TREM2 deficiency reprograms intestinal macrophages and microbiota to enhance anti-PD-1 tumor immunotherapy.

The gut microbiota and tumor-associated macrophages (TAMs) affect tumor responses to anti-programmed cell death protein 1 (PD-1) immune checkpoint blockade. Reprogramming TAM by either blocking or deleting the macrophage receptor triggering receptor on myeloid cells 2 (TREM2) attenuates tumor growth, and lack of functional TREM2 enhances tumor elimination by anti-PD-1. Here, we found that anti-PD-1 treatment combined with TREM2 deficiency in mice induces proinflammatory programs in intestinal macrophages and a concomitant expansion of Ruminococcus gnavus in the gut microbiota. Gavage of wild-type mice with R. gnavus enhanced anti-PD-1-mediated tumor elimination, recapitulating the effect occurring in the absence of TREM2. A proinflammatory intestinal environment coincided with expansion, increased circulation, and migration of TNF-producing CD4+ T cells to the tumor bed. Thus, TREM2 remotely controls anti-PD-1 immune checkpoint blockade through modulation of the intestinal immune environment and microbiota, with R. gnavus emerging as a potential probiotic agent for increasing responsiveness to anti-PD-1.

Gut-associated lymphoid tissue attrition associates with response to anti-α4ß7 therapy in ulcerative colitis.

Vedolizumab (VDZ) is a first-line treatment in ulcerative colitis (UC) that targets the α4ß7- mucosal vascular addressin cell adhesion molecule 1 (MAdCAM-1) axis. To determine the mechanisms of action of VDZ, we examined five distinct cohorts of patients with UC. A decrease in naïve B and T cells in the intestines and gut-homing (ß7+) plasmablasts in circulation of VDZ-treated patients suggested that VDZ targets gut-associated lymphoid tissue (GALT). Anti-α4ß7 blockade in wild-type and photoconvertible (KikGR) mice confirmed a loss of GALT size and cellularity because of impaired cellular entry. In VDZ-treated patients with UC, treatment responders demonstrated reduced intestinal lymphoid aggregate size and follicle organization and a reduction of ß7+IgG+ plasmablasts in circulation, as well as IgG+ plasma cells and FcγR-dependent signaling in the intestine. GALT targeting represents a previously unappreciated mechanism of action of α4ß7-targeted therapies, with major implications for this therapeutic paradigm in UC.

Human serous cavity macrophages and dendritic cells possess counterparts in the mouse with a distinct distribution between species.

In mouse peritoneal and other serous cavities, the transcription factor GATA6 drives the identity of the major cavity resident population of macrophages, with a smaller subset of cavity-resident macrophages dependent on the transcription factor IRF4. Here we showed that GATA6+ macrophages in the human peritoneum were rare, regardless of age. Instead, more human peritoneal macrophages aligned with mouse CD206+ LYVE1+ cavity macrophages that represent a differentiation stage just preceding expression of GATA6. A low abundance of CD206+ macrophages was retained in C57BL/6J mice fed a high-fat diet and in wild-captured mice, suggesting that differences between serous cavity-resident macrophages in humans and mice were not environmental. IRF4-dependent mouse serous cavity macrophages aligned closely with human CD1c+CD14+CD64+ peritoneal cells, which, in turn, resembled human peritoneal CD1c+CD14-CD64- cDC2. Thus, major populations of serous cavity-resident mononuclear phagocytes in humans and mice shared common features, but the proportions of different macrophage differentiation stages greatly differ between the two species, and dendritic cell (DC2)-like cells were especially prominent in humans.

Gut-associated lymphoid tissue attrition associates with response to anti-α4ß7 therapy in ulcerative colitis.

Targeting the α4ß7-MAdCAM-1 axis with vedolizumab (VDZ) is a front-line therapeutic paradigm in ulcerative colitis (UC). However, mechanism(s) of action (MOA) of VDZ remain relatively undefined. Here, we examined three distinct cohorts of patients with UC (n=83, n=60, and n=21), to determine the effect of VDZ on the mucosal and peripheral immune system. Transcriptomic studies with protein level validation were used to study drug MOA using conventional and transgenic murine models. We found a significant decrease in colonic and ileal naïve B and T cells and circulating gut-homing plasmablasts (ß7+) in VDZ-treated patients, pointing to gut-associated lymphoid tissue (GALT) targeting by VDZ. Murine Peyer's patches (PP) demonstrated a significant loss cellularity associated with reduction in follicular B cells, including a unique population of epithelium-associated B cells, following anti-α4ß7 antibody (mAb) administration. Photoconvertible (KikGR) mice unequivocally demonstrated impaired cellular entry into PPs in anti-α4ß7 mAb treated mice. In VDZ-treated, but not anti-tumor necrosis factor-treated UC patients, lymphoid aggregate size was significantly reduced in treatment responders compared to non-responders, with an independent validation cohort further confirming these data. GALT targeting represents a novel MOA of α4ß7-targeted therapies, with major implications for this therapeutic paradigm in UC, and for the development of new therapeutic strategies.

