprised IFA alone for 6 weeks postpartum (i.e., control). Biological specimens were collected at different timepoints. Multi-omics profiles will be characterized to assess the mediating effect of BEP supplementation on the different trial arms and its effect on maternal health, as well as birth and infant growth outcomes. The mediating effect of the exposome in the relationship between BEP supplementation and maternal health, birth outcomes and infant growth were characterized via biomonitoring markers of air pollution, mycotoxins and environmental contaminants. The results will provide holistic insight into the granular physiological effects of prenatal and postnatal BEP supplementation.

Regulation of dietary fiber on intestinal microorganisms and its effects on animal health

The animal gut harbors diverse microbes that play an essential role in the well-being of their host. Specific diets, such as those rich in dietary fiber, are vital in disease prevention and treatment because they affect intestinal flora and have a positive impact on the metabolism, immunity, and intestinal function of the host. Dietary fiber can provide energy to colonic epithelial cells, regulate the structure and metabolism of intestinal flora, promote the production of intestinal mucosa, stimulate intestinal motility, improve glycemic and lipid responses, and regulate the digestion and absorption of nutrients, which is mainly attributed to short-chain fatty acids (SCFA), which is the metabolite of dietary fiber. By binding with G protein-coupled receptors (including GPR41, GPR43 and GPR109A) and inhibiting the activity of histone deacetylases, SCFA regulate appetite and glucolipid metabolism, promote the function of the intestinal barrier, alleviate oxidative stress, suppress inflammation, and maintain immune system homeostasis. This paper reviews the physicochemical properties of dietary fiber, the interaction between dietary fiber and intestinal microorganisms, the role of dietary fiber in maintaining intestinal health, and the function of SCFA, the metabolite of dietary fiber, in inhibiting inflammation. Furthermore, we consider the effects of dietary fiber on the intestinal health of pigs, the reproduction and lactation performance of sows, and the growth performance and meat quality of pigs.

Stratification of enterochromaffin cells by single-cell expression analysis

Dynamic interactions between gut mucosal cells and the external environment are essential to maintain gut homeostasis. Enterochromaffin (EC) cells transduce both chemical and mechanical signals and produce 5-hydroxytryptamine (5-HT) to mediate disparate physiological responses. However, the molecular and cellular basis for functional diversity of ECs remains to be adequately defined. Here, we integrated single-cell transcriptomics with spatial image analysis to identify fourteen EC clusters that are topographically organized along the gut. Subtypes predicted to be sensitive to the chemical environment and mechanical forces were identified that express distinct transcription factors and hormones. A Piezo2+ population in the distal colon was endowed with a distinctive neuronal signature. Using a combination of genetic, chemogenetic and pharmacological approaches, we demonstrated Piezo2+ ECs are required for normal colon motility. Our study constructs a molecular map for ECs and offers a framework for deconvoluting EC cells with pleiotropic functions.

New Therapeutics for Heart Failure: Focusing on cGMP Signaling

Current drugs for treating heart failure (HF), for example, angiotensin II receptor blockers and β-blockers, possess specific target molecules involved in the regulation of the cardiac circulatory system. However, most clinically approved drugs are effective in the treatment of HF with reduced ejection fraction (HFrEF). Novel drug classes, including angiotensin receptor blocker/neprilysin inhibitor (ARNI), sodium-glucose co-transporter-2 (SGLT2) inhibitor, hyperpolarization-activated cyclic nucleotide-gated (HCN) channel blocker, soluble guanylyl cyclase (sGC) stimulator/activator, and cardiac myosin activator, have recently been introduced for HF intervention based on their proposed novel mechanisms. SGLT2 inhibitors have been shown to be effective not only for HFrEF but also for HF with preserved ejection fraction (HFpEF). In the myocardium, excess cyclic adenosine monophosphate (cAMP) stimulation has detrimental effects on HFrEF, whereas cyclic guanosine monophosphate (cGMP) signaling inhibits cAMP-mediated responses. Thus, molecules participating in cGMP signaling are promising targets of novel drugs for HF. In this review, we summarize molecular pathways of cGMP signaling and clinical trials of emerging drug classes targeting cGMP signaling in the treatment of HF.

The proteomic effects of ketone bodies: implications for proteostasis and brain proteinopathies

A growing body of evidence supports the beneficial effects of the ketone bodies (KBs), acetoacetate and β-hydroxybutyrate (BHB), on diverse physiological processes and diseases. Hence, KBs have been suggested as therapeutic tools for neurodegenerative diseases. KBs are an alternative fuel during fasting and starvation as they can be converted to Ac-CoA to produce ATP. A ketogenic diet (KD), enriched in fats and low in carbohydrates, induces KB production in the liver and favors their use in the brain. BHB is the most abundant KB in the circulation; in addition to its role as energy fuel, it exerts many actions that impact the set of proteins in the cell and tissue. BHB can covalently bind to proteins in lysine residues as a new post-translational modification (PTM) named β-hydroxybutyrylation (Kbhb). Kbhb has been identified in many proteins where Kbhb sites can be critical for binding to other proteins or cofactors. Kbhb is mostly found in proteins involved in chromatin structure, DNA repair, regulation of spliceosome, transcription, and oxidative phosphorylation. Histones are the most studied family of proteins with this PTM, and H3K9bhb is the best studied histone mark. Their target genes are mainly related to cell metabolism, chromatin remodeling and the control of circadian rhythms. The role of Kbhb on physiological processes is poorly known, but it might link KB metabolism to cell signaling and genome regulation. BHB also impacts the proteome by influencing proteostasis. This KB can modulate the Unfolded Protein Response (UPR) and autophagy, two processes involved in the maintenance of protein homeostasis through the clearance of accumulated unfolded and damaged proteins. BHB can support proteostasis and regulate the UPR to promote metabolism adaptation in the liver and prevent cell damage in the brain. Also, BHB stimulates autophagy aiding to the degradation of accumulated proteins. Protein aggregation is common to proteinopathies like Alzheimer's (AD) and Parkinson's (PD) diseases, where the KD and BHB treatment have shown favorable effects. In the present review, the current literature supporting the effects of KBs on proteome conformation and proteostasis is discussed, as well as its possible impact on AD and PD.

