Ablation of Cyclophilin D Results in an Activation of FAK, Akt, and ERK Pathways in the Mouse Heart

Improved exercise capacity in cyclophilin-D knockout mice associated with enhanced oxygen utilization efficiency and augmented glucose uptake via AMPK-TBC1D1 signaling nexus

We previously reported in HEK 293T cells that silencing the mitochondrial peptidyl prolyl isomerase cyclophilin-D (Cyp-D) reduces Vo2. We now report that in vivo Cyp-D ablation using constitutive Cyp-D knockout (KO) mice also reduces Vo2 both at rest (∼15%) and during treadmill exercise (∼12%). Yet, despite Vo2 reduction, these Cyp-D KO mice ran longer (1071 ± 77 vs. 785 ± 79 m; P = 0.002), for longer time (43 ± 3 vs. 34 ± 3 min; P = 0.004), and at higher speed (34 ± 1 vs. 29 ± 1 m/s; P ≤ 0.001), resulting in increased work (87 ± 6 vs. 58 ± 6 J; P ≤ 0.001). There were parallel reductions in carbon dioxide production, but of lesser magnitude, yielding a 2.3% increase in the respiratory exchange ratio consistent with increased glucose utilization as respiratory substrate. In addition, primary skeletal muscle cells of Cyp-D KO mice subjected to electrical stimulation exhibited higher glucose uptake (4.4 ± 0.55 vs. 2.6 ± 0.04 pmol/mg/min; P ≤ 0.001) with enhanced AMPK activation (0.58 ± 0.06 vs. 0.38 ± 0.03 pAMPK/β-tubulin ratio; P ≤ 0.01) and TBC1 (Tre-2/USP6, BUB2, Cdc16) domain family, member 1 (TBC1D1) inactivation. Likewise, pharmacological activation of AMPK also increased glucose uptake (3.2 ± 0.3 vs. 2.3 ± 0.2 pmol/mg/min; P ≤ 0.001). Moreover, lactate and ATP levels were increased in these cells. Taken together, Cyp-D ablation triggered an adaptive response resulting in increased exercise capacity despite less oxygen utilization associated with increased glucose uptake and utilization involving AMPK-TBC1D1 signaling nexus.-Radhakrishnan, J., Baetiong, A., Kaufman, H., Huynh, M., Leschinsky, A., Fresquez, A., White, C., DiMario, J. X., Gazmuri, R. J. Improved exercise capacity in cyclophilin-D knockout mice associated with enhanced oxygen utilization efficiency and augmented glucose uptake via AMPK-TBC1D1 signaling nexus.

Cyclophilin D knockout protects the mouse kidney against cyclosporin A-induced oxidative stress

Mitochondrial dysfunction and oxidative stress have been implicated in cyclosporin A (CsA)-induced nephrotoxicity. CsA interacts with cyclophilin D (CypD), an essential component of the mitochondrial permeability transition pore and regulator of cell death processes. Controversial reports have suggested that CypD deletion may or may not protect cells against oxidative stress-induced cell death. In the present study, we treated wild-type (WT) mice and mice lacking CypD [peptidylprolyl isomerase F knockout (Ppif-/-) mice] with CsA to test the role and contribution of CypD to the widely described CsA-induced renal toxicity and oxidative stress. Our results showed an increase in the levels of several known uremic toxins as well as the oxidative stress markers PGF2α and 8-isoprostane in CsA-treated WT animals but not in Ppif-/- animals. Similarly, a decline in S-adenosylmethionine and the resulting methylation potential indicative of DNA hypomethylation were observed only in CsA-treated WT mice. This confirms previous reports of the protective effects of CypD deletion on the mouse kidney mediated through a stronger resistance of these animals to oxidative stress and DNA methylation damage. However, a negative effect of CsA on the glycolysis and overall energy metabolism in Ppif-/- mice also indicated that additional, CypD-parallel pathways are involved in the toxic effects of CsA on the kidney. In summary, CsA-mediated induction of oxidative stress is associated with CypD, with CypD deletion providing a protective effect, whereas the reduction of energy production observed upon CsA exposure did not depend on the animals' CypD status.

Metabolic implications of organelle-mitochondria communication

Cellular organelles are not static but show dynamism-a property that is likely relevant for their function. In addition, they interact with other organelles in a highly dynamic manner. In this review, we analyze the proteins involved in the interaction between mitochondria and other cellular organelles, especially the endoplasmic reticulum, lipid droplets, and lysosomes. Recent results indicate that, on one hand, metabolic alterations perturb the interaction between mitochondria and other organelles, and, on the other hand, that deficiency in proteins involved in the tethering between mitochondria and the ER or in specific functions of the interaction leads to metabolic alterations in a variety of tissues. The interaction between organelles is an emerging field that will permit to identify key proteins, to delineate novel modulation pathways, and to elucidate their implications in human disease.

Impact of Mitochondrial Permeability on Endothelial Cell Immunogenicity in Transplantation

BACKGROUND

Microvascular endothelial cells (ECs) are central to an allograft's immunogenicity. Cold ischemia and reperfusion injury associated with static cold storage and warm reperfusion activates ECs and increases the immunogenicity of the allograft. After reperfusion, mitochondrial permeability transition pore (mPTP) opening contributes to mitochondrial dysfunction in the allograft, which correlates to alloimmune rejection. Current understanding of this relationship, however, centers on the whole allograft instead of ECs. This study aimed to elucidate the relationship between EC mPTP opening and their immunophenotype.

METHODS

Mitochondrial metabolic fitness and glycolysis in ECs were assessed in parallel with metabolic gene microarray postreperfusion. NIM811 was used to inhibit mPTP opening to rescue mitochondrial fitness. The immunogenicity of NIM811-treated ECs was determined via levels of EC's proinflammatory cytokines and allogeneic CD8 T cell cocultures. Finally, EC surface expression of adhesion, costimulatory, coinhibitory, MHC-I molecules, and MHC-I machinery protein levels were characterized.

RESULTS

Genes for glycolysis, tricarboxylic acid cycle, fatty acid synthesis, gluconeogenesis were upregulated at 6 hours postreperfusion but either normalized or downregulated at 24 hours postreperfusion. As mitochondrial fitness was reduced, glycolysis increased during the first 6 hours postreperfusion. Endothelial cell treatment with NIM811 during the early postreperfusion period rescued mitochondrial fitness and reduced EC immunogenicity by decreasing CCL2, KC release, and VCAM-1, MHC-I, TAP1 expression.

CONCLUSIONS

Static cold storage and warm reperfusion leads to a reduction in mitochondrial fitness in microvascular ECs due to mPTP opening. Further, mPTP opening promotes increased EC immunogenicity that can be prevented by NIM811 treatment.