Histidine Decarboxylase Expression by Immature Myeloid Cells May Affect Peak Bone Density in Mice
Jennifer Dunlap, Emily Larson, Jessica Hebert, Robert Klein, Terry Morgan. OHSU, Portland
Background: Our group has identified a major gene on chromosome 2 in mice that is associated with variation in peak bone mineral density and femoral bone strength. Variation in this gene may explain why C57BL/6 mice have significantly less bone density than DBA/2 mice. Taking advantage of the synteny between human genome sequence and the murine introgressed region on chromosome 2, we identified histidine decarboxylase (HDC), the rate-limiting enzyme in the biosynthesis of histamine, as a positional candidate gene for the observed variation in bone density. Notably, others have reported HDC knockout mice have increased bone formation and conversely increased HDC expression has been reported in circulating monocytes from patients with osteoporosis. We hypothesized that variance in HDC expression between C57BL/6 and DBA/2 mice may account for observed differences in bone density.
Design: Fresh femoral bone tissue samples were prepared from at least six adult C57BL/6 and six adult DBA/2 mice of each gender. Portions of each sample were prepared for nucleic acid and protein extraction, tissue embedding for immunohistochemistry, and subsequent cell sorting by flow cytometry (FACS). HDC expression was analyzed by real-time RT-PCR and Western blot analysis. Expression was localized by immunostaining for HDC (Progen) and mast cell contamination was excluded using CD117.
Results: C57BL/6 mice showed significantly increased marrow HDC expression compared with DBA/2 mice. We did not observe significant gender differences. Immunohistochemical staining suggested the source of HDC may be immature myeloid cells (IMCs). In turn, we have purified CD11b+Ly6G+ IMCs with low side scatter using FACS for future HDC expression and promoter methylation analysis.
Conclusions: Our data suggest histamine physiology in the bone marrow could be an important determinant of bone density. Moreover, we suspect that inherited variation in the HDC enzyme's promoter activity may explain some of the natural variation in peak bone density.
Category: Bone & Soft Tissue
Tuesday, March 20, 2012 9:30 AM
Poster Session III # 12, Tuesday Morning