Effects of age on molecular pathways regulating bone formation in humans: A key role for notch and Rorβ signaling

Document Type

Conference Paper

Department

Paediatrics and Child Health

Abstract

Despite extensive studies in mice, there is currently little information on the molecular pathways contributing to age-related bone loss in humans. In part, this stems from the difficulty of obtaining trephine bone biopsies (~5-7 mm diameter) in normal volunteers. Thus, we used the standard clinical approach hematologists employ for bone marrow aspirates and biopsies to obtain needle biopsies (1-2 mm diameter) from the posterior iliac crest in 20 young (30¡5 yr) and 20 old (73¡7 yr)women. We coupled this to customized, in-house QPCR analyses of 288 genes related to bone metabolism, including genes reflecting 17 pre-specified clusters/pathways (e.g.,Wnt targets) and 71 genes linked to SNPs from GWAS studies (Nat Genet 44:491,2012). Genes in pre-specified pathways were analyzed using a cluster analysis (O’Brien Umbrella Test) which tests for concordant changes in multiple genes in the pathway. One of the most highly upregulated pathways in the old women was Notch (P =0.003), which is known to modulate age-related bone loss in mice (Nat Med 14:306,2008). Individual significant (P,0.05) gene changes in this pathway werehes1(1.6x),hey1(1.8x),heyL(1.5x), andJag1(1.2x). In addition, recent studies have identified retinoic acid receptor-related orphan receptorβ (Rorβ) as an important regulator of osteogenesis that is markedly upregulated in bone marrow mesenchymal cells from aged versus young mice (JBMR 27:891, 2012).Rorβ itself (1.6x) as well as multiple Rorβ target genes (P = 0.001 for the pathway) were also upregulated in the biopsies from the old women. Both Notch and Rorβ signaling inhibit runx2 activity, there by potentially blocking osteoblast differentiation. Interestingly, a panel of stem cell markers was significantly upregulated with aging (P = 0.022), including nestin (2.0x),CD146(1.4x), and nanog (1.3x), suggesting that activation of Notch and Rorβ signaling may result in a block in osteoblast differentiation with resultant expansion of the stem cell pool within bone. Of the 71 GWAS genes, 11 were significantly altered with aging, most notablymmp7(4.0x). Other individual gene changes of interest with aging included rankl (1.6x) and fgf23(2.0x).In summary, we describe a novel approach coupling needle biopsies of bone to customized QPCR analyses to study genes/pathways regulating bone metabolism in humans. Our work validates, in humans, several pathways associated with age-related bone loss in mice, including Notch and Rorβ signaling.

Comments

This work was published before the author joined Aga Khan University.

Publication (Name of Journal)

Journal of Bone and Mineral Research

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