Likewise, main hepatocytes isolated from LTsc1KO mice exhibited insulin-independent activation of mTORC1 signaling . As a result, the LTsc1KO mice produce a model of hepatic mTORC1 activation that occurs independent in the upstream insulin-signaling pathway. To start to comprehend the function of mTORC1 signaling while in the manage of hepatic lipid metabolism, we examined the histological capabilities of livers from cohorts of Tsc1fl/fl and LTsc1KO mice. Contrary to our expectations, LTsc1KO mice have been protected from ageinduced hepatic steatosis at 9 months, exhibiting appreciably reduce levels of liver triglycerides . A relative reduce in lipid accumulation in LTsc1KO livers was also evident in H&E-stained liver sections at 6 months . Given the surprising decrease in lipid accumulation within the livers of LTsc1KO mice fed a normal chow diet, we challenged the LTsc1KO mice with a lard-based high fat diet to further examine this phenotype.
As on a chow diet , there was no significant difference in weight gain between the Tsc1fl/fl Tariquidar ic50 and LTsc1KO mice on the HFD . Dual-energy X-ray absorptiometry indicated that there was no difference in percentage body fat after 16 weeks of HFD . However, the LTsc1KO mice exhibited protection from HFD-induced hepatic steatosis . Blinded scoring of liver sections by a pathologist indicated that all Tsc1fl/fl mice had moderate to severe steatosis, while the majority of LTsc1KO mice exhibited negative to mild lipid accumulation . Consistent with these histological findings, LTsc1KO livers had drastically reduced levels of TGs . For that reason, constitutive mTORC1 signaling inside the LTsc1KO livers is accompanied by a lower, rather than the predicted increase, in hepatic lipid accumulation.
To determine the mechanism of protection from hepatic steatosis while in the LTsc1KO mice, we examined candidate pathways involved in lipid mobilization and metabolism. For instance, selleck hop over to here increased TG export could account for decreased accumulation while in the liver. However, serum amounts of TGs, non-esterified fatty acids , and cholesterol have been not drastically different in mice fed a HFD, but TG and NEFA amounts trended down in LTsc1KO compared to Tsc1fl/fl mice . Furthermore, LTsc1KO mice did not display significant differences in hepatic TG output under fasting conditions, and again, these levels trended reduced relative to controls .
Consistent with the lack of physiological evidence supporting a role for increased TG mobilization, transcript amounts of proteins involved in these processes, such as Mttp, Dgat1, and Dgat2, have been not substantially changed in LTsc1KO livers . To address the possibility that LTsc1KO livers burn more lipid than controls, we measured expression of genes important for the |-oxidation of fatty acids. We found that transcript levels of Ppar|á, Mcad, and Cpt1a have been not increased during the LTsc1KO livers, and in truth, Mcad expression was appreciably reduced in these livers relative to controls .