Using primary murine intestinal enteroids to study dietary TAG absorption, lipoprotein synthesis, and the role of apoC-III in the intestine

Abstract

The intestine plays a crucial role in regulating wholebody lipid homeostasis through dietary fat absorption and secretion, and through its endocrine secretions of incretin hormones and immune mediators. The intestine synthesizes a specialized lipoprotein, the chylomicron, which contains both dietary triglyceride (TAG) and cholesterol, in addition to both structural and functional apolipoprotein cargo. apoB-48 provides structure to the nascent chylomicron, while apoA-IV, apoA-I, and apoC-III function in the periphery to modify plasma lipid metabolism and clearance, interact with inflammatory apparatus for efficient clearance of dietary lipopolysaccharide and oxidized lipids, and modulate insulin signaling and glucose metabolism (1-3). Therefore, the intestine and its secreted chylomicron are critical regulators of metabolic disease.Despite the importance of the intestine in raising plasma TAG levels in the postprandial state and in apolipoprotein secretion, mechanistic studies are difficult to carry out. This is due to a lack of suitable ex vivo cell culture models that are nontransformed yet stable enough in culture for extended studies and genetic manipulations. The intestine is difficult to model ex vivo because enterocytes are in constant turnover, and are only replenished by intestinal stem cells

Key differences between apoC-III regulation and expression in intestine and liver

“…To determine how intestinal apoC-III is regulated, we utilized a primary intestinal enteroid culture system. Primary enteroids are derived from WT mouse duodenal and jejunal crypt stem cells, and we have previously established that this tissue culture system significantly improves upon Caco-2 cells as a model for dietary fat absorption and chylomicron secretion [16]. In Fig.…”

“…Because we have identified a unique consequence of apoC-III overexpression in the intestine (the inhibition of dietary fat absorption coupled with altered chylomicron secretion) [15,16], and because regulation of apoC-III in Caco-2 cell culture is so far removed from in vivo conditions that might regulate apoC-III, we wanted to establish the critical dietary factors in the regulation of intestinal apoC-III.…”

“…We isolated intestinal stem cells (ISCs) from crypts as described previously [16,24]. Primary crypts were isolated from WT mice, age 8–12 weeks.…”

“…We find that overexpression of apoC-III results in a delay in dietary lipid absorption and causes the secretion of smaller chylomicrons [15,16]. This is paradoxical to both the triglyceride-raising role apoC-III plays in the plasma, and cell culture data suggesting that intracellular apoC-III promotes the synthesis and secretion of larger, more triglyceride-rich VLDL from the liver [17,18,27].…”

Enteroids for Nutritional Studies

“…Enteroids have also been employed in a mitochondrial function study that demonstrated that the replacement of glucose with galactose increased crypt formation, differentiation, and mitochondrial activation . Of particular interest is the finding that metabolites (in particular butyrate) induced or produced by intestinal microbiota are able to inhibit colonic epithelial stem and progenitor proliferation . Basak et al.…”