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Liu T, Li X, Pang M, Wang L, Li Y, Sun X. Machine learning-based endoplasmic reticulum-related diagnostic biomarker and immune microenvironment landscape for osteoarthritis. Aging (Albany NY) 2024; 16:4563-4578. [PMID: 38428406 DOI: 10.18632/aging.205611] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2023] [Accepted: 01/23/2024] [Indexed: 03/03/2024]
Abstract
BACKGROUND Osteoarthritis (OA) is the most common degenerative joint disease worldwide. Further improving the current limited understanding of osteoarthritis has positive clinical value. METHODS OA samples were collected from GEO database and endoplasmic reticulum related genes (ERRGs) were identified. The WGCNA network was further built to identify the crucial gene module. Based on the expression profiles of characteristic ERRGs, LASSO algorithm was used to select key factors according to the minimum λ value. Random forest (RF) algorithm was used to calculate the importance of ERRGs. Subsequently, overlapping genes based on LASSO and RF algorithms were identified as ERRGs-related diagnostic biomarkers. In addition, OA specimens were also collected and performed qRT-PCR quantitative analysis of selected ERRGs. RESULTS We identified four ERRGs associated with OA risk assessment through machine learning methods, and verified the abnormal expressions of these screened markers in OA patients through in vitro experiments. The influence of selected markers on OA immune infiltration was also evaluated. CONCLUSIONS Our results provide new evidence for the role of ER stress in the OA progression, as well as new markers and potential intervention targets for OA.
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Affiliation(s)
- Tingting Liu
- Research Center for Drug Safety Evaluation of Hainan, Hainan Medical University, Haikou, Hainan 571199, China
| | - Xiaomao Li
- Jiangsu Food and Pharmaceutical Science College, Huaian, Jiangsu 223023, China
| | - Mu Pang
- The Fourth Clinical Medical College of Guangzhou University of Chinese Medicine (Shenzhen Traditional Chinese Medicine Hospital), Shenzhen, Guangdong 518000, China
| | - Lifen Wang
- Research Center for Drug Safety Evaluation of Hainan, Hainan Medical University, Haikou, Hainan 571199, China
| | - Ye Li
- Chongqing Three Gorges Medical College, Chongqing 404120, China
| | - Xizhe Sun
- Research Center for Drug Safety Evaluation of Hainan, Hainan Medical University, Haikou, Hainan 571199, China
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2
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Rellmann Y, Eidhof E, Dreier R. Review: ER stress-induced cell death in osteoarthritic cartilage. Cell Signal 2020; 78:109880. [PMID: 33307190 DOI: 10.1016/j.cellsig.2020.109880] [Citation(s) in RCA: 44] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2020] [Revised: 12/03/2020] [Accepted: 12/04/2020] [Indexed: 12/16/2022]
Abstract
In cartilage, chondrocytes are responsible for the biogenesis and maintenance of the extracellular matrix (ECM) composed of proteins, glycoproteins and proteoglycans. Various cellular stresses, such as hypoxia, nutrient deprivation, oxidative stress or the accumulation of advanced glycation end products (AGEs) during aging, but also translational errors or mutations in cartilage components or chaperone proteins affect the synthesis and secretion of ECM proteins, causing protein aggregates to accumulate in the endoplasmic reticulum (ER). This condition, referred to as ER stress, interferes with cartilage cell homeostasis and initiates the unfolded protein response (UPR), a rescue mechanism to regain cell viability and function. Chronic or irreversible ER stress, however, triggers UPR-initiated cell death. Due to unresolved ER stress in chondrocytes, diseases of the skeletal system, such as chondrodysplasias, arise. ER stress has also been identified as a contributing factor to the pathogenesis of cartilage degeneration processes such as osteoarthritis (OA). This review provides current knowledge about the biogenesis of ECM components in chondrocytes, describes possible causes for the impairment of involved processes and focuses on the ER stress-induced cell death in articular cartilage during OA. Targeting of the ER stress itself or intervention in UPR signaling to reduce death of chondrocytes may be promising for future osteoarthritis therapy.
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Affiliation(s)
- Yvonne Rellmann
- Institute of Physiological Chemistry and Pathobiochemistry, Waldeyerstraße 15, 48149 Münster, Germany
| | - Elco Eidhof
- Institute of Physiological Chemistry and Pathobiochemistry, Waldeyerstraße 15, 48149 Münster, Germany
| | - Rita Dreier
- Institute of Physiological Chemistry and Pathobiochemistry, Waldeyerstraße 15, 48149 Münster, Germany.
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Ding J, Jin F, Zhao X, Zhao L, Wu Z, Li J. Hemiepiphysiodesis stapling induces ER stress apoptosis and autophagy in rat growth plates. Am J Transl Res 2019; 11:1486-1497. [PMID: 30972176 PMCID: PMC6456511] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2018] [Accepted: 01/13/2019] [Indexed: 06/09/2023]
Abstract
Angular deformities of adolescents can be treated with temporary hemiepiphysiodesis. It is confirmed that mechanical staples leading to apoptosis of chondrocyte in the growth plate. In addition, clinical evidences revealed that release from growth-inhibition condition resulted in catch-up growth, which caused damage to the patients. Thus, the current study aimed to investigate the mechanisms underlying the cell growth inhibition and the rebound growth during the temporary hemiepiphysiodesis on the growth plate. Rats with knee stapling were housed for indicated weeks, then were separated into control group, hemiepiphysiodesis groups and removal of staple groups. The tissue samples were analyzed by histopathological staining or western blotting. The results indicated there was significant growth arrest and cell apoptosis in rats treated with mechanical stress loaded (hemiepiphysiodesis group). Additionally, immunohistochemistry staining and western blotting revealed the ER-stress induced cell apoptosis was involved in growth inhibition. In removal of staple group, growth-inhibition, apoptotic cells, ER stress and autophagy-related markers were all decreased when the staples were removed from mice. Moreover, IκB/NF-κB pathway were activated in the growth plate of rats when the loads were released. In conclusion, mechanical load leaded to growth inhibition in the growth plate. ER-stress induced apoptosis and autophagy might be responsible for this process. In contrast, the possible reason for the rebound growth of growth plate may be due to the elevated IκB/NF-κB activity.
