Mitochondrial electron transport and glycolysis are coupled in articular cartilage.
OBJECTIVE
Although the majority of the adenosine triphosphate (ATP) in chondrocytes is made by glycolysis rather than by oxidative phosphorylation in mitochondria there is evidence to suggest that reactive oxygen species produced by mitochondrial electron transport (ET) help to maintain cellular redox balance in favor of glycolysis. The objective of this study was to test this hypothesis by determining if rotenone, which inhibits ET and blocks oxidant production inhibits glycolytic ATP synthesis.


METHODS
Bovine osteochondral explants were treated with rotenone, an ET inhibitor; or oligomycin an ATP synthase inhibitor; or 2-fluoro-2-deoxy-D-glucose, a glycolysis inhibiter; or peroxide, an exogenous oxidant; or mitoquinone (MitoQ), a mitochondria-targeted anti-oxidant. Cartilage extracts were assayed for ATP, nicotine adenine dinucleotide (NAD+/H), and culture medium was assayed for pyruvate and lactate after 24 h of treatment. Imaging studies were used to measure superoxide production in cartilage.


RESULTS
Rotenone and 2-FG caused a significant decline in cartilage ATP (P < 0.001). In contrast, ATP levels were not affected by oligomycin. Peroxide treatment blocked rotenone effects on ATP, while treatment with MitoQ significantly suppressed ATP levels. Rotenone and 2-FG caused a significant decline in pyruvate, but not in lactate production. NADH:NAD+ ratios decreased significantly in both rotenone and 2-FG-treated explants (P < 0.05). Rotenone also significantly reduced superoxide production.


CONCLUSIONS
These findings showing a link between glycolysis and ET are consistent with previous reports on the critical need for oxidants to support normal chondrocyte metabolism. They suggest a novel role for mitochondria in cartilage homeostasis that is independent of oxidative phosphorylation.
Department of Orthopaedics and Rehabilitation, University of Iowa Hospitals and Clinics, Iowa City, IA, USA. james-martin@uiowa.edu
J A
JA
Martin
A
A
Martini
A
A
Molinari
W
W
Morgan
W
W
Ramalingam
J A
JA
Buckwalter
T O
TO
McKinley
D000255:Adenosine Triphosphate / Q000096:biosynthesis; D000818:Animals; D002358:Cartilage, Articular / Q000378:metabolism*; D002417:Cattle; D019902:Chondrocytes / Q000378:metabolism; D004579:Electron Transport / Q000187:drug effects / Q000502:physiology; D019788:Fluorodeoxyglucose F18 / Q000494:pharmacology; D006019:Glycolysis / Q000187:drug effects / Q000502:physiology; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism*; D012402:Rotenone / Q000494:pharmacology; D013481:Superoxides / Q000378:metabolism; D046509:Tissue Culture Techniques; D014475:Uncoupling Agents / Q000494:pharmacology
D014475:Uncoupling Agents; D012402:Rotenone; D019788:Fluorodeoxyglucose F18; D013481:Superoxides; D000255:Adenosine Triphosphate