血小板衍生生长因子对骨代谢的影响

骨折、骨不连、骨缺损、骨质疏松等一直是困扰骨科界的难题。骨折愈合期漫长 ,易产生各种并发症 ;而骨不连、骨缺损目前临床上尚无有效治疗方法。除了组织工程 ,近年研究热点主要集中在骨组织的代谢调节 ,包括各种生长因子的调节以及细胞间信号传导等。作为一种调节骨组织代谢的重要因子 ,血小板衍生生长因子 (platelet derivedgrowthfactor,PDGF)越来越受到国内外学者的重视。笔者就PDGF对骨代谢的影响加以综述1　生物学特性PDGF是一种耐热、耐酸、易被胰蛋白酶水解的阳离子多肽 ,主要由成熟的血小板分泌 ,与血小板因子 4、纤维蛋白…     

Skeletal unloading induces resistance to insulin-like growth factor I on bone formation

Skeletal unloading results in an inhibition of bone formation associated with a decrease in osteoblast number, impaired mineralization of bone, and altered proliferation and differentiation of osteoprogenitor cells. Although such changes are likely to be mediated by multiple factors, resistance to the growth-promoting action of insulin-like growth factor I (IGF-I) has been hypothesized to play an important role. To determine whether skeletal unloading induces resistance to IGF-I on bone formation, we examined the response of unloaded (hindlimb elevation) and normally loaded tibia and femur to IGF-I administration. To eliminate the variable of endogenous growth hormone production and secretion during exogenous IGF-I administration, we used growth hormone-deficient dwarf rats (dw-4). The rats were given IGF-I (2.5 mg/kg/day) or vehicle during 7 and 14 days of unloading or normal loading. This significantly increased the serum level of IGF-I in both the normally loaded and unloaded rats. Unloading did not affect the serum level of IGF-I in the vehicle-treated rats. IGF-I markedly increased periosteal bone formation at the tibiofibular junction of normally loaded rats. Unloading decreased bone formation in the vehicle-treated rats, and blocked the ability of IGF-I to increase bone formation. On the other hand, IGF-I increased periosteal bone formation at the midpoint of the humerus (normally loaded in this model) in both hindlimb-elevated and normally loaded rats. IGF-I significantly increased osteogenic colony number, total ALP activity, and total mineralization in bone marrow osteoprogenitor (BMOp) cells of normally loaded rats. Unloading reduced these parameters in the vehicle-treated rats, and blocked the stimulation by IGF-I. Furthermore, IGF-I administration (10 ng/ml) in vitro significantly increased cell proliferation of the BMOp cells isolated from normally loaded bone, but not that of cells from unloaded bone. These results indicate that skeletal unloading induces resistance to IGF-I on bone formation.     

Localized insulin-like growth factor I delivery to enhance new bone formation

Insulin-like growth factor I (IGF I) exerts an important role during skeletal growth and bone formation. Therefore, its localized delivery appears attractive for the treatment of bone defects. To prolong IGF I delivery, we entrapped the protein into biodegradable poly(lactide-co-glycolide) microspheres (PLGA MS) and evaluated the potential of this delivery system for new bone formation in two defect models of ovine long bones, i.e., a 8-mm methaphyseal drill hole and a 10-mm segmental tibia defect. Administration of 100 microg of IGF I in PLGA MS resulted in new bone formation within 3 weeks in the drill hole and bridging of the segmental defect within 8 weeks. The observed increase of 12% newly formed bone in the drill hole defect after 3 weeks was substantial, compared to the measured morphometric bone-to-total area ratio of 31% bone in normal cancellous bone. Bone regeneration was further explored by measuring gene expression of typical markers for local mediators and growth factors by real-time polymerase chain reaction. Inflammation was reduced in presence of IGF I and this in vivo observation was corroborated in vitro by quantifying gene expression of inflammatory proteins and by assessing the activation of the NF-kappaB pathway, playing an important role in the regulation of inflammation. Administration of the IGF I delivery system downregulated inflammatory marker gene expression at the site of bone injury, induced new bone formation and reduced bone resorption, and resulted in bridging of 10-mm segmental tibial defects within 8 weeks.     

Perturbations in bone formation and resorption in insulin-like growth factor binding protein-3 transgenic mice.