Swine gut microbiome associated with non-digestible carbohydrate utilization

Non-digestible carbohydrates are an unavoidable component in a pig's diet, as all plant-based feeds contain different kinds of non-digestible carbohydrates. The major types of non-digestible carbohydrates include non-starch polysaccharides (such as cellulose, pectin, and hemicellulose), resistant starch, and non-digestible oligosaccharides (such as fructo-oligosaccharide and xylo-oligosaccharide). Non-digestible carbohydrates play a significant role in balancing the gut microbial ecology and overall health of the swine by promoting the production of short chain fatty acids. Although non-digestible carbohydrates are rich in energy, swine cannot extract this energy on their own due to the absence of enzymes required for their degradation. Instead, they rely on gut microbes to utilize these carbohydrates for energy production. Despite the importance of non-digestible carbohydrate degradation, limited studies have been conducted on the swine gut microbes involved in this process. While next-generation high-throughput sequencing has aided in understanding the microbial compositions of the swine gut, specific information regarding the bacteria involved in non-digestible carbohydrate degradation remains limited. Therefore, it is crucial to investigate and comprehend the bacteria responsible for the breakdown of non-digestible carbohydrates in the gut. In this mini review, we have discussed the major bacteria involved in the fermentation of different types of non-digestible carbohydrates in the large intestine of swine, shedding light on their potential roles and contributions to swine nutrition and health.

Low Glucose plus β-Hydroxybutyrate Induces an Enhanced Inflammatory Response in Yak Alveolar Macrophages via Activating the GPR109A/NF-κB Signaling Pathway

Yaks are often subject to long-term starvation and a high prevalence of respiratory diseases and mortality in the withered season, yet the mechanisms that cause this remain unclear. Research has demonstrated that β-hydroxybutyrate (BHB) plays a significant role in regulating the immune system. Hence, we hypothesize that the low glucose and high BHB condition induced by severe starvation might have an effect on the pro-inflammatory response of the alveolar macrophages (AMs) in yaks. To validate our hypothesis, we isolated and identified primary AMs from freshly slaughtered yaks and cultured them in a medium with 5.5 mM of glucose or 2.8 mM of glucose plus 1-4 mM of BHB. Utilizing a real-time quantitative polymerase chain reaction (RT-qPCR), immunoblot assay, and enzyme-linked immunosorbent assay (ELISA), we evaluated the gene and protein expression levels of GPR109A (G-protein-coupled receptor 109A), NF-κB p65, p38, and PPARγ and the concentrations of pro-inflammatory cytokines interleukin (IL)-1β and IL-6 and tumor necrosis factor (TNF)-α in the supernatant. The results demonstrated that AMs exposed to low glucose plus BHB had significantly higher levels of IL-1β, IL-6, and TNF-α (p < 0.05) and higher activity of the GPR109A/NF-κB signaling pathway. A pretreatment of either pertussis toxin (PTX, inhibitor of GPR109A) or pyrrolidinedithiocarbamic (PDTC, inhibitor of NF-κB p65) was effective in preventing the elevated secretion of pro-inflammatory cytokines induced by low glucose plus BHB (p < 0.05). These results indicated that the low glucose plus BHB condition would induce an enhanced pro-inflammatory response through the activation of the GPR109A/NF-κB signaling pathway in primary yak AMs, which is probably the reason why yaks experience a higher rate of respiratory diseases and mortality. This study will offer new insight into the prevention and treatment of bovine respiratory diseases.

The Promise of Niacin in Neurology

Niacin (vitamin B3) is an essential nutrient that treats pellagra, and prior to the advent of statins, niacin was commonly used to counter dyslipidemia. Recent evidence has posited niacin as a promising therapeutic for several neurological disorders. In this review, we discuss the biochemistry of niacin, including its homeostatic roles in NAD+ supplementation and metabolism. Niacin also has roles outside of metabolism, largely through engaging hydroxycarboxylic acid receptor 2 (Hcar2). These receptor-mediated activities of niacin include regulation of immune responses, phagocytosis of myelin debris after demyelination or of amyloid beta in models of Alzheimer's disease, and cholesterol efflux from cells. We describe the neurological disorders in which niacin has been investigated or has been proposed as a candidate medication. These are multiple sclerosis, Alzheimer's disease, Parkinson's disease, glioblastoma and amyotrophic lateral sclerosis. Finally, we explore the proposed mechanisms through which niacin may ameliorate neuropathology. While several questions remain, the prospect of niacin as a therapeutic to alleviate neurological impairment is promising.

Pathophysiological mechanisms and therapeutic approaches in obstructive sleep apnea syndrome

Obstructive sleep apnea syndrome (OSAS) is a common breathing disorder in sleep in which the airways narrow or collapse during sleep, causing obstructive sleep apnea. The prevalence of OSAS continues to rise worldwide, particularly in middle-aged and elderly individuals. The mechanism of upper airway collapse is incompletely understood but is associated with several factors, including obesity, craniofacial changes, altered muscle function in the upper airway, pharyngeal neuropathy, and fluid shifts to the neck. The main characteristics of OSAS are recurrent pauses in respiration, which lead to intermittent hypoxia (IH) and hypercapnia, accompanied by blood oxygen desaturation and arousal during sleep, which sharply increases the risk of several diseases. This paper first briefly describes the epidemiology, incidence, and pathophysiological mechanisms of OSAS. Next, the alterations in relevant signaling pathways induced by IH are systematically reviewed and discussed. For example, IH can induce gut microbiota (GM) dysbiosis, impair the intestinal barrier, and alter intestinal metabolites. These mechanisms ultimately lead to secondary oxidative stress, systemic inflammation, and sympathetic activation. We then summarize the effects of IH on disease pathogenesis, including cardiocerebrovascular disorders, neurological disorders, metabolic diseases, cancer, reproductive disorders, and COVID-19. Finally, different therapeutic strategies for OSAS caused by different causes are proposed. Multidisciplinary approaches and shared decision-making are necessary for the successful treatment of OSAS in the future, but more randomized controlled trials are needed for further evaluation to define what treatments are best for specific OSAS patients.

