Time restricted feeding with or without ketosis influences metabolism-related gene expression in a tissue-specific manner in aged rats

Many of the "hallmarks of aging" involve alterations in cellular and organismal metabolism. One pathway with the potential to impact several traditional markers of impaired function with aging is the PI3K/AKT metabolic pathway. Regulation of this pathway includes many aspects of cellular function, including protein synthesis, proliferation, and survival, as well as many downstream targets, including mTOR and FOXOs. Importantly, this pathway is pivotal to the function of every organ system in the human body. Thus, we investigated the expression of several genes along this pathway in multiple organs, including the brain, liver, and skeletal muscle, in aged subjects that had been on different experimental diets to regulate metabolic function since mid-life. Specifically, rats were fed a control ad lib diet (AL), a time restricted feeding diet (cTRF), or a time restricted feeding diet with ketogenic macronutrients (kTRF) for the majority of their adult lives (from 8 to 25 months). We previously reported that regardless of macronutrient ratio, TRF-fed rats in both macronutrient groups required significantly less training to acquire a biconditional association task than their ad lib fed counterparts. The current experiments expand on this work by quantifying metabolism-related gene expression across tissues and interrogating for potential relationships with cognitive performance. Within the brain, SIRT1 and MAPK8 were reduced in CA3 of kTRF-fed rats. Additionally, IGF1 expression was significantly upregulated in the CA1 of cTRF-fed rats, but this effect was ameliorated in the kTRF fed group. AKT and FOXO1 expression were significantly reduced in kTRF-fed rats within liver. Interestingly, AKT expression within the perirhinal cortex (PER) was higher in kTRF rats with the best cognitive performance, and FOXO1 expression was higher in the CA3 of AL-fed rats correlated with the poorest cognitive performance. Together, these data demonstrate diet- and tissue-specific alterations in metabolism-related gene expression and their correlation with cognitive status.