WASHINGTON - UNITED States researchers have engineered a line of
'mighty mice' whose human equivalent would have similar abilities to
the bicycling champion Lance Armstrong, according to research published
on Thursday. The breed of mice can run six kilometres at a speed of 20 metres
per minute for up to six hours without stopping, according to
biochemistry professor Richard Hanson of the Case Western Reserve
University in Cleveland, Ohio. 'They are metabolically similar to Lance Armstrong biking up
the Pyrenees; they utilise mainly fatty acids for energy and produce
very little lactic acid,' said Prof Hanson, the senior author of the
article which was published in the Journal of Biological Chemistry. The genetically engineered mice can eat 60 per cent more than
wild mice in a control group but remain slim and fit. The 'mighty mice'
live longer, and some females were able to reproduce much later in life
than other mice. The researchers said some 'have had offspring at 2.5 years of
age, an amazing feat considering most mice do not reproduce after they
are one year old'.
Prof Hanson said the strength of the mice was made possible by
the fact that they produce very little lactic acid, which forms during
intense exercise.
Scientists bred 500 of the mice, which also showed more aggression than
other mice, over the past five years as part of a project aimed at
unlocking the metabolic and physiological function of PEPCK-C in
muscles and tissues.
The key to their unusual traits is the over-expression of the
gene that influence production of the enzyme PEPCK-C
(phosphoenolypyruvate carboxykinases), said Hanson. The transgenic mice are descended from six 'founder lines'
that 'contain a chimeric gene in which a copy of the cDNA for PEPCK-C
was linked to the skeletal actin gene promoter', the research said. The resulting mice showed different levels of PEPCK-C in
their muscles, but one particularly active group had levels of PEPCK-C
activity of nine units per gram of skeletal muscle, compared to just
0.08 units per gram in the muscles of control mice. 'From a very early age, the PEPCK-Cmus mice ran continuously
in their cages,' said Dr Parvin Hakimi, a researcher in the Hanson lab.
The 'mighty mice' primarily relied on 'fatty acids as a source
of energy during exercise, while the control animals rapidly switched
from fatty acid metabolism to using muscle glycogen (carbohydrates) as
a fuel; this dramatically raised the blood lactate levels', the
research said. -- AFP | 