The anorectic and thermogenic effects of pharmacological lactate in male mice are confounded by treatment osmolarity and co-administered counterions

Lactate is a circulating metabolite and a signalling molecule with pleiotropic physiological effects. Studies suggest that lactate modulates energy balance by lowering food intake, inducing adipose browning and increasing whole-body thermogenesis. Yet, like many other metabolites, lactate is often commercially produced as a counterion-bound salt and typically administered in vivo through hypertonic aqueous solutions of sodium L-lactate. Most studies have not controlled for injection osmolarity and the co-injected sodium ions. Here, we show that the anorectic and thermogenic effects of exogenous sodium L-lactate in male mice are confounded by the hypertonicity of the injected solutions. Our data reveal that this is in contrast to the antiobesity effect of orally administered disodium succinate, which is uncoupled from these confounders. Further, our studies with other counterions indicate that counterions can have confounding effects beyond lactate pharmacology. Together, these findings underscore the importance of controlling for osmotic load and counterions in metabolite research.

RGA1 alleviates low-light-repressed pollen tube elongation by improving the metabolism and allocation of sugars and energy

Low-light stress compromises photosynthetic and energy efficiency and leads to spikelet sterility; however, the effect of low-light stress on pollen tube elongation in the pistil remains poorly understood. The gene RGA1, which encodes a Gα-subunit of the heterotrimeric G-protein, enhanced low-light tolerance at anthesis by preventing the cessation of pollen tube elongation in the pistil of rice plants. In this process, marked increases in the activities of acid invertase (INV), sucrose synthase (SUS) and mitochondrial respiratory electron transport chain complexes, as well as the relative expression levels of SUTs (sucrose transporter), SWEETs (sugars will eventually be exported transporters), SUSs, INVs, CINs (cell-wall INV 1), SnRK1A (sucrose-nonfermenting 1-related kinase 1) and SnRK1B, were observed in OE-1 plants. Accordingly, notable increases in contents of ATP and ATPase were presented in OE-1 plants under low-light conditions, while they were decreased in d1 plants. Importantly, INV and ATPase activators (sucrose and Na₂ SO₃ , respectively) increased spikelet fertility by improving the energy status in the pistil under low-light conditions, and the ATPase inhibitor Na₂ VO₄ induced spikelet sterility and decreased ATPase activity. These results suggest that RGA1 could alleviate the low-light stress-induced impairment of pollen tube elongation to increase spikelet fertility by promoting sucrose unloading in the pistil and improving the metabolism and allocation of energy.

A comprehensive molecular profiling approach reveals metabolic alterations that steer bone tissue regeneration

Bone regeneration after fracture is a complex process with high and dynamic energy demands. The impact of metabolism on bone healing progression and outcome, however, is so far understudied. Our comprehensive molecular profiling reveals that central metabolic pathways, such as glycolysis and the citric acid cycle, are differentially activated between rats with successful or compromised bone regeneration (young versus aged female Sprague-Dawley rats) early in the inflammatory phase of bone healing. We also found that the citric acid cycle intermediate succinate mediates individual cellular responses and plays a central role in successful bone healing. Succinate induces IL-1β in macrophages, enhances vessel formation, increases mesenchymal stromal cell migration, and potentiates osteogenic differentiation and matrix formation in vitro. Taken together, metabolites-here particularly succinate-are shown to play central roles as signaling molecules during the onset of healing and in steering bone tissue regeneration.

Ketosis Prevents Abdominal Aortic Aneurysm Rupture Through CCR2 Downregulation and Enhanced MMP Balance

Abdominal aortic aneurysms (AAAs) are common in aging populations, and AAA rupture is associated with high morbidity and mortality. There is currently no effective medical preventative therapy for AAAs to avoid rupture. It is known that the monocyte chemoattractant protein (MCP-1) / C-C chemokine receptor type 2 (CCR2) axis critically regulates AAA tissue inflammation, matrix-metalloproteinase (MMP) production, and in turn extracellular matrix (ECM) stability. However, therapeutic modulation of the CCR2 axis for AAA disease has so far not been accomplished. Since ketone bodies (KBs) are known to trigger repair mechanisms in response to vascular tissue inflammation, we evaluated whether systemic in vivo ketosis can impact CCR2 signaling, and therefore impact AAA expansion and rupture. To evaluate this, male Sprague-Dawley rats underwent surgical AAA formation using porcine pancreatic elastase (PPE), and received daily β-aminopropionitrile (BAPN) to promote AAA rupture. Animals with formed AAAs received either a standard diet (SD), ketogenic diet (KD), or exogenous KB supplements (EKB). Animals that received KD and EKB reached a state of ketosis, and had significantly reduced AAA expansion and incidence of rupture. Ketosis also led to significantly reduced CCR2, inflammatory cytokine content, and infiltrating macrophages in AAA tissue. Additionally, animals in ketosis had improved balance in aortic wall matrix-metalloproteinase (MMP), reduced extracellular matrix (ECM) degradation, and higher aortic media Collagen content. This study demonstrates that ketosis plays an important therapeutic role in AAA pathobiology, and provides the impetus for future studies investigating the role of ketosis as a preventative strategy for individuals with AAAs.

Gut microbiome dysregulation drives bone damage in broiler tibial dyschondroplasia by disrupting glucose homeostasis

Tibial dyschondroplasia (TD) with multiple incentives is a metabolic skeletal disease that occurs in fast-growing broilers. Perturbations in the gut microbiota (GM) have been shown to affect bone homoeostasis, but the mechanisms by which GM modulates bone metabolism in TD broilers remain unknown. Here, using a broiler model of TD, we noted elevated blood glucose (GLU) levels in TD broilers, accompanied by alterations in the pancreatic structure and secretory function and damaged intestinal barrier function. Importantly, faecal microbiota transplantation (FMT) of gut microbes from normal donors rehabilitated the GM and decreased the elevated GLU levels in TD broilers. A high GLU level is a predisposing factor to bone disease, suggesting that GM dysbiosis-mediated hyperglycaemia might be involved in bone regulation. 16S rRNA gene sequencing and short-chain fatty acid analysis revealed that the significantly increased level of the metabolite butyric acid derived from the genera Blautia and Coprococcus regulated GLU levels in TD broilers by binding to GPR109A in the pancreas. Tibial studies showed reduced expression of vascular regulatory factors (including PI3K, AKT and VEFGA) based on transcriptomics analysis and reduced vascular distribution, contributing to nonvascularization of cartilage in the proximal tibial growth plate of TD broilers with elevated GLU levels. Additionally, treatment with the total flavonoids from Rhizoma drynariae further validated the improvement in bone homoeostasis in TD broilers by regulating GLU levels through the regulation of GM to subsequently improve intestinal and pancreatic function. These findings clarify the critical role of GM-mediated changes in GLU levels via the gut-pancreas axis in bone homoeostasis in TD chickens.

