Temporal expression of the chondrogenic and angiogenic growth factor CYR61 during fracture repair

A GCaMP reporter mouse with chondrocyte specific expression of a green fluorescent calcium indicator

One of the major processes occurring during the healing of a fractured long bone is chondrogenesis, leading to the formation of the soft callus, which subsequently undergoes endochondral ossification and ultimately bridges the fracture site. Thus, understanding the molecular mechanisms of chondrogenesis can enhance our knowledge of the fracture repair process. One such molecular process is calciun (Ca++) signaling, which is known to play a critical role in the development and regeneration of multiple tissues, including bone, in response to external stimuli. Despite the existence of various mouse models for studying Ca++ signaling, none of them were designed to specifically examine the skeletal system or the various musculoskeletal cell types. As such, we generated a genetically engineered mouse model that is specific to cartilage (crossed with Col2a1 Cre mice) to study chondrocytes. Herein, we report on the characterization of this transgenic mouse line using conditional expression of GCaMP6f, a Ca++-indicator protein. Specifically, this mouse line exhibits increased GCaMP6f fluorescence following Ca++ binding in chondrocytes. Using this model, we show real-time Ca++ signaling in embryos, newborn and adult mice, as well as in fracture calluses. Further, robust expression of GCaMP6f in chondrocytes can be easily detected in embryos, neonates, adults, and fracture callus tissue sections. Finally, we also report on Ca++ signaling pathway gene expression, as well as real-time Ca++ transient measurements in fracture callus chondrocytes. Taken together, these mice provide a new experimental tool to study chondrocyte-specific Ca++ signaling during skeletal development and regeneration, as well as various in vitro perturbations.

Activation of Wnt signaling in human fracture callus and nonunion tissues

The Wnt signaling pathway is a key molecular process during fracture repair. Although much of what we now know about the role of this pathway in bone is derived from in vitro and animal studies, the same cannot be said about humans. As such, we hypothesized that Wnt signaling will also be a key process in humans during physiological fracture healing as well as in the development of a nonunion (hypertrophic and oligotrophic). We further hypothesized that the expression of Wnt-signaling pathway genes/proteins would exhibit a differential expression pattern between physiological fracture callus and the pathological nonunion tissues. We tested these two hypotheses by examining the mRNA levels of key Wnt-signaling related genes: ligands (WNT4, WNT10a), receptors (FZD4, LRP5, LRP6), inhibitors (DKK1, SOST) and modulators (CTNNB1 and PORCN). RNA sequencing from calluses as well as from the two nonunion tissue types, revealed that all of these genes were expressed at about the same level in these three tissue types. Further, spatial expression experiments identified the cells responsible of producing these proteins. Robust expression was detected in osteoblasts for the majority of these genes except SOST which displayed low expression, but in contrast, was mostly detected in osteocytes. Many of these genes were also expressed by callus chondrocytes as well. Taken together, these results confirm that Wnt signaling is indeed active during both human physiological fracture healing as well as in pathological nonunions.

Cyr61 delivery promotes angiogenesis during bone fracture repair

Compromised vascular supply and insufficient neovascularization impede bone repair, increasing risk of non-union. Cyr61, Cysteine-rich angiogenic inducer of 61kD (also known as CCN1), is a matricellular growth factor that is regulated by mechanical cues during fracture repair. Here, we map the distribution of endogenous Cyr61 during bone repair and evaluate the effects of recombinant Cyr61 delivery on vascularized bone regeneration. In vitro, Cyr61 treatment did not alter chondrogenesis or osteogenic gene expression, but significantly enhanced angiogenesis. In a mouse femoral fracture model, Cyr61 delivery did not alter cartilage or bone formation, but accelerated neovascularization during fracture repair. Early initiation of ambulatory mechanical loading disrupted Cyr61-induced neovascularization. Together, these data indicate that Cyr61 delivery can enhance angiogenesis during bone repair, particularly for fractures with stable fixation, and may have therapeutic potential for fractures with limited blood vessel supply.

The Role of Osteocytes in Pre-metastatic Niche Formation

PURPOSE OF REVIEW

The formation of a pre-metastatic niche (PMN), in which primary cancer cells prime the distant site to be favorable to their engraftment and survival, may help explain the strong osteotropism observed in multiple cancers, such as breast and prostate. PMN formation, which includes extracellular matrix remodeling, increased angiogenesis and vascular permeability, enhanced bone marrow-derived cell recruitment and immune suppression, has mostly been described in soft tissues. In this review, we summarize current literature of PMN formation in bone. We also present evidence of a potential role for osteocytes to be the primary mediators of PMN development.

RECENT FINDINGS

Osteocytes regulate the bone microenvironment in myriad ways beyond canonical bone tissue remodeling, including changes that contribute to PMN formation. Perilacunar tissue remodeling, which has been observed in both bone and non-bone metastatic cancers, is a potential mechanism by which osteocyte-cancer cell signaling stimulates changes to the bone microenvironment. Osteocytes also protect against endothelial permeability, including that induced by cancer cells, in a loading-mediated process. Finally, osteocytes are potent regulators of cells within the bone marrow, including progenitors and immune cells, and might be involved in this aspect of PMN formation. Osteocytes should be examined for their role in PMN formation.

The regulation and functions of the matricellular CCN proteins induced by shear stress

Shear stress is a frictional drag generated by the flow of fluid, such as blood or interstitial fluid, and plays a critical role in regulating cellular gene expression and functional phenotype. The matricellular CCN family proteins are dynamically regulated by shear stress of different flow patterns, and their expression significantly alters the microenvironment of cells. Secreted CCN proteins mainly bind to several cell surface integrin receptors to mediate their diverse functions in regulating cell survival, function, and behavior. Gene-knockout studies indicate major functions of CCN proteins in the cardiovascular and skeletal systems, the two primary systems in which CCN expressions are regulated by shear stress. In the cardiovascular system, the endothelium is directly exposed to vascular shear stress. Unidirectional laminar blood flow generates laminar shear stress, which promotes a mature endothelial phenotype and upregulates anti-inflammatory CCN3 expression. In contrast, disturbed flow generates oscillatory shear stress, which induces endothelial dysfunction through the induction of CCN1 and CCN2. Shear-induced CCN1 binds to integrin α6β1 and promotes superoxide production, NF-κB activation, and inflammatory gene expression in endothelial cells. Although the interaction between shear stress and CCN4-6 is not clear, CCN 4 exhibits a proinflammatory property and CCN5 inhibits vascular cell growth and migration. The crucial roles of CCN proteins in cardiovascular development, homeostasis, and disease are evident but not fully understood. In the skeletal system, mechanical loading on bone generates shear stress from interstitial fluid in the lacuna-canalicular system and promotes osteoblast differentiation and bone formation. CCN1 and CCN2 are induced and potentially mediate fluid shear stress mechanosensing in osteocytes. However, the exact roles of interstitial shear stress-induced CCN1 and CCN2 in bone are still not clear. In contrast to other CCN family proteins, CCN3 inhibits osteoblast differentiation, although its regulation by interstitial shear stress in osteocytes has not been reported. The induction of CCN proteins by shear stress in bone and their functions remain largely unknown and merit further investigation. This review discusses the expression and functions of CCN proteins regulated by shear stress in physiological conditions, diseases, and cell culture models. The roles between CCN family proteins can be compensatory or counteractive in tissue remodeling and homeostasis.

Focused Low-Intensity Pulsed Ultrasound (FLIPUS) Mitigates Apoptosis of MLO-Y4 Osteocyte-like Cells

Long cytoplasmic processes of osteocytes orchestrate bone activity by integration of biochemical and mechanical signals and regulate load-induced bone adaptation. Low-Intensity Pulsed Ultrasound (LIPUS) is a clinically used technique for fracture healing that delivers mechanical impulses to the damaged bone tissue in a non-invasive and non-ionizing manner. The mechanism of action of LIPUS is still controversially discussed in the scientific community. In this study, the effect of focused LIPUS (FLIPUS) on the survival of starved MLO-Y4 osteocytes was investigated in vitro. Osteocytes stimulated for 10 min with FLIPUS exhibited extended dendrites, which formed frequent connections to neighboring cells and spanned longer distances. The sonicated cells displayed thick actin bundles and experienced increase in expression of connexin 43 (Cx43) proteins, especially on their dendrites, and E11 glycoprotein, which is responsible for the elongation of cellular cytoplasmic processes. After stimulation, expression of cell growth and survival genes as well as genes related to cell-cell communication was augmented. In addition, cell viability was improved after the sonication, and a decrease in ATP release in the medium was observed. In summary, FLIPUS mitigated apoptosis of starved osteocytes, which is likely related to the formation of the extensive dendritic network that ensured cell survival.

Identification of the miRNAome in human fracture callus and nonunion tissues

Background

Nonunions remain a challenging post-traumatic complication that often leads to a financial and health burden that affects the patient's quality of life. Despite a wealth of knowledge about fracture repair, especially gene and more recently miRNA expression, much remains unknown about the molecular differences between normal physiological repair (callus tissue) and a nonunion. To probe this lack of knowledge, we embarked on a study that sought to identify and compare the human miRNAome of normal bone to that present in a normal fracture callus and those from two different classic nonunion types, hypertrophic and oligotrophic.

