Front Immunol. 2026 Aug 18;17:1904638. doi: 10.3389/fimmu.2026.1904638. eCollection 2026.

ABSTRACT

BACKGROUND: Aberrant tissue repair and relentless fibroblast activation are hallmark features of idiopathic pulmonary fibrosis (IPF). Although IPF and Alzheimer's disease (AD) share underlying aging-related pathologies, including immune and metabolic dysregulation, the putative genetic mechanisms linking AD susceptibility to pathogenic macrophage remodeling in the fibrotic niche are not fully established.

METHODS: We performed a two-sample Mendelian randomization (MR) analysis to assess the genetic association and potential causal relationship between AD and IPF. Shared hub genes were identified via protein interaction networks. To characterize macrophage heterogeneity and intercellular crosstalk within the IPF microenvironment, we interrogated scRNA-seq data (GSE122960) utilizing Monocle 3 and CellChat algorithms. The functional essentiality of APOE was evaluated bridging computational virtual knockout (scTenifoldKnk) with laboratory in vitro assays. Specifically, downstream transcriptomic shifts and fibroblast activation capacities were validated using APOE-silenced THP-1 macrophages and a Transwell co-culture model with MRC-5 cells.

RESULTS: MR estimates indicated that genetic liability to AD is associated with a lower risk of developing IPF. Integrated profiling identified the lipid-metabolism gene APOE as a central hub, specifically enriched in lung macrophages. Pseudotime modeling captured a pathogenic bifurcation in IPF, where macrophages evolve toward a terminal state marked by profound oxidative phosphorylation defects and massive SPP1 secretion. These SPP1+ macrophages primarily activate fibroblasts via CD44 and integrin signaling axes. Furthermore, both virtual simulations and in vitro THP-1 experiments demonstrated that loss of APOE function triggers the hyperactivation of complement (C1QA) and antigen-presentation (HLA-DR) pathways. Co-culture assays ultimately confirmed that APOE ablation in macrophages strongly exacerbates myofibroblast differentiation (elevated α-SMA and collagen I) in adjacent MRC-5 cells.

CONCLUSION: APOE functions as a vital metabolic barrier against pro-fibrotic macrophage polarization in the lung. Disruption of this specific lipid metabolic network is strongly associated with SPP1-driven fibroblast activation and local immune imbalance, providing a theoretical framework that strictly warrants future in vivo investigation to determine its clinical relevance.

PMID:42682427 | PMC:PMC13529525 | DOI:10.3389/fimmu.2026.1904638

Acta Biochim Biophys Sin (Shanghai). 2026 Mar 25. doi: 10.3724/abbs.2025238. Online ahead of print.

ABSTRACT

The environmental pollutant benzo(a)pyrene (B(a)P), a representative polycyclic aromatic hydrocarbon (PAH), is a recognized carcinogen, and chronic pulmonary inflammation is closely associated with lung carcinogenesis. Although alveolar type 2 (AT2) cells are the origin of lung adenocarcinoma, the genetic and functional changes in AT2 cells and the mechanisms involved in inflammation-related lung tumorigenesis have not been elucidated. Here, C57BL/6J mice are exposed to B(a)P and the inflammatory irritant lipopolysaccharide (LPS) to establish a model of inflammation-related lung tumorigenesis. Single-cell RNA sequencing is performed on lung tissues. DNA mutations in AT2 cells are analyzed via whole-exome sequencing. The protein expression of AT2 cells in lung cancer tissue is determined by immunofluorescence staining. The results reveal that LPS promotes B(a)P-induced lung tumorigenesis; in the whole lungs of B(a)P/LPS, a decreased proportion, altered differentiation trajectory, and increased gene mutation number in AT2 cells are observed. Additionally, in B(a)P/LPS-treated lung cancer tissue, the levels of γ-H2AX DNA damage and the proliferation marker Ki67 in AT2 cells are increased, whereas the levels of differentiation markers are decreased. Single-cell RNA transcriptomics reveals that the autophagy-related genes Foxo3 and Ppp2r5, which are enriched in the PI3K-Akt pathway, and the autophagy-related genes in AT2 cells in lung cancer are decreased in the B(a)P/LPS group. Thus, chronic inflammation promotes DNA damage, gene mutation and dysfunction in AT2 cells, and decreased autophagy in AT2 cells may be an important mechanism for inflammation-related lung tumorigenesis.

PMID:41952558 | DOI:10.3724/abbs.2025238