Ketogenic diet alleviates renal fibrosis in mice by enhancing fatty acid oxidation through the free fatty acid receptor 3 pathway

Introduction

The ketogenic diet (KD), as a dietary intervention, has gained importance in the treatment of solid organ structural remodeling, but its role in renal fibrosis has not been explored.

Methods

Male C57BL/6 mice were fed a normal diet or a KD for 6 weeks prior to unilateral ureteral obstruction (UUO), a well-established in vivo model of renal fibrosis in rodents. Seven days after UUO, serum and kidney samples were collected. Serum β-hydroxybutyrate (β-OHB) concentrations and renal fibrosis were assessed. NRK52E cells were treated with TGFβ1, a fibrosis-inducing cytokine, and with or without β-OHB, a ketone body metabolized by KD, to investigate the mechanism underlying renal fibrosis.

Results

KD significantly enhanced serum β-OHB levels in mice. Histological analysis revealed that KD alleviated structural destruction and fibrosis in obstructed kidneys and reduced the expression of the fibrosis protein markers α-SMA, Col1a1, and Col3a1. Expression of the rate-limiting enzymes involved in fatty acid oxidation (FAO), Cpt1a and Acox1, significantly decreased after UUO and were upregulated by KD. However, the protective effect of KD was abolished by etomoxir (a Cpt1a inhibitor). Besides, our study observed that KD significantly suppressed UUO-induced macrophage infiltration and the expression of IL-6 in the obstructive kidneys. In NRK52E cells, fibrosis-related signaling was increased by TGFβ1 and reduced by β-OHB. β-OHB treatment restored the impaired expression of Cpt1a. The effect of β-OHB was blocked by siRNA targeting free fatty acid receptor 3 (FFAR3), suggesting that β-OHB might function through the FFAR3-dependent pathway.

Discussion

Our results highlight that KD attenuates UUO-induced renal fibrosis by enhancing FAO via the FFAR3-dependent pathway, which provides a promising dietary therapy for renal fibrosis.

Type 2 diabetes is associated with increased circulating levels of 3-hydroxydecanoate activating GPR84 and neutrophil migration

Obesity and diabetes are associated with inflammation and altered plasma levels of several metabolites, which may be involved in disease progression. Some metabolites can activate G protein-coupled receptors (GPCRs) expressed on immune cells where they can modulate metabolic inflammation. Here, we find that 3-hydroxydecanoate is enriched in the circulation of obese individuals with type 2 diabetes (T2D) compared with nondiabetic controls. Administration of 3-hydroxydecanoate to mice promotes immune cell recruitment to adipose tissue, which was associated with adipose inflammation and increased fasting insulin levels. Furthermore, we demonstrate that 3-hydroxydecanoate stimulates migration of primary human and mouse neutrophils, but not monocytes, through GPR84 and Gα_i signaling in vitro. Our findings indicate that 3-hydroxydecanoate is a T2D-associated metabolite that increases inflammatory responses and may contribute to the chronic inflammation observed in diabetes.

Insight into role of short chain fatty acids in regulating intestinal mucosal barrier and alleviating inflammatory bowel disease

In recent years, the importance of intestinal microbiota and its metabolites in maintaining the human intestinal environment has been gradually revealed. Therefore, short chain fatty acids (SCFAs), as the metabolites produced by the intestinal microbiota, play a momentous part in regulating the balance between the function and morphology of the mucosal barrier, regulating the proliferation and differentiation of mucosal cells, protecting the integrity and permeability of the mucosal barrier, and maintainingthe stability of tight junctions. Inflammatory bowel disease (IBD) is a chronic, inflammatory condition of the gastrointestinal tract, associated with a disturbance of intestinal barrier function and dysregulation of the intestinal immune responses, the etiology and pathogenesis of which, however, are not yet fully uncovered. Animal models and human studies have corroborated the contribution of SCFAs in enhancing the barrier function through protective effects. This review will summarize the potential role of SCFAs in IBD with regard to regulating intestinal function, hoping to provide a new target for clinical treatment of IBD.

Dihydromyricetin Enhances Exercise-Induced GLP-1 Elevation through Stimulating cAMP and Inhibiting DPP-4

The purpose of this study was to examine whether endogenous GLP-1 (glucagon-like peptide-1) could respond to exercise training in mice, as well as whether dihydromyricetin (DHM) supplementation could enhance GLP-1 levels in response to exercise training. After 2 weeks of exercise intervention, we found that GLP-1 levels were significantly elevated. A reshaped gut microbiota was identified following exercise, as evidenced by the increased abundance of Bifidobacterium, Lactococcus, and Alistipes genus, which are involved in the production of short-chain fatty acids (SCFAs). Antibiotic treatment negated exercise-induced GLP-1 secretion, which could be reversed with gut microbiota transplantation. Additionally, the combined intervention (DHM and exercise) was modeled in mice. Surprisingly, the combined intervention resulted in higher GLP-1 levels than the exercise intervention alone. In exercised mice supplemented with DHM, the gut microbiota composition changed as well, while the amount of SCFAs was unchanged in the stools. Additionally, DHM treatment induced intracellular cAMP in vitro and down-regulated the gene and protein expression of dipeptidyl peptidase-4 (DPP-4) both in vivo and in vitro. Collectively, the auxo-action of exercise on GLP-1 secretion is associated with the gut-microbiota-SCFAs axis. Moreover, our findings suggest that DHM interacts synergistically with exercise to enhance GLP-1 levels by stimulating cAMP and inhibiting DPP-4.

The Role of Short Chain Fatty Acids in Irritable Bowel Syndrome

Irritable bowel syndrome (IBS) is a functional gastrointestinal disorder that is characterized by abdominal pain and disordered bowel habits. The etiology of IBS is multifactorial, including abnormal gut-brain interactions, visceral hypersensitivity, altered colon motility, and psychological factors. Recent studies have shown that the intestinal microbiota and its metabolites short chain fatty acids (SCFAs) may be involved in the pathogenesis of IBS. SCFAs play an important role in the pathophysiology of IBS. We discuss the underlying mechanisms of action of SCFAs in intestinal inflammation and immunity, intestinal barrier integrity, motility, and the microbiota-gut-brain axis. Limited to previous studies, further studies are required to investigate the mechanisms of action of SCFAs in IBS and provide more precise therapeutic strategies for IBS.

