Malic enzyme 1 knockout has no deleterious phenotype and is favored in the male germline under standard laboratory conditions.

Malic Enzyme 1 (ME1) plays an integral role in fatty acid synthesis and cellular energetics through its production of NADPH and pyruvate. As such, it has been identified as a gene of interest in obesity, type 2 diabetes, and an array of epithelial cancers, with most work being performed in vitro. The current standard model for ME1 loss in vivo is the spontaneous Mod-1 null allele, which produces a canonically inactive form of ME1. Herein, we describe two new genetically engineered mouse models exhibiting ME1 loss at dynamic timepoints. Using murine embryonic stem cells and Flp/FRT and Cre/loxP class switch recombination, we established a germline Me1 knockout model (Me1 KO) and an inducible conditional knockout model (Me1 cKO), activated upon tamoxifen treatment in adulthood. Collectively, neither the Me1 KO nor Me1 cKO models exhibited deleterious phenotype under standard laboratory conditions. Knockout of ME1 was validated by immunohistochemistry and genotype confirmed by PCR. Transmission patterns favor Me1 loss in Me1 KO mice when maternally transmitted to male progeny. Hematological examination of these models through complete blood count and serum chemistry panels revealed no discrepancy with their wild-type counterparts. Orthotopic pancreatic tumors in Me1 cKO mice grow similarly to Me1 expressing mice. Similarly, no behavioral phenotype was observed in Me1 cKO mice when aged for 52 weeks. Histological analysis of several tissues revealed no pathological phenotype. These models provide a more modern approach to ME1 knockout in vivo while opening the door for further study into the role of ME1 loss under more biologically relevant, stressful conditions.

Opposing diet, microbiome, and metabolite mechanisms regulate inflammatory bowel disease in a genetically susceptible host.

Inflammatory bowel diseases (IBDs) are chronic conditions characterized by periods of spontaneous intestinal inflammation and are increasing in industrialized populations. Combined with host genetics, diet and gut bacteria are thought to contribute prominently to IBDs, but mechanisms are still emerging. In mice lacking the IBD-associated cytokine, interleukin-10, we show that a fiber-deprived gut microbiota promotes the deterioration of colonic mucus, leading to lethal colitis. Inflammation starts with the expansion of natural killer cells and altered immunoglobulin-A coating of some bacteria. Lethal colitis is then driven by Th1 immune responses to increased activities of mucin-degrading bacteria that cause inflammation first in regions with thinner mucus. A fiber-free exclusive enteral nutrition diet also induces mucus erosion but inhibits inflammation by simultaneously increasing an anti-inflammatory bacterial metabolite, isobutyrate. Our findings underscore the importance of focusing on microbial functions-not taxa-contributing to IBDs and that some diet-mediated functions can oppose those that promote disease.

Quiescence enables unrestricted cell fate in naive embryonic stem cells.

Quiescence in stem cells is traditionally considered as a state of inactive dormancy or with poised potential. Naive mouse embryonic stem cells (ESCs) can enter quiescence spontaneously or upon inhibition of MYC or fatty acid oxidation, mimicking embryonic diapause in vivo. The molecular underpinning and developmental potential of quiescent ESCs (qESCs) are relatively unexplored. Here we show that qESCs possess an expanded or unrestricted cell fate, capable of generating both embryonic and extraembryonic cell types (e.g., trophoblast stem cells). These cells have a divergent metabolic landscape comparing to the cycling ESCs, with a notable decrease of the one-carbon metabolite S-adenosylmethionine. The metabolic changes are accompanied by a global reduction of H3K27me3, an increase of chromatin accessibility, as well as the de-repression of endogenous retrovirus MERVL and trophoblast master regulators. Depletion of methionine adenosyltransferase Mat2a or deletion of Eed in the polycomb repressive complex 2 results in removal of the developmental constraints towards the extraembryonic lineages. Our findings suggest that quiescent ESCs are not dormant but rather undergo an active transition towards an unrestricted cell fate.

Feasibility of a dietary intervention to modify gut microbial metabolism in patients with hematopoietic stem cell transplantation.

