Long isoforms of NRF1 contribute to arsenic-induced antioxidant response in human keratinocytes

BACKGROUND

Human exposure to inorganic arsenic (iAs), a potent oxidative stressor, causes various dermal disorders, including hyperkeratosis and skin cancer. Nuclear factor-erythroid 2-related factor 1 (NRF1, also called NFE2L1) plays a critical role in regulating the expression of many antioxidant response element (ARE)-dependent genes.

OBJECTIVES

We investigated the role of NRF1 in arsenic-induced antioxidant response and cytotoxicity in human keratinocytes.

RESULTS

In cultured human keratinocyte HaCaT cells, inorganic arsenite (iAs3+) enhanced the protein accumulation of long isoforms (120-140 kDa) of NRF1 in a dose- and time-dependent fashion. These isoforms accumulated mainly in the nuclei of HaCaT cells. Selective deficiency of NRF1 by lentiviral short-hairpin RNAs in HaCaT cells [NRF1-knockdown (KD)] led to decreased expression of γ-glutamate cysteine ligase catalytic subunit (GCLC) and regulatory subunit (GCLM) and a reduced level of intracellular glutathione. In response to acute iAs3+ exposure, induction of some ARE-dependent genes, including NAD(P)H:quinone oxidoreductase 1 (NQO1), GCLC, and GCLM, was significantly attenuated in NRF1-KD cells. However, the iAs3-induced expression of heme oxygenase 1 (HMOX-1) was unaltered by silencing NRF1, suggesting that HMOX-1 is not regulated by NRF1. In addition, the lack of NRF1 in HaCaT cells did not disturb iAs3+-induced NRF2 accumulation but noticeably decreased Kelch-like ECH-associated protein 1 (KEAP1) levels under basal and iAs3+-exposed conditions, suggesting a potential interaction between NRF1 and KEAP1. Consistent with the critical role of NRF1 in the transcriptional regulation of some ARE-bearing genes, knockdown of NRF1 significantly increased iAs3+-induced cytotoxicity and apoptosis.

CONCLUSIONS

Here, we demonstrate for the first time that long isoforms of NRF1 contribute to arsenic-induced antioxidant response in human keratinocytes and protect the cells from acute arsenic cytotoxicity.

Curcumin protects human keratinocytes against inorganic arsenite-induced acute cytotoxicity through an NRF2-dependent mechanism

Human exposure to inorganic arsenic leads to various dermal disorders, including hyperkeratosis and skin cancer. Curcumin is demonstrated to induce remarkable antioxidant activity in a variety of cells and tissues. The present study aimed at identifying curcumin as a potent activator of nuclear factor erythroid 2-related factor 2 (NRF2) and demonstrating its protective effect against inorganic arsenite- (iAs(3+)-) induced cytotoxicity in human keratinocytes. We found that curcumin led to nuclear accumulation of NRF2 protein and increased the expression of antioxidant response element- (ARE-) regulated genes in HaCaT keratinocytes in concentration- and time-dependent manners. High concentration of curcumin (20 μM) also increased protein expression of long isoforms of NRF1. Treatment with low concentrations of curcumin (2.5 or 5 μM) effectively increased the viability and survival of HaCaT cells against iAs(3+)-induced cytotoxicity as assessed by the MTT assay and flow cytometry and also attenuated iAs(3+)-induced expression of cleaved caspase-3 and cleaved PARP protein. Selective knockdown of NRF2 or KEAP1 by lentiviral shRNAs significantly diminished the cytoprotection conferred by curcumin, suggesting that the protection against iAs(3+)-induced cytotoxicity is dependent on the activation of NRF2. Our results provided a proof of the concept of using curcumin to activate the NRF2 pathway to alleviate arsenic-induced dermal damage.

Cross-regulations among NRFs and KEAP1 and effects of their silencing on arsenic-induced antioxidant response and cytotoxicity in human keratinocytes

BACKGROUND

Nuclear factor E2-related factors (NRFs), including NRF2 and NRF1, play critical roles in mediating the cellular adaptive response to oxidative stress. Human exposure to inorganic arsenic, a potent oxidative stressor, causes various dermal disorders, including hyperkeratosis and skin cancer.

