The involvement of reactive oxygen species (ROS) in regulating vascular function both in normal vessels and as part of an adaptive response during disease has been intensively studied. From the recognition that ROS serve as important signaling molecules has emerged multiple lines of evidence that there is a functional connectivity between intracellular sites of ROS production. This cross talk has been termed ROS-induced ROS release (RIRR) and is supported by a variety of observations showing that RIRR is a common mechanism for ROS amplification and regional ROS generation. The compartmentalization of ROS production within a cell is critical to its signaling function and is facilitated by microlocalization of specific scavengers. This review will provide descriptions and examples of important mechanisms of RIRR.

Reactive oxygen species (ROS) can be beneficial or harmful in health and disease. While low levels of ROS serve as signaling molecules to regulate vascular tone and the growth and proliferation of endothelial cells, elevated levels of ROS contribute to numerous pathologies, such as endothelial dysfunctions, colon cancer, and fibrosis. ROS and their cellular sources have been extensively studied as potential targets for clinical intervention. Whereas various ROS sources are important for different pathologies, four NADPH oxidases (NOX1, NOX2, NOX4, and NOX5) play a prominent role in homeostasis and disease. NOX1-generated ROS have been implicated in hypertension, suggesting that inhibition of NOX1 may be a promising therapeutic approach. NOX2 and NOX4 oxidases are of specific interest due to their role in producing extra- and intracellular hydrogen peroxide (H₂O₂). NOX4-released hydrogen peroxide activates NOX2, which in turn stimulates the release of mitochondrial ROS resulting in ROS-induced ROS release (RIRR) signaling. Increased ROS production from NOX5 contributes to atherosclerosis. This review aims to summarize recent findings on NOX enzymes and clinical trials inhibiting NADPH oxidases to target pathologies including diabetes, idiopathic pulmonary fibrosis (IPF), and primary biliary cholangitis (PBC).

Background: Bone marrow (BM)-derived myeloid–lymphatic endothelial cell progenitors (M-LECPs) promote formation of tumor lymphatics that are responsible for metastasis to lymph nodes. The regenerative capacity of BM progenitors to other lineages is mediated through cell fusion, a process that delivers a pro-mitotic message directly to division-restricted cells. This suggested that M-LECPs might use a similar mechanism to induce division of lymphatic endothelial cells (LECs). Methods: To test this hypothesis, we determined expression of fusogenic markers in M-LECP produced in vitro and recruited to human or mouse tumors in vivo as well as quantified their fusion with LECs in both settings. Fusion in vivo was determined in female chimera mice grafted with male BM that have been implanted with MDA-MB-231 or EMT6 breast tumors. Co-staining for Y-chromosome and LEC-specific markers allowed us to quantify tumor lymphatic vessels fused with BM progenitors. Results: We found that both tumor-recruited and in-vitro-produced M-LECPs expressed multiple fusogenic regulators and possessed a significant fusogenic activity towards cultured and vessel-lining LECs. Y-chromosomes, a marker of fusion, were detected in nearly half of tumor lymphatics and were associated with mitotic division, vessel formation, and node metastasis. Both in vitro and in vivo assays showed dependency of fusion on Th2 and Toll-like receptor-4 (TLR4) pathways. Conclusions: This novel mechanism of tumor lymphatic formation triggered by fusion with BM myeloid–lymphatic progenitors suggests a variety of new targets for inhibition of metastatic spread.

Objective The objective of this study was to measure flow‐mediated dilation (FMD) prior to and following transient increases in intraluminal pressure (IILP) in resistance arterioles isolated from su...