IGF-I and not IGF-II expression is regulated by glucocorticoids in human fetal epiphyseal chondrocytes

Stage-Dependent Activity and Pro-Chondrogenic Function of PI3K/AKT during Cartilage Neogenesis from Mesenchymal Stromal Cells

Differentiating mesenchymal stromal cells (MSCs) into articular chondrocytes (ACs) for application in clinical cartilage regeneration requires a profound understanding of signaling pathways regulating stem cell chondrogenesis and hypertrophic degeneration. Classifying endochondral signals into drivers of chondrogenic speed versus hypertrophy, we here focused on insulin/insulin-like growth factor 1 (IGF1)-induced phosphoinositide 3-kinase (PI3K)/AKT signaling. Aware of its proliferative function during early but not late MSC chondrogenesis, we aimed to unravel the late pro-chondrogenic versus pro-hypertrophic PI3K/AKT role. PI3K/AKT activity in human MSC and AC chondrogenic 3D cultures was assessed via Western blot detection of phosphorylated AKT. The effects of PI3K inhibition with LY294002 on chondrogenesis and hypertrophy were assessed via histology, qPCR, the quantification of proteoglycans, and alkaline phosphatase activity. Being repressed by ACs, PI3K/AKT activity transiently rose in differentiating MSCs independent of TGFβ or endogenous BMP/WNT activity and climaxed around day 21. PI3K/AKT inhibition from day 21 on equally reduced chondrocyte and hypertrophy markers. Proving important for TGFβ-induced SMAD2 phosphorylation and SOX9 accumulation, PI3K/AKT activity was here identified as a required stage-dependent driver of chondrogenic speed but not of hypertrophy. Thus, future attempts to improve MSC chondrogenesis will depend on the adequate stimulation and upregulation of PI3K/AKT activity to generate high-quality cartilage from human MSCs.

Role of TGFβ Signaling in Maternal Ethanol-Induced Fetal Articular Cartilage Dysplasia and Adult Onset of Osteoarthritis in Male Rats

Based on our previous findings that prenatal ethanol exposure in offspring increased susceptibility to adult osteoarthritis, this study aimed to further investigate the direct toxicity of ethanol on fetal articular cartilage development. Rat bone marrow-derived stroma cells were capsulated in alginate beads, incubated in a chondrogenic differentiation medium, and cultured for 4 weeks with ethanol treatment at concentrations of 0, 4, 20, and 100 mM. Pregnant rats were treated with ethanol (4 g/kg/day) from gestational days (GDs) 9 to 20. At GD20 and postnatal weeks 2, 6, and 12, 8 male offspring were sacrificed, and 8 male offspring rats of 8-weeks old in each group were treated with or without intraarticular injection of papain for 4 weeks to verify the susceptibility of adult osteoarthritis. Ethanol treatment resulted in poor differentiation of bone marrow-derived stroma cells to chondrocytes and suppressed the expression of the transforming growth factor-β (TGFβ)-smad2/3-Sox9 signaling pathway. In animal experiments, the shape of articular cartilage in the ethanol treatment group was more disordered than that of the control group, the matrix was not deep, and the cartilage was thin, which showed poor cartilage development. The TGFβ signaling pathway in the ethanol treatment group was persistently low at all time points. After intraarticular injection of papain, histological analyses, and the Mankin score revealed increased cartilage destruction in the ethanol treatment group. Ethanol caused articular cartilage dysplasia that was programmed in adulthood via a low-functional TGFβ signaling pathway, and the tolerance of this articular cartilage to external stimuli was significantly decreased.

Prenatal food restriction induces poor-quality articular cartilage in female rat offspring fed a post-weaning high-fat diet and its intra-uterine programming mechanisms

Epidemiological data show that osteoarthritis (OA) is significantly associated with lower birth weight, and that OA may be a type of fetal-originated adult disease. The present study aimed to investigate the prenatal food-restriction (PFR) effect on the quality of articular cartilage in female offspring to explore the underlying mechanisms of fetal-originated OA. Maternal rats were fed a restricted diet from gestational day (GD) 11 to 20 to induce intra-uterine growth retardation. Female fetuses and female adult offspring fed a post-weaning high-fat diet were killed at GD20 and postnatal week 24, respectively. Serum and knee cartilage samples from fetuses and adult female offspring were collected and examined for cholesterol metabolism and histology. Fetal serum corticosterone and insulin-like growth factor-1 (IGF-1) in the PFR group were lower than those of the control, but the serum cholesterol level was not changed. The lower expression of IGF-1 in the PFR group lasted into adulthood. The expression of extracellular matrix (ECM) genes, including type II collagen, aggrecan and cholesterol efflux genes including liver X receptor, were significantly induced, but the ATP-binding-cassette transporter A1 was unchanged. PFR could induce a reduction in ECM synthesis and impaired cholesterol efflux in female offspring, and eventually led to poor quality of articular cartilage and OA.

