HHIP and chronic obstructive pulmonary disease: Two recent single cell RNA sequencing studies in lung tissue obtained from individuals with severe COPD and healthy individuals identified a distinct epithelial subpopulation in the alveolar niche that expressed hedgehog interacting protein (HHIP) and a ciliated epithelial cell population in peripheral lung parenchyma that expressed fibrosis associated proteins, Insulin Like Growth Factor Binding Protein 5 (IGFBP5) and protein quaking (QKI) [79].