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Affiliation(s)
- Jing Ding
- Department of Pediatric Orthopaedics, Xinhua Hospital, School of Medicine, Shanghai Jiao Tong UniversityShanghai 200092, China
| | - Fangchun Jin
- Department of Pediatric Orthopaedics, Xinhua Hospital, School of Medicine, Shanghai Jiao Tong UniversityShanghai 200092, China
| | - Xiang Zhao
- Department of Pediatric Orthopaedics, Xinhua Hospital, School of Medicine, Shanghai Jiao Tong UniversityShanghai 200092, China
| | - Li Zhao
- Department of Pediatric Orthopaedics, Xinhua Hospital, School of Medicine, Shanghai Jiao Tong UniversityShanghai 200092, China
- Department of Pediatric Orthopaedics, Ying-Hua Medical Group of Children’s Bone and Joint HealthcareShanghai 200000, China
| | - Zhenkai Wu
- Department of Pediatric Orthopaedics, Xinhua Hospital, School of Medicine, Shanghai Jiao Tong UniversityShanghai 200092, China
| | - Jiyu Li
- Department of General Surgery, Shanghai Tenth People’s Hospital of Tong Ji UniversityShanghai 200072, China
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Bell PA, Dennis EP, Hartley CL, Jackson RM, Porter A, Boot-Handford RP, Pirog KA, Briggs MD. Mesencephalic astrocyte-derived neurotropic factor is an important factor in chondrocyte ER homeostasis. Cell Stress Chaperones 2019; 24:159-173. [PMID: 30543055 PMCID: PMC6363614 DOI: 10.1007/s12192-018-0953-7] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2018] [Revised: 11/21/2018] [Accepted: 11/23/2018] [Indexed: 12/12/2022] Open
Abstract
Mesencephalic astrocyte-derived neurotrophic factor (MANF) is an endoplasmic reticulum (ER) resident protein that can be secreted due to an imperfect KDEL motif. MANF plays a cytoprotective role in several soft tissues and is upregulated in conditions resulting from intracellular retention of mutant protein, including two skeletal diseases, metaphyseal chondrodysplasia, Schmid type (MCDS) and multiple epiphyseal dysplasia (MED). The role of MANF in skeletal tissue homeostasis is currently unknown. Interestingly, cartilage-specific deletion of Manf in a mouse model of MED resulted in increased disease severity, suggesting its upregulation may be chondroprotective. Treatment of MED chondrocytes with exogenous MANF led to a decrease in the cellular levels of BiP (GRP78), confirming MANF's potential to modulate ER stress responses. However, it did not alleviate the intracellular retention of mutant matrilin-3, suggesting that it is the intracellular MANF that is of importance in the pathobiology of skeletal dysplasias. The Col2Cre-driven deletion of Manf from mouse cartilage resulted in a chondrodysplasia-like phenotype. Interestingly, ablation of MANF in cartilage did not have extracellular consequences but led to an upregulation of several ER-resident chaperones including BiP. This apparent induction of ER stress in turn led to dysregulated chondrocyte apoptosis and decreased proliferation, resulting in reduced long bone growth. We have previously shown that ER stress is an underlying disease mechanism for several skeletal dysplasias. The cartilage-specific deletion of Manf described in this study phenocopies our previously published chondrodysplasia models, further confirming that ER stress itself is sufficient to disrupt skeletal growth and thus represents a potential therapeutic target.
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Affiliation(s)
- P A Bell
- Institute of Genetic Medicine, International Centre for Life, Newcastle University, Newcastle Upon Tyne, NE1 3BZ, UK
- Centre for Blood Research, University of British Columbia, Vancouver, BC, V6T 1Z3, Canada
| | - E P Dennis
- Institute of Genetic Medicine, International Centre for Life, Newcastle University, Newcastle Upon Tyne, NE1 3BZ, UK
- Wellcome Trust Centre for Cell-Matrix Research, University of Manchester, Oxford Road, Manchester, M13 9PT, UK
| | - C L Hartley
- Wellcome Trust Centre for Cell-Matrix Research, University of Manchester, Oxford Road, Manchester, M13 9PT, UK
- Genomic Diagnostics Laboratory, Manchester Centre for Genomic Medicine, Central Manchester University Hospitals NHS Foundation Trust, Manchester, M13 9WL, UK
| | - R M Jackson
- Institute of Genetic Medicine, International Centre for Life, Newcastle University, Newcastle Upon Tyne, NE1 3BZ, UK
| | - A Porter
- Newcastle University Protein and Proteome Analysis Facility, Newcastle University, Newcastle Upon Tyne, NE1 7RU, UK
| | - R P Boot-Handford
- Wellcome Trust Centre for Cell-Matrix Research, University of Manchester, Oxford Road, Manchester, M13 9PT, UK
| | - K A Pirog
- Institute of Genetic Medicine, International Centre for Life, Newcastle University, Newcastle Upon Tyne, NE1 3BZ, UK.
