Clifford W. Bogue

Hex expression suggests a role in the development and function of organs derived from foregut endoderm.

Hex is a divergent homeobox gene expressed as early as E4.5 in the mouse and in a pattern that suggests a role in anterior‐posterior patterning. Later in embryogenesis, Hex is expressed in the developing thyroid, lung, and liver. We now show Hex expression during thymus, gallbladder, and pancreas development and in the adult thyroid, lung, and liver. At E10.0, Hex is expressed in the 3rd pharyngeal pouch, from which the thymus originates, the endodermal cells of liver that are invading the septum transversum, the thyroid, the dorsal pancreatic bud, and gallbladder primoridum. At E13.5, expression is maintained at high levels in the thyroid, liver, epithelial cells lining the pancreatic and extrahepatic biliary ducts and is present in both the epithelial and mesenchymal cells of the lung. Expression in the thymus at this age is less than in the other organs. In the E16.5 embryo, expression persists in the thyroid, pancreatic, and bile duct epithelium, lung, and liver, with thymic expression dropping to barely detectable levels. By E18.5, expression in the thyroid and bile ducts remains high, whereas lung expression is markedly decreased. At this age, expression in the pancreas and thymus is no longer present. Finally, we show the cell types in the adult thyroid, lung, and liver that express Hex in the mature animal. Our results provide more detail on the potential role of Hex in the development of several organs derived from foregut endoderm and in the maintenance of function of several of these organs in the mature animal.

A null mutation of Hhex results in abnormal cardiac development,defective vasculogenesis and elevated Vegfa levels

The homeobox gene Hhex has recently been shown to be essential for normal liver, thyroid and forebrain development. Hhex–/– mice die by mid-gestation (E14.5) and the cause of their early demise remains unclear. Because Hhex is expressed in the developing blood islands at E7.0 in the endothelium of the developing vasculature and heart at E9.0-9.5, and in the ventral foregut endoderm at E8.5-9.0, it has been postulated to play a critical role in heart and vascular development. We show here, for the first time, that a null mutation of Hhex results in striking abnormalities of cardiac and vascular development which include: (1) defective vasculogenesis, (2) hypoplasia of the right ventricle, (3) overabundant endocardial cushions accompanied by ventricular septal defects, outflow tract abnormalities and atrio-ventricular (AV) valve dysplasia and (4) aberrant development of the compact myocardium. The dramatic enlargement of the endocardial cushions in the absence of Hhex is due to decreased apoptosis and dysregulated epithelial-mesenchymal transformation (EMT). Interestingly, vascular endothelial growth factor A (Vegfa) levels in the hearts of Hhex–/– mice were elevated as much as three-fold between E9.5 and E11.5, and treatment of cultured Hhex–/– AV explants with truncated soluble Vegfa receptor 1, sFlt-1, an inhibitor of Vegf signaling, completely abolished the excessive epithelial-mesenchymal transformation seen in the absence of Hhex. Therefore, Hhex expression in the ventral foregut endoderm and/or the endothelium is necessary for normal cardiovascular development in vivo, and one function of Hhex is to repress Vegfa levels during development.

HNF3β and GATA-4 transactivate the liver-enriched homeobox gene, Hex

The orphan homeobox gene, Hex, has a limited domain of expression which includes the developing and adult mouse liver. Hex is expressed in the developing liver coincident with the forkhead/winged helix transcription factor, Hepatocyte Nuclear Factor 3beta (HNF3beta). Although preliminary characterization of the mouse Hex promoter has recently been reported, the identity of the molecular regulators that drive liver expression is not known. We hypothesized that putative HNF3beta and GATA-4 elements within the Hex promoter would confer liver-enriched expression. A series of Hex promoter-driven luciferase reporter constructs were transfected in liver-derived HepG2 and fibroblast-like Cos cells+/-HNF3beta or GATA expression plasmids. The Hex promoter region from nt -235/+22 conferred basal activity in both HepG2 and Cos cells, with the region from -103/+22 conferring liver-enriched activity. HNF3beta and GATA-4 transactivated the promoter via response elements located within nt -103/+22, whereas Sp1 activated the -235/+22 construct. Mutation of the HNF3 element significantly reduced promoter activity in HepG2 cells, whereas this element in isolation conferred HNF3beta responsiveness to a heterologous promoter. Electrophoretic mobility shift assays were performed to confirm transcription factor:DNA binding. We conclude that HNF3beta and GATA-4 contribute to liver-enriched expression of Hex.

Toll-like receptor signaling in sepsis.

