Objectives The adult response to myocardial infarction results in inflammation, scar formation, left ventricular dilatation, and loss of regional and global function. Regenerative scarless healing has been demonstrated in fetal dermis and tendon and is associated with diminished inflammation. We hypothesized that following fetal myocardial infarction there would be minimal inflammation, regenerative healing, and preservation of function. Methods Anteroapical myocardial infarction encompassing 20% of the left ventricle were created in adult or early gestation fetal sheep. Myocardial function was serially assessed using quantitative echocardiography. Infarct architecture was examined histologically for evidence of scar formation. Cellular inflammation, cellular proliferation, and apoptosis were assessed using immunohistochemistry. Results In the adult sheep 4 weeks following myocardial infarction, there was a significant decline in ejection fraction (41±7.4% to 26±7.4%, p<0.05), and the akinetic myocardial segment increased in size (6.9±0.8 cm to 7.9±1.1 cm, p<0.05). In contrast, there was no decline in the fetal ejection fraction (53±8.1% to 55±8.8%) and no akinetic fetal myocardial segment 4 weeks post-infarction. The fetal infarcts lacked an inflammatory cell infiltrate and healed with minimal fibrosis, compared to the adults. Fetal infarcts also demonstrated BrdU+ proliferating cells, including cardiomyocytes, within the infarct. Conclusions These data demonstrate that the fetal response to myocardial infarction is dramatically different than the adult and is characterized by minimal inflammation, lack of fibrosis, myocardial proliferation, and restoration of cardiac function. Diminished inflammation is associated with fetal regenerative cardiac healing following injury. Understanding the mechanisms involved in fetal myocardial regeneration may lead to applications to alter the adult response following myocardial infarction.

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Background In adults, MI results in a brisk inflammatory response, myocardium loss and scar formation. We have recently reported the first mammalian large animal model of cardiac regeneration following MI in fetal sheep. We hypothesize that the fetus ability to regenerate functional myocardium following MI is due to differential gene expression regulating the response to MI in the fetus compared to the adult. Methods MI was created in adult (n=4) or early gestation fetal (n=4) sheep. Tissue harvested after 3 or 30 days, RNA extracted for microarray, followed by PCA and global gene expression analysis for the gene ontology (GO) terms: “response to wounding”, “inflammatory response”, “extracellular matrix”, “cell cycle”, “cell migration”, “cell proliferation” and “apoptosis”. Results PCA demonstrated that the global gene expression pattern in adult infarcts was distinctly different from uninfarcted region at 3 days and remained different 30 days post-MI. In contrast, gene expression in the fetal infarct was different from the uninfarcted region at 3 days, but by 30 days it returned to a baseline expression pattern similar to the uninfarcted region. 3 days post-MI there was an increase in the expression of genes related to all GO terms in fetal and adult infarcts, but this increase was much more pronounced in adults. By 30 days, the fetal gene expression returned to baseline, whereas in the adult remained significantly elevated. Conclusions These data demonstrate that the global gene expression pattern is dramatically different in the fetal regenerative response to MI compared to the adult response and may partly be responsible for the regeneration.

Wound size impacts the threshold between scarless regeneration and reparative healing in the fetus with increased inflammation showed in fetal scar formation. We hypothesized that increased fetal wound size increases pro-inflammatory and fibrotic genes with resultant inflammation and fibroplasia and that transition to scar formation could be reversed by overexpression of interleukin-10 (IL-10). To test this hypothesis, 2-mm and 8-mm dermal wounds were created in mid-gestation fetal sheep. A subset of 8-mm wounds were injected with a lentiviral vector containing the IL-10 transgene (n = 4) or vehicle (n = 4). Wounds were harvested at 3 or 30 days for histology, immunohistochemistry, analysis of gene expression by microarray, and validation with real-time polymerase chain reaction. In contrast to the scarless 2-mm wounds, 8-mm wounds showed scar formation with a differential gene expression profile, increased inflammatory cytokines, decreased CD45+ cells, and subsequent inflammation. Lentiviral-mediated overexpression of the IL-10 gene resulted in conversion to a regenerative phenotype with decreased inflammatory cytokines and regeneration of dermal architecture. In conclusion, increased fetal wounds size leads to a unique gene expression profile that promotes inflammation and leads to scar formation and furthermore, these results show the significance of attenuated inflammation and IL-10 in the transition from fibroplasia to fetal regenerative healing.

