Basic Study
Copyright ©The Author(s) 2024. Published by Baishideng Publishing Group Inc. All rights reserved.
World J Stem Cells. Apr 26, 2024; 16(4): 389-409
Published online Apr 26, 2024. doi: 10.4252/wjsc.v16.i4.389
Unveiling the role of hypoxia-inducible factor 2alpha in osteoporosis: Implications for bone health
Ling-Ling Wang, Zhan-Jin Lu, Shun-Kui Luo, Yun Li, Zhe Yang, Hong-Yun Lu
Ling-Ling Wang, Department of Gerontology, The Fifth Affiliated Hospital of Sun Yat-sen University, Zhuhai 519000, Guangdong Province, China
Zhan-Jin Lu, Shun-Kui Luo, Department of Endocrinology and Metabolism, The Fifth Affiliated Hospital of Sun Yat-sen University, Zhuhai 519000, Guangdong Province, China
Yun Li, Guangdong Provincial Key Laboratory of Biomedical Imaging, The Fifth Affiliated Hospital of Sun Yat-sen University, Zhuhai 519000, Guangdong Province, China
Zhe Yang, Hong-Yun Lu, Department of Endocrinology and Metabolism, Zhuhai People’s Hospital (Zhuhai Clinical Medical College of Jinan University, the First Hospital Affiliated with Medical College of Macao University of Science and Technology), Zhuhai 519000, Guangdong Province, China
Co-first authors: Ling-Ling Wang and Zhan-Jin Lu.
Author contributions: Wang LL and Lu ZJ contributed equally to this work; Wang LL and Lu HY are involved in study concept and design; Wang LL, Lu ZJ, Luo SK, Li Y, and Yang Z performed experiments; Luo SK, Li Y, and Yang Z provided material support and analytic tools; Wang LL, Lu ZJ, and Lu HY analyzed the data and wrote the manuscript; Lu HY had supervision of all study; and all authors read and approved the final manuscript.
Supported by Basic and Applied Basic Research Foundation of Guangdong Province, No. 2020A1515010123 and No. 2021A1515010695; and Special Fund Project for Science and Technology Innovation Strategy of Guangdong Province, No. 2019A030317011.
Institutional animal care and use committee statement: The study was reviewed and approved by the Animal Care and Ethics Committee of the Fifth Affiliated Hospital of Sun Yat-sen University (Animal protocol number: 00054).
Conflict-of-interest statement: All the authors report no relevant conflicts of interest for this article.
Data sharing statement: No additional data are available.
ARRIVE guidelines statement: The authors have read the ARRIVE guidelines, and the manuscript was prepared and revised according to the ARRIVE guidelines.
Open-Access: This article is an open-access article that was selected by an in-house editor and fully peer-reviewed by external reviewers. It is distributed in accordance with the Creative Commons Attribution NonCommercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited and the use is non-commercial. See: https://creativecommons.org/Licenses/by-nc/4.0/
Corresponding author: Hong-Yun Lu, MD, PhD, Chief Doctor, Department of Endocrinology and Metabolism, Zhuhai People’s Hospital (Zhuhai Clinical Medical College of Jinan University, the First Hospital Affiliated with Medical College of Macao University of Science and Technology), No. 79 Kangning Road, Zhuhai 519000, Guangdong Province, China. luhongyun@jnu.edu.cn
Received: November 9, 2023
Peer-review started: November 9, 2023
First decision: December 17, 2023
Revised: January 12, 2024
Accepted: February 21, 2024
Article in press: February 21, 2024
Published online: April 26, 2024
Processing time: 167 Days and 14.7 Hours
Abstract
BACKGROUND

Osteoporosis (OP) has become a major public health problem worldwide. Most OP treatments are based on the inhibition of bone resorption, and it is necessary to identify additional treatments aimed at enhancing osteogenesis. In the bone marrow (BM) niche, bone mesenchymal stem cells (BMSCs) are exposed to a hypoxic environment. Recently, a few studies have demonstrated that hypoxia-inducible factor 2alpha (HIF-2α) is involved in BMSC osteogenic differentiation, but the molecular mechanism involved has not been determined.

AIM

To investigate the effect of HIF-2α on the osteogenic and adipogenic differentiation of BMSCs and the hematopoietic function of hematopoietic stem cells (HSCs) in the BM niche on the progression of OP.

METHODS

Mice with BMSC-specific HIF-2α knockout (Prx1-Cre;Hif-2αfl/fl mice) were used for in vivo experiments. Bone quantification was performed on mice of two genotypes with three interventions: Bilateral ovariectomy, semilethal irradiation, and dexamethasone treatment. Moreover, the hematopoietic function of HSCs in the BM niche was compared between the two mouse genotypes. In vitro, the HIF-2α agonist roxadustat and the HIF-2α inhibitor PT2399 were used to investigate the function of HIF-2α in BMSC osteogenic and adipogenic differentiation. Finally, we investigated the effect of HIF-2α on BMSCs via treatment with the mechanistic target of rapamycin (mTOR) agonist MHY1485 and the mTOR inhibitor rapamycin.

RESULTS

The quantitative index determined by microcomputed tomography indicated that the femoral bone density of Prx1-Cre;Hif-2αfl/fl mice was lower than that of Hif-2αfl/fl mice under the three intervention conditions. In vitro, Hif-2αfl/fl mouse BMSCs were cultured and treated with the HIF-2α agonist roxadustat, and after 7 d of BMSC adipogenic differentiation, the oil red O staining intensity and mRNA expression levels of adipogenesis-related genes in BMSCs treated with roxadustat were decreased; in addition, after 14 d of osteogenic differentiation, BMSCs treated with roxadustat exhibited increased expression of osteogenesis-related genes. The opposite effects were shown for mouse BMSCs treated with the HIF-2α inhibitor PT2399. The mTOR inhibitor rapamycin was used to confirm that HIF-2α regulated BMSC osteogenic and adipogenic differentiation by inhibiting the mTOR pathway. Consequently, there was no significant difference in the hematopoietic function of HSCs between Prx1-Cre;Hif-2αfl/fl and Hif-2αfl/fl mice.

CONCLUSION

Our study showed that inhibition of HIF-2α decreases bone mass by inhibiting the osteogenic differentiation and increasing the adipogenic differentiation of BMSCs through inhibition of mTOR signaling in the BM niche.

Keywords: Hypoxia-inducible factor-2α; Bone marrow niche; Bone mesenchymal stem cells; Osteoporosis; Osteogenic/adipogenic differentiation; Mechanistic target of rapamycin signaling pathway

Core Tip: This manuscript explores the role of hypoxia-inducible factor 2alpha (HIF-2α) in bone mesenchymal stem cell (BMSC) osteogenic differentiation in the bone marrow niche, a role that is still unclear and controversial, via in vivo and in vitro experiments. We verified that downregulation of HIF-2α inhibits osteogenesis in vivo by generating mice with BMSC-specific HIF-2α knockout and applying interventions such as bilateral ovariectomy, semilethal irradiation, and treatment with dexamethasone. In vitro, we found that downregulation of HIF-2α can inhibit osteogenesis and increase adipogenesis by suppressing the mechanistic target of rapamycin signaling pathway, which may lead to the identification of drug target genes for the clinical treatment of osteoporosis.