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Single Cell RNA Sequencing Identifies TGFβ as a Key Regenerative Cue following LPS-induced Lung Injury

ABSTRACT: Many lung diseases result from a failure of efficient regeneration of damaged alveolar epithelial cells (AECs) after lung injury. During regeneration, AEC2s proliferate to replace lost cells, after which proliferation halts and some AEC2s transdifferentiate into AEC1s to restore normal alveolar structure and function. Although the mechanisms underlying AEC2 proliferation have been studied, the mechanisms responsible for halting proliferation and inducing transdifferentiation are poorly understood. To identify candidate signaling pathways responsible for halting proliferation and inducing transdifferentiation, we performed single cell RNA sequencing on AEC2s during regeneration in a murine model of lung injury induced by intratracheal LPS. Unsupervised clustering revealed distinct subpopulations of regenerating AEC2s: proliferating, cell cycle arrest, and transdifferentiating. Gene expression analysis of these transitional subpopulations revealed that TGFβ signaling was highly upregulated in the cell cycle arrest subpopulation and relatively downregulated in transdifferentiating cells. In cultured AEC2s, TGFβ was necessary for cell cycle arrest but impeded transdifferentiation. We conclude that during regeneration after LPS-induced lung injury, TGFβ is a critical signal halting AEC2 proliferation but must be inactivated to allow transdifferentiation. This study provides insight into the molecular mechanisms regulating alveolar regeneration and the pathogenesis of diseases resulting from a failure of regeneration.

ORGANISM(S): Mus musculus

PROVIDER: GSE113049 | GEO | 2019/03/27

REPOSITORIES: GEO

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Project description:We performed transcriptomic profiling of freshly isolated primary adult human alveolar epithelial type 2 cells (AEC2s), their isogenic cultured progeny, and human induced pluripotent stem cell-derived AEC2s (iAEC2s). Distal lung preparations from adult donor lung explants from two individuals were cryopreserved using methods we have previously described. Primary AEC2s were purified using fluorescence activated cell sorting (FACS) to isolate cells co-expressing EPCAM and HTII-280. To establish cultures of primary AEC2s, these cells were combined with MRC5 fibroblasts at an 1:10 ratio on cell culture inserts in CK+DCI medium. iAEC2s were derived using our previously published lung directed differentiation protocol. We used the SPC2 human iPSC line and specifically the SPC2-ST-B2 (SFTPC tdT/WT ) clone containing a SFTPC tdTomato knock-in reporter. SFTPC tdTomato+ cells were sorted on day 41 of differentiation. iAEC2s were single-cell passaged in self-renewing feeder-free 3D cultures approximately every 2 weeks. We used the 10X Chromium System to generate single-cell transcriptomic data from 5 samples prepared in parallel and sequenced on the same day. We profiled (a) preculture primary AEC2s, (b) cultured primary AEC2s, (c) 3D feeder-free iAEC2s, (d) feeder-free iAEC2 cultured on cell culture inserts, and (e) iAEC2s cultured on cell inserts with MRC5 fibroblasts. The cultured primary AEC2 samples and the iAEC2 sample co-cultured with MRC5s were sorted for live EPCAM+ cells prior to encapsulation. All other samples were sorted for live cells. We find that although each population (fresh, primary cultured, and iPSC-derived AEC2s) occupies a distinct transcriptomic space, both cultured primary AEC2s and cultured feeder-free iAEC2s closely resemble their primary pre-cultured counterparts. We also find a continuum of progressively more proliferative states (from fresh primary to cultured primary to cultured iAEC2s) inversely associated with progressively less mature AEC2 states.

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Single Cell RNA Sequencing Identifies TGFβ as a Key Regenerative Cue following LPS-induced Lung Injury

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