Neonatal Mouse Gut Metabolites Influence Cryptosporidium parvum Infection in Intestinal Epithelial Cells

Cryptosporidium parvum disrupts intestinal epithelial barrier in neonatal mice through downregulation of cell junction molecules

BACKGROUND

Cryptosporidium spp. cause watery diarrhea in humans and animals, especially in infants and neonates. They parasitize the apical surface of the epithelial cells in the intestinal lumen. However, the pathogenesis of Cryptosporidium-induced diarrhea is not fully understood yet.

METHODOLOGY/PRINCIPAL FINDINGS

In this study, we infected C57BL/6j neonatal mice with C. parvum IIa and IId subtypes, and examined oocyst burden, pathological changes, and intestinal epithelial permeability during the infection. In addition, transcriptomic analyses were used to study the mechanism of diarrhea induced by the C. parvum IId subtype. The neonatal mice were sensitive to both C. parvum IIa and IId infection, but the IId subtype caused a wide oocyst shedding window and maintained the high oocyst burden in the mice compared with the IIa subtype. In addition, the mice infected with C. parvum IId resulted in severe intestinal damage at the peak of infection, leading to increased permeability of the epithelial barrier. The KEGG, GO and GSEA analyses revealed that the downregulation of adherens junction and cell junction molecules at 11 dpi. Meanwhile, E-cadherin, which is associated with adherens junction, was reduced at the protein level in mouse ileum at peak and late infection.

CONCLUSIONS/SIGNIFICANCE

C. parvum IId infection causes more severe pathological damage than C. parvum IIa infection in neonatal mice. Furthermore, the impairment of the epithelial barrier during C. parvum IId infection results from the downregulation of intestinal junction proteins.

Microbiome diversity is a modifiable virulence factor for cryptosporidiosis

Cryptosporidium spp. infection causes significant disease in immunosuppressed individuals and children under the age of 5 years. The severity of the pathological presentation of cryptosporidiosis is a function of the host and parasite genotypes, host immune status, and the enteric environment or microbiome of the host. Cryptosporidiosis often presents with abdominal pain and severe diarrhoea and is associated with intestinal dysbiosis and inflammation. Our systematic analysis of the available literature revealed that bacterial diversity is reduced during infection in larger animal models, lending support to recent studies which indicate that the use of probiotics or the presence of a naturally diverse gut microbiome can prevent or minimise pathology caused by gastrointestinal pathogens. In summary, we present evidence that the presence of a diverse gut microbiome, natural or induced, reduces both symptomatic pathology and oocyst output.

Specific pathway abundances in the neonatal calf faecal microbiome are associated with susceptibility to Cryptosporidium parvum infection: a metagenomic analysis

BACKGROUND

Cryptosporidium parvum is the main cause of calf scour worldwide. With limited therapeutic options and research compared to other Apicomplexa, it is important to understand the parasites' biology and interactions with the host and microbiome in order to develop novel strategies against this infection. The age-dependent nature of symptomatic cryptosporidiosis suggests a link to the undeveloped immune response, the immature intestinal epithelium, and its associated microbiota. This led us to hypothesise that specific features of the early life microbiome could predict calf susceptibility to C. parvum infection.

RESULTS

In this study, a single faecal swab sample was collected from each calf within the first week of life in a cohort of 346 animals. All 346 calves were subsequently monitored for clinical signs of cryptosporidiosis, and calves that developed diarrhoea were tested for Rotavirus, Coronavirus, E. coli F5 (K99) and C. parvum by lateral flow test (LFT). A retrospective case-control approach was taken whereby a subset of healthy calves (Control group; n = 33) and calves that went on to develop clinical signs of infectious diarrhoea and test positive for C. parvum infection via LFT (Cryptosporidium-positive group; n = 32) were selected from this cohort, five of which were excluded due to low DNA quality. A metagenomic analysis was conducted on the faecal microbiomes of the control group (n = 30) and the Cryptosporidium-positive group (n = 30) prior to infection, to determine features predictive of cryptosporidiosis. Taxonomic analysis showed no significant differences in alpha diversity, beta diversity, and taxa relative abundance between controls and Cryptosporidium-positive groups. Analysis of functional potential showed pathways related to isoprenoid precursor, haem and purine biosynthesis were significantly higher in abundance in calves that later tested positive for C. parvum (q ≤ 0.25). These pathways are either absent or streamlined in the C. parvum parasites. Though the de novo production of isoprenoid precursors, haem and purines are absent, C. parvum has been shown to encode enzymes that catalyse the downstream reactions of these pathway metabolites, indicating that C. parvum may scavenge those products from an external source.

