Microsomal Triglyceride Transfer Protein Is Required for Yolk Lipid Utilization and Absorption of Dietary Lipids in Zebrafish Larvae

Abstract

Although the absorption, transport, and catabolism of dietary lipids have been studied extensively in great detail in mammals and other vertebrates, a tractable genetic system for identifying novel genes involved in these physiologic processes is not available. To establish such a model, we monitored neutral lipid by staining fixed zebrafish larvae with oil red o (ORO). The head structures, heart, vasculature, and swim bladder stained with ORO until the yolk was consumed 6 days after fertilization (6 dpf). Thereafter, the heart and vasculature no longer had stainable neutral lipids. Following a high-fat meal, ORO stained the intestine and vasculature of 6 dpf larvae, and whole-larval triacylglycerol (TAG) and apolipoprotein B levels increased. Levels of microsomal triglyceride transfer protein (Mtp), the protein responsible for packaging TAG and betalipoproteins into lipoprotein particles, were unchanged by feeding. Since the developing zebrafish embryo expresses mtp in the yolk cell layer, liver, and intestine, we determined the effect of targeted knockdown of Mtp expression using an antisense morpholino oligonucleotide approach (Mtp MO) on the transport of yolk and dietary lipids. Mtp MO injection led to loss of Mtp expression and of lipid staining in the vasculature, heart, and head structures. Mtp MO-injected larvae were smaller than age-matched, uninjected larvae, consumed very little yolk, and did not absorb dietary neutral lipids; however, they absorbed a short chain fatty acid that does not require Mtp for transport. Importantly, the vasculature appeared unaffected in Mtp MO-injected larvae. These studies indicate that zebrafish larvae are suitable for genetic studies of lipid transport and metabolism.

Apo-14 is required for digestive system organogenesis during fish embryogenesis and larval development

“…To investigate whether yolk lipid transportation and utilization are affected in CagApo-14 morphants, we monitored neutral fat by staining the fixed larvae with Oil Red O (ORO) (Schlegel and Stainier, 2006). In wild-type embryos at 36 hpf, staining of yolk lipid was found in vasculature (Fig.…”

Optimizing methods for the study of intravascular lipid metabolism in zebrafish

“…The intravascular lipids of embryonic zebrafish are dyed by Oil Red O. Schlegel and Stainier (13) reported that the vasculature of zebrafish no longer had stainable neutral lipids six days post fertilization (dpf). Therefore, the changes in intravascular lipids among 1-8-dpf zebrafish were observed using Oil Red O staining in the present study.…”

Disruption of ldlr causes increased LDL-c and vascular lipid accumulation in a zebrafish model of hypercholesterolemia

“…Despite the large number of putative candidate genes identifi ed, the functions of many remain largely unknown, owing in part to the lack of physiologically relevant in vivo models with which to validate and characterize the functionality of associated variants ( 3, 4, 6-13 ). Development of novel models in which genes can be individually targeted will likely reveal functional roles for genetic determinants of blood lipid levels and may facilitate discovery of novel targets for drug development.The zebrafi sh is an excellent candidate for establishing genetic models of hyperlipidemia due to conservation of cell types and molecular pathways involved in lipid metabolism and cholesterol synthesis ( 8,(14)(15)(16)(17)(18)(19)(20). These include hepatocytes, adipocytes, and pancreatic acinar cells ( 17 ) as well as expression of genes involved in lipid transport and metabolism, such as LDL receptor ( ldlr ), sterol regulatory element binding protein ( srebp ) 1/2 , and HMG-CoA reductase ( Hmgcr ) ( 18-29 ).…”