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Rhythmic arylalkylamine N-acetyltransferase ( AANAT) synthesis is a prominent circadian-controlled response that occurs in most mammals. AANAT is the core enzyme in melatonin production; because melatonin participates in many physiological processes, the regulation of AANAT is an important research topic. In this study, we focused on the role of heterogeneous ribonucleoprotein R (hn RNP R) in the translation of AANAT. A novel RNA-binding protein hn RNP R widely interacted with the 5′ untranslated region ( UTR) of AANAT m RNA and contributed to translation through an internal ribosomal entry site ( IRES). Fine-tuning of AANAT protein synthesis occurred in response to knockdown and overexpression of hn RNP R. Nocturnal elevation of AANAT protein was dependent on the rhythmic changes of hn RNP R, whose levels are elevated in the pineal gland during nighttime. Increases in hn RNP R additionally improved AANAT production in rat pinealocytes under norepinephrine ( NE) treatment. These results suggest that cap-independent translation of AANAT m RNA plays a role in the rhythmic synthesis of melatonin through the recruitment of translational machinery to hn RNP R-bound AANAT m RNA. [ABSTRACT FROM AUTHOR]

Aging is associated with an inevitable and universal loss of cell homeostasis and restricts an organism's lifespan by an increased susceptibility to diseases and tissue degeneration. The glucose uptake associated with producing energy for cell survival is one of the major causes of ROS production under physiological conditions. However, the overall mechanisms by which glucose uptake results in cellular senescence remain mysterious. In this study, we found that TXNIP deficiency accelerated the senescent phenotypes of MEF cells under high glucose condition. TXNIP‐/‐ MEF cells showed greater induced glucose uptake and ROS levels than wild‐type cells, and N‐acetylcysteine (NAC) treatment rescued the cellular senescence of TXNIP‐/‐ MEF cells. Interestingly, TXNIP‐/‐ MEF cells showed continuous activation of AKT during long‐term subculture, and AKT signaling inhibition completely blocked the cellular senescence of TXNIP‐/‐ MEF cells. In addition, we found that TXNIP interacted with AKT via the PH domain of AKT, and their interaction was increased by high glucose or H2O2 treatment. The inhibition of AKT activity by TXNIP was confirmed using western blotting and an in vitro kinase assay. TXNIP deficiency in type 1 diabetes mice (Akita) efficiently decreased the blood glucose levels and finally increased mouse survival. However, in normal mice, TXNIP deficiency induced metabolic aging of mice and cellular senescence of kidney cells by inducing AKT activity and aging‐associated gene expression. Altogether, these results suggest that TXNIP regulates cellular senescence by inhibiting AKT pathways via a direct interaction under conditions of glucose‐derived metabolic stress. [ABSTRACT FROM AUTHOR]