mTOR dysregulation induces IL6 and paracrine AT2 cell senescence impeding lung repair in lymphangioleiomyomatosis.

<bold>Background:</bold> Lymphangioleiomyomatosis is a multisystem disease causing respiratory failure. LAM is rare as a sporadic disease but is common in women with the autosomal TSC complex. LAM cells have bi-allelic inactivation of TSC2 which codes for tuberin, a component of a multiprotein complex inhibiting the kinase mTOR. We hypothesis, due to mTOR dysregulated cells in LAM nodules become senescent, generate SASP which in turn induce senescence in adjacent cells including alveolar type II cell impairing alveolar repair and parenchymal lung destruction. <bold>Method:</bold> Using laser microdissection, we examined the transcriptional profile of LAM nodules compare to rest of lung and control lungs. <bold>Results:</bold> scRNAseq of human LAM lungs showed alterations in ATII cell regulation of cell death, apoptotic pathways, senescence and Wnt signalling. Dual label IHC staining of p21/p16 and the AT cell marker showed a large number of ATII cells became senescent. Upstream regulator analysis predicted the IL6 receptor as upstream of CDKN1A / p21 / Stat 3 / p53 dependent pathway governing apoptosis and alterations in lipolysis and ATI/II differentiation. LAM cells secreted IL6 in an mTOR dependent manner which slowed epithelial repair in vitro. IL6 was elevated in LAM patients' serum. In vitro LAM cell/ fibroblast /human ATII organoid co-cultures showed that senescence associated genes are upregulated in an mTOR dependent manner. Interrogation of scRNA seq data from nodules and epithelial areas validates these findings and is associated with lung function and disease duration in humans. <bold>Conclusions:</bold> mTOR dysregulated induce epithelial senescence and reduce ATII cell viability to impair the repair response.