Related Experiment Videos
Molecular basis for a link between complement and the vascular complications of diabetes
J Acosta1, J Hettinga, R Flückiger
1Laboratory for Membrane Transport, Harvard Medical School, 240 Longwood Avenue, C1-607, Boston, MA 02115, USA.
Insights
In diabetes, glucose damages CD59, a protein that normally prevents cell overgrowth. This damage allows the membrane attack complex (MAC) to stimulate blood vessel growth, contributing to diabetic complications.
Area of Science:
- Immunology
- Endocrinology
- Molecular Biology
Background:
- The membrane attack complex (MAC) promotes cell proliferation by stimulating growth factor release from endothelial cells.
- CD59 is a complement regulatory protein that inhibits MAC formation.
- Diabetic vascular complications are characterized by increased cell proliferation, potentially linked to protein glycation.
Purpose of the Study:
- To investigate if protein glycation, caused by high glucose levels in diabetes, inhibits the function of CD59.
- To determine if glycated CD59 leads to increased MAC deposition and subsequent cell proliferation.
Main Methods:
- In vivo analysis of human CD59 for glycation.
- Functional assays to assess MAC-inhibitory activity of glycated CD59.
- Site-directed mutagenesis to identify glycation sites on CD59.
Main Results:
- Human CD59 is glycated in vivo.
- Glycation inactivates CD59's ability to inhibit MAC formation.
- Inactivated CD59 enhances MAC-induced growth factor release from endothelial cells.
- Residues K41 and H44 were identified as a preferential glycation motif in human CD59.
Conclusions:
- Glycation of CD59 in diabetes impairs its regulatory function, leading to increased MAC activity.
- This mechanism contributes to the vascular proliferative complications observed in human diabetes.
- The specific glycation motif in human CD59 may explain its unique susceptibility to diabetic vascular disease.
Abstract:
Activated terminal complement proteins C5b to C9 form the membrane attack complex (MAC) pore. Insertion of the MAC into endothelial cell membranes causes the release of growth factors that stimulate tissue growth and proliferation. The complement regulatory membrane protein CD59 restricts MAC formation. Because increased cell proliferation characterizes the major chronic vascular complications of human diabetes and because increased glucose levels in diabetes cause protein glycation and impairment of protein function, we investigated whether glycation could inhibit CD59. Glycation-inactivation of CD59 would cause increased MAC deposition and MAC-stimulated cell proliferation. Here, we report that (i) human CD59 is glycated in vivo, (ii) glycated human CD59 loses its MAC-inhibitory function, and (iii) inactivation of CD59 increases MAC-induced growth factor release from endothelial cells. We demonstrate by site-directed mutagenesis that residues K41 and H44 form a preferential glycation motif in human CD59. The presence of this glycation motif in human CD59, but not in CD59 of other species, may help explain the distinct propensity of humans to develop vascular proliferative complications of diabetes.