Hematopoietic stem cells (HSCs) have the ability to self-renew, differentiate into various blood cell types, and reside in the bone marrow (BM) niche. Estrogen-related receptor α (ERRα) is an orphan nuclear receptor that has a role in mitochondrial biogenesis and metabolic regulation. Previous research has shown that ERRα contributes to the development of acute myeloid leukemia (AML) by acting as a key regulator of mitochondrial processes, though its role in HSC regulation remains mostly unknown. Flow cytometric analysis determined the population of the hematopoietic stem and progenitor cells (HSPC) using Errα knockout (KO) and conditional KO (cKO) mice. Furthermore, we investigated reconstitution with BM transplantation assay. Here, the ablation of Errα in the BM demonstrated that the production of mature blood cells, lineage distribution within hematopoietic organs, and frequencies of the HSPC populations were similar to those of controls. In addition, the ablation of Errα did not perturb HSC function under the stress of transplantation. Collectively, ERRα is not necessary for the control of HSPC populations, as well as for the maintenance of HSC characteristics and functions within the BM.

Hematopoietic stem cells (HSCs) have the ability to self-renew, differentiate into various blood cell types, and reside in the bone marrow (BM) niche. Estrogen-related receptor α (ERRα) is an orphan nuclear receptor that has a role in mitochondrial biogenesis and metabolic regulation. Previous research has shown that ERRα contributes to the development of acute myeloid leukemia (AML) by acting as a key regulator of mitochondrial processes, though its role in HSC regulation remains mostly unknown. Flow cytometric analysis determined the population of the hematopoietic stem and progenitor cells (HSPC) using Errα knockout (KO) and conditional KO (cKO) mice. Furthermore, we investigated reconstitution with BM transplantation assay. Here, the ablation of Errα in the BM demonstrated that the production of mature blood cells, lineage distribution within hematopoietic organs, and frequencies of the HSPC populations were similar to those of controls. In addition, the ablation of Errα did not perturb HSC function under the stress of transplantation. Collectively, ERRα is not necessary for the control of HSPC populations, as well as for the maintenance of HSC characteristics and functions within the BM.

Retinal angiogenesis was delayed in VSMC-specific Akt1-deficient mice (Akt1^∆SMC) but not in Akt2^∆SMC mice. The proliferation of ECs, recruitment of pericytes, and coverage of VSMCs to the endothelium were defective in Akt1^∆SMC. The silencing of Akt1 in VSMCs led to the downregulation of angiopoietin 1 (Ang1) and the upregulation of Ang2. The activation of Notch3 in VSMCs was significantly reduced in the retinas of Akt1^∆SMC mice. Silencing Akt1 suppressed the activation of Notch3. Moreover, the silencing of Notch3 downregulated Ang1, whereas the overexpression of Notch3 intracellular domain (NICD3) enhanced Ang1 expression. The nuclear localization and transcriptional activity of yes-associated protein (YAP) were affected by the expression level of Akt1. Silencing YAP downregulated Ang2 expression, whereas overexpression of YAP showed the opposite results. Ang1 antibody and Ang2 suppressed endothelial sprouting of wild-type aortic tissues, whereas the Ang2 antibody and Ang1 facilitated the endothelial sprouting of aortic tissues from Akt1^∆SMC mice. Finally, severe hemorrhage was observed in Akt1^∆SMC mice, which was further facilitated under streptozotocin (STZ)-induced diabetic conditions. Therefore, the Akt1-Notch3/YAP-Ang1/2 signaling cascade in VSMCs might play an essential role in the paracrine regulation of endothelial function.