Evaluation of the impact of dietary intervention on gastrointestinal microbiota and metabolites after allogeneic hematopoietic stem cell transplantation (HCT) is lacking. We conducted a feasibility study as the first of a two-phase trial. Ten adults received resistant potato starch (RPS) daily from day -7 to day 100. The primary objective was to test the feasibility of RPS and its effect on intestinal microbiome and metabolites, including the short-chain fatty acid butyrate. Feasibility met the preset goal of 60% or more, adhering to 70% or more doses; fecal butyrate levels were significantly higher when participants were on RPS than when they were not (P < 0.0001). An exploratory objective was to evaluate plasma metabolites. We observed longitudinal changes in plasma metabolites compared to baseline, which were independent of RPS (P < 0.0001). However, in recipients of RPS, the dominant plasma metabolites were more stable compared to historical controls with significant difference at engraftment (P < 0.05). These results indicate that RPS in recipients of allogeneic HCT is feasible; in this study, it was associated with significant alterations in intestinal and plasma metabolites. A phase 2 trial examining the effect of RPS on graft-versus-host disease in recipients of allogeneic HCT is underway. ClinicalTrials.gov registration: NCT02763033 .

Unravelling specific diet and gut microbial contributions to inflammatory bowel disease.

Inflammatory bowel disease (IBD) is a chronic condition characterized by periods of spontaneous intestinal inflammation and is increasing in industrialized populations. Combined with host genetic predisposition, diet and gut bacteria are thought to be prominent features contributing to IBD, but little is known about the precise mechanisms involved. Here, we show that low dietary fiber promotes bacterial erosion of protective colonic mucus, leading to lethal colitis in mice lacking the IBD-associated cytokine, interleukin-10. Diet-induced inflammation is driven by mucin-degrading bacteria-mediated Th1 immune responses and is preceded by expansion of natural killer T cells and reduced immunoglobulin A coating of some bacteria. Surprisingly, an exclusive enteral nutrition diet, also lacking dietary fiber, reduced disease by increasing bacterial production of isobutyrate, which is dependent on the presence of a specific bacterial species, Eubacterium rectale. Our results illuminate a mechanistic framework using gnotobiotic mice to unravel the complex web of diet, host and microbial factors that influence IBD.

OXPHOS promotes apoptotic resistance and cellular persistence in TH17 cells in the periphery and tumor microenvironment.

T cell proliferation and cytokine production are bioenergetically and biosynthetically costly. The inability to meet these metabolic demands results in altered differentiation, accompanied by impaired effector function, and attrition of the immune response. Interleukin-17-producing CD4 T cells (TH17s) are mediators of host defense, autoimmunity, and antitumor immunity in the setting of adoptive T cell therapy. TH17s are long-lived cells that require mitochondrial oxidative phosphorylation (OXPHOS) for effector function in vivo. Considering that TH17s polarized under standardized culture conditions are predominately glycolytic, little is known about how OXPHOS regulates TH17 processes, such as their ability to persist and thus contribute to protracted immune responses. Here, we modified standardized culture medium and identified a culture system that reliably induces OXPHOS dependence in TH17s. We found that TH17s cultured under OXPHOS conditions metabolically resembled their in vivo counterparts, whereas glycolytic cultures were dissimilar. OXPHOS TH17s exhibited increased mitochondrial fitness, glutamine anaplerosis, and an antiapoptotic phenotype marked by high BCL-XL and low BIM. Limited mitophagy, mediated by mitochondrial fusion regulator OPA-1, was critical to apoptotic resistance in OXPHOS TH17s. By contrast, glycolytic TH17s exhibited more mitophagy and an imbalance in BCL-XL to BIM, thereby priming them for apoptosis. In addition, through adoptive transfer experiments, we demonstrated that OXPHOS protected TH17s from apoptosis while enhancing their persistence in the periphery and tumor microenvironment in a murine model of melanoma. Together, our work demonstrates how metabolism regulates TH17 cell fate and highlights the potential for therapies that target OXPHOS in TH17-driven diseases.