| | - M D Briggs
- Institute of Genetic Medicine, International Centre for Life, Newcastle University, Newcastle Upon Tyne, NE1 3BZ, UK
- Wellcome Trust Centre for Cell-Matrix Research, University of Manchester, Oxford Road, Manchester, M13 9PT, UK
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5
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Paganini C, Monti L, Costantini R, Besio R, Lecci S, Biggiogera M, Tian K, Schwartz JM, Huber C, Cormier-Daire V, Gibson BG, Pirog KA, Forlino A, Rossi A. Calcium activated nucleotidase 1 (CANT1) is critical for glycosaminoglycan biosynthesis in cartilage and endochondral ossification. Matrix Biol 2018; 81:70-90. [PMID: 30439444 PMCID: PMC6598859 DOI: 10.1016/j.matbio.2018.11.002] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2018] [Revised: 11/05/2018] [Accepted: 11/05/2018] [Indexed: 11/24/2022]
Abstract
Desbuquois dysplasia type 1 (DBQD1) is a chondrodysplasia caused by mutations in CANT1 gene encoding an ER/Golgi calcium activated nucleotidase 1 that hydrolyses UDP. Here, using Cant1 knock-in and knock-out mice recapitulating DBQD1 phenotype, we report that CANT1 plays a crucial role in cartilage proteoglycan synthesis and in endochondral ossification. Specifically, the glycosaminoglycan synthesis was decreased in chondrocytes from Cant1 knock-out mice and their hydrodynamic size was reduced, whilst the sulfation was increased and the overall proteoglycan secretion was delayed. Interestingly, knock-out chondrocytes had dilated ER cisternae suggesting delayed protein secretion and cellular stress; however, no canonical ER stress response was detected using microarray analysis, Xbp1 splicing and protein levels of BiP and ATF4. The observed proteoglycan defects caused deregulated chondrocyte proliferation and maturation in the growth plate resulting in the reduced skeletal growth. In conclusion, the pathogenic mechanism of DBQD1 comprises deregulated chondrocyte performance due to defective intracellular proteoglycan synthesis and altered proteoglycan properties in the extracellular matrix. Desbuquois dysplasia type 1 (DBQD1) is a recessive skeletal dysplasia caused by mutations in CANT1 gene, a Calcium activated nucleotidase of the ER/Golgi. The Cant1 knock-out mouse recapitulates human DBQD1. Cant1 is critical for different steps of proteoglycan biosynthesis including glycosaminoglycan chain synthesis, length and sulfation. The intracellular GAG synthesis defects cause delayed proteoglycan secretion with ER enlargement. In Cant1 knock-out chondrocytes ER enlargement is not linked to canonical ER stress. The proteoglycan defects cause deregulated chondrocyte proliferation and maturation in the growth plate resulting in reduced skeletal growth.
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Affiliation(s)
- Chiara Paganini
- Department of Molecular Medicine, Unit of Biochemistry, University of Pavia, Pavia, Italy; Scuola Universitaria Superiore IUSS, Pavia, Italy
| | - Luca Monti
- Department of Molecular Medicine, Unit of Biochemistry, University of Pavia, Pavia, Italy
| | - Rossella Costantini
- Department of Molecular Medicine, Unit of Biochemistry, University of Pavia, Pavia, Italy
| | - Roberta Besio
- Department of Molecular Medicine, Unit of Biochemistry, University of Pavia, Pavia, Italy
| | - Silvia Lecci
- Department of Molecular Medicine, Unit of Biochemistry, University of Pavia, Pavia, Italy
| | - Marco Biggiogera
- Department of Biology & Biotechnology, University of Pavia, Pavia, Italy
| | - Kun Tian
- Faculty of Biology, Medicine and Health, University of Manchester, Manchester, UK
| | - Jean-Marc Schwartz
- Faculty of Biology, Medicine and Health, University of Manchester, Manchester, UK
| | - Céline Huber
- Department of Genetics, INSERM UMR1163, Université Paris Descartes-Sorbonne Paris Cité, Institut Imagine, AP-HP, Hôpital Necker Enfants Malades, Paris, France
| | - Valérie Cormier-Daire
- Department of Genetics, INSERM UMR1163, Université Paris Descartes-Sorbonne Paris Cité, Institut Imagine, AP-HP, Hôpital Necker Enfants Malades, Paris, France
| | - Beth G Gibson
- Institute of Genetic Medicine, Newcastle University, Newcastle upon Tyne, UK
| | - Katarzyna A Pirog
- Institute of Genetic Medicine, Newcastle University, Newcastle upon Tyne, UK
| | - Antonella Forlino
- Department of Molecular Medicine, Unit of Biochemistry, University of Pavia, Pavia, Italy
| | - Antonio Rossi
- Department of Molecular Medicine, Unit of Biochemistry, University of Pavia, Pavia, Italy.
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6
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Posey KL, Coustry F, Hecht JT. Cartilage oligomeric matrix protein: COMPopathies and beyond. Matrix Biol 2018; 71-72:161-173. [PMID: 29530484 PMCID: PMC6129439 DOI: 10.1016/j.matbio.2018.02.023] [Citation(s) in RCA: 108] [Impact Index Per Article: 18.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2018] [Revised: 02/27/2018] [Accepted: 02/27/2018] [Indexed: 02/06/2023]
Abstract
Cartilage oligomeric matrix protein (COMP) is a large pentameric glycoprotein that interacts with multiple extracellular matrix proteins in cartilage and other tissues. While, COMP is known to play a role in collagen secretion and fibrillogenesis, chondrocyte proliferation and mechanical strength of tendons, the complete range of COMP functions remains to be defined. COMPopathies describe pseudoachondroplasia (PSACH) and multiple epiphyseal dysplasia (MED), two skeletal dysplasias caused by autosomal dominant COMP mutations. The majority of the mutations are in the calcium binding domains and compromise protein folding. COMPopathies are ER storage disorders in which the retention of COMP in the chondrocyte ER stimulates overwhelming cellular stress. The retention causes oxidative and inflammation processes leading to chondrocyte death and loss of long bone growth. In contrast, dysregulation of wild-type COMP expression is found in numerous diseases including: fibrosis, cardiomyopathy and breast and prostate cancers. The most exciting clinical application is the use of COMP as a biomarker for idiopathic pulmonary fibrosis and cartilage degeneration associated osteoarthritis and rheumatoid and, as a prognostic marker for joint injury. The ever expanding roles of COMP in single gene disorders and multifactorial diseases will lead to a better understanding of its functions in ECM and tissue homeostasis towards the goal of developing new therapeutic avenues.
