Table 2. Effect of IRE1² deficiency in ApoE knockout mice on intestinal lipid transport.
Apoe−/− and Ire1b−/−/Apoe−/− male mice were fed a chow diet for 12 months or a western diet for 6 weeks. (A) Mice were fasted overnight and injected intraperitoneally with poloxamer 407 (30 mg/mouse). After 1 h, mice were fed 0.5 µCi of [3H]triolein or [14C]cholesterol with 0.2 mg of cholesterol in 15 µL of olive oil. Plasma was collected after 2 h and used to measure triolein and cholesterol counts. Plasma was also used to measure triglyceride and cholesterol mass. Proximal intestinal segment (~10 cm long) was solubilized and used to determine radioactivity. (B) Enterocytes were isolated from overnight fasted mice and incubated for 1 h with 0.5 µCi/ml of [3H]oleic acid or [3H]cholesterol. Enterocytes were washed and lipids were isolated to determine uptake of radiolabel oleic acid or cholesterol. Each measurement was done in triplicate with 3 mice per group. For secretion studies, enterocytes were isolated from overnight fasted mice, labeled for 1 h with 0.5 µCi/ml of [3H]oleic acid or [3H]cholesterol, washed and incubated with fresh media containing 1.4 mM oleic acid containing micelles. Media from oleic acid-labeled enterocytes was separated by thin layer chromatography to measure triglycerides and phospholipids. Media from cholesterol labeled enterocytes was directly quantified. Each measurement was done in triplicate.
| Apoe−/− (n) | Ire1b−/−/Apoe−/− (n) | Apoe−/− (n) | Ire1b−/−/Apoe−/− (n) | |
|---|---|---|---|---|
|
Chow diet fed |
Western diet fed |
|||
| A. Lipid absorption in mice: | ||||
| Plasma lipid mass (mg/dl) | ||||
| Triglycerides | 1550.2 ± 198.1 (4) | 2084.9 ± 167.5 (4)* | 1131.4 ± 71.1 (4) | 1557.7 ± 117.7 (4)** |
| Cholesterol | 1548.4 ± 233.7 (4) | 2076.4 ± 167.4 (4)* | 2371.4 ± 204.6 (4) | 3134.8 ± 216.7 (4)** |
| Plasma radioactivity (dpm/ml) | ||||
| [3H]Triolein | 39617 ± 5699 (4) | 58229 ± 6756 (4)* | 28624 ± 2699 (4) | 44351 ± 4353 (4)* |
| [14C]Cholesterol | 13080 ± 2003 (4) | 18735 ± 2297 (4)* | 9721 ± 1012 (4) | 16318 ± 1377 (4)** |
| Intestinal radioactivity (dpm/g tissue) | ||||
| [3H]Triolein | 224794 ± 38107 (4) | 188416 ± 30089 (4) | ND | ND |
| [14C]Cholesterol | 112552 ± 20185 (4) | 94330 ± 7997 (4) | ND | ND |
| B. Uptake and secretion of lipids by enterocytes: | ||||
| Lipid uptake (dpm/mg protein) | ||||
| Oleic acid | 290620 ±30506 (3) | 280441 ± 28029 (3) | ND | ND |
| Cholesterol | 305779 ± 28048 (3) | 341641 ± 61933 (3) | 340174 ± 24801 (3) | 374769 ± 29077 (3) |
| Lipid secretion (dpm/mg protein) | ||||
| Triglycerides | 63971 ± 7071 (3) | 110685 ± 23446 (3)* | ND | ND |
| Phospholipids | 18235 ± 2288 (3) | 25381 ± 3849 (3) | ND | ND |
| Cholesterol | 37382 ± 5871 (3) | 56306 ± 5137 (3)* | 41140 ± 4196 (3) | 67383 ± 4123 (3)*** |
Values are mean ± SD, n =3.
p<0.05,
p<0.01, and
p<0.001 compared to Apoe−/−. ND, not determined.