Association of HTRA1 promoter polymorphism with spinal disc degeneration in Japanese women

Proteolysis: a key post-translational modification regulating proteoglycans

Proteoglycans are composite molecules comprising a protein backbone, i.e., the core protein, with covalently attached glycosaminoglycan chains of distinct chemical types. Most proteoglycans are secreted or attached to the cell membrane. Their specialized structures, binding properties, and biophysical attributes underlie diverse biological roles, which include modulation of tissue mechanics, cell adhesion, and the sequestration and regulated release of morphogens, growth factors, and cytokines. As an irreversible post-translational modification, proteolysis has a profound impact on proteoglycan function, abundance, and localization. Proteolysis is required for molecular maturation of some proteoglycans, clearance of extracellular matrix proteoglycans during tissue remodeling, generation of bioactive fragments from proteoglycans, and ectodomain shedding of cell-surface proteoglycans. Genetic evidence shows that proteoglycan core protein proteolysis is essential for diverse morphogenetic events during embryonic development. In contrast, dysregulated proteoglycan proteolysis contributes to osteoarthritis, cardiovascular disorders, cancer, and inflammation. Proteolytic fragments of perlecan, versican, aggrecan, brevican, collagen XVIII, and other proteoglycans are associated with independent biological activities as so-called matrikines. Yet, proteoglycan proteolysis has been investigated to only a limited extent to date. Here, we review the actions of proteases on proteoglycans and illustrate their functional impact with several examples. We discuss the applications and limitations of strategies used to define cleavage sites in proteoglycans and explain how proteoglycanome-wide proteolytic mapping, which is desirable to fully understand the impact of proteolysis on proteoglycans, can be facilitated by integrating classical proteoglycan isolation methods with mass spectrometry-based proteomics.

The multifaced role of HtrA1 in the development of joint and skeletal disorders

HtrA1 (High temperature requirement A1) family proteins include four members, widely conserved from prokaryotes to eukaryotes, named HtrA1, HtrA2, HtrA3 and HtrA4. HtrA1 is a serine protease involved in a variety of biological functions regulating many signaling pathways degrading specific components and playing key roles in many human diseases such as neurodegenerative disorders, pregnancy complications and cancer. Due to its role in the breakdown of many ExtraCellular Matrix (ECM) components of articular cartilage such as fibronectin, decorin and aggrecan, HtrA1 encouraged many researches on studying its role in several skeletal diseases (SDs). These studies were further inspired by the fact that HtrA1 is able to regulate the signaling of one of the most important cytokines involved in SDs, the TGFβ-1. This review aims to summarize the data currently available on the role of HtrA1 in skeletal diseases such as Osteoporosis, Rheumatoid Arthritis, Osteoarthritis and Intervertebral Disc Degeneration (IDD). The use of HtrA1 as a marker of frailty in geriatric medicine would represent a powerful tool for identifying older individuals at risk of developing skeletal disorders, evaluating an appropriate intervention to improve quality care in these people avoiding or improving age-related SDs in the elderly population.

A Molecular Cascade Underlying Articular Cartilage Degeneration

Preserving of articular cartilage is an effective way to protect synovial joints from becoming osteoarthritic (OA) joints. Understanding of the molecular basis of articular cartilage degeneration will provide valuable information in the effort to develop cartilage preserving drugs. There are currently no disease-modifying OA drugs (DMOADs) available to prevent articular cartilage destruction during the development of OA. Current drug treatments for OA focus on the reduction of joint pain, swelling, and inflammation at advanced stages of the disease. However, based on discoveries from several independent research laboratories and our laboratory in the past 15 to 20 years, we believe that we have a functional molecular understanding of articular cartilage degeneration. In this review article, we present and discuss experimental evidence to demonstrate a sequential chain of the molecular events underlying articular cartilage degeneration, which consists of transforming growth factor beta 1, high-temperature requirement A1 (a serine protease), discoidin domain receptor 2 (a cell surface receptor tyrosine kinase for native fibrillar collagens), and matrix metalloproteinase 13 (an extracellularmatrix degrading enzyme). If, as we strongly suspect, this molecular pathway is responsible for the initiation and acceleration of articular cartilage degeneration, which eventually leads to progressive joint failure, then these molecules may be ideal therapeutic targets for the development of DMOADs.

