The quantitative and functional relation between insulin-like growth factor-I (IGF) and IGF-binding proteins during human osteoarthritis

METTL3-mediated m6A modification of IGFBP7-OT promotes osteoarthritis progression by regulating the DNMT1/DNMT3a-IGFBP7 axis

Osteoarthritis (OA) is the most common degenerative disorder, affecting approximately half of the elderly population. In this study, we find that the expressions of long noncoding RNA (lncRNA) IGFBP7-OT and its maternal gene, IGFBP7, are upregulated and positively correlated in osteoarthritic cartilage. Overexpression of IGFBP7-OT significantly inhibits chondrocyte viability, promotes chondrocyte apoptosis, and reduces extracellular matrix components, whereas IGFBP7-OT knockdown has the opposite effects. IGFBP7-OT overexpression promotes cartilage degeneration and markedly aggravates the monosodium iodoacetate-induced OA phenotype in vivo. Further mechanistic research reveals that IGFBP7-OT promotes OA progression by upregulating IGFBP7 expression. Specifically, IGFBP7-OT suppresses the occupancy of DNMT1 and DNMT3a on the IGFBP7 promoter, thereby inhibiting methylation of the IGFBP7 promoter. The upregulation of IGFBP7-OT in OA is partially controlled by METTL3-mediated N6-methyladenosine (m6A) modification. Collectively, our findings reveal that m6A modification of IGFBP7-OT promotes OA progression by regulating the DNMT1/DNMT3a-IGFBP7 axis and provide a potential therapeutical target for OA treatment.

Cationic peptide carriers enable long-term delivery of insulin-like growth factor-1 to suppress osteoarthritis-induced matrix degradation

BACKGROUND

Insulin-like growth factor-1 (IGF-1) has the potential to be used for osteoarthritis (OA) treatment but has not been evaluated in clinics yet owing to toxicity concerns. It suffers from short intra-joint residence time and a lack of cartilage targeting following its intra-articular administration. Here, we synthesize an electrically charged cationic formulation of IGF-1 by using a short-length arginine-rich, hydrophilic cationic peptide carrier (CPC) with a net charge of +14, designed for rapid and high uptake and retention in both healthy and arthritic cartilage.

METHODS

IGF-1 was conjugated to CPC by using a site-specific sulfhydryl reaction via a bifunctional linker. Intra-cartilage depth of penetration and retention of CPC-IGF-1 was compared with the unmodified IGF-1. The therapeutic effectiveness of a single dose of CPC-IGF-1 was compared with free IGF-1 in an IL-1α-challenged cartilage explant culture post-traumatic OA model.

RESULTS

CPC-IGF-1 rapidly penetrated through the full thickness of cartilage creating a drug depot owing to electrostatic interactions with negatively charged aggrecan-glycosaminoglycans (GAGs). CPC-IGF-1 remained bound within the tissue while unmodified IGF-1 cleared out. Treatment with a single dose of CPC-IGF-1 effectively suppressed IL-1α-induced GAG loss and nitrite release and rescued cell metabolism and viability throughout the 16-day culture period, while free IGF at the equivalent dose was not effective.

CONCLUSIONS

CPC-mediated depot delivery of IGF-1 protected cartilage by suppressing cytokine-induced catabolism with only a single dose. CPC is a versatile cationic motif that can be used for intra-cartilage delivery of other similar-sized drugs.

Transcriptome Analysis Reveals Novel Genes Associated with Cartilage Degeneration in Posttraumatic Osteoarthritis Progression

OBJECTIVE

The current therapeutic strategy for posttraumatic osteoarthritis (PTOA) focuses on early intervention to attenuate disease progression, preserve joint function, and defer joint replacement timing. Sequential transcriptomic changes of articular cartilage in a rat model were investigated to explore the molecular mechanism in early PTOA progression.

