Introduction:
Diabetes is a major risk factor for ischemic stroke. Evidence suggests that the deficiency in CD36 is linked to insulin resistance in humans, yet patients with type 2 diabetes often display elevated plasma level of soluble CD36 (sCD36). However, cell type specific expression of CD36 is not well understood in the context of type 2 diabetes.
Hypothesis:
We hypothesize that insulin resistance is correlated with a reduction in the surface expression of CD36 among inflammatory cells, coincident with an increase in sCD36.
Methods:
Middle-aged db/db and db/+ mice (30-50 weeks-old) were subjected to left distal middle cerebral artery occlusion (dMCAO) or sham surgery. One, 3, or 7 days after stroke, leukocytes from blood and left hemisphere of the brain were analyzed by flow cytometry for cell type specific expression of CD36. The level of sCD36 in platelet free plasma was determined by ELISA. PPAR-γ agonist pioglitazone was administered at 2.5 mg/kg/day by oral gavage. Oral glucose tolerance test was performed at baseline and following two weeks of drug treatment. Both form of CD36 was also measured in 3-week-old mice without stroke.
Results:
Infiltrating neutrophils in brain peaked at 1 day after dMCAO, in contrast to a delayed but sustained increase of macrophages from 3 to 7 days post stroke. The adult db/db mice had a lower leukocyte surface expression of CD36 in both blood and brain, but had a higher level of sCD36 compared to age-matched db/+ mice whether at baseline or after stroke. The sCD36 is unlikely to exist in the form of extracellular vesicles (EV) since there were very few CD36(+) EVs detected in either type of mice. Prior to the development of obesity, 3-week-old db/db mice had similar leukocyte CD36 surface expression and plasma level of sCD36 compared to juvenile db/+ mice. Pioglitazone improved glucose sensitivity and enhanced macrophage CD36 surface expression in db/db mice after stroke.
Conclusions:
The reduced surface expression of CD36 on leukocytes and increased sCD36 was directly correlated with insulin resistance. Ongoing studies will determine the molecular event induced by obesity that triggers the cleavage of CD36 and how it affects macrophage function in the setting of diabetes.
Single-cell transcriptomes identify human islet cell signatures and reveal cell-type–specific expression changes in type 2 diabetes