How Arrestins and GRKs Regulate the Function of Long Chain Fatty Acid Receptors

FFA1 and FFA4, two G protein-coupled receptors that are activated by long chain fatty acids, play crucial roles in mediating many biological functions in the body. As a result, these fatty acid receptors have gained considerable attention due to their potential to be targeted for the treatment of type-2 diabetes. However, the relative contribution of canonical G protein-mediated signalling versus the effects of agonist-induced phosphorylation and interactions with β-arrestins have yet to be fully defined. Recently, several reports have highlighted the ability of β-arrestins and GRKs to interact with and modulate different functions of both FFA1 and FFA4, suggesting that it is indeed important to consider these interactions when studying the roles of FFA1 and FFA4 in both normal physiology and in different disease settings. Here, we discuss what is currently known and show the importance of understanding fully how β-arrestins and GRKs regulate the function of long chain fatty acid receptors.

Stearic acid induces CCK and GLP-1 upregulation via GPR120/PLC-β, leading to reduced appetite in Hu sheep fed with rice straw

Due to the poor palatability of straw, feeding untreated rice straw reduces ruminant feed intake, thus affecting the production efficiency of animal husbandry. However, the detailed mechanism by which straw affects ruminants' feed intake is unclear. Therefore, this study aimed to elucidate the molecular mechanism by which a rice straw (RS)-based diet affects appetite regulation in Hu sheep. We found that RS promoted the secretion of cholecystokinin (CCK) and glucagon-like peptide-1 (GLP-1) and decreased feed intake. Blood metabolomics showed that RS activated the arachidonic acid metabolism, biosynthesis of unsaturated fatty acids, linoleic acid metabolism, and alpha-linolenic acid metabolism pathways, and the secretion of stearic acid (SA), their metabolic end product, increased significantly. GPR120, one of the classical receptors of long-chain fatty acids (LCFAs), can be involved in appetite regulation. However, the role of SA in satiety hormone regulation mediated by GPR120 in ruminants is unclear. In this study, in vivo experiments showed that in sheep fed with RS, SA increased significantly and activated GPR120/Ca²⁺, increasing the secretion of the satiety hormones CCK and GLP-1. In vitro mechanism studies showed that SA promotes GLP-1 and CCK secretion by activating GPR120-mediated downstream PKC and IP3R signaling pathways of PLCβ.

Gq Signaling in Autophagy Control: Between Chemical and Mechanical Cues

All processes in human physiology relies on homeostatic mechanisms which require the activation of specific control circuits to adapt the changes imposed by external stimuli. One of the critical modulators of homeostatic balance is autophagy, a catabolic process that is responsible of the destruction of long-lived proteins and organelles through a lysosome degradative pathway. Identification of the mechanism underlying autophagic flux is considered of great importance as both protective and detrimental functions are linked with deregulated autophagy. At the mechanistic and regulatory levels, autophagy is activated in response to diverse stress conditions (food deprivation, hyperthermia and hypoxia), even a novel perspective highlight the potential role of physical forces in autophagy modulation. To understand the crosstalk between all these controlling mechanisms could give us new clues about the specific contribution of autophagy in a wide range of diseases including vascular disorders, inflammation and cancer. Of note, any homeostatic control critically depends in at least two additional and poorly studied interdependent components: a receptor and its downstream effectors. Addressing the selective receptors involved in autophagy regulation is an open question and represents a new area of research in this field. G-protein coupled receptors (GPCRs) represent one of the largest and druggable targets membrane receptor protein superfamily. By exerting their action through G proteins, GPCRs play fundamental roles in the control of cellular homeostasis. Novel studies have shown Gαq, a subunit of heterotrimeric G proteins, as a core modulator of mTORC1 and autophagy, suggesting a fundamental contribution of Gαq-coupled GPCRs mechanisms in the control of this homeostatic feedback loop. To address how GPCR-G proteins machinery integrates the response to different stresses including oxidative conditions and mechanical stimuli, could provide deeper insight into new signaling pathways and open potential and novel therapeutic strategies in the modulation of different pathological conditions.

GPR84 signaling promotes intestinal mucosal inflammation via enhancing NLRP3 inflammasome activation in macrophages

The putative medium-chain free fatty acid receptor GPR84 is a G protein-coupled receptor primarily expressed in myeloid cells that constitute the innate immune system, including neutrophils, monocytes, and macrophages in the periphery and microglia in the brain. The fact that GPR84 expression in leukocytes is remarkably increased under acute inflammatory stimuli such as lipopolysaccharide (LPS) and TNFα suggests that it may play a role in the development of inflammatory and fibrotic diseases. Here we demonstrate that GPR84 is highly upregulated in inflamed colon tissues of active ulcerative colitis (UC) patients and dextran sulfate sodium (DSS)-induced colitis mice. Infiltrating GPR84⁺ macrophages are significantly increased in the colonic mucosa of both the UC patients and the mice with colitis. Consistently, GPR84^-/- mice are resistant to the development of colitis induced by DSS. GPR84 activation imposes pro-inflammatory properties in colonic macrophages through enhancing NLRP3 inflammasome activation, while the loss of GPR84 prevents the M1 polarization and properties of proinflammatory macrophages. CLH536, a novel GPR84 antagonist discovered by us, suppresses colitis by reducing the polarization and function of pro-inflammatory macrophages. These results define a unique role of GPR84 in innate immune cells and intestinal inflammation, and suggest that GPR84 may serve as a potential drug target for the treatment of UC.

Serum Free Fatty Acids and G-Coupled Protein Receptors Are Associated With the Prognosis of Epithelial Ovarian Cancer

Purpose

Fatty acid metabolism plays key role in cancer development, and free fatty acid receptors (FFARs) are involved in many cancers. However, the correlation between serum free fatty acids (FFAs)/FFARs levels and ovarian cancer (OC) prognosis remains largely unclear.