IGF-I and their binding proteins are important in bone health. Examination of BMD, osteoblast proliferation, and markers of bone resorption in transgenic mice that constitutively overexpress IGFBP-3 indicates that overexpression of IGFBP-3 increases osteoclast number and bone resorption, impairs osteoblast proliferation, and has a significant negative effect on bone formation. INTRODUCTION: Low serum insulin-like growth factor I (IGF-I) levels correlate with an increased risk of osteoporotic fractures. Serum IGF-I is largely bound to IGF-binding protein-3 (IGFBP-3), which can inhibit IGF-I action and enhance delivery of IGF-I to tissues. Its role in bone biology is unclear. METHODS: Bone mineral density (BMD), osteoblast proliferation, and markers of bone resorption were examined in transgenic (Tg) mice that constitutively overexpressed human IGFBP-3 cDNA driven by either the cytomegalovirus (CMV) or phosphoglycerate kinase (PGK) promoter. RESULTS: Cultured calvarial osteoblasts from Tg mice expressed the transgene and grew more slowly than cells from wild-type (Wt) mice, and the mitogenic response to IGF-I was attenuated in osteoblasts from Tg mice. Total volumetric BMD and cortical BMD, measured in the femur using peripheral quantitative computed tomography (pQCT) were significantly reduced in both Tg mouse strains compared with Wt mice. PGKBP-3 Tg mice showed the most marked reduction in bone density. Osteocalcin levels were similar in Wt and CMVBP-3 Tg mice but were significantly reduced in PGKBP-3 Tg mice. Urinary deoxypyridinoline and osteoclast perimeter, markers of bone resorption, were significantly increased in both Tg mouse strains compared with Wt mice. Using double labeling with tetracycline, we demonstrated that pericortical and endocortical mineral apposition rate was significantly reduced in PGKBP-3 Tg mice compared with Wt mice. CONCLUSIONS: These data show that overexpression of IGFBP-3 increases osteoclast number and bone resorption, impairs osteoblast proliferation, and has a significant negative effect on bone formation.     

The skeletal structure of insulin-like growth factor I-deficient mice.

The importance of insulin-like growth factor I (IGF-I) for growth is well established. However, the lack of IGF-I on the skeleton has not been examined thoroughly. Therefore, we analyzed the structural properties of bone from mice rendered IGF-I deficient by homologous recombination (knockout [k/o]) using histomorphometry, peripheral quantitative computerized tomography (pQCT), and microcomputerized tomography (muCT). The k/o mice were 24% the size of their wild-type littermates at the time of study (4 months). The k/o tibias were 28% and L1 vertebrae were 26% the size of wild-type bones. Bone formation rates (BFR) of k/o tibias were 27% that of the wild-type littermates. The k/o bones responded normally to growth hormone (GH; 1.7-fold increase) and supranormally to IGF-I (5.2-fold increase) with respect to BFR. Cortical thickness of the proximal tibia was reduced 17% in the k/o mouse. However, trabecular bone volume (bone volume/total volume [BV/TV]) was increased 23% (male mice) and 88% (female mice) in the k/o mice compared with wild-type controls as a result of increased connectivity, increased number, and decreased spacing of the trabeculae. These changes were either less or not found in L1. Thus, lack of IGF-I leads to the development of a bone structure, which, although smaller, appears more compact.     

Periosteal insulin-like growth factor I and bone formation Changes during tibial lengthening in rabbits

We investigated changes in periosteal insulin-like growth factor I (IGF-I) during tibial lengthening. In 37 rabbits, an osteotomy of the right middle tibia was made and fixed by a unilateral external fixator. The rabbits were randomized into 6 groups: the tibiae were distracted at 0.5 mm/day up to 4 weeks and the animals killed after 2 weeks, 4 weeks or 6 weeks, for each period there was a control group with no distraction. Periosteal IGF-I was measured by radio immunoassay and bone formation was quantified by CT scanning. During bone lengthening, CT showed moderate bone formation, while IGF-I was increased. When lengthening was stopped, IGF-I returned to a basal level, and CT scanning showed considerable bone formation. Our study suggests that IGF-I plays a role in an early stage of bone formation.     

