Hypertension Increases Susceptibility to Experimental Malaria in Mice

Global prevalence of hypertension is on the rise, burdening healthcare, especially in developing countries where infectious diseases, such as malaria, are also rampant. Whether hypertension could predispose or increase susceptibility to malaria, however, has not been extensively explored. Previously, we reported that hypertension is associated with abnormal red blood cell (RBC) physiology and anemia. Since RBC are target host cells for malarial parasite, Plasmodium, we hypothesized that hypertensive patients with abnormal RBC physiology are at greater risk or susceptibility to Plasmodium infection. To test this hypothesis, normotensive (BPN/3J) and hypertensive (BPH/2J) mice were characterized for their RBC physiology and subsequently infected with Plasmodium yoelii (P. yoelii), a murine-specific non-lethal strain. When compared to BPN mice, BPH mice displayed microcytic anemia with RBC highly resistant to osmotic hemolysis. Further, BPH RBC exhibited greater membrane rigidity and an altered lipid composition, as evidenced by higher levels of phospholipids and saturated fatty acid, such as stearate (C18:0), along with lower levels of polyunsaturated fatty acid like arachidonate (C20:4). Moreover, BPH mice had significantly greater circulating Ter119+ CD71+ reticulocytes, or immature RBC, prone to P. yoelii infection. Upon infection with P. yoelii, BPH mice experienced significant body weight loss accompanied by sustained parasitemia, indices of anemia, and substantial increase in systemic pro-inflammatory mediators, compared to BPN mice, indicating that BPH mice were incompetent to clear P. yoelii infection. Collectively, these data demonstrate that aberrant RBC physiology observed in hypertensive BPH mice contributes to an increased susceptibility to P. yoelii infection and malaria-associated pathology.

Sex Dimorphic Effects of Bile Acid Metabolism in Liver Cancer in Mice

BACKGROUND & AIMS

Hepatocellular carcinoma (HCC) is a male-dominant disease, but targeted sex hormone therapies have not been successful. Bile acids are a potential liver carcinogen and are biomolecules with hormone-like effects. A few studies highlight their potential sex dimorphism in physiology and disease. We hypothesized that bile acids could be a potential molecular signature that explains sex disparity in HCC.

METHODS & RESULTS

We used the farnesoid X receptor knockout (FxrKO) mouse model to study bile acid-dependent HCC. Temporal tracking of circulating bile acids determined more than 80% of FxrKO females developed spontaneous cholemia (ie, serum total bile acids ≥40 μmol/L) as early as 8 weeks old. Opposingly, FxrKO males were highly resistant to cholemia, with ∼23% incidence even when 26 weeks old. However, FxrKO males demonstrated higher levels of deoxycholate than females. Compared with males, FxrKO females had more severe cholestatic liver injury and further aberrancies in bile acid metabolism. Yet, FxrKO females expressed more detoxification transcripts and had greater renal excretion of bile acids. Intervention with CYP7A1 (rate limiting enzyme for bile acid biosynthesis) deficiency or taurine supplementation either completely or partially normalized bile acid levels and liver injury in FxrKO females. Despite higher cholemia prevalence in FxrKO females, their tumor burden was less compared with FxrKO males. An exception to this sex-dimorphic pattern was found in a subset of male and female FxrKO mice born with congenital cholemia due to portosystemic shunt, where both sexes had comparable robust HCC.

CONCLUSIONS

Our study highlights bile acids as sex-dimorphic metabolites in HCC except in the case of portosystemic shunt.

Urine-based Detection of Congenital Portosystemic Shunt in C57BL/6 Mice

Sporadic occurrence of congenital portosystemic shunt (PSS) at a rate of ∼1 out of 10 among C57BL/6 J mice, which are widely used in biomedical research, results in aberrancies in serologic, metabolic, and physiologic parameters. Therefore, mice with PSS should be identified as outliers in research. Accordingly, we sought methods to, reliably and efficiently, identify PSS mice. Serum total bile acids ≥ 40 µm is a bona fide biomarker of PSS in mice but utility of this biomarker is limited by its cost and invasiveness, particularly if large numbers of mice are to be screened. This led us to investigate if assay of urine might serve as a simple, inexpensive, noninvasive means of PSS diagnosis. Metabolome profiling uncovered that Krebs cycle intermediates, that is, citrate, α-ketoglutarate, and fumarate, were strikingly and distinctly elevated in the urine of PSS mice. We leveraged the iron-chelating and pH-lowering properties of such metabolites as the basis for 3 urine-based PSS screening tests: urinary iron-chelation assay, pH strip test, and phenol red assay. Our findings demonstrate the feasibility of using these colorimetric assays, whereby their readout can be assessed by direct observation, to diagnose PSS in an inexpensive, rapid, and noninvasive manner. Application of our urinary PSS screening protocols can aid biomedical research by enabling stratification of PSS mice, which, at present, likely confound numerous ongoing studies.

