Young Adult LEW.1WR1 Rats, a Model of Liver FAT10 Overexpression, Develop Insulin Resistance and Fatty Liver With Age

Abstract

As human lifespan increases, comorbid conditions that impact quality of life have become a serious problem. FAT10 has been identified as a gene that when knocked out, improves age associated metabolic dysfunctions and increased longevity in mice (1). There is increased Fat10 expression in the liver in obesity (2,5). Providing evidence that fat10 expression may be important for triggering the transition to metabolic dysfunction in aging. Adult LEW.1WR1(1WR1) rats have increased body mass without excess abdominal fat mass compared to control rats (3). Yet, it was unclear where the excess mass was stored. We hypothesized that the 1WR1 rat would develop increased liver fat mass as a product of increased insulin resistance in response to increased liver fat10 expression over time. To test this hypothesis, we did insulin tolerance tests(7 weeks & 15 weeks), triglyceride assays, and histological analysis of the liver(23 weeks), in 1WR1 rats(n=7) and Wistar Furth (WF) rats(n=7) on control diets. We analyzed images using histological scoring for nonalcoholic fatty liver disease from the literature (4). We also assessed the slides for Mallory Denk bodies (MBs). The body mass of 1WR1 rats were increased compared to WF rat groups starting from the age of 7 weeks (391.4∓8.572g vs. 271.8∓11.62g; p <0.0006). 1WR1 rats became more insulin resistant with age, the 1WR1 rat group has increased AUC of 7 and 15 week Insulin Tolerance Tests (401.5∓23.54 vs. 245.3∓10.20 7w ITT1; p= 0.0728, 15w ITT2 328.2∓14.86 vs. 217.8∓9.; p <0.0003) compared to WF rats. 1WR1 rats have increased liver mass (11.85g∓0.7699g vs. 7.235g∓0.3864g; p=0.0006) liver triglyceride levels compared to WF rats (192.8∓21.8 mg/mL vs. 130.1∓13.075 mg/mL; p=0.0728). 1WR1 rats have increased steatosis scores(1.857∓0.2608 vs. 1.143∓0.1429;p= 0.0862) yet significantly reduced inflammatory foci level (2∓0.8165 vs. 3∓0;p= 0.007), most 1WR1 hepatocytes are enlarged (ballooned) and contained MBs compared to WF rats suggesting 1WR1 rats have already passed the early inflammation stage. Adult 1WR1 rats developed reduced insulin sensitivity and lipid accumulation in the liver. These data support our hypothesis that 1WR1 rats would develop increased liver fat and impaired insulin resistance in response to aging and show that this process may be inflammation driven. (1) Canaan et al.,PNAS. April 2014; 111 (14): 5313-5318.(2)Vidal et al., FASEB.2020, 34: 1-1,(3) Collins et al., J Endocr Soc. 2019;3(1),(4).Kleiner et al., Hepatology, 2005; 41 (6): 1313–1321,(5).Dali-Youcef et al., Hepatol Commun. 2019;3(9):1205-1220.

Male LEW.1WR1 Rats Develop Metabolic Dysfunction, Steatohepatitis, and Liver Damage

“…However, insulin resistance did not cause significant differences in serum metabolites. The metabolites that were close to significant were from groups related to altered mitochondrial metabolism, a finding suggested by previous work in the LEW.1WR1 rat [39]. Microvesicular steatosis is also commonly associated with severe mitochondrial β-oxidation defects from genetic or acquired causes [40].…”