Keratinocyte‐associated Protein 3 , a Novel Adiposity Gene, May Act Through the Ileum

Abstract

Obesity poses a significant health burden in the United States, and investigating obesity-related genes remains an important area of research. A previous study from our lab used outbred heterogeneous stock (HS) rats to identify Keratinocyte-associated protein 3, (Krtcap3)as a candidate gene within a quantitative trait locus for adiposity. HS rats with the Wistar-Kyoto (WKY) haplotype at this locus had increased liver expression of Krtcap3, which correlated with decreased retroperitoneal fat mass (RetroFat) and decreased serum triglycerides. We developed an in vivo whole-body knock-out rat model of Krtcap3 in the inbred WKY rat using CRISPR/Cas9. Experimental wild-type (WT) and knock-out (KO) rats were placed onto a high-fat (HFD; 60% kcal fat) or low-fat diet (LFD; 10% kcal fat) at six weeks of age and were maintained on the diet for 13 weeks, with weekly measures of body weight and food intake. We hypothesized that KO rats would have increased fat mass compared to WT rats due to altered liver lipid pathways. In an initial pilot study, we found that male and female KO rats have significantly increased body weight at six weeks of age. At the end of the study, KO females—but not males—had a significantly greater fat mass compared to WT. KO females on HFD, but not LFD, had increased food consumption. We analyzed serum and liver lipids between WT and KO rats, and found no significant genotype-driven differences. This indicated that the KO did not alter liver lipid pathways, suggesting that Krtcap3 is affecting fat mass through a tissue other than liver. Previous work has shown that WKY rats exhibit increased liver Krtcap3 relative to the other HS founder strains, but expression in other tissues has not been investigated. We hypothesize that WKY rats will have a higher Krtcap3 expression compared to the other founder strains in the tissue of action of Krtcap3. We have investigated expression patterns in the following tissues in WKY, Fischer 344, and Brown Norway rats: white and brown adipose tissue, liver, heart, kidney, skeletal muscle, ileum, colon, arcuate nucleus, and nucleus accumbens. Krtcap3 expression is significantly higher only in the WKY liver and ileum. Coupled with our food intake phenotype from the pilot study, we propose that Krtcap3 may be participating in the gut-brain axis to alter food intake and influence adiposity. Future studies will evaluate expression patterns in additional inbred strains and investigate how gut hormones are altered in the KO.