Methods

A retrospective review of 534 primary OC patients and 1049 women with benign ovarian tumors was performed. Serum FFA levels data were extracted from the electronic medical record system. Repeated FFA results of 101 OC patients treated with standard chemotherapy were collected. The effects of FFAs on cells migration were evaluated in OC cell lines by Transwell assay. Gene Expression Profiling Interactive Analysis (GEPIA) was used to compare FFAR mRNA expression levels in cancer and noncancer tissues. Kaplan-Meier (KM) plotter was employed to analyze their prognostic values. SPSS 23.0 and Graphpad prism 7.0 software was used for analysis and graph construction.

Results

FFA levels in the serum of epithelial ovarian cancer (EOC) women were higher than in women with benign ovarian tumors independent of pathology, tumor stage,and grade. FFA levels decreased gradually after chemotherapy. FFAs enhanced the migration of OVCAR3 cells. FFAR1 mRNA expression was lower in OC cells than in control cells. FFAR3 was related to a better prognosis, and FFAR4 was related to poor prognosis in TP-53wild-type and mutated type OC, while FFAR1 and FFAR2 were related to a better prognosis in TP53 wild-type OC but FFAR2 was related to a poor prognosis in TP53-mutant OC.

Conclusion

The FFA levels are increased in OC and decreased with chemotherapy. High expression of FFARs was related to the prognosis of OC. The prognostic value of different FFARs differs depending on whether it is a TP53 wild or TP53 mutant ovarian cancer.Targeting FFARs may be an attractive treatment strategy for EOC.

Fatty acids role in multiple sclerosis as "metabokines"

Multiple sclerosis (MS), as an autoimmune neurological disease with both genetic and environmental contribution, still lacks effective treatment options among progressive patients, highlighting the need to re-evaluate disease innate properties in search for novel therapeutic targets. Fatty acids (FA) and MS bear an interesting intimate connection. FA and FA metabolism are highly associated with autoimmunity, as the diet-derived circulatory and tissue-resident FAs level and composition can modulate immune cells polarization, differentiation and function, suggesting their broad regulatory role as “metabokines”. In addition, FAs are indeed protective factors for blood–brain barrier integrity, crucial contributors of central nervous system (CNS) chronic inflammation and progressive degeneration, as well as important materials for remyelination. The remaining area of ambiguity requires further exploration into this arena to validate the existed phenomenon, develop novel therapies, and confirm the safety and efficacy of therapeutic intervention targeting FA metabolism.

Ketone body 3-hydroxybutyrate enhances adipocyte function

Ketone bodies, including 3HBA, are endogenous products of fatty acid oxidation, and Hmgcs2 is the first rate-limiting enzyme of ketogenesis. From database analysis and in vivo and in vitro experiments, we found that adipose tissue and adipocytes express Hmgcs2, and that adipocytes produce and secrete 3HBA. Treatment with 3HBA enhanced the gene expression levels of the antioxidative stress factors, PPARγ, and lipogenic factors in adipose tissue in vivo and in adipocytes in vitro, accompanied by reduced ROS levels. Knockdown of endogenous Hmgcs2 in adipocytes markedly decreased 3HBA levels in adipocytes and decreased the gene expression levels of the antioxidative stress factors, PPARγ, and lipogenic factors with increased ROS levels. Conversely, overexpression of Hmgcs2 in adipocytes increased 3HBA secretion from adipocytes and enhanced the gene expression levels of the antioxidative stress factors, PPARγ, and lipogenic factors. These results demonstrate that 3HBA plays significant roles in enhancing the physiological function of adipocytes.

Short Term Isocaloric Ketogenic Diet Modulates NLRP3 Inflammasome Via B-hydroxybutyrate and Fibroblast Growth Factor 21

A ketogenic diet (KD) is known to have beneficial health effects. Various types of KD interventions have been applied to manage metabolic syndrome based on modification of diet parameters such as duration of intervention, macronutrient components, and total calories. Nevertheless, the beneficial health impact of isocaloric KD is largely unknown, especially in healthy subjects. The present study investigated the acute effects of a 3-day isocaloric KD. In this non-randomized intervention study, we recruited 15 healthy volunteers aged 24-38 years (7 men and 8 women) and placed them on an isocaloric KD restricting intake of carbohydrates but not energy (75% fat, 20% protein, 5% carbohydrate) for 3 days. Biochemical profiles and laboratory measurements were performed. Peripheral blood monocular cells were cultured, and measured cell stimulated cytokines. After short-term isocaloric KD, subjects lost body weight and serum free fatty acid levels were increased. These results accompanied elevated serum β-hydroxybutyrate (BHB) concentration and fibroblast growth factor 21 (FGF21) levels and improved insulin sensitivity. Regarding the direct effect of BHB on inflammasome activation, interleukin-1β (IL-1β) and tumor necrosis factor-α secretion in response to adenosine triphosphate or palmitate stimulation in human macrophages decreased significantly after isocaloric KD. In ex-vivo experiments with macrophages, both FGF21 and BHB further reduced IL-1β secretion compared to either BHB or FGF21 alone. The inhibitory effect of FGF21 on IL-1β secretion was blunted with bafilomycin treatment, which blocked autophagy flux. In conclusion, isocaloric KD for 3 days is a promising approach to improve metabolic and inflammatory status.

Critical roles of G protein-coupled receptors in regulating intestinal homeostasis and inflammatory bowel disease

G protein-coupled receptors (GPCRs) are a group of membrane proteins that mediate most of the physiological responses to various signaling molecules such as hormones, neurotransmitters, and environmental stimulants. Inflammatory bowel disease (IBD) is a chronic relapsing disorder of the gastrointestinal tract and presents a spectrum of heterogeneous disorders falling under two main clinical subtypes including Crohn's disease (CD) and ulcerative colitis (UC). The pathogenesis of IBD is multifactorial and is related to a genetically dysregulated mucosal immune response to environmental drivers, mainly microbiotas. Although many drugs, such as 5-aminosalicylic acid, glucocorticoids, immunosuppressants, and biological agents, have been approved for IBD treatment, none can cure IBD permanently. Emerging evidence indicates significant associations between GPCRs and the pathogenesis of IBD. Here, we provide an overview of the essential physiological functions and signaling pathways of GPCRs and their roles in mucosal immunity and IBD regulation.

