Enhanced Oxygen Utilization Efficiency With Concomitant Activation of AMPK-TBC1D1 Signaling Nexus in Cyclophilin-D Conditional Knockout Mice

We have previously reported in HEK 293 T cells and in constitutive cyclophilin-D (Cyp-D) knockout (KO) mice that Cyp-D ablation downregulates oxygen consumption (VO2) and triggers an adaptive response that manifest in higher exercise endurance with less VO2. This adaptive response involves a metabolic switch toward preferential utilization of glucose via AMPK-TBC1D1 signaling nexus. We now investigated whether a similar response could be triggered in mice after acute ablation of Cyp-D using tamoxifen-induced ROSA26-Cre-mediated (i.e., conditional KO, CKO) by subjecting them to treadmill exercise involving five running sessions. At their first treadmill running session, CKO mice and controls had comparable VO2 (208.4 ± 17.9 vs. 209.1 ± 16.8 ml/kg min−1), VCO2 (183.6 ± 17.2 vs. 184.8 ± 16.9 ml/kg min−1), and RER (0.88 ± 0.043 vs. 0.88 ± 0.042). With subsequent sessions, CKO mice displayed more prominent reduction in VO2 (genotype & session interaction p = 0.000) with less prominent reduction in VCO2 resulting in significantly increased RER (genotype and session interaction p = 0.013). The increase in RER was consistent with preferential utilization of glucose as respiratory substrate (4.6 ± 0.8 vs. 4.0 ± 0.9 mg/min, p = 0.003). CKO mice also performed a significantly higher treadmill work for given VO2 expressed as a power/VO2 ratio (7.4 ± 0.2 × 10−3 vs. 6.7 ± 0.2 10−3 ratio, p = 0.025). Analysis of CKO skeletal muscle tissue after completion of five treadmill running sessions showed enhanced AMPK activation (0.669 ± 0.06 vs. 0.409 ± 0.11 pAMPK/β-tubulin ratio, p = 0.005) and TBC1D1 inactivation (0.877 ± 0.16 vs. 0.565 ± 0.09 pTBC1D1/β-tubulin ratio, p < 0.05) accompanied by increased glucose transporter-4 levels consistent with activation of the AMPK-TBC1D1 signaling nexus enabling increased glucose utilization. Taken together, our study demonstrates that like constitutive Cyp-D ablation, acute Cyp-D ablation also induces a state of increased O2 utilization efficiency, paving the way for exploring the use of pharmacological approach to elicit the same response, which could be beneficial under O2 limiting conditions.

Abstract 11036: Enhanced Oxygen Utilization Efficiency with Concomitant Activation of the AMPK-TBC1D1 Signaling Nexus in Cyclophilin-D Conditional Knock-Out Mice

We have previously reported in HEK 293T cells and in constitutive cyclophilin-D (Cyp-D) knock-out (KO) mice that Cyp-D ablation downregulates oxygen consumption (VO 2 ) and triggers an adaptive response that manifests in higher exercise endurance with less VO 2 . This adaptive response involves a metabolic switch toward preferential utilization of glucose via the AMPK-TBC1D1 signaling nexus. We now investigated whether a similar response could be triggered in mice after acute ablation of Cyp-D using conditional KO (CKO) mice by subjecting them to treadmill exercise involving five running sessions. At their first treadmill running session, CKO mice and controls had comparable VO 2 (208.4±17.9 vs 209.1±16.8 ml/kg·min -1 ), VCO 2 (183.6±17.2 vs 184.8±16.9 ml/kg·min -1 ), and RER (0.88±0.043 vs 0.88±0.042). With subsequent sessions, CKO mice displayed more prominent reduction in VO 2 (genotype & session interaction p<0.001) with less prominent reduction in VCO 2 resulting in significantly increased RER (genotype & session interaction p=0.013). The increase in RER was consistent with preferential utilization of glucose as respiratory substrate (4.6±0.8 vs 4.0± 0.9 mg/min, p=0.003). CKO mice also performed a significantly higher treadmill work for given VO 2 expressed as a power/VO 2 ratio (7.4±0.2 x 10 -3 vs 6.7±0.2 10 -3 ratio, p=0.025). Analysis of CKO skeletal muscle tissue after completion of five treadmill running sessions showed enhanced AMPK activation (0.669±0.06 vs 0.409±0.11 pAMPK/β-tubulin ratio, p=0.005) and TBC1D1 inactivation (0.877±0.16 vs 0.565±0.09 pTBC1D1/β-tubulin ratio, p<0.05) accompanied by increased glucose transporter-4 levels consistent with activation of the AMPK-TBC1D1 signaling nexus enabling increased glucose utilization. Taken together, our study demonstrates that like constitutive Cyp-D ablation, acute Cyp-D ablation also induces a state of increased O 2 utilization efficiency, paving the way for exploring the use of a pharmacological approach to elicit the same response, which could be beneficial under O 2 limiting conditions.