Expression and enhancement of FABP4 in septoclasts of the growth plate in FABP5-deficient mouse tibiae

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.

Integrin expression and extracellular matrix adhesion of septoclasts, pericytes, and endothelial cells at the chondro‐osseous junction and the metaphysis of the proximal tibia in young mice

“…Sections were subsequently treated with 4,6‐diamidino‐2‐phenylindole dihydrochloride (DAPI, ImmunoBioScience, Mukilteo, WA, USA) for nuclear staining. The specificity of the anti‐rat E‐FABP antibody used in this study has been described previously (Bando et al, 2021; Kitanaka et al, 2003; Owada et al, 2001; Sakashita et al, 2022). According to the findings of our previous study (Bando et al, 2018), the goat anti‐PDGFRβ antibody can be used as a septoclast marker instead of the rabbit anti‐E‐FABP antibody to avoid the cross‐reaction by primary antibodies from the same host species for double immunostaining with rabbit anti‐collagen antibodies.…”

“…Electron microscopic observation was performed using the methods described in our previous study (Bando et al, 2021). After perfusion with 4% paraformaldehyde in 0.1 M phosphate buffer, the tibiae were dissected and immersed in the same fixative overnight at 4°C, and for preparation of specimens for electron microscopy, the tibiae were immersed in 2% glutaraldehyde in 0.1 M cacodylate buffer (pH 7.4) for 2 h at 4°C and postfixed with 1% OsO4 for 2 h at 4°C.…”

In focus in HCB

“…In their previous work, Bando et al (2017) were unable to detect overt histological abnormalities in the growth plate of FABP5-deficient mice. Since it has been reported that FABP5 deficiency could be functionally compensated by another FABP subtype (Owada et al 2002), Bando et al (2021) have now investigated by immunohistochemistry the presence of FABP3, -4, -5, and -7 in septoclasts in mouse tibiae. They were able to detect FABP4 in septoclasts of FABP5-deficient mice and found that the number of FABP4-positive septoclasts was increased about 2.5fold as compared to wild-type mice (Fig.…”

“…Note the increased number of FABP4-immunoreactive cells in FABP5 −/− mice (g). From Bando et al (2021) FABP5 and FABP4 are important for the shape and function of septoclasts.…”