No abstract

Lung adenocarcinoma (LUAD) is the most common subtype of cancer arising in the distal lung. LUAD encompasses several pathologic subtypes, each with differing clinical outcomes and biological behaviors. However, the molecular and cellular underpinnings of the different subtypes are largely unknown. Understanding which cell populations in the distal lung contribute to LUAD could provide insights into the marked heterogeneity in pathologic features, clinical presentation and responses to therapy of LUAD. Differential expression analysis of lung adenocarcinoma transcriptomes from The Cancer Genome Atlas revealed distinct alveolar epithelial type 1 (AT1) and alveolar epithelial type 2 (AT2) cell signatures within human LUAD with significantly different survival outcomes between tumors expressing AT2 and AT1 gene signatures, suggesting AT1 cells might contribute to a subset of LUAD cases. To address this, we tested the ability of AT1 cells to give rise to LUAD following induction of KrasG12D, a known oncogenic driver of human LUAD. Activation of KrasG12D in Gram-domain containing 2 (Gramd2)+ AT1 cells gave rise to multiple LUAD lesions, primarily of papillary histology. In contrast, activation of KrasG12D in surfactant protein C (Sftpc+) AT2 cells resulted in LUAD lesions of lepidic histology. Immunohistochemistry established that Gramd2:KrasG12D lesions were of primary lung origin and not metastatic events. Spatial transcriptomic profiling revealed distinct pathway alterations within Gramd2- and Sftpc-derived LUAD. Immunofluorescence confirmed differences observed in the spatial transcriptomic analysis in expression patterns and distribution of cell-specific markers depending on cell of origin, while universal upregulation of the Krt8 intermediate cell state marker was observed. Our results are consistent with Gramd2+ AT1 cells serving as a putative cell of origin for LUAD and suggest that LUAD may be a collection of adenocarcinomas that share a common location within the distal lung but arise from different cells of origin.

Lung adenocarcinoma (LUAD) is the most commonly diagnosed form of non-small cell lung cancer, and is associated with high frequency of tumor recurrence, severe malignancy and vast heterogeneity (1). Moreover, this histological diversity is compounded by the LUAD tumor microenvironment's (TME) extensive cellular diversity and accompanying immune infiltration patterns. These properties have been linked to unpredictable tumor recurrence, poor patient response to therapy, and mortality (2). Integrative application of existing tools and methods geared towards understanding epigenetic contributions to LUAD heterogeneity is imperative to answering these questions (3).In the recent issue of Clinical Cancer Research, Guidry et al. repurposed established DNA methylation patterns associated with cellular age to define signatures that can act as an index for distinct subtypes of LUAD (4). In establishing the relationship between epigenetic signatures and LUAD subtypes, they were able to ascribe phenotypic and molecular characteristics to each subclassification, including enrichment for oncogenic driver mutations and immune composition of the TME (5-9). Further to this, Guidry drew correlations between immune microenvironment composition, ethnic background and patient smoking history.Previous studies have utilized genome-wide methylation alterations within LUAD to define relevant subtypes. These investigations yielded three [3] major DNA methylation classifications in LUAD; CpG-island methylation phenotype (CIMP)-low, CIMP-intermediate, and CIMPhigh (10). DNA methylation patterns have also been associated with TME molecular characteristics and immune cell composition within LUAD tumors (11). The study by Guidry et al., improves on these associations by refining genome-wide methylation patterning to the 353 CpG sites within the Horvath DNA methylation CLOCK (6). The authors were then able to use methylation levels at these sites to subdivide LUAD into six [6] distinct subgroups, each associated with distinct pathologic and molecular features of LUAD. Subgroups with higher DNAm age were associated with better patient survival and specific oncogenic driver mutations.Aberrant oncogenic driver gene expression plays an integral role in tumorigenesis and progression in LUAD. To understand the relationship between DNAm-defined LUAD subclusters and oncogenic drivers, Guidy et al. conducted mutational analysis on tumor samples and focused on established LUAD oncogenic driver mutations

Lung adenocarcinoma (LUAD) is the most common subtype of cancer arising in the distal lung. LUAD encompasses several pathologic histologies, some with important differing clinical outcomes and biological behaviors. However, the molecular and cellular underpinnings of the different subtypes are largely unknown. Understanding which cell populations in the distal lung contribute to LUAD could provide insights into the marked heterogeneity in pathologic features, clinical presentation and responses to therapy of LUAD. Differential expression analysis of LUAD transcriptomes from The Cancer Genome Atlas revealed distinct alveolar epithelial type 1 (AT1) and alveolar epithelial type 2 (AT2) cell signatures with significantly different survival outcomes between tumors expressing AT2 and AT1 gene signatures. The data suggests that AT1 cells might contribute to a subset of LUAD cases. To determine if AT1 cells could give rise to LUAD, we utilized transgenic mouse models to induce KrasG12D, a known oncogenic driver of human LUAD, in Gram-domain containing 2 (Gramd2)+ expressing AT1 cells. This gave rise to multiple LUAD lesions, as confirmed by micro computed tomography and pathologist-evaluated hematoxylin and eosin staining, primarily of papillary histology. In contrast, activation of KrasG12D in surfactant protein C (Sftpc+) AT2 cells resulted in LUAD lesions of exclusively lepidic histology. Immunohistochemistry established that Gramd2:KrasG12D lesions were of primary lung origin and not metastatic events. Spatial transcriptomic profiling revealed distinct pathway alterations within Gramd2- and Sftpc-derived LUAD, including specific upregulation of TGFβ-mediated epithelial to mesenchymal transition (EMT) in Gramd2+ AT1 LUAD. Immunofluorescence confirmed differences observed in the spatial transcriptomic analysis in expression patterns and distribution of cell-specific markers depending on cell of origin, while universal upregulation of a Krt8+ intermediate cell state marker was observed. Our results are consistent with Gramd2+ AT1 cells serving as a putative cell of origin for LUAD and suggest that LUAD may be a collection of adenocarcinomas that share a common location within the distal lung but arise from different cells of origin, a finding with potentially important therapeutic implications. Citation Format: Minxiao Yang, Hua Shen, Per Flodby, Michael Koss, Rania Bassiouni, Yixin Liu, Theresa Ryan Stueve, Daniel J. Mullen, Amy L. Ryan, Tea Jashashvili, John Carpten, Alessandra Castaldi, W. Dean Wallace, Beiyun Zhou, Zea Borok, Crystal N. Marconett. Alveolar epithelial type 1 cells can serve as a cell of origin for lung adenocarcinoma with distinct molecular and phenotypic presentation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5.