Convergence of multiple signaling pathways is required to coordinately up-regulate mtDNA and mitochondrial biogenesis during T cell activation.
The quantity and activity of mitochondria vary dramatically in tissues and are modulated in response to changing cellular energy demands and environmental factors. The amount of mitochondrial DNA (mtDNA), which encodes essential subunits of the oxidative phosphorylation complexes required for cellular ATP production, is also tightly regulated, but by largely unknown mechanisms. Using murine T cells as a model system, we have addressed how specific signaling pathways influence mitochondrial biogenesis and mtDNA copy number. T cell receptor (TCR) activation results in a large increase in mitochondrial mass and membrane potential and a corresponding amplification of mtDNA, consistent with a vital role for mitochondrial function for growth and proliferation of these cells. Independent activation of protein kinase C (via PMA) or calcium-related pathways (via ionomycin) had differential and sub-maximal effects on these mitochondrial parameters, as did activation of naïve T cells with proliferative cytokines. Thus, the robust mitochondrial biogenesis response observed upon TCR activation requires synergy of multiple downstream signaling pathways. One such pathway involves AMP-activated protein kinase (AMPK), which we show has an unprecedented role in negatively regulating mitochondrial biogenesis that is mammalian target of rapamycin (mTOR)-dependent. That is, inhibition of AMPK after TCR signaling commences results in excessive, but uncoordinated mitochondrial proliferation. Thus mitochondrial biogenesis is not under control of a single master regulatory circuit, but rather requires the convergence of multiple signaling pathways with distinct downstream consequences on the organelle's structure, composition, and function.
D'Souza
Anthony D
AD
Department of Pathology, Yale University School of Medicine, 310 Cedar Street, P.O. Box 208023, New Haven, CT 06520-8023, USA.
Parikh
Neal
N
Kaech
Susan M
SM
Shadel
Gerald S
GS
D055372:AMP-Activated Protein Kinases; D000818:Animals; D002118:Calcium / Q000378:metabolism; D049109:Cell Proliferation / Q000187:drug effects; D004272:DNA, Mitochondrial / Q000378:metabolism*; D015759:Ionomycin / Q000494:pharmacology; D008213:Lymphocyte Activation / Q000502:physiology*; D051379:Mice; D008810:Mice, Inbred C57BL; D008928:Mitochondria / Q000187:drug effects / Q000502:physiology*; D009097:Multienzyme Complexes / Q000037:antagonists & inhibitors; D011493:Protein Kinase C / Q000378:metabolism; D011494:Protein Kinases / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors; D011948:Receptors, Antigen, T-Cell / Q000187:drug effects / Q000502:physiology; D015398:Signal Transduction / Q000502:physiology*; D013601:T-Lymphocytes / Q000502:physiology*; D058570:TOR Serine-Threonine Kinases; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D015854:Up-Regulation
D004272:DNA, Mitochondrial; D009097:Multienzyme Complexes; D011948:Receptors, Antigen, T-Cell; D015759:Ionomycin; D011494:Protein Kinases; C546843:mTOR protein, mouse; D017346:Protein Serine-Threonine Kinases; D058570:TOR Serine-Threonine Kinases; D011493:Protein Kinase C; D055372:AMP-Activated Protein Kinases; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium