Biology Reference
In-Depth Information
fat are consumed, some dietary fat is stored in cytoplasmic lipid droplets (CLDs).
The balance between storage and secretion of dietary fat by enterocytes is
important in determining the physiological fate of dietary fat, including regulating
blood lipid concentrations and energy balance. The existence of CLDs within
enterocytes has likely evolved for three important physiological functions: (i) to
allow the small intestine to efficiently absorb large amounts of energy dense fat,
(ii) to control the rate of dietary fat entering circulation, and (iii) to alleviate lipotoxi-
city to enterocytes induced by high concentrations of free fatty acids, especially
when a high fat meal is consumed. The purpose of this chapter is to provide methods
for imaging CLDs in enterocytes and assessing different aspects of dietary fat
absorption.
Abbreviations
CARS
coherent anti-Stokes Raman scattering
CLD
cytoplasmic lipid droplet
TAG
triacylglycerol
INTRODUCTION AND RATIONALE
The primary function of the small intestine is digesting and absorbing nutrients from
consumed food. In this chapter, we will focus on methods used to image cytoplasmic
lipid droplets (CLDs) in enterocytes and assess the process of dietary fat absorption.
The digestion and absorption of triacylglycerol (TAG) by the small intestine is a
highly efficient process with greater than 95% of dietary fat consumed being
absorbed. In the intestinal lumen, dietary fat, in the form of TAG, is hydrolyzed
to monoacylglycerol and fatty acids, incorporated into micelles, and presented to ab-
sorptive cells of the intestine, enterocytes, for uptake. Once in enterocytes, the diges-
tive products are reincorporated into TAGs, phospholipids, and cholesteryl esters.
These products are primarily packaged in chylomicrons for secretion into circulation
via the lymphatic system. However, under high fat feeding conditions, some of these
lipids are stored in CLDs within enterocytes (
Zhu, Lee, Buhman, & Cheng, 2009
).
The balance between lipid storage and secretion is a dynamic process. The postpran-
dial triglyceridemic response, or the increase and decrease in blood TAGs after a
meal, and lipid storage in CLDs are influenced by multiple factors, including the
amount of TAG, type of fatty acids consumed, other components of the meal, genet-
ics, time post meal, and time of day (
Lee, Fast, Zhu, Cheng, & Buhman, 2010; Lee,
Zhu, Wolins, Cheng, & Buhman, 2009; Uchida, Slipchenko, Cheng, & Buhman,
2011; Uchida et al., 2012, 2013
).
Amechanistic understanding of dietary fat absorption is essential for determining
factors important in regulating energy balance and blood lipid concentrations—
contributors to obesity, cardiovascular disease, and diabetes. This chapter begins
with an introduction to the small intestine for collection of tissue from mice for
