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Proteoglycan metabolism in normal and inflammatory human macrophages
L Uhlin-Hansen1, T Wik, L Kjellén
1Department of Biochemistry, University of Tromsø, Norway.
Blood
|November 1, 1993
Summary
Inflammatory macrophages, stimulated by lipopolysaccharide (LPS), significantly increase secretion of chondroitin sulfate proteoglycan (CSPG). This enhanced proteoglycan release is primarily due to improved sorting to the secretory pathway, not just increased synthesis.
Area of Science:
- Cell Biology
- Biochemistry
- Immunology
Background:
- Macrophages play a crucial role in inflammation and tissue remodeling.
- Proteoglycans are key components of the extracellular matrix and cell surface.
- Understanding proteoglycan metabolism in macrophages is vital for inflammatory disease research.
Purpose of the Study:
- To investigate the metabolism of proteoglycans in human macrophages.
- To determine the effect of lipopolysaccharide (LPS) stimulation on proteoglycan secretion and biosynthesis.
- To elucidate the mechanisms regulating proteoglycan trafficking and degradation in macrophages.
Main Methods:
- Primary human macrophage cultures were established.
- Cells were stimulated with bacterial lipopolysaccharide (LPS).
- [35S]sulfate labeling was used to track proteoglycan synthesis and secretion.
- Cell adhesion was induced to study its effect on proteoglycan release.
- Proteoglycan degradation pathways were analyzed.
- Molecular size and disaccharide composition of glycosaminoglycan (GAG) chains were determined.
- N-terminal sequencing and Northern blot analysis identified the core protein.
Main Results:
- LPS-stimulated macrophages secreted approximately three times more chondroitin sulfate proteoglycan (CSPG) than control cells.
- Cell adhesion also increased proteoglycan secretion by twofold.
- Increased CSPG secretion resulted mainly from enhanced sorting to the secretory pathway (35% vs. 20% in unstimulated cells).
- LPS-treated cells synthesized smaller CSPG with GAG chains of 12 kD compared to 16 kD in controls.
- Degradation of CSPG occurred in lysosomes via a two-step process: rapid cleavage to GAG chains, followed by complete depolymerization.
- The core protein of secreted CSPG was identified as serglycin.
Conclusions:
- LPS stimulation profoundly alters proteoglycan metabolism in human macrophages, favoring secretion.
- Enhanced sorting of CSPG to the secretory pathway is the primary mechanism driving increased release.
- Macrophage-derived serglycin, a CSPG, is secreted and degraded through lysosomal pathways.
- These findings provide insights into the role of proteoglycans in macrophage function during inflammation.