Early Life Sex Differences and Alterations in Mitochondrial Function in IUGR Offspring after Weaning may Contribute to Adult Sex Differences in Cerebrovascular Dysfunction and Hypertension in Rodents


Background: Preeclampsia is a hypertensive pregnancy disorder that usually occurs in the third trimester. Preeclampsia, due to placental ischemia, decreases nutrient and oxygen delivery to the fetus, causing intrauterine growth restriction (IUGR). IUGR increases the risk for chronic conditions such as cerebrovascular dysfunction (CVD) and hypertension (HTN). Human and animal studies show sex differences in CVD and HTN development in IUGR offspring, with males exhibiting a higher prevalence of both. Preliminary data from our lab showed that 17-week-old IUGR male rodents developed CVD, HTN and mitochondrial dysfunction (mtDYS), while IUGR female rodents only developed CVD. The reason for these sex differences is unknown but may be attributed to mtDYS. Although mitochondrial differences appear at 17 weeks, earlier mitochondrial function is unknown. This study investigates changes in mitochondrial function in IUGR offspring after weaning. We hypothesize that mtDYS is elevated in3-week-old IUGR rodent offspring, with greater dysfunction in IUGR males.

Methods: Pregnant Sprague Dawley rats were divided into two groups: normal pregnant (NP) and preeclamptic pregnant rats, which underwent reduced uterine perfusion pressure (RUPP) surgery on gestational day 14. RUPP dams gave birth to IUGR offspring, and NP dams gave birth to control (CON) offspring. After 3 weeks of weaning, offspring were separated by sex and dam pregnancy status. Brains were collected from the following groups: IUGR males (n=6), IUGR females (n=6), CON males (n=4), and CON females (n=6) to measure mitochondrial function via respiration, electron transport chain (ETC) protein amounts, and mitochondrial dynamics of fission (DRP-1) and fusion (MFN-1) proteins. Mitochondrial respiration was assessed using the Oroboros Oxygraph O2K. Protein amounts of ETC complexes (I-V), DRP-1, and MFN-1 were quantified using Western blots.

Results: 3-week-oldIUGR females had increased cerebral mitochondrial respiration suggested by State 3 (490.41 ± 49.85 vs 257.32 ± 69.76pmol O2/sec/mg; p=0.02) and increased protein amounts of ETC Complex I (135.91 ± 9.27 vs 107.77 ± 4.23IU/Protein/CON%; p=0.02) and Complex III (141.76 ± 13.99 vs 110.43 ± 7.73IU/Protein/CON%; p=0.07). MFN-1 protein amounts (133.42 ± 18.75 vs 84.67 ± 6.89IU/Protein/CON%; p=0.03) and DRP-1 protein amounts (111.31 ± 1.89 vs 95.24 ± 2.14IU/Protein/CON%; p<0.0003) were increased in IUGR compared to CON females. Conversely, 3-week-old IUGR males showed decreased cerebral mitochondrial respiration in Basal state (21.48±5.49 vs 55.79 ± 6.96pmol O2/sec/mg; p=0.03) and State 2 (146.22 ± 25.55 vs 224.70 ± 23.13pmol O2/sec/mg; p=0.13). DRP-1 protein amounts were decreased in IUGR males (85.72 ± 3.07 vs 110.18 ± 1.82IU/Protein/CON%; p=0.02), with no changes in mitochondrial ETC complexes or MFN-1 protein amounts compared to CON males.

Conclusion: Early on, IUGR females show mitochondrial function, while IUGR males display mtDYS. Furthermore, the mtDYS in IUGR males at 3 weeks may contribute to HTN development observed in IUGR males and not IUGR females at 17 weeks of age. Future studies are warranted to investigate mtDYS and HTN development in IUGR males and possible protective mechanisms in IUGR females. This study highlights sex differences in cerebral mitochondrial function in prepubescent IUGR offspring, offering insight into the pathophysiology of HTN and CVD development in adulthood, along with suggestions for novel therapeutic targets to prevent HTN and CVD in adult IUGR offspring.