Methods

Normal bone and callus tissue samples were harvested during revision surgery from patients with physiological fracture repair and nonunions (hypertrophic and oligotrophic) and analyzed using histology. Also, miRNAs were isolated and screened using microarrays followed by bioinformatic analyses, including, differential expression, pathways and biological processes, as well as elucidation of target genes.

Results

Out of 30,424 mature miRNAs (from 203 organisms) screened via microarrays, 635 (∼2.1%) miRNAs were found to be upregulated and 855 (∼2.8%) downregulated in the fracture callus and nonunion tissues as compared to intact bone. As our tissue samples were derived from humans, we focused on the human miRNAs and out of the 4223 human miRNAs, 86 miRNAs (∼2.0%) were upregulated and 51 (∼1.2%) were downregulated. Although there were similarities between the three experimental samples, we also found specific miRNAs that were unique to individual samples. We further identified the predicted target genes from these differentially expressed miRNAs as well as the relevant biological processes, including specific signaling pathways that are activated in all three experimental samples.

Conclusion

Collectively, this is the first comprehensive study reporting on the miRNAome of intact bone as compared to fracture callus and nonunion tissues. Further, we identify specific miRNAs involved in normal physiological fracture repair as well as those of nonunions.

The translational potential of this article

The data generated from this study further increase our molecular understanding of the roles of miRNAs during normal and aberrant fracture repair and this knowledge can be used in the future in the development of miRNA-based therapeutics for skeletal regeneration.

Cellular communication network factor 1 interlinks autophagy and ERK signaling to promote osteogenesis of periodontal ligament stem cells

OBJECTIVES

To investigate the effects of cellular communication network factor 1 (CCN1), a critical matricellular protein, on alveolar bone regeneration, and to elucidate the underlying molecular mechanism.

BACKGROUND

In the process of orthodontic tooth movement, bone deposition on the tension side of human periodontal ligament stem cells (hPDLSCs) ensured high efficiency and long-term stability of the treatment. The matricellular protein CCN1 is responsive to mechanical stimulation, exhibiting important tasks in bone homoeostasis. However, the role and mechanism of CCN1 on alveolar bone remodeling of hPDLSCs remains unclear.

METHODS

The expression and distribution of CCN1 in rat periodontal ligament were detected by immunofluorescence staining and immunohistochemical staining. ELISA verified the secretion of CCN1 triggered by stretch loading. To examine the mineralization ability of hPDLSCs induced by CCN1, Western blotting, qRT-PCR, ARS, and ALP staining were performed. CCK-8 and cell migration assay were performed to detect the cell proliferation rate and the wound healing. PI3K/Akt, MAPK, and autophagy activation were examined via Western blotting and immunofluorescence.

RESULTS

Mechanical stimuli induced the release of CCN1 into extracellular environment by hPDLSCs. Knockdown of CCN1 attenuated the osteogenesis of hPDLSCs while rhCCN1 enhanced the expression of Runx2, Col 1, ALPL, and promoted the mineralization nodule formation. CCN1 activated PI3K/Akt and ERK signaling, and blockage of PI3K/Akt signaling reversed the accelerated cell migration triggered by CCN1. The enhanced osteogenesis induced by CCN1 was abolished by ERK signaling inhibitor PD98059 or autophagy inhibitor 3-MA. Further investigation demonstrated PD98059 abrogated the activation of autophagy.

CONCLUSION

This study demonstrated that CCN1 promotes osteogenesis in hPDLSCs via autophagy and MAPK/ERK pathway.

CCN proteins in the musculoskeletal system: current understanding and challenges in physiology and pathology

The acronym for the CCN family was recently revised to represent “cellular communication network”. These six, small, cysteine-enriched and evolutionarily conserved proteins are secreted matricellular proteins, that convey and modulate intercellular communication by interacting with structural proteins, signalling factors and cell surface receptors. Their role in the development and physiology of musculoskeletal system, constituted by connective tissues where cells are interspersed in the cellular matrix, has been broadly studied. Previous research has highlighted a crucial balance of CCN proteins in mesenchymal stem cell commitment and a pivotal role for CCN1, CCN2 and their alter ego CCN3 in chondrogenesis and osteogenesis; CCN4 plays a minor role and the role of CCN5 and CCN6 is still unclear. CCN proteins also participate in osteoclastogenesis and myogenesis. In adult life, CCN proteins serve as mechanosensory proteins in the musculoskeletal system providing a steady response to environmental stimuli and participating in fracture healing. Substantial evidence also supports the involvement of CCN proteins in inflammatory pathologies, such as osteoarthritis and rheumatoid arthritis, as well as in cancers affecting the musculoskeletal system and bone metastasis. These matricellular proteins indeed show involvement in inflammation and cancer, thus representing intriguing therapeutic targets. This review discusses the current understanding of CCN proteins in the musculoskeletal system as well as the controversies and challenges associated with their multiple and complex roles, and it aims to link the dispersed knowledge in an effort to stimulate and guide readers to an area that the writers consider to have significant impact and relevant potentialities.

Biomechanical, histological, and radiological effects of different phosphodiesterase inhibitors on femoral fracture healing in rats

PURPOSE

To investigate the biomechanical, histological, and radiological effects of sildenafil and pentoxifylline on femoral fracture healing in rats.

METHODS

Forty-eight Sprague-Dawley rats were divided into three groups equally according to the pharmacological agents to be investigated. Femoral shaft fractures were formed in the left side. Group 1 (control group), group 2, and group 3 were administered with saline, sildenafil, and pentoxifylline during the fracture healing process, respectively. Eight rats from each group were euthanized on days 15 and 30. X-ray images of the rats were taken after euthanasia for radiographical examination. Femur samples were subjected to histopathological and biomechanical (three-point bending) examinations.

RESULTS

Radiologically, no difference between the Goldberg scores of the groups was found for day 15 ( p > 0.05), while higher Goldberg scores were obtained from group 2 than that of group 1 ( p > 0.05) and group 3 ( p < 0.05) for day 30. In the biomechanical analysis, higher mean breaking forces were found both for day 15 and day 30 from group 2 than those obtained from group 1 (for day 15 p > 0.05 and day 30 p > 0.05) and group 3 (for day 15 p < 0.05 and day 30 p < 0.01). Higher mean absorbed energy values were obtained from group 2 than those obtained from group 1 (for day 15 p > 0.05 and day 30 p < 0.05) and group 3 (for day 15 p < 0.01 and day 30 p < 0.01). A significant difference was not found between the histological scores of all groups ( p > 0.05) for day 15, while the histological score of group 1 on day 30 was found to be significantly lower than that of sildenafil and pentoxifylline groups ( p < 0.05).

CONCLUSION

Sildenafil had a positive effect on fracture healing, while pentoxifylline did not provide consistent positive effect.

How much do we know about the role of osteocytes in different phases of fracture healing? A systematic review

Background

Although emerging studies have provided evidence that osteocytes are actively involved in fracture healing, there is a general lack of a detailed understanding of the mechanistic pathway, cellular events and expression of markers at different phases of healing.

Methods

This systematic review describes the role of osteocytes in fracture healing from early to late phase. Literature search was performed in PubMed and Embase. Original animal and clinical studies with available English full-text were included. Information was retrieved from the selected studies.

Results

A total of 23 articles were selected in this systematic review. Most of the studies investigated changes of various genes and proteins expression patterns related to osteocytes. Several studies have described a constant expression of osteocyte-specific marker genes throughout the fracture healing cascade followed by decline phase with the progress of healing, denoting the important physiological role of the osteocyte and the osteocyte lacuno-canalicular network in fracture healing. The reports of various markers suggested that osteocytes could trigger coordinated bone healing responses from cell death and expression of proinflammatory markers cyclooxygenase-2 and interleukin 6 at early phase of fracture healing. This is followed by the expression of growth factors bone morphogenetic protein-2 and cysteine-rich angiogenic inducer 61 that matched with the neo-angiogenesis, chondrogenesis and callus formation during the intermediate phase. Tightly controlled regulation of osteocyte-specific markers E11/Podoplanin (E11), dentin matrix protein 1 and sclerostin modulate and promote osteogenesis, mineralisation and remodelling across different phases of fracture healing. Stabilised fixation was associated with the finding of higher number of osteocytes with little detectable bone morphogenetic proteins expressions in osteocytes. Sclerostin-antibody treatment was found to result in improvement in bone mass, bone strength and mineralisation.

Conclusion

To further illustrate the function of osteocytes, additional longitudinal studies with appropriate clinically relevant model to study osteoporotic fractures are crucial. Future investigations on the morphological changes of osteocyte lacuno-canalicular network during healing, osteocyte-mediated signalling molecules in the transforming growth factor-beta-Smad3 pathway, perilacunar remodelling, type of fixation and putative biomarkers to monitor fracture healing are highly desirable to bridge the current gaps of knowledge.The translational potential of this article: This systematic review provides an up-to-date chronological overview and highlights the osteocyte-regulated events at gene, protein, cellular and tissue levels throughout the fracture healing cascade, with the hope of informing and developing potential new therapeutic strategies that could improve the timing and quality of fracture healing in the future.

