COL1A1 and idiopathic pulmonary fibrosis: HMGA2 is regulated by 33 other miRNAs, including let-7d, which is downregulated in the lungs of IPF patients [81] Lastly, along with its canonical role in targeting SMAD3 [69], miR-29 also targets the mRNA encoding type I collagen (COL1A1), which is a key component of scar tissue [82].