CONCLUSIONS

The host has previously been put forward as the source of essential metabolites, but our study suggests that C. parvum may also be able to harness specific metabolic pathways of the microbiota in order to survive and replicate. This finding is important as components of these microbial pathways could be exploited as potential therapeutic targets for the prevention or mitigation of cryptosporidiosis in bovine neonates.

Indole metabolites generated by microbiota inhibit Cryptosporidium growth

Funkhouser-Jones et al. recently identified gut metabolites that affected Cryptosporidium growth. A key focus, indole, was shown to inhibit the parasite in vivo and in vitro by decreasing the host mitochondria function and the membrane potential of parasite mitosomes. These findings help clarify the role microflora and metabolites play in host resistance.

Microbiota-produced indole metabolites disrupt mitochondrial function and inhibit Cryptosporidium parvum growth

Cryptosporidiosis is a leading cause of life-threatening diarrhea in young children in resource-poor settings. To explore microbial influences on susceptibility, we screened 85 microbiota-associated metabolites for their effects on Cryptosporidium parvum growth in vitro. We identify eight inhibitory metabolites in three main classes: secondary bile salts/acids, a vitamin B6 precursor, and indoles. Growth restriction of C. parvum by indoles does not depend on the host aryl hydrocarbon receptor (AhR) pathway. Instead, treatment impairs host mitochondrial function and reduces total cellular ATP, as well as directly reducing the membrane potential in the parasite mitosome, a degenerate mitochondria. Oral administration of indoles, or reconstitution of the gut microbiota with indole-producing bacteria, delays life cycle progression of the parasite in vitro and reduces the severity of C. parvum infection in mice. Collectively, these findings indicate that microbiota metabolites impair mitochondrial function and contribute to colonization resistance to Cryptosporidium infection.

Microbiota produced indole metabolites disrupt host cell mitochondrial energy production and inhibit Cryptosporidium parvum growth

Cryptosporidiosis is a leading cause of life-threatening diarrhea in young children in resource-poor settings. Susceptibility rapidly declines with age, associated with changes in the microbiota. To explore microbial influences on susceptibility, we screened 85 microbiota- associated metabolites enriched in the adult gut for their effects on C. parvum growth in vitro. We identified eight inhibitory metabolites in three main classes: secondary bile salts/acids, a vitamin B 6 precursor, and indoles. Growth restriction of C. parvum by indoles did not depend on the host aryl hydrocarbon receptor (AhR) pathway. Instead, treatment impaired host mitochondrial function and reduced total cellular ATP, as well as directly reduced the membrane potential in the parasite mitosome, a degenerate mitochondria. Oral administration of indoles, or reconstitution of the gut microbiota with indole producing bacteria, delayed life cycle progression of the parasite in vitro and reduced severity of C. parvum infection in mice. Collectively, these findings indicate that microbiota metabolites contribute to colonization resistance to Cryptosporidium infection.

Dendritic Cells and Cryptosporidium: From Recognition to Restriction

Host immune responses are required for the efficient control of cryptosporidiosis. Immunity against Cryptosporidium infection has been best studied in mice, where it is mediated by both innate and adaptive immune responses. Dendritic cells are the key link between innate and adaptive immunity and participate in the defense against Cryptosporidium infection. While the effector mechanism varies, both humans and mice rely on dendritic cells for sensing parasites and restricting infection. Recently, the use of mouse-adapted strains C. parvum and mouse-specific strain C. tyzzeri have provided tractable systems to study the role of dendritic cells in mice against this parasite. In this review, we provide an overview of recent advances in innate immunity acting during infection with Cryptosporidium with a major focus on the role of dendritic cells in the intestinal mucosa. Further work is required to understand the role of dendritic cells in the activation of T cells and to explore associated molecular mechanisms. The identification of Cryptosporidium antigen involved in the activation of Toll-like receptor signaling in dendritic cells during infection is also a matter of future study. The in-depth knowledge of immune responses in cryptosporidiosis will help develop targeted prophylactic and therapeutic interventions.

