Differential gene expression between adipsoe depots in cancer cachexia

Cancer cachexia (CC) is a poorly understood cause of morbidity and mortality, which has no efficacious treatment or generally-accepted management strategy. The consensus definition for CC identified skeletal muscle loss as a key marker in the diagnosis and classification of cachexia. The importance of fat wasting however, is less understood. During cachexia, different adipose depots demonstrate differential wasting rates. Studies from animal models have suggested adipose tissue may be a key driver of muscle wasting through fat-muscle crosstalk but human studies in this area are lacking. We performed global gene expression profiling of intra-abdominal (IAAT) and subcutaneous (SAT) adipose from weight stable and cachectic cancer patients and healthy controls. Cachexia was defined as >2% weight loss plus low CT-muscularity. Biopsies of SAT and IAAT were taken from patients undergoing resection for oesophago-gastric cancer, and healthy controls (donor nephrectomy) (n=16 and 8 respectively). RNA was isolated and reverse transcribed. cDNA was hybridised to the Affymetrix Clariom S Microarray and data was analysed using R/Bioconductor. Differential expression of genes was assessed using empirical Bayes and moderated-t-statistic approaches. Category enrichment analysis was used with a tissue-specific background to examine the biological context of differentially expressed genes. Selected differentially regulated genes were validated by qPCR. ELISA for Intelectin-1 was performed on IAAT samples for the corresponding patients. The current cohort plus 12 additional patients from each group also had plasma Intelectin-1 ELISA carried out. In IAAT versus SAT comparisons there were 2101, 1722 and 1659 significantly regulated genes in the cachectic, weight stable and control groups respectively. There were 2200 significantly regulated genes from IAAT in cachectic patients compared to controls and 1253 significantly regulated genes from IAAT in weight stable cancer patients compared to controls. The gene showing the largest difference in expression was Intelectin-1 (Omentin-1) (FDR corrected p=0.0001); a novel adipocytokine associated with weight loss in other groups. Genes involving inflammation were enriched in cancer and control IAAT versus SAT though different groups of genes contributed. Energy metabolism and fat browning genesets were downregulated in cancer IAAT as were key fat browning genes (e.g. UCP1). SAT and IAAT have unique gene expression signatures. IAAT is metabolically active in cancer, and maybe a target for therapeutic manipulation. IAAT may play a fundamental role in cachexia, but the downregulation of energy metabolism genes implies a limited role for fat browning in human cachectic patients, in contrast to pre-clinical models. 8 patients from 3 groups (cancer cachexia, cancer weight stable and control) were included. Gene expression in visceral and subcutaneous adipose tissue from each subject was analysed using the Clariom S microarray platform.