Parathyroid hormone 1-34 reduces dexamethasone-induced terminal differentiation in human articular chondrocytes

Intra-articular injection of dexamethasone (Dex) is occasionally used to relieve pain and inflammation in osteoarthritis (OA) patients. Dex induces terminal differentiation of chondrogenic mesenchymal stem cells in vitro and causes impaired longitudinal skeletal growth in vivo. Parathyroid hormone 1-34 (PTH 1-34) has been shown to reverse terminal differentiation of osteoarthritic articular chondrocytes. We hypothesized that Dex induces terminal differentiation of articular chondrocytes and that this effect can be mitigated by PTH 1-34 treatment. We tested the effect of Dex on terminal differentiation in human articular chondrocytes and further tested if PTH 1-34 reverses the effects. We found that Dex treatment downregulated chondrogenic-induced expressions of SOX-9, collagen type IIa1 (Col2a1), and aggrecan and reduced synthesis of cartilaginous matrix (Col2a1 and sulfated glycosaminoglycan) synthesis. Dex treatment upregulated chondrocyte hypertrophic markers of collagen type X and alkaline phosphatase at mRNA and protein levels, and it increased the cell size of articular chondrocytes and induced cell death. These results indicated that Dex induces terminal differentiation of articular chondrocytes. To test whether PTH 1-34 treatment reverses Dex-induced terminal differentiation of articular chondrocytes, PTH 1-34 was co-administered with Dex. Results showed that PTH 1-34 treatment reversed both changes of chondrogenic and hypertrophic markers in chondrocytes induced by Dex. PTH 1-34 also decreased Dex-induced cell death. PTH 1-34 treatment reduces Dex-induced terminal differentiation and apoptosis of articular chondrocytes, and PTH 1-34 treatment may protect articular cartilage from further damage when received Dex administration.

Intrauterine low-functional programming of IGF1 by prenatal nicotine exposure mediates the susceptibility to osteoarthritis in female adult rat offspring

This study aimed to evaluate whether female adult offspring born with intrauterine growth retardation induced by prenatal nicotine exposure (PNE) are susceptible to osteoarthritis (OA) and to explore the underlying programming mechanisms. Pregnant rats were treated with nicotine or saline at 2.0 mg/kg/d from gestational d 11 to 20. The female adult offspring with or without PNE were forced with a strenuous treadmill running for 6 wk to induce OA. Nicotine's effects on fetal articular chondrocytes were studied by exposing chondrocytes to nicotine for 10 d, and dihydro-β-erythroidine, a selective α4β2-nicotinic acetylcholine receptor (nAChR) inhibitor, was used to identify the change of nicotine's effect. For adult offspring, increased cartilage destruction and accelerated OA progression were observed in the PNE group with running; the expression of α1 chain of type II collagen (Col2A1), aggrecan, SRY-type high mobility group box 9 (Sox9), and IGF1 signaling molecules in the cartilage of PNE offspring were decreased. For fetuses, elevated serum corticosteroid and nicotine levels and suppressed IGF1 levels were observed; expression of Col2A1, aggrecan, Sox9, and IGF1 were reduced. The result of chondrocytes revealed that nicotine impeded the expression of Col2A1, aggrecan, and IGF1; blocking α4β2-nAChR rescued nicotine's suppression. In conclusion, PNE increases the susceptibility of adult offspring to OA; the potential mechanism involves IGF1 low-functional programming in articular cartilage caused directly by the action of nicotine on α4β2-nAChR.

Prenatal ethanol exposure increases osteoarthritis susceptibility in female rat offspring by programming a low-functioning IGF-1 signaling pathway

Epidemiological evidence indicates that osteoarthritis (OA) and prenatal ethanol exposure (PEE) are both associated with low birth weight but possible causal interrelationships have not been investigated. To investigate the effects of PEE on the susceptibility to OA in adult rats that experienced intrauterine growth retardation (IUGR), and to explore potential intrauterine mechanisms, we established the rat model of IUGR by PEE and dexamethasone, and the female fetus and 24-week-old adult offspring subjected to strenuous running for 6 weeks were sacrificed. Knee joints were collected from fetuses and adult offspring for histochemistry, immunohistochemistry and qPCR assays. Histological analyses and the Mankin score revealed increased cartilage destruction and accelerated OA progression in adult offspring from the PEE group compared to the control group. Immunohistochemistry showed reduced expression of insulin-like growth factor-1 (IGF-1) signaling pathway components. Furthermore, fetuses in the PEE group experienced IUGR but exhibited a higher postnatal growth rate. The expression of many IGF-1 signaling components was downregulated, which coincided with reduced amounts of type II collagen in the epiphyseal cartilage of fetuses in the PEE group. These results suggest that PEE enhances the susceptibility to OA in female adult rat offspring by down-regulating IGF-1 signaling and retarding articular cartilage development.