Lipid absorption and overall intestinal lymphatic transport are impaired following partial small bowel resection in mice.

Short bowel syndrome (SBS) is associated with diminished levels of serum fats caused by unknown mechanisms. We have shown that mesenteric lymphatics remodel to a more primitive state one week after small bowel resection (SBR); therefore, this study focuses on the effect of chronic lymphatic remodeling and magnitude of resection on intestinal lipid uptake and transport. C57BL6 and Prox1 creER-Rosa26LSLTdTomato (lymphatic reporter) mice underwent 50% or 75% proximal SBR or sham operations. Functional transport of lipids and fecal fat content was measured and lymphatic vasculature was compared via imaging. There was a significant reduction in functional transport of cholesterol and triglyceride after SBR with increasing loss of bowel, mirrored by a progressive increase in fecal fat content. We also describe significant morphological changes in the lymphatic vasculature in both the lamina propria and mesentery. Intestinal lymphatic drainage assay in vivo demonstrated a marked reduction of systemic absorption after resection. Intestinal lymphatic vessels significantly remodel in the setting of chronic SBS. This remodeling may account at least in part for impaired intestinal uptake and transport of fat via the compromised lymphatic architecture. We believe that these changes may contribute to the development of intestinal failure associated liver disease (IFALD), a major morbidity in patients with SBS.

Racial disparities in triage of adolescent patients after bullet injury.

BACKGROUND: While pediatric trauma centers (PTCs) and adult trauma centers (ATCs) exhibit equivalent trauma mortality, the optimal care environment for traumatically injured adolescents remains controversial. Race has been shown to effect triage within emergency departments (EDs) with people of color receiving lower acuity triage scores. We hypothesized that African-American adolescents were more likely triaged to an ATC than a PTC compared with their White peers. METHODS: Institutional trauma databases from a neighboring, urban Level I PTC and ATC were queried for gunshot wounds in adolescents (15-18 years) presenting to the ED from 2015 to 2017. The PTC and ATC were compared in terms of demographics, services, and outcomes. Results were analyzed using univariate analysis and logistic regression. RESULTS: Among 316 included adolescents, 184 were treated in an ATC versus 132 in a PTC. Patients at the PTC were significantly more likely to be younger (16.1 vs. 17.5 years; p < 0.001), White (16% vs. 5%; p = 0.001), and privately insured (41% vs. 30%; p = 0.002). At each age, the proportion of Whites treated at the PTC exceeded the proportion of African-Americans. At the PTC, patients were more likely to receive inpatient and outpatient social work follow-up (89% vs. 1%, p < 0.001). Adolescents treated at the PTC were less likely to receive opioids (75% vs. 56%, p = 0.001) at discharge and to return to ED within 6 months (25% vs. 11%, p = 0.005). On multivariate logistic regression, African-American adolescents were less likely to be treated at a PTC (odds ratio, 0.30; 95% confidence interval, 0.10-0.85; p = 0.02) after controlling for age and Injury Severity Score. CONCLUSION: Disparities in triage of African-American and White adolescents after bullet injury lead to unequal care. African-Americans were more likely to be treated at the ATC, which was associated with increased opioid prescription, decreased social work support, and increased return to ED. LEVEL OF EVIDENCE: Therapeutic/Care Management, Level IV.

SATB2 preserves colon stem cell identity and mediates ileum-colon conversion via enhancer remodeling.