Characterization of insulin-like growth factor I and epidermal growth factor receptors in meningioma

Receptors for insulin-like growth factor I (IGF-I) and epidermal growth factor (EGF) were localized and characterized in eight samples of human meningioma (four fibrous, two meningothelial, and two angioblastic types), using quantitative autoradiographic techniques. Effects of both growth factors on deoxyribonucleic acid (DNA) synthesis in the cultured meningioma cells were examined. High numbers of specific binding sites for both IGF-I and EGF were homogeneously present in tissue sections derived from fibrous and meningothelial types of meningiomas, whereas binding sites for these growth factors were not detectable in adjacent leptomeninges. While relatively large numbers of IGF-I binding sites were located in the wall of the intratumoral vasculature, the number of binding sites in the stromal component was lower in angioblastic-type meningiomas, including a low number of EGF binding sites detected only in the stromal portion. Scatchard analysis revealed the presence of a single class of high-affinity binding sites for both IGF-I and EGF in the meningiomas examined (dissociation constant (Kd) = 0.6 to 2.9 nM, and the maximum number of binding sites (Bmax) = 16 to 80 fmol/mg for IGF-I; and Kd = 0.6 to 4.0 nM, Bmax = 3 to 39 fmol/mg for EGF). Both growth factors increased the synthesis of DNA, in a dose-dependent manner, as measured by 3H-thymidine incorporation. The combination of IGF-I and EGF synergistically stimulated the synthesis of DNA, and the effects seen with 10% fetal bovine serum could be reproduced at a concentration of 10(-10) M. These observations can be interpreted to mean that both IGF-I and EGF may be involved in the growth modulation of meningiomas, possibly through paracrine or autocrine mechanisms.     

The effect of insulin-like growth factor I on postburn hypermetabolism

These studies were undertaken to examine the effects of insulin-like growth factor I (IGF-I) on the hypermetabolic state that follows major thermal injury. Male Sprague-Dawley rats weighing 275 to 325 gm were subjected to a 50% total body surface area, full-thickness scald burn. At the time of injury, osmotic pumps were surgically implanted and used to deliver IGF-I, 1000 micrograms/day, or an equivalent volume of placebo solution by constant infusion of 5 microliters/hr for 14 days. Metabolic rates were studied with oxygen-consumption measurements performed on days 3, 7, 10, and 14 after injury. Animal weight measurements were also performed at the above intervals, with serum total IFG-I levels measured at death. Total serum IGF-I levels were decreased significantly 14 days after injury compared with uninjured animals (p less than 0.05). Treatment with IGF-I resulted in a significant decrease in oxygen consumption and a significant increase in body weight compared with burned animals and those treated with placebo 10 and 14 days after injury (p less than 0.05). These data suggest that IGF-I causes a significant change in the metabolic response that follows severe thermal injury and point to a possible role for IGF-I in the treatment of patients after severe thermal injury.     

Expression of insulin-like growth factor I messenger ribonucleic acid in regenerating bone after fracture: influence of indomethacin.

Expression of insulin-like growth factor I (IGF-I) was studied during time in the callus formed after tibial fracture in rats. Levels of IGF-I mRNA in callus peaked on the day 8 postfracture, showing a 10- to 15-fold induction compared to control bone. Levels of IGF-I mRNA tended also to be increased in the fracture-adjacent musculus tibialis anterior. IGF-I immunoreactivity was found in cartilaginous cells, osteoblasts, and myocytes 6 and 8 days after fracture. No obvious differences were found between hypophysectomized animals and control animals with regard to IGF-I immunoreactivity. Administration of the antiinflammatory drug indomethacin decreased the IGF-I mRNA expression in the tibial fracture model. Previous findings have shown that IGF-I is activated during in vivo muscle regeneration, and also in this model indomethacin administration reduces the expression of IGF-I. The finding that indomethacin administration reduces IGF-I expression could indicate that an inflammatory response may be important for activation of IGF-I during tissue regeneration.     

The renal growth hormone/insulin-like growth factor I axis

Collecting duct is a major site of insulin-like growth factor-I (IGF-I) synthesis within kidney. Production of IGF-I at this site is stimulated by growth hormone (GH). IGF-I produced in collecting duct is likely to act on glomerulus and proximal tubule via IGF-I receptors present at these locations. Renal IGF-I may be causative of the glomerular and proximal tubular hypertrophy that occurs in hypersomatotropic states, of compensatory renal hypertrophy, and of renal regeneration following acute ischemic injury.     