Gut microbiota-derived metabolites confer protection against SARS-CoV-2 infection.

The gut microbiome is intricately coupled with immune regulation and metabolism, but its role in Coronavirus Disease 2019 (COVID-19) is not fully understood. Severe and fatal COVID-19 is characterized by poor anti-viral immunity and hypercoagulation, particularly in males. Here, we define multiple pathways by which the gut microbiome protects mammalian hosts from SARS-CoV-2 intranasal infection, both locally and systemically, via production of short-chain fatty acids (SCFAs). SCFAs reduced viral burdens in the airways and intestines by downregulating the SARS-CoV-2 entry receptor, angiotensin-converting enzyme 2 (ACE2), and enhancing adaptive immunity via GPR41 and 43 in male animals. We further identify a novel role for the gut microbiome in regulating systemic coagulation response by limiting megakaryocyte proliferation and platelet turnover via the Sh2b3-Mpl axis. Taken together, our findings have unraveled novel functions of SCFAs and fiber-fermenting gut bacteria to dampen viral entry and hypercoagulation and promote adaptive antiviral immunity.

Human Norovirus Triggers Primary B Cell Immune Activation In Vitro.

Human norovirus (HNoV) is a global health and socioeconomic burden, estimated to infect every individual at least five times during their lifetime. The underlying mechanism for the potential lack of long-term immune protection from HNoV infections is not understood and prompted us to investigate HNoV susceptibility of primary human B cells and its functional impact. Primary B cells isolated from whole blood were infected with HNoV-positive stool samples and harvested at 3 days postinfection (dpi) to assess the viral RNA yield by reverse transcriptase quantitative PCR (RT-qPCR). A 3- to 18-fold increase in the HNoV RNA yield was observed in 50 to 60% of donors. Infection was further confirmed in B cells derived from splenic and lymph node biopsy specimens. Next, we characterized infection of whole-blood-derived B cells by flow cytometry in specific functional B cell subsets (naive CD27- IgD+, memory-switched CD27+ IgD-, memory-unswitched CD27+ IgD+, and double-negative CD27- IgD- cells). While the susceptibilities of the subsets were similar, changes in the B cell subset distribution upon infection were observed, which were also noted after treatment with HNoV virus-like particles and the predicted recombinant NS1 protein. Importantly, primary B cell stimulation with the predicted recombinant NS1 protein triggered B cell activation and induced metabolic changes. These data demonstrate that primary B cells are susceptible to HNoV infection and suggest that the NS1 protein can alter B cell activation and metabolism in vitro, which could have implications for viral pathogenesis and immune responses in vivo. IMPORTANCE Human norovirus (HNoV) is the most prevalent causative agent of gastroenteritis worldwide. Infection results in a self-limiting disease that can become chronic and severe in the immunocompromised, the elderly, and infants. There are currently no approved therapeutic and preventative strategies to limit the health and socioeconomic burdens associated with HNoV infections. Moreover, HNoV does not elicit lifelong immunity as repeat infections are common, presenting a challenge for vaccine development. Given the importance of B cells for humoral immunity, we investigated the susceptibility and impact of HNoV infection on human B cells. We found that HNoV replicates in human primary B cells derived from blood, spleen, and lymph node specimens, while the nonstructural protein NS1 can activate B cells. Because of the secreted nature of NS1, we put forward the hypothesis that HNoV infection can modulate bystander B cell function with potential impacts on systemic immune responses.

GOT1 inhibition promotes pancreatic cancer cell death by ferroptosis.

Cancer metabolism is rewired to support cell survival in response to intrinsic and environmental stressors. Identification of strategies to target these adaptions is an area of active research. We previously described a cytosolic aspartate aminotransaminase (GOT1)-driven pathway in pancreatic cancer used to maintain redox balance. Here, we sought to identify metabolic dependencies following GOT1 inhibition to exploit this feature of pancreatic cancer and to provide additional insight into regulation of redox metabolism. Using pharmacological methods, we identify cysteine, glutathione, and lipid antioxidant function as metabolic vulnerabilities following GOT1 withdrawal. We demonstrate that targeting any of these pathways triggers ferroptosis, an oxidative, iron-dependent form of cell death, in GOT1 knockdown cells. Mechanistically, we reveal that GOT1 inhibition represses mitochondrial metabolism and promotes a catabolic state. Consequently, we find that this enhances labile iron availability through autophagy, which potentiates the activity of ferroptotic stimuli. Overall, our study identifies a biochemical connection between GOT1, iron regulation, and ferroptosis.

