A Bioassay-Guided Fractionation of Rosemary Leaf Extract Identifies Carnosol as a Major Hypertrophy Inducer in Human Skeletal Muscle Cells.

A good quality of life requires maintaining adequate skeletal muscle mass and strength, but therapeutic agents are lacking for this. We developed a bioassay-guided fractionation approach to identify molecules with hypertrophy-promoting effect in human skeletal muscle cells. We found that extracts from rosemary leaves induce muscle cell hypertrophy. By bioassay-guided purification we identified the phenolic diterpene carnosol as the compound responsible for the hypertrophy-promoting activity of rosemary leaf extracts. We then evaluated the impact of carnosol on the different signaling pathways involved in the control of muscle cell size. We found that activation of the NRF2 signaling pathway by carnosol is not sufficient to mediate its hypertrophy-promoting effect. Moreover, carnosol inhibits the expression of the ubiquitin ligase E3 Muscle RING Finger protein-1 that plays an important role in muscle remodeling, but has no effect on the protein synthesis pathway controlled by the protein kinase B/mechanistic target of rapamycin pathway. By measuring the chymotrypsin-like activity of the proteasome, we found that proteasome activity was significantly decreased by carnosol and Muscle RING Finger 1 inactivation. These results strongly suggest that carnosol can induce skeletal muscle hypertrophy by repressing the ubiquitin-proteasome system-dependent protein degradation pathway through inhibition of the E3 ubiquitin ligase Muscle RING Finger protein-1.

Potential role of Shh-Gli1-BMI1 signaling pathway nexus in glioma chemoresistance.

Chemoresistance is a common hurdle for the proper treatment of gliomas. The role of Shh-Gli1 signaling in glioma progression has been reported. However, its role in glioma chemoresistance has not been well studied yet. In this work, we found that Shh-Gli1 signaling regulates the expression of one stem cell marker, BMI1 (B cell-specific Moloney murine leukemia virus), in glioma. Interestingly, we also demonstrated high expression of MRP1 (multi-drug resistance protein 1) in glioma. MRP1 expression was decreased by BMI1 siRNA and Shh-Gli1 cell signaling specific inhibitor GANT61 in our experiments. GANT61 very efficiently inhibited cell colony growth in glioma cell lines, compared to temozolomide. Moreover, a synergic effect of GANT61 and temozolomide drastically decreased the LD50 of temozolomide in the cell colony experiments. Therefore, our results suggest that there is a potential nexus of Shh-Gli1-BMI1 cell signaling to regulate MRP1 and to promote chemoresistance in glioma. Henceforth, our study opens the possibility of facing new targets, Gli1 and BMI1, for the effective treatment of glioma suppression of chemoresistance with adjuvant therapy of GANT61 and temozolomide.