Inhibition of Cdk5 increases osteoblast differentiation and bone mass and improves fracture healing

Abstract

Identification of regulators of osteoblastogenesis that can be pharmacologically targeted is a major goal in combating osteoporosis, a common disease of the elderly population. Here, unbiased kinome RNAi screening in primary murine osteoblasts identified cyclin-dependent kinase 5 (Cdk5) as a suppressor of osteoblast differentiation in both murine and human preosteoblastic cells. Cdk5 knockdown by siRNA, genetic deletion using the Cre-loxP system, or inhibition with the small molecule roscovitine enhanced osteoblastogenesis in vitro. Roscovitine treatment significantly enhanced bone mass by increasing osteoblastogenesis and improved fracture healing in mice. Mechanistically, downregulation of Cdk5 expression increased Erk phosphorylation, resulting in enhanced osteoblast-specific gene expression. Notably, simultaneous Cdk5 and Erk depletion abrogated the osteoblastogenesis conferred by Cdk5 depletion alone, suggesting that Cdk5 regulates osteoblast differentiation through MAPK pathway modulation. We conclude that Cdk5 is a potential therapeutic target to treat osteoporosis and improve fracture healing.

Why Animal Experiments Are Still Indispensable in Bone Research: A Statement by the European Calcified Tissue Society

“…(40) A wide variety of in vitro screening approaches have been employed to identify potential regulators of bone cell differentiation. (41)(42)(43)(44)(45) For example, high-throughput siRNA (41,42) and compound screens have identified small molecules such as roscovitine, rapamycin, and FK506, which augment osteoblast differentiation in vitro. (43) These approaches allow us to reduce animal experimentation by testing potential drugs at a cellular level.…”

Novel Medicinal Chemistry Strategies Targeting CDK5 for Drug Discovery

“…It is anticipated that these advancements will facilitate the clinical translation of these inhibitors in the future. Inhibition of CDK5 has been shown to mediate the cell death of tumor-initiating cells (TICs), 148 promote the differentiation of ductal progenitors into β-cell, 149 promote the differentiation of osteoblasts and fracture healing, 150 reduce the proliferation of cancer cells and promote apoptosis, 73 and others. Despite the potential benefits of CDK5-selective inhibitors, progress in their development has been hindered at the primary stage.…”

Novel Peptide Derived from Gadus morhua Stimulates Osteoblastic Differentiation and Mineralization through Wnt/β-Catenin and BMP Signaling Pathways

“…However, the pharmacological advantages of these drugs often come with unwanted consequences including gastrointestinal distress, osteonecrosis of the jaw, and hypocalcemia, thus restricting their prolonged usage . Besides, an increasing number of studies have demonstrated that antiresorptive medications do not stimulate bone regeneration and have little effect on patients with severe bone loss . Therefore, researchers are becoming increasingly interested in the development of natural bioactive substances that directly stimulate bone formation with fewer adverse effects as active constituents for the prevention of OP.…”

“…6 Besides, an increasing number of studies have demonstrated that antiresorptive medications do not stimulate bone regeneration and have little effect on patients with severe bone loss. 7 Therefore, researchers are becoming increasingly interested in the development of natural bioactive substances that directly stimulate bone formation with fewer adverse effects as active constituents for the prevention of OP.…”