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Affiliation(s)
- Karen L Posey
- McGovern Medical School, UTHealth, Department of Pediatrics, United States.
| | - Francoise Coustry
- McGovern Medical School, UTHealth, Department of Pediatrics, United States
| | - Jacqueline T Hecht
- McGovern Medical School, UTHealth, Department of Pediatrics, United States; UTHealth, School of Dentistry, United States
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Wang D, Mohammad M, Wang Y, Tan R, Murray LS, Ricardo S, Dagher H, van Agtmael T, Savige J. The Chemical Chaperone, PBA, Reduces ER Stress and Autophagy and Increases Collagen IV α5 Expression in Cultured Fibroblasts From Men With X-Linked Alport Syndrome and Missense Mutations. Kidney Int Rep 2017; 2:739-748. [PMID: 29142990 PMCID: PMC5678609 DOI: 10.1016/j.ekir.2017.03.004] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/26/2016] [Revised: 03/20/2017] [Accepted: 03/20/2017] [Indexed: 12/21/2022] Open
Abstract
Introduction X-linked Alport syndrome (OMIM 301050) is caused by COL4A5 missense variants in 40% of families. This study examined the effects of chemical chaperone treatment (sodium 4-phenylbutyrate) on fibroblast cell lines derived from men with missense mutations. Methods Dermal fibroblast cultures were established from 2 affected men and 3 normals. Proliferation rates were examined, the collagen IV α5 chain localized with immunostaining, and levels of the intra- and extracellular chains quantitated with an in-house enzyme-linked immunosorbent assay. COL4A5 mRNA was measured using quantitative reverse transcriptase polymerase chain reaction. Endoplasmic reticulum (ER) size was measured on electron micrographs and after HSP47 immunostaining. Markers of ER stress (ATF6, HSPA5, DDIT3), autophagy (ATG5, BECN1, ATG7), and apoptosis (CASP3, BAD, BCL2) were also quantitated by quantitative reverse transcriptase polymerase chain reaction. Measurements were repeated after 48 hours of incubation with 10 mM sodium 4-phenylbutyrate acid. Results Both COL4A5 missense variants were associated with reduced proliferation rates on day 6 (P = 0.01 and P = 0.03), ER enlargement, and increased mRNA for ER stress and autophagy (all P values < 0.05) when compared with normal. Sodium 4-phenylbutyrate treatment increased COL4A5 transcript levels (P < 0.01), and reduced ER size (P < 0.01 by EM and P < 0.001 by immunostaining), ER stress (p HSPA5 and DDIT3, all P values < 0.01) and autophagy (ATG7, P < 0.01). Extracellular collagen IV α5 chain was increased in the M1 line only (P = 0.06). Discussion Sodium 4-phenylbutyrate increases collagen IV α5 mRNA levels, reduces ER stress and autophagy, and possibly facilitates collagen IV α5 extracellular transport. Whether these actions delay end-stage renal failure in men with X-linked Alport syndrome and missense mutations will only be determined with clinical trials.
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Affiliation(s)
- Dongmao Wang
- The University of Melbourne, Department of Medicine (Northern Health and Melbourne Health), Melbourne, Victoria, Australia
| | - Mardhiah Mohammad
- The University of Melbourne, Department of Medicine (Northern Health and Melbourne Health), Melbourne, Victoria, Australia.,Department of Biomedical Science, International Islamic University of Malaysia, Kuala Lumpur, Selangor, Malaysia
| | - Yanyan Wang
- The University of Melbourne, Department of Medicine (Northern Health and Melbourne Health), Melbourne, Victoria, Australia
| | - Rachel Tan
- The University of Melbourne, Department of Medicine (Northern Health and Melbourne Health), Melbourne, Victoria, Australia
| | - Lydia S Murray
- Institute of Cardiovascular and Medical Sciences, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, UK
| | - Sharon Ricardo
- Department of Anatomy and Developmental Cell Biology, Monash University, Clayton, Victoria, Australia
| | - Hayat Dagher
- The University of Melbourne, Department of Medicine (Northern Health and Melbourne Health), Melbourne, Victoria, Australia
| | - Tom van Agtmael
- Institute of Cardiovascular and Medical Sciences, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, UK
| | - Judy Savige
- The University of Melbourne, Department of Medicine (Northern Health and Melbourne Health), Melbourne, Victoria, Australia
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Alsofi L, Daley E, Hornstra I, Morgan EF, Mason ZD, Acevedo JF, Word RA, Gerstenfeld LC, Trackman PC. Sex-Linked Skeletal Phenotype of Lysyl Oxidase Like-1 Mutant Mice. Calcif Tissue Int 2016; 98:172-85. [PMID: 26538021 PMCID: PMC8627178 DOI: 10.1007/s00223-015-0076-4] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/23/2015] [Accepted: 10/25/2015] [Indexed: 01/22/2023]
Abstract
Lysyl oxidases are required for collagen and elastin cross-linking and extracellular matrix maturation including in bone. The lysyl oxidase family consists of lysyl oxidase (LOX) and 4 isoforms (LOXL1-4). Here we investigate whether deletion of LOXL1, which has been linked primarily to elastin maturation, leads to skeletal abnormalities. Left femurs (n = 8), L5 vertebrae (n = 8), and tibiae (n = 8) were analyzed by micro-computed tomography in 13-week-old wild-type (WT) and LOXL1-/- male and female mice. Right femurs (n = 8) were subjected to immunohistochemistry for LOXL1, and histochemical/histology analyses of osteoclasts and growth plates. Sera from all mice were analyzed for bone turnover markers. Results indicate strong expression of LOXL1 in wild-type growth plates in femurs. Significant deterioration of trabecular bone structure in long bones and vertebrae from female was observed but not from male, mutant mice compared with WT. Decreases in BV/TV, Conn.D, trabecular thickness, and number in the femoral distal metaphysis were observed in female, but not in male, mutant mice. Trabecular spacing was increased significantly in femurs of female mutant mice. Findings were similar in trabeculae of L5 vertebrae from female mutant mice. The number of TRAP positive osteoclasts at the trabecular bone surface was increased in female mutant mice compared with WT females, consistent with increased serum RANKL and decreased OPG levels. Analysis of bone turnover markers confirmed increased bone resorption as indicated by significantly elevated CTX-1 in the serum of female LOXL1-/- mice compared to their wild-type counterparts, as well as decreased bone formation as measured by decreased serum levels of PINP. Picrosirius red staining revealed a loss of heterogeneity in collagen organization in female LOXL1-/- mice only, with little to no yellow and orange birefringence. Organization was also impaired in chondrocyte columns in both female and male LOXL1-/- mice, but to a greater extent in females. Data indicate that LOXL1-/- mutant mice develop appendicular and axial skeletal phenotypes characterized by decreased bone volume fraction and compromised trabecular microstructure, predominantly in females.