Stretch-induced Expression of CYR61 Increases the Secretion of IL-8 in A549 Cells via the NF-κβ/lκβ Pathway

Mechanical ventilation (MV) with large tidal volumes can increase lung alveolar permeability and initiate inflammatory responses, resulting in ventilator-induced lung injury (VILI). The mechanisms of the injurious effects of MV and the genetic susceptibility remain unclear. VILI-related genes such as cysteine-rich angiogenic inducer 61 (Cyr61) have been demonstrated to play a detrimental role in the aggressive ventilation strategies. In the present study, we investigated the involvement of Cyr61 in the VILI and the underlying mechanism. A549 cells were exposed to cyclic stretch of varying durations and then the mRNA and protein levels of Cyr61 were measured by real-time PCR and Western blotting, respectively. Additionally, after exposure of A549 cells to cyclic stretch for 5 min to 1 h,the expression levels of nuclear factor kappaB (NF-κB) and IL-8 were detected by E L I S A and Western blotting. Thereafter, Cyr61 expression was depressed in A549 cells with the siRNA pGenesil1.1-Cyr61-3 before the cyclic stretch, and IL-8 secretion and the activation of NF-κB pathways were probed by ELISA and Western blotting, respectively. Moreover, A NF-κB inhibitor (PDTC) and an activator (TNF) were used before mechanical stretch. Realtime PCR and ELISA were performed to detect the mRNA and protein of IL-8, respectively. The results showed that the mechanical cyclic stretch led to increased Cyr61 expression at mRNA and protein levels in A549 cells. Additionally, cyclic stretch also mobilized NF-κB from the cytoplasm to the nucleus and increased IL-8 secretion in A549 cells. The inhibition of Cyr61 blocked the NF-κB activation and IL-8 secretion in response to cyclic stretch. Inhibition of NF-κB attenuated the mRNA and protein expression of IL-8 in A549 cells transfected with Cyr61 siRNA. It was suggested that Cyr61/NF-κB signaling pathway mediates the upregulation of IL-8 in response to cyclic stretch in A594 cells. These findings support the hypothesis that Cyr61 plays a critical role in acute lung inflammation triggered by mechanical strain.

The matricellular protein CCN1 in tissue injury repair

The expression of Ccn1 (Cyr61) is essential for cardiovascular development during embryogenesis, whereas in adulthood it is associated with inflammation, wound healing, injury repair, and related pathologies including fibrosis and cancer. Recent studies have found that CCN1 plays a critical role in promoting wound healing and tissue repair. Mechanistically, CCN1 functions through direct interaction with specific integrin receptors expressed in various cell types in the wound tissue microenvironment to coordinate diverse cellular functions for repair. Here we briefly summarize the current knowledge on the functions of CCN1 in tissue injury repair and discuss pertinent unanswered questions.

Hypoxia and Redox Signaling on Extracellular Matrix Remodeling: From Mechanisms to Pathological Implications

SIGNIFICANCE

The extracellular matrix (ECM) is an essential modulator of cell behavior that influences tissue organization. It has a strong relevance in homeostasis and translational implications for human disease. In addition to ECM structural proteins, matricellular proteins are important regulators of the ECM that are involved in a myriad of different pathologies. Recent Advances: Biochemical studies, animal models, and study of human diseases have contributed to the knowledge of molecular mechanisms involved in remodeling of the ECM, both in homeostasis and disease. Some of them might help in the development of new therapeutic strategies. This review aims to review what is known about some of the most studied matricellular proteins and their regulation by hypoxia and redox signaling, as well as the pathological implications of such regulation.

CRITICAL ISSUES

Matricellular proteins have complex regulatory functions and are modulated by hypoxia and redox signaling through diverse mechanisms, in some cases with controversial effects that can be cell or tissue specific and context dependent. Therefore, a better understanding of these regulatory processes would be of great benefit and will open new avenues of considerable therapeutic potential.

FUTURE DIRECTIONS

Characterizing the specific molecular mechanisms that modulate matricellular proteins in pathological processes that involve hypoxia and redox signaling warrants additional consideration to harness the potential therapeutic value of these regulatory proteins. Antioxid. Redox Signal. 27, 802-822.

Therapeutic Effects of Sildenafil on Experimental Mandibular Fractures

OBJECTIVES

No previous studies have examined the effect of sildenafil on fracture healing. This study was designed to investigate the effect of sildenafil on the fracture healing process.

METHODS

Thirty-six female Sprague-Dawley rats (3-month-old) were used in this study. Animals were randomly divided into 2 groups based on treatment duration (1 week versus 4 weeks) and each group was then divided further into 2 subgroups, control (C) and study (S) groups. Group C (C1, C2) was treated daily with saline solution and group S (S1, S2) was treated daily with 10 mg/kg of sildenafil. Histologic, histomorphometric, radiological, and immunohistochemical analyses were performed at 1 week and 4 weeks after a fracture.

RESULTS

The sildenafil group showed a significant increase in fracture healing scores (P = 0.00). The authors observed a transition from fibrous callus to cartilage tissue and immature bone tissue in group S1; and an increased transition of cartilage tissue to completely immature bone tissue in group S2, both of which were administered sildenafil. The strong expression of bone morphogenetic protein 2 and col-1 was observed in the fibrous matrix and osteoblasts within areas of new bone formation, especially in group S1. This group also showed an increase in bone density measurements at 1 week that was statistically significant (P = 0.03).

CONCLUSIONS

Sildenafil accelerates fracture healing and can be used as a supporting factor in the improvement of fracture healing under various conditions.

CYR61-An angiogenic biomarker to early predict the impaired healing in diaphyseal tibial fractures

Background

Angiogenesis is a prerequisite for fracture repair, whereas insufficient blood supply is likely to result in impaired healing. In the present study, we aimed to determine the correlation of simple tibial fracture healing outcome with serial estimation of CYR61 expressions in the early phase of healing.

Methods

In total, 107 adult fractured patients and 97 healthy controls were analysed. Peripheral blood samples were taken from controls (at once) and fractured patients at 4^th, 7^th, 10^th, 15^th, 20^th and 28^th days of post-fracture follow-ups to quantify the CYR61 mRNA and protein expression by qRT-PCR and Western blotting assay, respectively. Clinic-radiological follow-up was done at 6^th, 10^th, 16^th, 20^th, and 24^th weeks of post-fracture follow-ups using RUST scores to analyse the fracture healing progression and their final outcomes.

Results

By considering controls as Group I (n = 97), as per the clinico-radiological status at 24^th week, fracture patients were divided into two groups: Group II (normal healing, n = 91) and Group III (impaired healing, n = 16). Both CYR61 mRNA and protein expressions were lower (baseline) in Group I than in Groups II and III; however, a significant difference was observed only with the Group II. In both groups, expressions of CYR61 mRNA as well as protein gradually upregulated from the baseline to a peak and then declined. Both, the CYR61 mRNA as well as protein expressions were significantly higher at all follow-ups in Group II than in Group III. Mean RUST scores between Group II and Group III showed a significant statistical difference at each follow-up. Significant correlation was found between the CYR61 expressions and the RUST score (fracture healing progression).

Conclusion

We conclude that CYR61 expression provides an early prediction of the healing outcomes of simple diaphyseal tibial fractures.

The translational potential of this article

Such an approach would benefit not only the patients' wellbeing but also the entire health care system in terms of the cost implications associated with long lasting treatment interventions and hospitalisation. However, the authors recommend further multicentric study with a large sample size to increase the validity, reliability, and generalisability of our observation and inferences.

Adipose-derived stem cells in cartilage regeneration: current perspectives

Repair of cartilage injuries represents a musculoskeletal medicine criticism because of the poor ability to self-renewal of adult cartilage. Therefore, research focuses on developing new regenerative strategies combining chondrocytes or stem cells, scaffolds and growth factors. Because of the low proliferation capability of explanted chondrocytes, new chondrogenesis models, employing human adipose-derived stem cells (ASCs), have been investigated. ASCs are readily accessible with no morbidity and display the capability to differentiate into several cell lineages, including the spontaneous chondrogenic differentiation when entrapped in collagen gel scaffolds. Recent studies also defined some biomolecular mechanisms involved in ASC chondrogenesis in vitro, and their regenerative properties in bioengineered scaffolds and in the presence of growth factors. However, further investigations are required to validate these exciting preclinical results for the application of bioenginereed ASCs in the clinical practice.