The frontal cortex IGF system is down regulated in the term, intrauterine growth restricted fetal baboon

OBJECTIVE

The IGF system exerts systemic and local actions during development. We previously demonstrated that fetal cerebral cortical IGF1 is reduced at 0.5 gestation in our IUGR baboon nonhuman primate model. We hypothesized that by term protein expression of several key IGF system stimulatory peptide pathway components and downstream nutrient signaling effectors of IGF, mammalian target of rapamycin (mTOR) and S6, would decrease, indicating reduced cellular nutrient uptake and protein synthesis.

DESIGN

We fed 7 control baboons ad libitum while 6 baboons ate a globally reduced diet (70% of feed eaten by controls) from 0.16 gestation through pregnancy that produces IUGR. Fetuses were removed at Cesarean section at 0.9 gestation. Frontal cortex sections were stained for IGFI, IGFII, IGFRI, IGFR2, IGFBP2, 3, 5 and 6, and mTOR and ribosomal protein S6 and double stained with NeuN a neuron-specific nuclear antigen.

RESULTS

All proteins stained neuronal cytoplasm except IGFRI which showed only glial cell cytoplasmic and blood vessel staining. IUGR fetuses showed decreased frontal cortical immunoreactive IGFI, IGFII, IGFRI, IGFBP2, 5 and 6, and mTOR and S6 (p < 0.05). IGFBP3 increased (p < 0.05) and IGFR2 was unchanged (p > 0.05). There were no differences between male and female fetal brains.

CONCLUSIONS

When fetal nutrient availability is decreased, IUGR down regulates the IGF system and its mTOR signaling pathway in the fetal frontal cortex coincident with slowed growth. These findings emphasize the importance of the local tissue IGF system in fetal primate brain development.

Nicotine-induced retardation of chondrogenesis through down-regulation of IGF-1 signaling pathway to inhibit matrix synthesis of growth plate chondrocytes in fetal rats

Previous studies have confirmed that maternal tobacco smoking causes intrauterine growth retardation (IUGR) and skeletal growth retardation. Among a multitude of chemicals associated with cigarette smoking, nicotine is one of the leading candidates for causing low birth weights. However, the possible mechanism of delayed chondrogenesis by prenatal nicotine exposure remains unclear. We investigated the effects of nicotine on fetal growth plate chondrocytes in vivo and in vitro. Rats were given 2.0 mg/kg·d of nicotine subcutaneously from gestational days 11 to 20. Prenatal nicotine exposure increased the levels of fetal blood corticosterone and resulted in fetal skeletal growth retardation. Moreover, nicotine exposure induced the inhibition of matrix synthesis and down-regulation of insulin-like growth factor 1 (IGF-1) signaling in fetal growth plates. The effects of nicotine on growth plates were studied in vitro by exposing fetal growth plate chondrocytes to 0, 1, 10, or 100 μM of nicotine for 10 days. Nicotine inhibited matrix synthesis and down-regulated IGF-1 signaling in chondrocytes in a concentration-dependent manner. These results suggest that prenatal nicotine exposure induces delayed chondrogenesis and that the mechanism may involve the down-regulation of IGF-1 signaling and the inhibition of matrix synthesis by growth plate chondrocytes. The present study aids in the characterization of delayed chondrogenesis caused by prenatal nicotine exposure, which might suggest a candidate mechanism for intrauterine origins of osteoporosis and osteoarthritis.

Prednisolone reduces the ability of serum to activate the IGF1 receptor in vitro without affecting circulating total or free IGF1

OBJECTIVE

End-point bioassays based on thymidine or sulfate incorporation have demonstrated that glucocorticoid (GC) treatment inhibits serum IGF1 action, but the mechanism is unknown as serum IGF1 concentrations have been reported to either increase or remain unchanged.

AIM

To investigate whether GC treatment affects the ability of serum to activate the IGF1 receptor (IGF1R) in vitro (i.e. bioactive IGF1), using a specific cell-based IGF1 kinase receptor activation assay.

SUBJECTS AND METHODS

Twenty children with stable asthma (age 7.7-13.8 years) treated for 1 week with 5 mg prednisolone in a randomized, double-blind, placebo-controlled crossover study. Non-fasting serum samples were collected in the afternoon after each 7-day period and assayed for bioactive IGF1, free IGF1, total IGFs, IGF-binding proteins (IGFBPs), and insulin.

