Chronic mTOR activation induces a degradative smooth muscle cell phenotype
Guangxin Li, Mo Wang, Alexander W. Caulk, Nicholas A. Cilfone, Sharvari Gujja, Lingfeng Qin, Pei-Yu Chen, Zehua Chen, Sameh Yousef, Yang Jiao, Changshun He, Bo Jiang, Arina Korneva, Matthew R. Bersi, Guilin Wang, Xinran Liu, Sameet Mehta, Arnar Geirsson, Jeffrey R. Gulcher, Thomas W. Chittenden, Michael Simons, Jay D. Humphrey, George Tellides
Guangxin Li, Mo Wang, Alexander W. Caulk, Nicholas A. Cilfone, Sharvari Gujja, Lingfeng Qin, Pei-Yu Chen, Zehua Chen, Sameh Yousef, Yang Jiao, Changshun He, Bo Jiang, Arina Korneva, Matthew R. Bersi, Guilin Wang, Xinran Liu, Sameet Mehta, Arnar Geirsson, Jeffrey R. Gulcher, Thomas W. Chittenden, Michael Simons, Jay D. Humphrey, George Tellides
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Research Article Vascular biology

Chronic mTOR activation induces a degradative smooth muscle cell phenotype

Abstract

Smooth muscle cell (SMC) proliferation has been thought to limit the progression of thoracic aortic aneurysm and dissection (TAAD) because loss of medial cells associates with advanced disease. We investigated effects of SMC proliferation in the aortic media by conditional disruption of Tsc1, which hyperactivates mTOR complex 1. Consequent SMC hyperplasia led to progressive medial degeneration and TAAD. In addition to diminished contractile and synthetic functions, fate-mapped SMCs displayed increased proteolysis, endocytosis, phagocytosis, and lysosomal clearance of extracellular matrix and apoptotic cells. SMCs acquired a limited repertoire of macrophage markers and functions via biogenesis of degradative organelles through an mTOR/β-catenin/MITF–dependent pathway, but were distinguishable from conventional macrophages by an absence of hematopoietic lineage markers and certain immune effectors even in the context of hyperlipidemia. Similar mTOR activation and induction of a degradative SMC phenotype in a model of mild TAAD due to Fbn1 mutation greatly worsened disease with near-uniform lethality. The finding of increased lysosomal markers in medial SMCs from clinical TAAD specimens with hyperplasia and matrix degradation further supports the concept that proliferation of degradative SMCs within the media causes aortic disease, thus identifying mTOR-dependent phenotypic modulation as a therapeutic target for combating TAAD.

Authors

Guangxin Li, Mo Wang, Alexander W. Caulk, Nicholas A. Cilfone, Sharvari Gujja, Lingfeng Qin, Pei-Yu Chen, Zehua Chen, Sameh Yousef, Yang Jiao, Changshun He, Bo Jiang, Arina Korneva, Matthew R. Bersi, Guilin Wang, Xinran Liu, Sameet Mehta, Arnar Geirsson, Jeffrey R. Gulcher, Thomas W. Chittenden, Michael Simons, Jay D. Humphrey, George Tellides

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Figure 7

mTOR/β-catenin/MITF regulation of lysosomal biogenesis in SMCs.

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mTOR/β-catenin/MITF regulation of lysosomal biogenesis in SMCs. Myh11-Cr...
Myh11-CreERT2 mT/mG (Tsc1+/+) and Tsc1fl/fl Myh11-CreERT2 mT/mG (Tsc1−/−) mice were treated with tamoxifen at 1.5 weeks and the thoracic aortas were analyzed at 24 weeks. (A) Selected transcript expression by bulk RNA-seq. (B and C) Protein expression by Western blot (n = 8). (D and E) β-Catenin and MITF expression (white) with RFP (red), GFP (green), and DAPI (blue) overlay (scale bars: 100 μm), and quantified as medial percentage area (n = 5–7). Alternatively, cultured GFP+ SMCs were analyzed by P3. (F) Expression of signaling molecules and lysosomal membrane proteins after treatment with rapamycin (RAPA) at 0–100 ng/mL for 6 days in serum-supplemented medium. (G and H) Effects of Ctnnb1 and Mitf knockdown by siRNA versus control (Cntrl) for 3 days. (I) Fold inhibition after rapamycin or siRNA treatment relative to control treatment (dotted lines) in Tsc1−/− cells (n = 3–5). Data are represented as individual values with mean ± SEM bars or as box-and-whisker plots with interquartile range, median, minimum, and maximum. *P < 0.05; **P < 0.01; ***P < 0.001; FDR‑adjusted P values (A), 2-way ANOVA (B and I), or t test (D and E).