OBJECTIVE

We investigated the cross-regulations among NRF2, NRF1, and KEAP1, a cullin-3-adapter protein that allows NRF2 to be ubiquinated and degraded by the proteasome complex, in arsenic-induced antioxidant responses.

RESULTS

In human keratinocyte HaCaT cells, selective knockdown (KD) of NRF2 by lentiviral short hairpin RNAs (shRNAs) significantly reduced the expression of many antioxidant enzymes and sensitized the cells to acute cytotoxicity of inorganic arsenite (iAs(3+)). In contrast, silencing KEAP1 led to a dramatic resistance to iAs(3+)-induced apoptosis. Pretreatment of HaCaT cells with NRF2 activators, such as tert-butylhydroquinone, protects the cells against acute iAs(3+) toxicity in an NRF2-dependent fashion. Consistent with the negative regulatory role of KEAP1 in NRF2 activation, KEAP1-KD cells exhibited enhanced transcriptional activity of NRF2 under nonstressed conditions. However, deficiency in KEAP1 did not facilitate induction of NRF2-target genes by iAs(3+). In addition, NRF2 silencing reduced the expression of KEAP1 at transcription and protein levels but increased the protein expression of NRF1 under the iAs(3+)-exposed condition. In contrast, silencing KEAP1 augmented protein accumulation of NRF2 under basal and iAs3+-exposed conditions, whereas the iAs(3+)-induced protein accumulation of NRF1 was attenuated in KEAP1-KD cells.

CONCLUSIONS

Our studies suggest that NRF2, KEAP1, and NRF1 are coordinately involved in the regulation of the cellular adaptive response to iAs(3+)-induced oxidative stress.

Melatonin rescues glucocorticoid-induced inhibition of osteoblast differentiation in MC3T3-E1 cells via the PI3K/AKT and BMP/Smad signalling pathways

AIMS

High-dose glucocorticoid (GC) administration causes osteoporosis. Many previous studies from our group and other groups have shown that melatonin participates in the regulation of osteoblast proliferation and differentiation, especially low concentrations of melatonin, which enhance osteoblast osteogenesis. However, the role of melatonin in glucocorticoid-induced osteoblast differentiation remains unknown.

MATERIALS AND METHODS

An examination of the expression of osteoblast differentiation markers (ALP, OCN, COLL-1), as well as alkaline phosphatase staining and alkaline phosphatase enzymatic activity assay to measure osteoblast differentiation and quantifying Alizarin red S staining to measure mineralization, were performed to determine the effects of dexamethasone (Dex) and melatonin on the differentiation of MC3T3-E1 cells. We used immunofluorescence staining to detect the expression of Runx2 in melatonin-treated MC3T3-E1 cells. The expression of mRNA was determined by qRT-PCR, and protein levels were measured by western blotting.

KEY FINDINGS

In the present study, we found that 100 μM Dex significantly reduced osteoblast differentiation and mineralization in MC3T3-E1 cells and that 1 μM melatonin attenuated these inhibitory effects. We found that only inhibition of PI3K/AKT (MK2206) and BMP/Smad (LDN193189) signalling abolished melatonin-induced differentiation and mineralization. Meanwhile, MK2206 decreased the expression of P-AKT and P-Smad1/5/9 and LDN193189 decreased the expression of P-Smad1/5/9 but had no obvious effect on P-AKT expression in melatonin-treated and Dex-induced MC3T3-E1 cells.

SIGNIFICANCE

These findings suggest that melatonin rescues Dex-induced inhibition of osteoblast differentiation in MC3T3-E1 cells via the PI3K/AKT and BMP/Smad signalling pathways and that PI3K/AKT signalling may be the upstream signal of BMP/Smad signalling.

