UNRAVELLING THE ROLES OF THE NUCLEAR PROTEIN 1 DURING ER-STRESS INDUCTION

Background: NUPR1 was described as a transcriptional factor involved in the regulation of various cellular stress-response genes, playing a crucial role in the condition of the endoplasmic-reticulum (ER) stress, thus emerging as a common molecular factor of different pathologies, obesity, hepatic steatosis, and cancer. In the present work we aim to explore how NUPR1 interacts with some pivotal genes that are the major modulators of the ER stress and metabolic cell functions. In particular we investigated the biochemical and molecular effects arising from the loss of NUPR1 in ER stress physiological conditions. Methods: We used prolonged high fat diet (HFD) feeding to induce ER stress physiological in Nupr1+/+ and Nupr1-/- male mice compared with their respectively normal chow diet (ND) controls. We fed mice with a HFD (60% fat, 20% protein, and 20% carbohydrate) for 10 weeks to promote chronic ER stress condition (Old-HFD group, n=5). An additional group of mice (n=5) was maintained on HFD (60% fat, 20% protein, and 20% carbohydrate) for a longer duration (15 weeks) to distinguish between age-dependent and age-independent effects. Liver were collected for histological and molecular assessments. Western blots and RT-qPCR were performed to assess the expression levels of the major ER-stress response UPR-associated proteins and metabolic genes. Results: We showed the downregulation of the majority of UPR-associated proteins: BIP (p<0.0001 for protein and mRNA), ATF4 (p<0.0001 for mRNA), XBP1 (p<0.0001 for protein and mRNA), CHOP (p<0.0001 for protein and mRNA), GADD34 (p=0.0296 for mRNA) in in-vivo NUPR1-/- compared to NUPR1+/+ 10 weeks HFD mice. Western blot for the major UPR associated proteins in NURP1-/- mice at 15 weeks HFD showed similar expression trends reported at the time-point of 10 weeks. ERDj4 mRNA resulted down-regulated in NUPR1-/- compared to NUPR1+/+ 15 weeks HFD mice (p=0.0032). Among the multiple metabolic genes, we reported a down-regulation of the majority mRNA associated to lipogenesis (SREBP, ACLY, ChREBP) and lipoprotein (APOB, PPAR-alfa, MTTP) in NUPR1-/- compared to NUPR1+/ + HFD mice 15 weeks. Both LCAD and MCAD fatty acid metabolisms mRNA were also downregulated, as consequence of PPAR-alfa deficit. Similarly betaoxidation mRNA ACOX1 and CPT1-alfa, as well as MTC4 and PGK1 were downregulated in NUPR1-/- compared to NUPR1+/ + HFD mice 15 weeks. Conclusion: The results of this work confirm that NUPR1 act downstream of the PERK branch playing a crucial role of NUPR1 in the activation of UPR response in physio-pathological ER stress condition and suggest a potential contribution of NUPR1-mediated ER stress response to the development of liver steatosis.