NOX4 contributes to the initiation and progression of AAA in a cell type-specific manner

BackgroundAbdominal aortic aneurysm (AAA) is a disease with altered vessel wall architecture and integrity. AAA rupture is associated with high mortality. Reactive oxygen species, such as those produced by members of the NADPH oxidase (NOX) family, play a central role in several aspects of vascular physiology. In particular, the role of NOX4 appears to be highly cell and context specific. MethodsThis study analyzed the role of NOX4 in late-stage human AAA specimen and in Nox4-/- mice with experimentally induced AAA. ResultsNOX4 expression was reduced in human AAA. In a mouse model of AAA, loss of Nox4 conferred protection against AAA formation, suggesting a pathogenic role. Single cell analysis of human AAA revealed that NOX4 is primarily expressed in fibroblasts, s.mooth muscle, and endothelial cells. NOX4 mRNA expression was strongly associated with ECM synthesis and ECM remodeling pathways. Angiogenic signatures were reduced in AAA, and sub-cluster analysis of endothelial cells identified two major groups: microvascular and lymphatic endothelial cells (LEC), with very low NOX4 expression in LEC. Quantification of the vasa vasorum revealed a shift in vessel size distribution, with a reduction in the number of small vessels (<8 {micro}m) and an increase in large vessels (>26 {micro}m) correlating with increasing aortic diameter. Markers of lymphangiogenesis, including VEGFC and PROX1, were upregulated in AAA. Pseudotime trajectory analysis suggested transdifferentiation of LECs into myofibroblasts, a process associated with increased NOX4 mRNA expression. ConclusionNOX4 plays a role in the pathogenesis of AAA and is primarily expressed in fibroblasts, smooth muscle cells, and endothelial cells. Single-cell and pseudotime analyses revealed that NOX4 is associated with ECM remodeling, reduced angiogenic signatures, and the transdifferentiation of lymphatic endothelial cells into myofibroblasts. Clinical PerspectiveO_ST_ABSWhat is new?C_ST_ABSO_LIIn human AAA, NOX4 is associated with pro-fibrotic effects. C_LIO_LINOX4 appears to play a central role in cell differentiation processes in AAA, supporting the expansion of the fibroblast population. C_LIO_LIThe percentage of small microvessels (<8 {micro}m) is increased in human AAA, and NOX4 expression correlates positively with the proportion of small vessels. C_LIO_LIThe cell-cell communication network of endothelial cells in AAA appears to have a profile that supports fibrosis. C_LIO_LILymphatic endothelial cells and markers of lymphangiogenesis were found in AAA. C_LIO_LILymphatic endothelial cells transdifferentiate into myofibroblasts, a process accompanied by increased NOX4 expression. C_LIO_LINOX4 may serve as a mechanistic link between lymphangiogenesis and fibrosis, bridging vascular remodeling and fibrotic progression. C_LI Translational Perspective?O_LITargeting NOX4 represents a promising therapeutic strategy for mitigating fibrotic remodeling in late-stage AAA. C_LIO_LITargeting the specific receptors mediating the interaction between lymphatic endothelial cells, fibroblasts, and inflammatory cells may reveal novel therapeutic targets. C_LI Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=149 SRC="FIGDIR/small/26347161v1_ufig1.gif" ALT="Figure 1"> View larger version (34K): org.highwire.dtl.DTLVardef@688aeborg.highwire.dtl.DTLVardef@178673borg.highwire.dtl.DTLVardef@1c17f5aorg.highwire.dtl.DTLVardef@8fff06_HPS_FORMAT_FIGEXP M_FIG C_FIG