Local and systemic expression of insulin-like growth factor-I (IGF-I) mRNAs in rat after bone marrow ablation

Relationship of circulating insulin-like growth factor-I and binding proteins 1-7 with mammographic density among women undergoing image-guided diagnostic breast biopsy

Background

Mammographic density (MD) is a strong breast cancer risk factor that reflects fibroglandular and adipose tissue composition, but its biologic underpinnings are poorly understood. Insulin-like growth factor binding proteins (IGFBPs) are markers that may be associated with MD given their hypothesized role in breast carcinogenesis. IGFBPs sequester IGF-I, limiting its bioavailability. Prior studies have found positive associations between circulating IGF-I and the IGF-I:IGFBP-3 ratio and breast cancer risk. We evaluated the associations of IGF-I, IGFBP-3, and six other IGFBPs with MD.

Methods

Serum IGF measures were quantified in 296 women, ages 40–65, undergoing diagnostic image-guided breast biopsy. Volumetric density measures (MD-V) were assessed in pre-biopsy digital mammograms using single X-ray absorptiometry. Area density measures (MD-A) were estimated by computer-assisted thresholding software. Age, body mass index (BMI), and BMI²-adjusted linear regression models were used to examine associations of serum IGF measures with MD. Effect modification by BMI was also assessed.

Results

IGF-I and IGFBP-3 were not strongly associated with MD after BMI adjustment. In multivariable analyses among premenopausal women, IGFBP-2 was positively associated with both percent MD-V (β = 1.49, p value = 0.02) and MD-A (β = 1.55, p value = 0.05). Among postmenopausal women, positive relationships between IGFBP-2 and percent MD-V (β = 2.04, p = 0.003) were observed; the positive associations between IGFBP-2 and percent MD-V were stronger among lean women (BMI < 25 kg/m²) (β = 5.32, p = 0.0002; p interaction = 0.0003).

Conclusions

In this comprehensive study of IGFBPs and MD, we observed a novel positive association between IGFBP-2 and MD, particularly among women with lower BMI. In concert with in vitro studies suggesting a dual role of IGFBP-2 on breast tissue, promoting cell proliferation as well as inhibiting tumorigenesis, our findings suggest that further studies assessing the role of IGFBP-2 in breast tissue composition, in addition to IGF-1 and IGFBP-3, are warranted.

Electronic supplementary material

The online version of this article (10.1186/s13058-019-1162-8) contains supplementary material, which is available to authorized users.

Bone marrow ablation demonstrates that estrogen plays an important role in osteogenesis and bone turnover via an antioxidative mechanism

To assess the effect of estrogen deficiency on osteogenesis and bone turnover in vivo, 8-week-old mice were sham-operated or bilaterally ovariectomized (OVX), and after 8 weeks, mechanical bone marrow ablation (BMX) was performed and newly formed bone tissue was analyzed from 6 days to 2 weeks after BMX. Our results demonstrated that OVX mice following BMX displayed 2 reversed phase changes, one phase observed at 6 and 8 days after BMX delayed osteogenesis accompanied by a delay in osteoclastogenesis, and the other phase observed at 12 and 14 days after BMX increased osteoblastic activity and osteoclastic activity. Furthermore, we asked whether impaired osteogenesis caused by estrogen deficiency was associated with increased oxidative stress, and oxidative stress parameters were examined in bone tissue from sham-operated and OVX mice and OVX mice were administrated with antioxidant N-acetyl-l-cysteine (NAC) or vehicle after BMX. Results demonstrated that estrogen deficiency induced oxidative stress in mouse bone tissue with reduced antioxidase levels and activity, whereas NAC administration almost rescued the abnormalities in osteogenesis and bone turnover caused by OVX. Results from this study indicate that estrogen deficiency resulted in primarily impaired osteogenesis and subsequently accelerated bone turnover by increasing oxidative stress and oxidative stress promises to be an effective target in the process of treatment of postmenopausal osteoporosis.

