COL1A2 and chronic obstructive pulmonary disease: Post-PR collagen type I and type IV total protein and mRNA (COL1A2 and COL4A1, respectively) expression was significantly increased in nonatrophic patients with COPD (figure 2); no significant changes were observed in response to PR in mRNA (COL1A2 or COL4A1) or protein expression in atrophic patients with COPD (figure 2).