Sex dependent alterations in mitochondrial electron transport chain proteins following neonatal rat cerebral hypoxic-ischemia

Abstract

Males are more susceptible to brain mitochondrial bioenergetic dysfunction following neonatal cerebral hypoxic-ischemia (HI) than females. Mitochondrial biogenesis has been implicated in the cellular response to HI injury, but sex differences in biogenesis following HI have not been described. We tested the hypothesis that mitochondrial biogenesis or the expression of mitochondrial electron transport chain (ETC) proteins are differentially stimulated in the brains of 8 day old male and female rats one day following HI, and promoted by treatment with acetyl-L-carnitine (ALCAR). There were no sex differences in mitochondrial mass, as reflected by the ratio of mitochondrial to nuclear DNA (mtDNA/nDNA) and citrate synthase enzyme activity present one day following HI or sham surgery. There was an increase in mtDNA/nDNA, however, in the hypoxic and ischemic (ipsilateral) hemisphere after HI in both male and female brains at one day post-injury, which was suppressed by ALCAR. Citrate synthase activity was increased in the ipsilateral hemisphere of ALCAR treated male and female brain. Most importantly, the levels of representative mitochondrial proteins present in ETC complexes I, II and IV increased substantially one day following HI in female, but not male brain. This sex difference is consistent with the increase in the mitochondrial biogenesis-associated transcription factor NRF-2/GABPα following HI in females, in contrast to the decrease observed with males. In conclusion, the female sex-selective increase in ETC proteins following HI may at least partially explain the relative female resilience to mitochondrial respiratory impairment and neuronal death that occur after HI.

Neonatal Hypoxia Ischaemia: Mechanisms, Models, and Therapeutic Challenges

“…This sex difference has also been replicated in rodent in vitro models of hypoxic cell death (Zhu et al, 2006; Nijboer et al, 2007; Du et al, 2009). Although many molecular mechanisms are currently under investigation, this sexual dimorphism remains largely unexplained (Hill and Fitch, 2012; Chavez-Valdez et al, 2014; Demarest et al, 2016a,b; Waddell et al, 2016). Therefore, the unique state of the developmental brain should always be at the forefront of the researcher’s minds.…”

l-Carnitine and Acetyl-l-carnitine Roles and Neuroprotection in Developing Brain

“…The effects of neonatal HI have been widely studied in the postnatal day 7 rat pup using the Rice-Vannucci method of carotid artery ligation combined with 8% O 2 [37, 39, 138–145]. Our studies using 75 minutes exposure to 8% O 2 result in a moderate injury and evidence of more impairment in male pups compared to females [39, 146, 147]. Our group has determined the neuroprotective effects of ALCAR (100 mg/kg administered by subcutaneous injection) at 0, 4, 24 and 48 hours after HI on postnatal day 7.…”

“…Treatment with ALCAR after HI decreased the significant increase in protein carbonyl formation that was found only in the brain of male pups in both hemispheres of the cerebral cortex, hippocampus and perirhinal cortex [38]. Using the postnatal day 7 rat pup model of HI described above, Demarest et al [146] determined the effects of ALCAR on mitogenesis in brain. Pups treated with ALCAR after HI had a significant increase in the activity of citrate synthase in the ipsilateral hemisphere compared to sham pups and controls.…”

“…Pups treated with ALCAR after HI had a significant increase in the activity of citrate synthase in the ipsilateral hemisphere compared to sham pups and controls. HI led to a significant increase in the ratio of mitochondrial DNA to nuclear DNA (mtDNA/nDNA), in the ipsilateral side of brain in both male and female rat pups following HI [146]. This increase in mtDNA/nDNA ratio was prevented by treatment with ALCAR after HI; treated rats had ratios comparable to shams.…”

“…This increase in mtDNA/nDNA ratio was prevented by treatment with ALCAR after HI; treated rats had ratios comparable to shams. Electron transport chain subunits of Complex I, II and IV were upregulated in female brain, but not in male brain following HI; treatment with ALCAR after HI had no effect on the level of the oxidative phosphorylation proteins [146]. …”