Despite extensive research, bacterial sepsis and its associated systemic inflammation remain a major cause of morbidity and mortality in the pediatric intensive care unit. Advances in molecular biology, however, have improved our understanding of this disease process and have opened up new avenues of potential therapeutic approaches. One such exciting area has been the substantial and still growing evidence that the mammalian immune system uses a family of Toll-like receptors (TLRs) to generate a response to molecular patterns present on invading microorganisms. In particular, TLR4 is part of a recognition complex for bacterial lipopolysaccharide (LPS), thus raising the likelihood of its involvement in the inflammatory response to bacterial sepsis. This review highlights our understanding of the molecular biology of these receptors, focusing on the LPS response, and concluding with a summary of ongoing evaluation and potential therapeutic strategies for treating sepsis through blockade of TLR signaling.

Race, Ethnicity, and Socioeconomic Status in Research on Child Health

An extensive literature documents the existence of pervasive and persistent child health, development, and health care disparities by race, ethnicity, and socioeconomic status (SES). Disparities experienced during childhood can result in a wide variety of health and health care outcomes, including adult morbidity and mortality, indicating that it is crucial to examine the influence of disparities across the life course. Studies often collect data on the race, ethnicity, and SES of research participants to be used as covariates or explanatory factors. In the past, these variables have often been assumed to exert their effects through individual or genetically determined biologic mechanisms. However, it is now widely accepted that these variables have important social dimensions that influence health. SES, a multidimensional construct, interacts with and confounds analyses of race and ethnicity. Because SES, race, and ethnicity are often difficult to measure accurately, leading to the potential for misattribution of causality, thoughtful consideration should be given to appropriate measurement, analysis, and interpretation of such factors. Scientists who study child and adolescent health and development should understand the multiple measures used to assess race, ethnicity, and SES, including their validity and shortcomings and potential confounding of race and ethnicity with SES. The American Academy of Pediatrics (AAP) recommends that research on eliminating health and health care disparities related to race, ethnicity, and SES be a priority. Data on race, ethnicity, and SES should be collected in research on child health to improve their definitions and increase understanding of how these factors and their complex interrelationships affect child health. Furthermore, the AAP believes that researchers should consider both biological and social mechanisms of action of race, ethnicity, and SES as they relate to the aims and hypothesis of the specific area of investigation. It is important to measure these variables, but it is not sufficient to use these variables alone as explanatory for differences in disease, morbidity, and outcomes without attention to the social and biologic influences they have on health throughout the life course. The AAP recommends more research, both in the United States and internationally, on measures of race, ethnicity, and SES and how these complex constructs affect health care and health outcomes throughout the life course.

Relationship between hypoglycemia and mortality in critically ill children

Objectives: To determine the prevalence of hypoglycemia in critically ill nondiabetic children and the association of hypoglycemia with mortality and worsening organ function in critically ill children. Design: Retrospective cohort study with matched-cohort analysis. Setting: Academic pediatric intensive care unit. Patients: A total of 899 nondiabetic patients <18 yrs old admitted to the pediatric intensive care unit for >1 day with at least one blood glucose measurement. Forty-two patients with a blood glucose level of <50 mg/dL (<2.8 mmol/L) were matched with 126 nonhypoglycemic patients. Interventions: None. Measurements and Main Results: Hypoglycemia, based on point-of-care blood glucose measurements, occurred in 2.2% (<40 mg/dL [<2.2 mmol/L]) to 7.5% (<60 mg/dL [<3.3 mmol/L]) of the patients. Hypoglycemia was more common in patients on mechanical ventilation and/or vasopressor support. Severity of hypoglycemia correlated with an increased mortality rate. The highest odds ratio of mortality was 4.49 (95% confidence interval [CI], 1.69–11.96; p < .01) at a blood glucose level of <40 mg/dL (<2.2 mmol/L). In the matched analysis, hypoglycemia was an independent risk factor for mortality. The unadjusted, covariate-adjusted, and propensity score–adjusted odds ratios of mortality were 3.69 (95% CI, 1.78–7.68; p < .01), 4.16 (95% CI, 1.53–11.32; p < .01), and 8.45 (95% CI, 1.75–40.86; p < .01), respectively. Hypoglycemia was associated with worsening organ function in the covariate-adjusted model (odds ratio, 2.37; 95% CI, 1.12–5.01; p = .02) but not in the unadjusted and propensity-score adjusted models. Conclusions: Hypoglycemia is common in critically ill children. It is associated with increased mortality rates in critically ill nondiabetic children. Our data suggest that hypoglycemia is also associated with worsening organ function. Hypoglycemia may merely be a marker of severity of illness. Further investigations are needed to establish the mortality risk with hypoglycemia due to insulin compared to spontaneous hypoglycemia.