Adult stem cells maintain regenerative tissue structure and function by producing tissue-specific progeny, but the factors that preserve their tissue identities are not well understood. The small and large intestines differ markedly in cell composition and function, reflecting their distinct stem cell populations. Here we show that SATB2, a colon-restricted chromatin factor, singularly preserves LGR5+ adult colonic stem cell and epithelial identity in mice and humans. Satb2 loss in adult mice leads to stable conversion of colonic stem cells into small intestine ileal-like stem cells and replacement of the colonic mucosa with one that resembles the ileum. Conversely, SATB2 confers colonic properties on the mouse ileum. Human colonic organoids also adopt ileal characteristics upon SATB2 loss. SATB2 regulates colonic identity in part by modulating enhancer binding of the intestinal transcription factors CDX2 and HNF4A. Our study uncovers a conserved core regulator of colonic stem cells able to mediate cross-tissue plasticity in mature intestines.

Ileitis-associated tertiary lymphoid organs arise at lymphatic valves and impede mesenteric lymph flow in response to tumor necrosis factor.

Lymphangitis and the formation of tertiary lymphoid organs (TLOs) in the mesentery are features of Crohn's disease. Here, we examined the genesis of these TLOs and their impact on disease progression. Whole-mount and intravital imaging of the ileum and ileum-draining collecting lymphatic vessels (CLVs) draining to mesenteric lymph nodes from TNFΔARE mice, a model of ileitis, revealed TLO formation at valves of CLVs. TLOs obstructed cellular and molecular outflow from the gut and were sites of lymph leakage and backflow. Tumor necrosis factor (TNF) neutralization begun at early stages of TLO formation restored lymph transport. However, robustly developed, chronic TLOs resisted regression and restoration of flow after TNF neutralization. TNF stimulation of cultured lymphatic endothelial cells reprogrammed responses to oscillatory shear stress, preventing the induction of valve-associated genes. Disrupted transport of immune cells, driven by loss of valve integrity and TLO formation, may contribute to the pathology of Crohn's disease.

LYVE1+ macrophages of murine peritoneal mesothelium promote omentum-independent ovarian tumor growth.

Two resident macrophage subsets reside in peritoneal fluid. Macrophages also reside within mesothelial membranes lining the peritoneal cavity, but they remain poorly characterized. Here, we identified two macrophage populations (LYVE1hi MHC IIlo-hi CX3CR1gfplo/- and LYVE1lo/- MHC IIhi CX3CR1gfphi subsets) in the mesenteric and parietal mesothelial linings of the peritoneum. These macrophages resembled LYVE1+ macrophages within surface membranes of numerous organs. Fate-mapping approaches and analysis of newborn mice showed that LYVE1hi macrophages predominantly originated from embryonic-derived progenitors and were controlled by CSF1 made by Wt1+ stromal cells. Their gene expression profile closely overlapped with ovarian tumor-associated macrophages previously described in the omentum. Indeed, syngeneic epithelial ovarian tumor growth was strongly reduced following in vivo ablation of LYVE1hi macrophages, including in mice that received omentectomy to dissociate the role from omental macrophages. These data reveal that the peritoneal compartment contains at least four resident macrophage populations and that LYVE1hi mesothelial macrophages drive tumor growth independently of the omentum.

Enterically derived high-density lipoprotein restrains liver injury through the portal vein.

The biogenesis of high-density lipoprotein (HDL) requires apoA1 and the cholesterol transporter ABCA1. Although the liver generates most of the HDL in the blood, HDL synthesis also occurs in the small intestine. Here, we show that intestine-derived HDL traverses the portal vein in the HDL3 subspecies form, in complex with lipopolysaccharide (LPS)-binding protein (LBP). HDL3, but not HDL2 or low-density lipoprotein, prevented LPS binding to and inflammatory activation of liver macrophages and instead supported extracellular inactivation of LPS. In mouse models involving surgical, dietary, or alcoholic intestinal insult, loss of intestine-derived HDL worsened liver injury, whereas outcomes were improved by therapeutics that elevated and depended upon raising intestinal HDL. Thus, protection of the liver from injury in response to gut-derived LPS is a major function of intestinally synthesized HDL.

COVER: A Curriculum in the Management of Soft Tissue Injury and Infection for Junior Surgery Residents.