DESIGN

Anterior cruciate ligament transection and medial meniscectomy (ACLT + MMx)-induced PTOA model was applied on male Wistar rats. Articular cartilages were harvested at time 0 (naïve), 2 week, and 4 weeks after surgery. Affymetrix Rat genome 230 2.0 array was utilized to analyze the gene expression changes of articular cartilages.

RESULTS

We identified 849 differentially expressed genes (DEGs) at 2 weeks and 223 DEGs at 4 weeks post-ACLT + MMx surgery compared with time 0 (naïve group). Gene ontology and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis were performed to gain further insights from these DEGs. 22 novel genes and 1 novel KEGG pathway (axon guidance) in cartilage degeneration of osteoarthritis were identified. Axon guidance molecules-Gnai1, Sema4d, Plxnb1, and Srgap2 commonly dysregulated in PTOA progression. Gnai1 gene showed a concordant change in protein expression by immunohistochemistry staining.

CONCLUSIONS

Our study identified 22 novel dysregulated genes and axon guidance pathway associated with articular cartilage degeneration in PTOA progression. These findings provide the potential candidates of biomarkers and therapeutic targets for further investigation.

Microarray analysis of hub genes and pathways in damaged cartilage tissues of knee

The aim of this study was to identify genes and functional pathways associated with damaged cartilage tissues of knee using microarray analysis.The gene expression profile GSE129147 including including 10 knee cartilage tissues from damaged side and 10 knee nonweight-bearing healthy cartilage was downloaded and bioinformatics analysis was made.A total of 182 differentially-expressed genes including 123 up-regulated and 59 down-regulated genes were identified from the GSE129147 dataset. Gene ontology and pathway enrichment analysis confirmed that extracellular matrix organization, collagen catabolic process, antigen processing and presentation of peptide or polysaccharide antigen, and endocytic vesicle membrane were strongly associated with cartilage injury. Furthermore, 10 hub differentially-expressed genes with a higher connectivity degree in protein-protein interactions network were found such as POSTN, FBN1, LOX, insulin-like growth factor binding proteins3, C3AR1, MMP2, ITGAM, CDKN2A, COL1A1, COL5A1.These hub genes and pathways provide a new perspective for revealing the potential pathological mechanisms and therapy strategy of cartilage injury.

The attenuation of insulin-like growth factor signaling may be responsible for relative reduction in matrix synthesis in degenerated areas of osteoarthritic cartilage

Background

In osteoarthritis (OA), cartilage matrix is lost gradually despite enhanced matrix synthesis by chondrocytes. This paradox may be explained, at least partly, by reduced chondrocyte anabolism in degenerated area of OA cartilage. However, to date, it is not known why chondrocyte anabolism is suppressed in those areas.

Methods

Cartilage was obtained from control knees and end-stage OA knees in macroscopically preserved areas and degenerated areas, and gene expression was analyzed in respective regions of cartilage using laser capture microdissection and qPCR. For the cartilage protein analysis, cartilage was obtained from preserved areas and degenerated areas of OA knees in pairs, and proteins were extracted using urea buffer. Protein concentrations were determined by Luminex and compared between the areas. Cartilage explants prepared from preserved areas and degenerated areas of OA knees were cultured in the presence or absence of an AKT inhibitor, and the gene expression was evaluated by qPCR. Finally, the expression of SP1 was evaluated in OA and control cartilage, and the significance of Sp1 on the expression of IGF1R and IRS1 was investigated in experiments using primary cultured chondrocytes.

Results

Within OA cartilage, the expression of IGF-1, IGF-2, IGF1R and IRS1 was reduced in degenerated areas compared to preserved areas, while the expression of all six IGF-binding protein genes examined was enhanced in the former areas. Consistent results were obtained by a protein analysis. In explant culture, the inhibition of AKT signaling abrogated the abundant matrix gene expression in the preserved areas over the degenerated areas, indicating that suppressed matrix synthesis in degenerated areas may be ascribed, at least partly, to attenuated IGF signaling. Within OA cartilage, the expression of Sp1 was considerably reduced in severely degenerated areas compared to preserved areas, which correlated well with the expression of IGF1R and IRS1. In experiments using primary cultured chondrocytes, the expression of IGF1R and IRS1 was enhanced by the induction of Sp1 expression and reduced by the suppression of Sp1 expression.