Maternal breast milk microbiota and immune markers in relation to subsequent development of celiac disease in offspring

The potential impact of the composition of maternal breast milk is poorly known in children who develop celiac disease (CD). The aim of our study was to compare the microbiota composition and the concentrations of immune markers in breast milk from mothers whose offspring carried the genetic predisposition to CD, and whether they did or did not develop CD during follow-up for the first 3 years of life. Maternal breast milk samples [CD children (n = 6) and healthy children (n = 18)] were collected 3 months after delivery. Enzyme-linked immunosorbent assays were used to measure TGF-β1, TGF-β2, sIgA, MFG-E8 and sCD14. For microbiota analysis, next generation (Illumina) sequencing, real-time PCR and denaturing gradient gel electrophoresis were used. Phylotype abundance and the Shannon ‘H’ diversity index were significantly higher in breast milk samples in the CD group. There was higher prevalence of the phyla Bacteroidetes and Fusobacteria, the classes Clostridia and Fusobacteriia, and the genera Leptotrichia, Anaerococcus, Sphingomonas, Actynomyces and Akkermansia in the CD group. The immunological markers were differently associated with some Gram-negative bacterial genera and species (Chryseobacterium, Sphingobium) as well as Gram-positive species (Lactobacillusreuteri, Bifidobacteriumanimalis). In conclusion, the microbiota in breast milk from mothers of genetically predisposed offspring who presented CD showed a higher bacterial phylotype abundance and diversity, as well as a different bacterial composition, as compared with the mothers of unaffected offspring. These immune markers showed some associations with bacterial composition and may influence the risk for development of CD beyond early childhood.

An original amino acid formula favours in vitro corneal epithelial wound healing by promoting Fn1, ITGB1, and PGC-1α expression

Corneal disorders are frequent, involving most diabetic patients; among its manifestations, they include delayed wound healing. Since maintenance of mitochondrial homeostasis is fundamental for the cell, stimulation of mitochondrial biogenesis represents a unique therapeutic tool for preventing and treating disorders with a deficit in energy metabolism. We have recently demonstrated that a branched-chain amino acid (BCAA)-enriched mixture (BCAAem) supported mitochondrial biogenesis in cardiac and skeletal muscle, reduced liver damage caused by alcohol, and prevented the doxorubicin-dependent mitochondrial damage in cardiomyocytes. The present study aimed to investigate a new amino acid mixture, named six amino acids (6AA), to promote corneal epithelial wound healing by regulating mitochondrial biogenesis. A murine epithelium cell line (TKE2) exposed to this mixture showed increased mitochondrial biogenesis markers, fibronectin 1 (Fn1) and integrin beta 1 (ITGB1) involved in extracellular matrix synthesis and cell migration. Most importantly, the 6AA mixture completely restored the wound in scratch assays, confirming the potential of this new formula in eye disorders like keratopathy. Moreover, our results demonstrate for the first time that peroxisome proliferator-receptor γ coactivator 1 α (PGC-1α) is expressed in TKE2 cells, which controls mitochondrial function and corneal repair process. These results could be relevant for the treatment mainly focused on corneal re-epithelialisation.

Evaluation of Hydroxycarboxylic Acid Receptor 1 (HCAR1) as a Building Block for Genetically Encoded Extracellular Lactate Biosensors

The status of lactate has evolved from being considered a waste product of cellular metabolism to a useful metabolic substrate and, more recently, to a signaling molecule. The fluctuations of lactate levels within biological tissues, in particular in the interstitial space, are crucial to assess with high spatial and temporal resolution, and this is best achieved using cellular imaging approaches. In this study, we evaluated the suitability of the lactate receptor, hydroxycarboxylic acid receptor 1 (HCAR1, formerly named GPR81), as a basis for the development of a genetically encoded fluorescent lactate biosensor. We used a biosensor strategy that was successfully applied to molecules such as dopamine, serotonin, and norepinephrine, based on their respective G-protein-coupled receptors. In this study, a set of intensiometric sensors was constructed and expressed in living cells. They showed selective expression at the plasma membrane and responded to physiological concentrations of lactate. However, these sensors lost the original ability of HCAR1 to selectively respond to lactate versus other related small carboxylic acid molecules. Therefore, while representing a promising building block for a lactate biosensor, HCAR1 was found to be sensitive to perturbations of its structure, affecting its ability to distinguish between related carboxylic molecules.

Deprivation of Dietary Fiber Enhances Susceptibility of Piglets to Lung Immune Stress

Growing evidence suggests that dietary fiber enhances short-chain fatty acid (SCFA) producing gut microbes, improving lung immunity against invading pathogens via the gut–lung axis. This study investigated the effects of dietary fiber on lung immune stress after challenge with complete Freund's adjuvant (CFA) containing killed Mycobacterium tuberculosis. Thirty-six healthy hybrid Duroc, Landrace, and Yorkshire male piglets (9.7 ± 1.07 kg, 35 ± 3 days) were randomly fed a low fiber (LF) diet formulated with semipurified corn starch, soy protein concentrate, and fishmeal or a high fiber (HF) diet composed of 1,000 g LF diet plus 20 g inulin, and 100 g cellulose. Piglets were housed individually in the metabolism cages with eighteen replicates per group, with one pig per cage. All the piglets received similar levels of digestible energy and lysine and had similar weight gain. After dietary treatment for 28 days, nine piglets per group were intravenously administered CFA (0.4 mg/kg) or an equivalent amount of sterile saline in a 2 × 2 factorial arrangement. In piglets fed the LF diet, CFA caused lung damage and elevated serum C-reactive protein and relative mRNA expression of genes related to lung inflammation (NLRP3, Casp1, ASC, IL1β, IL18, Bax). Compared with the LF diet, the HF diet increased bacterial diversity and Deferribacteres (p = 0.01) in the phylum level and unidentified_Ruminococcaceae (p = 0.03) and Catenisphaera (p < 0.01) in the genus level. The HF diet improved increased short-chain fatty acids in feces, blood, cecal, and colonic digesta; reduced lung damage; and promoted lung recovery. Overall, dietary fiber deprivation enhanced the risk of piglets to lung immune stress, demonstrating the importance of dietary fiber in gut–lung health.

