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Up-regulation of glycolytic metabolism is required for HIF1?-driven bone formation.

ABSTRACT: The bone marrow environment is among the most hypoxic in the body, but how hypoxia affects bone formation is not known. Because low oxygen tension stabilizes hypoxia-inducible factor alpha (HIF?) proteins, we have investigated the effect of expressing a stabilized form of HIF1? in osteoblast precursors. Brief stabilization of HIF1? in SP7-positive cells in postnatal mice dramatically stimulated cancellous bone formation via marked expansion of the osteoblast population. Remarkably, concomitant deletion of vascular endothelial growth factor A (VEGFA) in the mouse did not diminish bone accrual caused by HIF1? stabilization. Thus, HIF1?-driven bone formation is independent of VEGFA up-regulation and increased angiogenesis. On the other hand, HIF1? stabilization stimulated glycolysis in bone through up-regulation of key glycolytic enzymes including pyruvate dehydrogenase kinase 1 (PDK1). Pharmacological inhibition of PDK1 completely reversed HIF1?-driven bone formation in vivo. Thus, HIF1? stimulates osteoblast formation through direct activation of glycolysis, and alterations in cellular metabolism may be a broadly applicable mechanism for regulating cell differentiation.

SUBMITTER: Regan JN

PROVIDER: S-EPMC4060724 | biostudies-literature | 2014 Jun

REPOSITORIES: biostudies-literature

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Up-regulation of glycolytic metabolism is required for HIF1α-driven bone formation.

Regan Jenna N JN Lim Joohyun J Shi Yu Y Joeng Kyu Sang KS Arbeit Jeffrey M JM Shohet Ralph V RV Long Fanxin F

Proceedings of the National Academy of Sciences of the United States of America 20140527 23

The bone marrow environment is among the most hypoxic in the body, but how hypoxia affects bone formation is not known. Because low oxygen tension stabilizes hypoxia-inducible factor alpha (HIFα) proteins, we have investigated the effect of expressing a stabilized form of HIF1α in osteoblast precursors. Brief stabilization of HIF1α in SP7-positive cells in postnatal mice dramatically stimulated cancellous bone formation via marked expansion of the osteoblast population. Remarkably, concomitant d ...[more]

PMID: 24912186

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Project description:Recent studies illustrate the importance of regulation of cellular metabolism, especially glycolysis and pathways branching from glycolysis, during vertebrate embryo development. For example, glycolysis generates cellular energy ATP. Glucose carbons are also directed to the pentose phosphate pathway, which is needed to sustain anabolic processes in the rapidly growing embryos. However, our understanding of the exact status of glycolytic metabolism as well as genes that regulate glycolytic metabolism are still incomplete. Sall4 is a zinc finger transcription factor that is highly expressed in undifferentiated cells in developing mouse embryos, such as blastocysts and the post-implantation epiblast. TCre; Sall4 conditional knockout mouse embryos exhibit various defects in the posterior part of the body, including hindlimbs. Using transcriptomics approaches, we found that many genes encoding glycolytic enzymes are upregulated in the posterior trunk, including the hindlimb-forming region, of Sall4 conditional knockout mouse embryos. In situ hybridization and qRT-PCR also confirmed upregulation of expression of several glycolytic genes in hindlimb buds. A fraction of those genes are bound by SALL4 at the promoters, gene bodies or distantly-located regions, suggesting that Sall4 directly regulates expression of several glycolytic enzyme genes in hindlimb buds. To further gain insight into the metabolic status associated with the observed changes at the transcriptional level, we performed a comprehensive analysis of metabolite levels in limb buds in wild type and Sall4 conditional knockout embryos by high-resolution mass spectrometry. We found that the levels of metabolic intermediates of glycolysis are lower, but glycolytic end-products pyruvate and lactate did not exhibit differences in Sall4 conditional knockout hindlimb buds. The increased expression of glycolytic genes would have caused accelerated glycolytic flow, resulting in low levels of intermediates. This condition may have prevented intermediates from being re-directed to other pathways, such as the pentose phosphate pathway. Indeed, the change in glycolytic metabolite levels is associated with reduced levels of ATP and metabolites of the pentose phosphate pathway. To further test whether glycolysis regulates limb patterning downstream of Sall4, we conditionally inactivated Hk2, which encodes a rate-limiting enzyme gene in glycolysis and is regulated by Sall4. The TCre; Hk2 conditional knockout hindlimb exhibited a short femur, and a lack of tibia and anterior digits in hindlimbs, which are defects similarly found in the TCre; Sall4 conditional knockout. The similarity of skeletal defects in Sall4 mutants and Hk2 mutants suggests that regulation of glycolysis plays a role in hindlimb patterning. These data suggest that Sall4 restricts glycolysis in limb buds and contributes to patterning and regulation of glucose carbon flow during development of limb buds.

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Up-regulation of glycolytic metabolism is required for HIF1?-driven bone formation.

Publications

Up-regulation of glycolytic metabolism is required for HIF1α-driven bone formation.

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