Figure 8. Stromal miR-21 leads to tumor progression in an in vivo orthotopic CRC model. (A) Confocal microscopy of tumor section generated by subcutaneous co-injection of PKH26-labeled MRC5 fibroblasts (red) and CRC cells, counterstained with DAPI (blue; 60x). (B) Liver (L), spleen (S) and colon from mice orthotopically injected with SW620 CRC cells and MRC5 control or miR-21-overexpressing fibroblasts. Arrowheads highlight liver metastases. The effect of miR-21-overexpressing cells was to increase the size and number of liver metastases. No splenic metastases were seen in either group. (C) Representative liver sections at 2x and 100x magnification. Bulky hepatic metastases are evident in the SW620/MRC5-miR-21 liver (arrowheads; 2x) with a clear histological demarcation between normal liver and metastatic tumor (NT – normal tissue, T – tumor; 100x). (D) Percentage liver replacement by metastatic tumor in SW620/MRC5-control (control) and SW620/MRC5-miR-21 (miR-21) mice. Data is presented as mean +/- SEM. Student’s t-test: *** p<0.001.