Hematopoiesis is regulated by crosstalk between long-term repopulating hematopoietic stem cells (LT-HSCs) and supporting niche cells in the bone marrow (BM). Here, we examine the role of CD82/KAI1 in niche-mediated LT-HSC maintenance. We found that CD82/KAI1 is expressed predominantly on LT-HSCs and rarely on other hematopoietic stem-progenitor cells (HSPCs). In Cd82(-/-) mice, LT-HSCs were selectively lost as they exited from quiescence and differentiated. Mechanistically, CD82-based TGF-β1/Smad3 signaling leads to induction of CDK inhibitors and cell-cycle inhibition. The CD82 binding partner DARC/CD234 is expressed on macrophages and stabilizes CD82 on LT-HSCs, promoting their quiescence. When DARC(+) BM macrophages were ablated, the level of surface CD82 on LT-HSCs decreased, leading to cell-cycle entry, proliferation, and differentiation. A similar interaction appears to be relevant for human HSPCs. Thus, CD82 is a functional surface marker of LT-HSCs that maintains quiescence through interaction with DARC-expressing macrophages in the BM stem cell niche.
Background:
Several mechanisms have been proposed to account for diabetes-induced microvasculopathy (DMV). Although Notch signaling was reported to be affected by glucose metabolism in endothelial cells during developmental angiogenesis, it has not been investigated in vascular remodeling of adult capillaries in relation to diabetes mellitus.
Methods:
We induced diabetes mellitus in 8-week-old adult mice by intravenously administering streptozotocin. After 6 weeks, we harvested organs, including retina, heart, and skeletal muscle, and evaluated the capillaries with immunofluorescence and confocal microscopy. We modulated endothelial Notch signaling using chemical inhibitors in wild-type mice or transgenic mice, inducing conditional knockout of Jagged1 or Mib1.
Results:
DMV was characterized by capillary remodeling, regression, and decreased density. Notch ligand Jagged1, but not δ-like ligand 4, was markedly increased in endothelial cells of diabetic mice. Using endothelium-specific Jagged1 knockdown mice, we found that blocking Jagged1 prevented DMV even under diabetic conditions. Furthermore, in the inducible endothelium-specific Jagged1 knockdown mice, blocking Jagged1 even at 4 weeks after the establishment of DMV could reverse it, leading to normalization of retinal vasculature. A search for downstream signals revealed that diabetes mellitus decreased the nuclear localization of Notch1 intracellular domain and reduced the expression of VE-cadherin and N-cadherin in endothelial cells. Chemical Notch inhibition phenocopied DMV in normal mice.
Conclusions:
Our findings indicate that diabetes mellitus induces Jagged1 overexpression and suppresses Notch signaling in endothelial cells, leading to DMV in adult mice. We conclude that dysregulated intercellular Notch signaling may be a novel mechanism of DMV.
Emerging studies suggested that murine podoplanin-positive monocytes (PPMs) are involved in lymphangiogenesis. The goal of this study was to demonstrate the therapeutic lymphangiogenesis of human PPMs by the interaction with platelets. Aggregation culture of human peripheral blood mononuclear cells (PBMCs) resulted in cellular aggregates termed hematospheres. During 5-day culture, PPMs expanded exponentially and expressed several lymphatic endothelial cell-specific markers including vascular endothelial growth factor receptor (VEGFR)-3 and well-established lymphangiogenic transcription factors. Next, we investigated the potential interaction of PPMs with platelets that had C-type lectin-like receptor-2 (CLEC-2), a receptor of podoplanin. In vitro coculture of PPMs and platelets stimulated PPMs to strongly express lymphatic endothelial markers and upregulate lymphangiogenic cytokines. Recombinant human CLEC-2 also stimulated PPMs through Akt and Erk signaling. Likewise, platelets in coculture with PPMs augmented secretion of a lymphangiogenic cytokine, interleukin (IL)-1-β, via podoplanin/CLEC-2 axis. The supernatant obtained from coculture was able to enhance the migration, viability, and proliferation of lymphatic endothelial cell. Local injection of hematospheres with platelets significantly increased lymphatic neovascularization and facilitated wound healing in the full-thickness skin wounds of nude mice. Cotreatment with PPMs and platelets augments lymphangiogenesis through podoplanin/CLEC-2 axis, which thus would be a promising novel strategy of cell therapy to treat human lymphatic vessel disease.
Brief ex vivo EPO-priming is a novel method to augment the vasculogenic potential of human (mob)PBMCs, which would help to achieve better results after intracoronary infusion in myocardial infarction patients.
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