BACKGROUND Pediatric firearm injury is a leading cause of death for U.S. children. We sought to further characterize children who die from these injuries using a validated national database. METHODS The National Trauma Data Bank 2010 to 2016 was queried for patients aged 0 to 19 years old. International Classification of Diseases external cause of injury codes were used to classify patients by intent. Differences between groups were analyzed using χ2 or Mann-Whitney U tests. Patterns over time were analyzed using nonparametric tests for trend. Multivariable logistic regression was used to investigate associations between the above factors and mortality. RESULTS There were a total of 45,288 children with firearm injuries, 12.0% (n = 5,412) of whom died. Those who died were younger and more often white than survivors. Mortality was associated with increased injury severity, shock on presentation, and polytrauma (p < 0.001 for all). There was an increasing trend in the proportion of self-inflicted injuries over the study period (p < 0.001), and mortality from these self-inflicted injuries increased concordantly (35.3% in 2010 to 47.8% in 2016, p = 0.001). Location of severe injuries had significant different mortality rates, ranging from 51.3% of head injuries to 3.9% in the extremities. In the multivariable model, treatment at a pediatric trauma center was protective against mortality, with odds ratios of 2.10 (confidence interval, 1.64–2.68) and 1.80 (confidence interval, 1.39–2.32) for death at adult and dual-designated trauma centers, respectively. This finding was confirmed in age-stratified cohorts. CONCLUSION Proportions of self-inflicted pediatric firearm injury in the National Trauma Data Bank increased from 2010 to 2016, as did mortality from self-inflicted injury. Because mortality is highest in this subpopulation, prevention and treatment efforts should be prioritized in this group of firearm-injured children. LEVEL OF EVIDENCE Epidemiological study, level V.

Recurrent injury has been implicated in the development of chronic diabetic wounds. We have developed a chronic diabetic wound model based upon recurrent injury in diabetic mice. We hypothesized that dysregulation of collagen production at both the mRNA and microRNA levels contributes to the development of chronic diabetic wounds. To test this, both diabetic and nondiabetic mice were made to undergo recurrent injury. Real-time PCR for TGF-β1, SMAD-3, Col1α1, Col3α1, microRNA-25, and microRNA-29a and Western blot for collagen I and III were performed 7 days following each injury. Diabetic wounds displayed decreased collagen at all time points. This was associated with dysregulated collagen production at both the gene and microRNA levels at all time points. Following the final injury, however, diabetic collagen production significantly improved. This appeared to be due to a substantial decrease in both microRNAs as well as an increase in the expression of collagen pathway genes. That dysregulated collagen production progressed throughout the course of wounding suggests that this is one factor contributing to the development of chronic diabetic wounds. Future studies using this model will allow for the determination of other factors that may also contribute to the development and/or persistence of chronic diabetic wounds.

Background In contrast to the adult, fetal sheep consistently regenerate functional myocardium after myocardial infarction. We hypothesize that this regeneration is due to the recruitment of cardiac progenitor cells to the infarct by stromal-derived factor-1α (SDF-1α) and that its competitive inhibition will block the regenerative fetal response. Methods A 20% apical infarct was created in adult and fetal sheep by selective permanent coronary artery ligation. Lentiviral overexpression of mutant SDF-1α competitively inhibited SDF-1α in fetal infarcts. Echocardiography was performed to assess left ventricular function and infarct size. Cardiac progenitor cell recruitment and proliferation was assessed in fetal infarcts at 1 month by immunohistochemistry for nkx2.5 and 5-bromo-2-deoxyuridine. Results Competitive inhibition of SDF-1α converted the regenerative fetal response into a reparative response, similar to the adult. SDF-inhibited fetal infarcts demonstrated significant infarct expansion by echocardiography (p < 0.001) and a significant decrease in the number of nkx2.5+ cells repopulating the infarct (p < 0.001). Conclusions The fetal regenerative response to myocardial infarction requires the recruitment of cardiac progenitor cells and is dependent on SDF1α. This novel model of mammalian cardiac regeneration after myocardial infarction provides a powerful tool to better understand cardiac progenitor cell biology and to develop strategies to cardiac regeneration in the adult.

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