Conclusions

The results of this study suggest that attenuated IGF signaling may be responsible, at least partly, for the reduced matrix synthesis in degenerated areas of OA cartilage.

Ageing and Osteoarthritis

The increase in global lifespan has in turn increased the prevalence of osteoarthritis which is now the most common type of arthritis. Cartilage tissue located on articular joints erodes during osteoarthritis which causes pain and may lead to a crippling loss of function in patients. The pathophysiology of osteoarthritis has been understudied and currently no disease modifying treatments exist. The only current end-point treatment remains joint replacement surgery. The primary risk factor for osteoarthritis is age. Clinical and basic research is now focused on understanding the ageing process of cartilage and its role in osteoarthritis. This chapter will outline the physiology of cartilage tissue, the clinical presentation and treatment options for the disease and the cellular ageing processes which are involved in the pathophysiology of the disease.

A whole-genome transcriptome analysis of articular chondrocytes in secondary osteoarthritis of the hip

Objective

To date, exhaustive gene expression analyses of chondrocytes in hip osteoarthritis (OA) have yielded specific gene expression patterns. No study has reported on the exhaustive transcriptome of secondary hip OA based on acetabular dysplasia in a Japanese population, while previous reports have focused on primary or idiopathic hip OA in Caucasian populations. This study aims to search for specific gene expression patterns of secondary hip OA chondrocytes by transcriptome analysis.

Design

Human articular cartilage was obtained from femoral heads following hemiarthroplasty for femoral neck fracture (N = 8; non-OA) and total hip arthroplasty for secondary hip OA (N = 12). Total RNA was extracted from the articular cartilage and submitted for microarray analysis. The obtained data were used to perform gene expression analysis, GO enrichment analysis and pathway analysis and were compared with data from primary hip OA in Caucasian populations in the literature.

Results

We identified 888 upregulated (fold change: FC ≥ 2) and 732 downregulated (FC ≤ 0.5) genes in hip OA versus non-OA chondrocytes, respectively. Only 10% of upregulated genes were common between the secondary and primary OA. The newly found genes prominently overexpressed in the secondary hip OA chondrocytes were DPT, IGFBP7, and KLF2. Pathway analysis revealed extracellular matrix (ECM)-receptor interaction as an OA-related pathway, which was similar to previous reports in primary hip OA.

Conclusions

This is the first study to report the genome-wide transcriptome of secondary hip OA chondrocytes and demonstrates new potential OA-related genes. Gene expression patterns were different between secondary and primary hip OA, although the results of pathway and functional analysis were similar.

miRNA‑27a regulates arthritis via PPARγ in vivo and in vitro

The present study investigated the role of microRNA (miR)‑27a in the development of arthritis and its mechanism of action. Initially, collagen was used to develop an in vivo rat model of arthritis. Changes in the miRs in the rats were analyzed. It was subsequently observed that miR‑27a expression was reduced in patients with arthritis, compared with the control group. In the present study an in vitro miR‑27a overexpression model of arthritis was established and it was observed that miR‑27a increased the proliferation of osteoblast‑like cells in vitro. miR‑27a overexpression promoted osteogenic differentiation, increased alkaline phosphatase (ALP) and osteoporosis (OST) content, induced insulin‑like growth factor binding protein-5 (IGFBP‑5) protein expression, reduced inflammation and suppressed peroxisome proliferator‑activated receptor γ (PPARγ) and matrix metalloproteinase-17 (MMP‑17) protein expression in arthritis. However, miR‑27a downregulation inhibited osteogenic differentiation, increased inflammation and PPARγ and MMP‑17 protein expression and suppressed ALP and OST content in an in vitro model of arthritis. The PPARγ inhibitor reduced the function of miR‑27a downregulation on arthritis. Therefore the results of the present study revealed that miR‑27a regulates arthritis via PPARγ.

