12 Metabolic gene expression between emaciated and moderately conditioned horses across various tissue types

Abstract

Effective refeeding of emaciated horses requires strategic management, including knowledge of tissue specific contributions to metabolic processes. To determine the differences in metabolic activity among body condition score (BCS) groups, 8 horses donated to this study were evaluated for BCS (1–9 scale,1 = emaciated and 9 = obese); where horses with BCS lower than 3 were considered emaciated (n = 4), and those with a BCS between 4 and 6 were considered moderate (n = 4). All horses were humanely euthanized using sodium barbiturate overdose, and during necropsy, tissue samples across 4 types were collected: muscle (M: cardiac and skeletal), fat (F: mesenteric, neck crest, omental, and peritoneal), gastrointestinal tract (G: stomach, duodenum, jejunum, ileum, and cecum), and organs (O: liver, kidney, and spleen). Samples were placed in liquid nitrogen and stored at −80°C before isolating RNA for gene expression analysis. Relative gene expression (using 2^-DCt) of RPL32, GLUT4, CPT1, and PDK4 were measured across tissues and between F, G, O and M, using geometric mean of GAPDH and TUBA4A as reference genes. Class, tissue, and BCS effects on PCR data were analyzed using generalized linear mixed models with breed and individual animals as random block effects. Shapiro-Wilk and Levine's test were used to determinenormality, and ranked transformation applied where appropriate. Post hoc multiple comparisons were performed with Tukey's adjustment and significance was identified at P < 0.05 (SAS 9.4, Cary, NC). No differences were detected between BCS groups (P > 0.05). Tissue classification had a significant effect on each target gene expression, where CPT 1 had lower expression in O [0.170 (0.440), 2^-DCt median (interquartile range), P < 0.001] than F [0.100 (0.125)] and M [0.06 (0.150), P < 0.0001). No differences were detected for tissue classification for GLUT4, PDK4 or RPL32 (P > 0.05). Further, no individual tissue, BCS, or interactions were identified across all tissue type and gene pairs (P > 0.05). Despite known physiologic and physical differences in emaciated versus moderate BCS equids, gene expression was relatively unaffected in this study, which may be due to the tightly controlled nature of each gene to maintaining life. Knowledge of gene activity in the horse, and especially across tissue profiles and in the presence of sodium barbiturate is limited within the existing literature. Further investigation into tissue-specific differences may aid in understanding metabolic changes associated with BCS and should be evaluated in the presence and absence of euthanasia solution to fully elicit potential effects.