Identification of the microRNA transcriptome during the early phases of mammalian fracture repair

Fracture repair is a complex process that involves multiple biological processes requiring spatiotemporal expression of thousands of genes. The molecular regulation of this process is not completely understood. MicroRNAs (miRNAs) regulate gene expression by promoting mRNA degradation or blocking translation. To identify miRNAs expressed during fracture repair, we generated murine bone fractures and isolated miRNA-enriched RNA from intact and post-fracture day (PFD) 1, 3, 5, 7, 11, and 14 femurs. RNA samples were individually hybridized to mouse miRNA microarrays. Results indicated that 959 (51%) miRNAs were absent while 922 (49%) displayed expression in at least one sample. Of the 922 miRNAs, 306 (33.2%) and 374 (40.6%) were up- and down-regulated, respectively, in the calluses in comparison to intact bone. Additionally, 20 (2.2%) miRNAs displayed combined up- and down-regulated expression within the time course and the remaining 222 (24%) miRNAs did not exhibit any changes between calluses and intact bone. Quantitative-PCR validated the expression of several miRNAs. Further, we identified 2048 and 4782 target genes that were unique to the up- and down-regulated miRNAs, respectively. Gene ontology and pathway enrichment analyses indicated relevant biological processes. These data provide the first complete analysis of the miRNA transcriptome during the early phases of fracture repair.

Characterization of the healing process in non-stabilized and stabilized femur fractures in mice

BACKGROUND

Although a variety of suitable fracture models for mice exist, in many studies bone healing was still analyzed without fracture stabilization. Because there is little information whether the healing of non-stabilized fractures differs from that of stabilized fractures, we herein studied the healing process of non-stabilized compared to stabilized femur fractures.

MATERIALS AND METHODS

Twenty-one CD-1 mice were stabilized after midshaft fracture of the femur with an intramedullary screw allowing micromovements and endochondral healing. In another 22 mice the femur fractures were left unstabilized. Bone healing was studied by radiological, biomechanical, histomorphometric and protein expression analyses.

RESULTS

Non-stabilized femur fractures revealed a significantly lower biomechanical stiffness compared to stabilized fractures. During the early phase of fracture healing non-stabilized fractures demonstrated a significantly lower amount of osseous tissue and a higher amount of cartilage tissue. During the late phase of fracture healing both non-stabilized and stabilized fractures showed almost 100 % osseous callus tissue. However, in stabilized fractures remodeling was almost completed with lamellar bone while non-stabilized fractures still showed large callus with great amounts of woven bone, indicating a delay in bone remodeling. Of interest, western blot analyses of callus tissue demonstrated in non-stabilized fractures a significantly reduced expression of vascular endothelial growth factor and a slightly lowered expression of bone morphogenetic protein-2 and collagen-10.

CONCLUSION

Non-stabilized femur fractures in mice show a marked delay in bone healing compared to stabilized fractures. Therefore, non-stabilized fracture models may not be used to analyze the mechanisms of normal bone healing.

Study of Cysteine-Rich Protein 61 Genetic Polymorphism in Predisposition to Fracture Nonunion: A Case Control

Background. Many factors are responsible for this impaired healing, especially in long bones, but a possible genetic predisposition for the development of this complication remains unknown till now. In the present study, we aim to examine the CYR61 gene polymorphism in fracture nonunion patients and the correlation with clinical findings. Materials and Methods. We performed SNP analysis of the CYR61 gene in 250 fracture nonunion patients and 250 healthy subjects were genotyped in this hospital-based case control study, and 56 cases were further evaluated for mRNA expression of CYR61 by real-time quantitative reverse-transcription PCR. Results. CYR61 gene TT, TG, and GG genotype frequencies of total fracture nonunion cases were 41.6%, 49.2%, and 9.20% and 54.4%, 39.2%, and 6.40% in healthy controls. Heterozygous TG genotype was found statistically significant in fracture nonunion cases compared with that in controls, whereas homozygous mutant GG genotype was not found significant. Moreover, we found that TG + GG genotypes were significantly different in serum expression of CYR61 mRNA when compared with cases (TT genotypes). Conclusions. Our result signifies that genotype of CYR61 affects the mRNA expression and acts as a risk factor that could synergistically increase the susceptibility of a patient to develop fracture nonunion.

Emerging role of CCN family proteins in tumorigenesis and cancer metastasis (Review)

The CCN family of proteins comprises the members CCN1, CCN2, CCN3, CCN4, CCN5 and CCN6. They share four evolutionarily conserved functional domains, and usually interact with various cytokines to elicit different biological functions including cell proliferation, adhesion, invasion, migration, embryonic development, angiogenesis, wound healing, fibrosis and inflammation through a variety of signalling pathways. In the past two decades, emerging functions for the CCN proteins (CCNs) have been identified in various types of cancer. Perturbed expression of CCNs has been observed in a variety of malignancies. The aberrant expression of certain CCNs is associated with disease progression and poor prognosis. Insight into the detailed mechanisms involved in CCN-mediated regulation may be useful in understanding their roles and functions in tumorigenesis and cancer metastasis. In this review, we briefly introduced the functions of CCNs, especially in cancer.

Expression profiles of human CCN genes in patients with osteoarthritis or rheumatoid arthritis

OBJECTIVE

Osteoarthritis (OA) and rheumatoid arthritis (RA) are widespread disabling joint disorders that are considered to be polygenic in nature. This study investigated the spatial expression patterns of all six known human CCN genes using end-stage OA and RA joint samples.

DESIGN

We performed in situ hybridization and histological analysis to investigate the spatial expression patterns of human CCN genes using joint tissues obtained during total knee and hip joint replacement procedures on patients with advanced OA or RA. Normal joint tissues taken while performing bipolar hip replacement surgeries were used as controls.

RESULTS

All CCN genes were expressed at higher levels in OA and RA synovial samples as compared with normal controls. Whereas CCN3 and CCN6 were undetectable in control, OA, and RA cartilage, CCN1, CCN2, CCN4, and CCN5 were expressed to a greater extent in OA and RA knee cartilage.

CONCLUSIONS

Our results indicate an involvement of several CCN genes in the pathophysiology of OA and RA.

Comparison of healing process in open osteotomy model and open fracture model: Delayed healing of osteotomies after intramedullary screw fixation

Murine osteotomy and fracture models have become the standard to study molecular mechanisms of bone healing. Because there is little information whether the healing of osteotomies differs from that of fractures, we herein studied in mice the healing of femur osteotomies compared to femur fractures. Twenty CD-1 mice underwent a standardized open femur osteotomy. Another 20 mice received a standardized open femur fracture. Stabilization was performed by an intramedullary screw. Bone healing was studied by micro-CT, biomechanical, histomorphometric and protein expression analyses. Osteotomies revealed a significantly lower biomechanical stiffness compared to fractures. Micro-CT showed a reduced bone/tissue volume within the callus of the osteotomies. Histomorphometric analyses demonstrated also a significantly lower amount of osseous tissue in the callus of osteotomies (26% and 88% after 2 and 5 weeks) compared to fractures (50% and 100%). This was associated with a delayed remodeling. Western blot analyses demonstrated comparable BMP-2 and BMP-4 expression, but higher levels of collagen-2, CYR61 and VEGF after osteotomy. Therefore, we conclude that open femur osteotomies in mice show a markedly delayed healing when stabilized less rigidly with an intramedullary screw. This should be considered when choosing a model for studying the mechanisms of bone healing in mice.

A new concept of endometriosis and adenomyosis: tissue injury and repair (TIAR)

Pelvic endometriosis, deeply infiltrating endometriosis and uterine adenomyosis share a common pathophysiology and may be integrated into the physiological mechanism and new nosological concept of 'tissue injury and repair' (TIAR) and may, in this context, just represent the extreme of a basically physiological, estrogen-related mechanism that is pathologically exaggerated in an extremely estrogen-sensitive reproductive organ. The acronym TIAR describes a fundamental and apparently ubiquitous biological system that becomes operative in mesenchymal tissues following tissue injury and, upon activation, results in the local production of estradiol. Endometriosis and adenomyosis are caused by trauma. In the spontaneously developing disease, chronic uterine peristaltic activity or phases of hyperperistalsis induce, at the endometrial-myometrial interface near the fundo-cornual raphe, microtraumatisations, with activation of the TIAR mechanism. With ongoing traumatisations, such sites of inflammation might accumulate and the increasingly produced estrogens interfere in a paracrine fashion with ovarian control over uterine peristaltic activity, resulting in permanent hyperperistalsis and a self-perpetuation of the disease process. Overt autotraumatisation of the uterus with dislocation of fragments of basal endometrium into the peritoneal cavity and infiltration of basal endometrium into the depth of the myometrial wall ensues. In most cases of endometriosis/adenomyosis a causal event early in the reproductive period of life must be postulated, rapidly leading to archimetral hyperestrogenism and uterine hyperperistalsis. In late premenopausal adenomyosis such an event might not have occurred. However, as indicated by the high prevalence of the disease, it appears to be unavoidable that, with time, chronic normoperistalsis throughout the reproductive period of life accumulates to the same extent of microtraumatisation. With activation of the TIAR mechanism followed by chronic inflammation and infiltrative growth, endometriosis/adenomyosis of the younger woman and premenopausal adenomyosis share in principal the same pathophysiology.

