Background Stem cell therapy has generated much interest in improving the function of ischaemic myocardium and peripheral tissue, while non-invasively tracking stem cells in vivo is a hurdle for its clinical application. Our group has addressed this concern by developing a bioluminescence tomography (BLT) prototype system with micro-CT (MicroCT) registration approach. In this subsequent study, we aimed to assess the mesenchymal stem cells (MSCs) as well as statins by this multimodality imaging platform and other strategies in the model of peripheral arterial disease (PAD).
Methods MSCs were isolated from adipose tissue of the transgenic mice carrying double-fusion reporter genes: firefly luciferase and enhanced green fluorescent protein (Fluc-eGFP). After eGFP flow sorting, 1×107 of Fluc-eGFP positive MSCs were injected into the ischaemic hindlimb, created by routine ligation, of the adult nude mice (n=20) with/without rosuvastatin pretreatment. Then we imaged the animals by our 3D BLT and MicroCT modalities as well as a 2D bioluminescence imaging (BLI). Detailed quantitative reconstruction were performed within the mice by adaptive hp finite element method (hp-FEM). Histological and molecular analysis are used to confirm MSCs' location and angiogenesis.
Results 1 week after engraftment, reconstructed BLT total power in MSCs group was 22.4±3.1 nW, while the 2D BLI data was 1.7×106±2.1×105 photons/s/cm2/sr. The total power decreased gradually from week 1 to week 6, from mean 22.4 nW to 1.9 nW, demonstrating MSCs' survival and proliferation. The combined treat by MSCs and rosuvastatin exhibited longer signal and higher power of the MSCs (p<0.01), which is also confirmed by 2D BLI with robust correlation (r2=0.93). Moreover, BLT with MicroCT provided detailed 3D images of MSCs and angiogenesis in the hindlimbs. Immunohistology, RT-PCR and Western Blot showed that MSCs with/without rosuvastatin recovered vessel density in contrast to the control and its signal pathway.
Conclusions Versatile 3D molecular imaging modalities facilitate the super spatiotemporal visualisation and quantification of the MSCs in the ischaemic hindlimb, while MSCs hold beneficial potential for treating PAD and its survival environment in vivo may be promoted by rosuvastatin.