PER2 and chronic obstructive pulmonary disease: The same study observed that the mRNA and protein levels of BMAL1, PER2, CRY1, and REV-ERBα were reduced in the peripheral blood mononuclear cells (PBMCs), lung tissue, and sputum cells of smokers and patients with chronic obstructive pulmonary disease (COPD) compared to non-smokers (77).