Renal cellular biology of growth hormone and insulin-like growth factor I

Growth hormone (GH) and insulin-like growth factor I (IGF I) exert a variety of actions in renal tissue. To shed light upon the renal GH-IGF I axis we have characterized the cell biology of GH and IGF in two parts of the nephron that are targets for these peptides, proximal tubule and collecting duct. Receptors for both GH and IGF I are present in the basolateral membrane of the renal proximal tubular cell. GH activates phospholipase C and IGF I stimulates phosphorylation of its receptor at this site. Both peptides directly enhance gluconeogenesis in proximal tubule. GH stimulates IGF I gene expression in collecting duct. IGFI of collecting duct origin could act as a paracrine growth factor in other portions of the nephron. IGF I may be causative of renal hypertrophy that occurs in the settings of hypersomatotropism, unilateral nephrectomy (compensatory hypertrophy) and diabetes mellitus.     

Regulation of cartilage growth by growth hormone and insulin-like growth factor I

A number of studies have shown that growth hormone (GH) and insulin-like growth factor-I (IGF-I) have important regulatory roles for skeletal growth. However, it has been a matter of controversy whether GH acts directly on cells in the growth plate or if the growth-promoting effects of GH are mediated by liver-derived (endocrine-acting) IGF-I. With the recognition that GH regulates the production of IGF-I in multiple extra-hepatic tissues, autocrine and paracrine functions of IGF-I have been suggested as important components of GH action. This review focuses on recent developments in our understanding of the cellular mechanisms by which GH promotes longitudinal bone growth and the inter-relationship between GH and IGF-I in the growth plate.     

Effects of insulin-like growth factor-I and insulin-like growth factor binding protein-1 on wound healing in a dermal ulcer model.

The effects on wound healing of insulin-like growth factor-I with and without insulin-like growth factor binding protein-1 were studied in a rabbit ear dermal ulcer model under both nonischemic and ischemic conditions. Wounds 6 mm in diameter were made on the ventral surface of rabbit ears for a total of 272 wounds in the nonischemic group and 77 wounds in the ischemic group. Insulin-like growth factor-I in varying doses (1 to 43 microg) and in combination with varying molar ratios of the binding protein were added at time of wounding to each wound. Wounds were analyzed histomorphometrically on day 7 after wounding. We found that insulin-like growth factor-I or binding protein alone at varying doses did not have any effects on wound healing parameters. Low to moderate doses (1 microg and 4 microg, respectively) of the combination of insulin-like growth factor-I with the binding protein in a molar ratio of 5:1 or 11:1 showed a 52% increase (p < 0.05) in new granulation tissue in the nonischemic model compared with controls but did not significantly augment new granulation tissue formation in the ischemic wound model. A high dose (43 microg) at a 10:1 molar ratio of growth factor to binding protein was required to elicit significantly enhanced wound healing in ischemic wounds. These results indicate that insulin-like growth factor binding protein-1 modulates the effects of insulin-like growth factor-I in promoting wound healing in vivo and that the combination is a highly effective vulnerary compound with effects comparable in magnitude with other growth factors previously tested in this model.     

The multi-functional role of insulin-like growth factor binding proteins in bone

The insulin-like growth factor (IGF) system is an important regulator of bone formation. The IGFs (IGF-I and IGF-II) are the most abundant growth factors produced by bone, and are regulated by their six high affinity binding proteins (IGFBPs). The IGFBPs are produced by osteoblasts and are responsible for transporting the IGFs and extending their half-lives. In general, IGFBP-1, -2, -4, and -6 inhibit and IGFBP-3 and –5 stimulate osteoblast function. IGFBP-4 and -5 are the most abundant IGFBPs produced by osteoblasts, and therefore they are the primary focus of this review. IGFBP-5 is an important stimulator of bone formation and may also function independently of IGFs. IGFBP-4 inhibits osteoblast function by sequestering IGF and preventing it from binding to its receptor. This review focuses on the specific IGF-dependent and IGF-independent roles of the IGFBPs in bone formation, as well as their potential mechanisms of action. In addition, discussion of the regulation of the IGFBPs by post-translational modification (i.e., proteolysis) has been included. Studies on the regulation of production and actions of IGFBPs suggest that the IGFBP system in bone is pleiotropic and capable of serving multiple effector inputs from systemic and local sources.This work was presented in part at the IPNA Seventh Symposium on Growth and Development in Children with Chronic Kidney Disease: The Molecular Basis of Skeletal Growth, 1–3 April 2004, Heidelberg, Germany     