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Affiliation(s)
- Loai Alsofi
- Department of Molecular and Cell Biology, Henry M. Goldman School of Dental Medicine, Boston University, 700 Albany Street, W-201, Boston, MA, 02118, USA
- Department of Endodontics, Faculty of Dentistry, King Abdulaziz University, Jeddah, Saudi Arabia
| | - Eileen Daley
- Department of Molecular and Cell Biology, Henry M. Goldman School of Dental Medicine, Boston University, 700 Albany Street, W-201, Boston, MA, 02118, USA
| | - Ian Hornstra
- Division of Dermatology, Washington University School of Medicine, Saint Louis, MO, USA
| | - Elise F Morgan
- Department of Mechanical Engineering, Boston University, 110 Cummington Mall, Boston, MA, 02215, USA
| | - Zachary D Mason
- Department of Mechanical Engineering, Boston University, 110 Cummington Mall, Boston, MA, 02215, USA
| | - Jesus F Acevedo
- Department of Obstetrics and Gynecology, University of Texas Southwestern Medical Center, Dallas, TX, 75390, USA
| | - R Ann Word
- Department of Obstetrics and Gynecology, University of Texas Southwestern Medical Center, Dallas, TX, 75390, USA
| | - Louis C Gerstenfeld
- Department of Orthopaedic Surgery, Boston University School of Medicine, Boston, MA, 02118, USA
| | - Philip C Trackman
- Department of Molecular and Cell Biology, Henry M. Goldman School of Dental Medicine, Boston University, 700 Albany Street, W-201, Boston, MA, 02118, USA.
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9
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Abstract
Introduction: Genetic skeletal diseases (GSDs) are a diverse and complex group of rare genetic conditions that affect the development and homeostasis of the skeleton. Although individually rare, as a group of related diseases, GSDs have an overall prevalence of at least 1 per 4,000 children. There are currently very few specific therapeutic interventions to prevent, halt or modify skeletal disease progression and therefore the generation of new and effective treatments requires novel and innovative research that can identify tractable therapeutic targets and biomarkers of these diseases. Areas covered: Remarkable progress has been made in identifying the genetic basis of the majority of GSDs and in developing relevant model systems that have delivered new knowledge on disease mechanisms and are now starting to identify novel therapeutic targets. This review will provide an overview of disease mechanisms that are shared amongst groups of different GSDs and describe potential therapeutic approaches that are under investigation. Expert opinion: The extensive clinical variability and genetic heterogeneity of GSDs renders this broad group of rare diseases a bench to bedside challenge. However, the evolving hypothesis that clinically different diseases might share common disease mechanisms is a powerful concept that will generate critical mass for the identification and validation of novel therapeutic targets and biomarkers.
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Affiliation(s)
- Michael D Briggs
- Newcastle University, Institute of Genetic Medicine, International Centre for Life , Central Parkway, Newcastle-upon-Tyne, NE1 3BZ, UK
| | - Peter A Bell
- Newcastle University, Institute of Genetic Medicine, International Centre for Life , Newcastle-upon-Tyne, NE1 3BZ, UK
| | - Michael J Wright
- Newcastle University, Institute of Genetic Medicine, International Centre for Life , Newcastle-upon-Tyne, NE1 3BZ, UK
| | - Katarzyna A Pirog
- Newcastle University, Institute of Genetic Medicine, International Centre for Life , Newcastle-upon-Tyne, NE1 3BZ, UK
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10
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Linz A, Knieper Y, Gronau T, Hansen U, Aszodi A, Garbi N, Hämmerling GJ, Pap T, Bruckner P, Dreier R. ER Stress During the Pubertal Growth Spurt Results in Impaired Long-Bone Growth in Chondrocyte-Specific ERp57 Knockout Mice. J Bone Miner Res 2015; 30:1481-93. [PMID: 25704664 DOI: 10.1002/jbmr.2484] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/13/2014] [Revised: 02/13/2015] [Accepted: 02/16/2015] [Indexed: 01/30/2023]
Abstract
Long-bone growth by endochondral ossification is cooperatively accomplished by chondrocyte proliferation, hypertrophic differentiation, and appropriate secretion of collagens, glycoproteins, and proteoglycans into the extracellular matrix (ECM). Before folding and entering the secretory pathway, ECM macromolecules in general are subject to extensive posttranslational modification, orchestrated by chaperone complexes in the endoplasmic reticulum (ER). ERp57 is a member of the protein disulfide isomerase (PDI) family and facilitates correct folding of newly synthesized glycoproteins by rearrangement of native disulfide bonds. Here, we show that ERp57-dependent PDI activity is essential for postnatal skeletal growth, especially during the pubertal growth spurt characterized by intensive matrix deposition. Loss of ERp57 in growth plates of cartilage-specific ERp57 knockout mice (ERp57 KO) results in ER stress, unfolded protein response (UPR), reduced proliferation, and accelerated apoptotic cell death of chondrocytes. Together this results in a delay of long-bone growth with the following characteristics: (1) enlarged growth plates; (2) expanded hypertrophic zones; (3) retarded osteoclast recruitment; (4) delayed remodeling of the proteoglycan-rich matrix; and (5) reduced numbers of bone trabeculae. All the growth plate and bone abnormalities, however, become attenuated after the pubertal growth spurt, when protein synthesis is decelerated and, hence, ERp57 function is less essential.
