Sex Differences in Senescence‐Related Gene Expression in a Rat Model of Bronchopulmonary Dysplasia

Rationale Bronchopulmonary dysplasia (BPD) is the most common complication of preterm birth. It is induced by hyperoxia exposure during the vulnerable saccular or early alveolar stage of lung development resulting in an arrest of alveolarization. Oxidative stress in the immature lung induced by this oxygen supplementation causes oxidative modifications leading to the initiation of senescence in damaged cells. A hallmark feature of senescence is persistent cell‐cycle arrest that is unresponsive to extrinsic or environmental growth factor induction. The senescence arrest is stringent; it is established and maintained by at least 2 major tumor suppressor pathways: the proteins p53/p21 and the p16Ink4a/retinoblastoma protein (pRb). We hypothesized that senescence is induced by hyperoxia exposure and has long term impacts in aged rats. Methods Newborn Sprague Dawley rats were exposed to hyperoxia (HYP, 85%, n = 13) or normoxia (NORM, 21%, n = 9) for 14 days and then normoxic conditions until one year of age. Pulmonary function was tested at day 14 and at age 1 year. Also, at age 1 year, the left lung was inflated and fixed (4% formaldehyde), the right lobes were flash frozen. Pulmonary tissue was kept at −80□ until analyzed for mRNA expression of proteins p16, p21, p53, and interleukin IL‐6 via qPCR. Differences in expression were calculated by the ddCt method using the reference gene GAPDH. Collagen levels were assessed in normoxia and hyperoxia rats using a colorimetric assay. Masson's trichrome staining was utilized to visualize collagen in histology lung slides. Two‐way ANOVA was utilized for comparison of ddCt values between sexes in HYP and NORM rats for each target gene. Results Lung compliance at day 14 was strongly reduced in HYP rats compared to NORM rats. At one year, compliance was reduced in female HYP compared to female NORM rats. In contrast, HYP males showed increased compliance compared to NORM males. Day 14 HYP rats showed a higher increase in p16, and a smaller increase in p21 and IL‐6 mRNA expression compared to NORM rats. At one year, male HYP males showed an increased p16 expression compared to NORM males, whereas HYP females showed increased p21 expression compared to NORM females. p53 expression did neither display a gender difference nor a change over time. The expression of p16 was significantly greater and the expression of p21 was significantly smaller in HYP males compared to HYP females (p<0.01). Total lung collagen levels were significantly higher in 1 year‐old HYP females compared to NORM females with clear histologic interstitial collagen deposition. One year‐old HYP males did not show a difference in total collagen between the two exposure groups. Conclusion At day 14 of neonatal rat hyperoxia exposure there is a similar upregulation of senescence markers in the lung between males and females. However, at one year, sex difference is presented with elevated p21 expression in female rats associated with reduced lung compliance and elevated lung collagen. p16 expression in HYP males is high at day 14 and remains highly expressed at 1 year. These data suggest that lung aging is accelerated in HYP rats. Moreover, there are sex differences in the mechanisms of the accelerated lung aging. Support or Funding Information National Heart Lung and Blood Institute grant: R01 HL115061‐01 This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .