Disfunción de la biogénesis de pre-mRNAs y pre-rRNAs en motoneuronas en el modelo murino SMNΔ7 de atrofia muscular espinal

RESUMEN: La atrofia muscular espinal (SMA) tipo I es una enfermedad neurodegenerativa que representa la principal causa de mortalidad infantil con base genética. Está causada por la deleción o mutación del gen SMN1 que codifica la proteína de supervivencia de las neuronas motoras (SMN). El déficit de SMN produce la degeneración selectiva de las alfa-motoneuronas espinales con atrofia, parálisis muscular y, normalmente, la muerte en los primeros meses de la vida. SMN es una proteína multifuncional implicada en la biogénesis de las ribonucleoproteínas espliceosomales (snRNPs) y nucleolares (snoRNPs). En esta Tesis, utilizando como modelo experimental de SMA tipo I el ratón SMN∆7, hemos demostrado que el déficit de SMN afecta al procesamiento de mRNAs y rRNAS en las alfa-motoneuronas, dando como resultado una severa disfunción del nucleolo y de los “Cajal bodies”, acompañada de disrupción de la maquinaria de síntesis de proteínas. Además, se producen defectos en el “splicing” con retención nuclear de mRNAs incorrectamente procesados que no pueden ser exportados. Sobre estas bases, consideramos que la SMA es una patología del RNA.Esta Tesis ha sido financiada con las siguientes ayudas: • Ministerio de Economía y Competitividad. Proyecto de investigación BFU2014-54754-P. • Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas. Red CIBERNED CB06/05/0037. • Instituto de Investigación Sanitaria Valdecilla. Proyecto de investigación NVAL17/22

Nucleolin reorganization and nucleolar stress in Purkinje cells of mutant PCD mice

The Purkinje cell (PC) degeneration (pcd) mouse harbors a mutation in Agtpbp1 gene that encodes for the cytosolic carboxypeptidase, CCP1. The mutation causes degeneration and death of PCs during the postnatal life, resulting in clinical and pathological manifestation of cerebellar ataxia. Monogenic biallelic damaging variants in the Agtpbp1 gene cause infantile-onset neurodegeneration and cerebellar atrophy, linking loss of functional CCP1 with human neurodegeneration. Although CCP1 plays a key role in the regulation of tubulin stabilization, its loss of function in PCs leads to a severe nuclear phenotype with heterochromatinization and accumulation of DNA damage. Therefore, the pcd mice provides a useful neuronal model to investigate nuclear mechanisms involved in neurodegeneration, particularly the nucleolar stress. In this study, we demonstrated that the Agtpbp1 gene mutation induces a p53-dependent nucleolar stress response in PCs, which is characterized by nucleolar fragmentation, nucleoplasmic and cytoplasmic mislocalization of nucleolin, and dysfunction of both pre-rRNA processing and mRNA translation. RT-qPCR analysis revealed reduction of mature 18S rRNA, with a parallel increase of its intermediate 18S-5'-ETS precursor, that correlates with a reduced expression of Fbl mRNA, which encodes an essential factor for rRNA processing. Moreover, nucleolar alterations were accompanied by a reduction of PTEN mRNA and protein levels, which appears to be related to the chromosome instability and accumulation of DNA damage in degenerating PCs. Our results highlight the essential contribution of nucleolar stress to PC degeneration and also underscore the nucleoplasmic mislocalization of nucleolin as a potential indicator of neurodegenerative processes.Acknowledgements: The authors declare no conflict of interest. The authors wish to thank Raquel García-Ceballos for technical assistance. This work was supported by the following grants: “Instituto de Salud Carlos III” (CIBERNED, CB06/05/0037) and CIBERONC (CB16/12/00352), “Instituto de Investigación Valdecilla” (IDIVAL, Santander, Spain), FIS PI16/02137 from ISCIII and SAF2016-79668-R (MINECO, Spain), SA043U16 (UIC076) and SA030P17 (UIC217) from JCyL (Spain)

Prenatal, but not Postnatal, Curcumin Administration Rescues Neuromorphological and Cognitive Alterations in Ts65Dn Down Syndrome Mice