Increased expressions and activations of apoptosis-related factors in cell signaling during incised skin wound healing in mice: a preliminary study for forensic wound age estimation

Recent studies have demonstrated that apoptosis plays a pivotal role during skin wound healing and apoptosis-related factors in cell signaling regulate a variety of cellular function. In this study, the expressions of p38MAPK, and JNK, iNOS, eNOS were detected and the activations of caspase-6, -7, -8, -9, and calpain, another signaling pathway of apoptosis, were also investigated by immunohistochemical staining and Western blotting in mice. A time-dependent increase of each protein level was observed by immunohistochemistry and Western blot in mouse skin incision. p38MAPK level peaked at 12 h and 3 d, calpain level peaked at 1 d and 5 d, iNOS level peaked at 1 d and 10 d, while the peak levels of eNOS, caspase-6, -7, -8, and -9 occurred at 3 d and p-JNK at 1 d post-injury. In the early phase of wound healing, infiltrating polymorphonulcear cells were labeled with all the factors except caspase-8. Thereafter, infiltrating mononuclear cells and proliferating spindle-shaped fibroblastic cells showed positive staining for p38MAPK, JNK, calpain, caspases and NOS. The activation of caspase-8, -9, -6, and -7 as detected by Western blot indicated that caspase apoptotic pathway may take effect in cellular elimination during skin wound healing. From the viewpoint of forensic pathology, the time-dependent expressions of the factors in apoptotic pathway during skin incised wound healing may be used as potential markers for wound age estimation.

Diagnostic aspects for epidemic hemorrhagic fever in legal medical autopsy: report of 2 cases and review

Epidemic hemorrhagic fever (EHF) is known also as hemorrhagic fever with renal syndrome (HFRS). Hantaviruses, a notorious cause of EHF is spreaded by rodents or biting insects, can cause epidemic hemorrhagic fever. This report describes two rare medico-legal autopsy cases died from epidemic hemorrhagic fever. The victims were two male individuals aged 34 years and 29 years. The medico-legal autopsies were requested for alleged medical negligence. In both cases, autopsy reveals lesions to kidneys and lungs with multiple organ hemorrhage and edema, indicative of the generalized capillary damage. On admission to hospital, both patients had the symptom of fever, lumbago, renal failure and recent outdoor activities. The laboratory diagnosis results indicating multiple organ dysfunction syndrome are also important for certificating of EHF. Though the ELISA-based detection of virus-specific IgM antibody which has the highest titers between 8 and 25d after onset of disease is positive in the 34-year-old case and negative in 29-year-old case, the pathological findings and clinical laboratory analysis suggested the both victims died of EHF. In addition, immunohistochemistry analysis for Hantavirus antigen in lung or in tubular cells and PCR having been used increasingly in recent years contribute to the diagnosis of Hantavirus infection.

[Immunohistochemical study on expression of iNOS and eNOS during skin incised wound healing in mice]

OBJECTIVE

To investigate the expressions of iNOS and eNOS during skin incised wound healing and the applicability of time-dependent expressions of iNOS and eNOS to timing of wound.

METHODS

An incised wound was made in the dorsal skin of mouse. By using S-P method, the expression of iNOS and eNOS were studied in cutaneous incised wound as well as normal skin in control mice.

RESULTS

iNOS and eNOS expressed in epidermis, hair follicle, sebaceous gland, and the eNOS were also found in vascular endothelium in control group. Three hours after injuryed, the expression of iNOS and eNOS were detected in polymorphonuclear cells (PMNs) in the wound and peripheral region. From 6h to 24h of wound interval, the expression of NOS isoforms were identified in a large number of infiltrating PMNs and part of mononuclear cells (MNCs), afterwards the MNCs and fibroblastic cells (FBCs) accounted for the most part of the iNOS and eNOS positive cells. In addition, during wound healing, the expressions of iNOS and eNOS were noticed in different level in vascular epithelial cells, especially neonatal capillary vessel in granulation tissue.

CONCLUSION

The results suggest that iNOS and eNOS express in polymorphonuclear cells, macrophages and fibroblasts during healing process of skin incised wound in mice. Furthermore, iNOS and eNOS may play pivotal roles in all the events relating to wound healing, and the time-dependent expressions of iNOS and eNOS may possibly be used as new markers for the wound age determination.