Crosstalk Between mTOR and TGFβ Pathways Alters the Alveolar Niche in Pulmonary Lymphangioleiomyomatosis

Emily Liu; Gregory Bonde; Lalit Gautam; Amy Ryan

doi:10.1152/physiol.2026.41.S1.2298149

Abstract only Lymphangioleiomyomatosis (LAM) is a rare, female-predominant lung disease characterized by cystic destruction of the distal lung parenchyma. The disorder is driven by sporadic or inherited TSC2 mutations that hyperactivate mTOR signaling; however, the broader consequences of TSC2 loss on other signaling pathways remain poorly defined, particularly given that mTOR inhibitors slow but do not halt disease progression. Multiple growth factors, including VEGF, FGF, and TGFβ, are elevated in LAM, and TGFβ is a key regulator of alveolar repair. Understanding how TSC2 loss impacts signaling within the alveolar niche is therefore essential for elucidating mechanisms of lung remodeling in LAM. Building on our prior findings implicating fibroblast activation and TGFβ as drivers of alveolar dysfunction, this study examined how TGFβ signaling from TSC2-deficient (TSC2-null) LAM cells alters the phenotype of native lung fibroblasts and alveolar epithelial cells. We hypothesized that TGFβ ligands, secreted by TSC2-null cells, activate fibroblasts and, directly or indirectly, disrupt alveolar type II (AT2) cell differentiation. Consistent with our earlier spatial transcriptomics and kinase array data, immunohistochemistry of non-diseased and LAM lung tissue revealed increased TGFβ-related protein expression in regions containing LAM nodules, identified by PMEL and ACTA2 expression. Using immortalized AML cell lines (TSC2-null AML102 and TSC2 + AML103) with shRNA-mediated TGFB1 or TGFB2 knockdown, we evaluated the effects of altered TGFβ signaling on primary human lung fibroblasts and AT2 cells via coculture and conditioned-media systems. TSC2-null cells exhibited elevated, rapamycin-insensitive TGFB1 and TGFB2 expression and secretion. TGFB1 knockdown, and to a lesser extent TGFB2 knockdown, reduced TSC2-null cell proliferation, indicating a TGFβ-dependent autocrine growth mechanism. Wild-type fibroblasts cocultured with TSC2-null cells significantly upregulated activation markers (FAP, ACTA2, TGFB1), an effect abolished when TSC2-null cells lacked TGFB1. AT2 cells differentiated at the air-liquid interface in conditioned media from TSC2-null cells showed increased KRT8, consistent with accumulation of transitional AT2/AT1 states. Conditioned media from TGFB1-knockdown TSC2-null cells restored normal AT2-to-AT1 differentiation, confirmed by AGER and AQP5 immunofluorescence. Together, these findings show that TSC2 loss drives TGFβ ligand overproduction in LAM cells, promoting fibroblast activation and impairing alveolar epithelial differentiation. These mechanisms contribute to alveolar niche dysfunction in LAM and highlight growth factor signaling pathways, particularly TGFβ, as potential therapeutic targets to address limitations of current mTOR-based treatments. This research was funded by the LAM Foundation, grant #LAM0154SG-22 and the Iowa STEAD Family Foundation, awarded to ALR and NIH; NHLBI grant #1F31HL182238, awarded to ECL. This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.

Crosstalk Between mTOR and TGFβ Pathways Alters the Alveolar Niche in Pulmonary Lymphangioleiomyomatosis

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