Preservation of type H vessels and osteoblasts by enhanced preosteoclast platelet-derived growth factor type BB attenuates glucocorticoid-induced osteoporosis in growing mice

Abstract

Survival of chronic diseases in childhood is often achieved utilizing glucocorticoids, but comes with significant side effects, including glucocorticoid-induced osteoporosis (GIO). Knowledge of the mechanism of GIO is limited to the adult skeleton. We explored the effect of genetic loss and inhibition of cathepsin K (Ctsk) as a potential treatment target in a young GIO mouse model as genetic loss of cathepsin K results in a mild form of osteopetrosis secondary to impaired osteoclast bone resorption with maintenance of bone formation. We first characterized the temporal osteoclast and osteoblast progenitor populations in Ctsk and wild type (WT) mice in the primary and secondary spongiosa, as sites representative of trabecular bone modeling and remodeling, respectively. In the primary spongiosa, Ctsk mice had decreased numbers of osteoclasts at young ages (2 and 4 weeks) and increased osteoblast lineage cells at later age (8 weeks) relative to WT littermates. In the secondary spongiosa, Ctsk mice had greater numbers of osteoclasts and osteoblast lineage cells relative to WT littermates. We next developed a young GIO mouse model with prednisolone 10 mg/m/day injected intraperitoneally daily from 2 through 6 weeks of age. Overall, WT-prednisolone mice had lower bone volume per tissue volume, whereas Ctsk-prednisolone mice maintained a similar bone volume relative to Ctsk-vehicle controls. WT-prednisolone mice exhibited a decreased number of osteoclasts, tartrate-resistant acid phosphatase and platelet-derived growth factor type BB (PDGF-BB) co-positive cells, type H endothelial cells, and osteoblasts relative to WT-vehicle mice in both the primary and secondary spongiosa. Interestingly, Ctsk-prednisolone mice demonstrated a paradoxical response with increased numbers of all parameters in primary spongiosa and no change in secondary spongiosa. Finally, treatment with a cathepsin K inhibitor prevented WT-prednisolone decline in osteoclasts, osteoblasts, type H vessels, and bone volume. These data demonstrate that cells in the primary and secondary spongiosa respond differently to glucocorticoids and genetic manipulation. Inhibition of osteoclast resorption that preserves osteoclast coupling factors, such as through inhibition of cathepsin K, may be a potential preventive treatment strategy against GIO in the growing skeleton.

Glucocorticoids Disrupt Skeletal Angiogenesis Through Transrepression of NF-κB–Mediated Preosteoclast Pdgfb Transcription in Young Mice

“…GCs can impair both processes. In our published model, prednisolone 10 mg/m 2 /day impaired bone volume, but not growth . Increasing prednisolone to 20 mg/m 2 /day resulted in more significant osteotoxic effects without mortality.…”

“…We and others have reported that GCs are associated with a decline in bone vasculature . However, how GCs disrupt the steps of angiogenesis/blood vessel maintenance remains unknown.…”

“…POCs were incubated with prednisolone 10 −6 M alone or with either RU486, GRsiRNA, or TNFα or prednisolone 10 −7 M alone for 24 hours. Total RNA was extracted and subjected to RT‐PCR as described . Relative expression was calculated for each gene by the 2 –ΔΔCt method, with GAPDH for normalization.…”

“…In a separate culture, endothelial progenitor cells (EPCs) were seeded in endothelial progenitor outgrowth cell growth medium (BioChain, Newark, CA, USA; Z7030033). Tube formation assays were performed by using Matrigel Matrix basement membrane (Corning, Corning, NY, USA; 356230) as reported . Briefly, 50 μL of Matrigel was added into 96‐well culture plates and incubated at 37°C for 30 min to allow the gel to solidify.…”

Dynamic expression of SMAD3 is critical in�osteoblast differentiation of PDMCs

“…Osteoporosis is a disease of the bones, in which the rate of bone resorption by osteoclasts exceeds the rate of bone formation by osteoblasts (41). The therapeutic strategy for treating patients with osteoporosis is straightforward: Either decrease the activity of osteoclasts with bisphosphonates and estrogen-associated compounds or increase the activity of osteoblasts with parathyroid hormones (42).…”