Serum Cyr61 is associated with clinical disease activity and inflammation in patients with systemic lupus erythematosus

Our previous studies have shown that secreted extracellular matrix-associated protein Cysteine rich angiogenic inducer 61 (Cyr61), a novel proinflammatory factor, is involved in the pathogenesis of rheumatoid arthritis (RA). However, whether Cyr61 has any effect in systemic lupus erythematosus (SLE) remains unknown. This study aims to assess the level of serum Cyr61 and to investigate the association of serum Cyr61 and clinical disease activity in SLE. We found the level of serum Cyr61 in patients with SLE was significantly higher than healthy controls (P < 0.001), and Cyr61 was high expressed in renal tubule of lupus nephritis compared to control. The sensitivity of Cyr61 in diagnosis of SLE was 47.3%. In receiver operating characteristic (ROC) curve analysis, the area under the curve (AUC) was 0.830, with a 95% confidence interval (CI) from 0.776 to 0.885. Cyr61 was present in 60.0%, 54.5%, and 41.5% of anti-double stranded DNA (dsDNA), anti-antinuclear antibodies (ANA), and anti-Sm negative SLE patients, respectively. Serum Cyr61 levels were significantly higher in high systemic lupus erythematosus disease activity index (SLEDAI) group than that in low SLEDAI group (P = 0.003). Correlation analyzes showed a significant negative correlation between serum Cyr61 and complements (C3) (P = 0.015), C4 (P = 0.04). Moreover, increased Cyr61 level in SLE was associated with serum level of TNF-α, interleukin 6 (IL-6), and IL-17. In conclusion, serum Cyr61 was increased in patients with SLE which was associated with clinical disease activity and inflammation in SLE, suggesting Cyr61 may be a novel potential auxiliary marker for the diagnosis of SLE.

The matricellular protein CCN1 regulates TNF-α induced vascular endothelial cell apoptosis

Due to the epidemic obesity and associated diabetes, the incidence of atherosclerosis is increasing worldwide. Atherosclerosis is a chronic inflammatory disease characterized by the hardening and narrowing of arteries with plaques that consist of inflammatory cells, dead endothelial cells, lipids, and often hyper proliferated vascular smooth muscle cells. During the development of atherosclerosis, vascular endothelial cell (EC) apoptosis induced by the adipokine tumor necrosis factor alpha (TNF-α), is an early event in the plaque formation. However, TNF-α alone is not sufficient to induce apoptosis of endothelial cells. Recent studies suggested that the matricellular protein CCN family member 1 (CCN1) involves in endothelial cell dysfunction besides its well-known angiogenic function during tissue repair by promoting vascular smooth muscle cells proliferation and migration. Herein, we explored the possibility and mechanism of CCN1 in TNF-α induced endothelial cells apoptosis. Both mRNA and protein levels of CCN1 are found up-regulated in endothelial cells after TNF-α treatment. In addition, overexpression of CCN1 promoted endothelial cell apoptosis in the presence of TNF-α. Furthermore, CCN1 directly up-regulated the expression of TNF-α-target genes, and this up-regulation required the activation of P53 and NF-κB both in vivo and in vitro. Taken together, CNN1 regulates TNF-α induced endothelial cells apoptosis that may underlie poor response to TNF-α therapy and hence may be a better therapeutic target for preventing vascular dysfunction in obesity.

Local manganese chloride treatment accelerates fracture healing in a rat model

This study investigated the effects of local delivery of manganese chloride (MnCl2), an insulin-mimetic compound, upon fracture healing using a rat femoral fracture model. Mechanical testing, histomorphometry, and immunohistochemistry were performed to assess early and late parameters of fracture healing. At 4 weeks post-fracture, maximum torque to failure was 70% higher (P<0.05) and maximum torsional rigidity increased 133% (P<0.05) in animals treated with 0.125 mg/kg MnCl2 compared to saline controls. Histological analysis of the fracture callus revealed percent new mineralized tissue was 17% higher (P<0.05) at day 10. Immunohistochemical analysis of the 0.125 mg/kg MnCl2 treated group, compared to saline controls, showed a 379% increase in the density of VEGF-C+ cells. In addition, compared to saline controls, the 0.125 mg/kg MnCl2 treated group showed a 233% and 150% increase in blood vessel density in the subperiosteal region at day 10 post-fracture as assessed by detection of PECAM and smooth muscle α actin, respectively. The results suggest that local MnCl2 treatment accelerates fracture healing by increasing mechanical parameters via a potential mechanism of amplified early angiogenesis leading to increased osteogenesis. Therefore, local administration of MnCl2 is a potential therapeutic adjunct for fracture healing.

The anti-fibrotic effects of CCN1/CYR61 in primary portal myofibroblasts are mediated through induction of reactive oxygen species resulting in cellular senescence, apoptosis and attenuated TGF-β signaling

Cysteine-rich protein 61 (CCN1/CYR61) is a CCN (CYR61, CTGF (connective tissue growth factor), and NOV (Nephroblastoma overexpressed gene)) family matricellular protein comprising six secreted CCN proteins in mammals. CCN1/CYR61 expression is associated with inflammation and injury repair. Recent studies show that CCN1/CYR61 limits fibrosis in models of cutaneous wound healing by inducing cellular senescence in myofibroblasts of the granulation tissue which thereby transforms into an extracellular matrix-degrading phenotype. We here investigate CCN1/CYR61 expression in primary profibrogenic liver cells (i.e., hepatic stellate cells and periportal myofibroblasts) and found an increase of CCN1/CYR61 expression during early activation of hepatic stellate cells that declines in fully transdifferentiated myofibroblasts. By contrast, CCN1/CYR61 levels found in primary parenchymal liver cells (i.e., hepatocytes) were relatively low compared to the levels exhibited in hepatic stellate cells and portal myofibroblasts. In models of ongoing liver fibrogenesis, elevated levels of CCN1/CYR61 were particularly noticed during early periods of insult, while expression declined during prolonged phases of fibrogenesis. We generated an adenovirus type 5 encoding CCN1/CYR61 (i.e., Ad5-CMV-CCN1/CYR61) and overexpressed CCN1/CYR61 in primary portal myofibroblasts. Interestingly, overexpressed CCN1/CYR61 significantly inhibited production of collagen type I at both mRNA and protein levels as evidenced by quantitative real-time polymerase chain reaction, Western blot and immunocytochemistry. CCN1/CYR61 further induces production of reactive oxygen species (ROS) leading to dose-dependent cellular senescence and apoptosis. Additionally, we demonstrate that CCN1/CYR61 attenuates TGF-β signaling by scavenging TGF-β thereby mitigating in vivo liver fibrogenesis in a bile duct ligation model.

CONCLUSION

In line with dermal fibrosis and scar formation, CCN1/CYR61 is involved in liver injury repair and tissue remodeling. CCN1/CYR61 gene transfer into extracellular matrix-producing liver cells is therefore potentially beneficial in liver fibrotic therapy.

NSAID therapy effects on healing of bone, tendon, and the enthesis

Nonsteroidal anti-inflammatory drugs (NSAIDs) are commonly used for the treatment of skeletal injuries. The ability of NSAIDs to reduce pain and inflammation is well-established. However, the effects of NSAID therapy on healing of skeletal injuries is less defined. NSAIDs inhibit cyclooxygenase activity to reduce synthesis of prostaglandins, which are proinflammatory, lipid-signaling molecules. Inhibition of cyclooxygenase activity can impact many physiological processes. The effects of NSAID therapy on healing of bone, tendon, and the tendon-to-bone junction (enthesis) have been studied in animal and cell culture models, but human studies are few. Use of different NSAIDs with different pharmacological properties, differences in dosing regimens, and differences in study models and outcome measures have complicated comparisons between studies. In this review, we summarize the mechanisms by which bone, tendon, and enthesis healing occurs, and describe the effects of NSAID therapy on each of these processes. Determining the impact of NSAID therapy on healing of skeletal tissues will enable clinicians to appropriately manage the patient's condition and improve healing outcomes.

Roles of Wnt/β-catenin signalling pathway in the bony repair of injured growth plate cartilage in young rats

Growth plate cartilage is responsible for longitudinal growth of the long bone in children, and its injury is often repaired by bony tissue, which can cause limb length discrepancy and/or bone angulation deformities. Whilst earlier studies with a rat growth plate injury repair model have identified inflammatory, mesenchymal infiltration, osteogenesis and remodeling responses, the molecular mechanisms involved in the bony repair remain unknown. Since our recent microarray study has strongly suggested involvement of Wnt-β-catenin signalling pathway in regulating the growth plate repair and the pathway is known to play a crucial role in the osteogenic differentiation of mesenchymal progenitor cells, the current study investigated the potential roles of Wnt-β-catenin signalling pathway in the bony repair of injured tibial growth plate in rats. Immunohistochemical analysis of the growth plate injury site revealed β-catenin immunopositive cells within the growth plate injury site. Treatment of the injured rats with the β-catenin inhibitor ICG-001 (oral gavage at 200mg/kg/day for 8days, commenced at day 2 post injury) enhanced COL2A1 gene expression (by qRT-PCR) and increased proportion of cartilage tissue (by histological analysis), but decreased level of osterix expression and amount of bone tissue, at the injury site by day 10 post-injury (n=8, P<0.01 compared to vehicle controls). Consistently, in vitro studies with bone marrow stromal cells from normal rats showed that β-catenin inhibitor ICG-001 dose dependently inhibited expression of Wnt target genes Cyclin D1 and survivin (P<0.01). At 25mM, ICG-001 suppressed osteogenic (by CFU-f-ALP assay) but enhanced chondrogenic (by pellet culture) differentiation. These results suggest that Wnt/β-catenin signalling pathway is involved in regulating growth plate injury repair by promoting osteoblastogenesis, and that intervention of this signalling could represent a potential approach in enhancing cartilage repair after growth plate injury.

