Plasminogen Activator Inhibitor-1 Is Involved in Streptozotocin-Induced Bone Loss in Female Mice

Abstract

In diabetic patients, the risk of fracture is high because of impaired bone formation. However, the details of the mechanisms in the development of diabetic osteoporosis remain unclear. In the current study, we investigated the role of plasminogen activator inhibitor (PAI)-1 in the pathogenesis of type 1 diabetic osteoporosis by using PAI-1–deficient mice. Quantitative computed tomography analysis showed that PAI-1 deficiency protected against streptozotocin-induced bone loss in female mice but not in male mice. PAI-1 deficiency blunted the changes in the levels of Runx2, osterix, and alkaline phosphatase in tibia as well as serum osteocalcin levels suppressed by the diabetic state in female mice only. Furthermore, the osteoclast levels in tibia, suppressed in diabetes, were also blunted by PAI-1 deficiency in female mice. Streptozotocin markedly elevated the levels of PAI-1 mRNA in liver in female mice only. In vitro study demonstrated that treatment with active PAI-1 suppressed the levels of osteogenic genes and mineralization in primary osteoblasts from female mouse calvaria. In conclusion, the current study indicates that PAI-1 is involved in the pathogenesis of type 1 diabetic osteoporosis in females. The expression of PAI-1 in the liver and the sensitivity of bone cells to PAI-1 may be an underlying mechanism.

Role of matrix metalloproteinase-10 in the BMP-2 inducing osteoblastic differentiation

“…Orbe et al suggested that MMP-10 can enhance tissue plasminogen activatorinduced fibrinolysis via a thrombin-activatable fibrinolysis inhibitor inactivation-mediated mechanism [16], and we recently reported that plasminogen has a crucial role in bone repair process in mice [17]. In addition, plasminogen activator inhibitor-1 is involved in diabetic bone loss in female mice [18]. However, the role of MMP-10 in osteoblast biology and differentiation has not been reported yet.…”

“…Calvarial osteoblastic cells were obtained from C57BL6 mice according to the method described previously [17,18]. Briefly, calvaria was removed from 3-day-old mice, cleaned of soft tissue, and digested 4 times with 1 mg/mL type IV collagenase and 0.25% trypsin for 20 min at 37°C with gentle agitation.…”

“…ALP activity was measured with LabAssay ALP (Wako Pure Chem.) followed the manufacturer's instructions, as previously described [18].…”

Role of Plasminogen Activator Inhibitor-1 in Glucocorticoid-Induced Diabetes and Osteopenia in Mice

“…TUNEL staining was performed to identify apoptotic cells, using In Situ Cell Death Detection Kit, Fluorescein (Roche Diagnostics, Tokyo, Japan). The numbers of osteoclasts and TUNELpositive and ALP-positive cells were counted in selected visual fields under a microscope in a blinded evaluation (16,27).…”

“…It has been suggested that elevated levels of circulating PAI-1 is a risk factor in cardiovascular diseases (atherosclerosis), obesity, and diabetes (13)(14)(15). Moreover, we recently demonstrated in female mice with streptozotocin-induced type 1 diabetes that PAI-1 is involved in bone loss (16). PAI-1 is upregulated in atrophic skeletal muscle (17), and this change is associated with impaired muscle regeneration (18,19).…”