Ferroptosis is an iron-dependent form of regulated nonapoptotic cell death, which contributes to damage in models of acute kidney injury (AKI). Heme oxygenase-1 (HO-1) is a cytoprotective enzyme induced in response to cellular stress, and is protective against AKI because of its antiapoptotic and anti-inflammatory properties. However, the role of HO-1 in regulating ferroptosis is unclear. The purpose of this study was to elucidate the role of HO-1 in regulating ferroptotic cell death in renal proximal tubule cells (PTCs). Immortalized PTCs obtained from HO-1 and HO-1 mice were treated with erastin or RSL3, ferroptosis inducers, in the presence or absence of antioxidants, an iron source, or an iron chelator. Cells were assessed for changes in morphology and metabolic activity as an indicator of cell viability. Treatment of HO-1 PTCs with erastin resulted in a time- and dose-dependent increase in HO-1 gene expression and protein levels compared with vehicle-treated controls. HO-1 cells showed increased dose-dependent erastin- or RSL3-induced cell death in comparison to HO-1 PTCs. Iron supplementation with ferric ammonium citrate in erastin-treated cells decreased cell viability further in HO-1 PTCs compared with HO-1 cells. Cotreatment with ferrostatin-1 (ferroptosis inhibitor), deferoxamine (iron chelator), or N-acetyl-l-cysteine (glutathione replenisher) significantly increased cell viability and attenuated erastin-induced ferroptosis in both HO-1 and HO-1 PTCs. These results demonstrate an important antiferroptotic role of HO-1 in renal epithelial cells.

The cardioprotective inducible enzyme heme oxygenase-1 (HO-1) degrades prooxidant heme into equimolar quantities of carbon monoxide, biliverdin, and iron. We hypothesized that HO-1 mediates cardiac protection, at least in part, by regulating mitochondrial quality control. We treated WT and HO-1 transgenic mice with the known mitochondrial toxin, doxorubicin (DOX). Relative to WT mice, mice globally overexpressing human HO-1 were protected from DOX-induced dilated cardiomyopathy, cardiac cytoarchitectural derangement, and infiltration of CD11b+ mononuclear phagocytes. Cardiac-specific overexpression of HO-1 ameliorated DOX-mediated dilation of the sarcoplasmic reticulum as well as mitochondrial disorganization in the form of mitochondrial fragmentation and increased numbers of damaged mitochondria in autophagic vacuoles. HO-1 overexpression promotes mitochondrial biogenesis by upregulating protein expression of NRF1, PGC1α, and TFAM, which was inhibited in WT animals treated with DOX. Concomitantly, HO-1 overexpression inhibited the upregulation of the mitochondrial fission mediator Fis1 and resulted in increased expression of the fusion mediators, Mfn1 and Mfn2. It also prevented dynamic changes in the levels of key mediators of the mitophagy pathway, PINK1 and parkin. Therefore, these findings suggest that HO-1 has a novel role in protecting the heart from oxidative injury by regulating mitochondrial quality control.

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Conflict of interest: MM reports grants and consulting fees from Otsuka Pharmaceutical and Sanofi. AA serves as a consultant for DynaMed and is on the advisory board of Goldilocks Therapeutics.

Renal ischemia-reperfusion injury is mediated by a complex cascade of events, including the immune response, that occur secondary to injury to renal epithelial cells. We tested the hypothesis that heme oxygenase-1 (HO-1) expression, which is protective in ischemia-reperfusion injury, regulates trafficking of myeloid-derived immune cells in the kidney. Age-matched male wild-type (HO-1 +/+ ), HO-1-knockout donor kidneys, to the peripheral lymphoid organs. This effect on renal DC migration was corroborated in myeloid-specific HO-1 2/2 mice subjected to bilateral ischemia. These mice also displayed impaired renal recovery and increased fibrosis at day 7 after injury. These results highlight an important role for HO-1 in orchestrating the trafficking of myeloid cells in AKI, which may represent a key pathway for therapeutic intervention.