Loss of toll-like receptor 5 potentiates spontaneous hepatocarcinogenesis in farnesoid X receptor-deficient mice

BACKGROUND

HCC is the most common primary liver cancer and a leading cause of cancer-related mortality. Gut microbiota is a large collection of microbes, predominately bacteria, that harbor the gastrointestinal tract. Changes in gut microbiota that deviate from the native composition, that is, "dysbiosis," is proposed as a probable diagnostic biomarker and a risk factor for HCC. However, whether gut microbiota dysbiosis is a cause or a consequence of HCC is unknown.

METHODS

To better understand the role of gut microbiota in HCC, mice deficient of toll-like receptor 5 (TLR5, a receptor for bacterial flagellin) as a model of spontaneous gut microbiota dysbiosis were crossed with farnesoid X receptor knockout mice (FxrKO), a genetic model for spontaneous HCC. Male FxrKO/Tlr5KO double knockout (DKO), FxrKO, Tlr5KO, and wild-type (WT) mice were aged to the 16-month HCC time point.

RESULTS

Compared with FxrKO mice, DKO mice had more severe hepatooncogenesis at the gross, histological, and transcript levels and this was associated with pronounced cholestatic liver injury. The bile acid dysmetabolism in FxrKO mice became more aberrant in the absence of TLR5 due in part to suppression of bile acid secretion and enhanced cholestasis. Out of the 14 enriched taxon signatures seen in the DKO gut microbiota, 50% were dominated by the Proteobacteria phylum with expansion of the gut pathobiont γ-Proteobacteria that is implicated in HCC.

CONCLUSIONS

Collectively, introducing gut microbiota dysbiosis by TLR5 deletion exacerbated hepatocarcinogenesis in the FxrKO mouse model.

Conjugated bile acids are nutritionally re-programmable antihypertensive metabolites

BACKGROUND

Hypertension is the largest risk factor affecting global mortality. Despite available medications, uncontrolled hypertension is on the rise, whereby there is an urgent need to develop novel and sustainable therapeutics. Because gut microbiota is now recognized as an important entity in blood pressure regulation, one such new avenue is to target the gut-liver axis wherein metabolites are transacted via host-microbiota interactions. Knowledge on which metabolites within the gut-liver axis regulate blood pressure is largely unknown.

METHOD

To address this, we analyzed bile acid profiles of human, hypertensive and germ-free rat models and report that conjugated bile acids are inversely correlated with blood pressure in humans and rats.

RESULTS

Notably intervening with taurine or tauro-cholic acid rescued bile acid conjugation and reduced blood pressure in hypertensive rats. Subsequently, untargeted metabolomics uncovered altered energy metabolism following conjugation of bile acids as a mechanism alleviating high blood pressure.

CONCLUSION

Together this work reveals conjugated bile acids as nutritionally re-programmable anti-hypertensive metabolites.

Psyllium Fiber Protects Against Colitis Via Activation of Bile Acid Sensor Farnesoid X Receptor

BACKGROUND & AIMS

Fiber-rich foods promote health, but mechanisms by which they do so remain poorly defined. Screening fiber types, in mice, revealed psyllium had unique ability to ameliorate 2 chronic inflammatory states, namely, metabolic syndrome and colitis. We sought to determine the mechanism of action of the latter.

METHODS

Mice were fed grain-based chow, which is naturally rich in fiber or compositionally defined diets enriched with semi-purified fibers. Mice were studied basally and in models of chemical-induced and T-cell transfer colitis.