Dietary Fat Intake and Radiographic Progression of Knee Osteoarthritis: Data From the Osteoarthritis Initiative

OBJECTIVE

Few studies have investigated the role of dietary factors on knee osteoarthritis (OA) progression. We examined the prospective association of dietary fat intake with radiographic progression of knee OA.

METHODS

In the Osteoarthritis Initiative, 2,092 participants with radiographic knee OA and having baseline dietary data were followed at yearly intervals up to 48 months. Dietary intakes of fatty acids were assessed with the Block Brief Food Frequency Questionnaire. To evaluate radiographic progression of knee OA, we used quantitative joint space width (JSW) between the medial femur and tibia of the knee based on fixed-flexion posteroanterior radiographs. Linear mixed models for repeated measures were used to test the association between dietary fat and JSW loss over time.

RESULTS

We observed significant positive relationships of total fat and saturated fatty acids (SFA) intakes with JSW loss. With increasing quartiles of total fat intake, JSW decreases over 48 months were 0.26 mm, 0.27 mm, 0.31 mm and 0.35 mm, respectively (P = 0.02 for trend). Similar association was observed between SFA intake and JSW loss. In contrast, higher intakes of mono- (MUFA) and polyunsaturated fatty acids (PUFA), and higher ratio of PUFA to SFA were associated with a reduced JSW loss.

CONCLUSION

High intakes of total fat and SFA may be associated with increased structural knee OA progression, while MUFA and PUFA may reduce radiographic progression. Replication of these novel findings in other prospective studies is needed to confirm if reduction in SFA intake and increase in unsaturated fat intake lead to delayed knee OA progression.

Conditioned Medium of Wharton's Jelly Derived Stem Cells Can Enhance the Cartilage Specific Genes Expression by Chondrocytes in Monolayer and Mass Culture Systems

Purpose: Mesenchymal stem cells (MSCs) have been introduced for cell therapy strategies in osteoarthritis (OA). Despite of their capacity for differentiation into chondrocyte, there are some evidences about their life-threatening problem after transplantation. So, some researchers shifted on the application of stem cells conditioned medium. The goal of this study is to evaluate whether Wharton's jelly derived stem cell conditioned medium (WJSCs-CM) can enhance the gene expression profile by chondrocytes in monolayer and mass culture systems. Methods: Conditioned medium was obtained from WJSCs at fourth passage. Isolated chondrocytes were plated at density of 1×106 for both monolayer and high density culture. Then cells in both groups were divided into control (received medium) and experiment group treated with WJ-CM for 3 and 6 days. Samples were prepared to evaluate gene expression profile of collagen II, aggrecan, cartilage oligomeric matrix protein (COMP) and sox-9 using real-time RT-PCR. Results: After 3 days, Chondrocytes treated with WJSCs-CM expressed significantly higher level of genes compared to the control group in both culture systems. After 6 days, the expression of genes in monolayer cultivated chondrocytes was decreased but that of the mass culture were up-regulated significantly. Conclusion: WJ-SCs-CM can increase the expression of cartilage-specific genes and can be introduced as a promoting factor for cartilage regeneration.

Cellular ageing mechanisms in osteoarthritis

Age is the strongest independent risk factor for the development of osteoarthritis (OA) and for many years this was assumed to be due to repetitive microtrauma of the joint surface over time, the so-called 'wear and tear' arthritis. As our understanding of OA pathogenesis has become more refined, it has changed our appreciation of the role of ageing on disease. Cartilage breakdown in disease is not a passive process but one involving induction and activation of specific matrix-degrading enzymes; chondrocytes are exquisitely sensitive to changes in the mechanical, inflammatory and metabolic environment of the joint; cartilage is continuously adapting to these changes by altering its matrix. Ageing influences all of these processes. In this review, we will discuss how ageing affects tissue structure, joint use and the cellular metabolism. We describe what is known about pathways implicated in ageing in other model systems and discuss the potential value of targeting these pathways in OA.

