Chronic mTOR activation induces a degradative smooth muscle cell phenotype

J Clin Invest. 2020 Mar 2;130(3):1233-1251. doi: 10.1172/JCI131048.

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.

Keywords: Cardiovascular disease; Vascular Biology.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aneurysm, Dissecting / enzymology*
  • Aneurysm, Dissecting / genetics
  • Aneurysm, Dissecting / pathology
  • Animals
  • Aorta / enzymology*
  • Aorta / pathology
  • Aortic Aneurysm, Thoracic / enzymology*
  • Aortic Aneurysm, Thoracic / genetics
  • Aortic Aneurysm, Thoracic / pathology
  • Disease Models, Animal
  • Lysosomes / enzymology
  • Lysosomes / genetics
  • Lysosomes / pathology
  • Mechanistic Target of Rapamycin Complex 1 / genetics
  • Mechanistic Target of Rapamycin Complex 1 / metabolism
  • Mice
  • Mice, Knockout, ApoE
  • Microphthalmia-Associated Transcription Factor / genetics
  • Microphthalmia-Associated Transcription Factor / metabolism
  • Myocytes, Smooth Muscle / enzymology*
  • Myocytes, Smooth Muscle / pathology
  • Signal Transduction*
  • TOR Serine-Threonine Kinases / genetics
  • TOR Serine-Threonine Kinases / metabolism*
  • Tuberous Sclerosis Complex 1 Protein / genetics
  • Tuberous Sclerosis Complex 1 Protein / metabolism
  • beta Catenin / genetics
  • beta Catenin / metabolism

Substances

  • CTNNB1 protein, mouse
  • Microphthalmia-Associated Transcription Factor
  • Mitf protein, mouse
  • Tsc1 protein, mouse
  • Tuberous Sclerosis Complex 1 Protein
  • beta Catenin
  • TOR Serine-Threonine Kinases
  • mTOR protein, mouse
  • Mechanistic Target of Rapamycin Complex 1