Biology subjects

Smith, C. O.

Publications and source records attributed to Smith, C. O..

3 recordsLinked to original sources

bioRxiv2020

Activation of mitochondria is an acute Akt-dependent response during osteogenic differentiation

Osteogenic differentiation, the process by which bone marrow mesenchymal stem/stromal (a.k.a. skeletal stem) cells and osteoprogenitors form osteoblasts, is a critical event for bone formation during development, fracture repair, and tissue maintenance. Extra- and intracellular signaling pathways triggering osteogenic differentiation are relatively well known; however, the ensuing change in cell energy metabolism is less clearly defined. Here we tested the effect of osteogenic media containing ascorbate and β-glycerol phosphate, or various osteogenic hormones and growth factors on energy metabolism in long bone (ST2)- and calvarial bone (MC3T3-E1)-derived osteoprogenitors. We show that osteogenic media, and differentiation factors, Wnt3a and BMP2, stimulate mitochondrial oxidative phosphorylation (OxPhos) with little effect on glycolysis. The activation of OxPhos occurs acutely, suggesting a metabolic signaling change rather than protein expression change. To this end, we found that the observed mitochondrial activation is Akt-dependent. Akt is activated by osteogenic media, Wnt3a, and BMP2, leading to increased phosphorylation of various mitochondrial Akt targets, a phenomenon known to stimulate OxPhos. In sum, our data provide comprehensive analysis of cellular bioenergetics during osteoinduction in cells of two different origins (mesenchyme vs neural crest) and identify Wnt3a and BMP2 as physiological stimulators of mitochondrial respiration via Akt activation.The abbreviations used areAAAntimycin AALPAlkaline phosphataseBMP2Bone Morphogenic Protein 2CVCrystal ViolateECARExtracellular Acidification RateFCCPCarbonyl cyanide 4-(trifluoromethoxy)phenylhydrazoneOBMOsteoblastic media a.k.a. Ascorbic acid and beta-gycero phosphateOBsOsteoblastsOCROxygen Consumption RateOligoOligomycinOxPhosOxidative PhosphorylationROSReactive Oxygen SpeciesROTRotenoneWnt3aWingless protein 3aView Full Text

developmental biology↗

bioRxiv2019

Inhibition of the mitochondrial permeability transition exerts sex-specific stimulatory effect on fracture repair

Bone fracture is accompanied by mechanical stresses and inflammation - conditions that impair mitochondria via the phenomenon of permeability transition. This phenomenon occurs due to opening of the mitochondrial permeability transition pore (MPTP) promoted by cyclophilin D (CypD). MPTP opening exacerbates inflammation and cell death and, thus can disrupt fracture repair. Here we tested a hypothesis that protecting mitochondria from MPTP opening via inhibition of CypD improves fracture repair. Our data indicate that osteoblast activity, bone formation, and biomechanical properties of repaired bones were significantly increased in CypD knock-out mice when compared to controls during fracture repair. These effects were observed in male but not female mice, thus showing sexual dimorphism. Pharmacological inhibition of CypD with NIM811 in male mice also stimulated fracture repair. In addition, CypD knock-out or pharmacological inhibition produced pro-osteogenic effect in isolated bone marrow osteoprogenitors. This in vitro effect was associated with higher mitochondrial respiration and increased {beta}-catenin activity regulated by mitochondria-dependent acetylation. Our findings implicate a sex-specific role of MPTP in bone fracture and suggest CypD inhibition as a modality to promote fracture repair.

biochemistry↗

bioRxiv2017

Evidence for, and Metabolic Consequences of, a Cardiac Mitochondrial KNa1.2 Channel

Controversy surrounds the molecular identity of mitochondrial K+ channels that are important for protection against cardiac ischemia-reperfusion injury. While KNa1.2 (Kcnt2 gene) is necessary for cardioprotection by volatile anesthetics, electrophysiologic evidence for a channel of this type in mitochondria is lacking. The endogenous physiologic role of a potential mito-KNa1.2 channel is also unclear. Herein, single channel patch-clamp of 27 independent cardiac mitochondrial inner membrane (mitoplast) preparations from wild type (WT) mice yielded 6 channels matching the known ion-sensitivity, ion-selectivity, pharmacology and conductance properties of KNa1.2 (slope conductance 138{+/-}1 pS). However, similar experiments on 40 preparations from Kcnt2-/- mice yielded zero such channels. The KNa opener bithionol uncoupled respiration in WT but not Kcnt2-/- cardiomyocytes. Furthermore, when oxidizing only fat as substrate, Kcnt2-/- cardiomyocytes and hearts were less responsive to increases in energetic demand. Kcnt2-/- mice also had elevated body fat, but no baseline differences in the cardiac metabolome. These data support the existence of a cardiac mitochondrial KNa1.2 channel, and a role for cardiac KNa1.2 in regulating metabolism under conditions of high energetic demand.

cell biology↗