| First Author | Anavi S | Year | 2012 |
| Journal | Free Radic Biol Med | Volume | 52 |
| Issue | 9 | Pages | 1531-42 |
| PubMed ID | 22343340 | Mgi Jnum | J:183261 |
| Mgi Id | MGI:5318144 | Doi | 10.1016/j.freeradbiomed.2012.02.014 |
| Citation | Anavi S, et al. (2012) Oxidative stress impairs HIF1alpha activation: a novel mechanism for increased vulnerability of steatotic hepatocytes to hypoxic stress. Free Radic Biol Med 52(9):1531-42 |
| abstractText | Steatosis increases the sensitivity of hepatocytes to hypoxic injury. Thus, this study was designed to elucidate the role of hypoxia-inducible factor-1alpha (HIF1alpha) in steatotic hepatocytes during hypoxia. AML12 hepatocytes and isolated rat hepatocytes were treated with a free fatty acid mixture of oleate and palmitate (2:1, 1 mM) for 18 h, which generated intrahepatocyte fat accumulation. The cells were then exposed to hypoxia (1% oxygen, 6-24 h). After hypoxia, a further increase in cellular fat accumulation was seen. In steatotic hepatocytes, a decreased HIF1alpha activation by hypoxia was observed. The capacity of these cells to express HIF1alpha-dependent genes responsible for the utilization of nutrients for energy was also impaired. This resulted in significantly lower intracellular ATP levels and greater cell death in steatotic hepatocytes compared with control hepatocytes. In contrast, overexpression of constitutively active HIF1alpha significantly increased cell viability as well as ATP and GLUT1 mRNA levels in steatotic hepatocytes under hypoxia. Hypoxia significantly enhanced HIF1alpha mRNA levels in control but not in steatotic hepatocytes. Concomitantly, an increase in oxidative stress was found in steatotic hepatocytes under hypoxic conditions compared with control cells. This included higher reactive oxygen species generation, lower cellular and nuclear GSH levels, and higher accumulation of 4-hydroxynonenal protein adducts. Hypoxia-mediated oxidative stress was accompanied by inactivation of basal nuclear factor-kappaB (NF-kappaB) DNA binding. Treatment with N-acetyl-l-cysteine, a reducing agent, improved NF-kappaB DNA-binding capacity and restored HIF1alpha induction. Conversely, overexpression of an NF-kappaB super-suppressor in control hepatocytes (IkappaBalphaDeltaN-transfected cells) resulted in complete inhibition of HIF1alpha expression, confirming that indeed NF-kappaB regulates HIF1alpha expression in hypoxic hepatocytes. In conclusion, hypoxia in combination with hepatic steatosis was shown to promote augmented oxidative stress, leading to NF-kappaB inactivation and impaired HIF1alpha induction and thereby increased susceptibility to hypoxic injury. |
