Download Full Text

Alternative aspects of adipocyte function
H. J. Mersmann1
ARS, USDA, Children’s Nutrition Research Center, Baylor College of Medicine, Houston, TX 77030-2600
This symposium was conceived, organized, and presented by members of NCR-97—Regulation of Adipose
Accretion in Meat Animals. This group was organized
over 25 yr ago and has been continuously involved in
investigation of the biology of the adipocyte, the regulation of adipocyte hyperplasia and hypertrophy, and
modulation of adipose tissue accretion in animals raised
for meat production. Cattle, pigs, and sheep have been
the major subjects, with some investigators using poultry. Rodent models and cells in culture have added to
the scope of the research, particularly in regard to cellular and molecular mechanisms. In recent years, the
adipocyte has become a more popular target for investigation, partly because of the interest in problems associated with human obesity, and partly because it has
become known that adipose tissue is an endocrine organ
secreting a number of compounds that can act at other
sites in the body. This symposium presented concepts
of the adipocyte that deviate from the usual discussions
of endocrine and pharmacological regulation of anabolic
and catabolic lipid metabolism, and hyperplasia and
hypertrophy of the cells. The symposium was sponsored
by Elanco Animal Health, Monsanto, Pharmacia Animal Health, and the USDA/CSREES. The publication
costs were funded by USDA/ARS.
The first presentation was “Usefulness of in vitro
and in vivo experimental models,” by Jan Novakofski.
Clonal cell cultures were compared with primary cell
cultures. Although cell culture is an important tool to
investigate regulatory and signaling pathways, its use
to study metabolism presents difficulties because cells
in culture become predominantly catabolic. Gene
knockouts have been extremely useful to understand
the biology of the adipocyte. Mike Azain discussed “The
role of fatty acids in adipocyte growth and development.” Fatty acids have multiple roles in the adipocyte;
they are building blocks for phospholipid and triacylglycerol synthesis, they are oxidative substrates, and
they can regulate gene expression to modify adipocyte
growth and differentiation. Individual fatty acids differentially modulate gene expression in the adipocyte.
Gary Hausman discussed “Adipose tissue angiogenesis.” Blood vessel development is intimately tied to
adipocyte development. A number of factors and receptors have been implicated in angiogenesis. Hypoxia is
a major trigger to induce the angiogenic process. Some
of the same factors involved in angiogenesis may also be
involved in adipogenesis, and some evidence suggests
angiogenesis may control adipose tissue accretion. Jess
Miner discussed “The adipocyte as an endocrine cell.”
The discovery of leptin—a peptide produced by the adipocyte—which binds to receptors in the hypothalamus
to suppress feed intake, introduced the concept of the
adipocyte as an endocrine organ. A number of other
endocrine substances are produced by the adipocyte
(e.g., resistin, adiponectin, tumor necrosis factor-α,
adenosine). The physiological function of many of these
adipocyte-produced signals is yet to be clarified. Steve
Smith discussed “Metabolism and development of bovine brown adipose tissue.” The brown adipocyte is a
specialized type of cell for thermogenesis present in
various trunkal depots in most mammalian newborns,
including cattle. Newborn Angus calves have greater
nonshivering thermogenic capacity than Brahman
calves. This observation does not result from differences
in adipocyte morphology, mitochondrial morphology, or
uncoupling protein 1. The Brahman calf mobilizes more
lipid and seems to exhaust substrate for brown adipocyte themogenesis compared with the Angus calf. These
topics are thoroughly discussed in the accompanying
manuscripts.
1
Correspondence—e-mail: [email protected].
Received July 3, 2003.
Accepted August 18, 2003.
J. Anim. Sci. 2004. 82:904
904