57 research outputs found
Role Of Heme Oxygenase-1 In Acute Kidney Injury
No full textAcute kidney injury (AKI), defined as the rapid loss of kidney function, is often seen in the setting of multiple organ failure in critically ill patients. Lack of established therapeutic approaches to overcome AKI has lead to unacceptably high incidence of morbidity and mortality in these patients. The molecular mechanisms that lead to AKI often have oxidative stress as a common pathogenic event. The kidney responds by prompt induction of its own anti-oxidant machinery including the highly inducible, anti-inflammatory and anti-apoptotic gene-heme oxygenase-1 (HO-1). This microsomal enzyme degrades pro-oxidant heme, which is released from heme proteins. The cytoprotective properties of HO-1 are not merely due to removal of heme but are also attributed to the beneficial properties of the by-products of the reaction. Biliverdin and bilirubin are potent peoxyl radical scavengers and carbon monoxide has anti-inflammatory and anti-apoptotic properties. This thesis discusses an undiscovered property of HO-1 in AKI, namely autophagy, which is a regulated intracellular degradation system in which cytoplasmic components are directed to the lysosome for breakdown. However, excessive autophagy is deleterious as it may destroy cell contents beyond a certain threshold that would lead to cell death. Therefore, regulation of autophagy during injury is extremely important for survival. The results of this thesis indicate that HO-1 modulates autophagy in renal epithelial cells during AKI and confers cytoprotection. Specifically, mice deficient in HO-1 had increased basal autophagy which upon cisplatin injury led to increased apoptosis. However, overexpression of HO-1 was associated with a delayed autophagic response and decreased apoptosis during injury. Also, HO-1 overexpression resulted in decreased reactive oxygen species (ROS) generation during injury. More importantly, restoring HO-1 expression in HO-1 deficient mice rescued mice from impaired autophagy and increased apoptosis during AKI. It is noteworthy that most of the ROS generation during AKI is attributed to mitochondria. We therefore targeted HO-1 to the mitochondria and rescued renal epithelial cells from loss of mitochondrial integrity, increased ROS accumulation and lipid peroxidation during oxidative stress. These findings demonstrate a novel mechanistic role for HO-1 in limiting oxidative stress and modulating autophagy and provide new avenues for therapeutic approaches in AKI
Mitochondria and Reactive Oxygen Species: Physiology and Pathophysiology
No full textThe air that we breathe contains nearly 21% oxygen, most of which is utilized by mitochondria during respiration. While we cannot live without it, it was perceived as a bane to aerobic organisms due to the generation of reactive oxygen and nitrogen metabolites by mitochondria and other cellular compartments. However, this dogma was challenged when these species were demonstrated to modulate cellular responses through altering signaling pathways. In fact, since this discovery of a dichotomous role of reactive species in immune function and signal transduction, research in this field grew at an exponential pace and the pursuit for mechanisms involved began. Due to a significant number of review articles present on the reactive species mediated cell death, we have focused on emerging novel pathways such as autophagy, signaling and maintenance of the mitochondrial network. Despite its role in several processes, increased reactive species generation has been associated with the origin and pathogenesis of a plethora of diseases. While it is tempting to speculate that anti-oxidant therapy would protect against these disorders, growing evidence suggests that this may not be true. This further supports our belief that these reactive species play a fundamental role in maintenance of cellular and tissue homeostasis
Neutrophils in acute kidney injury: not neutral any more
No full textAwad and colleagues elucidate the spatiotemporal profile of neutrophil infiltration in the kidney following ischemia–reperfusion injury. Using elegant in vivo labeling techniques, they demonstrate increased neutrophil content in the kidney following ischemia–reperfusion, which is largely due to transmigration from the circulation into the interstitial compartment. The authors also provide mechanistic insights into this phenomenon and show that adenosine 2A receptor agonists reduce interstitial neutrophil infiltration and improve renal function