BACKGROUND: While wound management is a common task for practicing surgeons, there is a paucity of dedicated education on soft tissue management during residency training. OBJECTIVE: The COVER (Causes of soft tissue injury, Obstacles to closure, Vacuums and stitches, Epithelialization, Rationale for wound care) curriculum was developed to engage junior surgery residents in the management of soft tissue injury and infection. METHODS: Junior surgery residents participated in the COVER lab during academic years 2018-2020. Residents applied appropriate surgical management and wound care to cadaveric models of soft tissue injury and infection. Assessments included a pre-/post-curriculum and pre-/post-lab multiple choice questionnaire and survey. RESULTS: All eligible residents (n = 45, 27) participated in the COVER lab for both academic years. Postgraduate year (PGY)-1s, PGY-2s, and PGY-3s showed improvement in wound management knowledge with an average increase in score of 17%, 8%, and 18%, respectively. They also showed a change in their self-reported perceived ability to achieve primary soft tissue closure with confidence levels 22%, 20%, and 16%, respectively. This was again seen in perceived ability to manage soft tissue injuries and infections (28%, 28%, and 23%, respectively). There was a significant increase in performing new wound management skills (PGY-1 mean 51.3%, PGY-2 33.5%, PGY-3 20%; ANOVA, P = .0001). CONCLUSIONS: The COVER curriculum provides a systematic approach to soft tissue injury and infection. Residents showed a significant increase in both soft tissue knowledge as well as confidence in ability to perform wound management.

Liver injury after small bowel resection is prevented in obesity-resistant 129S1/SvImJ mice.

Intestinal failure-associated liver disease is a major morbidity associated with short bowel syndrome. We sought to determine if the obesity-resistant mouse strain (129S1/SvImJ) conferred protection from liver injury after small bowel resection (SBR). Using a parenteral nutrition-independent model of resection-associated liver injury, C57BL/6J and 129S1/SvImJ mice underwent a 50% proximal SBR or sham operation. At postoperative week 10, hepatic steatosis, fibrosis, and cholestasis were assessed. Hepatic and systemic inflammatory pathways were evaluated using oxidative markers and abundance of tissue macrophages. Potential mechanisms of endotoxin resistance were also explored. Serum lipid levels were elevated in all mouse lines. Hepatic triglyceride levels were no different between mouse strains, but there was an increased accumulation of free fatty acids in the C57BL/6J mice. Histological and serum markers of hepatic fibrosis, steatosis, and cholestasis were significantly elevated in resected C57BL/6J SBR mice as well as oxidative stress markers and macrophage recruitment in both the liver and visceral white fat in C57BL/6J mice compared with sham controls and the 129S1/SvImJ mouse line. Serum endotoxin levels were significantly elevated in C57BL/6J mice with significant elevation of hepatic TLR4 and reduction in PPARα expression levels. Despite high levels of serum lipids, 129S1/SvImJ mice did not develop liver inflammation, fibrosis, or cholestasis after SBR, unlike C57BL/6J mice. These data suggest that the accumulation of hepatic free fatty acids as well as increased endotoxin-driven inflammatory pathways through PPARα and TLR4 contribute to the liver injury seen in C57BL/6J mice with short bowel syndrome.NEW & NOTEWORTHY Unlike C57BL/6 mice, the 129S1/SvImJ strain is resistant to liver inflammation and injury after small bowel resection. These disparate outcomes are likely due to the accumulation of hepatic free fatty acids as well as increased endotoxin-driven inflammatory pathways through PPARα and TLR4 in C57BL/6 mice with short bowel syndrome.

SAVE 2.0: Identifying and strengthening resident leadership skills through simulation based team training.

BACKGROUND: The "Surgery for Abdomino-thoracic ViolencE (SAVE)" animate lab engages surgical residents in the management of penetrating injuries in a team setting. Senior residents, representing postgraduate year (PGY) 3-5, assume the role of team leader and facilitate the junior residents, PGY1-2, in operative management of simulated penetrating wounds. Residents completed five scenarios with increasing level of difficulty within set time limits. Senior residents were evaluated on their team's ability to "SAVE" their patient within the time allotted, as well as their communication and leadership skills. METHODS: General, vascular, urology, and plastic surgery residents (n = 79) were divided into 25 teams of three to four residents by "resident scores" (R scores, the sum of the team members' PGY) to create balanced teams with comparable years of clinical experience. Residents completed assessments of their senior resident's leadership ability and style. RESULTS: Evaluation of a resident's desired learning style changed across PGY with junior residents preferring more hands-on guidance compared with senior residents preferring only verbal correction. Resident leadership evaluations demonstrated that team leaders of varied resident years achieved the highest scores. Greater differences in the mismatch between autonomy provided to and desired by junior residents correlated to greater junior resident discomfort in expressing their opinion, confidence, and leadership ratings of senior residents. However, greater autonomy mismatch also correlated to more rapid time to task completion. CONCLUSION: Different from our expectations, clinical experience alone did not define team leader success. Leadership is a powerful influence on the outcome of team performance and may be a skill, which can transcend overall clinical experience. A match between desired and provided resident autonomy and team cohesion may demonstrate a stronger effect on team success in stressful operative situations, such as trauma resuscitation. Enhancement of leadership skills early in residency training may represent an important focus for trauma surgery education.