Microbiome-Metabolomics Analysis of the Impacts of Cryptosporidium muris Infection in BALB/C Mice

Cryptosporidium is a leading cause of diarrheal disease and mortality in young children worldwide. Cryptosporidium invades small intestinal epithelial cells and forms a unique intracellular niche, a process that may alter gut microbes and their production metabolites. However, the mechanism of interactions between gut microbes, metabolites, and parasites is poorly understood. Here, we first characterized the impacts of Cryptosporidium infection on gut microbiota using a microbiome-to-metabolome association study. BALB/c mice were gavaged with Cryptosporidium muris, and fecal samples were collected at 0, 7, 14, 21, and 28 days postinfection (dpi) to observe changes in the intestinal microbes of the body during parasite infection. The infected group had a significantly increased relative abundance of bacterial taxa, such as Lachnospiraceae and Prevotella (P < 0.05), associated with the biosynthesis of short-chain fatty acids (SCFAs). Metabolites related to the metabolic pathways, steroid hormone biosynthesis, and biosynthesis of unsaturated fatty acids pathway were upregulated at 7 dpi, indicating that related metabolites in the biosynthesis of unsaturated fatty acids may be essential for C. muris reproduction in vivo. The metabolites involved in metabolic pathways, bile secretion, and primary bile acid biosynthesis were upregulated at 14 dpi, and we speculate that these metabolites may be critical to the growth and development of Cryptosporidium oocysts in the host. Correlation analysis revealed that Firmicutes bacteria are significantly associated with α-linolenic acid metabolism pathways (P< 0.05). The gut microbiota changes dynamically, and the metabolites involved in fatty acid and bile acid biosynthesis may play important roles during cryptosporidiosis. Details of the gut microbiota and the metabolome after infection with Cryptosporidium may aid in the discovery of specific diagnostic markers and help us understand the changes in parasite metabolic pathways. IMPORTANCE Cryptosporidiosis is a gastrointestinal disease in humans and animals caused by the protozoan parasite Cryptosporidium. Control and treatment of the disease is challenging due to the lack of sensitive diagnostic tools and effective chemotherapy. The dynamics of gut microbiota and metabolites during Cryptosporidium infection may be the key to finding drugs and targets for parasite infection control. Our results indicate that C. muris infection can disrupt gut microbiota and metabolites, resulting in decreased bacterial abundance at the parasitic site. Unsaturated fatty acid pathway biosynthesis-related metabolites are significantly elevated at the patent period. Interestingly, the metabolite pathway that significantly elevated during peak parasite growth was bile acid, the metabolites of which may be important for the circulation of infection of Cryptosporidium oocysts in the host. The enhancing effects of short-chain fatty acid and bile acid metabolism on the growth and development of Cryptosporidium proposed in this study may provide a theoretical basis for future research on novel drugs and vaccines against this intestinal parasite.