The G2019S mutation in LRRK2 is one of the most common known genetic causes of neurodegeneration and Parkinson disease (PD). LRRK2 mutations are thought to enhance LRRK2 kinase activity. Efficacious small molecule LRRK2 kinase inhibitors with favorable drug properties have recently been developed for pre-clinical studies in rodent models, and inhibitors have advanced to safety trials in humans. Rats that express human G2019S-LRRK2 protein and G2019S-LRRK2 knock-in mice provide newly characterized models to better understand the ostensible target for inhibitors. Herein, we explore the relationships between LRRK2 kinase inhibition in the brain and the periphery to establish the link between LRRK2 kinase activity and protein stability, induction of lysosomal defects in kidney and lung, and how G2019S-LRRK2 expression impacts these phenotypes. Using a novel ultra-sensitive scalable assay based on protein capillary electrophoresis with LRRK2 kinase inhibitors included in-diet, G2019S-LRRK2 protein was resilient to inhibition compared to wild-type (WT)-LRRK2 protein, particularly in the brain. Whereas WT-LRRK2 kinase activity could be completed blocked without lowering LRRK2 protein levels, higher inhibitor concentrations were necessary to fully reduce G2019S-LRRK2 activity. G2019S-LRRK2 expression afforded robust protection from inhibitor-induced kidney lysosomal defects, suggesting a gain-of-function for the mutation in this phenotype. In rodents treated with inhibitors, parallel measurements of phospho-Rab10 revealed a poor correlation to phospho-LRRK2, likely due to cells that express Rab10 but poorly express LRRK2 in heterogenous tissues and cell isolates. In summary, our results highlight several challenges associated with the inhibition of the G2019S-LRRK2 kinase that might be considered in initial clinical efforts.

The Leucine rich repeat kinase 2 (LRRK2) gene is genetically and biochemically linked to several diseases that involve innate immunity. LRRK2 protein is highly expressed in phagocytic cells of the innate immune system, most notably in myeloid cells capable of mounting potent pro-inflammatory responses. Knockdown of LRRK2 protein in these cells reduces pro-inflammatory responses. However, the effect of LRRK2 pathogenic mutations that cause Parkinson's disease on myeloid cell function is not clear but could provide insight into LRRK2-linked disease. Here, we find that rats expressing G2019S LRRK2 have exaggerated pro-inflammatory responses and subsequent neurodegeneration after lipopolysaccharide injections in the substantia nigra, with a marked increase in the recruitment of CD68 myeloid cells to the site of injection. While G2019S LRRK2 expression did not affect immunological homeostasis, myeloid cells expressing G2019S LRRK2 show enhanced chemotaxis both in vitro in two-chamber assays and in vivo in response to thioglycollate injections in the peritoneum. The G2019S mutation enhanced the association between LRRK2 and actin-regulatory proteins that control chemotaxis. The interaction between G2019S LRRK2 and actin-regulatory proteins can be blocked by LRRK2 kinase inhibitors, although we did not find evidence that LRRK2 phosphorylated these interacting proteins. These results suggest that the primary mechanism of G2019S LRRK2 with respect to myeloid cell function in disease may be related to exaggerated chemotactic responses.

Despite the prevalence and recognition of its detrimental impact, clinical complications of sepsis remain a major challenge. Here, we investigated the effects of myeloid ferritin heavy chain (FtH) in regulating the pathogenic sequelae of sepsis. We demonstrate that deletion of myeloid FtH leads to protection against lipopolysaccharide-induced endotoxemia and cecal ligation and puncture (CLP)-induced model of sepsis as evidenced by reduced cytokine levels, multi-organ dysfunction and mortality. We identified that such protection is predominantly mediated by the compensatory increase in circulating ferritin (ferritin light chain; FtL) in the absence of myeloid FtH. Our in vitro and in vivo studies indicate that prior exposure to ferritin light chain restrains an otherwise dysregulated response to infection. These findings are mediated by an inhibitory action of FtL on NF-κB activation, a key signaling pathway that is implicated in the pathogenesis of sepsis. We further identified that LPS mediated activation of MAPK pathways, specifically, JNK, and ERK were also reduced with FtL pre-treatment. Taken together, our findings elucidate a crucial immunomodulatory function for circulating ferritin that challenges the traditional view of this protein as a mere marker of body iron stores. Accordingly, these findings will stimulate investigations to the adaptive nature of this protein in diverse clinical settings.