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Studying the Epithelial Effects of Intestinal Inflammation <em>In Vitro</em> on Established Murine Colonoids

The intestinal epithelium plays an essential role in human health, providing a barrier between the host and the external environment. This highly dynamic ...

UPMC Children’s Hospital of Pittsburgh

University of Pittsburgh School of Medicine

Peroxisome proliferator-activated receptor-γ coactivator 1-α (PGC1α) is the primary regulator of mitochondrial biogenesis and was recently found to be highly expressed within the intestinal epithelium. PGC1α is decreased in the intestinal epithelium of patients with inflammatory bowel disease, but its role in pathogenesis is uncertain. We now hypothesize that PGC1α protects against the development of colitis and helps to maintain the integrity of the intestinal barrier. We selectively deleted PGC1α from the intestinal epithelium of mice by breeding a PGC1α(loxP/loxP) mouse with a villin-cre mouse. Their progeny (PGC1α(ΔIEC) mice) were subjected to 2% dextran sodium sulfate (DSS) colitis for 7 days. The SIRT1 agonist SRT1720 was used to enhance PGC1α activation in wild-type mice during DSS exposure. Mice lacking PGC1α within the intestinal epithelium were more susceptible to DSS colitis than their wild-type littermates. Pharmacologic activation of PGC1α successfully ameliorated disease and restored mitochondrial integrity. These findings suggest that a depletion of PGC1α in the intestinal epithelium contributes to inflammatory changes through a failure of mitochondrial structure and function as well as a breakdown of the intestinal barrier, which leads to increased bacterial translocation. PGC1α induction helps to maintain mitochondrial integrity, enhance intestinal barrier function, and decrease inflammation. 

Peroxisome Proliferator-activated Receptor-γ Coactivator 1-α (PGC1α) Protects against Experimental Murine Colitis.

Oxidative stress and persistent inflammation are exaggerated through chronic over-nutrition and a sedentary lifestyle, resulting in insulin resistance. In type 2 diabetes (T2D), impaired insulin signaling leads to hyperglycemia and long-term complications, including metabolic liver dysfunction, resulting in non-alcoholic fatty liver disease (NAFLD). The manganese metalloporphyrin superoxide dismustase (SOD) mimetic, manganese (III) meso-tetrakis (-ethylpyridinium-2-yl) porphyrin (MnP), is an oxidoreductase known to scavenge reactive oxygen species (ROS) and decrease pro-inflammatory cytokine production, by inhibiting nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) activation. We hypothesized that targeting oxidative stress-induced inflammation with MnP would assuage liver complications and enhance insulin sensitivity and glucose tolerance in a high-fat diet (HFD)-induced mouse model of T2D. During 12 weeks of feeding, we saw significant improvements in weight, hepatic steatosis, and biomarkers of liver dysfunction with redox modulation by MnP treatment in HFD-fed mice. Additionally, MnP treatment improved insulin sensitivity and glucose tolerance, while reducing serum insulin and leptin levels. We attribute these effects to redox modulation and inhibition of hepatic NF-κB activation, resulting in diminished ROS and pro-inflammatory cytokine production. This study highlights the importance of controlling oxidative stress and secondary inflammation in obesity-mediated insulin resistance and T2D. Our data confirm the role of NF-κB-mediated inflammation in the development of T2D, and demonstrate the efficacy of MnP in preventing the progression to disease by specifically improving liver pathology and hepatic insulin resistance in obesity.

Treatment with a Catalytic Superoxide Dismutase (SOD) Mimetic Improves Liver Steatosis, Insulin Sensitivity, and Inflammation in Obesity-Induced Type 2 Diabetes.

The incidence of pediatric-onset ulcerative colitis (UC) is rising. Children often present with a more severe disease phenotype as compared to adults with over a third requiring hospitalization for the management of acute severe ulcerative colitis (ASUC). Further, in pediatric patients presenting with inflammatory bowel disease (IBD) limited to the colon, a definitive diagnosis of UC vs. Crohn's disease is often unclear. Here, we review the unique aspects of pediatric ASUC including the epidemiology, diagnosis, medical, and surgical management of this disease.

Management of acute severe ulcerative colitis in children.

Plant-based Enteral Nutrition Modifies the Gut Microbiota and Improves Outcomes in Murine Models of Colitis.

