Intro: Impaired mitochondrial function plays a role in graft dysfunction after transplant, and recovery is facilitated by mitochondrial quality control (MQC). Two key elements of MQC are mitochondrial biogenesis and mitophagy (degradation of dysfunctional mitochondria). The peroxisome proliferator-activated receptor gamma coactivator 1-α (PGC-1α) co-activator regulates mitochondrial biogenesis, and may also play a role in mitophagy. We hypothesized that, in syngenic heterotopic mouse heart transplant (HMHT), PGC-1α knockout would decrease both mitochondrial biogenesis and mitophagy, increasing tissue damage and graft dysfunction.

Methods: With Institutional Animal Use approval, syngenic HMHT was with donor hearts from either BL/6 wild type (WT) or PGC-1α heterozygote (+/-) mice. Recipients were littermate BL/6 WT; non-surgical hearts were controls (0h). Functional assessment was by graft palpation (0-4). 24h and 7d after HMHT, donor WT or PGC-1α+/- hearts were fixed for fluorescence immunohistochemistry or flash frozen for myeloperoxidase (MPO) assay and western blot(n=3/group). Protein markers of mitophagy were quantified (PINK1, parkin, and LC3-II and I]). TUNEL allowed % apoptotic nuclei quantification. Fluorescence intensity (FI) was quantified for citrate synthase (CS), a surrogate for mitochondrial density. ANOVA with post-hoc Tukey-Kramer HSD was used for PGC-1α+/- vs. WT hearts at 0h, 24h, and 7d (p<0.05 significant).

Results: MPO and TUNEL assays showed increased oxidative stress and cell death at 7d in PGC-1α+/- (vs. WT, MPO: 0.15 vs. 0.11 OD/min/mg @24h, 0.10 vs. 0.05 @7d, p=NS; TUNEL: p=NS @24h; p=0.04 @7d). CS FI decreased in both PGC-1α+/- and WT, but was lower in PGC-1α+/- at both 24h and 7d (vs. WT, p=0.02 @24h; p=0.03 @7d). PINK1 decreased after HMHT, but was lower at 24h for PGC-1α+/- (vs. WT, p=0.005). Parkin decreased in WT, but was lower for PGC-1α+/- (vs. WT, p<0.001 @0h, 24h, 7d). The LC3 II/I ratio and graft function palpation were similar for PGC-1α+/- vs. WT (p=NS).

Conclusion: Syngenic HMHT imparts oxidative stress and results in decreased mitochondrial density, due to lack of physiologic afterload; this is pronounced in PGC-1α+/-, consistent with decreased mitochondrial biogenesis. Mitophagy markers are also decreased in PGC-1α+/-, suggesting an additional role in MQC. Identification of post-translational modifications and subcellular locations will clarify the role of PGC-1α in mitophagy.

CITATION INFORMATION: Cherry A., Porter K., Suliman H., Wang J., Mulvihill M., Kirk A. Mitochondrial Quality Control through PGC-1α in Syngenic Mouse Heart Transplant Am J Transplant. 2017;17 (suppl 3).

« Back to 2018 American Transplant Congress