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The microglia overactivation-induced neuroinflammation is a significant cause of the brain injury after intracerebral hemorrhage (ICH). Iron homeostasis is crucial for microglia activation, but the mechanism and causality still need further study. This study aimed to explore the roles and mechanism of the mitochondrial iron transporter SLC25A28 in microglia activation after ICH. Intrastriatal injection of autologous blood was used to establish ICH model, and the neuroinflammation, iron metabolism and brain injuries were assessed in wildtype or microglia-specific SLC25A28 knockout mice after ICH. Mitochondria iron levels and microglial function were determined in SLC25A28 overexpressed or deleted microglia. The extracellular acidification rate (ECAR), lactate production, and glycolytic enzyme levels were used to determine aerobic glycolysis. The results showed that ICH stimulated mitochondrial iron overload, and synchronously upregulated the SLC25A28 expression. In vitro, SLC25A28 overexpression increased mitochondrial iron levels in microglia. Interestingly, microglial SLC25A28 deficiency ameliorated neuroinflammation, brain edema, blood–brain barrier injury and ethological alterations in mice after ICH. Mechanically, SLC25A28 deficiency inhibited microglial activation by restricting the aerobic glycolysis. Moreover, zinc protoporphyrin could reduce SLC25A28 expression and mitigated brain injury. SLC25A28 plays crucial roles in mitochondrial iron homeostasis and microglia activation after ICH, and it might be a potential therapeutic target for ICH. [ABSTRACT FROM AUTHOR]

• Mitoferrin-2 is a disease-associated mitochondrial iron transporter. • Here, a quantitative image-based Mitoferrin-2 activity screen has been developed. • Optimization of conditions yields a robust 96-well plate-based activity screening assay. • This method can enable discovery of currently lacking Mitoferrin-2 activity modulators. Iron is a trace element that is critical for most living organisms and plays a key role in a wide variety of metabolic processes. In the mitochondrion, iron is involved in producing iron-sulfur clusters and synthesis of heme and kept within physiological ranges by concerted activity of multiple molecules. Mitochondrial iron uptake is mediated by the solute carrier transporters Mitoferrin-1 (SLC25A37) and Mitoferrin-2 (SLC25A28). While Mitoferrin-1 is mainly involved in erythropoiesis, the cellular function of the ubiquitously expressed Mitoferrin-2 remains less well defined. Furthermore, Mitoferrin-2 is associated with several human diseases, including cancer, cardiovascular and metabolic diseases, hence representing a potential therapeutic target. Here, we developed a robust approach to quantify mitochondrial iron uptake mediated by Mitoferrin-2 in living cells. We utilize HEK293 cells with inducible expression of Mitoferrin-2 and measure iron-induced quenching of rhodamine B[(1,10-phenanthroline-5-yl)-aminocarbonyl]benzyl ester (RPA) fluorescence and validate this assay for medium-throughput screening. This assay may allow identification and characterization of Mitoferrin-2 modulators and could enable drug discovery for this target. [ABSTRACT FROM AUTHOR]

