Long‐term Effect of a Post‐natal Hyperoxia on Cardiac Autophagy
Authors: Hopp Alexandria L , Tetri Laura Hope , Kumari Santosh , Haraldsdottir Kristin , Pegelow David F , Braun Rudolf K , Gross Kara N , Eldridge Marlowe W 
Published: November 2023

Introduction

Bronchopulmonary dysplasia (BPD) is a chronic lung disease affecting pre‐term infants characterized by decreased alveolarization and impaired vascular development, and may contribute to the development of pulmonary hypertension (PH) and subsequent right ventricular dysfunction. Currently, little is known about the long‐term cardiac outcomes of individuals with BPD. The aim of this project is to evaluate markers of autophagy and apoptosis in the right ventricle of aged rats exposed to brief postnatal hyperoxia. We hypothesize that the right ventricle from rats exposed to postnatal hyperoxia will demonstrate decreased or impaired autophagy with age.

Methods

Sprague‐Dawley rats were exposed to either 85% oxygen (HYP) (n=12, 6 males) or 21% oxygen (CTL) (n=8, 3 males) for 14 days within 12 hours following birth. After 14 days, these animals were allowed to age out for one year in room air. At one year, the rats were sacrificed and tissues collected. Markers of autophagy and apoptosis (BCL2, Bax, Beclin‐1, LC3B, LAMP2, and P62) in the right ventricle were evaluated using Western Blot analysis. Statistical analysis was done via t‐test.

Results

Aged HYP rats demonstrate a persistent right ventricular hypertrophy, with the right ventricle to left ventricle plus septum ratio significantly elevated compared to CTL rats (0.21 ± 0.02 CTL versus 0.25 ± 0.03 HYP, p=0.002). Beclin‐1, a protein necessary for nucleation of autophagosomes, is significantly upregulated in HYP as compared to CTL (46580±1405 CTL HYP versus 34633±3008, p=.004). LC3B, a protein needed for elongation of autophagosomes, is significantly downregulated in HYP rats than in CTL rats (.036 ± .001 HYP versus .052 ±.006 CTL, p=.01). Lamp2, a membrane bound lysosomal protein needed for phagosomal and autophagsomal maturation, is significantly downregulated in HYP compared to CTL (.01 ± .0008 HYP versus .017 ± .001 CTL, p=.001). p62 and Bax were not significantly different in the right ventricles of HYP as compared to CTL.

Conclusion

The purpose of this study was to determine if there are effects of post‐natal hyperoxic exposure in the right ventricle at one year of age. We found that the elevated Fulton Index persists which has previously been associated with pulmonary hypertension and right ventricular dysfunction. The significant upregulation of beclin‐1 in the aged HYP right ventricles suggests that there is an increase in autophagic activation. However, the downregulation of LC3B and LAMP2 in HYP may represent impaired phagosomal maturation and an accumulation of autophagosomes consistent with impaired completion of autophagy. The data suggests that while there is significant right ventricular hypertrophy and an upregulation of autophagic activation, this autophagy may not be completed in rats exposed to hyperoxia.

Support or Funding Information

Funding source: NHLBI, R01 HL115061‐03, Suppl (Eldridge) & NHLBI, R01 HL115061 (Eldridge)