RESULTS

Relative to all diets tested, mice consuming psyllium-enriched compositionally defined diets were markedly protected against both dextran sulfate sodium- and T-cell transfer-induced colitis, as revealed by clinical-type, histopathologic, morphologic, and immunologic parameters. Such protection associated with stark basal changes in the gut microbiome but was independent of fermentation and, moreover, maintained in mice harboring a minimal microbiota (ie, Altered Schaedler Flora). Transcriptomic analysis revealed psyllium induced expression of genes mediating bile acids (BA) secretion, suggesting that psyllium's known ability to bind BA might contribute to its ability to prevent colitis. As expected, psyllium resulted in elevated level of fecal BA, reflecting their removal from enterohepatic circulation but, in stark contrast to the BA sequestrant cholestyramine, increased serum BA levels. Moreover, the use of BA mimetics that activate the farnesoid X receptor (FXR), as well as the use of FXR-knockout mice, suggested that activation of FXR plays a central role in psyllium's protection against colitis.

CONCLUSIONS

Psyllium protects against colitis via altering BA metabolism resulting in activation of FXR, which suppresses pro-inflammatory signaling.

Crosstalk between Gut Microbiota and Host Immunity: Impact on Inflammation and Immunotherapy

Gut microbes and their metabolites are actively involved in the development and regulation of host immunity, which can influence disease susceptibility. Herein, we review the most recent research advancements in the gut microbiota-immune axis. We discuss in detail how the gut microbiota is a tipping point for neonatal immune development as indicated by newly uncovered phenomenon, such as maternal imprinting, in utero intestinal metabolome, and weaning reaction. We describe how the gut microbiota shapes both innate and adaptive immunity with emphasis on the metabolites short-chain fatty acids and secondary bile acids. We also comprehensively delineate how disruption in the microbiota-immune axis results in immune-mediated diseases, such as gastrointestinal infections, inflammatory bowel diseases, cardiometabolic disorders (e.g., cardiovascular diseases, diabetes, and hypertension), autoimmunity (e.g., rheumatoid arthritis), hypersensitivity (e.g., asthma and allergies), psychological disorders (e.g., anxiety), and cancer (e.g., colorectal and hepatic). We further encompass the role of fecal microbiota transplantation, probiotics, prebiotics, and dietary polyphenols in reshaping the gut microbiota and their therapeutic potential. Continuing, we examine how the gut microbiota modulates immune therapies, including immune checkpoint inhibitors, JAK inhibitors, and anti-TNF therapies. We lastly mention the current challenges in metagenomics, germ-free models, and microbiota recapitulation to a achieve fundamental understanding for how gut microbiota regulates immunity. Altogether, this review proposes improving immunotherapy efficacy from the perspective of microbiome-targeted interventions.

Bacterial flagellin is a dominant, stable innate immune activator in the gastrointestinal contents of mice and rats

Intestinal contents comprise the largest repository of immunogenic ligands of microbial origin. We undertook this study to assess the predominant microbe-associated molecular patterns (MAMPs) present therein and the receptors) that mediate the innate immune responses to them. Here, we demonstrated that intestinal contents from conventional, but not germ-free, mice and rats triggered robust innate immune responses in vitro and in vivo. Such immune responses were abrogated in the absence of either myeloid differentiation factor 88 (MyD88) or Toll-like receptor (TLR) 5, but not TLR4, suggesting that the stimuli was flagellin (i.e., protein subunit of flagella that drives bacterial motility). Accordingly, pre-treating intestinal extracts with proteinase, thereby degrading flagellin, was sufficient to block their ability to activate innate immune responses. Taken together, this work serves to underscore flagellin as a major, heat-stable and bioactive MAMP in the intestinal content that confers this milieu strong potential to trigger innate immune responses.

Psyllium fiber protects mice against western diet-induced metabolic syndrome via the gut microbiota-dependent mechanism

Impacts of dietary fiber on intestinal inflammation are complex, but some specific semi-purified fibers, particularly psyllium, can protect humans and rodents against colitis. Mechanisms underlying such protection are not fully understood but may involve activation of the FXR bile acid receptor. Obesity and its associated consequences, referred to as metabolic syndrome, are associated with, and promoted by, low-grade inflammation in a variety of tissues including the intestine. Hence, we examined whether psyllium might ameliorate the low-grade intestinal inflammation that occurs in diet-induced obesity and, moreover, the extent to which it might ameliorate adiposity and/or dysglycemia in this disease model. We observed that enriching a high-fat diet with psyllium provided strong protection against the low-grade gut inflammation and metabolic consequences that were otherwise induced by the obesogenic diet. Such protection was fully maintained in FXR-deficient mice, indicating that distinct mechanisms mediate psyllium's protection against colitis and metabolic syndrome. Nor did psyllium's protection associate with, or require, fermentation or IL-22 production, both of which are key mediators of beneficial impacts of some other dietary fibers. Psyllium's beneficial impacts were not evident in germfree mice but were observed in Altered Schaedler Flora mice, in which psyllium modestly altered relative and absolute abundance of the small number of taxa present in these gnotobiotic mice. Thus, psyllium protects mice against diet-induced obesity/metabolic syndrome by a mechanism independent of FXR and fermentation but nonetheless requires the presence of at least a minimal microbiota.