Background: The cognitive dysfunction in Down syndrome (DS) is partially caused by deficient neurogenesis during fetal stages. Curcumin enhances neurogenesis and learning and memory. Objectives: We aimed to test the ability of curcumin to rescue the neuromorphological and cognitive alterations of the Ts65Dn (TS) mouse model of DS when administered prenatally or during early postnatal stages, and to evaluate whether these effects were maintained several weeks after the treatment. Methods: To evaluate the effects of prenatal curcumin administration, 65 pregnant TS females were subcutaneously treated with curcumin (300 mg/kg) or vehicle from ED (Embryonic Day) 10 to PD (Postnatal Day) 2. All the analyses were performed on their TS and Control (CO) male and female progeny. At PD2, the changes in neurogenesis, cellularity, and brain weight were analyzed in 30 TS and CO pups. The long-term effects of prenatal curcumin were evaluated in another cohort of 44 TS and CO mice between PD30 and PD45. The neuromorphological effects of the early postnatal administration of curcumin were assessed on PD15 in 30 male and female TS and CO pups treated with curcumin (300 mg/kg) or vehicle from PD2 to PD15. The long-term neuromorphological and cognitive effects were assessed from PD60 to PD90 in 45 mice. Data was compared by ANOVAs. Results: Prenatal administration of curcumin increased the brain weight (+45%, P < 0.001), the density of BrdU (bromodeoxyuridine)- (+150%, P < 0.001) and DAPI (4',6-diamidino-2-phenylindole)- (+38%, P = 0.005) positive cells, and produced a long-term improvement of cognition in TS (+35%, P = 0.007) mice with respect to vehicle-treated mice. Postnatal administration of curcumin did not rescue any of the short- or long-term altered phenotypes of TS mice. Conclusion: The beneficial effects of prenatal curcumin administration to TS mice suggest that it could be a therapeutic strategy to treat DS cognitive disabilities.This study was supported by the “Fondazione Generali e Assicurazioni Generali”, Italy; Fundación Tatiana Pérez de Guzmán el Bueno, IDIVAL (NVAL 19/23), and the Spanish Ministry of Economy and Competitiveness (PSI-2016-76194-R, AEI/FEDER, EU)

Prenatal Administration of Oleic Acid or Linolenic Acid Reduces Neuromorphological and Cognitive Alterations in Ts65dn Down Syndrome Mice

Background: The cognitive impairments that characterize Down syndrome (DS) have been attributed to brain hypocellularity due to neurogenesis impairment during fetal stages. Thus, enhancing prenatal neurogenesis in DS could prevent or reduce some of the neuromorphological and cognitive defects found in postnatal stages. Objectives: As fatty acids play a fundamental role in morphogenesis and brain development during fetal stages, in this study, we aimed to enhance neurogenesis and the cognitive abilities of the Ts65Dn (TS) mouse model of DS by administering oleic or linolenic acid. Methods: In total, 85 pregnant TS females were subcutaneously treated from Embryonic Day (ED) 10 until Postnatal Day (PD) 2 with oleic acid (400 mg/kg), linolenic acid (500 mg/kg), or vehicle. All analyses were performed on their TS and Control (CO) male and female progeny. At PD2, we evaluated the short-term effects of the treatments on neurogenesis, cellularity, and brain weight, in 40 TS and CO pups. A total of 69 TS and CO mice were used to test the long-term effects of the prenatal treatments on cognition from PD30 to PD45, and on neurogenesis, cellularity, and synaptic markers, at PD45. Data were compared by ANOVAs. Results: Prenatal administration of oleic or linolenic acid increased the brain weight (+36.7% and +45%, P < 0.01), the density of BrdU (bromodeoxyuridine)- (+80% and +115%; P < 0.01), and DAPI (4',6-diamidino-2-phenylindole)-positive cells (+64% and +22%, P < 0.05) of PD2 TS mice with respect to the vehicle-treated TS mice. Between PD30 and PD45, TS mice prenatally treated with oleic or linolenic acid showed better cognitive abilities (+28% and +25%, P < 0.01) and a higher density of the postsynaptic marker PSD95 (postsynaptic density protein 95) (+65% and +44%, P < 0.05) than the vehicle-treated TS animals. Conclusion: The beneficial cognitive and neuromorphological effects induced by oleic or linolenic acid in TS mice suggest that they could be promising pharmacotherapies for DS-associated cognitive deficits.This study was supported by “Fondazione Generali e Assicurazioni Generali”, Italy; Fundación Tatiana Pérez de Guzmán el Bueno, IDIVAL (NVAL 19/23), and the Spanish Ministry of Economy and Competitiveness (PSI-2016- 76194-R, AEI/FEDER, EU)