Mitochondrial Permeability Transition Pore Regulates Endothelial Bioenergetics and Angiogenesis

Subject codes: [95] Endothelium/vascular type [129] Angiogenesis [140] Energy metabolism [145] Genetically altered mice ABSTRACT Rationale: The mitochondrial permeability transition pore (mPTP) is a well-known initiator of cell death that is increasingly recognized as a physiological modulator of cellular metabolism. Objective: We sought to identify how the genetic deletion of a key regulatory subunit of the mPTP, Cyclophilin D (CypD), influenced endothelial metabolism and intracellular signaling. Methods and Results: In cultured primary human endothelial cells (ECs), genetic targeting of CypD using siRNA or shRNA resulted in a constitutive increase in mitochondrial matrix Ca 2+ and NADH. Elevated matrix NADH in turn diminished the cytosolic NAD + /NADH ratio and triggered a subsequent downregulation of the NAD +-dependent deacetylase SIRT1. Downstream of SIRT1, CypD-deficient ECs exhibited reduced PTEN expression and a constitutive rise in the phosphorylation of angiogenic Akt. Similar changes in SIRT1, PTEN, and Akt were also noted in the aorta and lungs of CypD KO mice. Functionally, CypD-deficient ECs and aortic tissue from CypD KO mice exhibited a dramatic increase in angiogenesis at baseline and when exposed to vascular endothelial growth factor (VEGF). The NAD + precursor icotinamide mononucleotide restored the cellular NAD + /NADH ratio and normalized the CypD-deficient phenotype. CypD KO mice also presented accelerated wound healing and increased neovascularization upon tissue injury as monitored by optical microangiography (OMAG). Conclusion: Our study reveals the importance of the mPTP in the regulation of endothelial mitochondrial metabolism and vascular function. The mitochondrial regulation of SIRT1 has broad implications in the epigenetic regulation of endothelial phenotype. Nonstandard Abbreviations and Acronyms: CsA Cyclosporine A EC Endothelial cells ECAR Extracellular acidification rate HPAEC Human pulmonary artery endothelial cells HPMVEC Human pulmonary microvascular endothelial cells mNCLX Mitochondrial Na + /Ca 2+ exchanger mPTP Mitochondrial permeability transition pore NMN Nicotinamide mononucleotide NAM Nicotinamide OMAG Optical microangiography OCR Oxygen consumption rate ROSE Reactive Oxygen Species TSA Trichostatin A VEGF Vascular endothelial growth factor