Enterohepatic Shunt-Driven Cholemia Predisposes to Liver Cancer

BACKGROUND & AIMS

Pathogenesis of hepatocellular carcinoma (HCC), which kills millions annually, is poorly understood. Identification of risk factors and modifiable determinants and mechanistic understanding of how they impact HCC are urgently needed.

METHODS

We sought early prognostic indicators of HCC in C57BL/6 mice, which we found were prone to developing this disease when fed a fermentable fiber-enriched diet. Such markers were used to phenotype and interrogate stages of HCC development. Their human relevance was tested using serum collected prospectively from an HCC/case-control cohort.

RESULTS

HCC proneness in mice was dictated by the presence of congenitally present portosystemic shunt (PSS), which resulted in markedly elevated serum bile acids (BAs). Approximately 10% of mice from various sources exhibited PSS/cholemia, but lacked an overt phenotype when fed standard chow. However, PSS/cholemic mice fed compositionally defined diets, developed BA- and cyclooxygenase-dependent liver injury, which was exacerbated and uniformly progressed to HCC when diets were enriched with the fermentable fiber inulin. Such progression to cholestatic HCC associated with exacerbated cholemia and an immunosuppressive milieu, both of which were required in that HCC was prevented by impeding BA biosynthesis or neutralizing interleukin-10 or programmed death protein 1. Analysis of human sera revealed that elevated BA was associated with future development of HCC.

CONCLUSIONS

PSS is relatively common in C57BL/6 mice and causes silent cholemia, which predisposes to liver injury and HCC, particularly when fed a fermentable fiber-enriched diet. Incidence of silent PSS/cholemia in humans awaits investigation. Regardless, measuring serum BA may aid HCC risk assessment, potentially alerting select individuals to consider dietary or BA interventions.

Selective IgA Deficiency in Spontaneously Hypertensive Rats With Gut Dysbiosis

BACKGROUND

The spontaneously hypertensive rat (SHR) is extensively used to study hypertension. Gut microbiota dysbiosis is a notable feature in SHR for reasons unknown. Immunoglobulin A (IgA) is a major host factor required for gut microbiota homeostasis. We hypothesized that inadequate IgA contributes to gut microbiota dysbiosis in SHR.

METHODS

IgA was measured in feces, cecum, serum, liver, gut-associated lymphoid tissue, and milk from SHR and Wistar Kyoto rats. IgA regulatory factors like IgM, IgG, and pIgR (polymeric immunoglobulin receptor) were analyzed. IgA and IgG antibodies and blood pressure (BP) were measured before and after administrating a bacterial antigen (ie, flagellin).

RESULTS

Compared with Wistar Kyoto rats, SHR displayed remarkably near-deficient IgA levels accompanied by compensatory increases in serum IgM and IgG and gut-liver pIgR expression. Inadequate milk IgA in SHR emphasized this immune defect stemmed from the neonatal stage. Reduced IgA+ B cells in circulation and Peyer patches indicated a possible reason for the lower IgA in SHR. Noteworthy, a genetic insufficiency was unlikely because administering flagellin to SHR induced anti-flagellin IgA antibodies. This immune response surprisingly accelerated hypertension development in SHR, suggesting IgA quiescence may help maintain lower BP.

CONCLUSIONS

This study is the first to reveal IgA deficiency in SHR as one host factor associated with gut microbiota dysbiosis and invigorates future research to determine the pathophysiological role of IgA in hypertension.

