Tumour cell-released autophagosomes promote lung metastasis by upregulating PD-L1 expression in pulmonary vascular endothelial cells in breast cancer.

PURPOSE: Establishing an immunosuppressive premetastatic niche (PMN) in distant organs is crucial for breast cancer metastasis. Vascular endothelial cells (VECs) act as barriers to transendothelial cell migration. However, the immune functions of PMNs remain unclear. Tumour cell-released autophagosomes (TRAPs) are critical modulators of antitumour immune responses. Herein, we investigated the mechanism through which TRAPs modulate the immune function of pulmonary VECs in lung PMN in breast cancer. METHODS: Immortalised mouse pulmonary microvascular endothelial cells were incubated with TRAPs in vitro. RNA sequencing, flow cytometry, and western blotting were employed to assess immunosuppressive function and mechanism. In vivo, TRAP-trained and autophagy-deficient tumour mice were used to detect immunosuppression, and high-mobility group box 1 (HMGB1)-deficient TRAP-trained and TLR4 knockout mice were utilised to investigate the underlying mechanisms of pulmonary VECs. Additionally, the efficacy of anti-programmed cell death ligand-1 (PD-L1) immunotherapy was evaluated in early tumour-bearing mice. RESULTS: HMGB1 on TRAPs surfaces stimulated VECs to upregulate PD-L1 via a TLR4-MyD88-p38/STAT3 signalling cascade that depended on the cytoskeletal movement of VECs. Importantly, PD-L1 on TRAP-induced VECs can inhibit T cell function, promote lung PMN immunosuppression, and result in more pronounced lung metastasis. Treatment with anti-PD-L1 reduces lung metastasis in early stage tumour-bearing mice. CONCLUSIONS: These findings revealed a novel role and mechanism of TRAP-induced immunosuppression of pulmonary VECs in lung PMN. TRAPs and their surface HMGB1 are important therapeutic targets for reversing immunosuppression, providing a new theoretical basis for the treatment of early stage breast cancer using an anti-PD-L1 antibody.

Cellular heterogeneity and stem cells of vascular endothelial cells in blood vessel formation and homeostasis: Insights from single-cell RNA sequencing.

Vascular endothelial cells (ECs) that constitute the inner surface of blood vessels are essential for new vessel formation and organ homeostasis. ECs display remarkable phenotypic heterogeneity across different organs and the vascular tree during angiogenesis and homeostasis. Recent advances in single cell RNA sequencing (scRNA-seq) technologies have allowed a new understanding of EC heterogeneity in both mice and humans. In particular, scRNA-seq has identified new molecular signatures for arterial, venous and capillary ECs in different organs, as well as previously unrecognized specialized EC subtypes, such as the aerocytes localized in the alveolar capillaries of the lung. scRNA-seq has also revealed the gene expression profiles of specialized tissue-resident EC subtypes that are capable of clonal expansion and contribute to adult angiogenesis, a process of new vessel formation from the pre-existing vasculature. These specialized tissue-resident ECs have been identified in various different mouse tissues, including aortic endothelium, liver, heart, lung, skin, skeletal muscle, retina, choroid, and brain. Transcription factors and signaling pathways have also been identified in the specialized tissue-resident ECs that control angiogenesis. Furthermore, scRNA-seq has also documented responses of ECs in diseases such as cancer, age-related macular degeneration, Alzheimer's disease, atherosclerosis, and myocardial infarction. These new findings revealed by scRNA-seq have the potential to provide new therapeutic targets for different diseases associated with blood vessels. In this article, we summarize recent advances in the understanding of the vascular endothelial cell heterogeneity and endothelial stem cells associated with angiogenesis and homeostasis in mice and humans, and we discuss future prospects for the application of scRNA-seq technology.

Disruption of profilin1 function suppresses developmental and pathological retinal neovascularization.

