HIF1A and chronic obstructive pulmonary disease: Interestingly, this mouse (rtTATg+/HIF-1αTg+), when treated with doxycycline starting at the age of 6 weeks, developed an emphysematous lung phenotype with alveolar wall destruction and an abnormal enlargement of alveolar spaces compared to its transgene-negative control littermate (rtTATg+/HIF-1αTg−) (Figure 4C, 4D, and Supplementary Figure 3), suggesting a role for HIF-1α in COPD pathogenesis.