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

Abstract

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, Cdcl6) 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. FASEB J. 33, 11443–11457 (2019). http://www.fasebj.org

Cyclophilin inhibition as a potential treatment for nonalcoholic steatohepatitis (NASH)

“…The net effects of these metabolic alterations were found to be a slight increase in ATP production due to an increase in glycolysis and/or ATP synthasome activity, yet a reduction in oxygen consumption [82,83,88,89]. These metabolic changes were also evident in an examination of exercise capacity, where Cyp D knockout mice showed higher exercise capacity (longer and faster treadmill activity) but lower oxygen consumption both during exercise and at rest, compared to wildtype mice [90].The mechanisms through which Cyp D deletion results in this shift in metabolism have not been thoroughly studied, but one possibility is by downregulation of mitochondrial gene transcription. Cyp D silencing in cell culture by genetic knockdown or CsA was found to block Cyp D interaction with mitochondrial transcription factors 1 and 2 and in turn decrease mitochondrial RNA synthesis [91].…”

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

“…It was performed as previously described ( Radhakrishnan et al, 2019 ). Each mouse was first subjected to a 3-day habituation period.…”

“…Power (Joules/min) was calculated by dividing work performed (Joules) by time spent on treadmill (min). Fuel utilization (carbohydrate, g/min and fat, g/min) was calculated using VO 2 and VCO 2 data as previously described (Radhakrishnan et al, 2019)…”

“…Cyclophilin-D (Cyp-D) is a mitochondrial matrix-resident peptidyl-prolyl isomerase involved in various pleotropic functions of the cell including energy metabolism, metabolic adaptation, and nuclear/mitochondria signaling, and recently in nuclear translocation of apoptosis inducing factor ( Elrod et al, 2010 ; Tavecchio et al, 2013 ; Tubbs et al, 2014 ; Radhakrishnan et al, 2015 , 2019 ; Qamar et al, 2021 ). We first reported in HEK 293 T cells that Cyp-D interacts with mitochondrial transcription factors and that Cyp-D silencing downregulates the expression of mitochondrial genes initiated from the heavy strand promoter 2 (HSP2) encoding respiratory complex proteins leading to a reduction in oxygen consumption (VO 2 ; Radhakrishnan et al, 2015 ).…”

“…The VO 2 downregulation was accompanied by a reduction in VCO 2 but to a lesser extent resulting in an increased respiratory exchange ratio (RER) consistent with a metabolic shift favoring glucose utilization over fat. This effect was accompanied by enhanced exercise capacity demonstrating increased oxygen utilization efficiency ( Radhakrishnan et al, 2019 ). The response was mediated in part via adenosine monophosphate-activated protein kinase (AMPK) and its downstream partner tre-2/USP6, BUB2, cdc16 domain family member 1 (TBC1D1), the so-called “AMPK-TBC1D1 signaling nexus.”…”