Recombinant biglycan promotes bone morphogenetic protein-induced osteogenesis

Control of tissue homeostasis by the extracellular matrix: Synthetic heparan sulfate as a promising therapeutic for periodontal health and bone regeneration

Proteoglycans are core proteins associated with carbohydrate/sugar moieties that are highly variable in disaccharide composition, which dictates their function. These carbohydrates are named glycosaminoglycans, and they can be attached to proteoglycans or found free in tissues or on cell surfaces. Glycosaminoglycans such as hyaluronan, chondroitin sulfate, dermatan sulfate, keratan sulfate, and heparin/heparan sulfate have multiple functions including involvement in inflammation, immunity and connective tissue structure, and integrity. Heparan sulfate is a highly sulfated polysaccharide that is abundant in the periodontium including alveolar bone. Recent evidence supports the contention that heparan sulfate is an important player in modulating interactions between damage associated molecular patterns and inflammatory receptors expressed by various cell types. The structure of heparan sulfate is reported to dictate its function, thus, the utilization of a homogenous and structurally defined heparan sulfate polysaccharide for modulation of cell function offers therapeutic potential. Recently, a chemoenzymatic approach was developed to allow production of many structurally defined heparan sulfate carbohydrates. These oligosaccharides have been studied in various pathological inflammatory conditions to better understand their function and their potential application in promoting tissue homeostasis. We have observed that specific size and sulfation patterns can modulate inflammation and promote tissue maintenance including an anabolic effect in alveolar bone. Thus, new evidence provides a strong impetus to explore heparan sulfate as a potential novel therapeutic agent to treat periodontitis, support alveolar bone maintenance, and promote bone formation.

Mitigation of BMP-induced inflammation in craniofacial bone regeneration and improvement of bone parameters by dietary hesperidin

Based on anti-inflammatory and osteogenic properties of hesperidin (HE), we hypothesized its systemic administration could be a cost-effective method of improving BMP-induced bone regeneration. Sprague-Dawley rats were allocated into 4 groups (n = 10/group): a 5-mm critical-sized mandible defect + collagen scaffold or, scaffold + 1 µg of BMP2 with and without dietary HE at 100 mg/kg. HE was administered by oral gavage 4 weeks prior to surgeries until euthanasia at day 7 or 14 post-surgery. The healing tissue within the defect collected at day 7 was subjected to gene expression analysis. Mandibles harvested at day 14 were subjected to microcomputed tomography and histology. HE + BMP2-treated rats had a statistically significant decrease in expression of inflammatory genes compared to BMP2 alone. The high-dose BMP2 alone caused cystic-like regeneration with incomplete defect closure. HE + BMP2 showed virtually complete bone fusion. Collagen fibril birefringence pattern (red color) under polarized light indicated high organization in BMP2-induced newly formed bone (NFB) in HE-supplemented group (p < 0.05). Clear changes in osteocyte lacunae as well as a statistically significant increase in osteoclasts were found around NFB in HE-treated rats. A significant increase in trabecular volume and thickness, and trabecular and cortical density was found in femurs of HE-supplemented rats (p < 0.05). Our findings show, for the first time, that dietary HE has a remarkable modulatory role in the function of locally delivered high-dose BMP2 in bone regeneration possibly via control of inflammation, osteogenesis, changes in osteocyte and osteoclast function and collagen maturation in regenerated and native bone. In conclusion, HE had a significant skeletal bone sparing effect and the ability to provide a more effective BMP-induced craniofacial regeneration.

Biglycan neo-epitope (BGN262), a novel biomarker for screening early changes in equine osteoarthritic subchondral bone

OBJECTIVE

Native biglycan (BGN), which can undergo proteolytic cleavage in pathological conditions, is well known to be involved in bone formation and mineralization. This study aimed to delineate the specific cleavage fragment, a neo-epitope for BGN (BGN²⁶²), in synovial fluid (SF) from young racehorses in training, osteoarthritic (OA) joints with subchondral bone sclerosis (SCBS), and chip fracture joints.

DESIGN

A custom-made inhibition ELISA was developed to quantify BGN²⁶² in SF. Cohort 1: A longitudinal study comprising 10 racehorses undergoing long-term training. Cohort 2: A cross-sectional study comprising joints from horses (N = 69) with different stages of OA and radiographically classified SCBS. Cohort 3: A cross-sectional study comprising horses (N = 9) with chip fractures. Receiver operating characteristic (ROC) curve analysis was performed (healthy joints vs chip joints) to evaluate BGN²⁶² robustness.

