Functional characterization of mitochondria in neutrophils: a role restricted to apoptosis

Abstract

Mitochondria are known to combine life-supporting functions with participation in apoptosis by controlling caspase activity. Here, we report that in human blood neutrophils the mitochondria are different, because they preserve mainly death-mediating abilities. Neutrophil mitochondria hardly participate in ATP synthesis, and have a very low activity of the tested marker enzymes. The presence of mitochondria in neutrophils was confirmed by quantification of mitochondrial DNA copy number, by detection of mitochondrial porin, and by JC-1 measurement of Dw m . During neutrophilic differentiation, HL-60 cells demonstrated a profound cytochrome c depletion and mitochondrial shape change reminiscent of neutrophils. However, blood neutrophils containing extremely low amounts of cytochrome c displayed strong caspase-9 activation during apoptosis, which was also observed in apoptotic neutrophil-derived cytoplasts lacking any detectable cytochrome c. We suggest that other proapoptotic factors such as Smac/DIABLO and HtrA2/Omi, which are massively released from the mitochondria, have an important role in neutrophil apoptosis.

Intramitochondrial serine protease activity of Omi/HtrA2 is required for caspase-independent cell death of human neutrophils

“…This is likely to be regulated by Bax redistribution from the cytosol (in intact cells) to the mitochondria (in apoptotic cells), which was prevented in TNF-a þ zVAD-treated neutrophils but not in the neutrophils incubated with TNF-a alone. 5 The targeting of mitochondria by Bax was also observed under the 3-h TNF-a þ cycloheximide treatment 10 used in the present study. Hence, inhibition of caspases in the presence of TNF-a blocks the release of Omi/ HtrA2 from the mitochondria into the cytosol.…”

“…Since this type of cell death has been suggested to be mediated by the mitochondria-derived reactive oxygen species (ROS), 5 it is logical to suppose that a mitochondrial antioxidant system, which normally inactivates an excess of ROS, is destroyed in this experimental setting. Omi/HtrA2 might be involved in this inactivation, inhibiting for instance MnSOD, which is an antioxidant enzyme with high expression in neutrophils (Figure 1d, lanes 6-10; and see Maianski et al 10 ) and important especially for prevention of the TNF-ainduced damage.…”

“…All manipulations were carried out as described. 10 (e) Fresh neutrophils were incubated with MitoTracker GreenFM (100 nM) and ucf-101 (20 mM) for 15 min at 371C, and intracellular localization of ucf-101 was determined by confocal laser scanning microscopy. Colocalization of MitoTracker GreenFM and ucf-101 gave a shift to yellow.…”

Successful enrichment and recovery of whole mitochondrial genomes from ancient human dental calculus

“…The reasons for this are unclear, but may be related to differences in the cell types contributing to the human DNA component of dental calculus. For example, neutrophils, an abundant blood leukocyte involved in host innate immune response to dental plaque and calculus formation (Warinner et al 2014b), contain 10–15 times fewer mtDNA genome copies compared to peripheral blood mononuclear cells (PBMC) (Maianski et al 2004). However, during immune response, neutrophils utilize mtDNA as a structural molecule to bind cytotoxic proteins into neutrophil extracellular traps (NETs), which are then released onto advancing plaque biofilms (Yousefi et al 2009).…”

Impairment of Mitochondrial–Nuclear Cross Talk in Neutrophils of Patients with Type 2 Diabetes Mellitus

“…Apoptosis is the regular fate of neutrophils and apoptotic neutrophils are disposed of by macrophagemediated phagocytosis. The translocation of pro-apoptotic proteins such as caspases to mitochondrial outer membrane has been demonstrated to precede nuclear DNA fragmentation and apoptosis in neutrophils [29]. Furthermore, type 2 diabetic neutrophils possess highly deregulated mitochondrial morphology with putative involvement in apoptosis [30].…”