Small Bowel Resection Increases Paracellular Gut Barrier Permeability via Alterations of Tight Junction Complexes Mediated by Intestinal TLR4.

BACKGROUND: Short bowel syndrome resulting from small bowel resection (SBR) is associated with significant morbidity and mortality. Many adverse sequelae including steatohepatitis and bacterial overgrowth are thought to be related to increased bacterial translocation, suggesting alterations in gut permeability. We hypothesized that after intestinal resection, the intestinal barrier is altered via toll-like receptor 4 (TLR4) signaling at the intestinal level. METHODS: B6 and intestinal-specific TLR4 knockout (iTLR4 KO) mice underwent 50% SBR or sham operation. Transcellular permeability was evaluated by measuring goblet cell associated antigen passages via two-photon microscopy. Fluorimetry and electron microscopy evaluation of tight junctions (TJ) were used to assess paracellular permeability. In parallel experiments, single-cell RNA sequencing measured expression of intestinal integral TJ proteins. Western blot and immunohistochemistry confirmed the results of the single-cell RNA sequencing. RESULTS: There were similar number of goblet cell associated antigen passages after both SBR and sham operation (4.5 versus 5.0, P > 0.05). Fluorescein isothiocyanate-dextran uptake into the serum after massive SBR was significantly increased compared with sham mice (2.13 ± 0.39 ng/µL versus 1.62 ± 0.23 ng/µL, P < 0.001). SBR mice demonstrated obscured TJ complexes on electron microscopy. Single-cell RNA sequencing revealed a decrease in TJ protein occludin (21%) after SBR (P < 0.05), confirmed with immunostaining and western blot analysis. The KO of iTLR4 mitigated the alterations in permeability after SBR. CONCLUSIONS: Permeability after SBR is increased via changes at the paracellular level. However, these alterations were prevented in iTLR4 mice. These findings suggest potential protein targets for restoring the intestinal barrier and obviating the adverse sequelae of short bowel syndrome.

Anatomy of Gun Violence: Contextualized Curriculum to Train Surgical Residents in Both Technical and Non-Technical Skills in the Management of Gun Violence.

BACKGROUND: Gun violence (GV) is a complex public health issue, and the management of GV as a disease engages the surgeon in technical and nontechnical skills. The Anatomy of Gun Violence (AGV) curriculum was developed to teach surgical trainees these seemingly disparate skills, training residents to manage the multiple aspects of firearm injury. STUDY DESIGN: The AGV curriculum was delivered over 6 weeks in the 2017-2018 and 2018-2019 academic years (AY), and used multiple educational methods including didactic lectures, mock oral examinations, a Bleeding Control training session, a GV survivor's personal story, a Resuscitative Endovascular Balloon Occlusion of the Aorta (REBOA) training session, and the Surgery for Abdominal-thoracic ViolencE (SAVE) simulation lab. As surgical residents were involved over both AYs, components of the curriculum were available every other year to provide variety. As proof of concept, this novel curriculum was objectively evaluated by residents' improvement in knowledge and overall experience using pre- and post-surveys. RESULTS: Sixty surgical residents participated in the AGV curriculum in both AYs, with 41 and 36 residents completing the survey regarding their experiences with the curriculum. The curriculum was well received by residents overall in both AYs (median ± IQR 5 ± 0 and 5 ± 0.1, respectively), with the SAVE simulation lab being the most highly favored portion. Additionally, residents had an average 7.5% improvement in knowledge attributed to the curriculum, with a larger effect seen in the junior residents. CONCLUSIONS: This novel AGV curriculum created a well-received learning experience involving the technical and nontechnical skills necessary to care for GV victims. This comprehensive approach to GV may represent a unique opportunity to engage surgical trainees in both the treatment and prevention of firearm injury.

EGFR in enterocytes & endothelium and HIF1α in enterocytes are dispensable for massive small bowel resection induced angiogenesis.