The diabetes gene Hhex maintains δ-cell differentiation and islet function

The homeodomain transcription factor HHEX (hematopoietically expressed homeobox) has been repeatedly linked to type 2 diabetes mellitus (T2DM) using genome-wide association studies. We report here that within the adult endocrine pancreas, Hhex is selectively expressed in the somatostatin-secreting δ cell. Using two mouse models with Hhex deficiency in the endocrine pancreas, we show that Hhex is required for δ-cell differentiation. Decreased somatostatin levels in Hhex-deficient islets cause disrupted paracrine inhibition of insulin release from β cells. These findings identify Hhex as the first transcriptional regulator specifically required for islet δ cells and suggest compromised paracrine control as a contributor to T2DM.

Impaired B cell development and function in mice with a targeted disruption of the homeobox gene Hex

Hex is a homeobox gene that is expressed in all stages of B cell development except plasma cells. We studied lymphocyte development in the absence of Hex by using the RAG1-deficient blastocyst complementation system because homozygous disruption of Hex is embryonic lethal. Hex−/−;RAG1−/− chimeric mice had severely reduced numbers of mature B cells, pre-B cells, and CD5+ B cells with a striking 15-fold increase in the percentage of B220−CD19+ cells in the bone marrow. Hex−/−;RAG1−/− chimeric mice failed to generate IgG antibodies to T cell-independent antigens, although their serum IgM levels and antibody responses to T cell-dependent antigens were intact. Therefore, Hex is necessary for B cell development and function and its absence results in a dramatic increase in B220−CD19+ cells.

Decompensated Hyperglycemic Hyperosmolarity Without Significant Ketoacidosis in the Adolescent and Young Adult Population

AIM To identify patients aged 10-30 years with probable hyperglycemic hyperosmolar syndrome (HHS), to describe demographic and clinical profiles, and to attempt to assess risk factors for poor outcomes. STUDY DESIGN Retrospective cohort study (medical records review). SETTING A 944-bed tertiary care teaching and research hospital and a 425-bed affiliated facility. PATIENTS 10-30 year-old patients with a primary or secondary discharge diagnosis of HHS or diabetic ketoacidosis (DKA). Patients with a serum glucose >600 mg/dl in the absence of significant ketoacidosis (possible HHS) were profiled. Further stratification based on measured or calculated serum osmolarity >320 mOsm/kg (probable HHS) was undertaken. INTERVENTIONS Patients received treatment for hyperglycemic crises, consisting primarily of fluids, electrolyte replacement and insulin. MEASUREMENTS AND MAIN RESULTS Of the 629 admissions, 10 with a diagnosis of HHS and 33 with a diagnosis of DKA met the initial study criteria for HHS. 60% were African Americans and 89% were new-onset diabetics. From this group, 20 admissions had serum osmolarity > or =320 mOsm/kg. Fishers exact test and Pearson coefficients were used to examine associations between risk factor and poor outcomes and correlations between admission data and length of hospital stay, respectively. Serious complications occurred in four patients (including two deaths, 10% mortality) and were limited to those with unreversed shock over the first 24 hours of admission and who received <40 ml/kg of intravenous fluids over the first 6 hours of treatment. CONCLUSIONS HHS was underdiagnosed in this population and occurred disproportionately in African Americans. Serious complications occurred exclusively in those with unreversed shock and inadequate fluid resuscitation.

The homeobox gene Hhex regulates the earliest stages of definitive hematopoiesis

The development and emergence of the hematopoietic stem cell involves a series of tightly regulated molecular events that are not well characterized. The hematopoietically expressed homeobox (Hhex) gene, a member of the homeobox gene family, is an essential regulator of embryogenesis and hematopoietic progenitor development. To investigate the role of Hhex in hematopoiesis we adapted a murine embryonic stem (ES) cell coculture system, in which ES cells can differentiate into CD41(+) and CD45(+) hematopoietic progenitors in vitro. Our results show that in addition to delayed hemangioblast development, Hhex(-/-) ES-derived progeny accumulate as CD41(+) and CD41(+)c-kit(+) cells, or the earliest definitive hematopoietic progenitors. In addition, Hhex(-/-) ES-derived progeny display a significantly reduced ability to develop into mature CD45(+) hematopoietic cells. The observed reduction in hematopoietic maturation was accompanied by reduced proliferation, because Hhex(-/-) CD41(+)CD45(-)c-kit(+) hematopoietic progenitors accumulated in the G(2) phase of the cell cycle. Thus, Hhex is a critical regulator of hematopoietic development and is necessary for the maturation and proliferation of the earliest definitive hematopoietic progenitors.