OxLDL Triggers Retrograde Translocation of Arginase 2 in Aortic Endothelial Cells via ROCK and Mitochondrial Processing Peptidase
Rationale: Increased arginase activity contributes to endothelial dysfunction by competition for L-arginine substrate and reciprocal regulation of NOS. The rapid increase in arginase activity in human aortic endothelial cells (HAEC) exposed to oxidized LDL is consistent with post-translational modification or subcellular trafficking.
Objective: To test the hypotheses that OxLDL triggers reverse translocation of mitochondrial Arginase 2 (Arg2) to cytosol and Arg2 activation, and that this process is dependent upon mitochondrial processing peptidase (MPP), LOX-1 receptor and ROCK.
Methods and Results: OxLDL triggered translocation of Arg2 from mitochondria to cytosol in HAEC and in murine aortic intima with a concomitant rise in arginase activity. All of these changes were abolished by inhibition of MPP or by its siRNA-mediated knockdown. ROCK inhibition and the absence of the LOX-1 receptor in KO mice also ablated translocation. Amino-terminal sequencing of Arg2 revealed 2 candidate mitochondrial targeting sequences, and deletion of either of these confined Arg2 to the cytoplasm. Inhibitors of MPP or LOX-1 receptor KO attenuated OxLDL-mediated decrements in endothelial-specific NO production and increases in superoxide generation. Finally, Arg2-/- mice bred on an ApoE-/- background showed reduced plaque load, reduced ROS production, enhanced NO, and improved endothelial function as compared with ApoE-/- controls.
Conclusions: These data demonstrate dual distribution of Arg2, a protein with an unambiguous MTS, in mammalian cells, and its reverse translocation to cytoplasm by alterations in the extracellular milieu. This novel molecular mechanism drives OxLDL-mediated arginase activation, eNOS uncoupling, endothelial dysfunction, and atherogenesis.
- mitochondrial processing peptidase
- endothelial dysfunction
- endothelial nitric oxide synthase
- oxidized low-density lipoprotein
- Received April 25, 2014.
- Revision received May 30, 2014.
- Accepted June 5, 2014.