BACKGROUND: Short bowel syndrome (SBS) results from significant loss of small intestinal length. In response to this loss, adaptation occurs, with Epidermal Growth Factor Receptor (EGFR) being a key driver. Besides enhanced enterocyte proliferation, we have revealed that adaptation is associated with angiogenesis. Further, we have found that small bowel resection (SBR) is associated with diminished oxygen delivery and elevated levels of hypoxia-inducible factor 1-alpha (HIF1α). METHODS: We ablated EGFR in the epithelium and endothelium as well as HIF1α in the epithelium, ostensibly the most hypoxic element. Using these mice, we determined the effects of these genetic manipulations on intestinal blood flow after SBR using photoacoustic microscopy (PAM), intestinal adaptation and angiogenic responses. Then, given that endothelial cells require a stromal support cell for efficient vascularization, we ablated EGFR expression in intestinal subepithelial myofibroblasts (ISEMFs) to determine its effects on angiogenesis in a microfluidic model of human small intestine. RESULTS: Despite immediate increased demand in oxygen extraction fraction measured by PAM in all mouse lines, were no differences in enterocyte and endothelial cell EGFR knockouts or enterocyte HIF1α knockouts by POD3. Submucosal capillary density was also unchanged by POD7 in all mouse lines. Additionally, EGFR silencing in ISEMFs did not impact vascular network development in a microfluidic device of human small intestine. CONCLUSIONS: Overall, despite the importance of EGFR in facilitating intestinal adaptation after SBR, it had no impact on angiogenesis in three cell types-enterocytes, endothelial cells, and ISEMFs. Epithelial ablation of HIF1α also had no impact on angiogenesis in the setting of SBS.

Alterations in pancreatic islet cell function in response to small bowel resection.

After 50% proximal small bowel resection (SBR) in mice, we have demonstrated hepatic steatosis, impaired glucose metabolism without insulin resistance, and increased pancreatic islet area. We sought to determine the consequences of SBR on pancreatic ß-cell morphology, proliferation, and expression of a key regulatory hormone, glucagon-like peptide-1 (GLP-1). C57BL/6 mice underwent 50% SBR or sham operation. At 10 wk, pancreatic insulin content and secretion was measured by ELISA. Immunohistochemistry was performed to determine structural alterations in pancreatic α-and ß-cells. Western blot analysis was used to measure GLP-1R expression, and immunoassay was used to measure plasma insulin and GLP-1. Experiments were repeated by administering a GLP-1 agonist (exendin-4) to a cohort of mice following SBR. After SBR, there was pancreatic islet hypertrophy and impaired glucose tolerance. The proportion of α and ß cells was not grossly altered. Whole pancreas and pancreatic islet insulin content was not significantly different; however, SBR mice demonstrated decreased insulin secretion in both static incubation and islet perfusion experiments. The expression of pancreatic GLP-1R was decreased approximately twofold after SBR, compared with sham and serum GLP-1, was decreased. These metabolic derangements were mitigated after administration of the GLP-1 agonist. Following massive SBR, there is significant hypertrophy of pancreatic islet cells with morphologically intact α- and ß-cells. Significantly reduced pancreatic insulin release in both static and dynamic conditions demonstrate a perturbed second phase of insulin secretion. GLP-1 is a key mediator of this amplification pathway. Decreased expression of serum GLP-1 and pancreatic GLP-1R in face of no change in insulin content presents a novel pathway for enteropancreatic glucose regulation following SBR.NEW & NOTEWORTHY Metabolic changes occur following intestinal resection; however, the effects on pancreatic function are unknown. Prior studies have demonstrated that glucagon-like protein-1 (GLP-1) signaling is a crucial player in the improved insulin sensitivity after bariatric surgery. In this study, we explore the effect of massive small bowel resection on gut hormone physiology and provide novel insights into the enteropancreatic axis.

Effects of high-fat diet on liver injury after small bowel resection.