Medium-Chain Acyl-CoA Dehydrogenase Protects Mitochondria from Lipid Peroxidation in Glioblastoma.

Glioblastoma (GBM) is highly resistant to chemotherapies, immune-based therapies, and targeted inhibitors. To identify novel drug targets, we screened orthotopically implanted, patient-derived glioblastoma sphere-forming cells using an RNAi library to probe essential tumor cell metabolic programs. This identified high dependence on mitochondrial fatty acid metabolism. We focused on medium-chain acyl-CoA dehydrogenase (MCAD), which oxidizes medium-chain fatty acids (MCFA), due to its consistently high score and high expression among models and upregulation in GBM compared with normal brain. Beyond the expected energetics impairment, MCAD depletion in primary GBM models induced an irreversible cascade of detrimental metabolic effects characterized by accumulation of unmetabolized MCFAs, which induced lipid peroxidation and oxidative stress, irreversible mitochondrial damage, and apoptosis. Our data uncover a novel protective role for MCAD to clear lipid molecules that may cause lethal cell damage, suggesting that therapeutic targeting of MCFA catabolism may exploit a key metabolic feature of GBM. SIGNIFICANCE: MCAD exerts a protective role to prevent accumulation of toxic metabolic by-products in glioma cells, actively catabolizing lipid species that would otherwise affect mitochondrial integrity and induce cell death. This work represents a first demonstration of a nonenergetic role for dependence on fatty acid metabolism in cancer.This article is highlighted in the In This Issue feature, p. 2659.

Integrated Metabolic and Epigenomic Reprograming by H3K27M Mutations in Diffuse Intrinsic Pontine Gliomas.

H3K27M diffuse intrinsic pontine gliomas (DIPGs) are fatal and lack treatments. They mainly harbor H3.3K27M mutations resulting in H3K27me3 reduction. Integrated analysis in H3.3K27M cells, tumors, and in vivo imaging in patients showed enhanced glycolysis, glutaminolysis, and tricarboxylic acid cycle metabolism with high alpha-ketoglutarate (α-KG) production. Glucose and/or glutamine-derived α-KG maintained low H3K27me3 in H3.3K27M cells, and inhibition of key enzymes in glycolysis or glutaminolysis increased H3K27me3, altered chromatin accessibility, and prolonged survival in animal models. Previous studies have shown that mutant isocitrate-dehydrogenase (mIDH)1/2 glioma cells convert α-KG to D-2-hydroxyglutarate (D-2HG) to increase H3K27me3. Here, we show that H3K27M and IDH1 mutations are mutually exclusive and experimentally synthetic lethal. Overall, we demonstrate that H3.3K27M and mIDH1 hijack a conserved and critical metabolic pathway in opposing ways to maintain their preferred epigenetic state. Consequently, interruption of this metabolic/epigenetic pathway showed potent efficacy in preclinical models, suggesting key therapeutic targets for much needed treatments.

Multi-scale computational study of the Warburg effect, reverse Warburg effect and glutamine addiction in solid tumors.

