J. Adam Noah

Date of Award

1998

Degree Name

Biological Sciences

College

College of Science

Type of Degree

M.S.

Document Type

Thesis

First Advisor

E. Bowie Kahle

Second Advisor

Leonard J. Deutsch

Abstract

Mutant strains of obese rats are currently being studied to reveal the mechanisms of increased lipid synthesis and decreased lipid oxidation in these rats. It was originally thought that much of the fat production that leads to obesity is the result of metabolic processes in the liver and adipose tissue. Studies by Kahle et al.3 showed that the liver and adipose tissue account for only 22% and 7% respectively, of total fatty acid synthesis. It was also shown that 21 % of total de novo fatty acid was localized in the postural skeletal muscle.

The dry weight of the body is 40% skeletal muscle, thus it is likely that this tissue type has some role in controlling the body’s metabolism.1 Previous work has gone into characterizing differences present within the skeletal muscle of lean and obese phenotypes that may have an influence on metabolism. Electron microscopy was used to determine structural differences in skeletal muscle tissue as well as in myoblasts. It was shown that the myoblasts of the obese phenotype have a higher capacity metabolic synthesis. The work of this thesis was done in order to further investigate some of these previously studied parameters. The focus of this work was to characterize differences in metabolic potential in skeletal muscle myoblasts of the obese and lean phenotypes of the rodent model, the LA/Nfat rat.

One important parameter in question is the amount of intracellular lipid deposits present within the individual myoblasts. To determine differences between the two phenotypes, confocal microcopy was used to visually observe, with a lipid specific probe nile red, both intracellular lipid concentration and lipid distribution within the cell. After digitally capturing micrographs into specifically designed computer software, it was possible to determine the amount of fluorescence present within a single cell in a culture. Post-natal (14 days of age) animals were also studied in the same manner to determine if pre-obese pups (Figure 1b) showed the same situation as their adult counterparts.

The results of the experiment indicated a significant difference (p < 0.50) present within the lipid content between obese and lean adult rats. The same situation was not shown in post-natal animals. The size of the cells studied however, differed significantly (p < 0.05) between the two age groups studied, but not within them. This difference may be directly attributable to the increased rate of mitosis of the post-natal myoblasts. This increased rate of mitosis may also explain the similarity in lipid content of the obese and lean pups. Another parameter briefly examined was the role of the mitochondria in the metabolism of the cell. No results were attained from the mitochondrial studies.

Skeletal muscle has recently been proven to be an important tool in the delivery of proteins and drugs throughout the body. It has been shown that hybrid skeletal muscle myotubes can be used to deliver such necessary proteins as dystrophin and human growth hormone.33-37 Using this type of myoblast-mediated gene therapy it may be possible with continued study to determine regulatory hormones in lipid metabolism. These hormones when delivered to the body in the correct manner may be used as an effective means to not only study the effect of certain drugs on metabolism but perhaps as an effective treatment to obesity.

Subject(s)

Obesity – Research.

Myoblasts.

Lipids – Metabolism.

Lipids – Synthesis.

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