Douglas E. Wright

Hematopoietic Stem Cells Are Uniquely Selective in Their Migratory Response to Chemokines

Although hematopoietic stem cell (HSC) migration into and out of sites of active hematopoiesis is poorly understood, it is a critical process that underlies modern clinical stem cell transplantation and may be important for normal hematopoietic homeostasis. Given the established roles of chemotactic cytokine (chemokine)-directed migration of other leukocyte subsets, the migration of murine HSC to a large panel of CC and CXC chemokines was investigated. HSC migrated only in response to stromal derived factor-1α, the ligand for the CXC chemokine receptor 4 (CXCR4). CXCR4 expression by HSC was confirmed by reverse transcription polymerase chain reaction analysis. Surprisingly, HSC also expressed mRNA for CCR3 and CCR9, although they failed to migrate to the ligands for these receptors. The sharply restricted chemotactic responsiveness of HSC is unique among leukocytes and may be necessary for the specific homing of circulating HSC to bone marrow, as well as for the maintenance of HSC in hematopoietic microenvironments.

Circulation and Chemotaxis of Fetal Hematopoietic Stem Cells

The major site of hematopoiesis transitions from the fetal liver to the spleen and bone marrow late in fetal development. To date, experiments have not been performed to evaluate functionally the migration and seeding of hematopoietic stem cells (HSCs) during this period in ontogeny. It has been proposed that developmentally timed waves of HSCs enter the bloodstream only during distinct windows to seed the newly forming hematopoietic organs. Using competitive reconstitution assays to measure HSC activity, we determined the localization of HSCs in the mid-to-late gestation fetus. We found that multilineage reconstituting HSCs are present at low numbers in the blood at all timepoints measured. Seeding of fetal bone marrow and spleen occurred over several days, possibly while stem cell niches formed. In addition, using dual-chamber migration assays, we determined that like bone marrow HSCs, fetal liver HSCs migrate in response to stromal cell-derived factor-1α (SDF-1α); however, unlike bone marrow HSCs, the migratory response of fetal liver HSCs to SDF-1α is greatly increased in the presence of Steel factor (SLF), suggesting an important role for SLF in HSC homing to and seeding of the fetal hematopoietic tissues. Together, these data demonstrate that seeding of fetal organs by fetal liver HSCs does not require large fluxes of HSCs entering the fetal bloodstream, and that HSCs constitutively circulate at low levels during the gestational period from 12 to 17 days postconception. Newly forming hematopoietic tissues are seeded gradually by HSCs, suggesting initial seeding is occurring as hematopoietic niches in the spleen and bone marrow form and become capable of supporting HSC self-renewal. We demonstrate that fetal and adult HSCs exhibit specific differences in chemotactic behavior. While both migrate in response to SDF-1α, fetal HSCs also respond significantly to the cytokine SLF. In addition, the combination of SDF-1α and SLF results in substantially enhanced migration of fetal HSCs, leading to migration of nearly all fetal HSCs in this assay. This finding indicates the importance of the combined effects of SLF and SDF-1α in the migration of fetal HSCs, and is, to our knowledge, the first demonstration of a synergistic effect of two chemoattractive agents on HSCs.

Hematopoietic stem cells: challenges to expectations

The past year provided a number of challenges to our expectations regarding hematopoietic stem cell (HSC) biology. Evidence has emerged that HSCs arise intraembryonically before they can be detected in the yolk sac. A number of genes that may regulate the formation, self-renewal, or differentiation of HSC have been identified. New markers for purifying HSCs have also been described. Although different groups have attributed different properties to HSCs, it now appears that the differences may be explained by variations in assay conditions rather than by differences in the HSCs themselves. Finally, insights have emerged into the complexity of the regulation of HSC proliferation and adhesion properties.

From stem cells to lymphocytes; biology and transplantation

Summary: We review the development of the hematopoietic system, focusing on the transition from hematopoietic stem cells (HSCs) to T cell This includes the isolation of HSCs, and recent progress in understanding their ontogeny, homing properties, and differentiation. HSC transplantation is reviewed, including the kinetics of reconstitution, engraftment across histocompatibility barriers, the facilitation of allogeneic engraftment, and the mechanisms of graft rejection. We describe progress in understanding T‐cell development in the bone marrow and thymus as well as the establishment of lymph nodes. Finally, the role of bcl‐2 in regulating homeostasis in the hematopoietic system is discussed.

