Cellular iron, at the physiological level, is essential to maintain several metabolic pathways, while an excess of free iron may cause oxidative damage and/or provoke cell death. Consequently, iron homeostasis has to be tightly controlled. Under hypoxia these regulatory mechanisms for human macrophages are not well understood. Hypoxic primary human macrophages reduced intracellular free iron and increased ferritin expression, including mitochondrial ferritin (FTMT), to store iron. In parallel, nuclear receptor coactivator 4 (NCOA4), a master regulator of ferritinophagy, decreased and was proven to directly regulate FTMT expression. Reduced NCOA4 expression resulted from a lower rate of hypoxic NCOA4 transcription combined with a micro RNA 6862-5p-dependent degradation of NCOA4 mRNA, the latter being regulated by c-jun N-terminal kinase (JNK). Pharmacological inhibition of JNK under hypoxia increased NCOA4 and prevented FTMT induction. FTMT and ferritin heavy chain (FTH) cooperated to protect macrophages from RSL-3-induced ferroptosis under hypoxia as this form of cell death is linked to iron metabolism. In contrast, in HT1080 fibrosarcome cells, which are sensitive to ferroptosis, NCOA4 and FTMT are not regulated. Our study helps to understand mechanisms of hypoxic FTMT regulation and to link ferritinophagy and macrophage sensitivity to ferroptosis.
The effect of the aminoglycosides amikacin, gentamicin, netilmicin sisomicin and tobramycin on the proximal tubule of the human kidney was investigated in 78 healthy subjects. Fifteen adults were each given gentamicin, sisomicin or tobramycin 3 mg/kg bodyweight, 10 subjects received netilmicin 3 mg/kg or amikacin 15 mg/kg additionally seven subjects amikacin 10 mg and six subjects netilmicin 6 mg on three consecutive days. The principal enzyme of the brush border membrane of the proximal tubule, alanine aminopeptidase (AAP), was determined enzymatically and immunologically in 24-hour urines. The effects of the various aminoglycosides on the membranes were different. Less of membrane AAP was greatest after amikacin and was least after tobramycin. There was no difference between gentamicin, netilmicin, and sisomicin, which had an effect intermediate between the other two compounds. The elimination of AAP occurred at intervals which might possibly have been caused by impairment of cell cycles.
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