P4500Cellular senescence of endothelial cells impairs angiogenesis by altering energy metabolism through p53-tigar axis

Background

Ischemic disease is prevalent in elderly population due to impaired angiogenesis. Endothelial cell (EC) generates energy largely via glycolysis, which is further activated when angiogenesis actively occurs. PFK-1 is one of the most important regulatory enzymes for glycolysis, which is activated by PFKFB3. On the other hand, TIGAR inhibits PFK-1 under the control of p53. Crucial roles of PFKFB3 in EC functions under physiological and pathological conditions have been reported; however, a role of TIGAR in EC angiogenic functions remains to be elucidated. Furthermore, it remains unknown whether and how cellular senescence affect the energy metabolism in EC.

Purpose

The purpose of this study is to investigate molecular mechanisms underlying EC dysfunction associated with ageing, especially by focusing on endothelial energy metabolism.

Method and result

Senescent EC showed reduced glucose consumption assessed by [U-13C]-glucose tracer assay in association with increased expression of p53 and TIGAR. Angiogenic capacity assessed by tube-formation assay was reduced in senescent EC. Of note, either silencing of TIGAR by siRNA or lentivirus-mediated overexpression of PFKFB3 improved angiogenic capacity in senescent EC. These results collectively suggest that senescence impairs glycolysis in EC by activating p53-TIGAR axis, which leads to senescence-associated endothelial dysfunction. To analyze an impact of EC senescence in angiogenesis in vivo, we generated EC-specific progeroid mice in which dominant negative form of telomere repeat-binding factor 2 (TRF2) was overexpressed in EC under the control of the TIE2 promoter. After confirming EC-specific senescence in these endothelial progeroid mice, we generated hind-limb ischemia model. Recovery of blood flow assessed by laser doppler velocimeter was significantly impaired in endothelial progeroid mice, indicating that EC senescence is directly and causally implicated in age-related angiogenic dysfunction. Of note, genetic inactivation of TIGAR completely rescued the impaired ischemia-induced neovessel formation in EC-specific progeroid mice.

Conclusion

Using unique endothelial progeroid mice, we revealed that EC senescence is a bona fide risk for ischemic disease, largely by reducing glycolysis in EC through p53-TIGAR axis. Our data suggest that endothelial energy metabolism is an attracting therapeutic target for the prevention and/or treatment of ischemic diseases, especially in elderly population.

3306Endothelial cell senescence accelerates atherosclerosis by enhancing monocyte recruitment via hyper-reactivity to inflammatory stimuli

Background

Ageing is a significant risk factor for atherosclerotic diseases. Vascular senescence has been considered to play an important role in the progression of atherosclerosis; however, it remains unclear whether endothelial cell (EC) senescence is causally involved in the pathogenesis of atherosclerosis.

Purpose

The purpose of this study is to elucidate a causative role of senescent EC in the progression of atherosclerosis.

Methods

Telomeric repeat-binding factor 2 (TRF2) plays a central role in telomere maintenance and protection against end-to-end fusion of chromosome. We previously reported that overexpression of TRF2-dominant negative mutant (TRF2DN) induced premature senescence in EC. We recently generated EC-specific progeroid mice by overexpressing TRF2DN specifically in EC (TRF2DN-Tg), and then generated ApoE-KO/TRF2DN-Tg mice to analyze a role of EC senescence in atherosclerosis. These mice were fed with a high cholesterol-diet, and atherosclerosis was assessed by en face analysis of whole aorta and histological analysis of aortic sinus. In vitro studies to analyze the underlying mechanisms were performed using replicative senescent HUVECs.

Results

En face analysis of aorta revealed that atherosclerotic lesions were significantly increased in ApoE-KO/TRF2DN-Tg mice comparing with that in ApoE-KO mice at as early as 2 weeks after high-cholesterol diet. Histological analysis of aortic sinus also exhibited accelerated atherosclerosis in ApoE-KO/TRF2DN-Tg mice in association with increased macrophage infiltration. Mechanistically, we found that the induction of adhesion molecules such as VCAM-1, ICAM-1, and E-selectin in response to low-grade inflammatory stimuli was substantially augmented in senescent ECs comparing with that in young ECs. As a result, monocyte adhesion was significantly enhanced in senescent ECs. Of note, eNOS inhibition did not affect the hyper-reactivity of senescent EC to inflammation, while antagonizing NF-kB abolished it. Nuclear translocation of NF-kB in response to inflammation was not different between young and senescent ECs, suggesting that NF-kB transcriptional activity might be enhanced in senescent ECs.

Conclusion

We revealed a causative role of EC senescence in the progression of atherosclerosis in vivo using unique EC-specific progeroid mice. Our findings revealed that EC senescence is a bona fide risk for atherosclerosis, and thus senescent ECs are attracting pharmacotherapeutic targets for the prevention and/or treatment of atherosclerotic disease in elderly population.