Deletion of Murine Endothelial Bag3 Alters the Cellular Proteome among Organs of Origin

INTRODUCTION: Bcl-2 associated athanogene 3 (BAG3) is a multifunctional protein with pleiotropic effects in multiple cell types. Despite our knowledge of its role in cardiovascular disease, its specific role in endothelial cells (ECs) is unknown. The purpose of this study was to identify differences in the EC proteome of multiple tissues before and after cell-specific deletion of Bag3. We hypothesized that BAG3 loss would uniquely alter the baseline proteome landscape of ECs in each tissue. METHODS: Cdh5(PAC)-CreERT2;Bag3f/f mice received tamoxifen (KO; n = 18) or vehicle (WT; n = 18) and tissues (brain, heart, lung, and peripheral skeletal muscle-SkM) were collected for fluorescence-activated cell sorting of ECs from equal numbers of male and female mice at >22 weeks of age, followed by LC-MS/MS label-free proteomics. RESULTS: Initial comparisons of the WT proteomes between tissues revealed differential abundance of EC proteins (p < 0.05), including 367 brain vs heart; 338 brain vs. lung; 570 brain vs. SkM; 400 heart vs. lung; 104 heart vs. SkM; and 489 lung vs. SkM. Additionally, the EC mitochondrial proteome was unique to each tissue of origin, with significantly (p < 0.05) higher proportions dedicated to complexes I, III, IV, and V, in the heart compared to the other tissues. KO demonstrated the largest effect on SkM ECs, increasing 31 proteins (Mybpc2 Log2FC = 4.81; PFKM Log2FC = 3.02) and decreasing 65 (CDC42 Log2FC = -2.44; Prpf8 Log2FC = -2.24). CONCLUSION: Overall, these results demonstrate that the EC proteome of different tissues is unique and that the loss of BAG3 in these cells differentially alters a small proportion of the EC-specific proteome.