The intestinal epithelium is maintained by a population of rapidly cycling (Lgr5+) intestinal stem cells (ISCs). It has been postulated, however, that slowly cycling ISCs must also be present in the intestine to protect the genome from accumulating deleterious mutations and to allow for a response to tissue injury. Here, we identify a subpopulation of slowly cycling ISCs marked by mouse telomerase reverse transcriptase (mTert) expression that can give rise to Lgr5+ cells. mTert-expressing cells distribute in a pattern along the crypt–villus axis similar to long-term label-retaining cells (LRCs) and are resistant to tissue injury. Lineage-tracing studies demonstrate that mTert+ cells give rise to all differentiated intestinal cell types, persist long term, and contribute to the regenerative response following injury. Consistent with other highly regenerative tissues, our results demonstrate that a slowly cycling stem cell population exists within the intestine.

Stem cells hold great promise for regenerative medicine, but remain elusive in many tissues in part because universal markers of ''stemness'' have not been identified. The ribonucleoprotein complex telomerase catalyzes the extension of chromosome ends, and its expression is associated with failure of cells to undergo cellular senescence. Because such resistance to senescence is a common characteristic of many stem cells, we hypothesized that telomerase expression may provide a selective biomarker for stem cells in multiple tissues. In fact, telomerase expression has been demonstrated within hematopoietic stem cells. We therefore generated mouse telomerase reverse transcriptase (mTert)-GFP-transgenic mice and assayed the ability of mTert-driven GFP to mark tissue stem cells in testis, bone marrow (BM), and intestine. mTert-GFP mice were generated by using a two-step embryonic stem cell-based strategy, which enabled primary and secondary screening of stably transfected clones before blastocyst injection, greatly increasing the probability of obtaining mTert reporter mice with physiologically appropriate regulation of GFP expression. Analysis of adult mice showed that GFP is expressed in differentiating male germ cells, is enriched among BM-derived hematopoietic stem cells, and specifically marks long-term BrdU-retaining intestinal crypt cells. In addition, telomerase-expressing GFP ؉ BM cells showed longterm, serial, multilineage BM reconstitution, fulfilling the functional definition of hematopoietic stem cells. Together, these data provide direct evidence that mTert-GFP expression marks progenitor cells in blood and small intestine, validating these mice as a useful tool for the prospective identification, isolation, and functional characterization of progenitor/stem cells from multiple tissues.intestinal stem cell ͉ telomerase ͉ tissue stem cells

This paper extends knowledge about neonatal brain injury and long-term outcome in congenital heart disease. Children with white matter injury show lower IQ and more attention problems at school age. Injury of the posterior limb of the internal capsule increases the risk of motor problems. This study provides evidence for worse outcomes in neonates acquiring brain injury around cardiac surgery.

S urvival after neonatal cardiac surgery has improved over the past decades to >90% because of major advances in surgical techniques and perioperative management. However, it has also become evident that neurodevelopment is impaired in approximately one third of children who underwent surgery at a neonatal age.1 As seen on magnetic resonance imaging (MRI), 23% to 40% of neonates presenting with a complex cardiac defect already have evidence of cerebral injury preoperatively.2-6 After surgery, 36% to 73% of patients have evidence of new cerebral lesions on MRI. [2][3][4][5][6][7][8] This suggests that much of the injury develops perioperatively. Clinical Perspective on p 233Neonates diagnosed with aortic arch obstruction (ie, hypoplastic left heart syndrome or other complex cardiac defects) are consistently at the highest risk of cerebral injury. 5,7,9 This may be attributable to the fact that full-flow cardiopulmonary bypass (CPB) is not feasible during the reconstruction of the aortic arch, obligating the use of either deep hypothermic circulatory arrest (DHCA) or antegrade cerebral perfusion (ACP). Despite initial reports on the adverse cerebral effects after DHCA and the intuitive benefit of ACP, previous studies have not been able to show superiority of ACP in studies of neurodevelopmental outcome at 1 year of age. 10,11 However, these results may be confounded by the reoperations that frequently take place in the interim.Therefore, in the present randomized, controlled trial, we used preoperative and postoperative MRI as the most sensitive measure to assess perioperative cerebral injury. Specifically, in neonates undergoing aortic arch reconstruction, the incidence of new postoperative injury on MRI was compared between DHCA and ACP.Background-Complex neonatal cardiac surgery is associated with cerebral injury. In particular, aortic arch repair, requiring either deep hypothermic circulatory arrest (DHCA) or antegrade cerebral perfusion (ACP), entails a high risk of perioperative injury. It is unknown whether ACP results in less cerebral injury than DHCA. Methods and Results-Thirty-seven neonates with an aortic arch obstruction presenting for univentricular or biventricular repair were randomized to either DHCA or ACP. Preoperatively and 1 week after surgery, magnetic resonance imaging was performed in 36 patients (1 patient died during the hospital stay). The presence of new postoperative cerebral injury was scored, and results were entered into a sequential analysis, which allows for immediate data analysis. After the 36th patient, it was clear that there was no difference between DHCA and ACP in terms of new cerebral injury. Preoperatively, 50% of patients had evidence of cerebral injury.

BackgroundA robust inflammatory response occurs in the hours and days following cerebral ischemia. However, little is known about the immediate innate immune response in the first minutes after an ischemic insult in humans. We utilized the use of circulatory arrest during cardiac surgery to assess this.MethodsTwelve neonates diagnosed with an aortic arch obstruction underwent cardiac surgery with cardiopulmonary bypass and approximately 30 minutes of deep hypothermic circulatory arrest (DHCA, representing cerebral ischemia). Blood samples were drawn from the vena cava superior immediately after DHCA and at various other time points from preoperatively to 24 hours after surgery. The innate immune response was assessed by neutrophil and monocyte count and phenotype using FACS, and concentrations of cytokines IL-1β, IL-6, IL-8, IL-10, TNFα, sVCAM-1 and MCP-1 were assessed using multiplex immunoassay. Results were compared to a simultaneously drawn sample from the arterial cannula. Twelve other neonates were randomly allocated to undergo the same procedure but with continuous antegrade cerebral perfusion (ACP).ResultsImmediately after cerebral ischemia (DHCA), neutrophil and monocyte counts were higher in venous blood than arterial (P = 0.03 and P = 0.02 respectively). The phenotypes of these cells showed an activated state (both P <0.01). Most striking was the increase in the ‘non-classical’ monocyte subpopulations (CD16intermediate; arterial 6.6% vs. venous 14%; CD16+ 13% vs. 22%, both P <0.01). Also, higher IL-6 and lower sVCAM-1 concentrations were found in venous blood (both P = 0.03). In contrast, in the ACP group, all inflammatory parameters remained stable.ConclusionsIn neonates, approximately 30 minutes of cerebral ischemia during deep hypothermia elicits an immediate innate immune response, especially of the monocyte compartment. This phenomenon may hold important clues for the understanding of the inflammatory response to stroke and its potentially detrimental consequences.Trial registrationClinicalTrial.gov: NCT01032876