Two sides to every story: mitochondria as critical mediators of the divergent cerebrovascular responses to experimental stroke in male versus female rats
Authors: Rutkai Ibolya , Merdzo Ivan , Wunnava Sanjay , Curtin Genevieve , Katakam Prasad V. , Busija David W. 
Published: November 2023

Vascular mitochondria play a complicated role in the regulation of cerebrovascular function. We have shown a greater mitochondrial respiration, protein expression, and mitochondria‐derived vasodilation in isolated cerebral arteries from female (FR) compared with male (MR) rats. Furthermore, we have found a preserved mitochondria‐derived vasodilation in MR middle cerebral arteries (MCAs) from the ischemic (Ipsi) side 48 h after transient middle cerebral artery occlusion (tMCAO) when compared with arteries form the contralateral (Contra) side. The vasoconstrictor and vasodilator properties to non‐mitochondrial factors of the MR Ipsi MCAs were severely diminished in comparison with the Contra side. To further examine the role of sex‐differences in determining the outcome of ischemia‐reperfusion (I/R) injury, we examined whether estrogen mediates cerebrovascular protection against tMCAO via altering mitochondrial function.

We measured infarct size visualized by TTC staining, mitochondrial respiration measured by the Seahorse Bioscience Analyzer, and calcium sparks activity determined with confocal microscopy in freshly isolated MCAs from 8 – 10 week old FR and MR Sprague Dawley rats following exposure to 90 min of tMCAO followed by 48 h reperfusion.

The infarct size was significantly smaller by 28.62 % in the FR group compared with MR (P < 0.05). Mitochondrial oxygen consumption rate (OCR; pM/minute/μg protein) was similar in the FR Ipsi versus (vs) Contra sides suggesting no functional effect after tMCAO (non‐mitochondrial respiration 44.2 ± 7.9 vs. 39.6 ± 9.3; proton leak 116 ± 27.5 vs. 70.4 ± 14.9; ATP production 50.5 ± 7.2 vs. 47.9 ± 8.6; basal respiration 122.3 ± 28.3 vs. 78.8 ± 12.7; maximal respiration 216.2 ± 46.9 vs. 182 ± 38.7; and spare respiratory capacity 93.9 ± 23.8 vs. 103.2 ± 27.9; respectively). Interestingly, I/R resulted in an increase in the mitochondrial OCR in MR Ipsi in comparison with the MR Contra side (non‐mitochondrial respiration: 148.3 ± 13.9 vs. 96.6 ± 10.7; proton leak: 232 ± 53.7 vs. 183.3 ± 36.7; ATP production: 209.5 ± 21.45 vs. 69.3 ± 24.9; basal respiration: 293.2 ± 64.82 vs. 156 ± 26.6; maximal respiration: 691.1 ± 129.4 vs. 416.8 ± 55.3; and spare respiratory capacity: 397.9 ± 80.12 vs. 260.8 ± 45.7; respectively). Ca2+ sparks activity (Ca2+ sparks number/10 μm) was not affected by I/R at baseline level in the FR groups, whereas it resulted in a significant decrease in the MR Ipsi group when compared with MR Contra or with the FR groups (FR: 0.09 ± 0.01 and 0.07 ± 0.02 vs. MR: 0.02 ± 0.004 and 0.06 ± 0.01; respectively).

Our results indicate that estrogen‐mediates protection against I/R might occur by suppressing mitochondrial respiration, whereas the lack of this pattern in male Ipsi MCAs leads to an acute stress response after I/R, manifesting in a possibly energetically inappropriate mitochondrial respiration.

Support or Funding Information

This work was supported by National Institutes of Health grants (DWB: HL‐077731and HL093554), Louisiana Board of Regents Support Fund‐Research Competitiveness Subprogram (PVK: LEQSF(2014‐17)‐RD‐A‐11), American Heart Association National Center NRCP Scientist Development Grant (PVK: 14SDG20490359), and American Heart Association Post‐Doctoral Fellowship Grant (IR: 15POST23040005). This research was also supported by the Louisiana Board of Regents Endowed Chairs for Eminent Scholars program (DWB).