*4.3. Statistical Analyses*

The results were analyzed by the GraphPad Prism 5 software (La Jolla, CA, USA). The data were expressed as mean ± SD. In vivo experiments: At least three separate experiments were performed for each measurement (*n* = total animals from the three experiments). The effects of hyperoxia exposure on ERK1/2 activation were assessed by *t*-test, whereas the effects of time-point and exposure on pulmonary vascularization were assessed using two-way ANOVA. In vitro experiments: At least three separate experiments were performed for each measurement. One-way ANOVA was used to determine the dose-dependent effects of PD98059 on cell proliferation and ERK1/2 phosphorylation, while a nonparametric test (Kruskal–Wallis test) was used to determine the dose-dependent effects of PD98059 on cell migration. The effects of PD98059 on tubule and mesh formation were determined by *t*-test. A *p* value of <0.05 was considered significant.

**Author Contributions:** R.T.M., A.K.S., R.B., and B.S. participated in the research design, performed data analysis, and contributed to the writing of the manuscript. R.T.M., A.K.S., and B.S. conducted the experiments.

**Acknowledgments:** We thank Pamela Parsons for her timely processing of histopathology slides. This work was supported by National Institutes of Health grants: HD-073323 to Binoy Shivanna and P30DK056338 to the Digestive Disease Center Core at Baylor College of Medicine, and grants from the American Heart Association BGIA-20190008, American Lung Association RG-349917, and Texas Children's Hospital Pediatric Pilot Award program to Binoy Shivanna.

**Conflicts of Interest:** The authors report no conflicts of interest, financial or otherwise in this work.
