Complosome Regulates Hematopoiesis at the Mitochondria Level

The intracellular complement network, known as the complosome, regulates lymphocyte biology, which is well established. Recently, however, we demonstrated that the complosome is also expressed in hematopoietic stem/progenitor cells (HSPCs) in addition to lymphocytes. In our previous work, murine lineage-negative (Lin^-) bone marrow (BM) mononuclear cells (BMMNC) from mice lacking the intracellular C3 and C5 complosome proteins displayed different responses to stress. Specifically, while C3-KO cells were more sensitive to oxidative stress, C5-KO cells showed greater resistance. To explore this intriguing observation at the metabolic level, we evaluated anaerobic and aerobic glycolysis, along with mitochondrial function, in Lin^- BMMNC purified from C3-KO, C5-KO, and C5aR1-KO mice. We found that cells from complosome-deficient animals under steady-state conditions exhibited elevated lactate production and enhanced lactate dehydrogenase (LDH) release, indicating their reliance on anaerobic glycolysis. Interestingly, the uptake of a glucose fluorescent analog (2-NBDG) increased in C3-KO cells but decreased in C5-KO and C5aR1-KO cells compared to wild-type (WT) mice. Meanwhile, total ATP production in C3-KO cells, unlike that of C5 and C5aR1 mice, was reduced under steady-state conditions and did not change significantly after exposure to the mitochondrial-damaging agent hydrogen peroxide (H₂O₂). This suggests a greater dependence on anaerobic glycolysis in C3-KO cells than in C5-KO and C5aR1-KO cells. Finally, we assessed the integrity of mitochondrial membranes in the studied cells using MitoTracker green and deep red assays. Compared to WT cells, we observed that mitochondria from complosome mutant Lin-BMMNC accumulated fewer MitoTracker probes, indicating the presence of mitochondrial defects in these cells.