Angiogenesis-mediated neovascularization in the eye is usually associated with visual complications. Pathological angiogenesis is particularly prominent in the retina in the settings of proliferative diabetic retinopathy, in which it can lead to permanent loss of vision. In this study, by bioinformatics analyses, we provide evidence for elevated expression of actin-binding protein PFN1 (profilin1) in the retinal vascular endothelial cells (VECs) of individuals with proliferative diabetic retinopathy, findings further supported by gene expression analyses for PFN1 in experimentally induced abnormal retinal neovascularization in an oxygen-induced retinopathy murine model. We observed that in a conditional knockout mouse model, postnatal deletion of the Pfn1 gene in VECs leads to defects in tip cell activity (marked by impaired filopodial protrusions) and reduced vascular sprouting, resulting in hypovascularization during developmental angiogenesis in the retina. Consistent with these findings, an investigative small molecule compound targeting the PFN1-actin interaction reduced random motility, proliferation, and cord morphogenesis of retinal VECs in vitro and experimentally induced abnormal retinal neovascularization in vivo In summary, these findings provide the first direct in vivo evidence that PFN1 is required for formation of actin-based protrusive structures and developmental angiogenesis in the retina. The proof of concept of susceptibility of abnormal angiogenesis to small molecule intervention of PFN1-actin interaction reported here lays a conceptual foundation for targeting PFN1 as a possible strategy in angiogenesis-dependent retinal diseases.

High glucose induces dysfunction of human umbilical vein endothelial cells by upregulating miR-137 in gestational diabetes mellitus.

Recent studies have revealed considerable dysfunction of vascular endothelial cells (VECs) and abnormal expression of microRNA (miR)-137 in women with gestational diabetes mellitus (GDM), and the aim of this study was to clarify the underlying mechanism and possible role of microRNA (miR)-137 in dysfunction of VECs during GDM. We found increased levels of miR-137 in the plasma of GDM women and high-glucose (HG)-exposed HUVECs. Upregulating miR-137 in HUVECs elevated the chemokine (C-C motif) ligand 2 (CCL2) secretion and enhanced the chemotaxis and adhesion of U937 and THP-1 (two human acute monocytic leukemia cell lines) cells to HUVECs in a co-culture system. Moreover, HG stimulation and/or overexpression of miR-137 inhibited the viability, upregulated the expression levels of vascular cell adhesion molecule-1 (VCAM-1), intercellular cell adhesion molecule-1 (ICAM-1), E-selectin, and inflammatory cytokine interleukin (IL)-6, and downregulated the production of IL-8, vascular endothelial growth factor (VEGF), and angiogenesis of HUVECs in vitro. These results imply that up-regulated miR-137 by HG can restrict the viability and angiogenesis, promote the activation and inflammatory cytokine secretion of VECs, and stimulate the monocyte chemotaxis and adhesion to VECs. Ultimately, we have concluded that miR-137 is crucial to HG-induced VEC dysfunction and may be involved in pathology of GDM.

Microsomal Prostaglandin E Synthase-1 Facilitates an Intercellular Interaction between CD4⁺ T Cells through IL-1ß Autocrine Function in Experimental Autoimmune Encephalomyelitis.

Microsomal prostaglandin synthetase-1 (mPGES-1) is an inducible terminal enzyme that produces prostaglandin E2 (PGE2). In our previous study, we investigated the role of mPGES-1 in the inflammation and demyelination observed in experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis, using mPGES-1-deficient (mPGES-1-/-) and wild-type (wt) mice. We found that mPGES-1 facilitated inflammation, demyelination, and paralysis and was induced in vascular endothelial cells and macrophages and microglia around inflammatory foci. Here, we investigated the role of interleukin-1ß (IL-1ß) in the intercellular mechanism stimulated by mPGES-1 in EAE spinal cords in the presence of inflammation. We found that the area invaded by CD4-positive (CD4⁺) T cells was extensive, and that PGE2 receptors EP1-4 were more induced in activated CD4⁺ T cells of wt mice than in those of mPGES-1-/- mice. Moreover, IL-1ß and IL-1 receptor 1 (IL-1r1) were produced by 65% and 48% of CD4⁺ T cells in wt mice and by 44% and 27% of CD4⁺ T cells in mPGES-1-/- mice. Furthermore, interleukin-17 (IL-17) was released from the activated CD4⁺ T cells. Therefore, mPGES-1 stimulates an intercellular interaction between CD4⁺ T cells by upregulating the autocrine function of IL-1ß in activated CD4⁺ T cells, which release IL-17 to facilitate axonal and myelin damage in EAE mice.