McMaster University, Canada
The maintenance of a metabolically active
skeletal muscle mass is to a great extent underappreciated, particularly
where optimal health is concerned. Skeletal muscle, besides its obvious
role in locomotion, is a highly important thermogenic (i.e., energy
consuming) tissue and the prime determinant of our basal metabolic rate,
which for most of us is the largest single contributor to daily energy
expenditure. Hence, declines in skeletal muscle mass can lead to
increases in body fat mass. Because of its oxidative capacity (i.e.,
mitochondrial content) skeletal muscle is also a large site of fat
oxidation, potentially playing a role in maintaining lipoprotein
(cholesterol) and triglyceride homeostasis. Skeletal muscle is also,
mostly by virtue of its mass, the primary site of blood glucose
disposal; hence, maintaining skeletal muscle mass would also play a role
in reducing risk for development of type II diabetes. Finally, the
decline in maximal aerobic capacity with age, and with other muscular
wasting conditions, including weight loss, has also been found to be
due, to a large degree, to a decline in skeletal muscle mass and
skeletal muscle quality. My research program has at its centre the
following research question, what factors serve to maintain, increase,
or decrease skeletal muscle mass? In addition, my research does not only
address the absolute mass of skeletal muscle, but also its quality as
assessed by the quantity of force it can generate, but also by the
metabolic activity of various enzymes and energy consuming pathways.
We use a human model of resistance or aerobic exercise, immobilization, or aging to study the processes that govern: muscle accretion, in the case of resistance exercise; atrophy, in the case of immobilization; and sarcopenia, in the case of aging. In addition, my research group has studied the interaction of feeding different protein composition and varied meal timing on the processes regulating hypertrophy and disuse atrophy. We employ stable isotope tracers of amino acids to metabolically trace the fate of ingested proteins. Muscle biopsies provide us with mechanistic information regarding processes that regulate protein accretion and degradation. We use Western blotting, RT-PCR, histological, and immunohistochemical methods to examine these mechanisms. I am also very interested in conditions in which muscle wasting occurs, particularly in the elderly.