Hemin Reduces HMGB1 Release by UVB in an AMPK/HO-1-dependent Pathway in Human Keratinocytes HaCaT Cells.

BACKGROUND AND AIMS: High mobility group box 1 (HMGB1) plays an important role as a pro-inflammatory cytokine that regulates inflammation in various diseases. We hypothesized that hemin might reduce HMGB1 release through the induction of HO-1 in UVB-induced HaCaTs.

METHODS: The effects of hemin on the release of HMGB1 in UVB exposure were evaluated. The mechanisms were investigated using various signal inhibitors and small interfering RNA techniques.

RESULTS: Treatment with hemin inhibited reactive oxygen species (ROS) in UVB-induced HaCaTs in a dose-dependent manner. HMGB1 release by UVB was significantly reduced by hemin, N-acetyl-cysteine and DPI (NADPH oxidase inhibitor). Hemin increased HO-1 induction followed by phosphorylation of AMPK in a time- and dose-dependent manner. Additionally, hemin significantly increased the NAD+ /NADH ratio in HaCaTs. The inhibitory effects of UVB-induced HMGB1 release by hemin were significantly reversed not only with pharmacological inhibitors of AMPK (compound c) or HO-1 (ZnPPIX) but also through transfection of small interfering RNAs (siRNAs) for AMPK or HO-1. Interestingly, hemin decreased phosphor-AMPK expression by HO-1 siRNA transfection, but it failed to induce HO-1 in AMPK siRNA-transfected cells, which suggested that HO-1 was involved in AMPK activation by hemin in HaCaT. Moreover, recombinant HMGB1 induced Snail and inhibited E-Cadherin in HaCaTs, whereas hemin reversed those effects through rHMGB1.

CONCLUSIONS: It is concluded that the increased activity of HO-1/AMPK and scavenging ROS are, at least in part, responsible for the inhibition of UVB-induced HMGB1 release in keratinocyte HaCaTs. Therefore, hemin may be a useful agent for preventing UVB-induced skin cancer.