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Affiliation(s)
- Andrea Linz
- Institute of Physiological Chemistry and Pathobiochemistry, Westfalian Wilhelms-University Münster, Münster, Germany
| | - Yvonne Knieper
- Institute of Physiological Chemistry and Pathobiochemistry, Westfalian Wilhelms-University Münster, Münster, Germany
| | - Tobias Gronau
- Institute of Experimental Musculoskeletal Medicine (IEMM), University Hospital Münster, Münster, Germany
| | - Uwe Hansen
- Institute of Experimental Musculoskeletal Medicine (IEMM), University Hospital Münster, Münster, Germany
| | - Attila Aszodi
- Experimental Surgery and Regenerative Medicine, Department of Surgery, Ludwig-Maximilians-University, Munich, Germany
| | - Natalio Garbi
- Department of Molecular Immunology, Institute of Molecular Medicine and Experimental Immunology, University of Bonn, Bonn, Germany
| | - Günter J Hämmerling
- Division of Molecular Immunology, German Cancer Research Center, Heidelberg, Germany
| | - Thomas Pap
- Institute of Experimental Musculoskeletal Medicine (IEMM), University Hospital Münster, Münster, Germany
| | - Peter Bruckner
- Institute of Physiological Chemistry and Pathobiochemistry, Westfalian Wilhelms-University Münster, Münster, Germany
| | - Rita Dreier
- Institute of Physiological Chemistry and Pathobiochemistry, Westfalian Wilhelms-University Münster, Münster, Germany
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Tsang KY, Tsang SW, Chan D, Cheah KSE. The chondrocytic journey in endochondral bone growth and skeletal dysplasia. ACTA ACUST UNITED AC 2015; 102:52-73. [PMID: 24677723 DOI: 10.1002/bdrc.21060] [Citation(s) in RCA: 53] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2014] [Accepted: 02/23/2014] [Indexed: 12/29/2022]
Abstract
The endochondral bones of the skeleton develop from a cartilage template and grow via a process involving a cascade of chondrocyte differentiation steps culminating in formation of a growth plate and the replacement of cartilage by bone. This process of endochondral ossification, driven by the generation of chondrocytes and their subsequent proliferation, differentiation, and production of extracellular matrix constitute a journey, deviation from which inevitably disrupts bone growth and development, and is the basis of human skeletal dysplasias with a wide range of phenotypic severity, from perinatal lethality to progressively deforming. This highly coordinated journey of chondrocyte specification and fate determination is controlled by a myriad of intrinsic and extrinsic factors. SOX9 is the master transcription factor that, in concert with varying partners along the way, directs the different phases of the journey from mesenchymal condensation, chondrogenesis, differentiation, proliferation, and maturation. Extracellular signals, including bone morphogenetic proteins, wingless-related MMTV integration site (WNT), fibroblast growth factor, Indian hedgehog, and parathyroid hormone-related peptide, are all indispensable for growth plate chondrocytes to align and organize into the appropriate columnar architecture and controls their maturation and transition to hypertrophy. Chondrocyte hypertrophy, marked by dramatic volume increase in phases, is controlled by transcription factors SOX9, Runt-related transcription factor, and FOXA2. Hypertrophic chondrocytes mediate the cartilage to bone transition and concomitantly face a live-or-die situation, a subject of much debate. We review recent insights into the coordination of the phases of the chondrocyte journey, and highlight the need for a systems level understanding of the regulatory networks that will facilitate the development of therapeutic approaches for skeletal dysplasia.
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Affiliation(s)
- Kwok Yeung Tsang
- Department of Biochemistry, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Pokfulam, Hong Kong, China
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Briggs MD, Bell PA, Pirog KA. The utility of mouse models to provide information regarding the pathomolecular mechanisms in human genetic skeletal diseases: The emerging role of endoplasmic reticulum stress (Review). Int J Mol Med 2015; 35:1483-92. [PMID: 25824717 PMCID: PMC4432922 DOI: 10.3892/ijmm.2015.2158] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2015] [Accepted: 03/30/2015] [Indexed: 11/22/2022] Open
Abstract
Genetic skeletal diseases (GSDs) are an extremely diverse and complex group of rare genetic diseases that primarily affect the development and homeostasis of the osseous skeleton. There are more than 450 unique and well-characterised phenotypes that range in severity from relatively mild to severe and lethal forms. Although individually rare, as a group of related genetic diseases, GSDs have an overall prevalence of at least 1 per 4,000 children. Qualitative defects in cartilage structural proteins result in a broad spectrum of both recessive and dominant GSDs. This review focused on a disease spectrum resulting from mutations in the non-collagenous glycoproteins, cartilage oligomeric matrix protein (COMP) and matrilin-3, which together cause a continuum of phenotypes that are amongst the most common autosomal dominant GSDs. Pseudoachondroplasia (PSACH) and autosomal dominant multiple epiphyseal dysplasia (MED) comprise a disease spectrum characterised by varying degrees of disproportionate short stature, joint pain and stiffness and early-onset osteoarthritis. Over the past decade, the generation and deep phenotyping of a range of genetic mouse models of the PSACH and MED disease spectrum has allowed the disease mechanisms to be characterised in detail. Moreover, the generation of novel phenocopies to model specific disease mechanisms has confirmed the importance of endoplasmic reticulum (ER) stress and reduced chondrocyte proliferation as key modulators of growth plate dysplasia and reduced bone growth. Finally, new insight into related musculoskeletal complications (such as myopathy and tendinopathy) has also been gained through the in-depth analysis of targeted mouse models of the PSACH-MED disease spectrum.
