Functional Expression of Heme Oxygenase-1 in Human Differentiated Epidermis and Its Regulation by Cytokines

Abstract

Although heme oxygenase-1 (HO-1) is induced in keratinocytes after UV radiation, HO-1 expression during normal epidermal differentiation has not yet been reported. We showed by real-time PCR, western blotting, and ELISA that HO-1 mRNA and protein expression by cultured normal human keratinocytes was upregulated during epidermal differentiation induced by a high-calcium medium. Immunohistochemical staining and in situ hybridization showed the graduated expression of HO-1 in the upper epidermis, which was accompanied by suprabasal HO-1 mRNA expression, and the accumulation of bilirubin (BR) in the stratum corneum. We examined the activation of nuclear factor E2-related factor 2 (Nrf2), which is a pivotal transcription factor for HO-1 expression, by western blotting and by examining the mRNA expression of Nrf2 target genes, and excluded its role in HO-1 expression in epidermal differentiation. Next, we examined the regulation of HO-1 expression by inflammatory cytokines. IL-4 and IL-22 significantly reduced HO-1 mRNA and protein expression, whereas IL-1beta, IL-17A, and tumor necrosis factor-alpha (TNF-alpha) increased it. Finally, immunohistochemical studies on psoriatic lesional skin showed that HO-1 expression was downregulated in the parakeratotic epidermis, whereas it was retained in the orthokeratotic epidermis. These studies demonstrate that HO-1 is functionally expressed by keratinocytes in parallel with epidermal differentiation and that its expression is independently affected by several cytokines.

Nrf2-dependent and Nrf2-independent induction of phase 2 detoxifying and antioxidant enzymes during keratinocyte differentiation

“…Interestingly, this study demonstrates that only NQO-1, but not HO-1 and GSTpi, is Nrf2 dependent during KC diVerentiation. Numata et al [18] also reported that the diVerentiation-dependent HO-1 expression in KC was not dependent on Nrf2, implying that the regulatory mechanism of phase 2 enzymes in relation to Nrf2 pathway might be tissue or cell speciWc. Unexpectedly, HO-1 and GSTpi were rather up-regulated in Nrf2 siRNA-transfected NHEK, implying that Nrf2 knock-down by siRNA transfection produced more stressful condition of oxidative status in NHEK, which led to the induction of Nrf2-independent enzymes (HO-1 and GSTpi) to protect cells from oxidative stress.…”

“…When cells are exposed to stresses, then Nrf2 is translocated to the nucleus, leading to the transcriptional activation of a group of phase 2 enzyme genes such as heme oxygenase-1 (HO-1), NADP(H):quinone oxidoreductase-1 (NQO-1), and glutathione S-transferase pi (GSTpi) [11]. Interestingly, however, HO-1 was reported not to be mediated by Nrf2-transcriptional factor in diVerentiated keratinocyte (KC), implying that cell-speciWc modulation of phase 2 enzymes [18].…”

Bach1-dependent and -independent Regulation of Heme Oxygenase-1 in Keratinocytes

“…As keratinocytes begin to differentiate, they cease cell growth and migrate to the upper layers (the spinous, granular, and cornified layers). HO-1 is induced during the terminal differentiation and is expressed in the upper part of the epidermis (17). These layers of the skin are directly exposed to the environment and require defense mechanisms against environmental insults, including oxidative stress and ultraviolet light.…”

“…HO-1 is induced during keratinocyte differentiation and is highly expressed in the upper layers of the epidermis (17). However, the mechanism of Bach1-mediated HO-1 regulation in keratinocytes remains unclear.…”

Can nitroxides evoke the Keap1–Nrf2–ARE pathway in skin?

“…It has been shown that this enzyme can act as a powerful antioxidant (see below). We chose to follow the induction and level of this protein as a marker for the activation of the Keap1-Nrf2-ARE pathway [49]. Fig.…”