Hyperactive mTORC1 in lung mesenchyme induces endothelial cell dysfunction and pulmonary vascular remodeling

Lymphangioleiomyomatosis (LAM) is a progressive cystic lung disease caused by tuberous sclerosis complex 1/2 (TSC1/2) gene mutations in pulmonary mesenchymal cells resulting in activation of the mechanistic target of rapamycin complex 1 (mTORC1). A subset of LAM patients develops pulmonary vascular remodeling and pulmonary hypertension. Little, however, is known regarding how LAM cells communicate with endothelial cells (ECs) to trigger vascular remodeling. In end-stage LAM lung explants, we identified endothelial cell dysfunction characterized by increased proliferation, migration, defective angiogenesis, and dysmorphic endothelial tube network formation. To model LAM disease, we utilized an mTORC1 gain-of-function mouse model with a Tsc2 knock-out (Tsc2KO) specific to lung mesenchyme (Tbx4LME-CreTsc2fl/fl), similar to the mesenchyme specific genetic alterations seen in human disease. As early as 8 weeks of age, ECs from Tbx4LME-CreTsc2fl/fl mice exhibited marked transcriptomic changes despite absence of morphological changes to the distal lung microvasculature. In contrast, 1 year old Tbx4LME-CreTsc2fl/fl mice spontaneously developed pulmonary vascular remodeling with increased medial thickness. Single cell RNA-sequencing of 1 year old mouse lung identified paracrine ligands originating from Tsc2KO mesenchyme which can signal through receptors in arterial ECs. These ECs had transcriptionally altered genes including those in pathways associated with blood vessel remodeling. The proposed pathophysiologic mesenchymal ligand/ EC receptor crosstalk highlights the importance of an altered mesenchymal-EC axis in LAM and other hyperactive mTORC1-driven diseases. Since ECs in LAM patients and in Tbx4LME-CreTsc2fl/fl mice do not harbor TSC2 mutations, our study demonstrates that constitutively active mTORC1 lung mesenchymal cells orchestrate dysfunctional EC responses which contribute to pulmonary vascular remodeling.