Obesity is a widespread problem across the leisure population of horses and ponies in industrialised nations. Skeletal muscle is a major contributor to whole body resting energy requirements and communicates with other tissues through the secretion of
myokines into the circulation.
Myostatin, a
myokine and negative regulator of skeletal muscle mass, has been implicated in
obesity development in other species. This study evaluated gene and
protein expression of
myostatin and its receptor, ActRIIB in adipose tissues and skeletal muscles and serum
myostatin concentrations in six lean and six obese animals to explore putative associations between these factors and
obesity in horses and ponies.
Myostatin mRNA expression was increased while ActRIIB
mRNA was decreased in skeletal muscles of obese animals but these differences were absent at the
protein level.
Myostatin mRNA was increased in crest fat of obese animals but neither
myostatin nor ActRIIB
proteins were detected in this tissue. Mean circulating
myostatin concentrations were significantly higher in obese than in lean groups; 4.98 ng/ml (±2.71) and 9.00 ng/ml (±2.04) for the lean and obese groups, respectively. In addition, there was a significant positive association between these levels and
myostatin gene expression in skeletal muscles (average R2 = 0.58; p<0.05). Together, these results provide further basis for the speculation that
myostatin and its receptor may play a role in
obesity in horses and ponies.