Osteoblast-derived PTHrP is a potent endogenous bone anabolic agent that modifies the therapeutic efficacy of administered PTH 1-34

Abstract

Mice heterozygous for targeted disruption of Pthrp exhibit, by 3 months of age, diminished bone volume and skeletal microarchitectural changes indicative of advanced osteoporosis. Impaired bone formation arising from decreased BM precursor cell recruitment and increased apoptotic death of osteoblastic cells was identified as the underlying mechanism for low bone mass. The osteoporotic phenotype was recapitulated in mice with osteoblast-specific targeted disruption of Pthrp, generated using Cre-LoxP technology, and defective bone formation was reaffirmed as the underlying etiology. Daily administration of the 1-34 amino-terminal fragment of parathyroid hormone (PTH 1-34) to Pthrp +/-mice resulted in profound improvement in all parameters of skeletal microarchitecture, surpassing the improvement observed in treated WT littermates. These findings establish a pivotal role for osteoblast-derived PTH-related protein (PTHrP) as a potent endogenous bone anabolic factor that potentiates bone formation by altering osteoblast recruitment and survival and whose level of expression in the bone microenvironment influences the therapeutic efficacy of exogenous PTH 1-34.

The calcium-sensing receptor and 25-hydroxyvitamin D–1α-hydroxylase interact to modulate skeletal growth and bone turnover

“…(17) Distal femurs and proximal tibias were decalcified in EDTA glycerol solution for 14 days at 48C. Decalcified bones were dehydrated and embedded in paraffin, after which 5-mm sections were cut on a rotary microtome.…”

“…Decalcified bones were dehydrated and embedded in paraffin, after which 5-mm sections were cut on a rotary microtome. The sections were stained with hematoxylin and eosin (H&E) or histochemically for tartrate-resistant acid phosphatase (TRACP), (17) alkaline phosphatase (ALP) activity, and total collagen, as described below. Alternatively, undecalcified bones were embedded in methyl methacrylate (MMA), and 1-mm sections were cut on an ultramicrotome.…”

“…Enzyme histochemistry for TRACP was performed as described previously. (17) Immunohistochemical staining Decalcified paraffin sections were treated with goat anti-human type 1 collagen antibody (Southern Biotechnology Associates, Birmingham, AL, USA). As a negative control, pre-immune serum was substituted for the primary antibody.…”

“…Sections of decalcified bone and of kidney and parathyroid glands were immunostained with the avidin-biotin-peroxidase complex (ABC) technique as described previously. (17) Sections were counterstained with methyl green and mounted with Permount (Fisher Scientific, Montreal, Canada).…”

Advanced glycation end products stimulate osteoblast apoptosis via the MAP kinase and cytosolic apoptotic pathways

“…However, AGEs do not represent the only mechanism for diabetes-enhanced osteoblast apoptosis as inhibition of TNF in vivo also reduces apoptosis of periosteal cells and promotes new bone formation (31). These and other reports underscore the potential importance of osteoblast apoptosis as a mechanism for impaired bone formation in diabetic and aged individuals (5,34,35). A. CML-collagen (100 μg) or control unmodified collagen (100 μg) was injected into the scalp as described in Materials and Methods and mice were euthanized 24 hours later.…”