Search

Parathyroid hormone (PTH) is the only approved anabolic agent for osteoporosis treatment. It acts via osteoblasts to stimulate both osteoclast formation and bone formation, with the balance between these two activities determined by the mode of administration. Oncostatin M (OSM), a gp130-dependent cytokine expressed by osteoblast lineage cells, has similar effects and similar gene targets in the osteoblast lineage. In this study, we investigated whether OSM might participate in anabolic effects of PTH. Microarray analysis and quantitative real-time polymerase chain reaction (qPCR) of PTH-treated murine stromal cells and primary calvarial osteoblasts identified significant regulation of gp130 and gp130-dependent coreceptors and ligands, including a significant increase in OSM receptor (OSMR) expression. To determine whether OSMR signaling is required for PTH anabolic action, 6-week-old male Osmr(-/-) mice and wild-type (WT) littermates were treated with hPTH(1-34) for 3 weeks. In WT mice, PTH increased trabecular bone volume and trabecular thickness. In contrast, the same treatment had a catabolic effect in Osmr(-/-) mice, reducing both trabecular bone volume and trabecular number. This was not explained by any alteration in the increased osteoblast formation and mineral apposition rate in response to PTH in Osmr(-/-) compared with WT mice. Rather, PTH treatment doubled osteoclast surface in Osmr(-/-) mice, an effect not observed in WT mice. Consistent with this finding, when osteoclast precursors were cultured in the presence of osteoblasts, more osteoclasts were formed in response to PTH when Osmr(-/-) osteoblasts were used. Neither PTH1R mRNA levels nor cAMP response to PTH were modified in Osmr(-/-) osteoblasts. However, RANKL induction in PTH-treated Osmr(-/-) osteoblasts was sustained at least until 24 hours after PTH exposure, an effect not observed in WT osteoblasts. These data indicate that the transient RANKL induction by intermittent PTH administration, which is associated with its anabolic action, is changed to a prolonged induction in OSMR-deficient osteoblasts, resulting in bone destruction.

The gp130 receptor and its binding partners play a central role in cytokine signalling. Ciliary neurotrophic factor (CNTF) is one of the cytokines that signals through the gp130 receptor complex. CNTF has previously been shown to be a negative regulator of trabecular bone remodelling and important for motor neuron development. Since haematopoietic cell maintenance and differentiation is dependent on the bone marrow (BM) microenvironment, where cells of the osteoblastic lineage are important regulators, we hypothesised that CNTF may also have important roles in regulating haematopoiesis. Analysis of haematopoietic parameters in male and female Cntf−/− mice at 12 and 24 weeks of age revealed altered B lymphopoiesis. Strikingly, the B lymphocyte phenotype differed based on sex, age and also the BM microenvironment in which the B cells develop. When BM cells from wildtype mice were transplanted into Cntf−/− mice, there were minimal effects on B lymphopoiesis or bone parameters. However, when Cntf−/− BM cells were transplanted into a wildtype BM microenvironment, there were changes in both haematopoiesis and bone parameters. Our data reveal that haematopoietic cell-derived CNTF has roles in regulating BM B cell lymphopoiesis and both trabecular and cortical bone, the latter in a sex-dependent manner.

Mutations within the gene encoding the DNA helicase RECQL4 underlie the autosomal recessive cancer-predisposition disorder Rothmund-Thomson syndrome, though it is unclear how these mutations lead to disease. Here, we demonstrated that somatic deletion of Recql4 causes a rapid bone marrow failure in mice that involves cells from across the myeloid, lymphoid, and, most profoundly, erythroid lineages. Apoptosis was markedly elevated in multipotent progenitors lacking RECQL4 compared with WT cells. While the stem cell compartment was relatively spared in RECQL4-deficent mice, HSCs from these animals were not transplantable and even selected against. The requirement for RECQL4 was intrinsic in hematopoietic cells, and loss of RECQL4 in these cells was associated with increased replicative DNA damage and failed cell-cycle progression. Concurrent deletion of p53, which rescues loss of function in animals lacking the related helicase BLM, did not rescue BM phenotypes in RECQL4-deficient animals. In contrast, hematopoietic defects in cells from Recql4Δ/Δ mice were fully rescued by a RECQL4 variant without RecQ helicase activity, demonstrating that RECQL4 maintains hematopoiesis independently of helicase activity. Together, our data indicate that RECQL4 participates in DNA replication rather than genome stability and identify RECQL4 as a regulator of hematopoiesis with a nonredundant role compared with other RecQ helicases.

Osteoblasts and adipocytes are derived from common mesenchymal progenitor cells. The bone loss of osteoporosis is associated with altered progenitor differentiation from an osteoblastic to an adipocytic lineage. cDNA microarrays and quantitative real-time PCR (Q-PCR) were carried out in a differentiating mouse stromal osteoblastic cell line, Kusa 4b10, to identify gene targets of factors that stimulate osteoblast differentiation including parathyroid hormone (PTH) and gp130-binding cytokines, oncostatin M (OSM) and cardiotrophin-1 (CT-1). Zinc finger protein 467 (Zfp467) was rapidly down-regulated by PTH, OSM, and CT-1. Retroviral overexpression and RNA interference for Zfp467 in mouse stromal cells showed that this factor stimulated adipocyte formation and inhibited osteoblast commitment compared with controls. Regulation of adipocyte markers, including peroxisome proliferator-activated receptor (PPAR) γ, C/EBPα, adiponectin, and resistin, and late osteoblast/osteocyte markers (osteocalcin and sclerostin) by Zfp467 was confirmed by Q-PCR. Intra-tibial injection of calvarial cells transduced with retroviral Zfp467 doubled the number of marrow adipocytes in C57Bl/6 mice compared with vector control-transduced cells, providing in vivo confirmation of a pro-adipogenic role of Zfp467. Furthermore, Zfp467 transactivated a PPAR-response element reporter construct and recruited a histone deacetylase complex. Thus Zfp467 is a novel co-factor that promotes adipocyte differentiation and suppresses osteoblast differentiation. This has relevance to therapeutic interventions in osteoporosis, including PTH-based therapies currently available, and may be of relevance for the use of adipose-derived stem cells for tissue engineering.