A novel rat model of hip pain by intra-articular injection of nerve growth factor-characteristics of sensory innervation and inflammatory arthritis

OBJECTIVES

To determine the direct effects of intra-articular injection of nerve growth factor (NGF) into normal rat hips and the time course of pain-related mediator appearance.

METHODS

Using 36 numbers of 8-week-old male Sprague-Dawley rats, 30 μl of 1% Fluoro-Gold solution (FG) (Sham-operated group; n = 12), 30 μl of 1% FG with 50 μg/ml NGF (NGF50 group; n = 12), and 30 μl of 1% FG with 100 μg/ml NGF (NGF100 group; n = 12) were injected into the left hip joints. Neurons in the dorsal root ganglion (DRG) labeled with FG, and FG and calcitonin gene-related peptide-immunoreactivity (CGRP-IR) were counted. The synovia in the left hip joint was examined histologically.

RESULTS

The NGF50 and NGF100 groups showed evidence of synovitis without cartilage degeneration compared with the Sham-operated group. At 7 days, the proportions of CGRP-IR FG-labeled to total FG-labeled neurons were 12%, 18%, and 36% in the Sham-operated, NGF50, and NGF100 groups, respectively. At 14 days, the proportions were 13%, 22%, and 35% in the Sham-operated, NGF50, and NGF100 groups, respectively. At 7 and 14 days, the NGF50 and NGF100 groups showed a significantly higher proportion of CGRP-IR FG-labeled neurons than the Sham-operated group.

CONCLUSIONS

Intra-articular administration of NGF into the hip joint produces a novel rat model for hip pain.

Genome-wide association and functional studies identify a role for IGFBP3 in hip osteoarthritis

OBJECTIVES

To identify genetic associations with hip osteoarthritis (HOA), we performed a meta-analysis of genome-wide association studies (GWAS) of HOA.

METHODS

The GWAS meta-analysis included approximately 2.5 million imputed HapMap single nucleotide polymorphisms (SNPs). HOA cases and controls defined radiographically and by total hip replacement were selected from the Osteoporotic Fractures in Men (MrOS) Study and the Study of Osteoporotic Fractures (SOF) (654 cases and 4697 controls, combined). Replication of genome-wide significant SNP associations (p ≤5×10(-8)) was examined in five studies (3243 cases and 6891 controls, combined). Functional studies were performed using in vitro models of chondrogenesis and osteogenesis.

RESULTS

The A allele of rs788748, located 65 kb upstream of the IGFBP3 gene, was associated with lower HOA odds at the genome-wide significance level in the discovery stage (OR 0.71, p=2×10(-8)). The association replicated in five studies (OR 0.92, p=0.020), but the joint analysis of discovery and replication results was not genome-wide significant (p=1×10(-6)). In separate study populations, the rs788748 A allele was also associated with lower circulating IGFBP3 protein levels (p=4×10(-13)), suggesting that this SNP or a variant in linkage disequilibrium could be an IGFBP3 regulatory variant. Results from functional studies were consistent with association results. Chondrocyte hypertrophy, a deleterious event in OA pathogenesis, was largely prevented upon IGFBP3 knockdown in chondrocytes. Furthermore, IGFBP3 overexpression induced cartilage catabolism and osteogenic differentiation.

CONCLUSIONS

Results from GWAS and functional studies provided suggestive links between IGFBP3 and HOA.

