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Defining A New Cell Lineage In The Sagittal Suture And Its Key Pathway
Kavitha Ranganathan, M.D., David Cholok, B.S., Hsiao Sung, PhD, Shuli Li, M.D., PhD, Angela Yao, PhD, Shailesh Agarwal, M.D., John Li, M.D., Shawn Loder, B.S., Christopher Brueler, B.S., James Drake, B.S., Ernestina Schipani, M.D., PhD, Steven R. Buchman, M.D., Benjamin Levi, M.D..
University of Michigan Health Systems, Ann Arbor, MI, USA.

PURPOSE: Hypoxia signaling pathways are important for bone homeostasis, however, little is known about the role of hypoxia inducible factor-2 alpha (HIF-2α) in calvarial development. We have discovered a characteristic phenotype, namely alteration of the sagittal suture as a result of HIF-2α overexpression that has allowed us to define a new cell lineage and the role of HIF-2α in calvarial development.
METHODS: We modulated HIF-2α signaling in vivo within cells of paraxial mesodermal origin. Analysis of mutant (PRX-1Cre; HIF-2α dPAf/+) and control mice (PRX-1Cre) (n=3/timepoint) was conducted at E12.5, E15.5, P7, P21, and 6 weeks postnatally by microCT, histology, and whole mount staining. Sagittal suture cells were isolated from 1-week old HIF-2α dPAf/f mice, transduced with adenovirus encoding beta-galactosidase (control) or Cre recombinase (mutants), and evaluated for osteogenic potential.
RESULTS: Confocal microscopy demonstrated recombination at the widened suture, confirming our hypothesis that cells of paraxial mesodermal origin contribute to the sagittal suture and respond to Hif-2α. (Figure 1). Bone volume of mutant calvaria was significantly lower than control calvaria (30.77mm3 ± 7.21 vs. 55.51mm3 ± 1.83, p=.002). Affymetrix microarray demonstrated that upregulation of Hif-2α caused downregulation of fibroblast growth factor (FGF2R).
CONCLUSION: We demonstrate that HIF-2α contributes to calvarial and sagittal suture development by modulating cells within the paraxial mesodermal lineage. Defining the role of HIF-2α on calvarial osteogenesis provides knowledge critical to embryonic development.


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