Submitted to: Physiological Genomics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/2/2010
Publication Date: 5/3/2010
Citation: Barb, C.R., Hausman, G.J., Lents, C.A., Lkhagvadorj, S., Qu, L., Cai, W., Couture, L., Wang, L., Rekaya, R., Nettleton, D. 2010. Gene expression in hypothalamus, liver and adipose tissues and food intake reponse to melanocortin-4 receptor (MC4R) agonist in pigs expressing MC4R mutations. Physiological Genomics. 41:254-268. Interpretive Summary: A recently discovered class of receptors, melanocortin-3 and 4-receptor (MC3/4R), are located within the brain that modulate feed intake in mammals. Stimulation of the receptor (agonist) inhibits feed intake. Several mutations (genotype) in the MC4R gene have been reported in the pig. It is possible that the MC4-receptor mutation alters MC4-function. Our knowledge of how these different genotypes regulate voluntary feed intake in pig is very limited. Administration of a MC4R agonist, melanocortin stimulating hormone (MSH), suppressed feed intake similarly in all pigs regardless of mutation expressed. At 24 hours post-injection brain, liver and back fat was collected and gene expression analysis was conducted. MSH treatment altered 5070, 253 and 282 genes in back fat tissue, liver and brain, respectively. MC4R mutation affected 290 fat tissue genes, 49 liver genes and 1 hypothalamus gene. These results demonstrate that the MC4R mutation did not effect the feeding behavior reponse to MSH but genotype of MC4R gene did effect adipose tissue gene expression.
Technical Abstract: Transcriptional profiling was used to identify genetic mechanisms that respond to alpha- melanocortin stimulating hormone (MSH), a melanocortin-3 and 4-receptor (MC3/4-R) agonist. Three MC4R genotypes (2 homozygous and the heterozygous for MC4R) were selected. Six pigs per genotype per treatment were randomly assigned to one of the following treatments: ICV administration of 150 ul 0.9% saline, or 10 µg of MSH (agonist) in 150 ul of 0.9% saline. Feed intake was measure at 12 and 24 hous after treatment (time 0). All pigs were sacrificed 24 hours post-injection and hypothalamus, liver and middle layer of back fat was collected and mRNA was hybridized to 24,123 probe set Affymetrix Porcine Genome Arrays. MSH suppressed (P< 0.04) feed intake in all animals at 12 and 24 hr after treatment regardless of genotype with no teatment x genotype interaction detected (P > 0.8). A mixed linear model was fit to each tissue and gene using SAS Proc Mixed and interested contrasts were tested. The response to central administration of MSH resulted in 5070, 253 and 282 genes in adipose, liver and hypothalamic tissue were differentially expressed (q<0.07), respectively. A genotype affect was identified for 290 adipose tissue genes, 49 liver genes and 1 hypothalamus gene and a genotype x treatment interaction was identified for 1724 adipose genes, 40 liver genes and 2 hypothalamus genes. Genes representing lipid biosynthesis such as LPL, fatty acid synthase, aconitase-1 and acetyl CoA synthase were down regulated by MSH treatment as were leptin and heat shock protein 70.2 genes. Gene’s upregulated in adipose tissue tissue by MSH treatment included angiopoietin-like-4, pyruvate dehydrogenase kinase-4 isoform 1, UCP-3 and IGFBP- 3. Angiopoietin-like 4 inhibits LPL activity in rodent adipose tissue and was upregulated more than any other probe in the probe set. In the liver, genes representing carbohydrate metabolism, malate dehydrogenase-1, glyceraldehyde-3-phosphate deyhdrogenase and cytochrome-c-oxidase-7 protein-1 were down regulated as were genes representing lipid metabolism, fatty acid binding protein-3 and liver fatty acid binding protein. Genes in the hypothalamus that were deferentially expressed were solute carrier family1- member 1, a high affinity glutamate transporter, which was up regulated and bone morphogenetic protein receptor and insulin induced gene 1, located in endoplasmic reticulum membrane, which were down regulated. These results demonstrate that the MC4R mutation did not effect the feeding behavior reponse to MSH but genotype of MC4R gene had the greatest effect on adipose tissue gene expression.