The gut plays a vital role in critical illness, and alterations in the gut structure and function have been reported in endotoxemia and sepsis models. Previously, we have demonstrated a novel link between the diet-induced alteration of the gut microbiome with cellulose and improved outcomes in sepsis. As compared to mice receiving basal fiber (BF) diet, mice that were fed a non-fermentable high fiber (HF) diet demonstrated significant improvement in survival and decreased organ injury in both cecal-ligation and puncture (CLP) and endotoxin sepsis models. To understand if the benefit conferred by HF diet extends to the gut structure and function, we hypothesized that HF diet would be associated with a reduction in sepsis-induced gut epithelial loss and permeability in mice. We demonstrate that the use of dietary cellulose decreased LPS-mediated intestinal hyperpermeability and protected the gut from apoptosis. Furthermore, we noted a significant increase in epithelial cell proliferation, as evidenced by an increase in the percentage of bromodeoxyuridine-positive cells in HF fed mice as compared to BF fed mice. Thus, the use of HF diet is a simple and effective tool that confers benefit in a murine model of sepsis, and understanding the intricate relationship between the epithelial barrier, gut microbiota, and diet will open-up additional therapeutic avenues for the treatment of gut dysfunction in critical illness.

Effect of dietary cellulose supplementation on gut barrier function and apoptosis in a murine model of endotoxemia.

 Mitochondrial stress and dysfunction within the intestinal epithelium are known to contribute to the pathogenesis of inflammatory bowel disease (IBD). However, the importance of mitophagy during intestinal inflammation remains poorly understood. The primary aim of this study was to investigate how the mitophagy protein BCL2/adenovirus E1B 19 kDa protein-interacting protein 3-like (BNIP3L/NIX) mitigates mitochondrial damage during intestinal inflammation in the hopes that these data will allow us to target mitochondrial health in the intestinal epithelium as an adjunct to immune-based treatment strategies.  In the intestinal epithelium of patients with ulcerative colitis, we found that NIX was upregulated and targeted to the mitochondria. We obtained similar findings in wild-type mice undergoing experimental colitis. An increase in NIX expression was found to depend on stabilization of hypoxia-inducible factor-1 alpha (HIF1α), which binds to the  promoter region. Using the reactive oxygen species (ROS) scavenger MitoTEMPO, we were able to attenuate disease and inhibit both HIF1α stabilization and subsequent NIX expression, suggesting that mitochondrially derived ROS are crucial to initiating the mitophagic response during intestinal inflammation. We subjected a global  mouse to dextran sodium sulfate colitis and found that these mice developed worse disease. In addition,  mice were found to exhibit increased mitochondrial mass, likely due to the inability to clear damaged or dysfunctional mitochondria.  These results demonstrate the importance of mitophagy within the intestinal epithelium during IBD pathogenesis.  NIX-mediated mitophagy is required to maintain intestinal homeostasis during inflammation, highlighting the impact of mitochondrial damage on IBD progression.

Nix-Mediated Mitophagy Modulates Mitochondrial Damage During Intestinal Inflammation.

Appendicitis is a common indication for urgent abdominal surgery in the pediatric population. The postoperative management varies significantly in time to discharge and cost of care. The objective of this study was to investigate whether implementation of an evidence-based protocol after an appendectomy would lead to decreased length of stay and cost of care.

An Evidence-Based Care Protocol Improves Outcomes and Decreases Cost in Pediatric Appendicitis.

Diverse perspectives are critical components of effective teams in every industry. Underrepresentation of minorities in medicine leads to worse outcomes for minority patients, and efforts to increase diversity in the health care workforce are critical. Presently, about 70% of the pediatric surgery workforce is white, and pediatric surgeons at large do not reflect the racial or ethnic diversity of the populations they serve. Pediatric surgery fellowship training programs are the gateway to the field, and fellow selection processes should be optimized to support diversity and inclusion. The Association of Pediatric Surgery Training Program Directors (APSTPD) Diversity Equity and Inclusion subcommittee compiled best practices for bias mitigation during fellow selection, drawing from published literature and personal experiences in our own programs. A list of concrete recommendations was compiled, which can be implemented in every phase from applicant screening to rank list creation. We present these as a position statement that has been endorsed by the executive committee of the APSTPD. Pediatric surgery fellowship programs can utilize this focused review of best practices to mitigate bias and support diverse applicants.

Inclusion and representation in the pediatric surgery workforce: Strategies to mitigate bias in the fellowship application process.

