Arginase-2 enhances monocyte-endothelial interaction through regulation of integrin and membrane receptor expression:...

Circulating monocyte trans-endothelial migration is critical for vascular diseases. The monocyte surface proteins, i.e., integrins and membrane receptors are central in this process. Previous studies demonstrate that ablation of the mitochondrial arginase-2 (ARG2) reduces monocyte/macrophage infiltration in cardiovascular disease. We further investigate whether ARG2 regulates integrin and surface receptor levels in monocytes and facilitates trans-endothelial migration, contributing to atherogenesis.

For this purpose, human THP1 cells deficient in ARG2 gene (THP1^ARG2-/-) were generated by CRISPR-U^™-mediated genome engineering. Atherosclerotic Apoe^-/-Arg2^+/+ mice and Apoe^-/-Arg2^-/- mouse models are used. Proteomic profiling, cellular/molecular biology methods, and confocal microscopy were utilized for gene or protein expression analysis.

As compared to the control THP1^WT cells, the THP1^ARG2-/- cells reveal decreased adhesion and trans-endothelial migratory activities towards chemoattractants in a transwell co-culture system, accompanied by lower levels of αL and α4 integrins, CD99 and PECAM1 (CD31) (surface molecules for trans-endothelial activity) and CCR2 (the chemoattractant receptor). The monocyte adhesion to endothelial cells is reduced by blocking LFA-1 (αLβ2) or VLA-4 (α4β1) integrin. Pro-inflammatory polarization of the THP1 cells with LPS does not affect the integrin and surface receptor levels, however, enhances release of several pro-inflammatory cytokines, which is reduced in THP1^ARG2-/- cells due to reduced TLR4-ERK-NF-κB signaling. Conditioned medium from the LPS-primed THP1^WT reveals higher capacity to enhance endothelial VCAM-1 and ICAM-1 levels than the THP1^ARG2-/- cells, that is partly mediated by IL-1β. Moreover, ARG2-dependent TGF-β signaling was found to selectively regulate αL expression in monocytes. Finally, as compared to Apoe^-/-Arg2^+/+ mice, the ApoE^-/-Arg2^-/- mice show significantly decreased macrophage integrin, chemoattractant receptor levels, and atherosclerosis.

Our study identifies ARG2 as a key regulator of monocyte-mediated vascular inflammation and atherogenesis by controlling integrin, chemoattractant receptor expression, and pro-inflammatory cytokine release through TLR4-ERK-NFκB signaling, highlighting ARG2 as a potential therapeutic target for vascular and chronic inflammatory diseases.