RESULTS

Cohort 1: SF BGN²⁶² levels from racehorses showed a statistical increase during the first 6 months of the training period. Cohort 2: BGN²⁶² levels were significantly higher in the SF from severe SCBS joints. Cohort 3: SF BGN²⁶² levels in chip fracture joints showed a significant increase compared to normal joints. The ROC analysis showed an AUC of 0.957 (95% C.I 0.868-1.046), indicating good separation between the groups.

CONCLUSIONS

The data presented show that BGN²⁶² levels increase in SF in correlation with the initiation of training, severity of SCBS, and presence of chip fractures. This suggests that BGN²⁶² is a potential predictor and a novel biomarker for early changes in subchondral bone (SCB), aiming to prevent catastrophic injuries in racehorses.

3D Printed Integrated Bionic Oxygenated Scaffold for Bone Regeneration

The repair of large bone defects remains a challenging problem in bone tissue engineering. Ischemia and hypoxia in the bone defect area make it difficult for seed cells to survive and differentiate, which fail to perform effective tissue regeneration. Current oxygen-producing materials frequently encounter problems such as a rapid degradation rate, insufficient mechanical properties, difficult molding, and cumbersome fabrication. Here, a novel three-dimensional (3D) printed integrated bionic oxygenated scaffold was fabricated with gelatin-CaO₂ microspheres, polycaprolactone (PCL), and nanohydroxyapatite (nHA) using low-temperature molding 3D printing technology. The scaffold had outstanding mechanical properties with bionic hierarchical porous structures. In vitro reports showed that the scaffold exhibited excellent cytocompatibility and could release O₂ sustainably for more than 2 weeks, which significantly enhanced the survival, growth, and osteogenic differentiation of bone marrow mesenchymal stem cells under hypoxia. In vivo experiments revealed that the scaffold facilitated efficient bone repair after it was transplanted into a rabbit calvarial defect model. This result may be due to the scaffolds reducing hypoxia-inducible factor-1α accumulation, improving the expression of osteogenic regulatory transcription factors, and accelerating osteogenesis. In summary, the integrated bionic PCL/nHA/CaO₂ scaffold had excellent capabilities in sustainable O₂ release and bone regeneration, which provided a promising clinical strategy for bone defect repair.

Stability and remineralization of proteoglycan-infused dentin substrate

OBJECTIVE

This study tested the effects of small leucine-rich proteoglycan (SLRP) proteins on phosphoric acid (PA)-treated dentin bonding overtime and the role of such SLRPs in the remineralization potential of demineralized dentin collagen.

METHODS

Coronal dentin sections of human molars were used. SLRPs were either decorin (DCN) or biglycan (BGN) in core or proteoglycan form (with glycosaminoglycans, GAGs). Groups were: No treatment (control), DCN core, DCN + GAGs, BGN core, BGN + GAGs. Samples were etched with PA for 15 s and prior to application of Adper Single Bond Plus and composite buildup an aliquot of the specific SLRPs was applied over dentin. Twenty-four hours or 6 months after the bonding procedure, samples were tested for microtensile bond strength (MTBS). Debonded beams were analyzed by scanning electron microscopy (SEM). For remineralization studies, dentin blocks were fully demineralized, infused with the SLRPs, placed in artificial saliva for 2 weeks, and evaluated by transmission electron microscopy (TEM).

RESULTS

MTBS test presented a mean of 51.4 ± 9.1 MPa in control with no statistically significant difference to DCN core (47.6 ± 8.3) and BGN core (48.3 ± 6.5). The full proteoglycan groups DCN + GAGs (27.4 ± 4.5) and BGN + GAGs (36.4 ± 13.6) showed decreased MTBS compared to control (p < 0.001). At 6 months, control or core-treated samples did not have a statistically significant difference in MTBS. However, SLRPs with GAGs showed statistically significant improvement of bonding (62.5 ± 6.0 for DCN and 52.8 ± 8.1 for BGN, p < 0.001) compared to their baseline values. SEM showed that GAGs seem to favor water retention but overtime help remineralization. TEM of demineralized dentin indicated a larger collagen fibril diameter pattern of samples treated with core proteins compared to control and a smaller diameter with DCN + GAGs in water with evidence of mineralization with DCN + GAGS, BGN core and BGN + GAGs.

SIGNIFICANCE

In conclusion, core proteins seem not to affect dentin adhesion significantly but the presence of GAGs can be detrimental to immediate bonding. However, after ageing of samples, full proteoglycans, particularly DCN, can significantly improve bonding overtime while promoting remineralization which can prove to be clinically beneficial.

