The Hexosamine Biosynthetic Pathway as a Therapeutic Target after Cartilage Trauma: Modification of Chondrocyte Survival and Metabolism by Glucosamine Derivatives and PUGNAc in an Ex Vivo Model.

Jana Riegger,Frank Zaucke,Rolf E Brenner,Julia Baumert

doi:10.3390/ijms22147247

Abstract

The hexosamine biosynthetic pathway (HBP) is essential for the production of uridine diphosphate N-acetylglucosamine (UDP-GlcNAc), the building block of glycosaminoglycans, thus playing a crucial role in cartilage anabolism. Although O-GlcNAcylation represents a protective regulatory mechanism in cellular processes, it has been associated with degenerative diseases, including osteoarthritis (OA). The present study focuses on HBP-related processes as potential therapeutic targets after cartilage trauma. Human cartilage explants were traumatized and treated with GlcNAc or glucosamine sulfate (GS); PUGNAc, an inhibitor of O-GlcNAcase; or azaserine (AZA), an inhibitor of GFAT-1. After 7 days, cell viability and gene expression analysis of anabolic and catabolic markers, as well as HBP-related enzymes, were performed. Moreover, expression of catabolic enzymes and type II collagen (COL2) biosynthesis were determined. Proteoglycan content was assessed after 14 days. Cartilage trauma led to a dysbalanced expression of different HBP-related enzymes, comparable to the situation in highly degenerated tissue. While GlcNAc and PUGNAc resulted in significant cell protection after trauma, only PUGNAc increased COL2 biosynthesis. Moreover, PUGNAc and both glucosamine derivatives had anti-catabolic effects. In contrast, AZA increased catabolic processes. Overall, “fueling” the HBP by means of glucosamine derivatives or inhibition of deglycosylation turned out as cells and chondroprotectives after cartilage trauma.

Highlights

As the most common joint disease in the elderly population and one of the leading causes of disability in age, osteoarthritis (OA) has a high impact on today’s society [1].Preceding injuries are considered a major risk factor in joint degeneration, causing a special form called post-traumatic OA (PTOA), which can affect the younger population and accounts for about 10% of the total incidence of knee OA [2].The pathogenesis of PTOA is induced by a traumatic impact causing a sudden increase of cell death and subsequent synovial inflammation
Using a drop-tower model, as previously described [21]. This trauma suppressed gene expression levels of OGT by 25%, while increasing that of OGA by 35% (Figure 2A,B), significantly changing the ratio of OGA to OGT ([vs. C] 2-fold; Figure 2C). This alteration was markedly reduced by GlcNAc, PUGNAc, and AZA; the attenuating effect was only significant in the case of 10 mM GlcNAc
Despite increased gene expression of OGA in presence of its inhibitor PUGNAc, mRNA levels of OGT were likewise enhanced, resulting in an overall alleviated ratio of OGA to OGT, which was comparable to the control level

Summary

Introduction

As the most common joint disease in the elderly population and one of the leading causes of disability in age, osteoarthritis (OA) has a high impact on today’s society [1].Preceding injuries are considered a major risk factor in joint degeneration, causing a special form called post-traumatic OA (PTOA), which can affect the younger population and accounts for about 10% of the total incidence of knee OA [2].The pathogenesis of PTOA is induced by a traumatic impact causing a sudden increase of cell death and subsequent synovial inflammation. As the most common joint disease in the elderly population and one of the leading causes of disability in age, osteoarthritis (OA) has a high impact on today’s society [1]. Preceding injuries are considered a major risk factor in joint degeneration, causing a special form called post-traumatic OA (PTOA), which can affect the younger population and accounts for about 10% of the total incidence of knee OA [2]. The pathogenesis of PTOA is induced by a traumatic impact causing a sudden increase of cell death and subsequent synovial inflammation. II collagen and aggrecan [3]. These catabolic processes can persist over years, driving progressive cartilage degeneration. The development of efficient drugs, preventing or delaying the onset of PTOA, remains difficult, in particular due to the complex pathomechanisms

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Conclusion