Novel roles for podocalyxin in regulating stress myelopoiesis, Rap1a, and neutrophil migration

Abstract

Podocalyxin (Podxl) is a CD34 orthologue and cell surface sialomucin with reported roles in renal podocyte diaphragm slit development, vascular cell integrity, and the progression of blood, breast, and prostate cancers. Roles for Podxl during non-malignant hematopoiesis, however, are largely undefined. Presently we have developed a Vav-Cre Podxl knockout mouse model, and report on novel roles for Podxl in governing stress myelopoiesis. At steady-state, Podxl expression among hematopoietic progenitor cells was low-level but was induced by GCSF (granulocyte colony stimulating factor) in myeloid progenitors, and by TPO (thrombopoietin) in HSCs. In keeping with low level Podxl expression at steady-state, Vav-Cre deletion of Podxl did not markedly alter peripheral blood cell levels. G-CSF challenge in Podxl-KO mice, in contrast, hyper-elevated peripheral blood neutrophil and monocyte levels. Podxl-KO also substantially heightened neutrophil levels following 5-fluorouracil myeloablation. These LOF phenotypes were selective, and Podxl-KO did not alter lymphocyte, basophil or eosinophil levels. Within bone marrow (and following G-CSF challenge), Podxl deletion moderately decreased CFU-GEMM and CD16/32posCD11bpos progenitors but did not affect Gr-1pos cell populations. Notably, Podxl-KO did significantly heighten peripheral blood neutrophil migration capacities. To interrogate Podxl’s action mechanisms, a co-immunoprecipitation plus LC-MS/MS (liquid chromatography – mass spectrometry) approach was applied using hematopoietic progenitors from G-CSF-challenged mice. Rap1a, a Ras-related small GTPase, was a predominant co-retrieved Podxl partner. In bone marrow HPC’s, Podxl-KO led to heightened GCSF activation of Rap1aGTP, and Rap1aGTP inhibition attenuated Podxl-KO neutrophil migration. Studies reveal novel roles for Podxl as an important modulator of neutrophil and monocyte formation, and of Rap1a activation, during stress hematopoiesis.

PODXL might be a new prognostic biomarker in various cancers: a meta-analysis and sequential verification with TCGA datasets

“…PODXL expression has been reported in the cytoplasm of some tumor cells, in some cases protruding toward the cell membrane, but not in the nucleus [5]. PODXL is encoded on chromosome 7q32-q33, and highly expressed by glomerular podocytes, vascular endothelium, hematopoietic cells and breast epithelial cells [6][7][8], which involved in many physiologic processes, such as hematopoiesis [9], leucocyte-endothelial cell interaction [10], regulating vascular permeability [11] and neural development [12].…”

Improvement of membranous nephropathy by inhibition of miR‐193a to affect podocytosis via targeting WT1

“…Podocalyxin (Podxl) is a CD34 orthologue and cell surface sialomucin is reported to have roles in renal podocyte diaphragm slit development and vascular cell integrity. 6 NPHS1 encodes the structural protein nephrin, which has a crucial role in the filtration barrier of the glomerular podocyte. Mutations or deregulation of NPHS1 is associated with a variety of renal diseases.…”

“…The mechanisms of podocyte hypertrophy in MN are poorly defined. Podocalyxin (Podxl) is a CD34 orthologue and cell surface sialomucin is reported to have roles in renal podocyte diaphragm slit development and vascular cell integrity . NPHS1 encodes the structural protein nephrin, which has a crucial role in the filtration barrier of the glomerular podocyte.…”

Persistent expression of microRNA-125a targets is required to induce murine hematopoietic stem cell repopulating activity

“…Rap1a is a partner of podocalyxin (Podxl) and can be activated by erythropoietin (Epo) or IL-3. Rap1a is strongly activated when HSCs are challenged with granulocyte colony-stimulating factor (G-CSF) and can modulate cell migration and adhesion [17,18]. Previously, we established that miR-125a−overexpressing HSCs respond more strongly to G-CSF compared with control cells [8].…”