Signaling pathways in cartilage repair

In adult healthy cartilage, chondrocytes are in a quiescent phase characterized by a fine balance between anabolic and catabolic activities. In ageing, degenerative joint diseases and traumatic injuries of cartilage, a loss of homeostatic conditions and an up-regulation of catabolic pathways occur. Since cartilage differentiation and maintenance of homeostasis are finely tuned by a complex network of signaling molecules and biophysical factors, shedding light on these mechanisms appears to be extremely relevant for both the identification of pathogenic key factors, as specific therapeutic targets, and the development of biological approaches for cartilage regeneration. This review will focus on the main signaling pathways that can activate cellular and molecular processes, regulating the functional behavior of cartilage in both physiological and pathological conditions. These networks may be relevant in the crosstalk among joint compartments and increased knowledge in this field may lead to the development of more effective strategies for inducing cartilage repair.

A biological therapy to osteoarthritis treatment using platelet-rich plasma

INTRODUCTION

Osteoarthritis (OA) is a degenerative disease affecting the synovial joint. It is caused by cells exposure to non-physiological stimuli, either mechanical or biochemical, and the loss of bone-cartilage homeostasis. Some of these changes, however, may be reversed by the use of single or combined growth factors, suggesting that the treatment of OA could be addressed using a pool of growth factors.

AREAS COVERED

This review addresses current molecular and biological knowledge and implicates the recapitulation of some developmental processes during endochondral ossification in OA aetiology and pathogenesis. Platelets act as carriers of endogenous morphogens that may modulate cell fate and therefore affect joint tissues structure and function. We shed light on the platelet-rich plasma effects on biological level that might drive the osteoarthritic joint's improvement both in structure and function.

EXPERT OPINION

We present the therapeutic potential of plasma rich in growth factors (PRGF-Endoret), an endogenous biological therapy that might modulate the gene expression of cells such as chondrocytes, synoviocytes, macrophages, and mesenchymal stem cells, and thereby influence an anabolic microenvironment of synovial joint which is conducive to maintaining the homeostatic state of the joint's tissues, and hence reduce pain and improve the joint motion.

Rehabilitation and return-to-sports activity after debridement and bone marrow stimulation of osteochondral talar defects

An osteochondral defect (OD) is a lesion involving the articular cartilage and the underlying subchondral bone. ODs of the talus can severely impact on the quality of life of patients, who are usually young and athletic. The primary treatment for ODs that are too small for fixation, consists of arthroscopic debridement and bone marrow stimulation. This article delineates levels of activity, determines times for return to activity and reviews the factors that affect rehabilitation after arthroscopic debridement and bone marrow stimulation of a talar OD. Articles for review were obtained from a search of the MEDLINE database up to January 2012 using the search headings 'osteochondral defects', 'bone marrow stimulation', 'sports/activity', 'rehabilitation', various other related factors and 'talus'. English-, Dutch- and German-language studies were evaluated.The review revealed that there is no consensus in the existing literature about rehabilitation times or return-to-sports activity times, after treatment with bone marrow stimulation of ODs in the talus. Furthermore, scant research has been conducted on these issues. The literature also showed that potential factors that aid rehabilitation could include youth, lower body mass index, smaller OD size, mobilization and treatment with growth factors, platelet-rich plasma, biphosphonates, hyaluronic acid and pulse electromagnetic fields. However, most studies have been conducted in vitro or on animals. We propose a scheme, whereby return-to-sports activity is divided into four phases of increasing intensity: walking, jogging, return to non-contact sports (running without swerving) and return to contact sports (running with swerving and collision). We also recommend that research, conducted on actual sportsmen, of recovery times after treatment of talar ODs is warranted.