Age-Related Macular Degeneration in Primary Osteoarthritis Egyptian Patients

Introduction

Both primary osteoarthritis (OA) and age-related macular degeneration (AMD) cause disability in old people. This study aimed to detect the relation between primary osteoarthritis and age-related macular degeneration in a sample of geriatric Egyptian population.

Methods

This cross-sectional study included 222 primary OA patients. Medical history, musculoskeletal examination, body mass index (BMI) calculation, and ophthalmological examination, radiographs of anteroposterior view and weight-bearing position for both hips and both knees and posteroanterior view for hands, Kellgren and Lawrence grading score for radiological severity of OA, optical coherence tomography (OCT), and fundus fluorescence angiography FFA for evaluation of the macula were done. AMD was classified into early, intermediate, and late. The collected data were analyzed using SPSS version 25.0.

Results

Forty-six OA patients had AMD [19 cases had early, 15 cases had intermediate and 12 cases with late (7 neovascular (NV) and 5 geographic atrophy (GA))]. There was a significant correlation between AMD stages and OA grading score. There were significant differences between OA patient with AMD and those without AMD regarding age, disease duration, disease severity, family history of OA, daily mild exercise and calcium, and vitamin D intake. Multivariable analysis revealed that older age, more severe OA, low exercise and less calcium and vitamin D intake were considered independent risk factors for AMD development in primary OA.

Conclusion

Primary OA patients are more liable to AMD due to common risk factors and related pathogenesis. Ophthalmological follow up of those patients is recommended.

High-Temperature Requirement A1 Protease as a Rate-Limiting Factor in the Development of Osteoarthritis

Preserving the mature articular cartilage of joints is a critical focus in the prevention and treatment of osteoarthritis. We determined whether the genetic inactivation of high-temperature requirement A1 (HtrA1) can significantly attenuate the degradation of articular or condylar cartilage. Two types of mouse models of osteoarthritis were used, a spontaneous mutant mouse model [type XI collagen-haploinsufficient (Col11a1^+/-) mice] and two post-traumatic mouse models [destabilization of the medial meniscus (DMM) on the knee and a partial discectomy (PDE) on the temporomandibular joint]. Three different groups of mice were generated: i) HtrA1 was genetically deleted from Col11a1^+/- mice (HtrA1^-/-;Col11a1^+/-), ii) HtrA1-deficient mice (HtrA1^-/-) were subjected to DMM, and iii) HtrA1^-/- mice were subjected to PDE. Knee and temporomandibular joints from the mice were characterized for evidence of cartilage degeneration. The degradation of articular or condylar cartilage was significantly delayed in HtrA1^-/-;Col11a1^+/- mice and HtrA1^-/- mice after DMM or PDE. The amount of collagen type VI was significantly higher in the articular cartilage in HtrA1^-/-;Col11a1^+/- mice, compared with that in Col11a1^+/- mice. The genetic removal of HtrA1 may delay the degradation of articular or condylar cartilage in mice.

Hypoxia Is a Critical Parameter for Chondrogenic Differentiation of Human Umbilical Cord Blood Mesenchymal Stem Cells in Type I/III Collagen Sponges

