Collagenase and Tissue Plasminogen Activator Production in Developing Rat Calvariae: Normal Progression Despite Fetal Exposure to Microgravity

Abstract

Exposure to zero gravity has been shown to cause a decrease in bone formation. This implicates osteoblasts as the gravity-sensing cell in bone. Osteoblasts also are known to produce neutral proteinases, including collagenase and tissue plasminogen activator (tPA), which are thought to be important in bone development and remodeling. The present study investigated the effects of zero gravity on development of calvariae and their expression of collagenase and tPA. After in utero exposure to zero gravity for 9 days on the NASA STS-70 space shuttle mission, the calvariae of rat pups were examined by immunohistochemistry for the presence and location of these two proteinases. The ages of the pups were from gestational day 20 (G20) to postnatal (PN) day 35. Both collagenase and tPA were found to be present at all ages examined, with the greatest amount of both proteinases present in the PN14 rats. At later ages, high amounts were maintained for tPA but collagenase decreased substantially between ages PN21 to PN35. The location of collagenase was found to be associated with bone-lining cells, osteoblasts, osteocytes, and in the matrix along cement lines. In contrast, tPA was associated with endothelial cells lining the blood vessels entering bone. The presence and developmental expression of these two proteinases appeared to be unaffected by the exposure to zero gravity. The calvarial thickness of the pups was also examined; again the exposure to zero gravity showed little to no effect on the growth of the calvariae. Notably, from G20 to PN14, calvarial thickness increased dramatically, reaching a plateau after this age. It was apparent that elevated collagenase expression correlated with rapid bone growth in the period from G20 to PN14. To conclude, collagenase and tPA are present during the development of rat calvariae. Despite being produced by the same cell in vitro, i.e., the osteoblast, they are located in distinctly different places in bone in vivo. Their presence, developmental expression, and quantity do not seem to be affected by a brief exposure to zero gravity in utero.

Regulation of matrix metalloproteinase-13 and tissue inhibitor of matrix metalloproteinase-1 gene expression by WNT3A and bone morphogenetic protein-2 in osteoblastic differentiation

“…In other words, it may explain why canonical Wnt signaling may not be sufficient and indicate that a combination of BMP-2 and Wnt3a is required for MMP-13 expression in osteoblastic differentiation. Immunohistochemical studies have shown that MMP-13 is found in areas containing woven bone, such as developing bone and areas of fracture healing (54). Almost no MMP-13 is found in normal, adult bone.…”

Expression of stromelysin‐1 (MMP‐3), gelatinase B (MMP‐9), and plasminogen activator system during fetal calvarial development

“…10,11 On the other hand, bone-forming osteoblasts and osteocytes are not only responsible for the production of collagen and non-collagen proteins for bone matrix formation, but are also able to secrete MMPs. [12][13][14][15] Recently, the presence of MMP-3 in osteoblasts and osteocytes of the human neonatal rib was demonstrated and it was hypothesized that MMP-3 may be required for connective tissue degradation to allow cellular migration and expansion of bone. 12 Another cell-associated extravascular system of ECM-degrading proteases is the plasminogen ⁄ plasmin system.…”

Overexpression of Runx2 directed by the matrix metalloproteinase‐13 promoter containing the AP‐1 and Runx/RD/Cbfa sites alters bone remodeling in vivo

“…Geoffroy et al [2002] have reported that Runx2 controls not only genes that are important for osteoblast differentiation [Ducy et al, 1997] and function [Ducy et al, 1999] but also genes that are involved in osteoclast differentiation and bone formationresorption coupling [Geoffroy et al, 2002]. Even though MMP-13 has been shown to be expressed in skin, uterus, and ovary, it is mostly expressed in bone [Balbin et al, 1996;Davis et al, 1998;Tuckermann et al, 2000;Shum et al, 2002]. We report here that overexpression of Runx2 directed by the MMP-13 promoter increases the bone mineralization surface, bone formation rate, and matrix apposition rate (Fig.…”