Biological characteristics and effect of human umbilical cord mesenchymal stem cells (hUC-MSCs) grafting with blood plasma on bone regeneration in rats

We evaluated the biological characteristics/effect of human umbilical cord-derived mesenchymal stem cells (hUC-MSCs) grafting with blood plasma on bone regeneration in rat tibia nonunion. SD rats (142) were randomly divided into four groups: fracture group (positive control); nonunion group (negative control); hUC-MSCs grafting with blood plasma group; and hUC-MSCs grafting with saline group. Rats were administered tetracycline (30 mg/kg) and calcein blue (5 mg/kg) 8 days before killing. The animals were killed under deep anesthesia at 4 and 8 weeks post fracture for radiological evaluation and histological/immunohistological studies. The hUC-MSCs grafting with blood plasma group was similar to fracture group: the fracture line blurred in 4 weeks and disappeared in 8 weeks postoperatively. Histological/immunohistological studies showed that hUC-MSCs were of low immunogenicity which merged in rat bone tissue, differentiated into osteogenic lineages, and completed the healing of nonunion. After stem cell transplantation, regardless of whether plasma or saline was used, new multi-center bone formation was observed; fracture site density was better in stem cell grafting with blood plasma group. We, therefore, concluded that the biological characteristics of hUC-MSCs-treated nonunion were different from the standard fracture healing process, and the proliferative and localization capacity of hUC-MSCs might benefit from the use of blood plasma.

Pantoprazole, a proton pump inhibitor, delays fracture healing in mice

Proton pump inhibitors (PPIs), which are widely used in the treatment of dyspeptic problems, have been shown to reduce osteoclast activity. There is no information, however, on whether PPIs affect fracture healing. We therefore studied the effect of the PPI pantoprazole on callus formation and biomechanics during fracture repair. Bone healing was analyzed in a murine fracture model using radiological, biomechanical, histomorphometric, and protein biochemical analyses at 2 and 5 weeks after fracture. Twenty-one mice received 100 mg/kg body weight pantoprazole i.p. daily. Controls (n = 21) received equivalent amounts of vehicle. In pantoprazole-treated animals biomechanical analysis revealed a significantly reduced bending stiffness at 5 weeks after fracture compared to controls. This was associated with a significantly lower amount of bony tissue within the callus and higher amounts of cartilaginous and fibrous tissue. Western blot analysis showed reduced expression of the bone formation markers bone morphogenetic protein (BMP)-2, BMP-4, and cysteine-rich protein (CYR61). In addition, significantly lower expression of proliferating cell nuclear antigen indicated reduced cell proliferation after pantoprazole treatment. Of interest, the reduced expression of bone formation markers was associated with a significantly diminished expression of RANKL, indicating osteoclast inhibition. Pantoprazole delays fracture healing by affecting both bone formation and bone remodeling.

Periosteum: a highly underrated tool in dentistry

The ultimate goal of any dental treatment is the regeneration of lost tissues and alveolar bone. Under the appropriate culture conditions, periosteal cells secrete extracellular matrix and form a membranous structure. The periosteum can be easily harvested from the patient's own oral cavity, where the resulting donor site wound is invisible. Owing to the above reasons, the periosteum offers a rich cell source for bone tissue engineering; hence, the regenerative potential of periosteum is immense. Although the use of periosteum as a regenerative tool has been extensive in general medical field, the regenerative potential of periosteum is highly underestimated in dentistry; therefore, the present paper reviews the current literature related to the regenerative potential of periosteum and gives an insight to the future use of periosteum in dentistry.

Connective tissue growth factor is required for normal follicle development and ovulation

Connective tissue growth factor (CTGF) is a cysteine-rich protein the synthesis and secretion of which are hypothesized to be selectively regulated by activins and other members of the TGF-β superfamily. To investigate the in vivo roles of CTGF in female reproduction, we generated Ctgf ovarian and uterine conditional knockout (cKO) mice. Ctgf cKO mice exhibit severe subfertility and multiple reproductive defects including disrupted follicle development, decreased ovulation rates, increased numbers of corpus luteum, and smaller but functionally normal uterine horns. Steroidogenesis is disrupted in the Ctgf cKO mice, leading to increased levels of serum progesterone. We show that disrupted follicle development is accompanied by a significant increase in granulosa cell apoptosis. Moreover, despite normal cumulus expansion, Ctgf cKO mice exhibit a significant decrease in oocytes ovulated, likely due to impaired ovulatory process. During analyses of mRNA expression, we discovered that Ctgf cKO granulosa cells show gene expression changes similar to our previously reported granulosa cell-specific knockouts of activin and Smad4, the common TGF-β family intracellular signaling protein. We also discovered a significant down-regulation of Adamts1, a progesterone-regulated gene that is critical for the remodeling of extracellular matrix surrounding granulosa cells of preovulatory follicles. These findings demonstrate that CTGF is a downstream mediator in TGF-β and progesterone signaling cascades and is necessary for normal follicle development and ovulation.

CCN1/CYR61: the very model of a modern matricellular protein

CCN1 (CYR61) is a dynamically expressed, multifunctional matricellular protein that plays essential roles in cardiovascular development during embryogenesis, and regulates inflammation, wound healing and fibrogenesis in the adult. Aberrant CCN1 expression is associated with myriad pathologies, including various cancers and diseases associated with chronic inflammation. CCN1 promotes diverse and sometimes opposing cellular responses, which can be ascribed, as least in part, to disparate activities mediated through its direct binding to distinct integrins in different cell types and contexts. Accordingly, CCN1 promotes cell proliferation, survival and angiogenesis by binding to integrin α(v)β(3), and induces apoptosis and senescence through integrin α(6)β(1) and heparan sulfate proteoglycans. The ability of CCN1 to trigger the accumulation of a robust and sustained level of reactive oxygen species underlies some of its unique activities as a matrix cell-adhesion molecule. Emerging studies suggest that CCN1 might be useful as a biomarker or therapeutic target in certain diseases.

Sildenafil accelerates fracture healing in mice

Sildenafil, a cyclic guanosine monophosphate (cGMP)-dependent phospodiesterase-5 inhibitor, has been shown to be a potent stimulator of angiogenesis through upregulation of pro-angiogenic factors and control of cGMP concentration. Herein, we determined whether sildenafil also influences angiogenic growth factor expression and bone formation during the process of fracture healing. Bone healing was studied in a murine closed femur fracture model using radiological, biomechanical, histomorphometric, and protein biochemical analysis at 2 and 5 weeks after fracture. Thirty mice received 5 mg/kg body weight sildenafil p.o. daily. Controls (n  = 30) received equivalent amounts of vehicle. After 2 weeks of fracture healing sildenafil significantly increased osseous fracture bridging, as determined radiologically and histologically. This resulted in an increased biomechanical stiffness compared to controls. A smaller callus area with a slightly reduced amount of cartilaginous tissue indicated an accelerated healing process. After 5 weeks the differences were found blunted, demonstrating successful healing in both groups. Western blot analysis showed a significantly higher expression of the pro-angiogenic and osteogenic cysteine-rich protein (CYR) 61, confirming the increase of bone formation. We show for the first time that sildenafil treatment accelerates fracture healing by enhancing bone formation, most probably by a CYR61-associated pathway.

CCN1 promotes the differentiation of endothelial progenitor cells and reendothelialization in the early phase after vascular injury

Endothelial progenitor cells (EPCs) contribute to the process of reendothelialization and prevent neointimal formation after vascular injury. The present study was designed to investigate whether the cysteine-rich 61 (CYR61, CCN1), an important matricellular component of local vascular microenvironment, has effect on EPCs differentiation and reendothelialization in response to vascular injury in rat. Following balloon injury, CCN1 was rapidly induced and dynamically changed at vascular lesions. Overexpression of CCN1 by adenovirus (Ad-CCN1) accelerated reendothelialization and inhibited neointimal formation in the early phase (day 14) after vascular injury (p < 0.05), while no effect was shown on day 21. Ad-CCN1 treatment increased the adhering EPCs on the surface of injured vessels on day 7, and the ratio of GFP- and vWF-positive area to the total luminal length on day 14 was 2.3-fold higher in the Ad-CCN1-EPC-transplanted group than in controls. Consistent with these findings, CCN1-stimulated EPC differentiation in vitro and 20 genes were found differentially expressed during CCN1-induced EPC differentiation, including Id1, Vegf-b, Vegf-c, Kdr, Igf-1, Ereg, Tgf, Mdk, Ptn, Timp2, etc. Among them, negative transcriptional regulator Id1 was associated with CCN1 effect on EPC differentiation. Our data suggest that CCN1, from the microenvironment of injured vessels, enhances reendothelialization via a direct action on EPC differentiation, revealing a possible new mechanism underlying the process of vascular repair.