Functional relationship between high mobility group A1 (HMGA1) protein and insulin-like growth factor-binding protein 3 (IGFBP-3) in human chondrocytes

Introduction

Insulin-like growth factor I (IGF-I) regulates articular cartilage homeostasis. During osteoarthritis (OA), the anabolic responses of chondrocytes to IGF-I are likely to be prevented by the enhanced production of IGF-binding proteins (IGFBPs), especially IGFBP-3. The aim of this study is to evaluate whether the architectural transcription factor high mobility group A1 (HMGA1) influences IGFBP-3 overexpression in vitro, in cultured chondrocytic cell lines, and ex vivo, in human osteoarthritic cartilage compared to healthy human cartilage controls.

Methods

Quantitative real-time reverse transcription-PCR (qRT-PCR) was performed to assess the relative transcript levels of HMGA1 and IGFBP-3 in vitro, in the human chondrocytic cell lines T/C-28a4 and C-28/I2. An electrophoretic mobility shift assay (EMSA), chromatin immunoprecipitation (ChIP) and transient transfection assays were performed to investigate the HMGA1-IGFBP-3 gene interaction. Samples of articular cartilage were harvested from osteoarthritic patients and controls and analyzed by qRT-PCR for HMGA1 and IGFBP-3 mRNA levels.

Results

A parallelism between HMGA1 protein levels and IGFBP-3 gene expression has been observed in T/C-28a4 and C-28/I2 cells. The interaction of HMGA1 with the IGFBP-3 gene promoter has been demonstrated by EMSA and ChIP. In transient transfections, IGFBP-3 promoter activity increased in cells overexpressing HMGA1 and decreased in cells pretreated with siRNA detected against HMGA1. IGFBP-3 mRNA expression was higher in cartilage from patients with OA, where the increased expression of IGFBP-3 closely paralleled the increased expression of HMGA1 mRNA.

Conclusions

Our observations indicate that increased HMGA1 expression in human chondrocytes is associated with increased expression of IGFBP-3. It is tempting to speculate that, through the regulation of IGFBP3 expression, HMGA1 may act as a pathogenetic factor for OA.

Benefits of recombinant adeno-associated virus (rAAV)-mediated insulinlike growth factor I (IGF-I) overexpression for the long-term reconstruction of human osteoarthritic cartilage by modulation of the IGF-I axis

Administration of therapeutic genes to human osteoarthritic (OA) cartilage is a potential approach to generate effective, durable treatments against this slow, progressive disorder. Here, we tested the ability of recombinant adeno-associated virus (rAAV)-mediated overexpression of human insulinlike growth factor (hIGF)-I to reproduce an original surface in human OA cartilage in light of the pleiotropic activities of the factor. We examined the proliferative, survival and anabolic effects of the rAAV-hIGF-I treatment in primary human normal and OA chondrocytes in vitro and in explant cultures in situ compared with control (reporter) vector delivery. Efficient, prolonged IGF-I secretion via rAAV stimulated the biological activities of OA chondrocytes in all the systems evaluated over extended periods of time, especially in situ, where it allowed for the long-term reconstruction of OA cartilage (at least for 90 d). Remarkably, production of high, stable amounts of IGF-I in OA cartilage using rAAV advantageously modulated the expression of central effectors of the IGF-I axis by downregulating IGF-I inhibitors (IGF binding protein [IGFBP]-3 and IGFBP4) while up-regulating key potentiators (IGFBP5, the IGF-I receptor and downstream mitogen-activated protein kinase/extracellular signal-regulated kinase 1/2 [MAPK/ERK-1/2] and phosphatidylinisitol-3/Akt [PI3K/Akt] signal transduction pathways), probably explaining the enhanced responsiveness of OA cartilage to IGF-I treatment. These findings show the benefits of directly providing an IGF-I sequence to articular cartilage via rAAV for the future treatment of human osteoarthritis.

