Inflammatory Cell-derived MYDGF Attenuates LDL Transcytosis To Protect Against Atherogenesis

BackgroundOne of the earliest stages of atherosclerosis is the accumulation of low-density lipoprotein(LDL)cholesterol in the subendothelial space.However,how circulating LDL traverses the endothelial cell layer,which is known as transcytosis,remains to be further clarified.It is established that inflammation contributes to the pathogenesis of atherosclerosis,and chronic inflammation may become a therapeutic target.However,recent data have refuted the idea that inflammation for atherosclerosis is entirely detrimental.Anti-inflammation therapies do not always improve cardiovascular outcomes,and are even related to a signal toward harm in some clinical trials.Therefore,the divergent views on anti-inflammation therapies in atherosclerosis highlight the necessity to tease out the roles of both beneficial and detrimental inflammatory processes during atherosclerosis.Although the detrimental role of inflammatory cells in atherosclerosis has been proposed for many years,little is currently known about the potential benefits of inflammatory cells to atherosclerosis.Myeloid-derived growth factor(MYDGF),a secreted protein produced mainly by bone marrow-derived monocytes and macrophages(inflammatory cells),has been demonstrated to paly multiple roles in various pathological conditions,such as cardiovascular disease and metabolic diseases.However,no data are available on the relationship between MYDGF and endothelial LDL transcytosis.AimsThe present research aimed to investigate the function of inflammatory cells/endothelium axis,and investigate that whether inflammatory cell-derived MYDGF can improve atherosclerosis through inhibiting endothelial LDL transcytosis and explore the corresponding underlying mechanisms involved in.MethodsIn the in vivo experiments,we chose monocyte/macrophage-targeted MYDGFnull mice on Ldlr-/-background(MYDGFMΦKO)and their littermate controls(MYDGFflox).The mice were fed a western diet(WD)or fed a normal control diet(NCD).This diet interventions were continued for 12 weeks to establish atherosclerosis model.Furthermore,we also restored the inflammatory cell-derived MYDGF by bone marrow transplantation and inflammatory cell-specific overexpression of MYDGF mice model.The mice were fed by a WD or a NCD for 12 weeks to generate atherosclerosis.The serum MYDGF levels were detected by ELISA.The expressions of Cavl and Cavin-1 in endothelial cells were determined by Cavl/Cavin-1 and CD31 double immunofluorescence analyze.The morphology and number of caveolae were observed by transmission electron microscopy,and the number of caveolae in which Cav1 and ApoB were colocolized were observed by immunoelectron microscopy.The extent of atherosclerotic plaque formation in en face aortas and in cross-sections of aortic roots were detected by oil red O staining.The expressions of Cav1 and Cavin-1 were detected by PCR and Western blot.In in vitro experiments,primary mouse aortic endothelial cells(MAECs)were isolated from the aortas of mice,and then cultured for the experiments.Co-culture experiments between MAECs and macrophages from MYDGF+/+ mice,and MAECs supplemented with and without recombinant MYDGF(rMYDGF)were conducted to evaluate LDL transcytosis and uptake.Lastly,we performed the in vivo and in vitro experiments to investigate the mechanisms involved in the regulation of MYDGF on endothelial LDL transcytosis.ResultsResults found that inflammatory cell-derived MYDGF deficiency aggravated endothelial LDL transcytosis,drove LDL uptake by artery wall,and thus exacerbated atherosclerosis in vivo.Inflammatory cell-derived MYDGF restoration by bone marrow transplantation(BMT)and inflammatory cell MYDGF overexpression alleviated LDL transport across the endothelium,prevented infiltration of LDL particles into sub-endothelial space,and subsequently ameliorated atherosclerosis in vivo.Additionally,in vitro,macrophages from MYDGF+/+mice and rMYDGF attenuated LDL transcytosis and uptake in MAECs.Mechanistically,MYDGF inhibited mitogen-activated protein kinase kinase kinase kinase isoform 4(MAP4K4),enhanced protein kinase B(Akt1),and diminished forkhead box O 3a(FoxO3a)signaling cascade to exert protective effects of MYDGF on endothelial LDL transcytosis and atherosclerosis.ConclusionThe above findings support a role for inflammatory cell-derived MYDGF serves as a crosstalk factor between inflammatory cells and endothelial cells that inhibits LDL transcytosis across endothelium.MYDGF may become a novel therapeutic drug for atherosclerosis,and the beneficial effects of inflammatory cell in atherosclerosis deserve further attention.