Abstract P109: A Novel Murine Model Of Diet-induced Cholemia For Studies On The Gut-liver-kidney Axis In Blood Pressure Regulation

Bile acids (BA) are classically viewed as emulsifiers produced by the liver for aiding the absorption of fats in the gut. Accumulating evidence now recognizes BA as vasoactive agents capable of lowering blood pressure (BP). However, it remains unclear whether the ensuing hypotension can be associated with end-organ damage. To delineate the pathogenic role of BA in the gut-liver-kidney axis, we leveraged our prior finding that a subset of C57BL/6 mice developed cholemia ( i.e. , high circulating BA) when fed a diet supplemented with 7.5% inulin. Briefly, we challenged 4-week-old male mice (n=50) with the inulin diet for one week and identified the subset that developed cholemia (B6 BA ; n=6). Non-cholemic mice (B6; n=6) were maintained as control. Assessment on BP at 6 months of inulin feeding indicated that B6 BA mice (systolic BP: 107.6 ± 2.2 mmHg; diastolic BP: 78.6 ± 3.1 mmHg) are hypotensive relative to non-cholemic B6 mice (systolic BP: 139.8 ± 5.6 mmHg; diastolic BP: 109.0 ± 3.8 mmHg), which was accompanied by polydipsia (7.0 ± 0.4 ml/day in B6 BA vs 4.3 ± 0.2 ml/day water intake in B6), polyuria (2.5 ± 0.1 ml/day in B6 BA vs 1.2 ± 0.1 ml/day urine output in B6), and elevated urinary BA (28.5 ± 1.7 μM in B6 BA vs 3.3 ± 0.6 μM in B6) in B6 BA mice. B6 BA mice also excreted more urinary creatinine (50.4 ± 3.4 mg/dl in B6 BA vs 25.6 ± 1.3 mg/dl in B6), sodium (271.8 ± 20.1 μmol/day in B6 BA vs 103.0 ± 11.0 μmol/day in B6) and potassium (349.2 ± 16.7 μmol/day in B6 BA vs 128.7 ± 7.7 μmol/day in B6), which could be, in part, explained by their higher glomerular filtration rate (1209.0 ± 121.0 in B6 BA vs 681.2 ± 148.7 μl/min/100 g body weight in B6). Of note, B6 BA mice displayed renomegaly, interstitial nephritis, and bile casts in urine, as well as elevated renal transcripts (>2-fold increase relative to B6) for lipocalin 2, kidney injury molecule-1, tumor necrosis factor alpha, collagen type I α1 and endothelin-1. Taken together, these findings demonstrate that our mouse model of diet-induced cholemia presents with low BP and renal pathology. We envision that this model has notable advantages ( e.g. , ease in inducing cholemia, no early morbidity and tractable for long-term study), in lieu of the conventional bile duct ligation approach, for studying how BA regulate BP.

Abstract P077: Targeting Neutrophilia Is A Therapeutic Strategy To Regulate Blood Pressure

Neutrophils are important innate immune cells that are relatively understudied for their contributions to blood pressure (BP) regulation. As neutrophilia is a clinical marker for various pathologies, we hypothesized that neutrophilia is also a feature of hypertension and curtailing neutrophilia is beneficial for lowering BP. Peripheral neutrophil levels were quantitated in Dahl salt-sensitive (S) and Dahl salt-resistant (R) rats consuming either a low salt (0.3% NaCl) or high salt (2% NaCl) diet. Compared to R rats, S rats on a low-salt diet already exhibited neutrophilia (% neutrophils, 33.51±1.6 vs. 39.74±1.2, p<0.05). Introducing a high salt diet further potentiated the neutrophilia in S rats prone to salt-induced hypertension (% neutrophils, 48.21±0.6, p<0.05). These data suggest that neutrophilia is pro-hypertensive. To determine the possible mechanism for the pro-hypertensive effects of neutrophils, we investigated two major functions of neutrophils i.e., generation of reactive oxygen species (ROS) and neutrophil extracellular traps (NETs, web-like structures of expelled neutrophil DNA). Peripheral neutrophils stimulated with either PMA or LPS showed a ~ 3-fold induction of ROS and NETs, respectively, in S rats compared to R rats on a low-salt diet. Introducing a high-salt diet increased ROS and NETs (~2-fold), the extent of elevation being higher in S rats. Impressively, treatment of S rats on a high-salt diet with 1,3-butandiol [(β - hydroxybutyrate (βOHB, a ketone body) precursor] in the drinking water (20% v/v, 4 weeks) significantly lowered neutrophilia (vehicle: 1.74±0.5 vs βOHB: 0.73±0.3 x 10 9 cells/l, p<0.05) in tandem with their decreased BP (vehicle: 161.2±9.3 vs βOHB: 138.3±4.5 mmHg systolic BP, p<0.05). Interestingly, βOHB intervention also reduced neutrophil levels in R rats (vehicle: 1.15±0.5 vs βOHB: 0.95±0.5 x 10 9 cells/l), albeit to a lesser degree than S rats. Importantly, βOHB administration to S and R rats also reduced NETs and ROS (~2-fold), predominantly in S rats. Collectively, our data are the first to demonstrate that an exaggerated innate immune response via neutrophilia is pathological in hypertension, whereby curbing the neutrophilic response ( e.g., βOHB) could present therapeutic potential in lowering BP.

