Convergence of multiple signaling pathways is required to coordinately up-regulate mtDNA and mitochondrial biogenesis during T cell activation

Abstract

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 levels. T cell receptor (TCR) activation results in a large increase in mitochondrial mass and membrane potential and a corresponding increase of mtDNA copy number, indicating the vital role for mitochondrial function for the 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. We propose that mitochondrial biogenesis is not under control of a master regulatory circuit, but rather requires the convergence of multiple signaling pathways with distinct downstream consequences on the organelle's structure, composition, and function.

Mitochondria as Oxidative Signaling Organelles in T-cell Activation: Physiological Role and Pathological Implications

“…Moreover, a crucial role of mitochondria and metabolic pathways for T-cell physiology is becoming increasingly evident. The initial phase of activation-triggered proliferation of naive T cells is intimately associated with an increase in mitochondrial mass, mitochondrial DNA (mtDNA) content and oxidative phosphorylation (Darzynkiewicz et al 1981;D'Souza et al 2007;Frauwirth and Thompson 2004). Interestingly, as discussed below, at the later stage of an immune response, activated T cells rely predominantly on aerobic glycolysis for ATP production (Fox et al 2005).…”

Indoleamine 2,3-Dioxygenase and Metabolites Protect Murine Lung Allografts and Impair the Calcium Mobilization of T Cells

“…Mitochondria are believed to help regulate Ca 21 release upon TCR activation, with an increase in mitochondrial mass (13) inversely correlated with the Ca 21 response (14). We evaluated mitochondrial mass using the mitochondria-specific dye MTG, a lipophilic thiol-reactive dye that selectively labels the mitochondrial inner membrane and matrix (15).…”

A prospective study of mitochondrial DNA copy number and risk of non-Hodgkin lymphoma

“…3 Various internal and external factors associated with synthesis of adenosine triphosphate (ATP) demand influence mtDNA copy number in nonneoplastic tissue, including cell growth and differentiation, hormone treatment, age, and reaction to oxidative damage, which are thought to play a role in lymphomagenesis. [4][5][6] The mtDNA copy number has also been shown to be increased in T cells activated via the T-cell receptor, 7 and in workers exposed to benzene, an established leukemogen and suspect lymphomagen. 8 Finally, it is noteworthy that mtDNA copy number is increased in cells from patients with chronic lymphocytic leukemia (CLL), 9 in cell lines derived from Burkitt lymphoma, 10 and in Epstein-Barr virus (EBV)-transformed lymphoblastoid cell lines.…”