Umbilical cord blood (UCB) is an attractive alternative to bone marrow for isolation of mesenchymal stem cells (MSCs) to treat articular cartilage defects. Here, we set out to determine the growth factors (bone morphogenetic protein 2 (BMP-2) and transforming growth factor-β (TGF-β1)) and oxygen tension effects during chondrogenesis of human UCB-MSCs for cartilage engineering. Chondrogenic differentiation was induced using 3D cultures in type I/III collagen sponges with chondrogenic factors in normoxia (21% O₂) or hypoxia (<5% O₂) for 7, 14 and 21 days. Our results show that UCB-MSCs can be committed to chondrogenesis in the presence of BMP-2+TGF-β1. Normoxia induced the highest levels of chondrocyte-specific markers. However, hypoxia exerted more benefit by decreasing collagen X and matrix metalloproteinase-13 (MMP13) expression, two chondrocyte hypertrophy markers. However, a better chondrogenesis was obtained by switching oxygen conditions, with seven days in normoxia followed by 14 days in hypoxia, since these conditions avoid hypertrophy of hUCB-MSC-derived chondrocytes while maintaining the expression of chondrocyte-specific markers observed in normoxia. Our study demonstrates that oxygen tension is a key factor for chondrogenesis and suggests that UBC-MSCs 3D-culture should begin in normoxia to obtain a more efficient chondrocyte differentiation before placing them in hypoxia for chondrocyte phenotype stabilization. UCB-MSCs are therefore a reliable source for cartilage engineering.

Correlation Between Expression of High Temperature Requirement Serine Protease A1 (HtrA1) in Nucleus Pulposus and T2 Value of Magnetic Resonance Imaging

BACKGROUND Degrading enzymes play an important role in the process of disc degeneration. The objective of this study was to investigate the correlation between the expression of high temperature requirement serine protease A1 (HtrA1) in the nucleus pulposus and the T2 value of the nucleus pulposus region in magnetic resonance imaging (MRI). MATERIAL AND METHODS Thirty-six patients who had undergone surgical excision of the nucleus pulposus were examined by MRI before surgery. Pfirrmann grading of the target intervertebral disc was performed according to the sagittal T2-weighted imaging, and the T2 value of the target nucleus pulposus was measured according to the median sagittal T2 mapping. The correlation between the Pfirrmann grade and the T2 value was analyzed. The expression of HtrA1 in the nucleus pulposus was analyzed by RT-PCR and Western blot. The correlation between the expression of HtrA1 and the T2 value was analyzed. RESULTS The T2 value of the nucleus pulposus region was 33.11-167.91 ms, with an average of 86.64±38.73 ms. According to Spearman correlation analysis, there was a rank correlation between T2 value and Pfirrmann grade (P<0.0001), and the correlation coefficient (rs)=-0.93617. There was a linear correlation between the mRNA level of HtrA1 and T2 value in nucleus pulposus tissues (a=3.88, b=-0.019, F=112.63, P<0.0001), normalized regression coefficient=-0.88. There was a linear correlation between the expression level of HtrA1 protein and the T2 value in the nucleus pulposus tissues (a=3.30, b=-0.016, F=93.15, P<0.0001) and normalized regression coefficient=-0.86. CONCLUSIONS The expression of HtrA1 was strongly related to the T2 value, suggesting that HtrA1 plays an important role in the pathological process of intervertebral disc degeneration.

ASSOCIATIONS BETWEEN AGE-RELATED MACULAR DEGENERATION, OSTEOARTHRITIS AND RHEUMATOID ARTHRITIS: RECORD LINKAGE STUDY

PURPOSE

The epidemiologic relationship between age-related macular degeneration (AMD) and arthritis is unknown and has implications for understanding disease pathogenesis and treatment strategies.

METHODS

An AMD cohort of 245,912 people was constructed from English linked hospital episode statistics (1999-2011), principally comprising neovascular AMD patients undergoing anti-vascular endothelial growth factor therapy. We compared the AMD cohort with a reference cohort (2,134,771 people) for rates of subsequent osteoarthritis (OA) and rheumatoid arthritis. Osteoarthritis (2,032,472 people) and rheumatoid arthritis (261,232 people) cohorts were also constructed and compared with the reference cohort for rates of subsequent AMD.

RESULTS

Risk of arthritis after AMD was not elevated. The rate ratio for OA was 0.96 (95% confidence interval 0.95-0.97) and for rheumatoid arthritis was 0.98 (0.94-1.02). However, risk of AMD after arthritis was modestly raised. For OA, the rate ratio was 1.06 (1.04-1.08), but risk increased with longer OA duration, for example, 1.15 (1.08-1.23) for >10 years. For rheumatoid arthritis, the rate ratio was also modestly elevated at 1.15 (1.12-1.19).