Hesperidin Promotes Osteogenesis and Modulates Collagen Matrix Organization and Mineralization In Vitro and In Vivo

This study evaluated the direct effect of a phytochemical, hesperidin, on pre-osteoblast cell function as well as osteogenesis and collagen matrix quality, as there is little known about hesperidin's influence in mineralized tissue formation and regeneration. Hesperidin was added to a culture of MC3T3-E1 cells at various concentrations. Cell proliferation, viability, osteogenic gene expression and deposited collagen matrix analyses were performed. Treatment with hesperidin showed significant upregulation of osteogenic markers, particularly with lower doses. Mature and compact collagen fibrils in hesperidin-treated cultures were observed by picrosirius red staining (PSR), although a thinner matrix layer was present for the higher dose of hesperidin compared to osteogenic media alone. Fourier-transform infrared spectroscopy indicated a better mineral-to-matrix ratio and matrix distribution in cultures exposed to hesperidin and confirmed less collagen deposited with the 100-µM dose of hesperidin. In vivo, hesperidin combined with a suboptimal dose of bone morphogenetic protein 2 (BMP2) (dose unable to promote healing of a rat mandible critical-sized bone defect) in a collagenous scaffold promoted a well-controlled (not ectopic) pattern of bone formation as compared to a large dose of BMP2 (previously defined as optimal in healing the critical-sized defect, although of ectopic nature). PSR staining of newly formed bone demonstrated that hesperidin can promote maturation of bone organic matrix. Our findings show, for the first time, that hesperidin has a modulatory role in mineralized tissue formation via not only osteoblast cell differentiation but also matrix organization and matrix-to-mineral ratio and could be a potential adjunct in regenerative bone therapies.

From Translation to Protein Degradation as Mechanisms for Regulating Biological Functions: A Review on the SLRP Family in Skeletal Tissues

The extracellular matrix can trigger cellular responses through its composition and structure. Major extracellular matrix components are the proteoglycans, which are composed of a core protein associated with glycosaminoglycans, among which the small leucine-rich proteoglycans (SLRPs) are the largest family. This review highlights how the codon usage pattern can be used to modulate cellular response and discusses the biological impact of post-translational events on SLRPs, including the substitution of glycosaminoglycan moieties, glycosylation, and degradation. These modifications are listed, and their impacts on the biological activities and structural properties of SLRPs are described. We narrowed the topic to skeletal tissues undergoing dynamic remodeling.

Evidence of biglycan structure-function in bone homeostasis and aging

Purpose: Biglycan is a proteoglycan of the small leucine-rich repeat family. It is present in all connective tissues and plays key structural and signaling roles. This review aimed to compile available evidence in the characteristics and distribution of biglycan and its glycosylated and non-glycosylated forms in connective tissues with a specific focus on the contribution to homeostasis of bone and changes of biglycan structure with aging.Methods: The Pubmed database was searched and included the terms "biglycan", "proteoglycans", "glycosaminoglycans", "bone", "osteoblast", "osteocyte", "osteoclast", "aging", "inflammation", "cartilage". Abstracts were appraised and a series of original articles and reviews studied to generate this narrative review.Results: Based on the search, biglycan significantly affects bone development and homeostasis and can be significantly changed by the aging process in several connective tissues, which in turn affects the behavior of tissue and cell responses in aged networks. Further, as the understanding of the various forms of biglycan in vivo is expanded and the function of its components in vitro is dissected, this proteoglycan can potentially serve as a therapeutic or biomarker molecule to detect tissue destruction.Conclusions: Biglycan is a key player in skeletal bone homeostasis, and overall, there is more evidence on the role of biglycan in development and less in the adult physiological or diseased young and aged systems. Further understanding of its conformation, degradation peptides and post-translational modifications will be required to understand the role of biglycan in bone maintenance and to support the development of treatments for age-related bone dysfunctions.

Identification of the effector domain of biglycan that facilitates BMP-2 osteogenic function

We have reported that recombinant biglycan (BGN) core protein accelerates bone formation in vivo by enhancing bone morphogenetic protein (BMP)-2 function. The purpose of the present study was to identify the specific domain (“effector”) within the BGN core protein that facilitates BMP-2 osteogenic function. Thus, we generated various recombinant and synthetic peptides corresponding to several domains of BGN, and tested their effects on BMP-2 functions in vitro. The results demonstrated that the leucine-rich repeats 2–3 domain (LRR2-3) of BGN significantly enhanced the BMP-2 induced Smad1/5/9 phosphorylation, osteogenic gene expression, and alkaline phosphatase activity in myogenic C2C12 cells. Furthermore, addition of LRR2-3 to osteoblastic MC3T3-E1 cells accelerated in vitro mineralization without compromising the quality of the mineral and matrix. These data indicate that LRR2-3 is, at least in part, responsible for BGN’s ability to enhance BMP-2 osteogenic function, and it could be useful for bone tissue regeneration.

