Metabolic Reprogramming of Human Macrophages by Sickle Cell Hemoglobin
Authors: Jerebtsova Marina , Afangbedji Nowah , Nekhai Sergei 
Published: May 2024

BACKGROUND: Sickle cell disease is caused by a single nucleotide mutation in the β-globin gene, resulting in the substitution of valine for glutamic acid, polymerization of hemoglobin and sickling of red blood cells (RBCs) under low oxygen conditions causing chronic hemolysis, and organs damage. SCA is characterized by the presence of cell-free plasma hemoglobin. Organ damage is associated with chronic inflammation and pro-inflammatory macrophages phenotype. Typically, anti-inflammatory response is elicited by the phagocytosis of senescent RBCs and cell-free hemoglobin. We have demonstrated that treatment of human macrophages with sickle cell hemoglobin (HbS) leads to lysosome accumulation, autophagy activation, and pro-inflammatory phenotype. The propensity of mutant HbS to polymerize under low pH may promote lysosomal HbS polymer accumulation, hindering degradation, and inducing macrophage differentiation towards a pro-inflammatory state. The differentiation of macrophages into specific phenotypes is associated with significant metabolic reprogramming. HYPOTHESIS: We hypothesize that the uptake of HbS by human macrophages induces their metabolic reprogramming via mitochondrial remodeling. METHODS: Human THP-1 cells were differentiated into macrophages with PMA and treated with either purified HbS or normal hemoglobin (HbA). Mitochondria were detected with MitoTrackerTM Green FM dye, and mitochondrial ROS (mtROS) level was detected by Mito SOX Red Kit. Transmission electron microscopy imaging was performed at Talos 200X transmission electron microscope. EPView (Olympus) software was used for the structure analysis. Total RNA was isolated by Trizol and sequenced on an Illumina® NextSeq 500. Comparisons between treatments were conducted using Gene Set Enrichment Analysis (GSEA). RESULTS: Immunofluorescent staining demonstrated accumulation of mitochondria after treatment with HbS compared to untreated (ctrl) or HbA-treated macrophages. Electron microscopy revealed an increase in the number and size of mitochondria. In 25 random microphotographs of cytoplasm, we detected 51 mitochondria in control, 79 in HbA treated and, 96 in HbS treated macrophages. The mitochondria volume and cristae size were significantly increased in macrophages treated with HbS. There was no increase in mtROS production in HbS treatment compared to ctrl. As expected, HbA treatment reduced mtROS production. The mitochondrial gene set (242 genes) was the second most enriched GSEA set in HbS-treated compared to HbA-treated macrophages. The larger mitochondrial size may be associated with a reduction of fission or an increase in fusion. We did not find differences in the expression of mitochondrial fission and fusion genes between HbS and HbA-treated macrophages. The increase in the mitochondrial size and cristae size may also be associated with increased oxidative phosphorylation. We found significant enrichment of genes responsible for oxidative phosphorylation in the HbS-treated macrophages. We did not find significant differences in the expression of glycolysis genes. CONCLUSION: Treatment of human macrophages with HbS significantly increases the number and volume of mitochondria, size of the cristae, and oxidative phosphorylation without upregulation of mtROS production and reduction of glycolysis. This work was supported by NIH Research Grants SC1HL150685, P50HL118006, and R01HL125005. We thank Drs. Castle Raley and Keith Crandall, George Washington University SPH Genomics Core, for sequencing and guidance in data analysis; Dr. Christine Brantner, GW Nanofabrication and Imaging Center, for TEM imaging. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.