探討新生肺SSEA-1+前驅幹細胞之特徵及與免疫微環境之互動關係

Abstract

幹細胞/前驅幹細胞 (Stem/progenitor cells) 具備有自我更新以及可分化出多種細胞型態的能力，因此於再生醫學領域中備受關注。在過往的研究中指出，肺部有一群上皮細胞表現有幹細胞的標誌物 stage-specific embryonic antigen-1 (SSEA-1), 肺SSEA-1+ 細胞 (pulmonary SSEA-1+ cells)。相較於成年 (adult) 小鼠，新生兒 (neonatal) 階段的小鼠蘊含有較多的 pulmonary SSEA-1+ cells 的細胞群體。為探究此間差異，本篇研究進一步探討 neonatal 以及 adult pulmonary SSEA-1+ cells 的差異。透過類器官 (organoid) 的建構，結果顯示 neonatal pulmonary SSEA-1+ cells 具備有較旺盛的幹細胞/前驅幹細胞特性。Neonatal pulmonary SSEA-1+ cells 可發育成結構類似於氣管 (airway)、支氣管肺泡 (bronchoalveolar) 以及肺泡 (alveolar) 的類器官，這結果也顯示 neonatal pulmonary SSEA-1+ cells 同時具備了發育氣管與肺泡上皮細胞的能力。此外研究觀察到 fibroblast growth factor 7 的作用可促進 neonatal pulmonary SSEA-1+ cells 的幹細胞/前驅幹細胞活性，增加類器官的生成並且增加肺泡類器官的發育。進一步地透過無細胞的肺葉或氣管損傷的小鼠…等實驗模式，均可觀察到 neonatal pulmonary SSEA-1+ cells 在肺組織中的貼附、發育與修補。這些結果顯示 neonatal pulmonary SSEA-1+ cells 應用於再生醫學的潛力。此外許多研究指出新生小鼠的肺部微環境偏向於第二型免疫反應，雖然此時過敏原的暴露會增加過敏性氣喘發生的機率，但第二型免疫反應對於新生兒肺部的發育知之甚少。為探討新生兒肺部發育與免疫微環境的關聯性，研究設計在neonatal pulmonary SSEA-1+ cells 發育成類器官的過程中給予 IL-4 與 IL-13 的刺激。實驗結果顯示短暫的 IL-4/IL-13 的作用可增加 neonatal pulmonary SSEA-1+ cells 幹細胞/前驅幹細胞的活性，提高類器官的生成並且發育出正常的氣管類器官。然而當 neonatal pulmonary SSEA-1+ cells 持續地受到 IL-4/IL-13 的刺激，纖毛上皮細胞的分化則會受到抑制，而粘液 (mucus) 的生成反而增加，顯示上皮細胞的發育產生失衡。進一步研究顯示，IL-4/IL-13 透過 STAT6 訊息傳遞途徑刺激 neonatal pulmonary SSEA-1+ cells 的細胞增生與細胞分化反應。因此在新生兒階段，短暫誘發的第二型免疫反應有助於肺的生長，然而當此發炎反應未受到完善的調控，反而會造成肺部上皮細胞的發育失衡。本篇研究果驗證 neonatal pulmonary SSEA-1+ cells 具備有幹細胞/前驅幹細胞的能力，而肺部免疫微環境的變化更進一步地調控 neonatal pulmonary SSEA-1+ cells的幹細胞/前驅幹細胞能力，引導著肺部上皮細胞的發育。

Stem/progenitor cells, because of their self-renewal and multiple cell type differentiation abilities, have good potential in regenerative medicine. We previously reported a lung cell population that expressed the stem cell marker SSEA-1 was abundant in neonatal but scarce in adult mice. The current study further characterized the stem/progenitor property of neonatal and adult mouse lung-derived SSEA-1+ cells. The results showed that the neonatal pulmonary SSEA-1+ cells exhibited enhanced ability in organoid generation compared to those of adult cells, suggesting the stem/progenitor activity is increased in the neonatal stage. The neonatal pulmonary SSEA-1+ cells generated airway-like, bronchoalveolar-like, and alveolar-like organoids that suggested the multilineage cell differentiation ability. In addition, fibroblast growth factor 7 facilitated the activity of neonatal pulmonary SSEA-1+ cells in organoid generation with increased alveolar cell differentiation. Furthermore, neonatal pulmonary SSEA-1+ cells could colonize and develop in the decellularized and injured lungs. These results demonstrated the stem/progenitor property of lung-derived neonatal-stage SSEA-1+ cells that suggested the potential for regenerative medicine. In addition, studies have revealed that the type 2 immunity is transiently increased in neonatal lungs. However, little is known about the effect of type 2 immunity on postnatal lung development. For this purpose, the neonatal lung-derived SSEA-1+ cells were cultured with IL-4/IL-13 during the organoid development. Results showed that short-term exposed the cells with IL-4/IL-13 could enhance the stem/progenitor activity for the organoid generation with normal epithelium development. However, extended IL-4/IL-13 stimulation resulted in decreased ciliated cell differentiation and increased mucus accumulation, suggesting the impairment of epithelial homeostasis. The IL-4 and IL-13 were signaled through STAT6 to mediate the cell proliferation and cell differentiation of the neonatal pulmonary SSEA-1+ cells. The results suggested that the transiently higher type 2 immunity in postnatal lungs plays a role to facilitate neonatal lung growth, but the excessive inflammation leads to abnormal epithelium development. Collectively, we observed the cell population and the stem/progenitor activity of pulmonary SSEA-1+ cells are enriched in the neonatal stages. Moreover, the IL-4/IL-13 further enhanced the stem/progenitor activity of neonatal pulmonary SSEA-1+ cells. Our results suggested the interactions of the pulmonary stem/progenitor cells with their immune environment to mediate neonatal lung growth and development.