Mechanism Of Tumor-derived Exosome-mediated Adipose Tissue Atrophy In Cancer Cachexia

Cancer-associated cachexia(CAC)is a tumor-induced systemic metabolic disorder syndrome.Adipose tissue atrophy is one of the common symptoms of cancer cachexia,which is characterized by disorder of lipid metabolism,which ultimately leads to a reduction in fat quality and seriously affects patients' quality of life and survival.So far,there is no effective treatment in the clinic to alleviate adipose tissue atrophy.Therefore,in order to explore better therapeutic effects,it is important to explore the novel molecular mechanism of cancer cachexia.The mechanism for promoting the development of cachexia is complicated.Some cytokines secreted by the tumor interact with factors produced by the body itself,contributing to CAC.Exosomes,as one kind of extracellular vesicles with a size of 30-150 nm secreted by nearly all types of cells,can mediate the transmission of information between cells through many bioactive substances such as proteins,nucleic acids and lipids carried by them.However,studies on adipose tissue atrophy caused by exosomes in cancer cachexia have not been reported.Our team studied the relationship between tumor cell-derived exosomes and cancer cachexia in vivo and vitro.Our research consists of the following two parts:Part ? Adipose tissue browning in cancer-associated cachexia can be attenuated by inhibition of exosome generationPurpose: In this study,we investigate if exosomes from Lewis lung carcinoma(LLC)cells can induce lipolysis in vitro(in 3T3-L1 adipocytes)and in vivo(in tumor-bearing mice).Methods: In vitro,we added the exosome derived from LLC cells to adipocytes,and at the same time,we used GW4869 and the molecular level to knock down Rab27 A by sh RNA to inhibit the release of exosomes from LLC cells.We observe the changes of lipid metabolism in adipocytes.In vivo,we injected GW4869 into the tumor of mice to observe the symptoms of cachexia and adipose tissue atrophy in mice.Results: We find that exosomes from LLC cells do induce lipolysis in 3T3-L1 adipocytes and adipose tissues of mice with LLC tumors.We also find that this lipolysis can be inhibited using the neutral sphingomyelinase inhibitor GW4869.Our results indicate that GW4869 not only inhibits exosome generation and release from LLC cells,but can also inhibit lipolysis induced by LLC-derived exosomes in 3T3-L1 adipocytes.Furthermore,we also demonstrate that adipose tissue atrophy and cachexia in LLC tumor-bearing mice treated with GW4869 can be improved.In summary,our results suggest that inhibiting exosome generation and release can inhibit lipolysis and adipose tissue browning,and may be useful as a novel strategy for treating CAC.Conclusions: LLC cell-derived exosomes can result in enhanced lipid degradation both in vivo and in vitro.Part ? Exosome-released parathyroid hormone-related protein from Lewis lung carcinoma induces lipolysis and adipose tissue browning in cancer cachexiaPurpose: In the first part,we found that tumor cell-derived exosomes are involved in lipolysis and cachexia.In the second part,we will explore the further mechanism.Methods: The expression of parathyroid hormone-related protein(PTHr P)was detected in LLC-exos.After the adopocytes treated with PTHr P neutralizing antibody,the effects of exosomes and PTHr P on lipolysis were detected.Meanwhile,the adipose atrophy of cachexia caused by LLC knocking down Rab27 A and the plasma PTHr P and exosomes were detected.Results: exosomes fused directly with target 3T3-L1 adipocytes and transferred parathyroid hormone-related protein(PTHr P),activating the PKA signaling pathwayand induced lipolysis in adipocytes.Blocking PTHr P activity in LLC-exos using a neutralizing antibody and by knocking down PTHR expression prevented lipolysis in adipocytes.Inhibiting the PKA signaling pathway also prevents the lipolytic effects of exosomes.In vivo,suppression of LLC-exos release by knocking down Rab27 A alleviated white adipose tissue browning and lipolysis.Conclusions: Our data demonstrate that LLC-exos induce lipolysis in vitro and vivo by delivering PTHr P,which interacts with PTHR.