Positive and negative modulatory roles of Platelet Endothelial Cell Adhesion Molecule-1 signaling in endothelial cell migration: coordination of Rho signaling and targeting of SHP-2 tyrosine phosphatase activity

Platelet Endothelial Cell Adhesion Molecule-1 (PECAM-1), an immunoglobulin family adhesion molecule, is involved in endothelial migration and angiogenesis. We found that PECAM-1 deficient endothelial cells exhibit enhanced nondirected single cell motility and extension formation at the expense of wound-healing migration. These in vitro endothelial behaviors model aspects of highly developmentally and pathophysiologically relevant processes. Wound healing migration may model the reendothelialization of denuded vasculature following balloon angioplasty or the remodeling of vascular endothelium under variant flow conditions, while single cell motility is prominently involved in developmental processes such as endocardial-mesenchymal transition within the cardiac cushion. A specific deficiency of RhoGTP in PECAM-1 deficient endothelial cells accounted for their migratory phenotype. The serum sphingolipid sphingosine-1-phosphate (S1P) drives Rho-dependent migration and angiogenesis. Indeed PECAM-1 was necessary for an appropriate wound healing response to S1P. We have found that PECAM-1 localizes to rafts, and that in its absence heterotrimeric G protein components are differentially recruited to rafts, providing a potential mechanism for PECAM-1-mediated coordination of S1P signaling.PECAM-1 activates the tyrosine phosphatase SHP-2 via its phosphorylated immunoreceptor tyrosine-based inhibitory motif (ITIM). ITIM signaling is not required for the positive Rho-activating role of PECAM-1. Instead we found that ITIM signaling retards wound healing migration, and that during migration the second ITIM tyrosine becomes selectively dephosphorylated. The second ITIM tyrosine proved important for recruitment but not activation of SHP-2. Any SHP-2 that remains transiently associated with partially dephosphorylated PECAM-1 could amplify the migration signal by dephosphorylating adjacent PECAM-1 ITIMs. We found that PECAM-1 helps localize SHP-2 to the actin cytoskeleton, and to a subset of phosphoproteins. In fact, interfering with PECAM-1 ITIM signaling not only increased wound healing migration but decreased dephosphorylation of beta-catenin and focal adhesion kinase. SHP-2 targetting is instrumental in controlling endothelial wound healing migration, potentially via effects on adherens junction stability and focal contact dynamics

Elevated glucose inhibits VEGF-A–mediated endocardial cushion formation: modulation by PECAM-1 and MMP-2

Atrioventricular (AV) septal defects resulting from aberrant endocardial cushion (EC) formation are observed at increased rates in infants of diabetic mothers. EC formation occurs via an epithelial-mesenchymal transformation (EMT), involving transformation of endocardial cells into mesenchymal cells, migration, and invasion into extracellular matrix. Here, we report that elevated glucose inhibits EMT by reducing myocardial vascular endothelial growth factor A (VEGF-A). This effect is reversed with exogenous recombinant mouse VEGF-A165, whereas addition of soluble VEGF receptor-1 blocks EMT. We show that disruption of EMT is associated with persistence of platelet endothelial cell adhesion molecule-1 (PECAM-1) and decreased matrix metalloproteinase-2 (MMP-2) expression. These findings correlate with retention of a nontransformed endocardial sheet and lack of invasion. The MMP inhibitor GM6001 blocks invasion, whereas explants from PECAM-1 deficient mice exhibit MMP-2 induction and normal EMT in high glucose. PECAM-1–negative endothelial cells are highly motile and express more MMP-2 than do PECAM-1–positive endothelial cells. During EMT, loss of PECAM-1 similarly promotes single cell motility and MMP-2 expression. Our findings suggest that high glucose-induced inhibition of AV cushion morphogenesis results from decreased myocardial VEGF-A expression and is, in part, mediated by persistent endocardial cell PECAM-1 expression and failure to up-regulate MMP-2 expression

Correction. "The 5th edition of The World Health Organization Classification of Haematolymphoid Tumours: Lymphoid Neoplasms" Leukemia. 2022 Jul;36(7):1720-1748

We herein present an overview of the upcoming 5th edition of the World Health Organization Classification of Haematolymphoid Tumours focussing on lymphoid neoplasms. Myeloid and histiocytic neoplasms will be presented in a separate accompanying article. Besides listing the entities of the classification, we highlight and explain changes from the revised 4th edition. These include reorganization of entities by a hierarchical system as is adopted throughout the 5th edition of the WHO classification of tumours of all organ systems, modification of nomenclature for some entities, revision of diagnostic criteria or subtypes, deletion of certain entities, and introduction of new entities, as well as inclusion of tumour-like lesions, mesenchymal lesions specific to lymph node and spleen, and germline predisposition syndromes associated with the lymphoid neoplasms

Beyond the Niche: Myelodysplastic Syndrome Topobiology in the Laboratory and in the Clinic

We review the murine and human microenvironment and hematopoietic stem cell niche in the context of intact bone marrow architecture in man and mouse, both in normal and in myelodysplastic syndrome marrow. We propose that the complexity of the hematopoietic stem cell niche can usefully be approached in the context of its topobiology, and we provide a model that incorporates in vitro and in vivo models as well as in situ findings from intact human marrow to explain the changes seen in myelodysplastic syndrome patients. We highlight the clinical application of the study of the bone marrow microenvironment and its topobiology in myelodysplastic syndromes

Alkylator-Induced and Patient-Derived Xenograft Mouse Models of Therapy-Related Myeloid Neoplasms Model Clinical Disease and Suggest the Presence of Multiple Cell Subpopulations with Leukemia Stem Cell Activity.