Endogenous parathyroid hormone-related protein compensates for the absence of parathyroid hormone in promoting bone accrual in vivo in a model of bone marrow ablation

To assess the effect of hypoparathyroidism on osteogenesis and bone turnover in vivo, bone marrow ablation (BMXs) were performed in tibias of 8-week-old wild-type and parathyroid hormone-null (PTH(-/-)) mice and newly formed bone tissue was analyzed from 5 days to 3 weeks after BMX. At 1 week after BMX, trabecular bone volume, osteoblast numbers, alkaline phosphatase-positive areas, type I collagen-positive areas, PTH receptor-positive areas, calcium sensing receptor-positive areas, and expression of bone formation-related genes were all decreased significantly in the diaphyseal regions of bones of PTH(-/-) mice compared to wild-type mice. In contrast, by 2 weeks after BMX, all parameters related to osteoblastic bone accrual were increased significantly in PTH(-/-) mice. At 5 days after BMX, active tartrate-resistant acid phosphatase (TRAP)-positive osteoclasts had appeared in wild-type mice but were undetectable in PTH(-/-) mice, Both the ratio of mRNA levels of receptor activator of NF-κB ligand (RANKL)/osteoprotegerin (OPG) and TRAP-positive osteoclast surface were still reduced in PTH(-/-) mice at 1 week but were increased by 2 weeks after BMX. The expression levels of parathyroid hormone-related protein (PTHrP) at both mRNA and protein levels were upregulated significantly at 1 week and more dramatically at 2 weeks after BMX in PTH(-/-) mice. To determine whether the increased newly formed bones in PTH(-/-) mice at 2 weeks after BMX resulted from the compensatory action of PTHrP, PTH(-/-) PTHrP(+/-) mice were generated and newly formed bone tissue was compared in these mice with PTH(-/-) and wild-type mice at 2 weeks after BMX. All parameters related to osteoblastic bone formation and osteoclastic bone resorption were reduced significantly in PTH(-/-) PTHrP(+/-) mice compared to PTH(-/-) mice. These results demonstrate that PTH deficiency itself impairs osteogenesis, osteoclastogenesis, and osteoclastic bone resorption, whereas subsequent upregulation of PTHrP in osteogenic cells compensates by increasing bone accrual.

Bone marrow ablation demonstrates that excess endogenous parathyroid hormone plays distinct roles in trabecular and cortical bone

Mice null for Cyp27b1, which encodes the 25-hydroxyvitamin D-1α-hydroxylase [1α(OH)ase(-/-) mice], lack 1,25-dihydroxyvitamin D [1,25(OH)(2)D] and have hypocalcemia and high parathyroid hormone (PTH) secretion. Intermittent, exogenous PTH is anabolic for bone. To determine the effect of the chronic excess endogenous PTH on osteogenesis and bone turnover, bone marrow ablations (BMX) were performed in tibiae and femurs of 6-week-old 1α(OH)ase(-/-) mice and in wild-type (WT) controls. Newly formed bone tissue was analyzed at 1, 2, and 3 weeks after BMX. BMX did not alter the higher levels of PTH in 1α(OH)ase(-/-) mice. In the marrow cavity, trabecular volume, osteoblast number, alkaline phosphatase-positive areas, type I collagen-positive areas, bone formation-related genes, and protein expression levels all increased significantly after BMX in 1α(OH)ase(-/-) mice, compared with WT. Osteoclast numbers and surface and ratio of RANKL/OPG-relative mRNA levels decreased significantly after BMX in 1α(OH)ase(-/-) mice, compared with WT. In the cortex, alkaline phosphatase-positive osteoblasts and osteoclast numbers increased significantly after BMX in 1α(OH)ase(-/-) mice, compared with WT. These results demonstrate that chronic excess endogenous PTH exerts an anabolic role in trabecular bone by stimulating osteogenic cells and reducing bone resorption, but plays a catabolic role in cortical bone by enhancing bone turnover with an increase in resorption.

Regulation of human adipose-derived stromal cell osteogenic differentiation by insulin-like growth factor-1 and platelet-derived growth factor-alpha

BACKGROUND

Human adipose-derived stromal cells possess a great potential for tissue engineering purposes. The authors' laboratory is interested in harnessing human adipose-derived stromal cells for skeletal tissue regeneration and identifying those factors that enhance human adipose-derived stromal cell osteogenic differentiation. The authors hypothesized that insulin-like growth factor (IGF) and platelet-derived growth factor (PDGF) would stimulate human adipose-derived stromal cell osteogenesis and that IGF would stimulate adipogenesis.