Activation of CD81+ skin ILC2s by cold-sensing TRPM8+ neuron-derived signals maintains cutaneous thermal homeostasis

As the outermost barrier tissue of the body, the skin harbors a large number of innate lymphoid cells (ILCs) that help maintain local homeostasis in the face of changing environments. How skin-resident ILCs are regulated and function in local homeostatic maintenance is poorly understood. We here report the discovery of a cold-sensing neuron-initiated pathway that activates skin group 2 ILCs (ILC2s) to help maintain thermal homeostasis. In stearoyl-CoA desaturase 1 (SCD1) knockout mice whose skin is defective in heat maintenance, chronic cold stress induced excessive activation of CCR10^-CD81⁺ST2⁺ skin ILC2s and associated inflammation. Mechanistically, stimulation of the cold-sensing receptor TRPM8 expressed in sensory neurons of the skin led to increased production of IL-18, which, in turn, activated skin ILC2s to promote thermogenesis. Our findings reveal a neuroimmune link that regulates activation of skin ILC2s to support thermal homeostasis and promotes skin inflammation after hyperactivation.

Sterile neutrophilia induced via CXCR4 antagonism ameliorates colonic inflammation by increasing immunosuppressive regulatory T cells

Sterile neutrophilia (SN) is commonly associated with chronic disease, but its role in inflammatory bowel diseases (IBD) is largely unknown. AMD3100 (plerixafor; AMD) is a CXCR4 antagonist that promotes neutrophil egress from bone marrow resulting in SN. To study the role of SN in IBD, we induced chronic intestinal inflammation in C57BL6 mice via 4 weekly injections of IL-10R neutralizing antibody and administered AMD (10 mg/kg bw, i.p., twice weekly) or vehicle. As expected, AMD-treated control and colitic mice had increased peripheral and splenic neutrophils. AMD treatment remarkably reduced epithelial damage and hyperplasia, immune cell infiltration, and disease activity index. To elucidate the protective mechanism, we analyzed immune cells in peripheral circulation, spleen and lamina propria. In circulation, colitic mice with AMD treatment had elevated % CD3+CD4+ helper T cells (Th) but reduced % CD3+CD8+ cytotoxic T (Tc) cells. Yet, the % CD3+CD4+FoxP3+ cells (Tregs) and % CD3+CD4+RORγt+ cells (Th17) remained unchanged. In spleen, AMD treatment significantly increased Tregs, but decreased Th and Tc cells. In lamina propria, AMD treatment markedly elevated Tregs, including RORγt+ Tregs and tolerogenic IL-10+ Tregs. Conversely, the inflammatory IL-17+ Th cells were decreased in AMD-treated colitic mice. In addition to the immunosuppressive milieu, AMD-treated colitic mice had increased ileal expression of the antimicrobial peptide angiogenin 4, which further suggests SN to be important in maintaining gut microbiota homeostasis. Collectively, our results demonstrate that SN could be an adaptive and beneficial immune response during chronic intestinal inflammation.

This research was funded by R01 grant from the National Institutes of Health (NIH) [grant number CA219144] and Crohn’s and Colitis Foundation (CCF) [grant number 855256].