Macrophage and epithelial cell H-ferritin expression regulates renal inflammation
No full textInflammation culminating in fibrosis contributes to progressive kidney disease. Cross-talk between the tubular epithelium and interstitial cells regulates inflammation by a coordinated release of cytokines and chemokines. Here we studied the role of heme oxygenase-1 (HO-1) and the heavy subunit of ferritin (FtH) in macrophage polarization and renal inflammation. Deficiency in HO-1 was associated with increased FtH expression, accumulation of macrophages with a dysregulated polarization profile, and increased fibrosis following unilateral ureteral obstruction in mice: a model of renal inflammation and fibrosis. Macrophage polarization in vitro was predominantly dependent on FtH expression in isolated bone marrow-derived mouse monocytes. Using transgenic mice with conditional deletion of FtH in the proximal tubules (FtH(PT-/-)) or myeloid cells (FtH(LysM-/-)), we found that myeloid FtH deficiency did not affect polarization or accumulation of macrophages in the injured kidney compared with wild-type (FtH(+/+)) controls. However, tubular FtH deletion led to a marked increase in proinflammatory macrophages. Furthermore, injured kidneys from FtH(PT-/-) mice expressed significantly higher levels of inflammatory chemokines and fibrosis compared with kidneys from FtH(+/+) and FtH(LysM-/-) mice. Thus, there are differential effects of FtH in macrophages and epithelial cells, which underscore the critical role of FtH in tubular-macrophage cross-talk during kidney injury
Proximal tubule H-ferritin mediates iron trafficking in acute kidney injury
No full textFerritin plays a central role in iron metabolism and is made of 24 subunits of 2 types: heavy chain and light chain. The ferritin heavy chain (FtH) has ferroxidase activity that is required for iron incorporation and limiting toxicity. The purpose of this study was to investigate the role of FtH in acute kidney injury (AKI) and renal iron handling by using proximal tubule-specific FtH-knockout mice (FtHPT mice). FtHPT mice had significant mortality, worse structural and functional renal injury, and increased levels of apoptosis in rhabdomyolysis and cisplatin-induced AKI, despite significantly higher expression of heme oxygenase-1, an antioxidant and cytoprotective enzyme. While expression of divalent metal transporter-1 was unaffected, expression of ferroportin (FPN) was significantly lower under both basal and rhabdomyolysis-induced AKI in FtHPT mice. Apical localization of FPN was disrupted after AKI to a diffuse cytosolic and basolateral pattern. FtH, regardless of iron content and ferroxidase activity, induced FPN. Interestingly, urinary levels of the iron acceptor proteins neutrophil gelatinase-associated lipocalin, hemopexin, and transferrin were increased in FtHPT-/-mice after AKI. These results underscore the protective role of FtH and reveal the critical role of proximal tubule FtH in iron trafficking in AKI
Interleukin-1 promotes autoimmune neuroinflammation by suppressing endothelial heme oxygenase-1 at the blood–brain barrier
No full textThe proinflammatory cytokine interleukin 1 (IL-1) is crucially involved in the pathogenesis of multiple sclerosis (MS) and its animal model experimental autoimmune encephalomyelitis (EAE). Herein, we studied the role of IL-1 signaling in blood-brain barrier (BBB) endothelial cells (ECs), astrocytes and microglia for EAE development, using mice with the conditional deletion of its signaling receptor IL-1R1. We found that IL-1 signaling in microglia and astrocytes is redundant for the development of EAE, whereas the IL-1R1 deletion in BBB-ECs markedly ameliorated disease severity. IL-1 signaling in BBB-ECs upregulated the expression of the adhesion molecules Vcam-1, Icam-1 and the chemokine receptor Darc, all of which have been previously shown to promote CNS-specific inflammation. In contrast, IL-1R1 signaling suppressed the expression of the stress-responsive heme catabolizing enzyme heme oxygenase-1 (HO-1) in BBB-ECs, promoting disease progression via a mechanism associated with deregulated expression of the IL-1-responsive genes Vcam1, Icam1 and Ackr1 (Darc). Mechanistically, our data emphasize a functional crosstalk of BBB-EC IL-1 signaling and HO-1, controlling the transcription of downstream proinflammatory genes promoting the pathogenesis of autoimmune neuroinflammation
Heme oxygenase-1 mitigates ferroptosis in renal proximal tubule cells
No full text 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. </jats:p
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