METHODS

Adipose-derived stromal cells were harvested from human lipoaspirate. Previously, a microarray analysis examined gene expression throughout osteogenic differentiation. In a candidate fashion, the authors added recombinant IGF-1 and PDGF-alpha individually and in combination. Osteogenesis and adipogenesis were assessed by alkaline phosphatase, alizarin red, and oil red O staining, and quantitative real-time polymerase chain reaction (RUNX2, ALP, OCN, IGF1, PPARG, LPL, AP2, and GCP1). Finally, intersection between IGF and PDGF signaling pathways was evaluated.

RESULTS

IGF-1 was observed to increase osteogenic differentiation by all markers (p < 0.01). However, PDGF-alpha when added alone primarily did not affect osteogenic markers. PDGF-alpha positively regulated transcription of IGF1. Addition of PDGF-alpha in combination with or before IGF-1 enhanced osteogenesis more than either alone. IGF-1 increased whereas PDGF-alpha diminished human adipose-derived stromal cell adipogenesis.

CONCLUSIONS

IGF signaling significantly increased osteogenesis in human adipose-derived stromal cells and may be used for tissue-engineering purposes. The combination of PDGF and IGF may be more beneficial than either alone in driving adipose-derived stromal cell osteogenesis. Future in vivo applications will focus on the combination of adipose-derived stromal cells, biomimetic scaffolds, and recombinant IGF.

Replacement of bone marrow by bone in rat femurs: the bone bioreactor

During development and repair of bone, two distinct yet complementary mechanisms, intramembranous and endochondral, mediate new bone formation via osteoblasts. Because mechanical bone marrow ablation leads to the rapid and transient formation of new bone in the marrow cavity, we postulated that parathyroid hormone (PTH), which is a bone anabolic hormone, enhances the formation of new bone that forms after marrow ablation. We subjected the left femur of rats to mechanical marrow ablation, or sham operation, and injected the animals daily with PTH or vehicle for 1, 2, or 3 weeks in a first experiment, then with PTH, parathyroid hormone-related peptide (PTHrP), or vehicle for 3 weeks in a second experiment. We subjected both femurs from each rat to soft X-ray, peripheral quantitative computed tomography, computed tomography on a microscale, and histological analysis, and determined the concentration of serum osteocalcin. In addition, in the second experiment, we determined the serum concentration of calcium, tartrate-resistant acid phosphatase (TRAP), and receptor activator of NF-kappaB ligand (RANKL) at 3 weeks, and subjected femurs to biomechanical testing. Following treatment with PTH or PTHrP for 3 weeks, bone filled the marrow cavity of the shafts whose marrow had been ablated. PTH increased trabecular density in the right femur, but failed to induce bone formation in the medullary region of the right unoperated femoral shafts. The newly formed bone endowed left femoral shafts with improved biomechanical properties when compared to those of right femurs and left femurs from control, sham-operated, and vehicle-treated rats. PTHrP, like PTH, increased serum osteocalcin, but neither increased serum calcium, TRAP, or RANKL at 3 weeks. Our results reveal that the newly formed bone that follows marrow ablation is responsive to PTH, expand the role of PTH in bone, and might open new avenues of investigations to the field of regenerative medicine and tissue engineering. Local bone marrow removal in conjunction with pharmacologic intervention with an anabolic agent might provide a technique for rapid preferential site-directed bone growth in areas of high bone loss.

