Stripp Barry R, Reynolds Susan D
Division of Pulmonary, Allergy, and Critical Care, Duke University Medical Center, 2075 MSRBII, 106 Research Drive, DUMC Box 103000, Durham, NC 27710, USA.
Proc Am Thorac Soc. 2008 Apr 15;5(3):328-33. doi: 10.1513/pats.200711-167DR.
Bronchioles of the distal conducting airway are lined by a simple epithelium composed primarily of nonciliated secretory (Clara) cells and ciliated cells. These cells are long-lived in the normal lung; renewal is mediated by cells that constitute a nonclassical stem cell hierarchy. Within this type of hierarchy, facultative progenitor cells are responsible for normal epithelial maintenance and rare adult tissue-specific stem cells are activated only in response to depletion of the facultative progenitor cell pool. This organizational structure is a departure from the classical stem cell hierarchies that maintain rapidly renewing tissues such as the epithelium of the small intestine. This article compares cellular and molecular mechanisms of epithelial renewal in the relatively quiescent bronchiolar epithelium and in the mitotically active intestinal epithelium. Fundamental distinctions between stem cell hierarchies of slowly and rapidly renewing epithelia are highlighted and may provide insight into tissue-specific interpretation of signals that mediate repair in some tissues but lead to remodeling and chronic disease in other organ systems.
远端传导气道的细支气管由主要由无纤毛分泌（克拉拉）细胞和纤毛细胞组成的单层上皮排列。这些细胞在正常肺中寿命较长；更新由构成非经典干细胞层级的细胞介导。在这种层级类型中，兼性祖细胞负责正常上皮维持，罕见的成年组织特异性干细胞仅在兼性祖细胞池耗尽时才被激活。这种组织结构不同于维持快速更新组织（如小肠上皮）的经典干细胞层级。本文比较了相对静止的细支气管上皮和有丝分裂活跃的肠上皮中上皮更新的细胞和分子机制。强调了缓慢更新和快速更新上皮的干细胞层级之间的根本区别，这可能有助于深入了解介导某些组织修复但在其他器官系统中导致重塑和慢性疾病的信号的组织特异性解读。