Ferroptosis and necroptosis are two pro-inflammatory cell death programs contributing to major pathologies and their inhibition has gained attention to treat a wide range of disease states. Necroptosis relies on activation of RIP1 and RIP3 kinases. Ferroptosis is triggered by oxidation of polyunsaturated phosphatidylethanolamines (PUFA-PE) by complexes of 15-Lipoxygenase (15LOX) with phosphatidylethanolamine-binding protein 1 (PEBP1). The latter, also known as RAF kinase inhibitory protein, displays promiscuity towards multiple proteins. In this study we show that RIP3 K51A kinase inactive mice have increased ferroptotic burden and worse outcome after irradiation and brain trauma rescued by anti-ferroptotic compounds Liproxstatin-1 and Ferrostatin 16-86. Given structural homology between RAF and RIP3, we hypothesized that PEBP1 acts as a necroptosis-to-ferroptosis switch interacting with either RIP3 or 15LOX. Using genetic, biochemical, redox lipidomics and computational approaches, we uncovered that PEBP1 complexes with RIP3 and inhibits necroptosis. Elevated expression combined with higher affinity enables 15LOX to pilfer PEBP1 from RIP3, thereby promoting PUFA-PE oxidation and ferroptosis which sensitizes Rip3 kinase-deficient mice to total body irradiation and brain trauma. This newly unearthed PEBP1/15LOX-driven mechanism, along with previously established switch between necroptosis and apoptosis, can serve multiple and diverse cell death regulatory functions across various human disease states.

Inactivation of RIP3 kinase sensitizes to 15LOX/PEBP1-mediated ferroptotic death.

Perturbagen analysis of Crohn's disease (CD) ileal gene expression data identified small molecules including eicosatetraynoic acid (ETYA), which may exert an antifibrotic effect. We developed a patient-specific human intestinal organoid (HIO) model system to test small molecule regulation of mitochondrial and wound-healing functions implicated in stricturing behavior.

Eicosatetraynoic Acid and Butyrate Regulate Human Intestinal Organoid Mitochondrial and Extracellular Matrix Pathways Implicated in Crohn's Disease Strictures.

Inflammatory bowel disease (IBD) represents a set of idiopathic and chronic inflammatory diseases of the gastrointestinal tract. Central to the pathogenesis of IBD is a dysregulation of normal intestinal epithelial homeostasis. cGAS is a DNA-sensing receptor demonstrated to promote autophagy, a mechanism that removes dysfunctional cellular components. Beclin-1 is a crucial protein involved in the initiation of autophagy. We hypothesized that cGAS plays a key role in intestinal homeostasis by upregulating Beclin-1-mediated autophagy. We evaluated intestinal cGAS levels in humans with IBD and in murine colonic tissue after performing a 2% dextran sulfate sodium (DSS) colitis model. Autophagy and cell death mechanisms were studied in cGAS KO and WT mice via qPCR, WB analysis, H&E, IF, and TUNEL staining. Autophagy was measured in stimulated intestinal epithelial cells (IECs) via WB analysis. Our data demonstrates cGAS to be upregulated during human and murine colitis. Furthermore, cGAS deficiency leads to worsened colitis and decreased levels of autophagy proteins including Beclin-1 and LC3-II. Co-IP demonstrates a direct binding between cGAS and Beclin-1 in IECs. Transfection of cGAS in stimulated HCT-116 cells leads to increased autophagy. IECs isolated from cGAS KO have diminished autophagic flux. cGAS KO mice subjected to DSS have increased cell death and cleaved caspase-3. Lastly, treatment of cGAS KO mice with rapamycin decreased the severity of colitis. Our data suggest that cGAS maintains intestinal epithelial homeostasis during human IBD and murine colitis by upregulating Beclin-1-mediated autophagy and preventing IEC death. Rescue of autophagy can attenuate the severity of colitis associated with cGAS deficiency.

Cyclic GMP-AMP synthase contributes to epithelial homeostasis in intestinal inflammation via Beclin-1-mediated autophagy.

To assess the validity of the American College of Radiology Thyroid Imaging Reporting and Data System (ACR TI-RADS) for evaluating thyroid nodules in children.

Validity of the American College of Radiology Thyroid Imaging Reporting and Data System in Children.

The colonic epithelium requires continuous renewal by crypt resident intestinal stem cells (ISCs) and transit amplifying (TA) cells to maintain barrier integrity, especially after inflammatory damage. The diet of high-income countries contains increasing amounts of sugar, such as sucrose. ISCs and TA cells are sensitive to dietary metabolites, but whether excess sugar affects their function directly is unknown.

Kevin P. Mollen

Division of Pediatric Surgery

UPMC Children’s Hospital of Pittsburgh

Studying the Epithelial Effects of Intestinal Inflammation In Vitro on Established Murine Colonoids