| Cancer cachexia is defined as a multifactorial syndrome characterised by an ongoing loss of skeletal muscle mass(with or without loss of fat mass)that cannot be fully reversed by conventional nutritional support and leads to progressive functional impairment.Approximately more than 50% cancer patients develop the syndrome,which associated with reduced physical function,reduced tolerance to anticancer therapy,reduced survival and accounts for nearly 20% of all cancer deaths.The muscle loss,with the other name sarcopenia,is the key characteristic of cancer cachexia and is a very powerful prognostic factor,independent of the actual body weight loss.Despite a significant increase in research on cancer cachexia,limited therapeutic options are available and the underlying mechanisms are still poorly defined.Several studies measuring muscle protein turnover in cancer patients showed that muscle protein synthesis was not decreased and increase in protein breakdown might be the main mechanism accounting for muscle wasting in patients with cancer.In the present study,we firstly investigated the association between computed tomograph-quantified body composition and short-term outcomes after gastrectomy for gastric cancer,aiming to identify valuable new prognostic indicators.Then,we determined the synthesis and catabolism in skeletal muscle of gastric cancer patients using a series of techniques including light microscopy,electron microscopy,Western blot,q PCR,immunohistochemistry,exploring the molecular mechanism of the muscle loss in cancer cachexia.At last,we examined the differentially expressed proteins in the skeletal muscles of gastric cancer patients with or without cancer cachexia by quantitative proteomics technology and explored the biological function of those proteins,which contributed to systemically reveal the pathogenesis and mechanism of muscle loss in cancer cachexia.The results of this study will provide theoretical basis and therapeutic ideas for the clinical treatment of cancer cachexia.PART I Computed tomography-quantified body composition predicts short-term outcomes after gastrectomy in gastric cancerObjective: Malnutrition is a common and critical problem that influences outcome in cancer patients.Body composition reflects a patient’s metabolic profile and physiologic reserves,which might be the true determinant of prognosis.In the present study,which aimed to identify valuable new prognostic indicators,we investigated the association between computed tomography-quantified body composition and short-term outcomes after gastrectomy for gastric cancer.Methods: Skeletal muscle index,mean muscle attenuation,and ratio of visceral-to-subcutaneous fat area(VSR)were calculated from preoperative computed tomography images.Low skeletal muscle index,low mean muscle attenuation and high VSR were respectively termed “sarcopenia”,“myosteatosis” and “visceral obesity”.The association of body composition with postoperative complications and serum markers of nutrition and inflammation after radical gastrectomy were analyzed.Results: The overall complication rate was significantly higher in the sarcopenia(62.5% vs.27.3%,p = 0.001)and myosteatosis groups(38.2% vs.4%,p = 0.002).Patients with visceral obesity had a higher incidence of inflammatory complications(20.3% vs.6.5%,p = 0.01).Multivariate logistic regression analysis demonstrated that sarcopenia(p = 0.013),myosteatosis(p = 0.017)and low serum retinol-binding protein(p = 0.019)were independent risk factors for overall complications.Compared with control subjects,patients with sarcopenia had lower postoperative levels of serum retinol-binding protein(p = 0.007),and patients with visceral obesity had higher levels of C-reactive protein(p = 0.026).Conclusions: Sarcopenia,myosteatosis,and visceral obesity were significantly associated with increased rates of postoperative complications and affected the postoperative nutrition and inflammation status of patients with gastric cancer.PART II The molecular mechanism of muscle loss in cachexia induced by gastric cancerObjective: An impaired balance between muscle synthesis and breakdown leads to the development of muscle loss.In this study,we detemined the activity of autophagy-lysosome system(ALS),ubiquitin-protease system(UPS)and m TOR pathway in the rectus muscle of gastric cancer patients,which will help to elucidated the molecular mechanism of cancer cachexia.Method: 39 patients with resectable gastric cancer were divided into four groups based on the presence of cachexia(weight-loss)and/or sarcopenia(low musclularity)including non-cachexia and non-sarcopenia group(N group),cachexia and sarcopenia group(CS group),cachexia and non-sarcopenia group(C group),sarcopenia and non-cachexia group(S group).The biopsies of rectus muscle were obtained intraoperatively.The muscle fiber size and ultrastructural architecture,muscle expression of markers of ALS,UPS and m TOR pathway were analyzed between groups.Results: The muscle fiber cross-sectional areas were significantly decreased in CS and S groups compared to N group or C group.Compared with N group,the muscle ultrastructure exhibit tissue disorganization and autophagosomes formed in the other three groups.The expressions of autophagic markers including Beclin-1,LC3 B and P62/SQSTM1,were significantly increased in CS,C and S groups compared with N group and it was even higher in CS and S groups than C group.As for the expressions of UPS markers,the level of MURF1 and Ub proteins were upregulated in CS,especially in CS group compared with N group.However,there was no difference in Atrogin-1 level among the four groups.The expression of p-m TOR,which reflects the protein synthesis in muscle,has no significant difference among those four groups.The expression of p-AMPK,which plays as energy sensor in cell,was significantly upregulated in CS,C and S groups comparing to N group.Conclusion: ALS and UPS were activated in muscle of cachexia patients especially those with severe muscle loss but not those with obvious weight loss,which account for the muscle loss of cancer cachexia.PRAT III Comprehensive proteome analysis of skeletal muscle in gastric cancer patients with cachexia and sarcopeniaObjective: In this study,we analyzed the differentially expressed proteins in skeletal muscle of gastric caner patients with cachexia and sarcopenia(CS group)compared with non-cachexia and non-sarcopenia(N group)patients by quantitative proteomics technology and bioinformatics analysis to screen out the key protein and pathway contributing to muscle loss induced by cancer cachexia.Methods: The biopsies of rectus muscle of 3 CS patients and 3 N pateins were obtained and the total protein were extracted and quantitfied.Then,TMT proteomic experiments were used to identify and quantify the peptides and proteins.The differentially expressed proteins were analyzed by GO,KEGG pathway and STRING interaction analysis.Results: 2621 proteins were detected and the total of differentially expressed proteins were 114,among which there were 73 up-regulated and 41 down-regulated in CS group compared to N group.The functional groups of the differentially expressed proteins were analyzed by bioinformatics.It showed that the three most pronounced functional groups were muscle contraction and its regulation,substate/energy metabolism,cell catabolism and death.The upregulation of protein involved in muscle contraction and its regulation reflected the increased breakdown of muscle filaments and the enhanced catabolism of cancer cachexia.The distinct modification of substate/energy metabolism in muscle of cancer cachexia is characterized by carbohydrate metabolism change and mitochondrial dysfunction.The disturbance of energy metabolism in muscle is one of the important causes of muscle breakdown and loss.It also showed in the study that cell catabolism system such as autophagy-lysosome pathway and the programmed cell death including necroptosis and ferroptosis were activated,which might lead to the muscle loss in cancer cachexia.Conclusion: Our proteome analysis showed that the abnormal energy metabolism and the inceased catabolism and programed cell death of muscle might be the important leading cause of muscle loss in cancer cachexia.This study provides a basis and new direction for future mechanistic investigations of muscle loss in cancer cachexia. |
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