BACKGROUND: The optimal regimen for enteral nutritional support in the management of children with short bowel syndrome (SBS) is not well characterized. A high fat, enteral diet is theoretically beneficial due to increased caloric density and enhanced structural adaptation. We therefore sought to determine the long-term effects of a high fat diet (HFD) on liver injury, a common complication of SBS, compared to a standard chow (SC) diet. METHODS: Using a parenteral nutrition-independent model of resection-associated liver injury, C57BL/6 mice underwent a sham operation or a 50% or 75% proximal small bowel resection (SBR). Mice in each group were then fed either a HFD (35% kcal fat) or SC (13% kcal fat). At post-operative week 15, markers of liver injury were quantified. RESULTS: Liver triglyceride levels were increased from 7- to 19-fold in mice on the HFD compared to mice fed SC in the sham, 50%, and 75% resection groups. Serum ALT (2.2-fold increase in 75% resected mice compared to sham controls) and AST (2.0- and 2.7-fold increases in 50% and 75% resected mice, respectively) levels as well as fibrotic liver staining were elevated only in resected mice fed a HFD. CONCLUSION: Long-term enteral feeding of HFD in our murine SBS model is associated with hepatic steatosis and liver injury. Our observation that liver steatosis and injury occur independent of parenteral nutrition suggests that enteral feeding composition and magnitude of intestinal loss may make a significant contribution to intestinal failure-associated liver disease.

SCORE - Leveling the Playing Field for Surgical Training Programs.

OBJECTIVE: The Surgical Council on Resident Education (SCORE) web portal provides a uniform, comprehensive, competency-based curriculum for general surgery residents. One of SCORE's principal founding goals was to provide equal opportunity for access of educational resources at programs across the United States which reported having a range of resources. We aimed to determine if there was a difference in portal usage by trainees in independent versus university programs, and across geographic areas. METHODS: Using analytic software, we measured SCORE usage by trainees in 246 subscribing programs from August 2015 to March 2017. The primary outcome was the average duration of SCORE use per login. Secondary outcomes were the geographic region of each program, and university versus independent designation. Encounters lasting >8 hours (comprising 7% of the data set) were excluded to eliminate the likelihood of failure to log off the portal. RESULTS: Over the study period, there were 669,501 SCORE sessions with 22% of these lasting 1 to 5 minutes, 33% lasting 6 to 30 minutes, and 28% lasting 31 to 120 minutes. Between the university (64.4% of encounters) and independent (35.6% of encounters) program types, there was no significant difference in average visit length overall, or in the normally-distributed designated time categories (t test -1.0, p = 0.3). When mean encounter length per program was compared by geographic regions, there was also no difference in the three time categories (ANOVA p = 0.9, 0.2, and 0.5, respectively). CONCLUSIONS: Most (50%) of SCORE encounters lasted 30 minutes of less, confirming prior work that shows trainees use the portal in relatively short bursts of activity. While there were more encounters from university program trainees (proportional with their greater numbers), the mean duration of an individual encounter did not significantly differ by program type as a whole or by region. These results suggest that SCORE is an equally accessible educational resource and is used by surgical trainees, regardless of program type or geographic region.

Single-Cell Analysis Reveals Regional Reprogramming During Adaptation to Massive Small Bowel Resection in Mice.

BACKGROUND & AIMS: The small intestine (SI) displays regionality in nutrient and immunological function. Following SI tissue loss (as occurs in short gut syndrome, or SGS), remaining SI must compensate, or "adapt"; the capacity of SI epithelium to reprogram its regional identity has not been described. Here, we apply single-cell resolution analyses to characterize molecular changes underpinning adaptation to SGS. METHODS: Single-cell RNA sequencing was performed on epithelial cells isolated from distal SI of mice following 50% proximal small bowel resection (SBR) vs sham surgery. Single-cell profiles were clustered based on transcriptional similarity, reconstructing differentiation events from intestinal stem cells (ISCs) through to mature enterocytes. An unsupervised computational approach to score cell identity was used to quantify changes in regional (proximal vs distal) SI identity, validated using immunofluorescence, immunohistochemistry, qPCR, western blotting, and RNA-FISH. RESULTS: Uniform Manifold Approximation and Projection-based clustering and visualization revealed differentiation trajectories from ISCs to mature enterocytes in sham and SBR. Cell identity scoring demonstrated segregation of enterocytes by regional SI identity: SBR enterocytes assumed more mature proximal identities. This was associated with significant upregulation of lipid metabolism and oxidative stress gene expression, which was validated via orthogonal analyses. Observed upstream transcriptional changes suggest retinoid metabolism and proximal transcription factor Creb3l3 drive proximalization of cell identity in response to SBR. CONCLUSIONS: Adaptation to proximal SBR involves regional reprogramming of ileal enterocytes toward a proximal identity. Interventions bolstering the endogenous reprogramming capacity of SI enterocytes-conceivably by engaging the retinoid metabolism pathway-merit further investigation, as they may increase enteral feeding tolerance, and obviate intestinal failure, in SGS.