Anabolic Response to Testosterone in Transgenic Mice with Knocked-down Androgen Receptor in Skeletal Muscle Fibers

1

• Anabolic Response to Testosterone in Transgenic
  Mice with Knocked-down Androgen Receptor in
  Skeletal Muscle Fibers

Cindy D. Knaff, Douglas A. Monks, Ph.D., Cynthia
L. Jordan, Ph.D. Neuroscience Program and
Department of Psychology, Michigan State
University
STATISTICAL ANALYSES
RESULTS
INTRODUCTION

• Testosterone is an anabolic steroid hormone which
  increases muscle mass
• and regulates both size and number of levator ani
  (LA) muscle fibers

• Paired t-tests were used to examine mean
  differences in LA muscle
• fiber diameter and number of wild type and
  transgenic mice.

• No significant differences in mean diameter of
  muscle fibers and number were
• observed between animal groups
• Although, no significant differences were found,
  the number of muscle fibers
• between animal groups borders on significance.
• A larger sample size is needed in order to
  clarify and extend the results from
• the current study

• The LA muscle skeletal muscle is sexually
  dimorphic, very sensitive to
• the androgen testosterone and provides a useful
  model for understanding how
• anabolic steroids affect skeletal muscle
• Previous research has shown that testosterone
  acts on androgen receptors
• (AR) in skeletal muscle to regulate size and
  number of muscle fibers
• LA muscle fiber, fibroblasts and endothelial
  cells express AR
• This study determines whether the AR in LA
  muscle fibers themselves regulate
• LA muscle fiber size and number by studying a
  line of transgenic mice whose AR expression has
  been lowered in skeletal muscle fibers.

Graph 1.

CONCLUSIONS

• The results suggest that AR in LA muscle fibers
  may regulate LA
• muscle fiber number.
• Androgens can increase the number of LA muscle
  fibers in
• development and not in adulthood.
• Thus, the present results suggest that lowering
  the number
• of androgen receptors in developing LA muscle
  fibers will
• interfere with the effect of androgen on fiber
  number.

OBJECTIVE

• To determine whether the AR in LA muscle fibers
  regulates LA muscle size
• and number

Graph 2.
METHODS

• LA muscle was harvested from three transgenic and
  three wild type mice
• Muscles were sectioned in twelve micron sections
  with a cryostat, two slides
• per animal, six LA muscle sections per slide
• An HE stain was performed on all slides
• Cross sectional area of LA muscles were
  measured in micrometers using images captured at
  4x and imageJ public domain software
• Cross sectional area of individual LA muscle
  fibers were measured in micrometers using images
  captured at 40x and the minor axis of a fitted
  ellipse is used as a measure of muscle fiber
  diameter
• Muscle fiber number was estimated by multiplying
  cross sectional area by counts of individual
  muscle fibers sampled from three 40x images

FUTURE DIRECTIONS

• Examine the spinal cords from these same wild
  type and transgenic
• mice because the motoneurons that innervate the
  LA are also sensitive
• to androgen
• Increase our sample size for all measures

Figure A. Low magnification view of a cross
section of a LA Muscle
Table 1.
REFERENCES

• Breedlove, S.M., and A. P. Arnold (1983) Hormonal
  Control of a developing neuromuscular system. I.
  Complete demasculinazation of the male rat spinal
  nucleus of the bulbocavernosus using the
  anti-androgen flutamide. J. Neurosci. 3 417-423.
• Breedlove, S.M., and A. P. Arnold (1983) Hormonal
  Control of a developing neuromuscular system. II.
  Sensitive periods for the androgen-induced
  masculinization of the rat spinal nucleus of the
  bulbocavernosus. J. Neurosci. 3 424-432.
• Christensen, S. E., S. M. Breedlove, and C. L.
  Jordan (2000) Sexual Differentiation of a
  Neuromuscular System. Sexual Differentiation of
  the Brain 149-169.

Table 2.
ACKNOWLEDGEMENTS
The Breedlove Jordan Lab - Michigan State
University - Neuroscience Program
Figure B. High magnification view of cross
sectioned LA Muscle