Abstract 16591: Exosome-Mediated Endothelial Cell Apoptosis and Network Disruption by Lymphangioleiomyomatosis-Smooth Muscle Cells (LAM-SMCs) Derived from Human Induced Pluripotent Stem Cell (iPSC)

Abstract

Introduction: In LAM, SMC-like cells invade the lung thus compromising respiratory function which is dependent on normal vascular and alveoli structure. We posit that while healthy mural SMCs stabilize fragile neovessels and maintain vascular homeostasis, LAM-SMCs promote disruption of lung microvasculature by inducing endothelial cell (EC) apoptosis. Methods/Results: iPSCs derived from LAM patients or healthy subjects were differentiated into SMCs using a teratoma protocol. Co-culture of healthy iSMCs with HUVECs on Matrigel improved EC network persistence for ≥72Hrs, while LAM-SMC co-culture led to rapid network collapse in <15Hrs. Culture of ECs with LAM-SMC conditioned media (24-72Hrs) increased EC apoptosis as assessed by Annexin V/PI flow cytometry, confirmed by increases in cleaved Caspase-3 protein expression. To further elucidate mechanism and kinetics of EC apoptosis, Annexin V/PI flow cytometry and Western Blot with Caspases 8,9,12 were performed in parallel at 3hr intervals from 0-12 Hrs. Increase in EC apoptosis at 9hrs, corresponded with a 6-fold increase in Cas-12 protein expression, followed by a 3-fold increase in Cas-9 at 12hrs with little change in Cas-8. This is in line with our RNAseq study showing dysregulation in endoplasmic reticulum and mitochondria related genes in LAM-SMC. Culture of HUVECs with LAM-SMC exosomes similarly induced EC apoptosis, with a profound decrease in EC gene expression (eNOS,TIE2,TAL1; 5-7 fold; p<0.05) but increase expression of vessel-destabilizing, ANGPT2 (6-fold; p<0.05). Scratch-wound assay also showed ~60% reduction (p<0.05) in EC migratory capacity. Intriguingly, apoptotic ECs released exosomes containing translationally controlled tumor protein, TCTP, which were taken up by LAM-SMCs, as evidenced by immunofluorescence studies, associated with increases in the levels of proliferation-associated phospho-mTOR-and-S6k protein. Conclusions: LAM-SMCs derived exosomes resulted in EC apoptosis and network destabilization. Conversely, apoptotic ECs enhanced LAM-SMC growth, possibly by Caspase-dependent exosome release of TCTP, a positive regulator of mTOR signaling. These novel mechanisms may promote both microvasculature disruption and uncontrolled growth of LAM-SMCs.