Liquiritigenin, an Active Ingredient of Liquorice, Alleviates Acute Kidney Injury by VKORC1-Mediated Ferroptosis Inhibition.

Acute kidney injury (AKI) is a major public health problem worldwide that still lacks effective treatments. Recent studies have suggested that ferroptosis is a key mediator of AKI due to its activation of lipid peroxidation. Therefore, we hypothesized that antiferroptosis agents might be a novel potential therapeutic strategy for AKI. Herein, we demonstrated that liquiritigenin (LG), an active ingredient of liquorice, improves renal function by inhibiting vitamin K epoxide reductase complex subunit 1 (VKORC1)-mediated ferroptosis, both in vivo and in vitro. In a folic acid-induced murine AKI model, after a single pre-treatment intravenous injection, LG markedly alleviated the loss of renal function through suppressing ferroptosis induced by iron accumulation. LG prevented mitochondrial morphological changes and upregulated glutathione and glutathione peroxidase 4 levels, while downregulating malonaldehyde and divalent iron levels. An in vitro RNA-sequence analysis suggested that the protective role of LG may involve upregulation of VKORC1. Moreover, knockdown of VKORC1 diminished the renal protective and antiferroptosis roles of LG. Collectively, our findings demonstrated that LG protected against AKI by inhibiting VKORC1-mediated ferroptosis. This suggests that inhibiting ferroptosis might be a novel therapeutic approach in the future.

c-Cbl induced podocin ubiquitination contributes to the podocytes injury in diabetic nephropathy.

The ubiquitination function in diabetic nephropathy (DN) has attracted much attention, but there is a lack of information on its ubiquitylome profile. To examine the differences in protein content and ubiquitination in the kidney between db/db mice and db/m mice, we deployed liquid chromatography-mass spectrometry (LC-MS/MS) to conduct analysis. We determined 145 sites in 86 upregulated modified proteins and 66 sites in 49 downregulated modified proteins at the ubiquitinated level. Moreover, 347 sites among the 319 modified proteins were present only in the db/db mouse kidneys, while 213 sites among the 199 modified proteins were present only in the db/m mouse kidneys. The subcellular localization study indicated that the cytoplasm had the highest proportion of ubiquitinated proteins (31.87%), followed by the nucleus (30.24%) and the plasma membrane (20.33%). The enrichment analysis revealed that the ubiquitinated proteins are mostly linked to tight junctions, oxidative phosphorylation, and thermogenesis. Podocin, as a typical protein of slit diaphragm, whose loss is a crucial cause of proteinuria in DN. Consistent with the results of ubiquitination omics, the K261R mutant of podocin induced the weakest ubiquitination compared with the K301R and K370R mutants. As an E3 ligase, c-Cbl binds to podocin, and the regulation of c-Cbl can impact the ubiquitination of podocin. In conclusion, in DN, podocin ubiquitination contributes to podocyte injury, and K261R is the most significant site. c-Cbl participates in podocin ubiquitination and may be a direct target for preserving the integrity of the slit diaphragm structure, hence reducing proteinuria in DN.