Bone turnover and its related molecular mechanism in STZ-induced diabetic rats

Abstract

Objective To study the bone turnover and its related molecular mechanism in STZ-induced diabetic rats. Methods Of 30 male SD rats studied, 15 were induced diabetics by intravenous injection of streptozotocin (50 mg/kg)and fed for 8 weeks. After the sacrifice of both the diabetic and control groups, serum Ca, P, alkaline phosphatase (ALP), and osteocalcin were determined, and 24 h urinary Ca and urinary cross-linked N-telopeptide of type Ⅰ collagen (NTx)and creatinine (Cr)ratio were also determined. The left tibia was dissected for bone histomorphometry analysis. Right femur and lumbar vertebrae (L1-L4) were reserved for bone mineral density (BMD) determination. The right tibia was separated for the study of bone tissue RANKL/osteoprotegerin, Core binding factor 1 (Cbfa1) ,osterix and osteocalcin mRNA level which was performed by real-time quantitative reverse transcription polymerase chain reaction assay. Results No significant difference was found in serum Ca, P, and ALP levels between 2 groups of rats. ST-Z-induced diabetic rats were characterized by extreme hyperglycemia, marked weight loss, polyuria, and hypercalciuria. A low-turnover osteopenia was evidenced in diabetic rats by decreased BMD in both femur [(0. 099±0.013) vs (0. 139 ± 0.013 g/cm~3) , P < 0.01] and lumbar vertebrae [(0. 107±0.011)vs (0. 149±0.009) g/cm~3, P<0.01] , reduced serum osteoealcin level [a marker of formation, (3.03±0.52) vs (6. 18±0.71) ng/ml ,P<0. 01]) ,decreased urine NTx/Cr ratio [(5. 67±0.86) vs (5.23±0.98) nmol/g Cr, P<0. 05], decreased trabeeular volume and thickness, and reduced bone label surface and bone formation rate [(0. 44±0. 11) vs (0. 78±0. 14) μm/d,P<0. 01] by bone dynamic study. The RANKL/ osteoprotegerin [(0.57±0.11)vs (0.89±0.13) ,P<0.01] ,osterix [(1.93×10~(-4)±0.65×10(~-4))vs (4.19×10~(-4)± 0.71×10~(-4)) ,P<0.01] ,Cbfa1 [(26.68×10~(-4)±6.53×10~(-4))vs (37.21×10~(-4)±7.14×10~(-4)) ,P<0.01] ,and osteocalcin [(2.25×10~(-4)±1.19×10~(-4))vs (3.43×10~(-4)±1.63×10~(-4)) ,P<0.01] mRNA expressions were declined in the bone tissue of the tibia in the ST-Z-induced diabetic rats, as compared with the control. Conclusion A low-turnover osteopenia is evidenced in STZ-induced diabetic rats by significant decrease of both osteoclastic marker(RANKL/ osteoprotegerin)and osteoblastic marker (osterix ,Cbfa1 ,osteocalcin)mRNA levels in tibia. Key words: Diabetic mellitas, experimental; Bone histomorpbometry; Real-time quantitative polymerase reaction; RANK ligand; Osteoprotegerin; Core binding factor 1; Osterix; Osteocalcin; Cross-linked N-telopeptide of typelcollagen