Understanding the Impact of Endothelial Cd36 in the Progression of Dyslipidemia‐induced Dysfunction
Authors: Aguilar Victor , Le Master Elizabeth , Ahn Sang Jon , Paul Amit , Levitan Irena 
Published: May 2022

The negative impacts of an enriched Western‐style high‐fat diet have been extensively interconnected with dyslipidemia. Our prior studies showed that feeding male mice high‐fat diet (42% kcal from fat) results in significant cortical stiffening of aortic endothelium and that a global deletion of CD36, a scavenger receptor responsible for the uptake of oxidized modifications of LDL, abrogates this effect. We also showed previously that exposing endothelial cells to oxLDL results in endothelial stiffening, an effect also mediated by CD36. Here we expand our studies to determine the role endothelial CD36 using a new inducible mouse model of endothelial (EC) knock down of CD36 (VE‐CDH5.CreERT2xCD36fl/fl). The model was validated through PCR assessment of EC‐specific knockdown of CD36 in lungs (with smooth muscle as a comparison). Further, use of a tdTomato/eGFP reporter system showed EC‐specific targeting by tamoxifen in the aorta. VE‐CDH5.CreERT2xCD36fl/fl male and female mice were either injected with tamoxifen or with oil, and fed high‐fat diet (HFD) for 4‐6 weeks. First, we observed a significant difference between sexes in weight, plasma lipid levels and endothelial stiffening: the EC‐specific knockdown of CD36 had no impact in weight gain over the course of the six weeks. However, males gained significant weight while females didn’t (23% body weight gain for males compared to 13% for females). This weight gain was accompanied by increases in serum levels for both LDL‐ and HDL‐associated cholesterol in both males (2‐fold) and females (1.5‐fold).

We found that induction of CD36 deletion in the endothelial cells was sufficient to abrogate the cortical stiffening of the endothelium induced by HFD. Males experienced stiffening of the endothelial layer of the descending aorta, which was not observed in females. Use of tamoxifen in Cre‐only mice did not abrogate HFD‐induced stiffening, illustrating the EC‐specific role of CD36 in mediating stiffening observed during a global CD36 knockdown. Furthermore, we assessed the integrity of the endothelial barrier in two major regions of the aorta, the atherogenic arch region and the atheroprotective thoracic region. Disruption was tracked via confocal imaging of leakage of albumin‐bound Evans blue (delivered retro‐orbitally). Unexpectedly, endothelial CD36 deletion exacerbated the disruption of the endothelial barrier induced by HFD in both regions in males. In terms of the mechanism, we found that while CD36 is required for oxLDL‐induced endothelial stiffening, it is not required for the stiffening effect induced by 7‐ketocholesterol, a major oxysterol component, that can be incorporated in a receptor‐independent way.

These observations show that CD36 facilitates the uptake and processing of oxLDL‐bound lipids, which contribute to endothelial stiffening. The abrogation of these mechanisms however disrupted the endothelial barrier, highlight the heterogenous role of the receptor in endothelial function.