Localization of vascular endothelial growth factor during the early stages of osteochondral regeneration using a bioabsorbable synthetic polymer scaffold

Vascular endothelial growth factor (VEGF) plays a critical role in chondrogenic differentiation in the growth plate of the epiphysis. This function is necessary for chondrocyte survival in cartilage development. We investigated the localization of VEGF in the osteochondral regeneration process using a bioabsorbable polymer scaffold. Osteochondral defects (5 mm in diameter and 5 mm in depth) were made on the femoral condyle of forty-eight skeletally mature female Japanese white rabbits. In total, twenty-four defects were filled with poly(DL-lactide-co-glycolide) scaffolds and the others were left untreated. The regeneration process was investigated macroscopically, histologically, immunohistochemically, and by gene expression analysis. In the early stages of osteochondral regeneration, bone ingrowth was observed in the deep zone of the scaffold with continuous VEGF expression; cartilage regeneration was observed in the superficial zone of the scaffold with decreased VEGF expression. In contrast, when the defect was left untreated, VEGF localization was observed throughout the entire defect area, and cartilage regeneration at the articular surface was delayed. We conclude that decrease in localization of VEGF at the articular surface in the postoperative early stage is closely related to the progression of cartilage regeneration in osteochondral defects.

The role of growth factors in cartilage repair

BACKGROUND

Full-thickness chondral defects and early osteoarthritis continue to present major challenges for the patient and the orthopaedic surgeon as a result of the limited healing potential of articular cartilage. The use of bioactive growth factors is under consideration as a potential therapy to enhance healing of chondral injuries and modify the arthritic disease process.

QUESTIONS/PURPOSES

We reviewed the role of growth factors in articular cartilage repair and identified specific growth factors and combinations of growth factors that have the capacity to improve cartilage regeneration. Additionally, we discuss the potential use of platelet-rich plasma, autologous-conditioned serum, and bone marrow concentrate preparations as methods of combined growth factor delivery.

METHODS

A PubMed search was performed using key words cartilage or chondrocyte alone and in combination with growth factor. The search was open for original manuscripts and review papers and open for all dates. From these searches we selected manuscripts investigating the effects of growth factors on extracellular matrix synthesis and excluded those investigating molecular mechanisms of action.

RESULTS

By modulating the local microenvironment, the anabolic and anticatabolic effects of a variety of growth factors have demonstrated potential in both in vitro and animal studies of cartilage injury and repair. Members of the transforming growth factor-β superfamily, fibroblast growth factor family, insulin-like growth factor-I, and platelet-derived growth factor have all been investigated as possible treatment augments in the management of chondral injuries and early arthritis.

CONCLUSIONS

The application of growth factors in the treatment of local cartilage defects as well as osteoarthritis appears promising; however, further research is needed at both the basic science and clinical levels before routine application.

Binding and release characteristics of insulin-like growth factor-1 from a collagen-glycosaminoglycan scaffold

Tissue engineering is a promising technique for cartilage repair, but to optimize novel scaffolds before clinical trials, it is necessary to determine their characteristics for binding and release of growth factors. Toward this goal, a novel, porous collagen-glycosaminoglycan scaffold was loaded with a range of concentrations of insulin-like growth factor-1 (IGF-1) to evaluate its potential as a controlled delivery device. The kinetics of IGF-1 adsorption and release from the scaffold was demonstrated using radiolabeled IGF-1. Adsorption was rapid, and was approximately proportional to the loading concentration. Ionic bonding contributed to this interaction. IGF-1 release was studied over 14 days to compare the release profiles from different loading groups. Two distinct phases occurred: first, a burst release of up to 44% was noted within the first 24 h; then, a slow, sustained release (13%-16%) was observed from day 1 to 14. When the burst release was subtracted, the relative percentage of remaining IGF-1 released was similar for all loading groups and broadly followed t(½) kinetics until approximately day 6. Scaffold cross-linking using dehydrothermal treatment did not affect IGF-1 adsorption or release. Bioactivity of released IGF-1 was confirmed by seeding scaffolds (preadsorbed with unlabeled IGF-1) with human osteoarthritic chondrocytes and demonstrating increased proteoglycan production in vitro.