Eliminating senescent cells can promote pulmonary hypertension development and progression

BACKGROUND: Senescent cells (SCs) are involved in proliferative disorders, but their role in pulmonary hypertension remains undefined. We investigated SCs in patients with pulmonary arterial hypertension and the role of SCs in animal pulmonary hypertension models. METHODS: We investigated senescence (p16, p21) and DNA damage (γ-H2AX, 53BP1) markers in patients with pulmonary arterial hypertension and murine models. We monitored p16 activation by luminescence imaging in p16-luciferase (p16LUC/+) knock-in mice. SC clearance was obtained by a suicide gene (p16 promoter-driven killer gene construct in p16-ATTAC mice), senolytic drugs (ABT263 and cell-permeable FOXO4-p53 interfering peptide [FOXO4-DRI]), and p16 inactivation in p16LUC/LUC mice. We investigated pulmonary hypertension in mice exposed to normoxia, chronic hypoxia, or hypoxia+Sugen, mice overexpressing the serotonin transporter (SM22-5-HTT+), and rats given monocrotaline. RESULTS: Patients with pulmonary arterial hypertension compared with controls exhibited high lung p16, p21, and γ-H2AX protein levels, with abundant vascular cells costained for p16, γ-H2AX, and 53BP1. Hypoxia increased thoracic bioluminescence in p16LUC/+ mice. In wild-type mice, hypoxia increased lung levels of senescence and DNA-damage markers, senescence-associated secretory phenotype components, and p16 staining of pulmonary endothelial cells (P-ECs, 30% of lung SCs in normoxia), and pulmonary artery smooth muscle cells. SC elimination by suicide gene or ABT263 increased the right ventricular systolic pressure and hypertrophy index, increased vessel remodeling (higher dividing proliferating cell nuclear antigen-stained vascular cell counts during both normoxia and hypoxia), and markedly decreased lung P-ECs. Pulmonary hemodynamic alterations and lung P-EC loss occurred in older p16LUC/LUC mice, wild-type mice exposed to Sugen or hypoxia+Sugen, and SM22-5-HTT+ mice given either ABT263 or FOXO4-DRI, compared with relevant controls. The severity of monocrotaline-induced pulmonary hypertension in rats was decreased slightly by ABT263 for 1 week but was aggravated at 3 weeks, with loss of P-ECs. CONCLUSION: Elimination of senescent P-ECs by senolytic interventions may worsen pulmonary hemodynamics. These results invite consideration of the potential impact on pulmonary vessels of strategies aimed at controlling cell senescence in various contexts

A specific ChREBP and PPAR alpha cross-talk is required for the glucose-mediated FGF21 response

While the physiological benefits of the fibroblast growth factor 21 (FGF21) hepatokine are documented in response to fasting, little information is available on Fgf21 regulation in a glucose-overload context. We report that peroxisome-proliferator-activated receptor alpha (PPAR alpha), a nuclear receptor of the fasting response, is required with the carbohydrate-sensitive transcription factor carbohydrate-responsive element-binding protein (ChREBP) to balance FGF21 glucose response. Microarray analysis indicated that only a few hepatic genes respond to fasting and glucose similarly to Fgf21. Glucose-challenged Chrebp(-/-) mice exhibit a marked reduction in FGF21 production, a decrease that was rescued by re-expression of an active ChREBP isoform in the liver of Chrebp(-/-) mice. Unexpectedly, carbohydrate challenge of hepatic Ppar alpha knockout mice also demonstrated aPPAR alpha-dependent glucose response for Fgf21 that was associated with an increased sucrose preference. This blunted response was due to decreased Fgf21 promoter accessibility and diminished ChREBP binding onto Fgf21 carbohydrate-responsive element (ChoRE) in hepatocytes lacking PPAR alpha. Our study reports that PPAR alpha is required for the ChREBP-induced glucose response of FGF21

Usher type 1G protein sans is a critical component of the tip-link complex, a structure controlling actin polymerization in stereocilia

The mechanotransducer channels of auditory hair cells are gated by tip-links, oblique filaments that interconnect the stereocilia of the hair bundle. Tip-links stretch from the tips of stereocilia in the short and middle rows to the sides of neighboring, taller stereocilia. They are made of cadherin-23 and protocadherin-15, products of the Usher syndrome type 1 genes USH1D and USH1F, respectively. In this study we address the role of sans, a putative scaffold protein and product of the USH1G gene. In Ush1g−/− mice, the cohesion of stereocilia is disrupted, and both the amplitude and the sensitivity of the transduction currents are reduced. In Ush1gfl/flMyo15-cre+/− mice, the loss of sans occurs postnatally and the stereocilia remain cohesive. In these mice, there is a decrease in the amplitude of the total transducer current with no loss in sensitivity, and the tips of the stereocilia in the short and middle rows lose their prolate shape, features that can be attributed to the loss of tip-links. Furthermore, stereocilia from these rows undergo a dramatic reduction in length, suggesting that the mechanotransduction machinery has a positive effect on F-actin polymerization. Sans interacts with the cytoplasmic domains of cadherin-23 and protocadherin-15 in vitro and is absent from the hair bundle in mice defective for either of the two cadherins. Because sans localizes mainly to the tips of short- and middle-row stereocilia in vivo, we conclude that it belongs to a molecular complex at the lower end of the tip-link and plays a critical role in the maintenance of this link