Dynamics of antimicrobial protein secretion in mouse milk

Breast milk is the preferred food for the newborns and considered as complete ‘edible immune system’. In addition, breast milk is a source of innate and adaptive proteins which not only protects the naïve infant gastrointestinal tract from enteropathogens but also aid in the appropriate initial colonization of gut microbiota. In this study, we analyzed antimicrobial immune proteins in the milk from C57BL/6 dams at several time points, and observed distinctive patterns in the immune protein levels throughout the lactation period. The presence of innate immune proteins serum amyloid A (SAA), CD14, and notably lipocalin-2 (Lcn2) were observed in high quantities with Lcn2 and SAA present at microgram levels suggesting a potential niche for these proteins during neonatal immune development. Moreover, low dose LPS administration to dams significantly increased some of these proteins in the milk. In addition, adaptive immune proteins immunoglobulins (Ig) A and G with IgG were present in milk at higher quantities compared to IgA at day 5 post-delivery. Interestingly, class-switching occurs by day 15 indicating a selective adaptive immune preference towards IgA, which could be due to gut colonization of newborns with more complex gut microbiota with aging and IgA being a major gut homeostatic factor. Additionally, milk from IgA-deficient dams allowed for robust proliferation of E. coli compared to wild-type milk further signifying the potential involvement of IgA during the early colonization of microbes in the neonatal gut. Collectively, our findings provide insight in the various immune proteins with antimicrobial activity may play a major role in the initial microbial colonization in the gut, which has long-lasting consequences on the host.

Supported by NIH R01-CA219144, NCI Diversity Supplement (CA219144-05S1)

Low-dose 1,3-butanediol reverses age-associated vascular dysfunction independent of ketone body β-hydroxybutyrate

With an aging global population, identifying novel therapeutics are necessary to increase longevity and decrease the deterioration of essential end organs such as the vasculature. Secondary alcohol, 1,3-butanediol (1,3-BD), is commonly administered to stimulate the biosynthesis of the most abundant ketone body β-hydroxybutyrate (βHB), in lieu of nutrient deprivation. However, suprapharmacological concentrations of 1,3-BD are necessary to significantly increase systemic βHB, and 1,3-BD per se can cause vasodilation at nanomolar concentrations. Therefore, we hypothesized that 1,3-BD could be a novel antiaging therapeutic, independent of βHB biosynthesis. To test this hypothesis, we administered a low-dose (5%) 1,3-BD to young and old Wistar-Kyoto (WKY) rats via drinking water for 4 wk and measured indices of vascular function and metabolism posttreatment. We observed that low-dose 1,3-BD was sufficient to reverse age-associated endothelial-dependent and -independent dysfunction, and this was not associated with increased βHB bioavailability. Further analysis of the direct vasodilator mechanisms of 1,3-BD revealed that it is predominantly an endothelium-dependent vasodilator through activation of potassium channels and nitric oxide synthase. In summary, we report that 1,3-BD, at a concentration that does not stimulate βHB biosynthesis, could be a nutraceutical that can reverse the age-associated decline in vascular function. These results emphasize that 1,3-BD has multiple, concentration-dependent mechanisms of action. Therefore, we suggest alternative approaches to study the physiological and cardiovascular effects of βHB.NEW & NOTEWORTHY 1,3-Butanediol (1,3-BD) is often administered to stimulate the biosynthesis of the most abundant ketone body, β-hydroxybutyrate (βHB), and its purported salubrious effects. Here, we report that a low dose of 1,3-BD (5%) is sufficient to reverse age-associated vascular dysfunction, independent of βHB. Therefore, low-dose 1,3-BD could be a novel therapeutic to increase blood flow and improve the quality of life in the elderly.

Reconstitution of the host holobiont in germ-free born male rats acutely increases bone growth and affects marrow cellular content

Integration of microbiota in a host begins at birth and progresses during adolescence, forming a multidirectional system of physiological interactions. Here, we present an instantaneous effect of natural, bacterial gut colonization on the acceleration of longitudinal and radial bone growth in germ-free born, 7-wk-old male rats. Changes in bone mass and structure were analyzed after 10 days following the onset of colonization through cohousing with conventional rats and revealed unprecedented acceleration of bone accrual in cortical and trabecular compartments, increased bone tissue mineral density, improved proliferation and hypertrophy of growth plate chondrocytes, bone lengthening, and preferential deposition of periosteal bone in the tibia diaphysis. In addition, the number of small in size adipocytes increased, whereas the number of megakaryocytes decreased, in the bone marrow of conventionalized germ-free rats indicating that not only bone mass but also bone marrow environment is under control of gut microbiota signaling. The changes in bone status paralleled with a positive shift in microbiota composition toward short-chain fatty acids (SCFA)-producing microbes and a considerable increase in cecal SCFA concentrations, specifically butyrate. Furthermore, reconstitution of the host holobiont increased hepatic expression of IGF-1 and its circulating levels. Elevated serum levels of 25-hydroxy vitamin D and alkaline phosphatase pointed toward an active process of bone formation. The acute stimulatory effect on bone growth occurred independently of body mass increase. Overall, the presented model of conventionalized germ-free rats could be used to study microbiota-based therapeutics for combatting dysbiosis-related bone disorders.