Matricellular protein CCN1 activates a proinflammatory genetic program in murine macrophages

CCN1 (CYR61) is a matricellular protein that is highly expressed at sites of inflammation and wound repair. In these contexts, CCN1 can modify the activities of specific cytokines, enabling TNF-alpha to be cytotoxic without blocking NF-kappaB activity and enhancing the apoptotic activity of Fas ligand and TRAIL. In this paper, we show that CCN1 supports the adhesion of macrophages through integrin alpha(M)beta(2) and syndecan-4, activates NFkappaB-mediated transcription, and induces a proinflammatory genetic program characteristic of classically activated M1 macrophages that participates in Th1 responses. The effects of CCN1 include upregulation of cytokines (TNF-alpha, IL-1alpha, IL-1beta, IL-6, and IL-12b), chemokines (MIP-1alpha; MCP-3; growth-related oncogenes 1 and 2; and inflammatory protein 10), and regulators of oxidative stress and complement (inducible NO synthase and C3) and downregulation of specific receptors (TLR4 and IL-10Rbeta) and anti-inflammatory factors (TGF-beta1). CCN1 regulates this genetic program through at least two distinct mechanisms: an immediate-early response resulting from direct activation of NF-kappaB by CCN1, leading to the synthesis of cytokines including TNF-alpha and inflammatory protein 10; and a delayed response resulting from CCN1-induced TNF-alpha, which acts as an autocrine/paracrine mediator to activate the expression of other cytokines including IL-1beta and IL-6. These results identify CCN1 as a novel component of the extracellular matrix that activates proinflammatory genes in macrophages, implicating its role in regulating macrophage function during inflammation.

Pharmacological inhibition of 5-lipoxygenase accelerates and enhances fracture-healing

BACKGROUND

Loss of cyclooxygenase-2 activity is known to impair fracture-healing in animal models and to inhibit heterotopic ossification in humans. Cyclooxygenase-2 is the rate-limiting enzyme involved in the conversion of arachidonic acid into prostaglandins. Arachidonic acid also is a substrate for 5-lipoxygenase, which catalyzes the initial steps in leukotriene synthesis. In contrast to cyclooxygenase-2, genetic ablation of 5-lipoxygenase accelerates and enhances fracture-healing in mice. The goal of this study was to determine if systemic inhibition of 5-lipoxygenase with an orally delivered drug could accelerate fracture-healing.

METHODS

Closed femoral fractures were made in Sprague-Dawley rats. The rats were treated with oral doses of vehicle (ninety-five rats), celecoxib (fifty-nine rats), or AA-861 (a 5-lipoxygenase inhibitor; eighty-nine rats). Fracture-healing was measured with use of radiographs, histomorphometry, and biomechanical testing. Effects of drug treatments on callus cell proliferation and gene expression were determined by incorporation of bromodeoxyuridine and quantitative polymerase chain reactions, respectively.

RESULTS

AA-861 treatment decreased fracture-bridging time, significantly increased early callus cartilage (5.6-fold; p < 0.001) and bone formation (4.2-fold; p = 0.015), and significantly increased callus mechanical properties compared with the vehicle-treated rat fractures. Callus cell proliferation rate was increased by AA-861 treatment, compared with vehicle, at day 2 after fracture (3.68% compared with 2.08%; p < 0.001; 95% confidence interval, -2.81 to -0.039) but was reduced by celecoxib treatment at day 4 after fracture (4.22% compared with 1.84%; p < 0.001; 95% confidence interval, 2.27 to 4.07). At day 10 after fracture, AA-861 and celecoxib treatment increased Type-II collagen mRNA levels (16.0-fold and 6.1-fold, respectively; p < 0.001 for both), but only AA-861 treatment caused an increase in Type-X collagen mRNA (6.3-fold; p < 0.001). AA-861 treatment significantly increased cyclooxygenase-2 (4.0-fold at day 10; p < 0.001) and osteopontin mRNA levels (3.6-fold at day 7; p = 0.024), while decreasing 5-lipoxygenase mRNA levels (5.6-fold at day 4; p < 0.001).

CONCLUSIONS

Systemic inhibition of 5-lipoxygenase with an orally delivered drug significantly accelerated and enhanced fracture-healing in this rat model. Gene expression analysis indicates that cyclooxygenase-2 is necessary for callus chondrocytes to progress into hypertrophy so as to complete endochondral ossification. Conversely, inhibition of 5-lipoxygenase alters the inflammatory response, which enhances callus chondrocyte hypertrophy and accelerates endochondral ossification.

The periosteum as a cellular source for functional tissue engineering

The periosteum, a specialized fibrous tissue composed of fibroblast, osteoblast, and progenitor cells, may be an optimal cell source for tissue engineering based on its accessibility, the ability of periosteal cells to proliferate rapidly both in vivo and in vitro, and the observed differentiation potential of these cells. However, the functional use of periosteum-derived cells as a source for tissue engineering requires an understanding of the ability of such cells to elaborate matrix of different tissues. In this study, we subjected a population of adherent primary periosteum-derived cells to both adipogenic and osteogenic culture conditions. The commitment propensity of periosteal cells was contrasted with that of well-characterized phenotypically pure populations of NIH3T3 fibroblast and MC3T3-E1 osteoblast cell lines. Our results demonstrate that the heterogeneous populations of periosteal cells and NIH3T3 fibroblasts have the ability to express both osteoblast-like and adipocyte-like markers with similar potential. This raises the question of whether fibroblasts within the periosteum may, in fact, have the potential to behave like progenitor cells and play a role in the tissue's multilineage potential or whether there are true stem cells within the periosteum. Further, this study suggests that expanded periosteal cultures may be a source for tissue engineering applications without extensive enrichment or sorting by molecular markers. Thus, this study lays the groundwork for future investigations that will more deeply enumerate the cellular sources and molecular events governing periosteal cell differentiation.

The pathophysiology of endometriosis and adenomyosis: tissue injury and repair

INTRODUCTION

This study presents a unifying concept of the pathophysiology of endometriosis and adenomyosis. In particular, a physiological model is proposed that provides a comprehensive explanation of the local production of estrogen at the level of ectopic endometrial lesions and the endometrium of women affected with the disease.

METHODS

In women suffering from endometriosis and adenomyosis and in normal controls, a critical analysis of uterine morphology and function was performed using immunohistochemistry, MRI, hysterosalpingoscintigraphy, videohysterosonography, molecular biology as well as clinical aspects. The relevant molecular biologic aspects were compared to those of tissue injury and repair (TIAR) mechanisms reported in literature.

RESULTS AND CONCLUSIONS

Circumstantial evidence suggests that endometriosis and adenomyosis are caused by trauma. In the spontaneously developing disease, chronic uterine peristaltic activity or phases of hyperperistalsis induce, at the endometrial-myometrial interface near the fundo-cornual raphe, microtraumatizations with the activation of the mechanism of 'tissue injury and repair' (TIAR). This results in the local production of estrogen. With ongoing peristaltic activity, such sites might increase and the increasingly produced estrogens interfere in a paracrine fashion with the ovarian control over uterine peristaltic activity, resulting in permanent hyperperistalsis and a self-perpetuation of the disease process. Overt auto-traumatization of the uterus with dislocation of fragments of basal endometrium into the peritoneal cavity and infiltration of basal endometrium into the depth of the myometrial wall ensues. In most cases of endometriosis/adenomyosis, a causal event early in the reproductive period of life must be postulated leading rapidly to uterine hyperperistalsis. In late premenopausal adenomyosis, such an event might not have occurred. However, as indicated by the high prevalence of the disease, it appears to be unavoidable that, with time, chronic normoperistalsis throughout the reproductive period of life leads to the same extent of microtraumatization. With the activation of the TIAR mechanism followed by infiltrative growth and chronic inflammation, endometriosis/adenomyosis of the younger woman and premenopausal adenomyosis share in principle the same pathophysiology. In conclusion, endometriosis and adenomyosis result from the physiological mechanism of 'tissue injury and repair' (TIAR) involving local estrogen production in an estrogen-sensitive environment normally controlled by the ovary.

Rac1 signaling regulates CTGF/CCN2 gene expression via TGFbeta/Smad signaling in chondrocytes

OBJECTIVE

Connective tissue growth factor (CTGF) has been implicated in regulation of chondrocyte differentiation at multiple steps and has been implicated in the progression of diseases such as scleroderma and osteoarthritis. However, the pathways mediating the expression of CTGF/CCN2 and related factors in cartilage are not fully understood. We have previously shown that the Rho family of proteins and the actin cytoskeleton regulate both early and late chondrocyte differentiation.