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Affiliation(s)
- Michael D Briggs
- Institute of Genetic Medicine, Newcastle University, International Centre for Life, Newcastle upon Tyne, NE1 3BZ, UK
| | - Peter A Bell
- Institute of Genetic Medicine, Newcastle University, International Centre for Life, Newcastle upon Tyne, NE1 3BZ, UK
| | - Katarzyna A Pirog
- Institute of Genetic Medicine, Newcastle University, International Centre for Life, Newcastle upon Tyne, NE1 3BZ, UK
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Kung LHW, Rajpar MH, Preziosi R, Briggs MD, Boot-Handford RP. Increased classical endoplasmic reticulum stress is sufficient to reduce chondrocyte proliferation rate in the growth plate and decrease bone growth. PLoS One 2015; 10:e0117016. [PMID: 25693198 PMCID: PMC4334961 DOI: 10.1371/journal.pone.0117016] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2014] [Accepted: 12/17/2014] [Indexed: 01/14/2023] Open
Abstract
Mutations in genes encoding cartilage oligomeric matrix protein and matrilin-3 cause a spectrum of chondrodysplasias called multiple epiphyseal dysplasia (MED) and pseudoachondroplasia (PSACH). The majority of these diseases feature classical endoplasmic reticulum (ER) stress and activation of the unfolded protein response (UPR) as a result of misfolding of the mutant protein. However, the importance and the pathological contribution of ER stress in the disease pathogenesis are unknown. The aim of this study was to investigate the generic role of ER stress and the UPR in the pathogenesis of these diseases. A transgenic mouse line (ColIITgcog) was generated using the collagen II promoter to drive expression of an ER stress-inducing protein (Tgcog) in chondrocytes. The skeletal and histological phenotypes of these ColIITgcog mice were characterised. The expression and intracellular retention of Tgcog induced ER stress and activated the UPR as characterised by increased BiP expression, phosphorylation of eIF2α and spliced Xbp1. ColIITgcog mice exhibited decreased long bone growth and decreased chondrocyte proliferation rate. However, there was no disruption of chondrocyte morphology or growth plate architecture and perturbations in apoptosis were not apparent. Our data demonstrate that the targeted induction of ER stress in chondrocytes was sufficient to reduce the rate of bone growth, a key clinical feature associated with MED and PSACH, in the absence of any growth plate dysplasia. This study establishes that classical ER stress is a pathogenic factor that contributes to the disease mechanism of MED and PSACH. However, not all the pathological features of MED and PSACH were recapitulated, suggesting that a combination of intra- and extra-cellular factors are likely to be responsible for the disease pathology as a whole.
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Affiliation(s)
- Louise H. W. Kung
- Wellcome Trust Centre for Cell-Matrix Research, Faculty of Life Sciences, The University of Manchester, Manchester, United Kingdom
| | - M. Helen Rajpar
- Wellcome Trust Centre for Cell-Matrix Research, Faculty of Life Sciences, The University of Manchester, Manchester, United Kingdom
| | - Richard Preziosi
- Environment, Ecology and Evolution Research Group, Faculty of Life Sciences, The University of Manchester, Manchester, United Kingdom
| | - Michael D. Briggs
- Institute of Genetic Medicine, Newcastle University, International Centre for Life, Central Parkway, Newcastle Upon Tyne, United Kingdom
| | - Raymond P. Boot-Handford
- Wellcome Trust Centre for Cell-Matrix Research, Faculty of Life Sciences, The University of Manchester, Manchester, United Kingdom
- * E-mail:
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Abstract
Chronic, low-grade inflammation in osteoarthritis (OA) contributes to symptoms and disease progression. Effective disease-modifying OA therapies are lacking, but better understanding inflammatory pathophysiology in OA could lead to transformative therapy. Networks of diverse innate inflammatory danger signals, including complement and alarmins, are activated in OA. Through inflammatory mediators, biomechanical injury and oxidative stress compromise the viability of chondrocytes, reprogramming them to hypertrophic differentiation and proinflammatory and pro-catabolic responses. Integral to this reprogramming are 'switching' pathways in transcriptional networks, other than the well-characterized effects of NFκB and mitogen-activated protein kinase signalling; HIF-2α transcriptional signalling and ZIP8-mediated Zn(2+) uptake, with downstream MTF1 transcriptional signalling, have been implicated but further validation is required. Permissive factors, including impaired bioenergetics via altered mitochondrial function and decreased activity of bioenergy sensors, interact with molecular inflammatory responses and proteostasis mechanisms such as the unfolded protein response and autophagy. Bioenergy-sensing by AMPK and SIRT1 provides 'stop signals' for oxidative stress, inflammatory, and matrix catabolic processes in chondrocytes. The complexity of molecular inflammatory processes in OA and the involvement of multiple inflammatory mediators in tissue repair responses, raises daunting questions about how to therapeutically target inflammatory processes and macroscopic inflammation in OA. Bioenergy sensing might provide a pragmatic 'entry point'.
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Affiliation(s)
- Ru Liu-Bryan
- San Diego VA Healthcare System and Division of Rheumatology, Allergy and Immunology, Department of Medicine, University of California San Diego, 111K, 3350 La Jolla Village Drive, San Diego, CA 92161, USA
| | - Robert Terkeltaub
- San Diego VA Healthcare System and Division of Rheumatology, Allergy and Immunology, Department of Medicine, University of California San Diego, 111K, 3350 La Jolla Village Drive, San Diego, CA 92161, USA
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Abstract
Growth plate is a specialized cartilaginous structure that mediates the longitudinal growth of skeletal bones. It consists of ordered zones of chondrocytes that secrete an extracellular matrix (ECM) composed of specific types of collagens and proteoglycans. Several heritable human skeletal dysplasias are caused by mutations in these ECM components and this review focuses on the roles of type II, IX, X, and XI collagens, aggrecan, matrilins, perlecan, and cartilage oligomeric matrix protein in the growth plate as deduced from human disease phenotypes and mouse models. Substantial advances have been achieved in deciphering the interaction networks and individual roles of these components in the construction of the growth plate ECM. Furthermore, ER stress and other cellular responses have been identified as key downstream effects of the ECM mutations contributing to abnormal growth plate development. The next challenge is to utilize the molecular level knowledge for the development of potential therapeutics.