Acute myeloid leukemia (AML) is a heterogeneous group of aggressive bone marrow cancers arising from transformed hematopoietic stem and progenitor cells (HSPC). Therapy-related AML and MDS (t-AML/MDS) comprise a subset of AML cases occurring after exposure to alkylating chemotherapy and/or radiation and are associated with a very poor prognosis. Less is known about the pathogenesis and disease-initiating/leukemia stem cell (LSC) subpopulations of t-AML/MDS compared to their de novo counterparts. Here, we report the development of mouse models of t-AML/MDS. First, we modeled alkylator-induced t-AML/MDS by exposing wild type adult mice to N-ethyl-N-nitrosurea (ENU), resulting in several models of AML and MDS that have clinical and pathologic characteristics consistent with human t-AML/MDS including cytopenia, myelodysplasia, and shortened overall survival. These models were limited by their inability to transplant clinically aggressive disease. Second, we established three patient-derived xenograft models of human t-AML. These models led to rapidly fatal disease in recipient immunodeficient xenografted mice. LSC activity was identified in multiple HSPC subpopulations suggesting there is no canonical LSC immunophenotype in human t-AML. Overall, we report several new t-AML/MDS mouse models that could potentially be used to further define disease pathogenesis and test novel therapeutics

Pitfalls in the Diagnosis of Nodular Lymphocyte Predominant Hodgkin Lymphoma: Variant Patterns, Borderlines and Mimics.

Nodular lymphocyte predominant Hodgkin lymphoma (NLPHL) represents approximately 5% of Hodgkin lymphoma and typically affects children and young adults. Although the overall prognosis is favorable, variant growth patterns in NLPHL correlate with disease recurrence and progression to T-cell/histiocyte-rich large B-cell lymphoma or frank diffuse large B-cell lymphoma (DLBCL). The diagnostic boundary between NLPHL and DLBCL can be difficult to discern, especially in the presence of variant histologies. Both diagnoses are established using morphology and immunophenotype and share similarities, including the infrequent large tumor B-cells and the lymphocyte and histiocyte-rich microenvironment. NLPHL also shows overlap with other lymphomas, particularly, classic Hodgkin lymphoma and T-cell lymphomas. Similarly, there is overlap with non-neoplastic conditions, such as the progressive transformation of germinal centers. Given the significant clinical differences among these entities, it is imperative that NLPHL and its variants are carefully separated from other lymphomas and their mimics. In this article, the characteristic features of NLPHL and its diagnostic boundaries and pitfalls are discussed. The current understanding of genetic features and immune microenvironment will be addressed, such that a framework to better understand biological behavior and customize patient care is provided

Alkylator-Induced and Patient-Derived Xenograft Mouse Models of Therapy-Related Myeloid Neoplasms Model Clinical Disease and Suggest the Presence of Multiple Cell Subpopulations with Leukemia Stem Cell Activity

<div><p>Acute myeloid leukemia (AML) is a heterogeneous group of aggressive bone marrow cancers arising from transformed hematopoietic stem and progenitor cells (HSPC). Therapy-related AML and MDS (t-AML/MDS) comprise a subset of AML cases occurring after exposure to alkylating chemotherapy and/or radiation and are associated with a very poor prognosis. Less is known about the pathogenesis and disease-initiating/leukemia stem cell (LSC) subpopulations of t-AML/MDS compared to their <i>de novo</i> counterparts. Here, we report the development of mouse models of t-AML/MDS. First, we modeled alkylator-induced t-AML/MDS by exposing wild type adult mice to N-ethyl-N-nitrosurea (ENU), resulting in several models of AML and MDS that have clinical and pathologic characteristics consistent with human t-AML/MDS including cytopenia, myelodysplasia, and shortened overall survival. These models were limited by their inability to transplant clinically aggressive disease. Second, we established three patient-derived xenograft models of human t-AML. These models led to rapidly fatal disease in recipient immunodeficient xenografted mice. LSC activity was identified in multiple HSPC subpopulations suggesting there is no canonical LSC immunophenotype in human t-AML. Overall, we report several new t-AML/MDS mouse models that could potentially be used to further define disease pathogenesis and test novel therapeutics.</p></div

Treatment of mice with ENU leads to development of therapy-related myeloid neoplasms.

<p><b>(a)</b> Forty DBA/2J and ten SWR/J mice were treated with 100–300 mg/kg ENU, monitored for disease, and sacrificed when moribund. Diagnostic analysis revealed AML, MDS, and non-AML/MDS diseases in 16%, 22%, and 32% of mice respectively. The remaining 30% of mice died from ENU-toxicity or were not analyzable. <b>(b)</b> Kaplan-Meier survival analysis of ENU-treated (n = 35) mice shows a median overall survival of 162 days from the date of treatment. There were no statistically significant differences in survival by diagnosis (n = 8, n = 11, and n = 16 for AML, MDS, and non-AML/MDS diseases respectively). <b>(c)</b> Kaplan-Meier survival analysis of ENU-treated mice shows no significant difference in survival among the various ENU dose levels tested (n = 35, n = 9, n = 10, n = 16 for total, 100 mg/kg, 200 mg/kg, and 300 mg/kg respectively).</p