Early immune and host cell responses to Cryptosporidium infection

Cryptosporidium spp. are opportunistic protozoan parasites that infect epithelial cells of the small intestine and cause diarrheal illness in both immunocompetent and immunodeficient individuals. These infections may be more severe in immunocompromised individuals and young children, especially in children under 2 in developing countries. The parasite has a global distribution and is an important cause of childhood diarrhea where it may result in cognitive impairment and growth deficits. Current therapies are limited with nitazoxanide being the only FDA-approved drug. However, it is not efficacious in immunocompromised patients. Additionally, there are no vaccines for cryptosporidiosis available. While acquired immunity is needed to clear Cryptosporidium parasites completely, innate immunity and early responses to infection are important in keeping the infection in check so that adaptive responses have time to develop. Infection is localized to the epithelial cells of the gut. Therefore, host cell defenses are important in the early response to infection and may be triggered through toll receptors or inflammasomes which induce a number of signal pathways, interferons, cytokines, and other immune mediators. Chemokines and chemokine receptors are upregulated which recruit immune cells such neutrophils, NK cells, and macrophages to the infection site to help in host cell defense as well as dendritic cells that are an important bridge between innate and adaptive responses. This review will focus on the host cell responses and the immune responses that are important in the early stages of infection.

Lentinan -triggered butyrate-producing bacteria drive the expulsion of the intestinal helminth Trichinella spiralis in mice

Trichinellosis caused by Trichinella spiralis is a serious zoonosis with a worldwide distribution. Lentinan (LNT) is known to modulate the intestinal environment with noted health benefits, yet the effect of LNT against intestinal helminth is unknown. In our study, we first observed that LNT could trigger worm expulsion by promoting mucus layer functions through alteration of gut microbiota. LNT restored the abundance of Bacteroidetes and Proteobacteria altered by T. spiralis infection to the control group level. Interestingly, LNT triggered the production of butyrate. Then, we determined the deworming capacity of probiotics (butyrate-producing bacteria) in mice. Collectively, these findings indicated that LNT could modulate intestinal dysbiosis by T. spiralis, drive the expulsion of intestinal helminth and provided an easily implementable strategy to improve the host defence against T. spiralis infection.

Development of Two Mouse Models for Vaccine Evaluation against Cryptosporidiosis

Cryptosporidiosis was shown a decade ago to be a major contributor to morbidity and mortality of diarrheal disease in children in low-income countries. A serious obstacle to develop and evaluate immunogens and vaccines to control this disease is the lack of well-characterized immunocompetent rodent models. Here, we optimized and compared two mouse models for the evaluation of vaccines: the Cryptosporidium tyzzeri model, which is convenient for screening large numbers of potential mixtures of immunogens, and the Cryptosporidium parvum-infected mouse pretreated with interferon gamma-neutralizing monoclonal antibody.

Effect of Caging on Cryptosporidium parvum Proliferation in Mice

Cryptosporidiosis is an enteric infection caused by several protozoan species in the genus Cryptosporidium (phylum Apicomplexa). Immunosuppressed mice are commonly used to model this infection. Surprisingly, for a pathogen like Cryptosporidium parvum, which is readily transmitted fecal-orally, mice housed in the same cage can develop vastly different levels of infection, ranging from undetectable to lethal. The motivation for this study was to investigate this phenomenon and assess the association between the severity of cryptosporidiosis and the fecal microbiota. To this aim, the association between severity of cryptosporidiosis and caging (group caged vs. individually caged) and between the microbiota taxonomy and the course of the infection was examined. In contrast to mice caged in groups of four, a majority of mice caged individually did not excrete a detectable level of oocysts. Microbiota α diversity in samples collected between three days prior to infection and one day post-infection was negatively correlated with the severity of cryptosporidiosis, suggesting a causal negative relationship between microbiota diversity and susceptibility to C. parvum.

Curcumin mitigates Cryptosporidium parvum infection through modulation of gut microbiota and innate immune-related genes in immunosuppressed neonatal mice

