Mechanical stress and ATP synthesis are coupled by mitochondrial oxidants in articular cartilage

Abstract

Metabolic adaptation of articular cartilage under joint loading is evident and matrix synthesis seems to be critically tied to ATP. Chondrocytes utilize the glycolytic pathway for energy requirements but seem to require mitochondrial reactive oxygen species (ROS) to sustain ATP synthesis. The role of ROS in regulating ATP reserves under a mechanically active environment is not clear. It is believed that physiological strains cause deformation of the mitochondria, potentially releasing ROS for energy production. We hypothesized that mechanical loading stimulates ATP synthesis via mitochondrial release of ROS. Bovine osteochondral explants were dynamically loaded at 0.5Hz with amplitude of 0.25MPa for 1 Hour. Cartilage response to mechanical loading was assessed by imaging with dihydroethidium (ROS indicator) and a Luciferase based ATP assay. Electron transport inhibitor rotenone and mitochondrial ROS scavenger MitoQ significantly suppressed mechanically induced ROS production and ATP synthesis. Our findings indicate that mitochondrial ROS are produced as a result of physiological mechanical strains. Taken together with our previous findings of ROS involvement in blunt impact injuries, mitochondrial ROS are important contributors to cartilage metabolic adaptation and their precise role in the pathogenesis of osteoarthritis warrants further investigation.

Targeting mitochondrial responses to intra-articular fracture to prevent posttraumatic osteoarthritis

“…Previous work with MitoQ supports the hypothesis that this oxidative stress centers around the mitochondria, targeted in this study with amobarbital (15). The efficacy of NAC, a compound that supports thiol redox metabolism and GSH-using enzymes (11, 15), suggests peroxidases commonly supported by GSH are critical to oxidative stress responses.…”

“…Previous work with MitoQ supports the hypothesis that this oxidative stress centers around the mitochondria, targeted in this study with amobarbital (15). The efficacy of NAC, a compound that supports thiol redox metabolism and GSH-using enzymes (11, 15), suggests peroxidases commonly supported by GSH are critical to oxidative stress responses. This is corroborated by experiments showing that pretreatment with high concentrations of α-tocopherol, which prevents lipid peroxidation chain reactions, provides benefit in vitro; however, it is important to note that dietary supplementation of vitamin E during osteoarthritis treatment has proven ineffective (40).…”

Mitochondrial Function in Sepsis

“…A rising ratio of AMP to ATP indicates energy supply limitations, with AMPK - mediated blockade of ATP-consuming processes, especially mitogenic pathways controlled by mTOR (80). Perturbations of cell architecture, such as those accompanying mechanical deformation, affect membrane potential by altering mitochondrial volume (77), an effect that likely results in ROS liberation (81, 82). …”

Injurious Loading of Articular Cartilage Compromises Chondrocyte Respiratory Function

“…Studies suggest that manipulations of key factors including surface mechanics, inflammation, or oxidative injury can alleviate different aspects of cellular injury from overloading [5,6,7]. Among the outcomes, antioxidants appear to combat overactivity after overload of a mechanotransductive pathway whereby loading stimulates rotenone-inhibitable electron transport chain (ETC) activity, subsequent ROS generation as a byproduct of respiration, and, ultimately, increased anabolism by chondrocytes [8,9,10,11,12]. The hypothesis that ROS function as a metabolism-mediating signal in chondrocytes was put forth as early as 1997 by Lee and Urban in studies showing that without oxygen, chondrocyte anabolic function ceases and that this can be restored with addition of exogenous oxidants [13,14].…”