The dual roles of autophagy and the GPCRs-mediating autophagy signaling pathway after cerebral ischemic stroke

Ischemic stroke, caused by a lack of blood supply in brain tissues, is the third leading cause of human death and disability worldwide, and usually results in sensory and motor dysfunction, cognitive impairment, and in severe cases, even death. Autophagy is a highly conserved lysosome-dependent process in which eukaryotic cells removal misfolded proteins and damaged organelles in cytoplasm, which is critical for energy metabolism, organelle renewal, and maintenance of intracellular homeostasis. Increasing evidence suggests that autophagy plays important roles in pathophysiological mechanisms under ischemic conditions. However, there are still controversies about whether autophagy plays a neuroprotective or damaging role after ischemia. G-protein-coupled receptors (GPCRs), one of the largest protein receptor superfamilies in mammals, play crucial roles in various physiological and pathological processes. Statistics show that GPCRs are the targets of about one-fifth of drugs known in the world, predicting potential values as targets for drug research. Studies have demonstrated that nutritional deprivation can directly or indirectly activate GPCRs, mediating a series of downstream biological processes, including autophagy. It can be concluded that there are interactions between autophagy and GPCRs signaling pathway, which provides research evidence for regulating GPCRs-mediated autophagy. This review aims to systematically discuss the underlying mechanism and dual roles of autophagy in cerebral ischemia, and describe the GPCRs-mediated autophagy, hoping to probe promising therapeutic targets for ischemic stroke through in-depth exploration of the GPCRs-mediated autophagy signaling pathway.

Effects of Probiotic Supplementation on Exercise with Predominance of Aerobic Metabolism in Trained Population: A Systematic Review, Meta-Analysis and Meta-Regression

The scientific literature about probiotic intake and its effect on sports performance is growing. Therefore, the main aim of this systematic review, meta-analysis and meta-regression was to review all information about the effects of probiotic supplementation on performance tests with predominance of aerobic metabolism in trained populations (athletes and/or Division I players and/or trained population: ≥8 h/week and/or ≥5 workouts/week). A structured search was performed in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA®) statement and PICOS guidelines in PubMed/MEDLINE, Web of Science (WOS), and Scopus international databases from inception to 1 November 2021. Studies involving probiotic supplementation in trained population and execution of performance test with aerobic metabolism predominance (test lasted more than 5 min) were considered for inclusion. Fifteen articles were included in the final systematic review (in total, 388 participants were included). After 3 studies were removed due to a lack of data for the meta-analysis and meta-regression, 12 studies with 232 participants were involved. With the objective of assessing the risk of bias of included studies, Cochrane Collaboration Guidelines and the Physiotherapy Evidence Database (PEDro) scale were performed. For all included studies the following data was extracted: authors, year of publication, study design, the size of the sample, probiotic administration (dose and time), and characteristics of participants. The random effects model and pooled standardized mean differences (SMDs) were used according to Hedges’ g for the meta-analysis. In order to determine if dose and duration covariates could predict probiotic effects, a meta-regression was also conducted. Results showed a small positive and significant effect on the performance test with aerobic metabolic predominance (SMD = 0.29; CI = 0.08−0.50; p < 0.05). Moreover, the subgroup analysis displayed significant greater benefits when the dose was ≥30 × 109 colony forming units (CFU) (SMD, 0.47; CI, 0.05 to 0.89; p < 0.05), when supplementation duration was ≤4 weeks (SMD, 0.44; CI, 0.05 to 0.84; p < 0.05), when single strain probiotics were used (SMD, 0.33; CI, 0.06 to 0.60; p < 0.05), when participants were males (SMD, 0.30; CI, 0.04 to 0.56; p < 0.05), and when the test was performed to exhaustion (SMD, 0.45; CI, 0.05 to 0.48; p < 0.05). However, with references to the findings of the meta-regression, selected covariates did not predict probiotic effects in highly trained population. In summary, the current systematic review and meta-analysis supported the potential effects of probiotics supplementation to improve performance in a test in which aerobic metabolism is predominant in trained population. However, more research is needed to fully understand the mechanisms of action of this supplement.

Glucagon-Like Peptide-1 Receptor Regulates Macrophage Migration in Monosodium Urate-Induced Peritoneal Inflammation

Glucagon-like peptide-1 (GLP-1) is an insulinotropic peptide that signals through the GLP-1 receptor (GLP-1R). GLP-1R, therefore, plays a critical role in diabetes and cardiovascular disease. Whether GLP-1R is involved in inflammatory disease such as gout remains unclear. Macrophages are critical effector cells in the pathogenesis of gout, a common form of inflammatory arthritis caused by the deposition of uric acid in joints. The expression of GLP-1R at the protein level is controversial due to the lack of specificity of existing antibodies against GLP-1R. Using a transgenic mouse model expressing enhanced green fluorescent protein (EGFP) under the control of GLP-1R promoter, here we confirmed the expression of GLP-1R by macrophages. M2 type macrophages and Ly6C⁺ macrophages expressed higher levels of GLP-1R, compared to their counterparts. GLP-1R deficient macrophages displayed a reduced the migratory ability and an enhanced expression of interleukin (IL)-6, while the expression of IL-1β was not affected. In monosodium urate (MSU) crystal-induced peritonitis, an experimental model of gout, the recruitment of macrophages, especially M2 macrophages, was significantly suppressed in GLP-1R knockout mice compared to wild-type mice. In conclusion, our data suggests that GLP-1R plays a critical role in macrophage migration in MSU-induced inflammation.

Gut-derived short-chain fatty acids modulate skin barrier integrity by promoting keratinocyte metabolism and differentiation

Barrier integrity is central to the maintenance of healthy immunological homeostasis. Impaired skin barrier function is linked with enhanced allergen sensitization and the development of diseases such as atopic dermatitis (AD), which can precede the development of other allergic disorders, for example, food allergies and asthma. Epidemiological evidence indicates that children suffering from allergies have lower levels of dietary fibre-derived short-chain fatty acids (SCFA). Using an experimental model of AD-like skin inflammation, we report that a fermentable fibre-rich diet alleviates systemic allergen sensitization and disease severity. The gut-skin axis underpins this phenomenon through SCFA production, particularly butyrate, which strengthens skin barrier function by altering mitochondrial metabolism of epidermal keratinocytes and the production of key structural components. Our results demonstrate that dietary fibre and SCFA improve epidermal barrier integrity, ultimately limiting early allergen sensitization and disease development.The Graphical Abstract was designed using Servier Medical Art images ( https://smart.servier.com ).