CD47 decline in pancreatic islet cells promotes macrophage-mediated phagocytosis in type I diabetes

Figure 1 Increased macrophage migration to pancreatic islet cells with the reduction of CD47 expression under streptozotocin treatment. A: The experimental design. Mice were treated by five daily intraperitoneal injections of streptozotocin (STZ) to construct a diabetes model; B: Macrophage infiltration into pancreatic islet cells which was indicated by increased F4/80 labeling accompanied by decreased insulin secretion in STZ treated cells; C: Statistical data; D and E: CD47 expression decreased under STZ condition. Student's t-test was performed. ^aP < 0.01 vs CTL. CD47: Cluster of differentiation 47; STZ: Streptozotocin; CFSE: Carboxy fluorescein succinimidyl ester.

Figure 2 Macrophage phagocytosis assay in vitro. A and B: Flow cytometry results displayed declined CD47 expression of Min6 cells. C: Insulin secretion decreased with STZ stimulation. D: More LPS activated macrophages were recruited to phagocyte CD47 down-regulated Min6 cells. Arrows indicate phagocytosis. Student's t-test was performed. ^aP < 0.01 vs CTL. CD47: Cluster of differentiation 47; STZ: Streptozotocin; CFSE: Carboxy fluorescein succinimidyl ester.

Figure 3 Macrophage phagocytosis is increased by CD47 siRNA transfection while recovered with CD47 overexpression. A and B: Western blot analysis revealing CD47 relative protein expression with CD47 siRNA transfection and statistical data; C: Macrophage phagocytosis was enhanced when Min6 cells were transfected with CD47 siRNA; D and E: Western blot analysis indicating CD47 relative protein expression when transfection with CD47 open reading frame (ORF; CD47 overexpression) and statistical data; F: Macrophage phagocytosis was impaired by CD47 ORF transfection under STZ condition. GAPDH served as a loading control. Western blot analysis represents the results of three independent experiments. Student's ttest was performed. ^aP < 0.01 vs CTL. CTL: Control. CD47: Cluster of differentiation 47.

Figure 4 Hypothetical model of CD47-SIRPα-regulated inhibition phagocytosis in STZ-induced diabetes. Normally, CD47 is universally expressed on pancreatic islet beta cells. CD47-SIRPα interaction effectively governs macrophage phagocytosis toward healthy self-cells by a “not attach-self” default mode. With the stimulation of STZ, macrophages infiltrate into the pancreatic islet and phagocytose cells when CD47-SIRPα interaction could not be maintained under inflammation condition. “Eat me” signal is transferred with declined expression of CD47 on pancreatic islet cells. CD47: Cluster of differentiation 47; SIRPα: Signal regulatory protein α.