CONCLUSION

Age-related macular degeneration and arthritis are degenerative aging conditions that share some disease mechanisms and extracellular matrix involvement. However, considering arthritis after AMD, they are not positively associated. By contrast, people with OA experience modestly increased AMD risk, perhaps owing to medical treatments for OA.

Fibrotic-like changes in degenerate human intervertebral discs revealed by quantitative proteomic analysis

OBJECTIVE

Intervertebral disc degeneration (IDD) can lead to symptomatic conditions including sciatica and back pain. The purpose of this study is to understand the extracellular matrix (ECM) changes in disc biology through comparative proteomic analysis of degenerated and non-degenerated human intervertebral disc (IVD) tissues of different ages.

DESIGN

Seven non-degenerated (11-46 years of age) and seven degenerated (16-53 years of age) annulus fibrosus (AF) and nucleus pulposus (NP) samples were used. Proteins were extracted using guanidine hydrochloride, separated from large proteoglycans (PGs) by caesium chloride (CsCl) density gradient ultracentrifugation, and identified using liquid chromatography (LC) coupled with tandem mass spectrometry (MS/MS). For quantitative comparison, proteins were labeled with iTRAQ reagents. Collagen fibrils in the NP were assessed using scanning electron microscopy (SEM).

RESULTS

In the AF, quantitative analysis revealed increased levels of HTRA1, COMP and CILP in degeneration when compared with samples from older individuals. Fibronectin showed increment with age and degeneration. In the NP, more CILP and CILP2 were present in degenerated samples of younger individuals. Reduced protein solubility was observed in degenerated and older non-degenerated samples correlated with an accumulation of type I collagen in the insoluble fibers. Characterization of collagen fibrils in the NP revealed smaller mean fibril diameters and decreased porosity in the degenerated samples.

CONCLUSIONS

Our study identified distinct matrix changes associated with aging and degeneration in the intervertebral discs (IVDs). The nature of the ECM changes, together with observed decreased in solubility and changes in fibril diameter is consistent with a fibrotic-like environment.

Attenuation of the progression of articular cartilage degeneration by inhibition of TGF-β1 signaling in a mouse model of osteoarthritis

Transforming growth factor beta 1 (TGF-β1) is implicated in osteoarthritis. We therefore studied the role of TGF-β1 signaling in the development of osteoarthritis in a developmental stage-dependent manner. Three different mouse models were investigated. First, the Tgf-β receptor II (Tgfbr2) was specifically removed from the mature cartilage of joints. Tgfbr2-deficient mice were grown to 12 months of age and were then euthanized for collection of knee and temporomandibular joints. Second, Tgfbr2-deficient mice were subjected to destabilization of the medial meniscus (DMM) surgery. Knee joints were then collected from the mice at 8 and 16 weeks after the surgery. Third, wild-type mice were subjected to DMM at the age of 8 weeks. Immediately after the surgery, these mice were treated with the Tgfbr2 inhibitor losartan for 8 weeks and then euthanized for collection of knee joints. All joints were characterized for evidences of articular cartilage degeneration. Initiation or acceleration of articular cartilage degeneration was not observed by the genetic inactivation of Tgfbr2 in the joints at the age of 12 months. In fact, the removal of Tgfbr2 and treatment with losartan both delayed the progression of articular cartilage degeneration induced by DMM compared with control littermates. Therefore, we conclude that inhibition of Tgf-β1 signaling protects adult knee joints in mice against the development of osteoarthritis.

Advances in understanding cartilage remodeling

Cartilage remodeling is currently among the most popular topics in osteoarthritis research. Remodeling includes removal of the existing cartilage and replacement by neo-cartilage. As a loss of balance between removal and replacement of articular cartilage develops (particularly, the rate of removal surpasses the rate of replacement), joints will begin to degrade. In the last few years, significant progress in molecular understanding of the cartilage remodeling process has been made. In this brief review, we focus on the discussion of some current "controversial" observations in articular cartilage degeneration: (1) the biological effect of transforming growth factor-beta 1 on developing and mature articular cartilages, (2) the question of whether aggrecanase 1 (ADAMTS4) and aggrecanase 2 (ADAMTS5) are key enzymes in articular cartilage destruction, and (3) chondrocytes versus chondron in the development of osteoarthritis. It is hoped that continued discussion and investigation will follow to better clarify these topics. Clarification will be critical for those in search of novel therapeutic targets for the treatment of osteoarthritis.