Caveolin-1 and Altered Neuregulin Signaling Contribute to the Pathophysiological Progression of Diabetic Peripheral Neuropathy

OBJECTIVE Evaluate if Erb B2 activation and the loss of caveolin-1 (Cav1) contribute to the pathophysiological progression of diabetic peripheral neuropathy (DPN). RESEARCH DESIGN AND METHODS Cav1 knockout and wild-type C57BL/6 mice were rendered diabetic with streptozotocin, and changes in motor nerve conduction velocity (MNCV), mechanical and thermal hypoalgesia, Erb B2 phosphorylation (pErb B2), and epidermal nerve fiber density were assessed. The contribution of Erb B2 to DPN was assessed using the Erb B2 inhibitors PKI 166 and erlotinib and a conditional bitransgenic mouse that expressed a constitutively active form of Erb B2 in myelinated Schwann cells (SCs). RESULTS Diabetic mice exhibited decreased MNCV and mechanical and thermal sensitivity, but the extent of these deficits was more severe in diabetic Cav1 knockout mice. Diabetes increased pErb B2 levels in both genotypes, but the absence of Cav1 correlated with a greater increase in pErb B2. Erb B2 activation contributed to the mechanical hypoalgesia and MNCV deficits in both diabetic genotypes because treatment with erlotinib or PKI 166 improved these indexes of DPN. Similarly, induction of a constitutively active Erb B2 in myelinated SCs was sufficient to decrease MNCV and induce a mechanical hypoalgesia in the absence of diabetes. CONCLUSIONS Increased Erb B2 activity contributes to specific indexes of DPN, and Cav1 may be an endogenous regulator of Erb B2 signaling. Altered Erb B2 signaling is a novel mechanism that contributes to SC dysfunction in diabetes, and inhibiting Erb B2 may ameliorate deficits of tactile sensitivity in DPN.

Diabetes‐induced expression of activating transcription factor 3 in mouse primary sensory neurons

Abstractu2003 Diabetic neuropathy (DN) is a complication of diabetes that affects the distal terminals of lengthy‐projecting sensory axons. To determine whether diabetes‐induced axonal degeneration induces gene expression similar to nerve injury, the expression of activating transcription factor 3 (ATF3) by primary sensory neurons was examined in an experimental mouse model of DN. Diabetes was induced using streptozotocin in C57BL/6 mice, and ATF3 expression in lumbar dorsal root ganglia was assessed at different time points and correlated with the markers of unmyelinated and myelinated neuronal populations. ATF expression was first evident 3 weeks after diabetes induction in both small unmyelinated and large myelinated neurons, but it was more prevalent in larger neurons. At 6 weeks, ATF3 was expressed by neurons among smaller size ranges, but this shift occurred principally within myelinated populations. The retrograde labeling of neurons innervating the flank and paw skin using Fluoro‐Gold labeled appropriate percentages of ATF3‐positive neurons at 3 weeks, suggesting ATF3 is expressed by neurons capable of transporting substances. However, the percentage of double‐labeled neurons was substantially reduced at 6 weeks, suggesting this capacity decreases during disease progression. Finally, behavioral responses to noxious cutaneous stimuli were assessed. Although no differences to radiant heat were observed, diabetic mice developed severe mechanical hypoalgesia 4–5 weeks after diabetes induction. These results demonstrate that the diabetes‐induced damage of sensory axons can induce the expression of genes linked to peripheral nerve injury and may identify neurons undergoing nerve damage. Finally, the ability to detect sensory deficits in diabetic mice occurs after the expression of injury‐related gene ATF3, suggesting that nerve damage may be underway prior to the appearance of behavioral deficits.