Cancer metabolism has received renewed interest as a potential target for cancer therapy. In this study, we use a multi-scale modeling approach to interrogate the implications of three metabolic scenarios of potential clinical relevance: the Warburg effect, the reverse Warburg effect and glutamine addiction. At the intracellular level, we construct a network of central metabolism and perform flux balance analysis (FBA) to estimate metabolic fluxes; at the cellular level, we exploit this metabolic network to calculate parameters for a coarse-grained description of cellular growth kinetics; and at the multicellular level, we incorporate these kinetic schemes into the cellular automata of an agent-based model (ABM), iDynoMiCS. This ABM evaluates the reaction-diffusion of the metabolites, cellular division and motion over a simulation domain. Our multi-scale simulations suggest that the Warburg effect provides a growth advantage to the tumor cells under resource limitation. However, we identify a non-monotonic dependence of growth rate on the strength of glycolytic pathway. On the other hand, the reverse Warburg scenario provides an initial growth advantage in tumors that originate deeper in the tissue. The metabolic profile of stromal cells considered in this scenario allows more oxygen to reach the tumor cells in the deeper tissue and thus promotes tumor growth at earlier stages. Lastly, we suggest that glutamine addiction does not confer a selective advantage to tumor growth with glutamine acting as a carbon source in the tricarboxylic acid (TCA) cycle, any advantage of glutamine uptake must come through other pathways not included in our model (e.g., as a nitrogen donor). Our analysis illustrates the importance of accounting explicitly for spatial and temporal evolution of tumor microenvironment in the interpretation of metabolic scenarios and hence provides a basis for further studies, including evaluation of specific therapeutic strategies that target metabolism.

When Cancer Cells Are Given Lemo[NH3]s, They Make Lemo[NH3]ade.

In normal physiology, end-products of metabolism are excreted from the body. In tumors, these metabolic wastes accumulate due to deregulated metabolism and vascular insufficiency. Spinelli et al. (2017) show that breast cancer cells adapt to ammonia buildup by recycling it for amino acid synthesis, which can support cancer cell growth.

Adipose-derived stem cells increase angiogenesis through matrix metalloproteinase-dependent collagen remodeling.

Adipose-derived stem cells (ASCs) are key regulators of new blood vessel formation and widely investigated for their role in tissue regeneration and tumorigenesis. However, the cellular and molecular mechanisms through which ASCs regulate angiogenesis are not well understood. Here, it was our goal to test the functional contribution of ASC-mediated extracellular matrix (ECM) remodeling on endothelial cell invasion. To isolate the effect of ECM-remodeling, ASCs were embedded within 3-D collagen type I hydrogels and pre-cultured for 7 days; controls were not pre-cultured. A confluent monolayer of human umbilical vein endothelial cells (HUVECs) was seeded on top and its invasion into the underlying hydrogel was analyzed. Without pre-culture, ASCs inhibited vascular sprouting by stabilizing the endothelium. In contrast, 7 day pre-culture of ASCs drastically increased invasion by HUVECs. This effect was largely mediated by proteolytic ECM degradation by ASC-derived matrix metalloproteinases (MMPs) rather than vascular endothelial growth factor (VEGF), as our results indicated that blockade of MMPs, but not VEGF, inhibited endothelial sprouting. Collectively, these data suggest that the angiogenic capability of ASCs is modulated by their proteolytic remodeling of the ECM, opening new avenues for pro- and anti-angiogenic therapies.

Endothelial cell dynamics during anastomosis in vitro.

Vascular anastomosis - the fusion of vessels from two distinct branches of the vascular system - represents a critical step in vascular growth under both healthy and pathological conditions, in vivo, and presents an important target for engineering of vascularized tissues, in vitro. Recent works in animal models have advanced our understanding of the molecular and cellular players in vascular anastomosis, but questions remain related to cellular dynamics and control of this process, in vitro. In this study, we exploited a three-dimensional (3-D) culture platform to examine the dynamics of endothelial cell (EC) during and after vascular anastomosis by allowing angiogenesis and vasculogenesis to proceed in parallel. We show that anastomosis occurs between sprouts formed by angiogenesis from an endothelium and tubes formed by vasculogenesis in the bulk of a 3-D matrix. This fusion leads to highly connected vessels that span from the surface of the matrix into the bulk in a manner that depends on cell density and identity. Further, we observe and analyze intermixing of endothelial cells of distinct origin (surface versus bulk) within the vessels structures that are formed; we provide evidence that the cells migrate along pre-existing vessels segments as part of this intermixing process. We conclude that anastomosis can occur between vessels emerging by angiogenesis and vasculogenesis and that this process may play an important role in contexts such as wound healing.