Cardiac Fibroblasts Adopt Osteogenic Fates and Can Be Targeted to Attenuate Pathological Heart Calcification

Mammalian tissues calcify with age and injury. Analogous to bone formation, osteogenic cells are thought to be recruited to the affected tissue and induce mineralization. In the heart, calcification of cardiac muscle leads to conduction system disturbances and is one of the most common pathologies underlying heart blocks. However the cell identity and mechanisms contributing to pathological heart muscle calcification remain unknown. Using lineage tracing, murine models of heart calcification and in vivo transplantation assays, we show that cardiac fibroblasts (CFs) adopt an osteoblast cell-like fate and contribute directly to heart muscle calcification. Small-molecule inhibition of ENPP1, an enzyme that is induced upon injury and regulates bone mineralization, significantly attenuated cardiac calcification. Inhibitors of bone mineralization completely prevented ectopic cardiac calcification and improved post injury heart function. Taken together, these findings highlight the plasticity of fibroblasts in contributing to ectopic calcification and identify pharmacological targets for therapeutic development.

Extracellular matrix disruption is an early event in the pathogenesis of skeletal disease in mucopolysaccharidosis I

Progressive skeletal and connective tissue disease represents a significant clinical burden in all of the mucopolysaccharidoses. Despite the introduction of enzyme replacement strategies for many of the mucopolysaccharidoses, symptomatology related to bone and joint disease appears to be recalcitrant to current therapies. In order to address these unmet medical needs a clearer understanding of skeletal and connective tissue disease pathogenesis is required. Historically the pathogenesis of the mucopolysaccharidoses has been assumed to directly relate to progressive storage of glycosaminoglycans. It is now apparent for many lysosomal storage disorders that more complex pathogenic mechanisms underlie patients' clinical symptoms. We have used proteomic and genome wide expression studies in the murine mucopolysaccharidosis I model to identify early pathogenic events occurring in micro-dissected growth plate tissue. Studies were conducted using 3 and 5-week-old mice thus representing a time at which no obvious morphological changes of bone or joints have taken place. An unbiased iTRAQ differential proteomic approach was used to identify candidates followed by validation with multiple reaction monitoring mass spectrometry and immunohistochemistry. These studies reveal significant decreases in six key structural and signaling extracellular matrix proteins; biglycan, fibromodulin, PRELP, type I collagen, lactotransferrin, and SERPINF1. Genome-wide expression studies in embryonic day 13.5 limb cartilage and 5 week growth plate cartilage followed by specific gene candidate qPCR studies in the 5week growth plate identified fourteen significantly deregulated mRNAs (Adamts12, Aspn, Chad, Col2a1, Col9a1, Hapln4, Lum, Matn1, Mmp3, Ogn, Omd, P4ha2, Prelp, and Rab32). The involvement of biglycan, PRELP and fibromodulin; all members of the small leucine repeat proteoglycan family is intriguing, as this protein family is implicated in the pathogenesis of late onset osteoarthritis. Taken as a whole, our data indicates that alteration of the extracellular matrix represents a very early event in the pathogenesis of the mucopolysaccharidoses and implies that biomechanical failure of chondro-osseous tissue may underlie progressive bone and joint disease symptoms. These findings have important therapeutic implications.

Soluble biglycan as a biomarker of inflammatory renal diseases

Chronic renal inflammation is often associated with a progressive accumulation of various extracellular matrix constituents, including several members of the small leucine-rich proteoglycan (SLRP) gene family. It is becoming increasingly evident that the matrix-unbound SLRPs strongly regulate the progression of inflammation and fibrosis. Soluble SLRPs are generated either via partial proteolytic processing of collagenous matrices or by de novo synthesis evoked by stress or injury. Liberated SLRPs can then bind to and activate Toll-like receptors, thus modulating downstream inflammatory signaling. Preclinical animal models and human studies have recently identified soluble biglycan as a key initiator and regulator of various inflammatory renal diseases. Biglycan, generated by activated macrophages, can enter the circulation and its elevated levels in plasma and renal parenchyma correlate with unfavorable renal function and outcome. In this review, we will focus on the critical role of soluble biglycan in inflammatory signaling in various renal disorders. Moreover, we will provide new data implicating proinflammatory effects of soluble decorin in unilateral ureteral obstruction. Finally, we will critically evaluate the potential application of soluble biglycan vis-à-vis other SLRPs (decorin, lumican and fibromodulin) as a promising target and novel biomarker of inflammatory renal diseases.