Skeletal muscle extracellular matrix remodelling after aestivation in the green striped burrowing frog, Cyclorana alboguttata

Connective tissue has recently been found to play a role in mediating mammalian skeletal muscle atrophy. We investigated connective tissue remodelling in the skeletal muscle of a species of the Australian burrowing frog, Cyclorana alboguttata. Despite being inactive whilst aestivating, the frog shows an inhibition of muscle atrophy. Connective tissue size and distribution was measured in histological sections of the cruralis muscle of control and aestivating C. alboguttata. Using a custom written software application we could detect no significant difference in any connective tissue morphological parameter between the two treatment groups. Biochemical measurements of gelatinase activity showed 2-fold higher activity in aestivating gastrocnemius muscle than in controls (p < 0.001). We measured the messenger RNA transcript levels for C. alboguttata metalloproteinase 2 (MMP2) and tissue inhibitor of metalloproteinase 2 (TIMP2) in cruralis skeletal muscle using quantitative real-time PCR. The trend of reduced expression of the two genes in the aestivators did not meet statistical significance. This work indicates that aestivation in C. alboguttata leads to subtle and specific changes in some extracellular matrix remodelling factors. Their main impact is to maintain proportional representation of extracellular matrix components of skeletal muscle and therefore preserve the active frog phenotype.