David C. Yao

Protein O-fucosyltransferase 1 (Pofut1) regulates lymphoid and myeloid homeostasis through modulation of Notch receptor ligand interactions

Notch signaling is essential for lymphocyte development and is also implicated in myelopoiesis. Notch receptors are modified by O-fucosylation catalyzed by protein O-fucosyltransferase 1 (Pofut1). Fringe enzymes add N-acetylglucosamine to O-fucose and modify Notch signaling by altering the sensitivity of Notch receptors to Notch ligands. To address physiologic functions in hematopoiesis of Notch modified by O-fucose glycans, we examined mice with inducible inactivation of Pofut1 using Mx-Cre. These mice exhibited a reduction in T lymphopoiesis and in the production of marginal-zone B cells, in addition to myeloid hyperplasia. Restoration of Notch1 signaling rescued T lymphopoiesis and the marrow myeloid hyperplasia. After marrow transfer, both cell-autonomous and environmental cues were found to contribute to lymphoid developmental defects and myeloid hyperplasia in Pofut1-deleted mice. Although Pofut1 deficiency slightly decreased cell surface expression of Notch1 and Notch2, it completely abrogated the binding of Notch receptors with Delta-like Notch ligands and suppressed downstream Notch target activation, indicating that O-fucose glycans are critical for efficient Notch-ligand binding that transduce Notch signals. The combined data support a key role for the O-fucose glycans generated by Pofut1 in Notch regulation of hematopoietic homeostasis through modulation of Notch-ligand interactions.

O-fucose modulates Notch-controlled blood lineage commitment.

Notch receptors are cell surface molecules essential for cell fate determination. Notch signaling is subject to tight regulation at multiple levels, including the posttranslational modification of Notch receptors by O-linked fucosylation, a reaction that is catalyzed by protein O-fucosyltransferase-1 (Pofut1). Our previous studies identified a myeloproliferative phenotype in mice conditionally deficient in cellular fucosylation that is attributable to a loss of Notch-dependent suppression of myelopoiesis. Here, we report that hematopoietic stem cells deficient in cellular fucosylation display decreased frequency and defective repopulating ability as well as decreased lymphoid but increased myeloid developmental potential. This phenotype may be attributed to suppressed Notch ligand binding and reduced downstream signaling of Notch activity in hematopoietic stem cells. Consistent with this finding, we further demonstrate that mouse embryonic stem cells deficient in Notch1 (Notch1(-/-)) or Pofut1 (Pofut1(-/-)) fail to generate T lymphocytes but differentiate into myeloid cells while coculturing with Notch ligand-expressing bone marrow stromal cells in vitro. Moreover, in vivo hematopoietic reconstitution of CD34(+) progenitor cells derived from either Notch1(-/-) or Pofut1(-/-) embryonic stem cells show enhanced granulopoiesis with depressed lymphoid lineage development. Together, these results indicate that Notch signaling maintains hematopoietic lineage homeostasis by promoting lymphoid development and suppressing overt myelopoiesis, in part through processes controlled by O-linked fucosylation of Notch receptors.

Gastrogastric fistula following Roux-en-Y bypass is attributed to both surgical technique and experience

BACKGROUND The stomach can either be divided or undivided in performing Roux-en-Y gastric bypass (RGB) for morbid obesity. We evaluated whether surgical technique is the sole contributing factor to the formation of gastrogastric fistula (GGF). METHODS A retrospective analysis of 1,036 consecutive patients was evaluated. RGB was performed as open undivided, open divided, and laparoscopic (divided). Incidence of GGF was identified for each technique and its relationship to surgical experience was assessed. RESULTS Overall incidence of GGF was 1.3%. All fistulae occurred in patients who received undivided open RGB. There was a significant difference between the undivided open group and the divided open+laparoscopic groups (2.1% vs 0%, P<.01). Incidence of GGF decreased over time with increasing open undivided RGB volume. CONCLUSIONS GGF was only identified in undivided RGB. The occurrence decreased with increasing surgical experience. Together, overall surgical technique in addition to gastric division must play a role in fistula formation.

Utility of the p53 mutant protein in patients with low-risk myelodysplastic syndrome

Patients withthis condition demonstrate clonal hematopoietic expansion,cytopenias, myelodysplasia, ineffective hematopoiesis andan increased propensity to develop acute myeloid leukemia.Not surprisingly, prognosis is related to severity of cytopenias,presence of cytogenetic abnormalities and clonal evolutiondemonstrated by blast counts, and other ‘traditional’ progno-stic elements. There is heterogeneity even among patientsdiagnosed with lower-risk disease, since a subset of thesepatients have more aggressive disease. Recent efforts havedemonstrated that several molecular parameters linked tothe pathophysiology of MDS may affect overall survival.