The expression levels of Notch-related signaling molecules in pulmonary microvascular endothelial cells in bleomycin-induced rat pulmonary fibrosis

Pathophysiology in Brain Arteriovenous Malformations: Focus on Endothelial Dysfunctions and Endothelial-to-Mesenchymal Transition

Brain arteriovenous malformations (bAVMs) substantially increase the risk for intracerebral hemorrhage (ICH), which is associated with significant morbidity and mortality. However, the treatment options for bAVMs are severely limited, primarily relying on invasive methods that carry their own risks for intraoperative hemorrhage or even death. Currently, there are no pharmaceutical agents shown to treat this condition, primarily due to a poor understanding of bAVM pathophysiology. For the last decade, bAVM research has made significant advances, including the identification of novel genetic mutations and relevant signaling in bAVM development. However, bAVM pathophysiology is still largely unclear. Further investigation is required to understand the detailed cellular and molecular mechanisms involved, which will enable the development of safer and more effective treatment options. Endothelial cells (ECs), the cells that line the vascular lumen, are integral to the pathogenesis of bAVMs. Understanding the fundamental role of ECs in pathological conditions is crucial to unraveling bAVM pathophysiology. This review focuses on the current knowledge of bAVM-relevant signaling pathways and dysfunctions in ECs, particularly the endothelial-to-mesenchymal transition (EndMT).

Injured Endothelial Cell: A Risk Factor for Pulmonary Fibrosis

The pathological features of pulmonary fibrosis (PF) are the abnormal activation and proliferation of myofibroblasts and the extraordinary deposition of the extracellular matrix (ECM). However, the pathogenesis of PF is still indistinct. In recent years, many researchers have realized that endothelial cells had a crucial role in the development of PF. Studies have demonstrated that about 16% of the fibroblasts in the lung tissue of fibrotic mice were derived from endothelial cells. Endothelial cells transdifferentiated into mesenchymal cells via the endothelial-mesenchymal transition (E(nd)MT), leading to the excessive proliferation of endothelial-derived mesenchymal cells and the accumulation of fibroblasts and ECM. This suggested that endothelial cells, a significant component of the vascular barrier, played an essential role in PF. Herein, this review discusses E(nd)MT and its contribution to the activation of other cells in PF, which could provide new ideas for further understanding the source and activation mechanism of fibroblasts and the pathogenesis of PF.

Molecular mechanism by which the Notch signaling pathway regulates autophagy in a rat model of pulmonary fibrosis in pigeon breeder's lung

This study investigated the molecular mechanisms underlying the involvement of the Notch signaling pathway and autophagy in the development of pulmonary fibrosis in pigeon breeder's lung (PBL). Rats were divided into control (Ctrl), PBL model (M), M + D (Notch signaling inhibition), M + W (autophagy inhibition), and M + R (autophagy induction) groups. Lyophilized protein powder from pigeon shedding materials was used as an allergen to construct a fibrotic PBL rat model. The mechanism by which Notch signaling regulated autophagy in the pulmonary fibrosis of PBL was investigated by inhibiting the Notch pathway and interfering with autophagy. Pulmonary interstitial fibrosis was significantly greater in the M group and the M + W group than in the M + D and M + R groups. The expression of α-smooth muscle actin was significantly higher in the M, M + D, and M + W groups than in the Ctrl group (P < 0.05). The expression of the cell autophagy markers Beclin1 and LC3 was lower in the M, M + D, and M + W groups than in the Ctrl group (P < 0.05), whereas Beclin1 and LC3 expressions were higher in the M + D and M + R groups than in the M group. The levels of reactive oxygen species in serum and lung tissues were higher in the M, M + D, M + W, and M + R groups than in the Ctrl group (P < 0.05). The Notch signaling pathway is involved in the pathological process of pulmonary fibrosis in the rat model of PBL by regulating autophagy.

