👤 Florencia Schlamp

ApoB is an essential structural protein for the assembly and secretion of triglyceride-rich lipoproteins and therefore remains a potential target to lower plasma cholesterol levels in hypercholesterolemia patients. To understand the global consequences of APOB gene deficiency, we employed CRISPR-Cas9 system to generate apoB-deficient human hepatoma Huh-7 cells (Ako cells). ApoB was not detectable in the cells and media of the Ako cells. ApoB deficiency had no effect on microsomal triglyceride transfer protein expression and activity. These cells supported apoB48 secretion when transfected with plasmids for the expression of apoB48 suggesting that these cells retain all the lipoprotein assembly and secretion machinery except for apoB expression. APOB gene deficiency had no significant effect on cellular lipid levels, cell growth, and ER stress markers. Proteome analysis of secreted proteins revealed that the most upregulated protein was the vitamin D binding protein, while the most downregulated protein was apoB in Ako cells compared to control cells. This analysis also identified coagulation as an upregulated pathway. Total RNA transcriptome analysis identified DNA replication and complement and coagulation pathways as the most upregulated pathways in Ako cells. Further detailed studies are needed to establish how apoB regulates these pathways. These Ako cells may be useful in studying structure-function analysis of apoB peptides and to address the cellular consequences of disruptions in lipoprotein assembly and secretion. Show less

Cholesterol efflux capacity (CEC) of HDL (high-density lipoprotein) is inversely associated with incident cardiovascular events, independent of HDL cholesterol. Obesity is characterized by low HDL cholesterol and impaired HDL function, such as CEC. Bariatric surgery, including Roux-en-Y gastric bypass (RYGB) and sleeve gastrectomy (SG), broadly leads to improved cardiovascular outcomes, but impacts on risk factors differ by procedure, with greater improvements in weight loss, blood pressure, and glycemic control after RYGB, but greater improvements in HDL cholesterol and CEC levels after SG. This study sought to determine effects of RYGB and SG on HDL protein and lipid cargo and investigate associations with CEC changes. We prospectively studied nondiabetic, premenopausal Hispanic women with severe obesity not using lipid medications undergoing RYGB (n=31) or SG (n=36). Anthropometric measurements and blood sampling were obtained before and at 6 and 12 months after surgery. HDL was isolated from plasma, and quantitative proteomic and lipidomic assessments were performed with LC-MS/MS (liquid chromatography with tandem mass spectrometry). CEC was assessed ex vivo using apoB-depleted serum. Participants experienced similar, significant weight loss over 12 months following bariatric surgery (38.0±10.4 kg) regardless of the procedure. Relative quantities of 47 proteins (34 increased, 13 decreased) and 150 lipids (71 increased, 79 decreased) carried on HDL were significantly altered following either surgical procedure. Proteins with similar aggregate response patterns were clustered into 15 groups (5 increased, 5 decreased, 5 minimal change) and lipids with similar aggregate responses into 25 groups (7 increased, 11 decreased, 7 minimal change). Network mediation analyses suggested that changes in 4 protein and 2 lipid clusters mediated changes in ABCA1 (ATP-binding cassette transporter A1) CEC and that 1 lipid cluster mediated changes in non-ABCA1 CEC. The protein and lipid clusters that mediated changes in CEC were distinct between SG and RYGB. Bariatric surgery produces substantial changes in HDL lipid and protein cargo, and specific changes may mediate changes in HDL function in CEC. Further study of these mechanisms may lead to improved interventions to reduce cardiovascular risk in patients with obesity. Show less