RESULTS

Prednisolone treatment reduced IGF1 bioactivity by 12.6% from 2.22±0.18 to 1.94±0.15 μg/l (P=0.01) compared with placebo. In contrast, no changes were observed for (μg/l; placebo vs prednisolone) total IGF1 (215±27 vs 212±24), free IGF1 (1.50±0.16 vs 1.43±0.17), total IGF2 (815±26 vs 800±31), IGFBP3 (3140±101 vs 3107±95), IGFBP2 (238±21 vs 220±19), IGFBP1 (32±6 vs 42±10), or IGFBP1-bound IGF1 (24±5 vs 26±7). Insulin remained unchanged as did IGFBP levels as estimated by western ligand blotting. Prednisolone had no direct effects on IGF1R phosphorylation.

CONCLUSIONS

Our study gives evidence that GC treatment induces a circulating substance that is able to inhibit IGF1R activation in vitro without affecting circulating free or total IGF1. This may be one of the mechanisms by which GC inhibits IGF1 action in vivo. However, the nature of this circulating substance remains to be identified.

Caffeine-induced fetal rat over-exposure to maternal glucocorticoid and histone methylation of liver IGF-1 might cause skeletal growth retardation

Several epidemiological investigations, including previous work by our laboratory, indicate that maternal caffeine consumption is associated with intrauterine growth retardation and impaired fetal length growth. Skeletal development is critical for length growth. In the present study, our goals were to determine the effects of prenatal caffeine exposures on fetal skeletal growth and to investigate the mechanisms associated with such effects. Pregnant Wistar rats were injected intragastrically with 120mg/kg of caffeine intragastrically each day from gestational days 11-20. Maternal prenatal caffeine exposure was associated with decreased fetal femur lengths and inhibited of synthesis of extracellular matrices in fetal growth plates Moreover, caffeine exposure significantly increased the levels of fetal blood corticosterone and decreased IGF-1mRNA expression levels in the liver and growth plate. The expression levels of IGF-1 signaling pathway components (IGF-1R, IRS-1, AKT1/2 and Col2A1) were also reduced. In addition, the results of chromatin immunoprecipitation assays indicated that caffeine exposure down-regulated histone methylation of fetal IGF-1 in the liver. These results suggest that prenatal caffeine exposure may inhibit fetal skeletal growth through a mechanism that is associated with increased fetal exposure to maternal glucocorticoids and results in lower IGF-1 signaling pathway activity. Taken together, these results raise important concerns regarding the skeletal growth toxicity of caffeine and potentially indicate the intrauterine origins of adult osteoporosis and osteoarthritis.

IGF-I-IGFBP-3-acid-labile subunit (ALS) complex in children and adolescents with classical congenital adrenal hyperplasia due to 21-hydroxylase deficiency (CAH)

It has been shown that changes in IGF-I and IGFBP levels in children with classical congenital adrenal hyperplasia due to 21-hydroxylase deficiency (CAH) are correlated with different states of metabolic control. Our approach was to analyze the serum levels of IGF-I, IGFBP-3, their molar ratio IGF-I:IGFBP-3 (MR), and ALS in a cohort of CAH children and adolescents, and their associations with different clinical and biochemical parameters.

DESIGN AND PATIENTS

56 patients, aged between 5.6 and 19.0 years were studied cross-sectionally. All patients had genetically proven CAH and received standard steroid substitution therapy. We measured serum levels of IGF-I, IGFBP-3, and ALS by commercial ELISA and calculated MR and assigned population-based SD scores (SDS).

RESULTS

(median, quartiles) Overall IGF-I was not significantly altered (0.05 SDS, -1.21, 0.92), whereas IGFBP-3 was significantly elevated (1.50 SDS; 0.58, 1.95, p<0.0001) compared to the reference population. Consecutively, MR was decreased (-0.64 SDS; -1.38, 0.32; p=0.0017). ALS was clearly decreased (-1.95 SDS; -3.075, -1.00; p<0.0001). ALS, IGF-I, MR, and IGFBP-3 SDS were lower in pubertal than in prepubertal patients (p<0.05). ALS SDS were lower in girls (p=0.0038). Correlation analyses (r(s), p) revealed correlations between MR/ALS and chronological age (-0.583, <0.0001/-0.428, 0.0010), MR/ALS and Tanner stages (-0.500, <0.0001/-0.334, 0.0118), MR/ALS and bone age (0.407, 0.0075/0.426, 0.0049), and between MR and ALS (0.405, 0.0020), respectively. For MR and ALS, we found no significant correlations for BMI, HOMA-IR, hydrocortisone and fludrocortisone dosage, or parameters of metabolic control.

CONCLUSIONS

Our data provide evidence that the components of the trimeric IGF-I-IGFBP-3-ALS complex are altered in CAH children with possible implications on pubertal growth and final height.