MMP9 and bronchopulmonary dysplasia: Some genes showed greater positive association with the progression of BPD including MMP25, MMP9, SIRPA, CKAP4, SLCO4C1, and SLC2A3. The red module contained genes showing greater negative association with the progression of BPD including LEF1, ITK, CD6, RASGRP1, IL7R, SKAP1, CD3E, and ICOS. These genes can be considered as hub genes and also play important roles in other co-expression modules.