Endothelial to Mesenchymal Transition: Role in Physiology and in the Pathogenesis of Human Diseases

Numerous studies have demonstrated that endothelial cells are capable of undergoing endothelial to mesenchymal transition (EndMT), a newly recognized type of cellular transdifferentiation. EndMT is a complex biological process in which endothelial cells adopt a mesenchymal phenotype displaying typical mesenchymal cell morphology and functions, including the acquisition of cellular motility and contractile properties. Endothelial cells undergoing EndMT lose the expression of endothelial cell-specific proteins such as CD31/platelet-endothelial cell adhesion molecule, von Willebrand factor, and vascular-endothelial cadherin and initiate the expression of mesenchymal cell-specific genes and the production of their encoded proteins including α-smooth muscle actin, extra domain A fibronectin, N-cadherin, vimentin, fibroblast specific protein-1, also known as S100A4 protein, and fibrillar type I and type III collagens. Transforming growth factor-β1 is considered the main EndMT inducer. However, EndMT involves numerous molecular and signaling pathways that are triggered and modulated by multiple and often redundant mechanisms depending on the specific cellular context and on the physiological or pathological status of the cells. EndMT participates in highly important embryonic development processes, as well as in the pathogenesis of numerous genetically determined and acquired human diseases including malignant, vascular, inflammatory, and fibrotic disorders. Despite intensive investigation, many aspects of EndMT remain to be elucidated. The identification of molecules and regulatory pathways involved in EndMT and the discovery of specific EndMT inhibitors should provide novel therapeutic approaches for various human disorders mediated by EndMT.

Notch1 promotes the pericyte-myofibroblast transition in idiopathic pulmonary fibrosis through the PDGFR/ROCK1 signal pathway

The goals of this study were to investigate the role of the Notch1/PDGFRβ/ROCK1 signaling pathway in the pathogenesis of pulmonary fibrosis and to explore the possibility of treating fibrosis by targeting Notch1. Lung tissues from patients with pulmonary fibrosis were examined for the expression of Notch1/PDGFRβ/ROCK1 using RT-qPCR, western blotting, and immunostaining. Cultured mouse lung pericytes were transfected with Notch1-overexpressed vectors or shRNA targeting PDGFRβ/ROCK1 to examine cell behaviors, including proliferation, cell cycle arrest, and differentiation toward myofibroblasts. Finally, a mouse pulmonary fibrosis model was prepared, and a Notch1 inhibitor was administered to observe tissue morphology and pericyte cell behaviors. Human pulmonary fibrotic tissues presented with overexpression of Notch1, PDGFRβ, and ROCK1, in addition to a prominent transition of pericytes into myofibroblasts. In cultured mouse lung pericytes, overexpression of Notch1 led to the accelerated proliferation and differentiation of cells, and it also increased the expression of the PDGFRβ and ROCK1 proteins. The knockdown of PDGFRβ/ROCK1 in pericytes remarkably suppressed pericyte proliferation and differentiation. As further substantiation, the administration of a Notch1 inhibitor in a mouse model of lung fibrosis inhibited the PDGFRβ/ROCK1 pathway, suppressed pericyte proliferation and differentiation, and alleviated the severity of fibrosis. Our results showed that the Notch1 signaling pathway was aberrantly activated in pulmonary fibrosis, and this pathway may facilitate disease progression via mediating pericyte proliferation and differentiation. The inhibition of the Notch1 pathway may provide one promising treatment strategy for pulmonary fibrosis.

A cell membrane protein called Notch1, which binds to signaling molecules outside cells and then alters the activity of genes inside the cells, might be a promising target for drugs to treat the lung damage of pulmonary fibrosis. This condition, generally of unknown cause, involves thickening, stiffening and scarring of lung tissue. It can lead to serious breathing difficulties and eventually death, especially in people aged over 70. Hui Wang and colleagues at Central South University, Changsha, investigated the significance of the Notch1 signaling pathway by examining lung tissue from patients and manipulating the activity of the pathway in mouse cells. They conclude that Notch1 signaling is activated in pulmonary fibrosis. Drugs that could inhibit the pathway, for example by binding to the Notch1 protein, might open a promising new avenue toward treatment.