Abstract
Treatment with dexamethasone in human osteoblasts leads to oxidative stress and cell injures. NF-E2-related factor 2 (Nrf2) is a key anti-oxidant signaling. We want to induce Nrf2 activation via microRNA-mediated silencing its suppressor Keap1. Our results show that microRNA-200a (“miR-200a”) expression depleted Keap1, causing Nrf2 protein stabilization in OB-6 osteoblastic cells. Reversely, the miR-200a anti-sense led to Keap1 upregulation and Nrf2 degradation. miR-200a expression activated Nrf2 signaling, which inhibited dexamethasone-induced reactive oxygen species production and OB-6 cell death/apoptosis. Keap1 shRNA also activated Nrf2 and protected OB-6 cells from dexamethasone. Importantly, miR-200a was in-effective in Keap1-silenced (by shRNA) OB-6 cells. In the primary human osteoblasts, Keap1 silence by targeted-shRNA or miR-200a protected cells from dexamethasone. Significantly, miR-200a level was decreased in necrotic femoral head tissues, which was correlated with Keap1 mRNA upregulation. Together, miR-200a expression activates Nrf2 signaling and protects human osteoblasts from dexamethasone.
Highlights
Existing literatures have demonstrated that dexamethasone (Dex) and other glucocorticoids shall exert direct injuries to human osteoblasts [1,2,3]
Our results show that microRNA-200a (“miR-200a”) expression depleted Keap1, causing NF-E2-related factor 2 (Nrf2) protein stabilization in OB-6 osteoblastic cells
We demonstrate that miR-200a (“-3p”) putatively targets the 3’-untranslated region (UTR) of Keap1 mRNA (Figure 1A), as reported by other studies [26, 27]
Summary
Existing literatures have demonstrated that dexamethasone (Dex) and other glucocorticoids shall exert direct injuries to human osteoblasts [1,2,3]. Our group [6,7,8,9,10,11,12] and others [1315] have been treating human osteoblasts/osteoblastic cells with Dex, which mimicked glucocorticoid-induced injuries. Keap silence, mutation or inactivation could lead to Nrf stabilization [21, 22]. The latter translocates to nuclei, where it dictates transcription www.impactjournals.com/oncotarget of multiple anti-oxidant genes via binding to antioxidant response element (ARE) [19, 20]. Forced-expression of miR-200a silences Keap to activate Nrf signaling, which protects human osteoblasts/osteoblastic cells from Dex
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