Ketone body β-hydroxybutyrate is an autophagy-dependent vasodilator

Autophagy has long been associated with longevity, and it is well established that autophagy reverts and prevents vascular deterioration associated with aging and cardiovascular diseases. Currently, our understanding of how autophagy benefits the vasculature is centered on the premise that reduced autophagy leads to the accumulation of cellular debris, resulting in inflammation and oxidative stress, which are then reversed by reconstitution or upregulation of autophagic activity. Evolutionarily, autophagy also functions to mobilize endogenous nutrients in response to starvation. Therefore, we hypothesized that the biosynthesis of the most physiologically abundant ketone body, β-hydroxybutyrate (βHB), would be autophagy dependent and exert vasodilatory effects via its canonical receptor, Gpr109a. To the best of our knowledge, we have revealed for the first time that the biosynthesis of βHB can be impaired by preventing autophagy. Subsequently, βHB caused potent vasodilation via potassium channels but not Gpr109a. Finally, we observed that chronic consumption of a high-salt diet negatively regulates both βHB biosynthesis and hepatic autophagy and that reconstitution of βHB bioavailability prevents high-salt diet–induced endothelial dysfunction. In summary, this work offers an alternative mechanism to the antiinflammatory and antioxidative stress hypothesis of autophagy-dependent vasculoprotection. Furthermore, it reveals a direct mechanism by which ketogenic interventions (e.g., intermittent fasting) improve vascular health.

Immunoglobulin A, an Active Liaison for Host-Microbiota Homeostasis

Mucosal surfaces in the gastrointestinal tract are continually exposed to native, commensal antigens and susceptible to foreign, infectious antigens. Immunoglobulin A (IgA) provides dual humoral responses that create a symbiotic environment for the resident gut microbiota and prevent the invasion of enteric pathogens. This review features recent immunological and microbial studies that elucidate the underlying IgA and microbiota-dependent mechanisms for mutualism at physiological conditions. IgA derailment and concurrent microbiota instability in pathological diseases are also discussed in detail. Highlights of this review underscore that the source of IgA and its structural form can dictate microbiota reactivity to sustain a diverse niche where both host and bacteria benefit. Other important studies emphasize IgA insufficiency can result in the bloom of opportunistic pathogens that encroach the intestinal epithelia and disseminate into circulation. The continual growth of knowledge in these subjects can lead to the development of therapeutics targeting IgA and/or the microbiota to treat life threatening diseases.

IL-10 Receptor Neutralization-Induced Colitis in Mice: A Comprehensive Guide

Interleukin-10 (IL-10) and its receptor (IL-10R) have been foremost targets to understand inflammatory bowel disease (IBD) pathogenesis. For the past several decades, IL-10-deficient (Il10^-/- ) mice were considered one of the best models to study immune-mediated colitis. Several physiologic limitations with this model, e.g., delayed and varied disease onset, have hindered investigators in testing new clinical therapies for IBD. In this article, we provide comprehensive guidance for using anti-IL-10R monoclonal antibody (αIL-10R mAb) neutralization as a superior alternative model to study IBD. This article describes the feasibility of using αIL-10R mAb to induce chronic colitis (within 4 weeks), perform time-dependent mechanistic studies, and assess the efficacy of IBD therapeutics. This article also delineates protocols for in-house assays to critically assess colitis and associated inflammatory parameters. Overall, we underscore αIL-10R mAb neutralization as a relevant immune-mediated murine colitis model to study human Crohn's disease. © 2021 Wiley Periodicals LLC. Basic Protocol 1: Induction of chronic colitis in mice via αIL-10R mAb neutralization Basic Protocol 2: Biochemical evaluation of αIL-10R mAb neutralization-induced chronic colitis Support Protocol 1: Stool analysis and scoring Support Protocol 2: Swiss roll method.