Icaritin requires phosphatidylinositol 3kinase/Akt signaling to counteract skeletal muscle atrophy following mechanical unloading

OBJECTIVE Skeletal muscle undergoes rapid and profound atrophy in response to decreased mechanical loading,e.g.,limb immobilization and bed rest.Phosphatidylinositol 3 kinase(PI3K)/Akt signaling pathway is critical for regulating the balance between protein synthesis and degradation during disuse/inactivity-induced muscle atrophy.The present study aimed to investigate whether natural product Icaritin(ICT)required PI3K/Akt signaling to exert counteractive effect on skeletal muscle atrophy following mechanical unloading.METHODS Two oral dosages of ICT(80and 120mg·kg-1·d-1)were administrated daily to adult male rats with or without daily injection of PI3K/Akt signaling inhibitor wortmannin(15μg·kg-1·d-1)during 28-d hindlimb suspension(HS).Ex vivo muscle functional testing,histological and immunohistochemical analysis were performed to determine the changes of soleus muscle function,mean muscle fiber cross-sectional area(CSA)and fiber type distribution.Western blot and real-time PCR analysis were also performed to evaluate the protein or mRNA expression of the markers involved in PI3K/Akt signaling pathway.RESULTS After 28-d HS,soleus muscle underwent profound muscle atrophy(-52.7% muscle mass vs.pre-HS baseline).The high dose ICT treatment significantly attenuated the decreases in soleus muscle mass(+22.6% vs.HS),muscle fiber CSA(+52.8% vs.HS),as well as the muscle functional testing parameters during the unloading.Molecularly,the high dose ICT treatment significantly attenuated the decreases in protein synthesis markers at protein levels(phosphorylation of Akt and its downstream proteins)during the unloading,whereas the increases in protein degradation markers at mRNA(atrogin-1and MuRF-1)and protein(nuclear FOXO1 and FOXO3a)levels during the unloading were significantly attenuated by the high dose ICT treatment.The low dose ICT treatment moderately attenuated the above changes induced by the unloading.Mechanistically,Wortmannin could abolish the above effects of ICT.CONCLUSION ICT requires participation of PI3K/Akt signaling to counteract skeletal muscle atrophy following mechanical unloading in a dose-dependent manner.

Photodynamic therapy-mediated modulation of inflammatory cytokine production by Epstein–Barr virus-infected nasopharyngeal carcinoma cells

Nasopharyngeal carcinoma(NPC)is a malignant disease associated with Epstein–Barr virus(EBV)infection.This study aims to examine the effects of EBV infection on the production of proinflammatory cytokines in NPC cells after the Zn-BC-AM photodynamic therapy(PDT)treatment.Cells were treated with the photosensitiser Zn-BC-AM for 24 h before light irradiation.Quantitative ELISA was used to evaluate the production of cytokines.Under the same experimental condition,HK-1-EBV cells produced a higher basal level of IL-1a(1561 pg/ml),IL-1b(16.6 pg/ml)and IL-8(422.9 pg/ml)than the HK-1 cells.At the light dose of 0.25–0.5 J/cm2,Zn-BC-AM PDT-treated HK-1-EBV cells were found to produce a higher level of IL-1a and IL-1b than the HK-1 cells.The production of IL-1b appeared to be mediated via the IL-1b-converting enzyme(ICE)-independent pathway.In contrast,the production of angiogenic IL-8 was downregulated in both HK-1 and HK-1-EBV cells after Zn-BC-AM PDT.Our results suggest that Zn-BC-AM PDT might indirectly reduce tumour growth through the modulation of cytokine production.