Inhibition of lysosomal function in macrophages incubated with elevated glucose concentrations: a potential contributory factor in diabetes-associated atherosclerosis.
OBJECTIVE
People with diabetes have an elevated risk of atherosclerosis. The accumulation of lipid within macrophage cells in the artery wall is believed to arise via the uptake and subsequent processing of modified low-density lipoproteins (LDL) via the endo-lysosomal system. In this study the effects of prolonged exposure to elevated glucose upon macrophage lysosomal function was examined to determine whether this contributes to modulated protein catabolism.


METHODS
Human monocytes were isolated from white-cell concentrates and differentiated, in vitro, into monocyte-derived macrophages over 11 days in medium containing 5-30 mmol/L glucose. Murine macrophage-like J774A.1 cells were incubated similarly. Lysosomal cathepsin (B, D, L and S) and acid lipase activities were assessed using fluorogenic substrates; cathepsin protein levels were examined by Western blotting. Lysosomal numbers were examined using the lysomotropic fluorescent dye LysoTracker DND-99, measurement of aryl sulfatase activity, and quantification of lysosome-associated membrane glycoprotein-1 (LAMP-1) by Western blotting.


RESULTS
Exposure to elevated glucose, but not mannitol, resulted in a concentration-dependent decrease in the activity, and to a lesser extent protein levels, of four lysosomal cathepsins. Acid lipase activity was also significantly reduced. Arysulfatase activity, LAMP-1 levels and lysosomal numbers were also decreased at the highest glucose concentrations, though to a lesser extent.


CONCLUSIONS
Long term exposure of human and murine macrophage cells to elevated glucose levels result in a depression of lysosomal proteolytic and lipase activities. This may result in decreased clearance and cellular accumulation of (lipo)proteins and contribute to the accumulation of modified proteins and lipids in diabetes-associated atherosclerosis.
The Heart Research Institute, Sydney, NSW, Australia.
Fatemeh
F
Moheimani
Christine H J
CH
Kim
Aldwin Suryo
AS
Rahmanto
David M
DM
van Reyk
Michael J
MJ
Davies
D000818:Animals; D001192:Arylsulfatases / Q000378:metabolism; D050197:Atherosclerosis / Q000209:etiology* / Q000378:metabolism; D015153:Blotting, Western; D002403:Cathepsins / Q000378:metabolism; D002460:Cell Line; D003925:Diabetic Angiopathies / Q000209:etiology* / Q000378:metabolism; D015536:Down-Regulation; D005947:Glucose / Q000378:metabolism*; D006801:Humans; D051907:Lysosomal Membrane Proteins / Q000378:metabolism; D008247:Lysosomes / Q000378:metabolism*; D008264:Macrophages / Q000378:metabolism*; D051379:Mice; D008856:Microscopy, Fluorescence; D002787:Sterol Esterase / Q000378:metabolism; D013997:Time Factors; D052118:Lysosomal-Associated Membrane Protein 1
D001192:Arylsulfatases; D002403:Cathepsins; D005947:Glucose; D051907:Lysosomal Membrane Proteins; D002787:Sterol Esterase; C489116:LAMP1 protein, human; D052118:Lysosomal-Associated Membrane Protein 1; C052255:Lamp1 protein, mouse