Articular Cartilage Proteoglycan Synthesis and Sulfation
Docent Anna-Marja Säämänen, University of Turku, Finland
Professor Eeva Moilanen, University of Tampere, Finland
Docent Hannu Järveläinen, University of Turku, Finland
Docent Mikko Lammi, University of Kuopio, Finland
Professor Heikki Helminen, University of Kuopio, Finland
Docent Juha Töyräs, University of Kuopio, Finland
Articles of the thesis
Glucosamine (GlcN) and glucosamine sulfate (GS) have been used to treat the patients with osteoarthritis (OA) as a disease-modifying agent. Previous in vitro studies have focused on the effects of GlcN or GS on cartilage metabolism, whereas in vivo studies have investigated their potential for the treatment of OA. Although these results have raised promises of the disease-modifying effects of GlcN or GS, the cellular mechanisms behind these proposed effects are not clear. In general, the effectiveness of GS in the treatment of OA as a symptomatic and as a disease-modifying agent is a matter of debate.
Loss of proteoglycans (PGs) in OA could be partly due to deficient water binding e.g., by undersulfation of glycosaminoglycans (GAGs). In this study, the molar ratios of chondroitin sulfate (CS) disaccharide isoforms were analyzed with fluorophore-assisted carbohydrate electrophoresis to investigate the hypothesis that sulfate deficiency is involved with the development of bovine and human OA. Our present results indicate that the molar ratio of non-sulfated CS disaccharide in human samples was much lower than that detected in bovine samples, and it did not increase in human OA samples. Conversely, this ratio significantly decreased in bovine OA samples. Furthermore, the steady-state levels of aggrecan mRNA expression and sulfated GAG synthesis were analyzed by using Northern blot assay, quantitative real time reverse transcription polymerase chain reaction and [35S]sulfate incorporation analyses in bovine primary chondrocyte cultures. Aggrecan which is a large CS-PG of cartilage provides osmotic resistance for the cartilage helping it to absorb the compressive loads. Loss of PGs is a major cause of joint dysfunction and disability in OA. However, our results from 25 individual animals showed that none of the different forms of hexosamines, nor the GS salt, could stimulate aggrecan mRNA expression or GAG synthesis in bovine primary chondrocytes.
Glucosamine is produced intracellularly from endogenous glucose, and is one of the basic sugar structures required for CS synthesis. It is converted to UDP-glucuronic acid (GlcA) and UDP-N-acetylgalactosamine (UDP-GalNAc) before use for the synthesis of CS polysaccharide chain. If exogenous GS is made available to the cultured cells, it can be directly incorporated into the CS synthesis by UDP-GalNAc via GlcN-6-phosphate bypassing fructose-6-phosphate. Thus, the levels of intracellular UDP-N-acetylhexosamines and UDP-GlcA were explored with reversed-phase high-performance liquid chromatography-electrospray ionization mass spectrometry in bovine primary chondrocytes to analyze whether a physiologically attainable level of GS could stimulate CS synthesis by increasing intracellular UDP-sugar levels. Our present results with the cells from nine individual animals did not support this
In conclusion, bovine and human articular cartilage PGs were not undersulfated in the early stage of OA. Exogenous GS did not increase steady state levels of aggrecan mRNA expression, GAG synthesis or intracellular levels of nucleotide-activated precursors of GAG synthesis in bovine primary chondrocytes.
Lammi MJ, Qu CJ, Laasanen MS, Saarakkala S, Rieppo J, Jurvelin JS, Töyräs J: Undersulfated chondroitin sulfate does not increase in osteoarthritic cartilage. J Rheumatol 31(12):2449-2453, 2004 [Pubmed] [Full text]
Qu CJ, Karjalainen HM, Helminen HJ, Lammi MJ: The lack of effect of glucosamine sulphate on aggrecan mRNA expression and 35S-sulphate incorporation in bovine primary chondrocytes. Biochim Biophys Acta - Mol Bas Dis 1762(4):453-459, 2006 [Pubmed] [Full text]
Qu CJ, Rieppo J, Hyttinen MM, Lammi MJ, Kiviranta I, Kurkijärvi J, Jurvelin JS, Töyräs J: Human articular cartilage proteoglycans are not undersulfated in osteoarthritis. Connect Tissue Res 48(1):27-33, 2007 [Pubmed] [Full text]
Qu CJ, Jauhiainen M, Auriola S, Helminen HJ, Lammi MJ: Effects of glucosamine sulfate on intracellular UDP-hexosamine and UDP-glucuronic acid levels in bovine primary chondrocytes. Osteoarthritis Cartilage 15(7):773-779, 2007 [Pubmed] [Full text]
Qu CJ, Pöytäkangas T, Jauhiainen M, Auriola S, Lammi MJ: Glucosamine sulphate does not increase extracellular matrix production at low oxygen tension. Cell Tissue Res 337(1):103-111, 2009 [Pubmed] [Full text]
Qu C, Lindeberg H, Ylärinne JH, Lammi MJ: Five percent oxygen tension is not beneficial for the neocartilage formation in scaffold-free cell culture. Cell Tissue Res 348(1): 109-117, 2012 [Pubmed] [Full text]
Last updated January 29, 2019