LIM kinase 1 deficient mice have reduced bone mass

Abstract

The cytoskeleton determines cell shape and is involved in cell motility. It also plays a role in differentiation and in modulating specialized cellular functions. LIM kinase 1 (LIMK1) participates in cytoskeletal remodeling by phosphorylating and inactivating the actin-severing protein, cofilin. Severing F-actin to release G-actin monomers is required for actin cytoskeletal remodeling. Although less well established, LIMK1 may also influence the cell cycle and modulate metalloproteinase activity. Since the role of LIMK1 in bone cell biology has not been reported, the skeletal phenotype of LIMK1−/− mice was examined. LIMK1−/− mice had significantly reduced trabecular bone mass when analyzed by micoCT (p <0.01). Histomorphometric analyses demonstrated a 31% reduction in the number osteoblasts (p=0.0003) and a 23% reduction in osteoid surface (p=0.0005). The number of osteoclasts was no different in control and knock out animals. Consistent with the in vivo findings in osteoblasts, the number of osteoblast colony forming units in LIMK1−/− bone marrow was reduced by nearly 50%. Further, osteoblasts isolated from LIMK1−/− mice showed significantly reduced rates of mineralization in vitro. Osteoclasts from LIMK1−/− mice evidenced more rapid cytoskeletal remodeling in response to treatment with CSF1. In keeping with this latter finding, basal levels of phospho-cofilin were reduced in LIMK1−/− osteoclasts. LIMK1−/− osteoclasts also resorbed dentine slices to a greater extent in vitro and were more active in a pit assay. These data support the hypothesis that LIMK1 is required for normal osteoblast differentiation. In addition, its absence leads to increased cytoskeletal remodeling and bone resorption in osteoclasts.

Inhibiting actin depolymerization enhances osteoblast differentiation and bone formation in human stromal stem cells

“…Third, some studies have reported that the upstream regulator of ADFs, such as Rho GTPase/Rho-Associated kinase (Rock), extracellular matrix (ECM) components, and adhesion kinases, act as regulators for OB differentiation (Harmey et al, 2004;Hamidouche et al, 2009;Mathews et al, 2012). However, evidence for the direct role of ADFs and dynamic organization of actin in MSCs biology and OB differentiation are not clear (Kawano et al, 2013;Shuang et al, 2013).…”

The Transcription Factor T-box 3 Regulates Colony-stimulating Factor 1-dependent Jun Dimerization Protein 2 Expression and Plays an Important Role in Osteoclastogenesis

“…Osteoclastogenesis Assay-Preparation of bone marrow cells and the osteoclastogenesis assay were described previously (16). Briefly, unfractionated bone marrow cells were isolated from 8-week-old male CD-1 mice and centrifuged for 10 min at 1000 ϫ g. The cell pellet was resuspended, and the cells were plated overnight in 10 ml of ␣-MEM containing 10% FBS and 50 ng/ml CSF1 in 10-cm dishes.…”

“…The coefficient of variation for total body bone mineral density is 1.5%. Microcomputed tomography was performed as reported previously (16). Femurs and the L3 lumbar vertebra were stripped of soft tissue, stored in 70% EtOH at 4°C, and scanned using a Scanco CT-35 instrument (Scanco, Bruttisellen, Switzerland).…”

Cellular retinoic acid binding protein 2 inhibits osteogenic differentiation by modulating LIMK1 in C2C12 cells

“…It has recently been demonstrated that osteoblasts isolated from LIMK1 À/À mice significantly showed the reduced rates of mineralization in vitro (Kawano et al 2013). Therefore, we thought that CRABP2 affected osteogenic differentiation via LIMK1.…”

“…Actin cytoskeleton regulates osteogenic differentiation of osteoblasts and this differentiation is decreased when treated with cytochalasin D, an actin polymerization inhibitor (Fu et al 2013). It has been recently demonstrated that osteoblasts isolated from LIMK1 À/À mice show significantly reduced rates of mineralization in vitro (Kawano et al 2013). Based on the above reports, we suppose that LIMK1 may play an important role in the process of osteogenesis.…”