RESULTS

Here we demonstrate that several CTGF/Cyr61/Nov (CCN) family members are differentially affected by either inhibition of actin polymerization (cytochalasin D treatment), promotion of actin polymerization (jasplakinolide treatment), inhibition of RhoA/rho kinase (ROCK) signaling (Y27632 treatment) and Rac1 signaling. We also show that the Smad site in the CTGF/CCN2 promoter is responsive to both Rac1 inhibition and cytochalasin D treatment, suggesting a role of TGFbeta/Smad signaling in mediating the effects of actin dynamics and Rac1.

CONCLUSION

Collectively, these data show that Rac1 and actin pathways control CTGF/CCN2 expression in chondrocytes which might be relevant to both skeletal development and associated diseases such as osteoarthritis.

Characterization of a rat osteotomy model with impaired healing

Background

Delayed union or nonunion are frequent and feared complications in fracture treatment. Animal models of impaired bone healing are rare. Moreover, specific descriptions are limited although understanding of the biological course of pathogenesis of fracture nonunion is essential for therapeutic approaches.

Methods

A rat tibial osteotomy model with subsequent intramedullary stabilization was performed. The healing progress of the osteotomy model was compared to a previously described closed fracture model. Histological analyses, biomechanical testing and radiological screening were undertaken during the observation period of 84 days (d) to verify the status of the healing process. In this context, particular attention was paid to a comparison of bone slices by histological and immunohistological (IHC) methods at early points in time, i.e. at 5 and 10 d post bone defect.

Results

In contrast to the closed fracture technique osteotomy led to delayed union or nonunion until 84 d post intervention. The dimensions of whole reactive callus and the amounts of vessels in defined regions of the callus differed significantly between osteotomized and fractured animals at 10 d post surgery. A lower fraction of newly formed bone and cartilaginous tissue was obvious during this period in osteotomized animals and more inflammatory cells were observed in the callus. Newly formed bone tissue accumulated slowly on the anterior tibial side with both techniques. New formation of reparative cartilage was obviously inhibited on the anterior side, the surgical approach side, in osteotomized animals only.

Conclusion

Tibial osteotomy with intramedullary stabilisation in rats leads to pronounced delayed union and nonunion until 84 d post intervention. The early onset of this delay can already be detected histologically within 10 d post surgery. Moreover, the osteotomy technique is associated with cellular and vascular signs of persistent inflammation within the first 10 d after bone defect and may be a contributory factor to impaired healing. The model would be excellent to test agents to promote fracture healing.

Functions and mechanisms of action of CCN matricellular proteins

Members of the CCN (CYR61/CTGF/NOV) family have emerged as dynamically expressed, extracellular matrix-associated proteins that play critical roles in cardiovascular and skeletal development, injury repair, fibrotic diseases and cancer. The synthesis of CCN proteins is highly inducible by serum growth factors, cytokines, and environmental stresses such as hypoxia, UV exposure, and mechanical stretch. Consisting of six secreted proteins in vertebrate species, CCNs are typically comprised of four conserved cysteine-rich modular domains. They function primarily through direct binding to specific integrin receptors and heparan sulfate proteoglycans, thereby triggering signal transduction events that culminate in the regulation of cell adhesion, migration, proliferation, gene expression, differentiation, and survival. CCN proteins can also modulate the activities of several growth factors and cytokines, including TGF-beta, TNFalpha, VEGF, BMPs, and Wnt proteins, and may thereby regulate a broad array of biological processes. Recent studies have uncovered novel CCN activities unexpected for matricellular proteins, including their ability to induce apoptosis as cell adhesion substrates, to dictate the cytotoxicity of inflammatory cytokines such as TNFalpha, and to promote hematopoietic stem cell self-renewal. As potent regulators of angiogenesis and chondrogenesis, CCNs are essential for successful cardiovascular and skeletal development during embryogenesis. In the adult, the expression of CCN proteins is associated with injury repair and inflammation, and has been proposed as diagnostic or prognostic markers for diabetic nephropathy, hepatic fibrosis, systemic sclerosis, and several types of cancer. Targeting CCN signaling pathways may hold promise as a strategy of rational therapeutic design.

The lipogenic gene spot 14 is activated in bone by disuse yet remains unaffected by a mechanical signal anabolic to the skeleton

There is increasing evidence of the interaction of fat and bone metabolism and the role mechanical signals may have in regulating the adaptation of these tissues. The rat hindlimb suspension model of disuse osteoporosis was used to identify genes differentially expressed relative to normal weight-bearing bones and whether the relative expression of these genes is sensitive to anabolic mechanical stimuli. Ten days of hindlimb suspension suppressed percent labeled surface and bone volume/trabecular volume of the proximal tibia by 46% and 69%, respectively, compared to controls. Differential display polymerase chain reaction (DD-PCR) and Northern blot analysis identified and verified, respectively, that expression of Spot 14 (S14), an important gene in lipogenesis, was upregulated fourfold in tibiae of tail-suspended animals compared to long-term controls. Anabolic mechanical stimulation (45 Hz, 10 min/day at 0.25 g) did not show a statistically significant effect on S14 expression. These results indicate a potential role for lipogenic genes during bone loss caused by disuse, further supporting a link between bone and fat tissue, and, considering the insensitivity of these genes to mechanical signals which promote bone formation in the skeleton, the independence of resorptive and formative processes in bone.

The matricellular protein CYR61 inhibits osteoclastogenesis by a mechanism independent of alphavbeta3 and alphavbeta5

Cysteine-rich protein 61 (CYR61/CCN1) belongs to the family of CCN matricellular proteins. Most of the known effects of CCN proteins appear to be due to binding to extracellular growth factors or integrins, including alpha(v)beta(3) and alpha(v)beta(5). Although CYR61 can stimulate osteoblast differentiation, until now the effect of CYR61 on osteoclasts was unknown. We demonstrate that recombinant human CYR61 inhibits the formation of multinucleated, alpha(v)beta(3)-positive, or tartrate-resistant acid phosphatase-positive human, mouse, and rabbit osteoclasts in vitro. CYR61 markedly reduced the expression of the osteoclast phenotypic markers tartrate-resistant acid phosphatase, matrix metalloproteinase-9, calcitonin receptor, and cathepsin K. However, CYR61 did not affect the formation of multinucleated osteoclasts when added to osteoclast precursors prior to fusion or affect the number or resorptive activity of osteoclasts cultured on dentine discs, indicating that CYR61 affects early osteoclast precursors but not mature osteoclasts. CYR61 did not affect receptor activator of nuclear factor-kappaB (RANK) ligand-induced phosphorylation of p38 or ERK1/2 in human macrophages and did not affect RANK ligand-induced activation of nuclear factor-kappaB, indicating that CYR61 does not appear to inhibit osteoclastogenesis by affecting RANK signaling. Furthermore, a mutant form of CYR61 defective in binding to alpha(v)beta(3) also inhibited osteoclastogenesis, and CYR61 inhibited osteoclastogenesis similarly in cultures of mouse wild-type or beta(5)(-/-) macrophages. Thus, CYR61 does not appear to inhibit osteoclast formation by interacting with alpha(v)beta(3) or alpha(v)beta(5). These observations demonstrate that CYR61 is a hitherto unrecognized inhibitor of osteoclast formation, although the exact mechanism of inhibition remains to be determined. Given that CYR61 also stimulates osteoblasts, CYR61 could represent an important bifunctional local regulator of bone remodeling.

Functional properties and intracellular signaling of CCN1/Cyr61

CCN1/Cyr61 is a member of the protein family that can be promptly induced by growth factors. CCN1/Cyr61 promotes cell proliferation, adhesion, and differentiation. It plays important roles in angiogenesis and extracellular matrix production. In addition, CCN1/Cyr61 has many potential functions in tumorigenesis, development, embryo implantation, as well as formation of endometriotic lesions. Expression of CCN1/Cyr61 is regulated by a variety of agents including cytokines, growth factors, steroid hormones, and some drugs. These inducers regulate the transcription of CCN1/Cyr61 through several signaling transduction pathways. CCN1/Cyr61 is able to interact either with the cell itself or the surrounding cells through an autocrine-paracrine mechanism. It has been reported that CCN1/Cyr61 exerts its functions via interacting with at least five integrins as well as heparan sulfate proteoglycan. By activating Wnt, NF-kappaB, or tyrosine kinase signaling pathways, CCN1/Cyr61 is not only able to control the growth of epithelial cells and fibroblasts, but also induce or suppress apoptosis in a cell type-specific manner.

The extracellular matrix and blood vessel formation: not just a scaffold

The extracellular matrix plays a number of important roles, among them providing structural support and information to cellular structures such as blood vessels imbedded within it. As more complex organisms have evolved, the matrix ability to direct signalling towards the vasculature and remodel in response to signalling from the vasculature has assumed progressively greater importance. This review will focus on the molecules of the extracellular matrix, specifically relating to vessel formation and their ability to signal to the surrounding cells to initiate or terminate processes involved in blood vessel formation.