Cryptosporidium parvum is a major cause of diarrheal disease in immature or weakened immune systems, mainly in infants and young children in resource-poor settings. Despite its high prevalence, fully effective and safe drugs for the treatment of C. parvum infections remain scarce, and there is no vaccine. Meanwhile, curcumin has shown protective effects against C. parvum infections. However, the mechanisms of action and relationship to the gut microbiota and innate immune responses are unclear. Immunosuppressed neonatal mice were infected with oocysts of C. parvum and either untreated or treated with a normal diet, curcumin or paromomycin. We found that curcumin stopped C. parvum oocysts shedding in the feces of infected immunosuppressed neonatal mice, prevented epithelial damage, and villi degeneration, as well as prevented recurrence of infection. Curcumin supplementation increased the relative abundance of Bacteroidetes and decreased the relative abundance of Firmicutes and Proteobacteria in mice infected with C. parvum as shown by 16S rRNA gene sequencing analysis. The relative abundance of Lactobacillus, Bacteroides, Akkermansia, Desulfovibrio, Prevotella, and Helicobacter was significantly associated with C. parvum infection inhibited by curcumin. Curcumin significantly (P < 0.01) suppressed IFN-γ and IL -18 gene expression levels in immunosuppressed neonatal C. parvum-infected mice. We demonstrate that the therapeutic effects curcumin are associated with alterations in the gut microbiota and innate immune-related genes, which may be linked to the anti-Cryptosporidium mechanisms of curcumin.

Developmental Stage, Solid Food Introduction, and Suckling Cessation Differentially Influence the Comaturation of the Gut Microbiota and Intestinal Epithelium in Rabbits

BACKGROUND

In mammals, the establishment around weaning of a symbiotic relationship between the gut microbiota and its host determines long-term health.

OBJECTIVES

The aim of this study was to identify the factors driving the comaturation of the gut microbiota and intestinal epithelium at the suckling-to-weaning transition. We hypothesized that the developmental stage, solid food ingestion, and suckling cessation contribute to this process.

METHODS

From birth to day 18, Hyplus rabbits were exclusively suckling. From day 18 to day 25, rabbits were 1) exclusively suckling; 2) suckling and ingesting solid food; or 3) exclusively ingesting solid food. The microbiota (16S amplicon sequencing), metabolome (nuclear magnetic resonance), and epithelial gene expression (high-throughput qPCR) were analyzed in the cecum at days 18 and 25.

RESULTS

The microbiota structure and metabolic activity were modified with age when rabbits remained exclusively suckling. The epithelial gene expression of nutrient transporters, proliferation markers, and innate immune factors were also regulated with age (e.g., 1.5-fold decrease of TLR5). Solid food ingestion by suckling rabbits had a major effect on the gut microbiota by increasing its α diversity, remodeling its structure (e.g., 6.3-fold increase of Ruminococcaceae), and metabolic activity (e.g., 4.6-fold increase of butyrate). Solid food introduction also regulated the gene expression of nutrient transporters, differentiation markers, and innate immune factors in the epithelium (e.g., 3-fold increase of nitric oxide synthase). Suckling cessation had no effect on the microbiota, while it regulated the expression of genes involved in epithelial differentiation and immunoglobulin transport (e.g., 2.5-increase of the polymeric immunoglobulin receptor).

CONCLUSIONS

In rabbits, the maturation of the microbiota at the suckling-to-weaning transition is driven by the introduction of solid food and, to a lesser extent, by the developmental stage. In contrast, the maturation of the intestinal epithelium at the suckling-to-weaning transition is under the influence of the developmental stage, solid food introduction, and suckling cessation.

Serum metabolomics in chickens infected with Cryptosporidium baileyi

Background

Cryptosporidium baileyi is an economically important zoonotic pathogen that causes serious respiratory symptoms in chickens for which no effective control measures are currently available. An accumulating body of evidence indicates the potential and usefulness of metabolomics to further our understanding of the interaction between pathogens and hosts, and to search for new diagnostic or pharmacological biomarkers of complex microorganisms. The aim of this study was to identify the impact of C. baileyi infection on the serum metabolism of chickens and to assess several metabolites as potential diagnostic biomarkers for C. baileyi infection.

Methods

Ultraperformance liquid chromatography-mass spectrometry (UPLC-MS) and subsequent multivariate statistical analysis were applied to investigate metabolomics profiles in the serum samples of chickens infected with C. baileyi, and to identify potential metabolites that can be used to distinguish chickens infected with C. baileyi from non-infected birds.

