Abstract
In our previous study, fatty acid-binding protein 5 (FABP5) was expressed in septoclasts with long processes which are considered to resorb uncalcified matrix of the growth plate (GP) cartilage, and no apparent abnormalities were detected in the histo-architecture of the GP of FABP5-deficient (FABP5−/−) mice. Those finding lead us to hypothesize that another FABP can compensate the deletion of FABP5 in septoclasts of its gene-mutant mice. Based on the hypothesis, the present study examined the expression levels of several other FABPs in septoclasts and their morphology in FABP5−/− mouse tibiae. Processes of FABP5−/− septoclasts tend to be shorter than wild septoclasts. FABP4-positive septoclasts in FABP5−/− mice were more numerous than those cells in wild mice.Peroxisome proliferator-activated receptor (PPAR) γ was expressed in FABP4-positive septoclasts of FABP5−/− mice as well as mice administered with GW1929, a PPARγ agonist, suggesting that the occurrence of PPARγ induces an increase of FABP4-positive septoclasts. The present finding suggests that the functional exertion of FABP5 in septoclasts is supplemented by FABP4 in normal and FABP5−/− mice, and that the expression of FABP4 is up-regulated in accompany with PPARγ in FABP5−/− for maintenance of resorptive activity in the GP.
Highlights
Bone development is carried out by membranous or endochondral ossification
No significant differences between tibiae of fatty acid-binding protein 5 (FABP5)−/− mice and those of WT mice were seen in macroscopic observation (Fig. 1a, b) as well as bone length, number and thickness of the trabeculae, pattern of trabecular separation and the growth plate (GP) thickness measured by
No apparent difference was found in whole sagittal section of the GP (Fig. 1c, d), a notable difference was found in the last cartilaginous lacunae just below the chondro-osseous junction (COJ), in which hypertrophic chondrocytes were often contained in the FABP5−/− mice (Fig. 1f) in contrast to infrequent occurrence of chondrocytes in WT mice (Fig. 1e)
Summary
Bone development is carried out by membranous or endochondral ossification. Endochondral ossification participates continuously in pre- and post-natal bone growth in the epiphyseal growth plate (GP) of long bones. Septoclasts are located along the chondro-osseous junction (COJ) of the GP and adjacent to growing capillaries of invading vessels, and the cells are, previously termed perivascular cells (Schenk et al.1967). They produce proteinases such as cathepsin B (Lee et al 1995) and MMP13 (Nakamura et al 2004) which resolve the collagenous substrate. A shortening of septoclastic processes and a decrease in their number lead septoclasts to diminish the mechanical linkage between the cells and the transverse septa, resulting in the reduction of the cleavage of the transverse septa in the GP (Bando et al 2014, 2017)
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