Moderate Nrf2 Activation by Genetic Disruption of Keap1 Has Sex-Specific Effects on Bone Mass in Mice

Yukun Yin,John P Loughran,Jiliang Li,Kylie A Corry

doi:10.1038/s41598-019-57185-1

Yukun Yin, John P Loughran + Show 2 more

Open Access

https://doi.org/10.1038/s41598-019-57185-1

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Abstract

Keap1 is a negative controller of the transcription factor Nrf2 for its activity. The Keap1/Nrf2 signaling pathway has been considered as a master regulator of cytoprotective genes, and exists in many cell types including osteoblasts and osteoclasts. Our previous study shows Nrf2 deletion decreases bone formation. Recent studies show hyperactivation of Nrf2 causes osteopenia in Keap1−/− mice, and Keap1−/− osteoblasts have significantly less proliferative potential than Keap1+/− osteoblasts. We aimed to examine if moderate Nrf2 activation by disruption of Keap1 impacts bone metabolism. We examined bone phenotype of Keap1 heterozygotic mice (Ht) in comparison with Keap1 wild type (WT) mice. Deletion or knockdown of Keap1 enhanced the gene expression of Nrf2, ALP and wnt5a in cultured primary osteoblasts compared to WT control. In male mice, compared with their age-matched littermate WT controls, Keap1 Ht mice showed significant increase in bone formation rate (+30.7%, P = 0.0029), but did not change the ultimate force (P < 0.01). The osteoclast cell numbers (−32.45%, P = 0.01) and surface (−32.58%, P = 0.03) were significantly reduced by Keap1 deficiency in male mice. Compared to male WT mice, serum bone resorption marker in male Keap1 Ht mice was significantly decreased. Our data suggest that moderate Nrf2 activation by disruption of Keap1 improved bone mass by regulating bone remodeling in male mice.

Highlights

Keap[1] is a negative controller of the transcription factor Nrf[2] for its activity
The Kelch-like ECH-associated protein 1 (Keap1)/Nuclear factor erythroid 2-related factor 2 (Nrf2) protein axis plays an important role in regulating cytoprotective enzymes[2]
It is reported that reactive oxygen species (ROS) acts as intracellular signaling molecules to regulate osteoclast differentiation, and the Keap1/Nrf[2] axis plays a role in osteoclast differentiation by regulating intracellular ROS signaling[8]

Summary

Introduction

Keap[1] is a negative controller of the transcription factor Nrf[2] for its activity. Because the juvenile death of Keap1−/− mice is caused by the obstruction of the esophagus and starvation[15], the other lab generated a viable model by crossing the floxed Nrf[2] mice, keratin5-drived-Cre mice and Keap1−/− mice in which a squamous epithelium-specific Nrf[2] deficiency in the context of systemic Keap[1] deletion[14,16] These unique mice (Keap1−/−; Nrf2Flox/Flox; Keratin5-Cre), which display a complication of nephrogenic diabetes insipidus[16], present smaller bone size and lower bone density compared to the control mice despite the osteoclast number and bone resorption are significantly inhibited[14]. An in vivo mouse model and an in vitro cell culture system from Keap[1] knockdown and knockout mice were utilized

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