Probing microstructural changes in muscles of leptin-deficient zebrafish by non-invasive ex-vivo magnetic resonance microimaging

Leptin is a hormone that plays a key role in controlling food intake and energy homeostasis. Skeletal muscle is an important target for leptin and recent studies have shown that leptin deficiency may lead to muscular atrophy. However, leptin deficiency-induced structural changes in muscles are poorly understood. The zebrafish has emerged as an excellent model organism for studies of vertebrate diseases and hormone response mechanisms. In this study, we explored ex-vivo magnetic resonance microimaging (μMRI) methods to non-invasively assess muscle wasting in leptin-deficient (lepb-/-) zebrafish model. The fat mapping performed by using chemical shift selective imaging shows significant fat infiltration in muscles of lepb-/- zebrafish compared to control zebrafish. T2 relaxation measurements show considerably longer T2 values in the muscle of lepb-/- zebrafish. Multiexponential T2 analysis detected a significantly higher value and magnitude of long T2 component in the muscles of lepb-/- as compared to control zebrafish. For further zooming into the microstructural changes, we applied diffusion-weighted MRI. The results show a significant decrease in the apparent diffusion coefficient indicating increased constraints of molecular movements within the muscle regions of lepb-/- zebrafish. The use of the phasor transformation for the separation of diffusion-weighted decay signals showed a bi-component diffusion system which allows us to estimate each fraction on a voxel-wise basis. A substantial difference was found between the ratio of two components in lepb-/- and control zebrafish muscles, indicating alterations in diffusion behavior associated with the tissue microstructural changes in muscles of lepb-/- zebrafish as compared to control zebrafish. Taken together, our results demonstrate that the muscles of lepb-/- zebrafish undergo significant fat infiltration and microstructural changes leading to muscle wasting. This study also demonstrates that μMRI provides excellent means to non-invasively study the microstructural changes in the muscles of the zebrafish model.