Results

Multivariate statistical analysis identified 138 differential serum metabolites between mock- and C. baileyi-infected chickens at 5 days post-infection (dpi), including 115 upregulated and 23 downregulated compounds. These metabolites were significantly enriched into six pathways, of which two pathways associated with energy and lipid metabolism, namely glycerophospholipid metabolism and sphingolipid metabolism, respectively, were the most enriched. Interestingly, some important immune-related pathways were also significantly enriched, including the intestinal immune network for IgA production, autophagy and cellular senescence. Nine potential C. baileyi-responsive metabolites were identified, including choline, sirolimus, all-trans retinoic acid, PC(14:0/22:1(13Z)), PC(15:0/22:6(4Z,7Z,10Z,13Z,16Z,19Z)), PE(16:1(9Z)/24:1(15Z)), phosphocholine, SM(d18:0/16:1(9Z)(OH)) and sphinganine.

Conclusions

This is the first report on serum metabolic profiling of chickens with early-stage C. baileyi infection. The results provide novel insights into the pathophysiological mechanisms of C. baileyi in chickens.

Graphic abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-021-04834-y.

Cryptosporidiosis Modulates the Gut Microbiome and Metabolism in a Murine Infection Model

Cryptosporidiosis is a major human health concern globally. Despite well-established methods, misdiagnosis remains common. Our understanding of the cryptosporidiosis biochemical mechanism remains limited, compounding the difficulty of clinical diagnosis. Here, we used a systems biology approach to investigate the underlying biochemical interactions in C57BL/6J mice infected with Cryptosporidium parvum. Faecal samples were collected daily following infection. Blood, liver tissues and luminal contents were collected 10 days post infection. High-resolution liquid chromatography and low-resolution gas chromatography coupled with mass spectrometry were used to analyse the proteomes and metabolomes of these samples. Faeces and luminal contents were additionally subjected to 16S rRNA gene sequencing. Univariate and multivariate statistical analysis of the acquired data illustrated altered host and microbial energy pathways during infection. Glycolysis/citrate cycle metabolites were depleted, while short-chain fatty acids and D-amino acids accumulated. An increased abundance of bacteria associated with a stressed gut environment was seen. Host proteins involved in energy pathways and Lactobacillus glyceraldehyde-3-phosphate dehydrogenase were upregulated during cryptosporidiosis. Liver oxalate also increased during infection. Microbiome–parasite relationships were observed to be more influential than the host–parasite association in mediating major biochemical changes in the mouse gut during cryptosporidiosis. Defining this parasite–microbiome interaction is the first step towards building a comprehensive cryptosporidiosis model towards biomarker discovery, and rapid and accurate diagnostics.

Polymicrobial Interactions Operative during Pathogen Transmission

Pathogen transmission is a key point not only for infection control and public health interventions but also for understanding the selective pressures in pathogen evolution. The “success” of a pathogen lies not in its ability to cause signs and symptoms of illness but in its ability to be shed from the initial hosts, survive between hosts, and then establish infection in a new host. Recent insights have shown the importance of the interaction between the pathogen and both the commensal microbiome and coinfecting pathogens on shedding, environmental survival, and acquisition of infection. Pathogens have evolved in the context of cooperation and competition with other microbes, and the roles of these cooperations and competitions in transmission can inform novel preventative and therapeutic strategies.

Cryptosporidium: Host-Parasite Interactions and Pathogenesis

Purpose of Review

Cryptosporidium spp. (C. hominis and C. parvum) are a major cause of diarrhea-associated morbidity and mortality in young children globally. While C. hominis only infects humans, C. parvum is a zoonotic parasite that can be transmitted from infected animals to humans. There are no treatment or control measures to fully treat cryptosporidiosis or prevent the infection in humans and animals. Our knowledge on the molecular mechanisms of Cryptosporidium-host interactions and the underlying factors that govern infectivity and disease pathogenesis is very limited.

Recent Findings

Recent development of genetics and new animal models of infection, along with progress in cell culture platforms to complete the parasite lifecycle in vitro, is greatly advancing the Cryptosporidium field.

Summary

In this review, we will discuss our current knowledge of host-parasite interactions and how genetic manipulation of Cryptosporidium and promising infection models are opening the doors towards an improved understanding of parasite biology and disease pathogenesis.