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Affiliation(s)
- Johanna Myllyharju
- Oulu Center for Cell-Matrix Research, Biocenter Oulu and Faculty of Biochemistry and Molecular Medicine, University of Oulu, PO Box 5000, FIN-90014, Oulu, Finland,
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Arita M, Fertala J, Hou C, Steplewski A, Fertala A. Mechanisms of aberrant organization of growth plates in conditional transgenic mouse model of spondyloepiphyseal dysplasia associated with the R992C substitution in collagen II. THE AMERICAN JOURNAL OF PATHOLOGY 2014; 185:214-29. [PMID: 25451152 DOI: 10.1016/j.ajpath.2014.09.003] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/03/2014] [Revised: 08/28/2014] [Accepted: 09/03/2014] [Indexed: 11/24/2022]
Abstract
Mutations in collagen II, a main structural protein of cartilage, are associated with various forms of spondyloepiphyseal dysplasia (SED), whose main features include aberrations of linear growth. Here, we analyzed the pathomechanisms responsible for growth alterations in transgenic mice with conditional expression of the R992C collagen II mutation. Specifically, we studied the alterations of the growth plates of mutant mice in which chondrocytes lacked their typical columnar arrangement. Our studies demonstrated that chondrocytes expressing the thermolabile R992C mutant collagen II molecules endured endoplasmic reticulum stress, had atypical polarization, and had reduced proliferation. Moreover, we demonstrated aberrant organization and morphology of primary cilia. Analyses of the extracellular collagenous deposits in mice expressing the R992C mutant collagen II molecules indicated their poor formation and distribution. By contrast, transgenic mice expressing wild-type collagen II and mice in which the expression of the transgene encoding the R992C collagen II was switched off were characterized by normal growth, and the morphology of their growth plates was correct. Our study with the use of a conditional mouse SED model not only indicates a direct relation between the observed aberration of skeletal tissues and the presence of mutant collagen II, but also identifies cellular and matrix elements of the pathomechanism of SED.
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Affiliation(s)
- Machiko Arita
- Department of Orthopaedic Surgery, Sidney Kimmel Medical College, Thomas Jefferson University, Philadelphia, Pennsylvania
| | - Jolanta Fertala
- Department of Orthopaedic Surgery, Sidney Kimmel Medical College, Thomas Jefferson University, Philadelphia, Pennsylvania
| | - Cheryl Hou
- Department of Orthopaedic Surgery, Sidney Kimmel Medical College, Thomas Jefferson University, Philadelphia, Pennsylvania
| | - Andrzej Steplewski
- Department of Orthopaedic Surgery, Sidney Kimmel Medical College, Thomas Jefferson University, Philadelphia, Pennsylvania
| | - Andrzej Fertala
- Department of Orthopaedic Surgery, Sidney Kimmel Medical College, Thomas Jefferson University, Philadelphia, Pennsylvania.
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Involvement of mitochondrial dysfunction and ER-stress in the physiopathology of equine osteochondritis dissecans (OCD). Exp Mol Pathol 2014; 96:328-38. [DOI: 10.1016/j.yexmp.2014.03.004] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2013] [Revised: 03/12/2014] [Accepted: 03/13/2014] [Indexed: 12/21/2022]
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Patterson SE, Dealy CN. Mechanisms and models of endoplasmic reticulum stress in chondrodysplasia. Dev Dyn 2014; 243:875-93. [DOI: 10.1002/dvdy.24131] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2013] [Revised: 03/10/2014] [Accepted: 03/17/2014] [Indexed: 12/14/2022] Open
Affiliation(s)
- Sara E. Patterson
- Center for Regenerative Medicine and Skeletal Development; Department of Reconstructive Sciences; University of Connecticut Health Center; Farmington Connecticut
| | - Caroline N. Dealy
- Center for Regenerative Medicine and Skeletal Development; Department of Reconstructive Sciences; University of Connecticut Health Center; Farmington Connecticut
- Center for Regenerative Medicine and Skeletal Development; Department of Orthopedic Surgery; University of Connecticut Health Center; Farmington Connecticut
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Al-Kindi A, Kizhakkedath P, Xu H, John A, Sayegh AA, Ganesh A, Al-Awadi M, Al-Anbouri L, Al-Gazali L, Leitinger B, Ali BR. A novel mutation in DDR2 causing spondylo-meta-epiphyseal dysplasia with short limbs and abnormal calcifications (SMED-SL) results in defective intra-cellular trafficking. BMC MEDICAL GENETICS 2014; 15:42. [PMID: 24725993 PMCID: PMC4001364 DOI: 10.1186/1471-2350-15-42] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/16/2014] [Accepted: 04/04/2014] [Indexed: 02/08/2023]
Abstract
Background The rare autosomal genetic disorder, Spondylo-meta-epiphyseal dysplasia with short limbs and abnormal calcifications (SMED-SL), is reported to be caused by missense or splice site mutations in the human discoidin domain receptor 2 (DDR2) gene. Previously our group has established that trafficking defects and loss of ligand binding are the underlying cellular mechanisms of several SMED-SL causing mutations. Here we report the clinical characteristics of two siblings of consanguineous marriage with suspected SMED-SL and identification of a novel disease-causing mutation in the DDR2 gene. Methods Clinical evaluation and radiography were performed to evaluate the patients. All the coding exons and splice sites of the DDR2 gene were sequenced by Sanger sequencing. Subcellular localization of the mutated DDR2 protein was determined by confocal microscopy, deglycosylation assay and Western blotting. DDR2 activity was measured by collagen activation and Western analysis. Results In addition to the typical features of SMED-SL, one of the patients has an eye phenotype including visual impairment due to optic atrophy. DNA sequencing revealed a novel homozygous dinucleotide deletion mutation (c.2468_2469delCT) on exon 18 of the DDR2 gene in both patients. The mutation resulted in a frameshift leading to an amino acid change at position S823 and a predicted premature termination of translation (p.S823Cfs*2). Subcellular localization of the mutant protein was analyzed in mammalian cell lines, and it was found to be largely retained in the endoplasmic reticulum (ER), which was further supported by its N-glycosylation profile. In keeping with its cellular mis-localization, the mutant protein was found to be deficient in collagen-induced receptor activation, suggesting protein trafficking defects as the major cellular mechanism underlying the loss of DDR2 function in our patients. Conclusions Our results indicate that the novel mutation results in defective trafficking of the DDR2 protein leading to loss of function and disease. This confirms our previous findings that DDR2 missense mutations occurring at the kinase domain result in retention of the mutant protein in the ER.
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Affiliation(s)
| | | | | | | | | | | | | | | | | | | | - Bassam R Ali
- Department of Pathology, College of Medicine and Heath Sciences, United Arab Emirates University, P,O, Box 17666 Al Ain, United Arab Emirates.
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