Senescence in lymphangioleiomyomatosis as a paradigm for the remodelling of lung microenvironment

Lymphangioleiomyomatosis (LAM) is a rare disease in which tuberin-deficient LAM cells featuring the hyperactivation of the mammalian Target of Rapamycin Complex 1 (mTORC1), cause the disruption of the lung parenchyma leading to respiratory failure. Recently senescence was proposed to explain LAM onset and progression, considering the pivotal role of mTOR activity. We demonstrated that the chromatin remodeling agent 5-Azacytidine significantly reduced the senescent features of human primary LAM cells (LAM/TSC cells), in which TSC2 loss of heterozygosity is due to an epigenetic modification. A similar decrease of senescence is obtained after mTOR inhibition through rapamycin, indicating a correlation between tuberin absence, mTOR constitutive activation and senescence. LAM/TSC cells spread senescence in LAM microenvironment: indeed, primary lung fibroblasts (PLFs) grown in LAM/TSC conditioned medium (CM) increased their positivity to senescent markers, and enhanced the expression and secretion of interleukin (IL)-8, highly secreted by LAM/TSC cells. To explore the communication in LAM microenvironment, for the first time we assessed that LAM/TSC cells secrete extracellular vesicles (EVs), which can be carriers of senescence-inducing insoluble mediators. Both 5-Azacytidine and rapamycin treatment reduced LAM/TSC cell EVs secretion, implying a modulation of mTOR pathway on EVs release. To deepen the role of IL-8 in LAM, we supplemented the CM of PLFs with IL-8, observing a significant increase of senescence, while blocking IL-8 receptor with monoclonal antibodies modulates senescence in LAM/TSC cells. These results suggest that, among SASP, IL-8 might be directly involved in the detrimental effects that LAM cells exert on lung tissue. Indeed, the high IL-8 levels might induce senescence and promote a pro-inflammatory milieu, ultimately causing the disruption of lung parenchyma. Taken together and using LAM as a paradigm, these results make senescence, and its modulation through chromatin-remodeling agents, an intriguing field of study to understand the mechanisms underlying lung disruption in pulmonary chronic diseases. Moreover, dissecting the pathological communication in the senescent lung microenvironment might allow to identify targets for early diagnosis and novel therapies