Upregulation of Hemoglobin Expression by Oxidative Stress in Hepatocytes and Its Implication in Nonalcoholic Steatohepatitis

Abstract

Recent studies revealed that hemoglobin is expressed in some non-erythrocytes and it suppresses oxidative stress when overexpressed. Oxidative stress plays a critical role in the pathogenesis of non-alcoholic steatohepatitis (NASH). This study was designed to investigate whether hemoglobin is expressed in hepatocytes and how it is related to oxidative stress in NASH patients. Analysis of microarray gene expression data revealed a significant increase in the expression of hemoglobin alpha (HBA1) and beta (HBB) in liver biopsies from NASH patients. Increased hemoglobin expression in NASH was validated by quantitative real time PCR. However, the expression of hematopoietic transcriptional factors and erythrocyte specific marker genes were not increased, indicating that increased hemoglobin expression in NASH was not from erythropoiesis, but could result from increased expression in hepatocytes. Immunofluorescence staining demonstrated positive HBA1 and HBB expression in the hepatocytes of NASH livers. Hemoglobin expression was also observed in human hepatocellular carcinoma HepG2 cell line. Furthermore, treatment with hydrogen peroxide, a known oxidative stress inducer, increased HBA1 and HBB expression in HepG2 and HEK293 cells. Importantly, hemoglobin overexpression suppressed oxidative stress in HepG2 cells. We concluded that hemoglobin is expressed by hepatocytes and oxidative stress upregulates its expression. Suppression of oxidative stress by hemoglobin could be a mechanism to protect hepatocytes from oxidative damage in NASH.

Oxidative stress promotes pathologic polyploidization in nonalcoholic fatty liver disease

“…As expected, markers of oxidative stress are detectable in ob/ob hepatocytes both in vivo and in vitro: accumulation of ROS, a high abundance of glutathione peroxidase-3 (GPX3) (reflecting the adaptive activation of antioxidant defenses), and a high abundance of hemoglobin α (HBA1) recently correlated with oxidative stress in patients with NASH (ref. 65 and Supplemental Figure 6, A-C). We treated primary ob/ob hepatocytes with the antioxidant NAC and examined cell cycle progression.…”

Upregulation and Mitochondrial Sequestration of Hemoglobin Occur in Circulating Leukocytes during Critical Illness, Conferring a Cytoprotective Phenotype

“…For instance, hypoxia upregulates hemoglobin expression in alveolar epithelial cells in vitro (22) and bacterial lipopolysaccharide upregulates the β hemoglobin subunit in murine macrophages (23). H 2 O 2 increases Hb-α1 and Hb-β expression in HepG2 and HEK293 cells, which, in turn, protects the cells from oxidative stress (24). Hemoglobin has been localized in kidney mesangial cells, where it confers oxidative stress resistance (25).…”

“…; n = 3; *p < 0.05; **p < 0.01. stress, the rate of the gaseous transmitters produced, as well as many additional factors. Based on several sets of independent investigations, it appears that when oxidative stress is relatively low, hemoglobin (and its degradation products, for example, heme) increases oxidative stress, and scavenges physiologically necessary amounts of NO, but when the degree of oxidative stress is high, hemoglobin tends to protect from cellular damage (22)(23)(24)(25)(26)(27)31). One also has to keep in mind that hemoglobin decomposes into multiple products, including heme (which increases oxidative stress, but also acts as a substrate of the gasotransmitter carbon monoxide, produced by heme oxygenase), while other degradation products (for example, bilirubin) have significant antioxidant effects (31).…”

“…It remains to be elucidated if similar reactive responses can also be elicited by other stimuli (for example, hypoxia, oxidative stress, NO, CO and others) in PBMCs. In this context, it is worth mentioning that, in other cell types, Hb upregulation has been demonstrated in response to bacterial lipopolysaccharide stimulation in murine monocytemacrophages (23), in response to hypoxia in epithelial cells (22) or in response to oxidative stress in hepatocytes (24). (d) What is the exact functional role of Hbs in the mitochondria, and how does Hbs translocation occurs into the mitochondria?…”

Associations Between Liver Function, Bone Turnover Biomarkers and Adipokines in Older Patients With Hip Fracture

“…In addition, our study showed involvement of other factors which have also been proposed as indices of oxidant stress status, namely serum hemoglobin levels were significantly and independently associated with GGT activity (inversely) and albumin concentration (positively), while OC correlated with bilirubin level. Hemoglobin [116,117], albumin [118][119][120] and bilirubin [118,121] exhibit potent antioxidant properties. Increases in GGT activity may reflect the responses of counteracting mechanisms to protect against oxidative damage.…”