Mast Cell Tryptase Release Contributes to Disease Progression in Lymphangioleiomyomatosis.

RATIONALE Lymphangioleiomyomatosis is a multisystem disease causing lung cysts and respiratory failure. Loss of tuberous sclerosis complex (TSC) gene function results in a clone of 'LAM cells' with dysregulated mTOR activity. LAM cells and fibroblasts form lung nodules that also contain mast cells although their significance is unknown. OBJECTIVES To understand the mechanism of mast cell accumulation and their role in the pathogenesis of LAM. Methods, Measurements and Main Results: Transcriptional profiling, quantitative RT-PCR and ELISA showed that LAM derived cell / fibroblast co-cultures induced multiple CXC chemokines in fibroblasts. Compared with normal tissue, LAM lungs had increased tryptase positive mast cells expressing CXC chemokine receptors (p<0.05). Mast cells located around the periphery of LAM nodules were positively associated with rate of lung function loss (p=0.016). In vitro, LAM spheroid TSC2 null cell / fibroblast co-cultures attracted mast cells, which was inhibited by pharmacologic and CRISPR-cas9 inhibition of CXCR1 and 2. LAM spheroids caused mast cell tryptase release, which induced fibroblast proliferation and increased LAM spheroid size (1.36±0.24 fold, p=0.0019). The tryptase inhibitor APC366 and sodium cromoglycate inhibited mast cell induced spheroid growth. Using an immuno-competent Tsc2 null murine homograft model, sodium cromoglycate markedly reduced mast cell activation and Tsc2 null lung tumour burden (vehicle: 32.5.3%±23.6 and cromoglycate: 5.5%±4.3. p=0.0035). CONCLUSIONS LAM cell / fibroblast interactions attract mast cells where tryptase release contributes to disease progression. Repurposing sodium cromoglycate for use in LAM should be studied as an alternative or adjunct to mTOR inhibitor therapy.