Similar to the mRNA analysis in human skeletal muscle from active smokers,11 signficant elevations in the mRNA levels of the AHR, CYP1B1, AHRR, as well as a trending increase in CYP1A1 (P = 0.0645) and decrease in VEGFA (Figure 1A) provide evidence of AHR activation in skeletal muscle of patients with COPD. Here, CYP1B1 is linked to chronic obstructive pulmonary disease.