Overexpression of insulin-like growth factor binding protein-1 in transgenic mice

Overexpression of insulin-like growth factor-1 binding protein (IGFBP-1) in transgenic mice has provided insight into the physiological role of this binding protein in modulating the metabolic and growth-promoting effects of the IGFs. IGFBP-1 transgenic mice demonstrate both intrauterine and postnatal growth retardation. Organ weight was proportionately reduced relative to body weight in most organs, with the exception of the brain, which was disproportionately small in transgenic mice. There were no gross neurological manifestations of the reduction in brain size. Transgenic mice also demonstrated fasting hyperglycemia, impaired glucose tolerance, and modest insulin resistance in skeletal muscle and hepatic tissue. From these data, we can conclude that overexpression of IGFBP-1 results in inhibition of IGF action and in profound impairment of brain development, modest inhibition of fetal and postnatal growth, and inhibition of the metabolic effects of the IGFs. Increased expression of IGFBP-1 has been documented in a variety of situations, such as fetal nutritional deprivation and hypoxia, and has been considered to be a marker of metabolic disturbances that cause fetal growth retardation. The observations in IGFBP-1 transgenic mice suggest expression of IGFBP-1 may itself contribute to the growth retardation and impaired fetal brain development. Received: 8 June 1999 / Revised: 9 December 1999 / Accepted: 16 December 1999     

防己诺林碱对去卵巢小鼠骨代谢及骨微结构的影响

目的探讨防己诺林碱对去卵巢小鼠骨质疏松的保护作用。方法将40只C57BL/6小鼠随机分为空白(假手术)对照组、模型(去卵巢)组、阳性(雌二醇,E2)对照组、防己诺林碱组共4组,每组10只。连续腹腔给药7周后处死小鼠,取股骨及外周血清,通过ELISA法检测骨代谢相关血清学指标:抗酒石酸酸性磷酸酶(TRAc P)、I型胶原羧基末端肽(CTX)及I型胶原氨基末端肽(NTX);通过Micro-CT评估各组小鼠骨组织微结构相关指标:骨小梁百分比(BV/TV)、骨小梁数量(Tb.N)、骨小梁分离度(Tb.Sp)和骨小梁厚度(Tb.Th);通过实时荧光定量PCR检测小鼠骨质疏松骨吸收相关基因的表达情况,包括TRAc P、组织蛋白酶K(Cathepsin K)、活化T细胞核因子1(NFATc1)以及降钙素受体(CTR)。结果与去卵巢模型组比较,防己诺林碱治疗组小鼠BV/TV、Tb.N、Tb.Th显著升高,Tb.Sp明显降低,骨代谢相关指标(TRAc P、CTX、NTX)显著降低,破骨细胞标志基因(TRAc P、Cathepsin K、NFATc1以及CTR)表达水平明显下降。结论防己诺林碱对去卵巢小鼠骨质疏松有保护作用,有望为骨质疏松的临床用药提供新思路。     

Age-related changes in insulin-like growth factor I and II in human femoral cortical bone: lack of correlation with bone mass

The concentration of insulin-like growth factor-I (IGF-I) in human cortical bone declines with age, but the relevance of this decline for cortical bone turnover and bone mass is unknown. In the present study, we simultaneously assessed the concentration of IGF-I and -II in cortical bone matrix and histomorphometric parameters of bone mass and bone turnover in 125 samples from the proximal human femur shaft. Bone width decreased by 27% and porosity increased by 100% in female cortical bone between the fourth and the ninth decade. Similar, but weaker, changes tended to occur in male cortical bone. The concentrations of both IGF species were correlated with the percentage of osteons undergoing bone remodeling. However, despite age-related decreases in both IGF species in men and in IGF-I in women, neither of the IGFs accounted for age-related or age-independent variability in cortical porosity or bone width. In conclusion, these data suggest that the local concentrations of IGF-I and -II are related to cortical bone turnover. In contrast, our study provides no evidence for a major role of bone matrix IGF-I and -II as determinants of cortical bone mass in elderly individuals. Whether other components of the IGF system may be stronger determinants of cortical bone loss remains to be determined.