Cartilage tissue engineering: molecular control of chondrocyte differentiation for proper cartilage matrix reconstruction

BACKGROUND

Articular cartilage defects are a veritable therapeutic problem because therapeutic options are very scarce. Due to the poor self-regeneration capacity of cartilage, minor cartilage defects often lead to osteoarthritis. Several surgical strategies have been developed to repair damaged cartilage. Autologous chondrocyte implantation (ACI) gives encouraging results, but this cell-based therapy involves a step of chondrocyte expansion in a monolayer, which results in the loss in the differentiated phenotype. Thus, despite improvement in the quality of life for patients, reconstructed cartilage is in fact fibrocartilage. Successful ACI, according to the particular physiology of chondrocytes in vitro, requires active and phenotypically stabilized chondrocytes.

SCOPE OF REVIEW

This review describes the unique physiology of cartilage, with the factors involved in its formation, stabilization and degradation. Then, we focus on some of the most recent advances in cell therapy and tissue engineering that open up interesting perspectives for maintaining or obtaining the chondrogenic character of cells in order to treat cartilage lesions.

MAJOR CONCLUSIONS

Current research involves the use of chondrocytes or progenitor stem cells, associated with "smart" biomaterials and growth factors. Other influential factors, such as cell sources, oxygen pressure and mechanical strain are considered, as are recent developments in gene therapy to control the chondrocyte differentiation/dedifferentiation process.

GENERAL SIGNIFICANCE

This review provides new information on the mechanisms regulating the state of differentiation of chondrocytes and the chondrogenesis of mesenchymal stem cells that will lead to the development of new restorative cell therapy approaches in humans. This article is part of a Special Issue entitled Matrix-mediated cell behaviour and properties.

The emerging roles of HTRA1 in musculoskeletal disease

High-temperature requirement serine protease A1 (HTRA1) is one of four known proteases belonging to the broadly conserved family of HTRA proteins. Although it was originally considered as representing an important modulator of tumorigenesis, an increasing number of reports have suggested that its influence on human disease may extend beyond cancer. HTRA1 has the capacity to degrade numerous extracellular matrix proteins, and as such, its potential involvement in diseases of the musculoskeletal system has been gaining increased attention. Musculoskeletal disease constitutes a wide variety of degenerative conditions that can manifest themselves in different ways such as joint and back pain, as well as deficiencies in skeletal bone quality, and ultimately result in significant suffering and reduced quality of life. Convincing data now exist to support a detrimental role for HTRA1 in the pathogenesis of joint and intervertebral disk degeneration. However, the function of HTRA1 in other closely related musculoskeletal diseases affecting bone and muscle remains unclear and largely unexplored. To help set the stage for future research, we discuss here some of the recent advances in our understanding of the role played by HTRA1 in musculoskeletal pathology.

Detrimental role for human high temperature requirement serine protease A1 (HTRA1) in the pathogenesis of intervertebral disc (IVD) degeneration

