State Key Laboratory of Respiratory Disease, National Clinical Research Center for Respiratory Disease, Guangzhou Institute of Respiratory Health.
Department of Nuclear Medicine, and.
Am J Respir Crit Care Med. 2023 Jan 15;207(2):160-172. doi: 10.1164/rccm.202110-2414OC.
Sustained activation of lung fibroblasts and the resulting oversynthesis of the extracellular matrix are detrimental events for patients with interstitial lung diseases (ILDs). Lung biopsy is a primary evaluation technique for the fibrotic status of ILDs, and is also a major risk factor for triggering acute deterioration. Fibroblast activation protein (FAP) is a long-known surface biomarker of activated fibroblasts, but its expression pattern and diagnostic implications in ILDs are poorly defined. The present study aims to comprehensively investigate whether the expression intensity of FAP could be used as a potential readout to estimate or measure the amounts of activated fibroblasts in ILD lungs quantitatively. FAP expression in human primary lung fibroblasts as well as in clinical lung specimens was first tested using multiple experimental methods, including real-time quantitative PCR (qPCR), Western blot, immunofluorescence staining, deep learning measurement of whole slide immunohistochemistry, as well as single-cell sequencing. In addition, FAP-targeted positron emission tomography/computed tomography imaging PET/CT was applied to various types of patients with ILD, and the correlation between the uptake of FAP tracer and pulmonary function parameters was analyzed. Here, it was revealed, for the first time, FAP expression was upregulated significantly in the early phase of lung fibroblast activation event in response to a low dose of profibrotic cytokine. Single-cell sequencing data further indicate that nearly all FAP-positive cells in ILD lungs were collagen-producing fibroblasts. Immunohistochemical analysis validated that FAP expression level was closely correlated with the abundance of fibroblastic foci on human lung biopsy sections from patients with ILDs. We found that the total standard uptake value (SUV) of FAP inhibitor (FAPI) PET (SUVtotal) was significantly related to lung function decline in patients with ILD. Our results strongly support that and detection of FAP can assess the profibrotic activity of ILDs, which may aid in early diagnosis and the selection of an appropriate therapeutic window.
肺成纤维细胞的持续激活以及细胞外基质的过度合成是间质性肺疾病（ILDs）患者的不利事件。肺活检是ILD 纤维化状态的主要评估技术，也是引发急性恶化的主要危险因素。成纤维细胞激活蛋白（FAP）是一种已知的激活成纤维细胞的表面生物标志物，但它在ILDs 中的表达模式和诊断意义尚不清楚。本研究旨在全面研究 FAP 的表达强度是否可作为潜在的读数，用于定量估计或测量ILD 肺部激活成纤维细胞的数量。首先使用多种实验方法测试了 FAP 在人原代肺成纤维细胞和临床肺标本中的表达，包括实时定量 PCR（qPCR）、Western blot、免疫荧光染色、全切片免疫组化的深度学习测量以及单细胞测序。此外，还应用 FAP 靶向正电子发射断层扫描/计算机断层扫描成像 PET/CT 对各种类型的 ILD 患者进行了检测，并分析了 FAP 示踪剂摄取与肺功能参数之间的相关性。首次揭示，在低剂量促纤维化细胞因子作用下，肺成纤维细胞激活事件的早期，FAP 表达显著上调。单细胞测序数据进一步表明，ILD 肺中的几乎所有 FAP 阳性细胞都是产生胶原蛋白的成纤维细胞。免疫组织化学分析验证了 FAP 表达水平与 ILD 患者肺活检切片中成纤维细胞灶的丰度密切相关。我们发现 FAP 抑制剂（FAPI）PET 的总标准摄取值（SUVtotal）与 ILD 患者的肺功能下降显著相关。我们的研究结果强烈支持 FAP 的检测可以评估 ILD 的促纤维化活性，这可能有助于早期诊断和选择合适的治疗窗。