The increased expression of receptors for advanced glycation end-product (RAGE) is known as a key player in the progression of vascular remodeling. However, the precise signal pathways regulating RAGE expression in vascular smooth muscle cells (VSMCs) in the injured vasculatures are unclear. Given the importance of mitogen-activated protein kinase (MAPK) signaling in cell proliferation, we investigated the importance of MAPK signaling in high-mobility group box 1 (HMGB1)-induced RAGE expression in VSMCs. In HMGB1 (100 ng/ml)-stimulated human VSMCs, the expression of RAGE mRNA and protein was increased in association with an increase in AGE-induced VSMC proliferation. The HMGB1-induced RAGE expression was attenuated in cells pretreated with inhibitors for ERK (PD98059, 10 μM) and p38 MAPK (SB203580, 10 μM) as well as in cells deficient in ERK and p38 MAPK using siRNAs, but not in cells deficient of JNK signaling. In cells stimulated with HMGB1, the phosphorylation of ERK, JNK, and p38 MAPK was increased. This increase in ERK and p38 MAPK phosphorylation was inhibited by p38 MAPK and ERK inhibitors, respectively, but not by JNK inhibitor. Moreover, AGE-induced VSMC proliferation in HMGB1-stimulated cells was attenuated in cells treated with ERK and p38 MAPK inhibitors. Taken together, our results indicate that ERK and p38 MAPK signaling are involved in RAGE expression in HMGB1-stimulated VSMCs. Thus, the ERK/p38 MAPK-RAGE signaling axis in VSMCs was suggested as a potential therapeutic target for vascular remodeling in the injured vasculatures.

HMGA1 plays an essential role in the phenotypic modulation of VSMCs. Therefore, paracrine factors such as PDGF may affect vascular remodeling through the regulation of HMGA1.

SIRT1 signaling pathways modulate vascular inflammation; however, the precise role of SIRT1 in monocyte adhesion to the vascular endothelium, a key event initiating vascular inflammation, is unclear. Thus, this study investigated the roles and molecular interaction of SIRT1 and TLR2 in regulating monocyte adhesion to the vascular endothelium. In vitro, both Mac-1 expression and the endothelial adhesion of THP-1 cells stimulated with Pam3CSK4, a TLR2 ligand, were markedly increased in association with a decreased expression of SIRT1. In THP-1 cells stimulated with Pam3CSK4, the promoter activity and expression of SIRT1 were decreased. The TLR2-dependent suppression of SIRT1 expression in THP-1 cells was mediated by the transcription factors NF-κB and CREB, suggesting that the TLR2-mediated NF-κB and CREB signaling downregulated SIRT1 expression in monocytes. In peripheral blood monocytes (PBMCs) isolated from SIRT1 transgenic (TG) mice and THP-1 cells treated with recombinant SIRT1, both the increased Mac-1 expression and endothelial adhesion induced by Pam3CSK4 were significantly attenuated. In addition, the en face immunohistochemical study showed a marked increase in monocyte adhesion to the aortic endothelium of WT mice treated with Pam3CSK4, which was significantly attenuated in Pam3CSK4-treated SIRT1 TG mice. Moreover, a greater number of atherosclerotic plaques formed in WT mice fed a high-fat diet than in SIRT1 TG mice, indicating a pivotal role for SIRT1 in preventing vascular inflammation. Based on these results, SIRT1 might be a potential target for researchers aiming to develop therapeutic interventions for vascular inflammation, including atherosclerosis.

Angiogenesis plays a critical role in embryo development, tissue repair, tumor growth and wound healing. In the present study, we investigated the role of the serine/threonine kinase Akt in angiogenesis. Silencing of Akt1 in human umbilical vein endothelial cells significantly inhibited vascular endothelial growth factor (VEGF)-induced capillary-like tube formation. Mice lacking Akt1 exhibited impaired retinal angiogenesis with delayed endothelial cell (EC) proliferation. In addition, VEGF-induced corneal angiogenesis and tumor development were significantly inhibited in mice lacking Akt1. Loss of Akt1 resulted in reduced angiogenic sprouting, as well as the proliferation of ECs and mural cells. Addition of culture supernatant of vascular smooth muscle cells (VSMCs) in which Akt1 was silenced suppressed tube formation, the stability of preformed tubes and the proliferation of ECs. In addition, attachment of VSMCs to ECs was significantly reduced in cells in which Akt1 was silenced. Mural cell coverage of retinal vasculature was reduced in mice lacking Akt1. Finally, mice lacking Akt1 showed severe retinal hemorrhage compared to the wild-type. These results suggest that the regulation of EC function and mural cell coverage by Akt1 is important for blood vessel maturation during angiogenesis.