Human HTRA1 is a highly conserved secreted serine protease that degrades numerous extracellular matrix proteins. We have previously identified HTRA1 as being up-regulated in osteoarthritic patients and as having the potential to regulate matrix metalloproteinase (MMP) expression in synovial fibroblasts through the generation of fibronectin fragments. In the present report, we have extended these studies and investigated the role of HTRA1 in the pathogenesis of intervertebral disc (IVD) degeneration. HTRA1 mRNA expression was significantly elevated in degenerated disc tissue and was associated with increased protein levels. However, these increases did not correlate with the appearance of rs11200638 single nucleotide polymorphism in the promoter region of the HTRA1 gene, as has previously been suggested. Recombinant HTRA1 induced MMP production in IVD cell cultures through a mechanism critically dependent on MEK but independent of IL-1β signaling. The use of a catalytically inactive mutant confirmed these effects to be primarily due to HTRA1 serine protease activity. HTRA1-induced fibronectin proteolysis resulted in the generation of various sized fragments, which when added to IVD cells in culture, caused a significant increase in MMP expression. Furthermore, one of these fragments was identified as being the amino-terminal fibrin- and heparin-binding domain and was also found to be increased within HTRA1-treated IVD cell cultures as well as in disc tissue from patients with IVD degeneration. Our results therefore support a scenario in which HTRA1 promotes IVD degeneration through the proteolytic cleavage of fibronectin and subsequent activation of resident disc cells.

Cerebral autosomal recessive arteriopathy with subcortical infarcts and leukoencephalopathy (CARASIL): from discovery to gene identification

Cerebral autosomal recessive arteriopathy with subcortical infarcts and leukoencephalopathy (CARASIL) is a single-gene disorder directly affecting the cerebral small blood vessels, that is caused by mutations in the HTRA1 gene encoding HtrA serine peptidase/protease 1 (HTRA1). CARASIL is the second known genetic form of ischemic, nonhypertensive, cerebral small-vessel disease with an identified gene, along with cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL). The exact prevalence of CARASIL is currently unknown, and to date approximately 50 patients have been reported, most of them from Japan and two from China. Genetically, no founder haplotype has been identified, and thus the disease is expected to be found more widely. The main clinical manifestations of CARASIL are ischemic stroke or stepwise deterioration in brain functions, progressive dementia, premature baldness, and attacks of severe low back pain or spondylosis deformans/disk herniation. The most characteristic findings on brain magnetic resonance imaging are diffuse white matter changes and multiple lacunar infarctions in the basal ganglia and thalamus. Histopathologically, CARASIL is characterized by intense arteriosclerosis, mainly in the small penetrating arteries, without granular osmiophilic materials or amyloid deposition. CARASIL is a prototype single-gene disorder of cerebral small vessels secondary to and distinct from CADASIL. CARASIL-associated mutant HTRA1 exhibited decreased protease activity and failed to repress transforming growth factor-β family signaling, indicating that the increased signaling causes arteriopathy in CARASIL. Therefore, HTRA1 represents another new gene to be considered in future studies of cerebral small-vessel diseases, as well as alopecia and degenerative vertebral/disk diseases.

Single-nucleotide polymorphism in the hyaluronan and proteoglycan link protein 1 (HAPLN1) gene is associated with spinal osteophyte formation and disc degeneration in Japanese women

Spinal osteoarthritis including disc degeneration is a very common condition in the axial skeletons of aged people. Recently, spinal osteoarthritis has been shown to be influenced by specific genetic risk factors. Vertebral osteophytes, endplate sclerosis, and intervertebral disc narrowing are recognized as radiographic features of spinal disc degeneration. HAPLN1 is a key component of the cartilage extracellular matrix; thus, variations in this gene may affect the pathogenesis of cartilage-related diseases such as spinal degeneration. Here, we examine the association between an HAPLN1 gene polymorphism and the radiographic features of spinal degeneration. We evaluated the degree of endplate sclerosis, osteophyte formation, and disc space narrowing in 622 Japanese postmenopausal women. Four SNPs in the HAPLN1 gene-in the 5' flanking region, intron 1, intron 2, and intron 4-were analyzed using the TaqMan polymerase chain reaction method. We found that compared to subjects with the CC or CT genotype, those with the TT genotype for an SNP at intron 2 (rs179851) were significantly overrepresented among the subjects with higher scores for osteophyte formation (P = 0.0001; odds ratio 2.12; 95% confidence interval 1.45-3.11, as determined by logistic regression analysis) and disc space narrowing (P = 0.0057; odds ratio 1.83; 95% confidence interval 1.19-2.83). Consistent with the involvement of the HAPLN1 gene in cartilage metabolism, a variation in a specific HAPLN1 gene locus may be associated with spinal degeneration.