Ferroptosis is a recently discovered form of programmed cell death, but its regulatory mechanisms are not fully understood. In the current study, we reported that the BRD7-P53-SLC25A28 axis played a crucial role in regulating ferroptosis in hepatic stellate cells (HSCs). Upon exposure to ferroptosis inducers, bromodomain-containing protein 7 (BRD7) protein expression was remarkably increased through the inhibition of the ubiquitin-proteasome pathway. CRISPR/Cas9-mediated BRD7 knockout conferred resistance to HSC ferroptosis, whereas specific BRD7 plasmid-mediated BRD7 overexpression facilitated HSC ferroptosis. Interestingly, the elevated BRD7 expression exhibited to promote p53 mitochondrial translocation via direct binding with p53 N-terminal transactivation domain (TAD), which may be the underlying mechanisms for BRD7-enhanced HSC ferroptosis. Site-directed mutations of serine 392 completely blocked the binding of BRD7 to p53, and, in turn, prevented p53 mitochondrial translocation and HSC ferroptosis. Importantly, mitochondrial p53 interacted with solute carrier family 25 member 28 (SLC25A28) to form complex and enhanced the activity of SLC25A28, which could lead to the abnormal accumulation of redox-active iron and hyperfunction of electron transfer chain (ETC). SLC25A28 knockdown impaired BRD7-or p53-mediated ferroptotic events. In mice, erastin treatment ameliorated pathological damage of liver fibrosis through inducing HSC ferroptosis. HSC-specific blockade of BRD7-P53-SLC25A28 axis could abrogate erastin-induced HSC ferroptosis. Of note, we analyzed the effect of sorafenib on HSC ferroptosis in advanced fibrotic patients with hepatocellular carcinoma receiving sorafenib monotherapy. Attractively, BRD7 upregulation, p53 mitochondrial translocation, combination of SLC25A28 and p53, and ferroptosis induction occurred in primary human HSCs. Overall, these findings reveal novel signal transduction and regulatory mechanism of ferroptosis, and also suggest BRD7-P53-SLC25A28 axis as potential targets for liver fibrosis.

Mitochondrial quality control is an essential process required to maintain cellular homeostasis and functions. Mutations of PINK1 and PRKN/PARK2 contribute to the risk of Parkinson disease. Our recent findings indicate that depletion of Pink1 and Prkn promotes pancreatic tumorigenesis in KRAS-driven engineered mouse models. Mechanistically, PINK1- and PRKN-mediated autophagic degradation of mitochondrial iron importers (e.g., SLC25A37 and SLC25A28) suppresses pancreatic tumor growth by attenuating mitochondrial iron accumulation, inflammasome activation, HMGB1 release, and subsequent immune checkpoint expression. Consequently, pharmacological or genetic inhibition of mitochondrial iron-dependent signals prolongs animal survival and reverses pancreatic tumor phenotype in vivo. Thus, PINK1- and PRKN-mediated immunometabolism provides new insights into the tumor microenvironment and could be a suitable target for new pancreatic cancer treatments. [ABSTRACT FROM AUTHOR]

Mitochondrial iron import is essential for iron-sulfur cluster formation and heme biosynthesis. Two nuclear-encoded vertebrate mitochondrial high-affinity iron importers, mitoferrin1 (Mfrn1) and Mfrn2, have been identified in mammals. In mice, the gene encoding Mfrn1, solute carrier family 25 member 37 ( Slc25a37 ), is highly expressed in sites of erythropoiesis, and whole-body Slc25a37 deletion leads to lethality. Here, we report that mice with a deletion of Slc25a28 (encoding Mfrn2) are born at expected Mendelian ratios, but show decreased male fertility due to reduced sperm numbers and sperm motility. Mfrn2 -/- mice placed on a low-iron diet exhibited reduced mitochondrial manganese, cobalt, and zinc levels, but not reduced iron. Hepatocyte-specific loss of Slc25a37 (encoding Mfrn1) in Mfrn2 -/- mice did not affect animal viability, but resulted in a 40% reduction in mitochondrial iron and reduced levels of oxidative phosphorylation proteins. Placing animals on a low-iron diet exaggerated the reduction in mitochondrial iron observed in liver-specific Mfrn1/2 -knockout animals. Mfrn1 -/- / Mfrn2 -/- bone marrow-derived macrophages or skin fibroblasts in vitro were unable to proliferate, and overexpression of Mfrn1-GFP or Mfrn2-GFP prevented this proliferation defect. Loss of both mitoferrins in hepatocytes dramatically reduced regeneration in the adult mouse liver, further supporting the notion that both mitoferrins transport iron and that their absence limits proliferative capacity of mammalian cells. We conclude that Mfrn1 and Mfrn2 contribute to mitochondrial iron homeostasis and are required for high-affinity iron import during active proliferation of mammalian cells., Competing Interests: Conflict of interest—The authors declare no competing interests., (© 2020 Seguin et al.)