Role of mitochondria and reactive oxygen species in dendritic cell differentiation and functions

Abstract

Dendritic cells (DC) are potent antigen-presenting cells capable of inducing T and B responses and immune tolerance. We have characterized some aspects of energy metabolism accompanying the differentiation process of human monocytes into DC. Compared to precursor monocytes, DC exhibited a much larger number of mitochondria and consistently (i) a higher endogenous respiratory activity and (ii) a more than sixfold increase in ATP content and an even larger increase in the activity of the mitochondrial marker enzyme citrate synthase. The presence in the culture medium of rotenone, an inhibitor of the respiratory chain Complex I, prevented the increase in mitochondrial number and ATP level, without affecting cell viability. Rotenone inhibited DC differentiation, as revealed by the observation that the expression of CD1a, which is a specific surface marker of DC differentiation, was strongly reduced. Cells cultured in the presence of rotenone displayed a lower content of growth factor-induced, mitochondrially generated, hydrogen peroxide. A similar drop in ROS was observed upon addition of catalase, which caused functional effects similar to those produced by rotenone treatment. These results suggest that ROS play a crucial role in DC differentiation and that mitochondria are an important source of ROS in this process. © 2008 Elsevier Inc. All rights reserved.Keywords: Dendritic cells; Mitochondria; Reactive oxygen species; Oxidative phosphorylation; Free radicals Effective immune responses require correct localization and functioning of dendritic cells (DC). Dendritic cells are the most potent and versatile antigen-presenting cells, with a unique ability to induce specific immune responses as well as tolerance [1,2]. In peripheral tissues they reside in an immature state waiting for incoming antigens. After capturing and processing the antigens, DC undergo a maturation process which culminates in dramatic changes in functions and migratory properties [3,4]. The localization of mature DC to the draining lymph nodes coincides with the presentation of processed antigens to naïve T cells, triggering the initiation of specific immune responses [2,5]. An in vitro method to differentiate immature DC from CD14 + monocyte precursors cultured in the presence of granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-4 (IL-4) is very well established [6,7].Reactive oxygen species (ROS) have been identified as important second messengers involved in the transduction of several signaling pathways [8,9], gene expression, and cell proliferation [10]. Furthermore, recent studies have shown that growth factors, through the actions of their specific receptors, are able to increase

An active mitochondrial biogenesis occurs during dendritic cell differentiation

“…In a previous report (Del Prete et al, 2008) we showed that, after differentiation, DC exhibited increased number of condensed mitochondria and dynamic changes in their energy metabolism. A study is presented here showing that the DC differentiation process is characterized by increased expression level and activity of mitochondrial respiratory complexes, as well as by an increased mitochondrial DNA (mtDNA) copy number.…”

“…Ultrastructural analysis revealed a significant increment in the number of condensed mitochondria in immature DC compared to monocytes (Del Prete et al, 2008). To investigate whether the differentiation was accompanied by structural as well as functional changes in mitochondrial respiratory chain complexes, we analysed the expression level of protein subunits of respiratory complexes, as well as their specific enzymatic activities.…”

“…In a previous report, we showed that the differentiation process of peripheral blood monocytes to DC requires growth factor dependent production of intracellular Reactive Oxygen Species (ROS) (Del Prete et al, 2008; see also Sattler et al, 1999;Sheng et al, 2010). As revealed by ultrastructural analysis, DC exhibited an increased number of condensed mitochondria compared to monocyte precursors.…”

“…Analysis of lactate released into the culture medium was carried out spectrophotometrically by following NAD + reduction at 340 nm, as previously described (Del Prete et al, 2008). …”

“…A higher endogenous respiratory activity together with an increase in ATP content and mitochondrial enzyme citrate synthase activity was also found. Moreover, the presence of mitochondrial Complex I inhibitor rotenone into the culture medium caused inhibition of the DC differentiation process, through inhibition of mitochondrial ROS production (Del Prete et al, 2008).…”