Peri-implant bone formation and implant integration strength of peptide-modified p(AAM-co-EG/AAC) interpenetrating polymer network-coated titanium implants

Interpenetrating polymer networks (IPNs) of poly (acrylamide-co-ethylene glycol/acrylic acid) functionalized with an -Arg-Gly-Asp- (RGD) containing 15 amino acid peptides, derived from rat bone sialoprotein (bsp-RGD(15), were grafted to titanium implants in an effort to modulate bone formation in the peri-implant region in the rat femoral ablation model. Bone-implant contact (BIC) and bone formation within the medullary canal were determined using microcomputed tomography at 2 and 4 weeks postimplantation. BIC for bsp-RGD(15)-IPN implants was enhanced relative to hydroxyapatite tricalcium phosphate (HA-TCP) coated implants, but was similar to all other groups. Aggregate bone formation neither indicated a dose-dependent effect of bsp-RGD(15) nor a meaningful trend. Mechanical testing of implant fixation revealed that only the HA-TCP coated implants supported significant (>1 MPa) interfacial shear strength, despite exhibiting lower overall BIC, an indication that bone ingrowth into the rougher coating was the primary mode of implant fixation. While no evidence was found to support the hypothesis that bsp-RGD(15)-modified IPN coated implants significantly impacted bone-implant bonding, these results point to the lack of correlation between in vitro studies employing primary osteoblasts and in vivo wound healing in the peri-implant region.

ED-71, a novel vitamin D analog, promotes bone formation and angiogenesis and inhibits bone resorption after bone marrow ablation

ED-71, a novel analog of 1alpha,25-(OH)2 D3, increases bone mass to a greater extent than alfacalcidol, an 1alpha,25-(OH)2 D3 prodrug. In this study, we used a murine bone marrow ablation model to compare the effect of ED-71 on bone formation and resorption in vivo with that of 1alpha,25-(OH)2 D3. We discovered that bone matrix remodeling occurring within the first week after bone marrow ablation was enhanced by a single injection of ED-71, but not by 1alpha,25-(OH)2 D3. This enhancement was associated with an increase in bone surface. Trabecular bone resorption occurring from 1 to 2 weeks after the procedure was suppressed by a single injection of ED-71, but not 1alpha,25-(OH)2 D3, with treated mice exhibiting a reduction in osteoclast numbers, despite increases in osteoblast surface. As seen with the single injection, daily administration of ED-71 also enhanced bone modeling. Bone marrow osteoblast differentiation was also augmented by ED-71 pretreatment. Furthermore, ED-71 treatment immediately after bone marrow ablation enhanced angiogenesis within the bone marrow cavity via enhancement of VEGF(120) expression. In this paper, we clearly demonstrate that ED-71 is an orally administered small molecular weight compound with an anabolic effect on bone metabolism.

Patterns and localization of gene expression during intramembranous bone regeneration in the rat femoral marrow ablation model

Tissue formation and repair are dependent upon cascades of biological events, but the signals involved and the possible gene coexpression patterns during intramembranous bone repair are only poorly understood. We sought to place this mode of regeneration in context by profiling quantitative gene expression for a panel of 39 genes between days 1 and 14 following rat femoral marrow ablation. In situ hybridization was employed to localize a subset of genes. Additionally, principal components analysis was conducted to identify underlying factors suggestive of coexpression patterns. During inflammation (days 1-5), several genes, including cyclooxygenase-1 and -2, showed downregulation. Other proinflammatory cytokines, tumor necrosis factor-alpha and interleukin-1beta, exhibited increasing levels around day 5. During repair (days 3-10), growth factors, receptors, and inhibitor genes for transforming growth factor- beta; basic fibroblast growth factor; bone morphogenetic proteins 2, 4, and 7; vascular endothelial growth factor; and insulin-like growth factor-I were upregulated. In addition, the gene for core binding factor-alpha1 and markers of osteoblast function such as alkaline phosphatase, collagen type I, osteonectin, osteopontin, and osteocalcin had peak expression at day 5 or 7. The remodeling phase (days 10-14) was characterized by peaks for cytokines associated with osteoclastic activity including receptor activator of nuclear factor-kappaB, receptor activator of nuclear factor-kappaB ligand (RANKL), cathepsin K, tumor necrosis factor-alpha, interleukin-6, and cyclooxygenase-2. In situ hybridization showed that the most common sites of increased signal were within osteoblastic cells on trabecular and endosteal surfaces. Principal components analysis identified eight underlying factors that together explained over 80% of the variance in the data.