Perioperative Surveillance for Adverse Myocardial Events

Perioperative myocardial infarctions occur in 1 to 4% of unselected noncardiac surgical patients, and are associated with high mortality. Detection of these events can be challenging, because ‘typical’ symptoms of myocardial ischemia may not be present or may be masked in the perioperative period. Therefore, surveillance by means of intraoperative cardiac monitoring and postoperative serial electrocardiograms (ECGs) and troponins may be needed. Cardiac monitoring not infrequently detects ST-segment changes suggestive of ischemia during or shortly after surgery. To respond to these changes, the risk for coronary artery disease should be assessed before recommending additional interventions. For all vascular surgery patients, and for patients who have or are felt to be at risk for coronary artery disease, serial postoperative 12-lead ECGs and troponins should be considered. Among surgical patients not meeting these criteria, obtaining routine ECGs in the absence of signs or symptoms that suggest a cardiac event may be falsely reassuring and is not felt to be useful. The presence of elevated postoperative troponins predicts worsened prognosis, and argues for intensified risk factor modification. The need for noninvasive cardiac testing or cardiac catheterization should be made on an individual basis.

An Educational and Administrative Intervention to Promote Rational Laboratory Test Ordering on an Academic General Medicine Service

BACKGROUNDnOveruse of clinical laboratory testing in the inpatient setting is a common problem. The objective of this project was to develop an inexpensive and easily implemented intervention to promote rational laboratory use without compromising resident education or patient care.nnnMETHODSnThe study comprised of a cluster-randomized, controlled trial to assess the impact of a multifaceted intervention of education, guideline development, elimination of recurring laboratory orders, unbundling of laboratory panels, and redesign of the daily progress note on laboratory test ordering. The population included all patients hospitalized general medicine was duplicated during 2 consecutive months on a general medicine teaching service within a 999-bed tertiary care hospital in Boston, Massachusetts. The primary outcome was the total number of commonly used laboratory tests per patient day during 2 months in 2008. Secondary outcomes included a subgroup analysis of each individual test per patient day, adverse events, and resident and nursing satisfaction.nnnRESULTSnA total of 5392 patient days were captured. The intervention produced a 9% decrease in aggregate laboratory use (rate ratio, 0.91; Pxa0= .021; 95% confidence interval, 0.84-0.98). Six instances of delayed diagnosis of acute kidney injury and 11 near misses were reported in the intervention arm.nnnCONCLUSIONSnA bundled educational and administrative intervention promoting rational ordering of laboratory tests on a single academic general medicine service led to a modest but significant decrease in laboratory use. To our knowledge, this was the first study to examine the daily progress note as a tool to limit excessive test ordering. Unadjudicated near misses and possible harm were reported with this intervention. This finding warrants further study.

Deletion of the insulin receptor in sensory neurons increases pancreatic insulin levels

ABSTRACT Insulin is known to have neurotrophic properties and loss of insulin support to sensory neurons may contribute to peripheral diabetic neuropathy (PDN). Here, genetically‐modified mice were generated in which peripheral sensory neurons lacked the insulin receptor (SNIRKO mice) to determine whether disrupted sensory neuron insulin signaling plays a crucial role in the development of PDN and whether SNIRKO mice develop symptoms of PDN due to reduced insulin neurotrophic support. Our results revealed that SNIRKO mice were euglycemic and never displayed significant changes in a wide range of sensorimotor behaviors, nerve conduction velocity or intraepidermal nerve fiber density. However, SNIRKO mice displayed elevated serum insulin levels, glucose intolerance, and increased insulin content in the islets of Langerhans of the pancreas. These results contribute to the growing idea that sensory innervation of pancreatic islets is key to regulating islet function and that a negative feedback loop of sensory neuron insulin signaling keeps this regulation in balance. Our results suggest that a loss of insulin receptors in sensory neurons does not lead to peripheral nerve dysfunction. The SNIRKO mice will be a powerful tool to investigate sensory neuron insulin signaling and may give a unique insight into the role that sensory neurons play in modifying islet physiology. HIGHLIGHTSMice were generated in which peripheral sensory neurons lacked the insulin receptor (SNIRKO mice).A lack of insulin receptors on sensory neurons does not lead to peripheral nerve dysfunction.SNIRKO mice display elevated insulin and impaired glucose tolerance.Disruption of insulin signaling in sensory neurons may impact insulin and glucose regulation.

Core competency review: Aortic stenosis and noncardiac surgery

Aortic stenosis (AS) poses a risk of adverse cardiac events for patients undergoing surgical procedures. Perioperative mortality for patients with severe AS is as high as 14%. This review examines the accuracy of the history and physical examination in detecting AS and, subsequently, in assessing severity. The utility of echocardiography is addressed, and the relevant pathophysiology of AS is summarized. We also summarize what is known about perioperative risk for patients with AS.