Microarray profiling of diaphyseal bone of rats suffering from hypervitaminosis A.
Vitamin A is the only known compound that produces spontaneous fractures in rats. In an effort to resolve the molecular mechanism behind this effect, we fed young male rats high doses of vitamin A and performed microarray analysis of diaphyseal bone with and without marrow after 1 week, i.e., just before the first fractures appeared. Of the differentially expressed genes in cortical bone, including marrow, 98% were upregulated. In contrast, hypervitaminotic cortical bone without marrow showed reduced expression of 37% of differentially expressed genes. Gene ontology (GO) analysis revealed that only samples containing bone marrow were associated with a GO term, which principally represented extracellular matrix. This is consistent with the histological findings of increased endosteal/marrow osteoblast number. Fourteen genes, including Cyp26b1, which is known to be upregulated by vitamin A, were selected and verified by real-time PCR. In addition, immunohistochemical staining of bone sections confirmed that the bone-specific molecule osteoadherin was upregulated. Further analysis of the major gene-expression changes revealed apparent augmented Wnt signaling in the sample containing bone marrow but reduced Wnt signaling in cortical bone. Moreover, induced expression of hypoxia-associated genes was found only in samples containing bone marrow. Together, these results highlight the importance of compartment-specific analysis of bone and corroborate previous observations of compartment-specific effects of vitamin A, with reduced activity in cortical bone but increased activity in the endosteal/marrow compartment. We specifically identify potential key osteoblast-, Wnt signaling-, and hypoxia-associated genes in the processes leading to spontaneous fractures.
Department of Medical Sciences, Section of Clinical Pharmacology, Uppsala University, UAS, Ing 70 3tr Foa2 Lab22, 75185 Uppsala, Sweden. thomas.lind@medsci.uu.se
Thomas
T
Lind
Lijuan
L
Hu
P Monica
PM
Lind
Rachael
R
Sugars
Göran
G
Andersson
Annica
A
Jacobson
Håkan
H
Melhus
D000818:Animals; D018483:Diaphyses / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D004195:Disease Models, Animal; D016326:Extracellular Matrix Proteins / Q000096:biosynthesis; D050723:Fractures, Bone / Q000209:etiology / Q000235:genetics* / Q000378:metabolism; D006986:Hypervitaminosis A / Q000235:genetics* / Q000378:metabolism; D008297:Male; D020411:Oligonucleotide Array Sequence Analysis / Q000379:methods; D011509:Proteoglycans / Q000096:biosynthesis; D051381:Rats; D017207:Rats, Sprague-Dawley; D015854:Up-Regulation / Q000502:physiology; D014801:Vitamin A / Q000633:toxicity*
D016326:Extracellular Matrix Proteins; D011509:Proteoglycans; C113360:osteoadherin; D014801:Vitamin A