The Effect Of Different Stress On Bone Metabolism Of Rat

Mechanics stimulation influencing the bone metabolism was proved inmany ways. Exercise could increase the bone formation and osteopenia occurred inlower stress state, howerer, it is not totally clear about its molecular mechanism. In thisstudy, ovariectomized rat and tail-suspend lower stress stimulation(disuse-DIS) modelwere established .to explore the role of different stress on bone metabolism and itsrelated mechnism with the method including bone-mineral density, biochemical testing'of serum, cell culture, histomorphometric parameters, immunochemical stain,apoptosistesting.The experiments were designed as follows: (1)Twenty-four female rats Weredivided into 3 groups: (1) normal control(CON); (2) ovariectomized model(OVX); (3)ovariectomized model with exercise(OVX+Ex). The ovarietomy was performed inOVX and OVX+Ex. Rats in OVX+Ex group were trained on a treadmill. The ratswere sacrificed at 10 week postoperatively and biochemical testing of serumconcentrations of ionized calcium, ALP, BGP and urine concentrations of calcium,creatinine, HOP was performed to evaluate the status of bone turnover. BMP-2,IL-6 andTNF-a proteins in trabecular bone of proximal femur were examined by usingimmunochemical stain and the intensity were determined with the use of imaginganalysis techniques. Marrow stromal stem cells isolated from femur were induced todifferentiate into osteoblasts. Total RNA was extracted with TRIzol reagent when theosteoblasts were cultured for 14 days. mRNA expressions of OPG were determined withRT-PCR semi quantitatively and compared among different groups. Bone mineraldensity of left femoral was determined. (2) Thirty male rats with 5 months old weredivided into normal control(CON) and exercise(Ex) group. Rats in Ex group weretrained on a treadmill. The rats were sacrificed at 8 week and biochemical testing ofserum concentrations of ionized calcium, ALP, BGP and urine concentrations of calcium,creatine were performed to evaluate the status of bone metabolism. The intensity ofIGF-1 protein expression was determined by using immunochemical stain combinedwith the imaging analysis techniques. Dual-energy X-ray absorptiometry was carriedout to determine the bone mineral density (BMD) in femur. The apoptotic osteocytes indistal femur were detected by using terminal-deoxynucleotidyl mediated nick end labeling (TUNEL) technique. (3)Thirty male rats with 5 months old were divided intonormal control (CON), tail-suspend lower stress stimulation (disuse-DIS) group andexercise high stress stimulation (Ex) group. Rats in Ex group were trained on a treadmilland were suspended by tail in DIS group. The rats were sacrificed at 6 week and thebone histomorphometric parameters of femur were measured. Marrow stromal stemcells isolated from femur were induced to differentiate into osteoblasts and ALP, BGPwere determined to evaluate the status of bone-formation metabolism. The apoptosis ofosteoblasts were also measuredResults: (1) Bone resorption increased and high bone turnover status was detectedin OVX group compared with the CON group and this tendency was deterred inexercise group. Immunochemistry stain of TNF-a and IL-6 Were more intensive in OVXgroup than that in CON group (P＜0.05, 0.01), however, no difference was foundbetween Ex group and CON group. Immunochemistry stain of BMP-2 was moreintensive in OVX group than that in CON group, however, no difference was foundbetween OVX+Ex group and CON group. Also, the intensity of BMP-2, TNF-a andIL-6 were decreased in OVX+Ex group compared with the OVX group.(2) Serumconcentrations of ALP, BGP were higher in Ex group than that in CON group(P＜0.05,P＜0.01), however, there was no statistics difference in serum concentrations of ionizedcalcium and urine concentrations of calcium/creatine between two groups. BMD washigher in Ex group than that in CON group (P＜0.05); apoptotic index of osteocytes wassignificantly lower in the Ex group compared with the CON group in trabecular bone(P＜0.05). The intensity of IGF-1 was increased significantly in Ex group compared withthe CON group (P＜0.01). (3) Goncentrations of ALP, BGP were higher in Ex groupthan that in CON group(P＜0.05, P＜0.01). There was no statistics difference of ALPconcentration between DIS and CON group, however, BGP concentration wassignificantly lower in DIS group by comparison with CON group. There was nostatistics difference in apoptosis of osteoblasts between CON and Ex group, however,apoptotic osteoblasts was significantly high in DIS group compared with the CONgroup.Conclusion:(1) Estrogen defecience lead to increased bone resorption and suchtendency was deterred by exercise. Exercise could depress the high turnover status andbone resorption of ovariectomized rats. (2)Ovariectomy cause the rising of BMP-2 andTNF-alL-6in bone tissue and OPG mRNA expression and exercise could decreasing the expression of TNF-a, BMP-2 ,IL-6,OPG in bone marrow in rats with ovariectomy.(3)Exercise cause the rising of IGF-1 in local bone tissue and decreasing the apoptosisof osteocytes in rats. Lower stress stimulation lead to the increase of apoptosis ofosteoblast which would influence the bone metabolism.