Inhibition of Cdk5 Ameliorates Skeletal Bone Loss in Glucocorticoid-Treated Mice.

Benjamin Thilo Krüger,Sabine Vettorazzi,Anita Ignatius,Lena Steppe,Mubashir Ahmad,Melanie Haffner-Luntzer,Sooyeon Lee,Ann-Kristin Dorn,Jan Tuckermann

doi:10.3390/biomedicines10020404

Abstract

Glucocorticoids (GCs) are widely used to treat inflammatory diseases. However, their long-term use leads to glucocorticoid-induced osteoporosis, increasing morbidity and mortality. Both anabolic and anti-resorptive drugs are used to counteract GC-induced bone loss, however, they are expensive and/or have major side effects. Therefore, identifying new targets for cost-effective, small-molecule inhibitors is essential. We recently identified cyclin-dependent kinase 5 (Cdk5) as a suppressor of osteoblast differentiation and showed that its inhibition with roscovitine promoted osteoblastogenesis, thus improving the skeletal bone mass and fracture healing. Here, we assessed whether Cdk5 knockdown or inhibition could also reverse the GC-mediated suppression of osteoblast differentiation, bone loss, and fracture healing. We first demonstrated that Cdk5 silencing abolished the dexamethasone (Dex)-induced downregulation of alkaline phosphatase (Alp) activity, osteoblast-specific marker gene expression (Runx2, Sp7, Alpl, and Bglap), and mineralization. Similarly, Cdk5 inhibition rescued Dex-induced suppression of Alp activity. We further demonstrated that Cdk5 inhibition reversed prednisolone (Pred)-induced bone loss in mice, due to reduced osteoclastogenesis rather than improved osteoblastogenesis. Moreover, we revealed that Cdk5 inhibition failed to improve Pred-mediated impaired fracture healing. Taken together, we demonstrated that Cdk5 inhibition with roscovitine ameliorated GC-mediated bone loss but did not reverse GC-induced compromised fracture healing in mice.

Highlights

Introduction published maps and institutional affilGlucocorticoids (GCs) are potent anti-inflammatory agents to treat inflammatory diseases including rheumatoid arthritis, chronic obstructive pulmonary disease, and inflammatory bowel disease [1–5]
We found that cyclin-dependent kinase 5 (Cdk5) mRNA and protein expression was not regulated by Dex treatment and that it was significantly reduced upon Small Interfering RNA (siRNA) knockdown (Figure 1A–C)
We further showed that the Dex treatment significantly reduced cellular alkaline phosphatase (Alp) activity, while the co-treatment with siCdk5 abrogated the GC-induced suppression of Alp activity (Figure 1D,E)

Summary

Introduction

Introduction published maps and institutional affilGlucocorticoids (GCs) are potent anti-inflammatory agents to treat inflammatory diseases including rheumatoid arthritis, chronic obstructive pulmonary disease, and inflammatory bowel disease [1–5]. Long-term GC therapy is associated with glucocorticoid-induced osteoporosis (GIO), the most prevalent form of secondary osteoporosis [6,7]. The adverse effects of long-term GC therapy on bone increase the risk for fragility fractures in a dose-dependent manner, which exacerbates the cause of disability and mortality [8,9]. High-dose GCs increase the receptor activator of nuclear factor kappa-B ligand (RANKL) and reduce osteoprotegerin (OPG) levels, inducing osteoclastogenesis and bone resorption [14,18,19]. In addition to their well-known negative effects on bone mass, GCs influence the complex process of bone fracture healing that includes the consecutive phases of iations

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Conclusion